Internet Draft R. Braden, Ed.
Expiration: May 1996 ISI
File: draft-ietf-rsvp-spec-08.txt L. Zhang
PARC
S. Berson
ISI
S. Herzog
ISI
J. Wroclaswki
MIT
Resource ReSerVation Protocol (RSVP) --
Version 1 Functional Specification
November 22, 1995
Status of Memo
This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
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Abstract
This memo describes version 1 of RSVP, a resource reservation setup
protocol designed for an integrated services Internet. RSVP provides
receiver-initiated setup of resource reservations for multicast or
unicast data flows, with good scaling and robustness properties.
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Table of Contents
1. Introduction ........................................................5
1.1 Data Flows ......................................................8
1.2 Reservation Model ...............................................9
1.3 Reservation Styles ..............................................11
1.4 Examples of Styles ..............................................14
2. RSVP Protocol Mechanisms ............................................18
2.1 RSVP Messages ...................................................18
2.2 Port Usage ......................................................20
2.3 Merging Flowspecs ...............................................21
2.4 Soft State ......................................................22
2.5 Teardown ........................................................24
2.6 Errors and Acknowledgments ......................................25
2.7 Policy and Security .............................................27
2.8 Automatic RSVP Tunneling ........................................28
2.9 Host Model ......................................................28
3. RSVP Functional Specification .......................................30
3.1 RSVP Message Formats ............................................30
3.2 Sending RSVP Messages ...........................................42
3.3 Avoiding RSVP Message Loops .....................................44
3.4 Local Repair ....................................................48
3.5 Time Parameters .................................................48
3.6 Traffic Policing and TTL ........................................50
3.7 Multihomed Hosts ................................................51
3.8 Future Compatibility ............................................52
3.9 RSVP Interfaces .................................................55
4. Message Processing Rules ............................................65
APPENDIX A. Object Definitions .........................................82
APPENDIX B. Error Codes and Values .....................................97
APPENDIX C. UDP Encapsulation ..........................................101
APPENDIX D. Experimental and Open Issues ...............................103
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What's Changed
The most important changes in this document from the rsvp-spec-07 draft
are:
o The role and interpretation of the IP Protocol Id is changed.
The Protocol Id is now a required part of the session
definition, and filter specs and sender templates now assume
the Protocol Id from the session rather than stating it
explicitly.
o A "soft" reservation confirmation message is added.
o The text states explicitly that an erroneous reservation
message is not forwarded. A mechanism to allow a receiver
more flexible control over forwarding of its messages after
an admission control failure has not been designed and is
therefore not included in this version of the protocol.
o A terminology confusion is eliminated. The term "scope" was
used both for a set of senders and for a set of sender hosts.
A new term "sender selection" is introduced for the first,
leaving "scope" for the second.
o The FILTER_SPEC object is dropped from a wildcard sender
selection (WF) style reservation, which now selects "all
senders" without qualification.
o The StyleID byte is dropped from a STYLE object, as
redundant.
o An SE style flow descriptor is simplified to a single
flowspec.
o The IP Router Alert option is now required in PATH, PTEAR,
and RACK messages.
o The TIME_VALUES object is now required in RESV and PATH
messages; there is no default.
o Policing at branch points is now defined in a new section on
policing (3.6).
o A 2-second delay is inserted into local repair.
o Merging of SE with WF objects is no longer allowed.
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o The Rmax end-to-end bound on the refresh rate R is removed,
since its utility was unclear.
o A rule for randomizing refresh timeouts is included.
o The suggestion that TCP could be used for carrying RSVP state
through a congested non-RSVP cloud is removed.
o SENDER_TSPECS are now required in PATH| messages.
o There are new sections on multihomed hosts (3.7) and future
compatibility (3.8). The latter section makes clear that a
message containing an object with unknown C-Type should be
rejected. Any more forgiving treatment seems too complex.
o Appendix C on UDP encapsulation is completely changed.
o Some text was rearranged in Sections 1 and 2.
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1. Introduction
This document defines RSVP, a resource reservation setup protocol
designed for an integrated services Internet [RSVP93,ISInt93].
On behalf of an application data stream, a host uses the RSVP
protocol to request a specific quality of service (QoS) from the
network. RSVP delivers QoS requests to routers along the path(s) of
the data stream and maintains router and host state to provide the
requested service. RSVP requests will generally, although not
necessarily, result in resources being reserved along the data path.
RSVP requests resources for simplex data streams, i.e., it requests
resources in only one direction. Therefore, a sender is logically
distinct from a receiver, although the same application process may
act as both a sender and a receiver at the same time. RSVP operates
on top of IP (either IPv4 or IP6), occupying the place of a transport
protocol in the protocol stack. However, like ICMP, IGMP, and
routing protocols, RSVP does not transport application data but is
rather an Internet control protocol. Like the implementations of
routing and management protocols, an implementation of RSVP will
typically execute in the background, not in the data forwarding path,
as shown in Figure 1.
RSVP is not itself a routing protocol; RSVP is designed to operate
with current and future unicast and multicast routing protocols. The
RSVP daemon consults the local routing protocol(s) to obtain routes.
In the multicast case, for example, a host sends IGMP messages to
join a multicast group and then sends RSVP messages to reserve
resources along the delivery path(s) of that group. Routing
protocols determine where packets get forwarded; RSVP only concerns
with the QoS of those packets that are forwarded by routing.
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HOST ROUTER
_________________________ RSVP _____________________________
| | .--------------. |
| _______ ______ | / | ________ . ______ |
| | | | | | / || | . | | | RSVP
| |Applic-| | RSVP <----/ ||Routing | -> RSVP <---------->
| | App <----->daemon| | ||Protocol| |daemon| |
| | | | | | || daemon <----> | |
| |_______| |___.__| | ||_ ._____| |__.__.| |
| | | | | | | . |
|===|===============|=====| |===|=============|====.======|
| data .........| | | | ...........| .____ |
| | ____V_ ____V____ | | _V__V_ _____V___ | Adm.||
| | |Class-| | || data | |Class-| | ||Cntrl||
| |=> ifier|=> Packet ============> ifier|==> Packet ||_____|| data
| |______| |Scheduler|| | |______| |Scheduler|===========>
| |_________|| | |_________| |
|_________________________| |_____________________________|
Figure 1: RSVP in Hosts and Routers
Each router that is capable of resource reservation passes incoming
data packets through a packet classifier and then queues them as
necessary in a packet scheduler. The packet classifier determines
the route and the QoS class for each packet. There is a scheduler
for each interface, to allocate resources for transmission on the
particular link-layer medium used by that interface. If the link-
layer medium is QoS-active, i.e., if it has its own QoS management
capability, then the packet scheduler is responsible for negotiation
with the link layer to obtain the QoS requested by RSVP. This
mapping to the link layer QoS may be accomplished in a number of
possible ways; the details will be medium-dependent. On a QoS-
passive medium such as a leased line, the scheduler itself allocates
packet transmission capacity. The scheduler may also allocate other
system resources such as CPU time or buffers.
In order to efficiently accommodate heterogeneous receivers and
dynamic group membership, RSVP makes receivers responsible for
requesting resource reservations [RSVP93]. A QoS request, which
typically originates from a receiver host application, is passed to
the local RSVP implementation, shown as a user daemon in Figure 1.
The RSVP protocol then carries the request to all the nodes (routers
and hosts) along the reverse data path(s) to the data source(s).
At each node, the RSVP daemon communicates with a local decision
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module, called "admission control", to determine if the router can
supply the requested QoS. If the admission control check succeeds,
the RSVP daemon sets parameters in the packet classifier and
scheduler to obtain the desired QoS. If the admission control check
fails, the RSVP program immediately returns an error notification to
the application process that originated the request. We refer to the
packet classifier, packet scheduler, and admission control components
as " traffic control".
RSVP is designed to scale well for very large multicast groups.
Since both the membership of a large group and the topology of large
multicast trees are likely to change with time, the RSVP design
assumes that router state for traffic control will be built and
destroyed incrementally. For this purpose, RSVP uses "soft state" in
the routers. That is, RSVP sends periodic refresh messages to
maintain the state along the reserved path(s); in absence of
refreshes, the state will automatically time out and be deleted.
RSVP protocol mechanisms provide a general facility for creating and
maintaining distributed reservation state across a mesh of multicast
or unicast delivery paths. RSVP transfers reservation parameters as
opaque data (except for certain well-defined operations on the data),
which it simply passes to traffic control for interpretation.
Although the RSVP protocol mechanisms are largely independent of the
encoding of these parameters, the encodings must be defined in the
reservation model that is presented to an application; see Appendix A
for more details.
In summary, RSVP has the following attributes:
o RSVP makes resource reservations for both unicast and many-to-
many multicast applications, adapting dynamically to changing
group membership as well as changing routes.
o RSVP is simplex, i.e., it reserves for data flow in one
direction only.
o RSVP is receiver-oriented, i.e., the receiver of a data flow
initiates and maintains the resource reservation used for that
flow.
o RSVP maintains "soft state" in the routers, providing graceful
support for dynamic membership changes and automatic adaptation
to routing changes.
o RSVP provides several reservation models or "styles" (defined
below) to fit a variety of applications.
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o RSVP provides transparent operation through routers that do not
support it.
Further discussion on the objectives and general justification for
RSVP design are presented in [RSVP93,ISInt93].
The remainder of this section describes the RSVP reservation
services. Section 2 presents an overview of the RSVP protocol
mechanisms. Section 3 contains the functional specification of RSVP,
while Section 4 presents explicit message processing rules. Appendix
A defines the variable-length typed data objects used in the RSVP
protocol. Appendix B defines error codes and values. Appendix C
defines an extension for UDP encapsulation of RSVP messages.
Finally, some experimental RSVP features are documented in Appendix D
for future reference.
1.1 Data Flows
RSVP defines a "session" as a data flow with a particular
destination and transport-layer protocol. The destination for a
particular session is generally defined by DestAddress, the IP
destination address of the data packets, and perhaps by DstPort, a
" generalized destination port", i.e., some further demultiplexing
point in the transport or application protocol layer. RSVP treats
each session independently, and this document often assumes the
qualification "for the same session".
DestAddress is a group address for multicast delivery or the
unicast address of a single receiver. DstPort could be defined by
a UDP/TCP destination port field, by an equivalent field in
another transport protocol, or by some application-specific
information. Although the RSVP protocol is designed to be easily
extendible for greater generality, the present version supports
only UDP/TCP ports as generalized ports.
Figure 2 illustrates the flow of data packets in a single RSVP
session assuming multicast data distribution. The arrows indicate
data flowing from senders S1 and S2 to receivers R1, R2, and R3,
and the cloud represents the distribution mesh created by
multicast routing. Multicast distribution forwards a copy of each
data packet from a sender Si to every receiver Rj; a unicast
distribution session has a single receiver R. Each sender Si and
each receiver Rj may be running in a unique Internet host, or a
single host may contain multiple senders and/or receivers,
distinguished by generalized ports.
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Senders Receivers
_____________________
( ) ===> R1
S1 ===> ( Multicast )
( ) ===> R2
( distribution )
S2 ===> ( )
( by Internet ) ===> R3
(_____________________)
Figure 2: Multicast Distribution Session
For unicast transmission, there will be a single destination host
but there may be multiple senders; RSVP can set up reservations
for multipoint-to-single-point transmission.
1.2 Reservation Model
An elementary RSVP reservation request consists of a "flowspec"
together with a "filter spec"; this pair is called a "flow
descriptor". The flowspec specifies a desired QoS. The filter
spec, together with session definition, specifies the set of data
packets -- the "flow" -- to receive the QoS defined by the
flowspec. The flowspec is used to set parameters to the node's
packet scheduler (assuming that admission control succeeds), while
the filter spec is used to set parameters in the packet
classifier. Data packets that are addressed to a particular
session but do not match any of the filter specs for that session
are handled as best-effort traffic.
Note that the action to control QoS occurs at the place where the
data enters the medium, i.e., at the upstream end of the link,
although an RSVP reservation request originates from receiver(s)
downstream. In this document, we define the directional terms
"upstream" vs. "downstream", "previous hop" vs. "next hop", and
"incoming interface" vs "outgoing interface" with respect to the
direction of data flows.
The flowspec in a reservation request will generally include a
service class and two sets of numeric parameters: (1) an "Rspec"
(R for `reserve') that defines the desired QoS, and (2) a "Tspec"
(T for `traffic') that describes the data flow. The formats and
contents of Tspecs and Rspecs are determined by the integrated
service model [ServTempl95a], and are generally opaque to RSVP.
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In the most general approach [RSVP93], filter specs may select
arbitrary subsets of the packets in a given session. Such subsets
might be defined in terms of senders (i.e., sender IP address and
generalized source port), in terms of a higher-level protocol, or
generally in terms of any fields in any protocol headers in the
packet. For example, filter specs might be used to select
different subflows in a hierarchically-encoded signal by selecting
on fields in an application-layer header. However, in the
interest of simplicity (and to minimize layer violation), the
present RSVP version uses a much more restricted form of filter
spec, consisting of sender IP address and optionally the UDP/TCP
port number SrcPort.
RSVP reservation request messages originate at receivers and are
passed upstream towards the sender(s). When a reservation request
is received at a node, two general actions are taken.
1. Make a reservation
The flowspec and the filter spec are passed to traffic
control. Admission control determines the admissibility of
the request (if it's new); if this test fails, the
reservation is rejected and RSVP returns an error message to
the appropriate receiver(s). If admission control succeeds,
the node uses the flowspec to set up the packet scheduler for
the desired QoS and the filter spec to set the packet
classifier to select the appropriate data packets.
2. Forward the request upstream
The reservation request is propagated upstream towards the
appropriate senders. The set of sender hosts to which a
given reservation request is propagated is called the "scope"
of that request.
The reservation request that a node forwards upstream may differ
from the request that it received from downstream, for two
reasons. First, it is possible in theory for the traffic control
mechanism to modify the flowspec hop-by-hop, although none of the
currently defined services does so. Second, reservations for the
same sender, or the same set of senders, from different downstream
branches of the multicast tree(s) are "merged" as reservations
travel upstream; that is, a node forwards upstream only the
reservation request with the "maximum" flowspec.
When a receiver originates a reservation request, it can also
request a confirmation message to indicate that its request was
(probably) installed in the network. A successful reservation
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request propagates as far as the closest point(s) along the sink
tree to the sender(s) where there is an existing reservation level
equal or greater than that being requested. At that point, the
arriving request will be dropped in favor of the equal or larger
reservation in place; the node may then send a reservation
confirmation message back to the receiver. Note that the receipt
of a confirmation is only a high-probability indication, not a
guarantee that the requested service is in place all the way to
the sender(s), as explained in Section 2.6.
The basic RSVP reservation model is "one pass": a receiver sends a
reservation request upstream, and each node in the path either
accepts or rejects the request. This scheme provides no easy way
for a receiver to find out the resulting end-to-end service.
Therefore, RSVP supports an enhancement to one-pass service known
as "One Pass With Advertising" (OPWA) [Shenker94]. With OPWA,
RSVP control packets are sent downstream, following the data
paths, to gather information that may be used to predict the end-
to-end QoS. The results ("advertisements") are delivered by RSVP
to the receiver hosts and perhaps to the receiver applications.
The advertisements may then be used by the receiver to construct,
or to dynamically adjust, an appropriate reservation request.
1.3 Reservation Styles
A reservation request includes a set of control options, which are
collectively called the reservation "style".
One option concerns the treatment of reservations for different
senders within the same session: establish a "distinct"
reservation for each upstream sender, or else make a single
reservation that is " shared" among all packets of selected
senders.
Another option controls the selection of senders: an "explicit"
list of all selected senders, or a "wildcard" that implicitly
selects all the senders to the session. In an explicit-selection
reservation, each filter spec must match exactly one sender, while
in a wildcard-selection no filter spec is needed.
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Sender || Reservations:
Selection || Distinct | Shared
_________||__________________|____________________
|| | |
Explicit || Fixed-Filter | Shared-Explicit |
|| (FF) style | (SE) Style |
__________||__________________|____________________|
|| | |
Wildcard || (None defined) | Wildcard-Filter |
|| | (WF) Style |
__________||__________________|____________________|
Figure 3: Reservation Attributes and Styles
The styles currently defined are as follows (see Figure 3):
o Wildcard-Filter (WF) Style
The WF style implies the options: "shared" reservation and "
wildcard" sender selection. Thus, a WF-style reservation
creates a single reservation into which flows from all
upstream senders are mixed; this reservation may be thought
of as a shared "pipe", whose "size" is the largest of the
resource requests from all receivers, independent of the
number of senders using it. A WF-style reservation is
propagated upstream towards all sender hosts, and
automatically extends to new senders as they appear.
Symbolically, we can represent a WF-style reservation request
by:
WF( * {Q})
where the asterisk represents wildcard sender selection and Q
represents the flowspec.
o Fixed-Filter (FF) Style
The FF style implies the options: "distinct" reservations and
"explicit" sender selection. Thus, an elementary FF-style
reservation request creates a distinct reservation for data
packets from a particular sender, not sharing them with other
senders' packets for the same session.
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The total reservation on a link for a given session is the
total of the FF reservations for all requested senders. On
the other hand, FF reservations requested by different
receivers Rj but selecting the same sender Si must be merged
to share a single reservation.
Symbolically, we can represent an elementary FF reservation
request by:
FF( S{Q})
where S is the selected sender and Q is the corresponding
flowspec; the pair forms a flow descriptor. RSVP allows
multiple elementary FF-style reservations to be requested at
the same time, using a list of flow descriptors:
FF( S1{Q1}, S2{Q2}, ...)
o Shared Explicit (SE) Style
The SE style implies the options: "shared" reservation and "
explicit" sender selection. Thus, an SE-style reservation
creates a single reservation into which flows from all
upstream senders are mixed. However, like the FF style, the
SE style allows a receiver to explicitly specify the set of
senders.
Symbolically, we can represent an SE reservation request by:
SE( (S1,S2,...){Q} ),
i.e., a flow descriptor composed of a flowspec Q and a list
of senders S1, S2, etc.
Both WF and SE are shared reservations, appropriate for those
multicast applications whose application-specific constraints make
it unlikely that multiple data sources will transmit
simultaneously. Packetized audio is an example of an application
suitable for shared reservations; since a limited number of people
talk at once, each receiver might issue a WF or SE reservation
request for twice the bandwidth required for one sender (to allow
some over-speaking). On the other hand, the FF style, which
creates independent reservations for the flows from different
senders, is appropriate for video signals.
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The RSVP rules disallow merging of shared reservations with
distinct reservations, since these modes are fundamentally
incompatible. They also disallow merging explict sender selection
with wildcard sender selection, since this might produce an
unexpected service for a receiver that specified explicit
selection. As a result of these prohibitions, WF, SE, and FF
styles are all mutually incompatible.
Other reservation options and styles may be defined in the future
(see Appendix D.4, for example).
1.4 Examples of Styles
This section presents examples of each of the reservation styles
and show the effects of merging.
Figure 4 shows schematically a router with two incoming interfaces
through which data streams will arrive, labeled (a) and (b), and
two outgoing interfaces through which data will be forwarded,
labeled (c) and (d). This topology will be assumed in the
examples that follow. There are three upstream senders; packets
from sender S1 (S2 and S3) arrive through previous hop (a) ((b),
respectively). There are also three downstream receivers; packets
bound for R1 (R2 and R3) are routed via outgoing interface (c)
((d), respectively). We furthermore assume that R2 and R3 arrive
via different next hops, e.g., via the two routers D and D' in
Figure 9. This illustrates the effect of a non-RSVP cloud or a
broadcast LAN on interface (d).
In addition to the connectivity shown in 4, we must also specify
the multicast routes within this node. Assume first that data
packets from each Si shown in Figure 4 is routed to both outgoing
interfaces. Under this assumption, Figures 5, 6, and 7 illustrate
Wildcard-Filter, Fixed-Filter, and Shared-Explicit reservations,
respectively.
________________
(a)| | (c)
( S1 ) ---------->| |----------> ( R1 )
| Router |
(b)| | (d)
( S2,S3 ) ------->| |----------> ( R2, R3 )
|________________|
Figure 4: Router Configuration
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For simplicity, these examples show flowspecs as one-dimensional
multiples of some base resource quantity B. The "Receive" column
shows the RSVP reservation requests received over outgoing
interfaces (c) and (d), and the "Reserve" column shows the
resulting reservation state for each interface. The "Send"
column shows the reservation requests that are sent upstream to
previous hops (a) and (b). In the "Reserve" column, each box
represents one reserved "pipe" on the outgoing link, with the
corresponding flow descriptor.
Figure 5, showing the WF style, illustrates the two possible
merging situations. Each of the two next hops on interface (d)
results in a separate RSVP reservation request, as shown. These
two requests are merged into the effective flowspec 3B, which is
used to make the reservation on interface (d). To forward the
reservation requests upstream, the reservations on the interfaces
(c) and (d) are merged; as a result, the larger flowspec 4B is
forwarded upstream to each previous hop.
|
Send | Reserve Receive
|
| _______
WF( *{4B} ) <- (a) | (c) | * {4B}| (c) <- WF( *{4B} )
| |_______|
|
-----------------------|----------------------------------------
| _______
WF( *{4B} ) <- (b) | (d) | * {3B}| (d) <- WF( *{3B} )
| |_______| <- WF( *{2B} )
Figure 5: Wildcard-Filter (WF) Reservation Example
Figure 6 shows Fixed-Filter (FF) style reservations. The flow
descriptors for senders S2 and S3, received from outgoing
interfaces (c) and (d), are packed into the request forwarded to
previous hop (b). On the other hand, the three different flow
descriptors for sender S1 are merged into the single request FF(
S1{4B} ), which is sent to previous hop (a). For each outgoing
interface, there is a separate reservation for each source that
has been requested, but this reservation is shared among all the
receivers that made the request.
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|
Send | Reserve Receive
|
| ________
FF( S1{4B} ) <- (a) | (c) | S1{4B} | (c) <- FF( S1{4B}, S2{5B} )
| |________|
| | S2{5B} |
| |________|
---------------------|---------------------------------------------
| ________
<- (b) | (d) | S1{3B} | (d) <- FF( S1{3B}, S3{B} )
FF( S2{5B}, S3{B} ) | |________| <- FF( S1{B} )
| | S3{B} |
| |________|
Figure 6: Fixed-Filter (FF) Reservation Example
Figure 7 shows an example of Shared-Explicit (SE) style
reservations. When SE-style reservations are merged, the
resulting filter spec is the union of the original filter specs.
|
Send | Reserve Receive
|
| ________
SE( S1{3B} ) <- (a) | (c) |(S1,S2) | (c) <- SE( (S1,S2){B} )
| | {B} |
| |________|
---------------------|---------------------------------------------
| __________
<- (b) | (d) |(S1,S2,S3)| (d) <- SE( (S1,S3){3B} )
SE( (S2,S3){3B} ) | | {3B} | <- SE( S2{2B} )
| |__________|
Figure 7: Shared-Explicit (SE) Reservation Example
The three examples just shown assume that data packets from S1,
S2, and S3 are routed to both outgoing interfaces. The top part
of Figure 8 shows another routing assumption: data packets from S2
and S3 are not forwarded to interface (c), e.g., because the
network topology provides a shorter path for these senders towards
R1, not traversing this node. The bottom part of Figure 8 shows
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WF style reservations under this assumption. Since there is no
route from (b) to (c), the reservation forwarded out interface (b)
considers only the reservation on interface (d).
_______________
(a)| | (c)
( S1 ) ---------->| >-----------> |----------> ( R1 )
| - |
| - |
(b)| - | (d)
( S2,S3 ) ------->| >-------->--> |----------> ( R2, R3 )
|_______________|
Router Configuration
|
Send | Reserve Receive
|
| _______
WF( *{rB} ) <- (a) | (c) | * {B} | (c) <- WF( *{4B} )
| |_______|
|
-----------------------|----------------------------------------
| _______
WF( *{3B} ) <- (b) | (d) | * {3B}| (d) <- WF( * {3B} )
| |_______| <- WF( * {2B}
Figure 8: WF Reservation Example -- Partial Routing
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2. RSVP Protocol Mechanisms
2.1 RSVP Messages
Previous Incoming Outgoing Next
Hops Interfaces Interfaces Hops
_____ _____________________ _____
| | data --> | | data --> | |
| A |-----------| a c |--------------| C |
|_____| Path --> | | Path --> |_____|
<-- Resv | | <-- Resv _____
_____ | ROUTER | | | |
| | | | | |--| D |
| B |--| data-->| | data --> | |_____|
|_____| |--------| b d |-----------|
| Path-->| | Path --> | _____
_____ | <--Resv|_____________________| <-- Resv | | |
| | | |--| D' |
| B' |--| | |_____|
|_____| | |
Figure 9: Router Using RSVP
Figure 9 illustrates RSVP's model of a router node. Each data
stream arrives from a "previous hop" through a corresponding
"incoming interface" and departs through one or more "outgoing
interface(s)". The same physical interface may act in both the
incoming and outgoing roles for different data flows in the same
session. Multiple previous hops and/or next hops may be reached
through a given physical interface, as a result of the connected
network being a shared medium, or the existence of non-RSVP
routers in the path to the next RSVP hop (see Section 2.8). An
RSVP daemon preserves the next and previous hop addresses in its
reservation and path state, respectively.
There are two fundamental RSVP message types: RESV and PATH.
Each receiver host sends RSVP reservation request (RESV) messages
upstream towards the senders. These reservation messages must
follow exactly the reverse of the routes the data packets will
use, upstream to all the sender hosts included in the sender
selection. RESV messages must be delivered to the sender hosts
themselves so that the hosts can set up appropriate traffic
control parameters for the first hop.
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Each RSVP sender host transmits RSVP PATH messages downstream
along the uni-/multicast routes provided by the routing
protocol(s), following the paths of the data. These "Path"
messages store " path state" in each node along the way. This
path state includes at least the unicast IP address of the
previous hop node, which is used to route the RESV messages hop-
by-hop in the reverse direction. (In the future, some routing
protocols may supply reverse path forwarding information directly,
replacing the reverse-routing function of path state).
A PATH message may carry the following information in addition to
the previous hop address:
o Sender Template
A PATH message is required to carry a Sender Template, which
describes the format of data packets that the sender will
originate. This template is in the form of a filter spec
that could be used to select this sender's packets from
others in the same session on the same link.
Like a filter spec, the Sender Template is less than fully
general at present, specifying only the sender IP address and
optionally the UDP/TCP sender port. It assumes the protocol
Id for the session.
o Sender Tspec
A PATH message is required to carry a Sender Tspec, which
defines the traffic characteristics of the data stream that
the sender will generate. This Tspec is used by traffic
control to prevent over-reservation (and perhaps unnecessary
Admission Control failure) on all links on which the named
sender is the only source sending to the session.
o Adspec
A PATH message may optionally carry a package of OPWA
advertising information, known as an "Adspec". An Adspec
received in a PATH message is passed to the local traffic
control, which returns an updated Adspec; the updated version
is then forwarded downstream.
For protocol efficiency, RSVP also allows multiple sets of
reservation information for the same session to be "packed" into a
single RESV message. Unlike merging, packing preserves
information. For simplicity, however, the protocol currently
prohibits packing reservations of different sessions into the same
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RSVP message.
PATH messages are sent with the same source and destination
addresses as the data, so that they will be routed correctly
through non-RSVP clouds (see Section 2.8). On the other hand,
RESV messages are sent hop-by-hop; each RSVP-speaking node
forwards a RESV message to the unicast address of a previous RSVP
hop.
2.2 Port Usage
At present an RSVP session is defined by the triple: (DestAddress,
ProtocolId, DstPort). Here DstPort is a UDP/TCP destination port
field (i.e., a 16-bit quantity carried at octet offset +2 in the
transport header). DstPort may be omitted (set to zero) if the
ProtocolId specifies a protocol that does not have a destination
port field in the format used by UDP and TCP.
RSVP allows any value for ProtocolId. However, end-system
implementations of RSVP may know about certain values for this
field, and in particular must know about the values for UDP and
TCP (17 and 6, respectively). An end system should give an error
to an application that either:
o specifies a non-zero DstPort for a protocol that does not
have UDP/TCP-like ports, or
o specifies a zero DstPort for a protocol that does have
UDP/TCP-like ports.
Filter specs and sender templates are defined by the pair:
(SrcAddress, SrcPort), where SrcPort is a UDP/TCP source port
field (i.e., a 16-bit quantity carried at octet offset +0 in the
transport header). SrcPort may be omitted (set to zero) in
certain cases. The following rules hold for the use of zero
DstPort and/or SrcPort fields in RSVP.
1. Destination ports must be consistent.
Path state and/or reservation state for the same DestAddress
and ProtocolId must have DstPort values that are all zero or
all non-zero. Violation of this condition in a node is a
"Conflicting Dest Port" error.
2. Destination ports rule.
If DstPort in a session definition is zero, all SrcPort
fields used for that session must also be zero. The
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assumption here is that the protocol does not have TCP/UDP-
like ports. Violation of this condition in a node is a
"Conflicting Src Port" error.
3. Source Ports must be consistent.
A sender host must not send path state both with and without
a zero SrcPort. Violation of this condition is an "Ambiguous
Path" error.
2.3 Merging Flowspecs
As noted earlier, a single physical interface may receive multiple
reservation request from different next hops for the same session
and with the same filter spec, but RSVP should install only one
reservation on that interface. This reservation should an
effective flowspec that is the "maximum" of the flowspecs
requested by the different next hops. Similarly, a RESV message
forwarded to a previous hop should carry a flowspec that is the
"maximum" of the flowspecs requested by the different next hops.
Both cases represent flowspec merging.
Merging flowspecs requires calculating the "largest" of a set of
flowspecs, which are otherwise opaque to RSVP. Since flowspecs
are multi-dimensional vectors (they contain both Tspec and Rspec
components, each of which may itself be multi-dimensional),
generally speaking they cannot be strictly ordered. However, in
many cases one can easily determine the "larger" of two flowspecs,
such as when both request the same bandwidth but one requests a
tighter delay, or when one of the two requests both a higher
bandwidth and a tighter delay bound. When the "larger" of the two
cannot be determined, RSVP must compute and use a third flowspec
that is at least as large as each, i.e., a "least upper bound"
(LUB). If the two flowspecs are incomparable, their comparison
will treated as an error.
We can now give the complete rules for calculating the effective
flowspec (Te, Re) to be installed on an interface. Here Te is the
effective Tspec and Re is the effective Rspec. As an example,
consider interface (d) in Figure 9.
1. Re is calculated as the largest (using an LUB if necessary)
of the Rspecs in RESV messages from different next hops
(e.g., D and D') but the same outgoing interface (d).
2. All Tspecs that were supplied in PATH messages from different
previous hops (e.g., some or all of A, B, and B' in Figure 9)
are summed; call this sum Path_Te.
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3. The maximum Tspec supplied in RESV messages from different
next hops (e.g., D and D') is calculated; call this Resv_Te.
4. Te is the GLB (greatest lower bound) of Path_Te and Resv_Te.
For Tspecs defined by token bucket parameters, this means to
take the smaller of the bucket size and the rate parameters.
Flowspecs, Tspecs, and Adspecs are opaque to RSVP. Therefore, the
last of these steps is actually performed by traffic control. The
definition and implementation of the rules for comparing
flowspecs, calculating LUB's, and summing Tspecs are outside the
definition of RSVP [ServTempl95a]. Section 3.9.4 shows generic
calls that an RSVP daemon could use for these functions.
2.4 Soft State
RSVP takes a "soft state" approach to managing the reservation
state in routers and hosts. RSVP soft state is created and
periodically refreshed by PATH and RESV messages. The state is
deleted if no matching refresh messages arrive before the
expiration of a "cleanup timeout" interval. It may also be
deleted by an explicit "teardown" message, described in the next
section. At the expiration of each "refresh timeout" period and
after a state change, RSVP scans its state to build and forward
PATH and RESV refresh messages to succeeding hops.
PATH and RESV messages are idempotent. When a route changes, the
next PATH message will initialize the path state on the new route,
and future RESV messages will establish reservation state there;
the state on the now-unused segment of the route will time out.
Thus, whether a message is "new" or a "refresh" is determined
separately at each node, depending upon the existing state at that
node.
RSVP sends its messages as IP datagrams with no reliability
enhancement. Periodic transmission of refresh messages by hosts
and routers is expected to handle the occasional loss of RSVP
messages. If the effective cleanup timeout is set to K times the
refresh timeout period, then RSVP can tolerate K-1 successive RSVP
packet losses without falsely erasing a reservation. We recommend
that the network traffic control mechanism be statically
configured to grant some minimal bandwidth for RSVP messages to
protect them from congestion losses.
The state maintained by RSVP is dynamic; to change the set of
senders Si or to change any QoS request, a host simply starts
sending revised PATH and/or RESV messages. The result should be
an appropriate adjustment in the RSVP state in all nodes along the
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path.
In steady state, refreshing is performed hop-by-hop to allow
merging. If the received state differs from the stored state, the
stored state is updated. If this update results in modification
of state to be forwarded in refresh messages, these refresh
messages must be generated and forwarded immediately, so that
state changes can be propagated end-to-end without delay.
However, propagation of a change stops when and if it reaches a
point where merging causes no resulting state change. This
minimizes RSVP control traffic due to changes and is essential for
scaling to large multicast groups.
State that is received through a particular interface I* should
never be forwarded out the same interface. Conversely, state that
is forwarded out interface I* must be computed using only state
that arrived on interfaces different from I*. A trivial example
of this rule is illustrated in Figure 10, which shows a transit
router with one sender and one receiver on each interface (and
assumes one next/previous hop per interface). Interfaces (a) and
(c) serve as both outgoing and incoming interfaces for this
session. Both receivers are making wildcard-scope reservations,
in which the RESV messages are forwarded to all previous hops for
senders in the group, with the exception of the next hop from
which they came. The result is independent reservations in the
two directions.
There is an additional rule governing the forwarding of RESV
messages: state from RESV messages received from outgoing
interface Io should be forwarded to incoming interface Ii only if
PATH messages from Ii are forwarded to Io.
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________________
a | | c
( R1, S1 ) <----->| Router |<-----> ( R2, S2 )
|________________|
Send | Receive
|
WF( *{3B}) <-- (a) | (c) <-- WF( *{3B})
|
Receive | Send
|
WF( *{4B}) --> (a) | (c) --> WF( *{4B})
|
Reserve on (a) | Reserve on (c)
__________ | __________
| * {4B} | | | * {3B} |
|__________| | |__________|
|
Figure 10: Independent Reservations
2.5 Teardown
Upon arrival, RSVP "teardown" messages remove path and reservation
state immediately. Although it is not necessary to explicitly
tear down an old reservation, we recommend that all end hosts send
a teardown request as soon as an application finishes.
There are two types of RSVP teardown message, PTEAR and RTEAR. A
PTEAR message travels towards all receivers downstream from its
point of initiation and deletes path state along the way. An
RTEAR message deletes reservation state and travels towards all
senders upstream from its point of initiation. A PTEAR (RTEAR)
message may be conceptualized as a reversed-sense Path message
(Resv message, respectively).
A teardown request may be initiated either by an application in an
end system (sender or receiver), or by a router as the result of
state timeout. Once initiated, a teardown request must be
forwarded hop-by-hop without delay. A teardown message deletes
the specified state in the node where it is received. As always,
this state change will be propagated immediately to the next node,
but only if there will be a net change after merging. As a
result, an RTEAR message will prune the reservation state back
(only) as far as possible.
Like all other RSVP messages, teardown requests are not delivered
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reliably. The loss of a teardown request message will not cause a
protocol failure because the unused state will eventually time out
even though it is not explicitly deleted. If a teardown message
is lost, the router that failed to receive that message will time
out its state and initiate a new teardown message beyond the loss
point. Assuming that RSVP message loss probability is small, the
longest time to delete state will seldom exceed one refresh
timeout period.
2.6 Errors and Acknowledgments
There are two RSVP error messages, RERR and PERR, and a
reservation confirmation message RACK.
There are a number of ways for a syntactically valid reservation
request to fail at some node along the path, triggering a RERR
message:
1. The effective flowspec that is computed using the new request
may fail admission control.
2. Administrative policy may prevent the requested reservation.
3. There may be no matching path state, so that the request
cannot be forwarded towards the sender(s).
4. A reservation style that requires the explicit selection of a
unique sender may have a filter spec that is ambiguous, i.e.,
that matches more than one sender in the path state, due to
the use of wildcard fields in the filter spec.
5. The requested style may be incompatible with the style(s) of
existing reservations. The incompatibility may occur among
reservations for the same session on the same outgoing
interface, or among effective reservations on different
outgoing interfaces.
In any of these cases, a RERR message is returned to the
receiver(s) responsible for the erroneous request. A node may
also decide to preempt an established reservation. A preemption
will trigger a RERR message to all affected receivers. An error
message does not modify state in the nodes through which it
passes. Therefore, any reservations established downstream of the
node where the failure occurred will persist until the responsible
receiver(s) explicitly tear down the state or allow it to time
out.
In this version of RSVP, detection of an error in a reservation
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request not only generates a RERR message, it also prevents the
request from being forwarded further. This may not always be the
desirable behavior; for example, a receiver may want a reservation
request to propagate all the way to the sender despite an
admission control failure at a particular link along the path.
However, design of the appropriate mechanism has proved difficult,
and therefore this version take the simplest approach.
When admission control fails for a reservation request, any
existing reservation is left in place. This prevents a new, very
large, reservation from disrupting the existing QoS by merging
with an existing reservation and then failing admission control
(this has been called the "killer reservation" problem).
To request a confirmation for its reservation request, a receiver
Rj includes in the RESV message a confirmation-request object
containing its IP address. At each merge point, only the largest
flowspec and any accompanying confirmation-request object is
forwarded upstream. If the reservation request from Rj is equal
to or smaller than the reservation in place on a node, its RESV
are not forwarded further, and if the RESV included an
confirmation-request object, a RACK message is sent back to Rj.
This mechanism has the following consequences:
o A new reservation request with a flowspec larger than any in
place for a session will normally result in either a RERR or
a RACK message back to the receiver from each sender. In
this case, the RACK message will be an end-to-end
confirmation.
o The receipt of a RACK gives no guarantees. Assume the first
two reservation requests from receivers R1 and R2 arrive at
the node where they are merged. R2, whose reservation was
the second to arrive at that node, may receive a RACK from
that node while R1's request has not yet propagated all the
way to a matching sender and may still fail. In this case,
R2 will receive a RACK although there is no end-to-end
reservation in place. Furthermore, if the two flowspecs are
equal, R2 may receive a RACK followed by a RERR. However, if
its flowspec is smaller, R2 will receive only the RACK.
o Despite these uncertainties, receipt of a RACK indicates a
high probability that the reservation is in place.
o Finally, note that RERR and/or RACK messages may be lost.
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2.7 Policy and Security
RSVP-mediated QoS requests will result in particular user(s)
getting preferential access to network resources. To prevent
abuse, some form of back pressure on users is likely to be
required. This back pressure might take the form of
administrative rules, or of some form of real or virtual billing
for the "cost" of a reservation. The form and contents of such
back pressure is a matter of administrative policy that may be
determined independently by each administrative domain in the
Internet.
Therefore, admission control at each node is likely to contain a
policy component in addition to a resource reservation component.
As input to the policy-based admission decision, RSVP messages may
carry policy data. This data may include credentials identifying
users or user classes, account numbers, limits, quotas, etc.
To protect the integrity of the policy-based admission control
mechanisms, it may be necessary to ensure the integrity of RSVP
messages against corruption or spoofing, hop by hop. For this
purpose, RSVP messages may carry integrity objects that can be
created and verified by neighbor RSVP-capable nodes. These
objects are expected to contain an encrypted part and to assume a
shared secret between neighbors.
User policy data in reservation request messages presents a
scaling problem. When a multicast group has a large number of
receivers, it will be impossible or undesirable to carry all
receivers' policy data upstream to the sender(s). The policy data
will have to be administratively merged at places near the
receivers, to avoid excessive policy data. Administrative merging
implies checking the user credentials and accounting data and then
substituting a token indicating the check has succeeded. A chain
of trust established using an integrity field will allow upstream
nodes to accept these tokens.
In summary, different administrative domain in the Internet may
have different policies regarding their resource usage and
reservation. The role of RSVP is to carry policy data associated
with each reservation to the network as needed. Note that the
merge points for policy data are likely to be at the boundaries of
administrative domains. It may be necessary to carry accumulated
and unmerged policy data upstream through multiple nodes before
reaching one of these merge points.
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2.8 Automatic RSVP Tunneling
It is impossible to deploy RSVP (or any new protocol) at the same
moment throughout the entire Internet. Furthermore, RSVP may
never be deployed everywhere. RSVP must therefore provide correct
protocol operation even when two RSVP-capable routers are joined
by an arbitrary "cloud" of non-RSVP routers. Of course, an
intermediate cloud that does not support RSVP is unable to perform
resource reservation. However, if such a cloud has sufficient
capacity, it may still provide acceptable realtime service.
RSVP automatically tunnels through such a non-RSVP cloud. Both
RSVP and non-RSVP routers forward PATH messages towards the
destination address using their local uni-/multicast routing
table. Therefore, the routing of PATH messages will be unaffected
by non-RSVP routers in the path. When a PATH message traverses a
non-RSVP cloud, it carries to the next RSVP-capable node the IP
address of the last RSVP-capable router before entering the cloud.
This effectively constructs a tunnel through the cloud for RESV
messages, which can then be forwarded directly to the next RSVP-
capable router on the path(s) back towards the source.
Some interconnection topologies of RSVP and non-RSVP routers can
cause RESV messages to arrive at the wrong RSVP-capable node, or
to arrive at the wrong interface at the correct node. An RSVP
daemon must be prepared to handle either situation. When a RESV
message arrives, its IP destination address should normally be the
address of one of the local interfaces. If so, the reservation
should be made on the addressed interface, even if it is not the
one on which the message arrived. If the destination address does
not match any local interface and the message is not a PATH or
PTEAR, it should be forwarded without further processing by this
node.
2.9 Host Model
Before a session can be created, the session identification,
comprised of DestAddress and perhaps the generalized destination
port, must be assigned and communicated to all the senders and
receivers by some out-of-band mechanism. When an RSVP session is
being set up, the following events happen at the end systems.
H1 A receiver joins the multicast group specified by
DestAddress, using IGMP.
H2 A potential sender starts sending RSVP PATH messages to the
DestAddress.
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H3 A receiver application receives a PATH message.
H4 A receiver starts sending appropriate RESV messages,
specifying the desired flow descriptors.
H5 A sender application receives a RESV message.
H6 A sender starts sending data packets.
There are several synchronization considerations.
o H1 and H2 may happen in either order.
o Suppose that a new sender starts sending data (H6) but there
are no multicast routes because no receivers have joined the
group (H1). Then the data will be dropped at some router
node (which node depends upon the routing protocol) until
receivers(s) appear.
o Suppose that a new sender starts sending PATH messages (H2)
and data (H6) simultaneously, and there are receivers but no
RESV messages have reached the sender yet (e.g., because its
PATH messages have not yet propagated to the receiver(s)).
Then the initial data may arrive at receivers without the
desired QoS. The sender could mitigate this problem by
awaiting arrival of the first RESV message (H5); however,
receivers that are farther away may not have reservations in
place yet.
o If a receiver starts sending RESV messages (H4) before
receiving any PATH messages (H3), RSVP will return error
messages to the receiver.
The receiver may simply choose to ignore such error messages,
or it may avoid them by waiting for PATH messages before
sending RESV messages. [LZ: should recommend that a receiver
wait for at least PATH messages to arrive before sending RESV
messages.]
A specific application program interface (API) for RSVP is not
defined in this protocol spec, as it may be host system dependent.
However, Section 3.9.1 discusses the general requirements and
presen
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3. RSVP Functional Specification
3.1 RSVP Message Formats
An RSVP message consists of a common header followed by a variable
number of variable-length, typed "objects". The subsections that
follow define the formats of the common header, the object
structures, and each of the RSVP message types.
For each RSVP message type, there is a set of rules for the
permissible choice and ordering of object types. These rules are
specified using Backus-Naur Form (BNF) augmented with square
brackets surrounding optional sub-sequences.
3.1.1 Common Header
0 1 2 3
+-------------+-------------+-------------+-------------+
| Vers | Flags| Type | RSVP Checksum |
+-------------+-------------+-------------+-------------+
| RSVP Length | (Reserved) | Send_TTL |
+-------------+-------------+-------------+-------------+
| Message ID |
+----------+--+-------------+-------------+-------------+
|(Reserved)|MF| Fragment offset |
+----------+--+-------------+-------------+-------------+
The fields in the common header are as follows:
Vers: 4 bits
Protocol version number. This is version 1.
Flags: 4 bits
(None defined yet)
Type: 8 bits
1 = PATH
2 = RESV
3 = PERR
4 = RERR
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5 = PTEAR
6 = RTEAR
7 = RACK
RSVP Checksum: 16 bits
A standard TCP/UDP checksum over the contents of the RSVP
message, with the checksum field replaced by zero.
RSVP Length: 16 bits
The total length of this RSVP packet in bytes, including
the common header and the variable-length objects that
follow. If the MF flag is on or the Fragment Offset field
is non-zero, this is the length of the current fragment of
a larger message.
Send_TTL: 8 bits
The IP TTL value with which the message was sent.
Message ID: 32 bits
A label shared by all fragments of one message from a
given next/previous RSVP hop. An RSVP implementation
assigns a unique Message ID to each message it sends.
MF: More Fragments Flag: 1 bit
This flag is the low-order bit of a byte; the seven high-
order bits are reserved. It is on for all but the last
fragment of a message.
Fragment Offset: 24 bits
This field gives the byte offset of the fragment in the
message.
3.1.2 Object Formats
Every object consists of one or more 32-bit words with a one-
word header, in the following format:
0 1 2 3
+-------------+-------------+-------------+-------------+
| Length (bytes) | Class-Num | C-Type |
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+-------------+-------------+-------------+-------------+
| |
// (Object contents) //
| |
+-------------+-------------+-------------+-------------+
An object header has the following fields:
Length
A 16-bit field containing the total object length in
bytes. Must always be a multiple of 4, and at least 4.
Class-Num
Identifies the object class; values of this field are
defined in Appendix A. Each object class has a name,
which is always capitalized in this document. An RSVP
implementation must recognize the following classes:
NULL
A NULL object has a Class-Num of zero, and its C-Type
is ignored. Its length must be at least 4, but can
be any multiple of 4. A NULL object may appear
anywhere in a sequence of objects, and its contents
will be ignored by the receiver.
SESSION
Contains the IP destination address (DestAddress),
the IP protocol id, and a generalized destination
port, to define a specific session for the other
objects that follow. Required in every RSVP message.
RSVP_HOP
Carries the IP address of the RSVP-capable node that
sent this message. This document refers to a
RSVP_HOP object as a PHOP ("previous hop") object for
downstream messages or as a NHOP ("next hop") object
for upstream messages.
TIME_VALUES
Contains the value for the refresh period R used by
the creator of the message; see 3.5. Required in
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every PATH and RESV message.
STYLE
Defines the reservation style plus style-specific
information that is not in FLOWSPEC or FILTER_SPEC
objects. Required in every RESV message.
FLOWSPEC
Defines a desired QoS, in a RESV message.
FILTER_SPEC
Defines a subset of session data packets that should
receive the desired QoS (specified by an FLOWSPEC
object), in a RESV message.
SENDER_TEMPLATE
Contains a sender IP address and perhaps some
additional demultiplexing information to identify a
sender, in a PATH message.
SENDER_TSPEC
Defines the traffic characteristics of a sender's
data stream, in a PATH message.
ADSPEC
Carries OPWA data, in a PATH message.
ERROR_SPEC
Specifies an error, in a PERR or RERR message.
POLICY_DATA
Carries information that will allow a local policy
module to decide whether an associated reservation is
administratively permitted. May appear in a PATH or
RESV message.
INTEGRITY
Contains cryptographic data to authenticate the
originating node, and perhaps to verify the contents,
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of this RSVP message.
SCOPE
An explicit list of sender hosts towards which to
forward a message. May appear in a RESV, RERR, or
RTEAR message.
RESV_CONFIRM
Carries the IP address of a receiver that requested a
confirmation. May appear in a RESV or RACK message.
C-Type
Object type, unique within Class-Num. Values are defined
in Appendix A.
The maximum object content length is 65528 bytes. The Class-
Num and C-Type fields may be used together as a 16-bit number
to define a unique type for each object.
The high-order bit of the Class-Num is used to determine what
action a node should take if it does not recognize the Class-
Num of an object; see Section 3.8.
3.1.3 Path Message
Each sender host periodically sends a PATH message containing a
description of each data stream it originates. The PATH
message travels from a sender to receiver(s) along the same
path(s) used by the data packets. The IP source address of a
PATH message is an address of the sender it describes, while
the destination address is the DestAddress for the session.
These addresses assure that the message will be correctly
routed through a non-RSVP cloud.
Each RSVP-capable node along the path(s) captures PATH messages
and processes them to build local path state. The node then
forwards the PATH messages towards the receiver(s), replicating
it as dictated by multicast routing, while preserving the
original IP source address. PATH messages eventually reach the
applications on all receivers; however, they are not looped
back to a receiver running in the same application process as
the sender.
The format of a PATH message is as follows:
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<Path Message> ::= <Common Header> <SESSION> <RSVP_HOP>
[ <INTEGRITY> ] <TIME_VALUES>
<sender descriptor>
<sender descriptor> ::= <SENDER_TEMPLATE> <SENDER_TSPEC>
[ <POLICY_DATA> ] [ <ADSPEC> ]
The PHOP (i.e., the RSVP_HOP) object of each PATH message
contains the address of the interface through which the PATH
message was most recently sent. The SENDER_TEMPLATE object
defines the format of data packets from this sender, while the
SENDER_TSPEC object specifies the traffic characteristics of
the flow. Optionally, there may be a POLICY_DATA object
specifying user credential and accounting information and/or an
ADSPEC object carrying advertising (OPWA) data.
A PATH message received at a node is processed to create path
state for the sender defined by the SENDER_TEMPLATE and SESSION
objects. Any POLICY_DATA, SENDER_TSPEC, and ADSPEC objects are
also saved in the path state. If an error is encountered while
processing a PATH message, a PERR message is sent to the
originating sender of the PATH message. PATH messages must
satisfy the rules on SrcPort and DstPort in Section 2.2.
Periodically, the RSVP daemon at a node scans the path state to
create new PATH messages to forward downstream. Each message
contains a sender descriptor defining one sender. The RSVP
daemon forwards these messages using routing information it
obtains from the appropriate uni-/multicast routing daemon.
The route depends upon the session DestAddress, and for some
routing protocols also upon the source (sender's IP) address.
The routing information generally includes the list of none or
more outgoing interfaces to which the PATH message to be
forwarded. Because each outgoing interface has a different IP
address, the PATH messages sent out different interfaces
contain different PHOP addresses. In addition, any ADSPEC or
POLICY_DATA objects carried in PATH messages will also
generally differ for different outgoing interfaces.
Some IP multicast routing protocols (e.g., DVMRP, PIM, and
MOSPF) also keep track of the expected incoming interface for
each source host to a multicast group. Whenever this
information is available, RSVP should check the incoming
interface of each PATH message and immediately discard those
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messages that have arrived on the wrong interface.
3.1.4 Resv Messages
RESV messages carry reservation requests hop-by-hop from
receivers to senders, along the reverse paths of data flows for
the session. The IP destination address of a RESV message is
the unicast address of a previous-hop node, obtained from the
path state. The IP source address is an address of the node
that sent the message.
The RESV message format is as follows:
<Resv Message> ::= <Common Header> <SESSION> <RSVP_HOP>
[ <INTEGRITY> ] <TIME_VALUES>
[ <S_POLICY_DATA> ]
[ <RESV_CONFIRM> ] [ <SCOPE> ]
<STYLE> <flow descriptor list>
<S_POLICY_DATA> ::= <POLICY_DATA>
<flow descriptor list> ::= <flow descriptor> |
<flow descriptor list> <flow descriptor>
The NHOP (i.e., the RSVP_HOP) object contains the IP address of
the (incoming) interface through which the RESV message is
sent. The appearance of a RESV_CONFIRM object signals a
request for a reservation confirmation and carries the IP
address of the receiver to which the RACK should be sent. The
S_POLICY_DATA object is a POLICY_DATA object that is associated
with the entire session. There may also be flow-specific
POLICY_DATA objects, as described below.
The BNF above defines a flow descriptor list as simply a list
of flow descriptors. The following style-dependent rules
specify in more detail the composition of a valid flow
descriptor list for each of the reservation styles.
o WF Style:
<flow descriptor list> ::= <WF flow descriptor>
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<WF flow descriptor> ::= <FLOWSPEC> [ <F_POLICY_DATA> ]
<F_POLICY_DATA> ::= <POLICY_DATA>
o FF style:
<flow descriptor list> ::= <First FF flow descriptor> |
<flow descriptor list> <FF flow descriptor>
<First FF flow descriptor> ::=
<FLOWSPEC> [ <F_POLICY_DATA> ] <FILTER_SPEC>
<FF flow descriptor> ::=
[ <FLOWSPEC> ] [ <F_POLICY_DATA> ] <FILTER_SPEC>
Each elementary FF style request is defined by a single
(FLOWSPEC, FILTER_SPEC) pair, and multiple such requests
may be packed into the flow descriptor list of a single
RESV message. A FLOWSPEC object can be omitted if it is
identical to the most recent such object that appeared in
the list; the first FF flow descriptor must contain a
FLOWSPEC.
o SE style:
<flow descriptor list> ::= <SE flow descriptor>
<SE flow descriptor> ::=
<FLOWSPEC> [ <F_POLICY_DATA> ] <filter spec list>
<filter spec list> ::= <FILTER_SPEC>
| <filter spec list> <FILTER_SPEC>
Each elementary SE style request is defined by a single SE
descriptor, which includes a FLOWSPEC defining the shared
reservation, optionally a POLICY_DATA object, and a list
of FILTER_SPEC objects.
The reservation scope, i.e., the set of senders towards which a
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particular reservation is to be forwarded, is determined as
follows:
o Explicit sender selection
Match each FILTER_SPEC object against the path state
created from SENDER_TEMPLATE objects to select a
particular sender. An ambiguous match, i.e., a
FILTER_SPEC matching more than one SENDER_TEMPLATE (e.g.
through use of a wildcard port), is an error. Any SCOPE
object associated with the reservation should be ignored
in this case.
o Wildcard sender selection
All senders that route to the given outgoing interface
match this request. A SCOPE object, if present, contains
an explicit list of sender IP addresses. If there is no
SCOPE object, the scope is determined by the relevant set
of senders in the path state. Whenever a RESV message
with wildcard sender selection is forwarded to more than
one previous hop, a SCOPE object must be included in the
message. See Section 3.3 below.
3.1.5 Error and Confirmation Messages
There are three types of RSVP error/confirmation messages.
o PERR messages result from PATH messages and travel towards
senders. PERR messages are routed hop-by-hop using the
path state; at each hop, the IP destination address is the
unicast address of a previous hop.
o RERR messages result from RESV messages and travel towards
the appropriate receivers. They are routed hop-by-hop
using the reservation state; at each hop, the IP
destination address is the unicast address of a next-hop
node.
o RACK messages are sent to (probabilistically) acknowledge
reservation requests. A RACK message is sent as the
result of the appearance of a RESV_CONFIRM object in a
RESV message, and contains a copy of that RESV_CONFIRM.
The RACK message is sent to the unicast address of a
receiver host; the address is obtained from the
RESV_CONFIRM object. A RACK message is forwarded to the
receiver hop-by-hop by (to accommodate the hop-by-hop
integrity check mechanism).
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Errors encountered while processing error messages must cause
the error message to be discarded without creating further
error messages; however, logging of such events may be useful.
None of these messages modify the state of any node through
which they pass; instead, they are only reported to the end
application.
<PathErr message> ::= <Common Header> <SESSION>
[ <INTEGRITY> ] <ERROR_SPEC>
<sender descriptor>
<sender descriptor> ::= (see earlier definition)
<ResvErr Message> ::= <Common Header> <SESSION>
[ <INTEGRITY> ] <ERROR_SPEC>
[S_POLICY_DATA] [ <SCOPE> ]
<STYLE> <error flow descriptor>
<ResvConf Message> ::= <Common Header> <SESSION>
[ <INTEGRITY> ] <ERROR_SPEC>
<RESV_CONFIRM>
<STYLE> <flow descriptor list>
<flow descriptor list> ::= (see earlier definition)
The RESV_CONFIRM object in a RACK message is a copy of the
object from the RESV message that triggered the confirmation.
The following style-dependent rules define the composition of a
valid error flow descriptor:
o WF Style:
<error flow descriptor> ::= <WF flow descriptor>
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o FF style:
<error flow descriptor> ::= <FF flow descriptor>
o SE style:
<error flow descriptor> ::= <SE flow descriptor>
The ERROR_SPEC object specifies the error and includes the IP
address of the node that detected the error (Error Node
Address). POLICY_DATA objects are included in error messages
in cases where they may provide relevant information (i.e.,
when an administrative failure is being reported). In a RACK
message, the ERROR_SPEC is used only to carry the IP address of
the originating node, in the Error Node Address; the error
specification is a special value that indicates a confirmation.
When a RESV message contains a list of flow descriptors (e.g.,
FF style), the RSVP implementation should process each flow
descritor independently and return a separate RERR message for
each that is in error.
Generally speaking, a RERR message should be forwarded towards
all receivers that may have caused the error being reported.
More specifically:
o The node that detects an error in a reservation request
sends a RERR message to the next hop from which the
erroneous reservation came.
The message must contain the information required to
define the error and to route the error message. Routing
requires at least a STYLE object and one or more
FILTER_SPEC object(s) from the erroneous RESV message.
For an admission control failure, for example, the
erroneous FLOWSPEC must be included.
o Succeeding nodes forward the RERR message using their
local reservation state, to the next hops of reservations
that match the FILTER_SPEC(s) in the message. For
reservations with wildcard scope, there is an additional
limitation on forwarding RERR messages, to avoid loops;
see Section 3.3.
When the error is an admission control failure, a node is
allowed (but not required) to match the FLOWSPEC as well as the
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FILTER_SPEC object(s), to limit the distribution of a RERR
message to those receivers that `caused' the error. Suppose
that a RERR message contains a FLOWSPEC Qerr that is being
matched against the FLOWSPEC Qlocal in the local reservation
state in node N. Qerr, which originated in a node upstream
from N, resulted from merging of flowspecs that included
Qlocal. Generally, a RERR message can be forwarded to the
receiver(s) that specified the `biggest' flowspec. The
comparison of Qerr against a particular Qlocal to determine
whether Qlocal qualifies as (one of) the `biggest', may be
called `de-merging'. As with merging, the details of de-
merging depend upon the service and the FLOWSPEC format, and
are outside RSVP itself.
A RERR message that is forwarded should carry the FILTER_SPEC
from the corresponding reservation state (thus `de-merging' the
filter spec).
When a RERR or RACK message reaches a receiver, the STYLE
object, flow descriptor list, and ERROR_SPEC object (which
contains the LUB-Used flag) should be delivered to the receiver
application. In the case of an Admission Control error, the
flow descriptor list will contain the FLOWSPEC object that
failed. If the LUB-Used flag is off, this should be
semantically equivalent (but not necessarily identical) to the
FLOWSPEC originated by this application; otherwise, they may
differ.
3.1.6 Teardown Messages
There are two types of RSVP Teardown message, PTEAR and RTEAR.
o A PTEAR message deletes path state (which in turn deletes
the reservation state for that sender, if there is any)
and travels towards all receivers that are downstream from
the point of initiation. A PTEAR message is routed like a
PATH message, and its IP destination address is
DestAddress for the session.
o A RTEAR message deletes reservation state and travels
towards all matching senders upstream from the point of
teardown initiation. A RTEAR message is routed in the
same way as a corresponding RESV message (using the same
scope rules). Its IP destination address is the unicast
address of a previous hop.
<PathTear Message> ::= <Common Header> <SESSION> <RSVP_HOP>
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[ <INTEGRITY> ]
<sender descriptor>
<sender descriptor> ::= (see earlier definition)
<ResvTear Message> ::= <Common Header> <SESSION> <RSVP_HOP>
[ <INTEGRITY> ] [ <SCOPE> ]
<STYLE> <flow descriptor list>
<flow descriptor list> ::= (see earlier definition)
FLOWSPEC or POLICY_DATA objects in the flow descriptor list of
a RTEAR message will be ignored and may be omitted.
Note that, unless it is accidentally dropped along the way, a
PTEAR message will reach all the receivers down stream from its
origination. On the other hand, a RTEAR message will cease to
be forwarded at the same node where merging suppresses
forwarding of the corresponding RESV messages. In each node N
along the way, if the RTEAR message causes the removal of all
state for this session, N will create a new teardown message to
be propagated further upstream; otherwise, the RTEAR message
may result in the immediate forwarding of a modified RESV
refresh message.
Deletion of path state as the result of a PTEAR message or a
timeout may force adjustments in related reservation state, to
maintain state consistency in the local node. The adjustment
in reservation state depends upon the style. For example,
suppose a PTEAR deletes the path state for a sender S. If the
style specifies explicit sender selection (FF or SE), delete
any reservation with a filter spec matching S; otherwise, the
style is wildcard sender selection (WF) and the reservation
should be deleted if S is the last sender to the session.
These reservation changes should not trigger an immediate RESV
refresh message, since the PTEAR message have already made the
required changes upstream. However, at the node in which a
RTEAR message stops, the change of reservation state may
trigger a RESV refresh starting at that node.
3.2 Sending RSVP Messages
RSVP messages are sent hop-by-hop between RSVP-capable routers as
"raw" IP packets with protocol number 46. Raw IP packets are
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intended to be used between an end system and the first/last hop
router, although it is also possible to encapsulate RSVP messages
as UDP datagrams for end-system communication, as described in
Appendix C. UDP encapsulation is needed for systems that cannot
do raw network I/O.
PATH, PTEAR, and RACK messages must be sent with the Router Alert
IP option [Katz95] in their IP headers. This option may be used
by in the fast forwarding path of a high-speed router to detect
datagrams that require special processing.
Upon the arrival of an RSVP message M that changes the state, a
node must forward the modified state immediately. However, this
must not trigger sending an message out the interface through
which M arrived (as could happen if the implementation simply
triggered an immediate refresh of all state for the session).
This rule is necessary to prevent packet storms on broadcast LANs.
An RSVP message must be fragmented when necessary to fit into the
MTU of the interface through which it will be sent. All fragments
of the message should carry the same unique value of the Message
ID field, as well as appropriate Fragment Offset and MF bits, in
their common headers. When an RSVP message arrives, it must be
reassembled before it can be processed. The refresh period R can
be used as an appropriate reassembly timeout time.
Since RSVP messages are normally generated and sent hop-by-hop,
using the RSVP-level fragmentation mechanism should avoid further
fragmentation at the IP level. However, IP fragmentation may
still occur when RSVP messages travel through a non-RSVP cloud.
In case of IP6, which does not support IP fragmentation at
routers, an RSVP implementation must use Path MTU Discovery or
hand configuration to obtain an appropriate MTU between adjacent
RSVP neighbors.
RSVP recovers from occasional packet losses by its periodic
refresh mechanism. Under network overload, however, substantial
losses of RSVP messages could cause a failure of resource
reservations. To control the queueing delay and dropping of RSVP
packets, routers should be configured to offer them a preferred
class of service. If RSVP packets experience noticeable losses
when crossing a congested non-RSVP cloud, a larger value can be
used for the timeout factor K (see section 3.5 below).
Some multicast routing protocols provide for "multicast tunnels",
which encapsulate multicast packets for transmission through
routers that do not have multicast capability. A multicast tunnel
looks like a logical outgoing interface that is mapped into some
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physical interface. A multicast routing protocol that supports
tunnels will describe a route using a list of logical rather than
physical interfaces. RSVP can run through multicast tunnels in
the following manner:
1. When a node N forwards a PATH message out a logical outgoing
interface L, it includes in the message some encoding of the
identity of L, called the "logical interface handle" or LIH.
The LIH value is carried in the RSVP_HOP object.
2. The next hop node N' stores the LIH value in its path state.
3. When N' sends a RESV message to N, it includes the LIH value
from the path state (again, in the RSVP_HOP object).
4. When the RESV message arrives at N, its LIH value provides
the information necessary to attach the reservation to the
appropriate logical interface. Note that N creates and
interprets the LIH; it is an opaque value to N'.
3.3 Avoiding RSVP Message Loops
Forwarding of RSVP messages must avoid looping. In steady state,
PATH and RESV messages are forwarded only once per refresh period
on each hop. This avoids looping packets, but there is still the
possibility of an " auto-refresh" loop, clocked by the refresh
period. Such auto-refresh loops keep state active "forever", even
if the end nodes have ceased refreshing it, until either the
receivers leave the multicast group and/or the senders stop
sending PATH messages. On the other hand, error and teardown
messages are forwarded immediately and are therefore subject to
looping.
Consider each message type.
o PATH Messages
PATH messages are forwarded in exactly the same way as IP
data packets. Therefore there should be no loops of PATH
messages, even in a topology with cycles.
o PTEAR Messages
PTEAR messages use the same routing as PATH messages and
therefore cannot loop.
o PERR Messages
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Since PATH messages do not loop, they create path state
defining a loop-free reverse path to each sender. PERR
messages are always directed to particular senders and
therefore cannot loop.
o RESV Messages
RESV messages directed to particular senders (i.e., with
explicit sender selection) cannot loop. However, RESV
messages with wildcard sender selection (WF style) have a
potential for auto-refresh looping.
o RTEAR Messages
Although RTEAR messages are routed the same as RESV messages,
during the second pass around a loop there will be no state
so any RTEAR message will be dropped. Hence there is no
looping problem here.
o RERR Messages
RERR messages for WF style reservations may loop for
essentially the same reasons that RESV messages loop.
o RACK Messages
RACK messages are forwarded towards a fixed unicast receiver
address and cannot loop.
If the topology has no loops, then looping of "wildcard" RESV and
RERR messages, i.e., messages with wildcard sender selection, can
be avoided by simply enforcing the rule given earlier: state that
is received through a particular interface must never be forwarded
out the same interface. However, when the topology does have
cycles, further effort is needed to prevent auto-refresh loops of
wildcard RESV messages and fast loops of wildcard RERR messages.
The solution to this problem adopted by this protocol
specification is for such messages to carry an explicit sender
address list in a SCOPE object.
When a RESV message with WF style is to be forwarded to a
particular previous hop, a new SCOPE object is computed from the
SCOPE objects that were received in matching RESV messages. If
the computed SCOPE object is empty, the message is not forwarded
to the previous hop; otherwise, the message is sent containing the
new SCOPE object. The rules for computing a new SCOPE object for
a RESV message are as follows:
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1. The union is formed of the sets of sender IP addresses listed
in all SCOPE objects in the reservation state for the given
session.
If reservation state from some NHOP does not contain a SCOPE
object, a substitute sender list must be created and included
in the union. For a message that arrived on outgoing
interface OI, the substitute list is the set of senders that
route to OI.
2. Any local senders (i.e., any sender applications on this
node) are removed from this set.
3. If the SCOPE object is to be sent to PHOP, remove from the
set any senders that did not come from PHOP.
Figure 11 shows an example of wildcard-scoped (WF style) RESV
messages. The address lists within SCOPE objects are shown in
square brackets. Note that there may be additional connections
among the nodes, creating looping topology that is not shown.
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________________
a | | c
R4, S4<----->| Router |<-----> R2, S2, S3
| |
b | |
R1, S1<----->| |
|________________|
Send on (a): | Receive on (c):
|
<-- WF( [S4] ) | <-- WF( [S4, S1])
|
Send on (b): |
|
<-- WF( [S1] ) |
|
Receive on (a): | Send on (c):
|
WF( [S1,S2,S3]) --> | WF( [S2, S3]) -->
|
Receive on (b): |
|
WF( [S2,S3,S4]) --> |
|
Figure 11: SCOPE Objects in Wildcard-Scope Reservations
SCOPE objects are not necessary if the multicast routing uses
shared trees or if the reservation style has explicit sender
selection. Furthermore, attaching a SCOPE object to a reservation
may be deferred to a node which has more than one previous hop
upstream.
The following rules are used for SCOPE objects in RERR messages
with WF style:
1. The node that detected the error initiates an RERR message
containing a copy of the SCOPE object associated with the
reservation state or message in error.
2. Suppose a wildcard-scoped RERR message arrives at a node with
a SCOPE object containing the sender host address list L.
The node forwards the RERR message using the rules of Section
3.1.5. However, the RERR message forwarded out OI must
contain a SCOPE object derived from L by including only those
senders that route to OI. If this SCOPE object is empty, the
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RERR message should not be sent out OI.
3.4 Local Repair
When a route changes, the next PATH or RESV refresh message will
establish path or reservation state (respectively) along the new
route. To provide fast adaptation to routing changes without the
overhead of short refresh periods, the local routing protocol
module can notify the RSVP daemon of route changes for particular
destinations. The RSVP daemon should use this information to
trigger a quick refresh of state for these destinations, using the
new route.
More specifically, the rules are as follows:
o When routing detects a change of the set of outgoing
interfaces for destination G, RSVP should wait for a short
period W, and then send PATH refreshes for all sessions G/*
(i.e., for any session with destination G, regardless of
destination port).
The short wait period before sending PATH refreshes is to
allow the routing protocol getting settled with the new
change(s), and the exact value for W should be chosen
accordingly. Currently W = 2 sec is suggested; however, this
value should be configurable per interface.
o When a PATH message arrives with a Previous Hop address that
differs from the one stored in the path state, RSVP should
send immediate RESV refreshes for that session.
3.5 Time Parameters
There are two time parameters relevant to each element of RSVP
path or reservation state in a node: the refresh period R between
generation of successive refreshes for the state by the neighbor
node, and the local state's lifetime L. Each RSVP RESV or PATH
message may contain a TIME_VALUES object specifying the R value
that was used to generate this (refresh) message. This R value is
then used to determine the value for L when the state is received
and stored. The values for R and L may vary from hop to hop.
In more detail:
1. Floyd and Jacobson [FJ94] have shown that periodic messages
generated by independent network nodes can become
synchronized. This can lead to disruption in network
services as the periodic messages contend with other network
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traffic for link and forwarding resources. Since RSVP sends
periodic refresh messages, it must avoid message
synchronization and ensure that any synchronization that may
occur is not stable.
For this reason, the refresh timer should be randomly set to
a value in the range [0.5R, 1.5R].
2. To avoid premature loss of state, L must satisfy L >= (K +
0.5)*1.5*R, where K is a small integer. Then in the worst
case, K-1 successive messages may be lost without state being
deleted. To compute a lifetime L for a collection of state
with different R values R0, R1, ..., replace R by max(Ri).
Currently K = 3 is suggested as the default. However, it may
be necessary to set a larger K value for hops with high loss
rate. K may be set either by manual configuration per
interface, or by some adaptive technique that has not yet
been specified.
3. Each message that creates state (PATH or RESV message)
carries a TIME_VALUES object containing the R used to
generate refreshes; the recipient node uses this R to
determine L of the stored state.
4. R is chosen locally by each node. If the node does not
implement local repair of reservations disrupted by route
changes, a smaller R speeds up adaptation to routing changes,
while increasing the RSVP overhead. With local repair, a
router can be more relaxed about R since the periodic refresh
becomes only a backstop robustness mechanism. A node may
therefore adjust the effective R dynamically to control the
amount of overhead due to refresh messages.
The current suggested default for R is 30 seconds. However,
the default should be configurable per interface.
5. When R is changed dynamically, there is a limit to how fast
it may increase. Specifically, the ratio of two successive
values R2/R1 must not exceed 1 + Slew.Max.
Currently, Slew.Max is 0.30. With K = 3, one packet may be
lost without state timeout while R is increasing 30 percent
per refresh cycle.
6. To improve robustness, a node may temporarily send refreshes
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more often than R after a state change (including initial
state establishment).
7. The values of Rdef, K, and Slew.Max used in an implementation
should be easily modifiable per interface, as experience may
lead to different values. The possibility of dynamically
adapting K and/or Slew.Max in response to measured loss rates
is for future study.
3.6 Traffic Policing and TTL
RSVP is required to compute and pass several service-related flags
to traffic control: policing flags and a non-RSVP flag.
Some QoS services may require traffic policing at some or all of
(1) the edge of the network, (2) a merging point for data from
multiple senders, and/or (3) a branch point where traffic flow
from upstream may be greater than the downstream reservation.
RSVP knows where such points occur and must so indicate to the
traffic control mechanism. On the other hand, RSVP does not
interpret the service embodied in the flowspec and therefore does
not know whether policing will actually be applied in any
particular case.
The RSVP daemon passes to traffic control a separate policing flag
for each of these three situations.
o E_Police_Flag -- Entry Policing
This flag is set in the first-hop RSVP node that implements
traffic control (and is therefore capable of policing).
For example, sender hosts must implement RSVP but currently
many of them do not implement traffic control. In this case,
the E_Police_Flag should be off in the sender host, and it
should only be set on when the first hop capable of traffic
control is reached. This is controlled by the E_Police flag
in SESSION objects.
o M_Police_Flag -- Merge Policing
This flag should be set on for a reservation using a shared
style (WF or SE) when flows from more than one sender are
being merged.
o B_Police_Flag -- Branch Policing
This flag should be set on when the flowspec being installed
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is smaller than, or incomparable to, a FLOWSPEC in place on
any other interface, for the same FILTER_SPEC and SESSION.
RSVP must also detect and report to receivers the presence of
non-RSVP hops in the path. For this purpose, an RSVP daemon must
place into each PATH message that it sends the value of the IP TTL
with which the message was sent. The RSVP-capable node that
receives this message compares this field to the TTL with which
the message was actually received, and if they differ it turns on
the Non_RSVP flag. This flag is carried forward to receivers in
the ADSPEC [??].
3.7 Multihomed Hosts
Accommodating multihomed hosts requires some special rules in
RSVP. We use the term `multihomed host' to cover both hosts (end
systems) with more than one network interface [could ref. section
3.3.4 of RFC-1122], and routers that are supporting local
application programs.
An application executing on a multihomed host may explicitly
specify which interface any given flow will use for sending and/or
for receiving data packets, to override the system-specified
default interface. The RSVP daemon must be aware of the default,
and if an application sets a specific interface, it must also pass
that information to RSVP.
o Sending Data
A sender application uses an API call (SENDER in Section
3.9.1) to declare to RSVP the characteristics of the data
flow it will originate. This call may optionally include the
local IP address of the sender. If it is set by the
application, this parameter must be the interface address for
sending the data packets; otherwise, the system default
interface is implied.
The RSVP daemon on the host then sends PATH messages for this
application out the specified interface (only).
o Making Reservations
A receiver application uses an API call (called RESERVE in
Section 3.9.1) to request a reservation from RSVP. This call
may optionally include the local IP address of the receiver,
i.e., the interface address for receiving data packets. In
the case of multicast sessions, this is the interface on
which the group has been joined. If the parameter is
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omitted, the system default interface is used.
In general, the RSVP daemon should send RESV messages for
application out the specified interface. However, when the
application is executing on a router and the session is
multicast, a more complex situation arises. Suppose in this
case that a receiver application joins the group on an
interface Iapp that differs from Isp, the shortest-path
interface to the sender. Then there are two possible ways
for multicast routing to deliver data packets to the
application. The RSVP daemon must determine which case holds
by examining the path state, to decide which incoming
interface to use for sending RESV messages.
1. The multicast routing protocol may create a separate
branch of the multicast distribution `tree' to deliver
to Iapp. In this case, there will be path state for
both Isp and Iapp. The path state on Iapp should only
match a reservation from the local application; it must
be marked "Local_only" by the RSVP daemon. If
"Local_only" path state for Iapp exists, the RESV
message should be sent out Iapp.
Note that it is possible for the path state blocks for
Isp and Iapp to have the same next hop, if there is an
intervening non-RSVP cloud.
2. The multicast routing protocol may forward data within
the router from Isp to Iapp. In this case, Iapp will
appear in the list of outgoing interfaces of the path
state for Isp, and the RESV message should be sent out
Isp.
3.8 Future Compatibility
We may expect that in the future new object C-Types will be
defined for existing object classes, and perhaps new object
classes will be defined. It will be desirable to employ such new
objects within the Internet using older implementations that do
not recognize them. Unfortunately, this is only possible to a
limited degree with reasonable complexity. The rules are as
follows.
1. Unknown Class
There are two possible ways that an RSVP implementation can
treat an object with unknown class. This choice is
determined by the high-order bit of the Class-Num octet, as
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follows.
o Class-Num >= 128
In this case, the entire message should be rejected and
an "Unknown Object Class" error returned.
o Class-Num < 128
In this case, the node should ignore the object but
forward it, unexamined and unmodified, in all messages
resulting from the state contained in this message.
For example, suppose that a RESV message that is
received contains an object of unknown class. Such an
object should be saved in the reservation state without
further examination; however, only the latest object
with a given (unknown class, C-Type) pair should be
saved. When a RESV message is forwarded, it should
include copies of such saved unknown-class objects from
all reservations that are merged to form the new RESV
message.
Note that objects with unknown class cannot be merged;
however, unmerged objects may be forwarded until they
reach a node that knows how to merge them. Forwarding
objects with unknown class enables incremental
deployment of new objects; however, the scaling
limitations of doing so must be carefully examined
before a new object class is deployed with Class-Num <
128.
These rules should be considered when any new Class-Num is
defined.
2. Unknown C-Type for Known Class
One might expect the known Class-Num to provide information
that could allow intelligent handling of such an object.
However, in practice such class-dependent handling is
complex, and in many cases it is not useful.
Generally, the appearance of an object with unknown C-Type
should result in rejection of the entire message and
generation of an error message (RERR or PERR as appropriate).
The error message will include the Class-Num and C-Type that
failed (see Appendix B); the end system that originated the
failed message may be able to use this information to retry
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the request using a different C-Type object, repeating this
process until it runs out of alternatives or succeeds.
Objects of certain classes (FLOWSPEC, ADSPEC, and
POLICY_DATA) are opaque to RSVP, which simply hands them to
traffic control or policy modules. Depending upon its
internal rules, either of the latter modules may reject a C-
Type and inform the RSVP daemon; RSVP should then reject the
message and send an error, as described in the previous
paragraph.
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3.9 RSVP Interfaces
RSVP on a router has interfaces to routing and to traffic control.
RSVP on a host has an interface to applications (i.e, an API) and
also an interface to traffic control (if it exists on the host).
3.9.1 Application/RSVP Interface
This section describes a generic interface between an
application and an RSVP control process. The details of a real
interface may be operating-system dependent; the following can
only suggest the basic functions to be performed. Some of
these calls cause information to be returned asynchronously.
o Register Session
Call: SESSION( DestAddress , ProtocolId, DstPort ,
[ , SESSION_object ]
[ , Upcall_Proc_addr ] ) -> Session-id
This call initiates RSVP processing for a session, defined
by DestAddress together with ProtocolId and possibly a
port number DstPort. If successful, the SESSION call
returns immediately with a local session identifier
Session-id, which may be used in subsequent calls.
The Upcall_Proc_addr parameter defines the address of an
upcall procedure to receive asynchronous error or event
notification; see below. The SESSION_object parameter is
included as an escape mechanism to support some more
general definition of the session ("generalized
destination port"), should that be necessary in the
future. Normally SESSION_object will be omitted.
o Define Sender
Call: SENDER( Session-id,
[ , Source_Address ] [ , Source_Port ]
[ , Sender_Template ]
[ , Sender_Tspec ] [ , Data_TTL ]
[ , Sender_Policy_Data ] )
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A sender uses this call to define, or to modify the
definition of, the attributes of the data stream. The
first SENDER call for the session registered as `Session-
id' will cause RSVP to begin sending PATH messages for
this session; later calls will modify the path
information.
The SENDER parameters are interpreted as follows:
- Source_Address
This is the address of the interface from which the
data will be sent. If it is omitted, a default
interface will be used. This parameter is needed on
a multihomed sender host.
- Source_Port
This is the UDP/TCP port from which the data will be
sent. If it is omitted or zero, the port is "wild"
and can match any port in a FILTER_SPEC.
- Sender_Template
This parameter is included as an escape mechanism to
support a more general definition of the sender
("generalized source port"). Normally this parameter
may be omitted.
- Sender_Tspec
This optional parameter describes the traffic flow to
be sent. It may be included to prevent over-
reservation on the initial hops.
- Data_TTL
This is the (non-default) IP Time-To-Live parameter
that is being supplied on the data packets. It is
needed to ensure that Path messages do not have a
scope larger than multicast data packets.
- Sender_Policy_Data
This optional parameter passes policy data for the
sender. This data may be supplied by a system
service, with the application treating it as opaque.
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o Reserve
Call: RESERVE( session-id, [ receiver_address , ]
[ ACK_flag, ] style, style-dependent-parms )
A receiver uses this call to make or to modify a resource
reservation for the session registered as `session-id'.
The first RESERVE call will initiate the periodic
transmission of RESV messages. A later RESERVE call may
be given to modify the parameters of the earlier call (but
note that changing existing reservations may result in
admission control failure).
The optional `receiver_address' parameter may be used by a
receiver on a multihomed host (or router); it is the IP
address of one of the node's interfaces. The ACK_flag
should be set on if a reservation ACK is desired, off
otherwise. The `style' parameter indicates the
reservation style. The rest of the parameters depend upon
the style, but generally these will include appropriate
flowspecs, filter specs, and possibly receiver policy data
objects.
The RESERVE call returns immediately. Following a RESERVE
call, an asynchronous ERROR/EVENT upcall may occur at any
time.
o Release
Call: RELEASE( session-id )
This call removes RSVP state for the session specified by
session-id. The node then sends appropriate teardown
messages and ceases sending refreshes for this session-id.
o Error/Event Upcalls
Upcall: <Upcall_Proc>( ) -> session-id, Info_type,
[ Error_code , Error_value ,
Error_Node , LUB-Used, ]
List_count, [ Flowspec_list,]
[ Filter_spec_list, ] [ Advert_list, ]
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[ Policy_data ]
Here "Upcall_Proc" represents the upcall procedure whose
address was supplied in the SESSION call.
This upcall may occur asynchronously at any time after a
SESSION call and before a RELEASE call, to indicate an
error or an event. Currently there are five upcall types,
distinguished by the Info_type parameter:
1. Info_type = Path Event
A Path Event upcall results from receipt of the first
PATH message for this session, indicating to a
receiver application that there is at least one
active sender.
This upcall provides synchronizing information to the
receiver application, and it may also provide
parallel lists of senders (in Filter_spec_list),
traffic descriptions (in Flowspec_list), and service
advertisements (in Advert_list). `List_count' will
be the number in each list; where these objects are
missing, corresponding null objects must appear. The
Error_code, Error_value, LUB-Used flag, and
Policy_data parameters will be undefined in this
upcall.
2. Info_type = Resv Event
A Resv Event upcall is triggered by the receipt of
the first reservation message or by modification of a
previous reservation state, for this session.
`List_count' will be 1, and Flowspec_list will
contain one FLOWSPEC, the effective QoS that would be
applicable to the application itself.
Filter_spec_list and Advert_list will contain one
NULL object. The Error_code, Error_value, LUB-Used
flag, and Policy_data parameters will be undefined in
this upcall.
3. Info_type = Path Error
An Path Error event indicates an error in sender
information that was specified in a SENDER call.
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The Error_code parameter will define the error, and
Error_value may supply some additional (perhaps
system-specific) data about the error. The
Error_Node parameter will specify the IP address of
the node that detected the error.
`List_count' will be 1, and Filter_spec_list will
contain the Sender_Template supplied in the SENDER
call; Flow_Spec_list and Advert_list will each
contain one NULL object. The Policy_data parameter
will contain any POLICY_DATA objects in the PERR
message.
4. Info_type = Resv Error/Confirmation
An Resv Error/Confirmation event indicates an error
in a reservation message to which this application
contributed, or the receipt of a RACK message. The
Error_code parameter will define the error or
confirmation. For an error, Error_value may supply
some additional (perhaps system-specific) data. The
Error_Node parameter will specify the IP address of
the node that detected the event being reported.
Filter_spec_list and Flowspec_list will contain the
FILTER_SPEC and FLOWSPEC objects from the error flow
descriptor (see Section 3.1.5). List_count will
specify the number of FILTER_SPECS in
Filter_spec_list, while there will be one FLOWSPEC in
Flowspec_list. For an error, the Policy_data
parameter will contain any POLICY_DATA objects in the
RERR message.
Although RSVP messages indicating path or resv events may
be received periodically, the API should make the
corresponding asynchronous upcall to the application only
on the first occurrence or when the information to be
reported changes. All error and confirmation events
should be reported to the application.
3.9.2 RSVP/Traffic Control Interface
In an RSVP-capable node, enhanced QoS is achieved by a group of
inter-related traffic control functions: a packet classifier,
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an admission control module, and a packet scheduler. This
section describes a generic RSVP interface to traffic control.
o Make a Reservation
Call: Rhandle = TC_AddFlowspec( Interface, TC_Flowspec,
TC_Tspec, E_Police_Flag,
M_Police_Flag, B_Police_Flag )
The TC_Flowspec parameter defines the desired effective
QoS to admission control; its value is computed as the
maximum over the flowspecs of different next hops (see the
Compare_Flowspecs call below). It contains the effective
reservation Tspec Resv_Te (although the RSVP daemon itself
has no means to extract the Tspec). The TC_Tspec
parameter defines the effective sender Tspec Path_Te (see
Section 2.3). We assume that traffic control takes the
min of Resv_Te and Path_Te (see step (4) in Section 2.3).
E_Police_Flag, M_Police_Flag, and B_Police_Flag are
Boolean parameters whose values should be set as described
in Section 3.6.
The TC_AddFlowspec call returns an error code if Flowspec
is malformed or if the requested resources are
unavailable. Otherwise, it establishes a new reservation
channel corresponding to Rhandle. It returns the opaque
number Rhandle for subsequent references to this
reservation.
o Modify Reservation
Call: TC_ModFlowspec( Rhandle, new_Flowspec,
Sender_Tspec, E_Police_flag,
M_Police_Flag, B_Police_Flag )
This call can modify an existing reservation. If
new_Flowspec is included, it is passed to Admission
Control; if it is rejected, the current flowspec is left
in force. The corresponding filter specs, if any, are not
affected. The other parameters are defined as in
TC_AddFlowspec.
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o Delete Flowspec
Call: TC_DelFlowspec( Rhandle )
This call will delete an existing reservation, including
the flowspec and all associated filter specs.
o Add Filter Spec
Call: FHandle = TC_AddFilter( Rhandle, Session , FilterSpec )
This call is used to associate an additional filter spec
with the reservation specified by the given Rhandle,
following a successful TC_AddFlowspec call. This call
returns a filter handle FHandle.
o Delete Filter Spec
Call: TC_DelFilter( FHandle )
This call is used to remove a specific filter, specified
by FHandle.
o OPWA Update
Call: TC_Advertise( interface, Adspec,
[ , Non_RSVP_flag ] ) -> New_Adspec
This call is used for OPWA to compute the outgoing
advertisement New_Adspec for a specified interface.
o Preemption Upcall
Upcall: TC_Preempt() -> RHandle, Reason_code
In order to grant a new reservation request, the admission
control and/or policy modules may be allowed to preempt an
existing reservation. This might be reflected in an
upcall to RSVP, passing the RHandle of the preempted
reservation, and some indication of the reason.
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3.9.3 RSVP/Routing Interface
An RSVP implementation needs the following support from the
packet forwarding and routing mechanisms of the node.
o Promiscuous Receive Mode for RSVP Messages
Any packet received for IP protocol 46 must be diverted to
the RSVP program for processing, without being forwarded.
On a router, the identity of the interface, real or
virtual, on which it is received must also be available to
the RSVP daemon.
o Route Query
To forward PATH and PTEAR messages, an RSVP daemon must be
able to query the routing daemon(s) for routes.
Ucast_Route_Query( [ SrcAddress, ] DestAddress, Notify_flag )
-> OutInterface
Mcast_Route_Query( [ SrcAddress, ] DestAddress, Notify_flag )
-> [ IncInterface, ] OutInterface_list
Depending upon the routing protocol, the query may or may
not depend upon SrcAddress, i.e., upon the sender host IP
address, which is also the IP source address of the
message. Here IncInterface is the interface through which
the packet is expected to arrive; some multicast routing
protocols may not provide it.
If the Notify_flag is True, routing will save state
necessary to issue unsolicited route change notification
callbacks (see below) whenever the specified route
changes. Such callbacks will be enabled until routing
receives a route query call with the Notify_Flag set
False.
A multicast route query may return an empty
OutInterface_list if there are no receivers downstream of
a particular router. A route query may also return a `No
such route' error, probably as a result of a transient
inconsistency in the routing (since a PATH or PTEAR
message for the requested route did arrive at this node).
In either case, the local state should be updated as
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requested by the message, although it cannot be forwarded
further. Updating local state will make path state
available immediately for a new local receiver, or it will
tear down path state immediately.
o Route Change Notification
If requested by a route query with the Notify_flag True,
the routing daemon may provide an asynchronous callback to
the RSVP daemon that a specified route has changed.
Ucast_Route_Change( ) -> DestAddress, OutInterface
Mcast_Route_Change( ) -> [ SrcAddress, ] DestAddress,
[ IncInterface, ] OutInterface_list
o Outgoing Link Specification
RSVP must be able to force a (multicast) datagram to be
sent on a specific outgoing virtual link, bypassing the
normal routing mechanism. A virtual link may be a real
outgoing link or a multicast tunnel. Outgoing link
specification is necessary to send different versions of
an outgoing PATH message on different interfaces. It is
also necessary in some cases to avoid routing loops.
o Source Address Specification
RSVP must be able to specify the IP source address to be
used when sending PATH messages.
o Interface List Discovery
RSVP must be able to learn what real and virtual
interfaces are active, with their IP addresses.
3.9.4 Service-Dependent Manipulations
Flowspecs, Tspecs, and Adspecs are opaque objects to RSVP;
their contents are defined in service specification documents.
In order to manipulate these objects, RSVP daemon must have
available to it the following service-dependent routines.
o Compare Flowspecs
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Compare_Flowspecs( Flowspec_1, Flowspec_2 ) -> result_code
The possible result_codes indicate: flowspecs are equal,
Flowspec_1 is greater, Flowspec_2 is greater, flowspecs
are incomparable but LUB can be computed, or flowspecs are
incompatible.
Note that comparing two flowspecs implicitly compares the
Tspecs that are contained. Although the RSVP daemon
cannot itself parse a flowspec to extract the Tspec, it
can use the Compare_Flowspecs call to implicitly calculate
Resv_Te (see Section 2.3).
o Compute LUB of Flowspecs
LUB_of_Flowspecs( Flowspec_1, Flowspec_2 ) ->
Flowspec_LUB
o Compare Tspecs
Compare_Tspecs( Tspec_1, Tspec_2 ) -> result_code
The possible result_codes indicate: Tspecs are equal, or
Tspecs are unequal.
o Sum Tspecs
Sum_Tspecs( Tspec_1, Tspec_2 ) -> Tspec_sum
This call is used to compute Path_Te (see Section 2.3).
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4. Message Processing Rules
This section provides a generic description of the rules for RSVP
operation. It is intended to outline a set of algorithms that will
accomplish the needed function. An actual implementation may use
different but equivalent algorithms. This section assumes the
generic interface calls defined in Section 3.9 and the following data
structures. An actual implementation may use additional or different
data structures and interfaces.
[NOTE: This section is always the last to be updated when changes are
made, and it is neither correct nor complete at the present time.
Therefore, when this section disagrees with the rest of the text, you
should believe the rest of the text!]
o PSB -- Path State Block
Each PSB holds path state for a particular (session, sender)
pair, defined by SESSION and SENDER_TEMPLATE objects,
respectively, received in a PATH message.
PSB contents include the following values from a PATH message:
- The previous hop IP address from a PHOP object (required)
- LIH, the Logical Interface Handle from the previous hop,
from a PHOP object (required).
- The remaining IP TTL (required)
- SENDER_TSPEC (required)
- POLICY_DATA and/or ADSPEC objects (optional)
- Non_RSVP flag (required); see Section 3.6.
In addition, the PSB contains the following information provided
by routing: OutInterface_list, the list of outgoing interfaces
for this (sender, destination), and IncInterface, the expected
incoming interface. For a unicast destination,
OutInterface_list contains one entry and IncInterface is
undefined.
o RSB -- Reservation State Block
Each RSB holds a reservation request that arrived in a
particular RESV message, corresponding to the triple: (session,
next hop, filter_spec_list). Here "filter_spec_list" may be a
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list of FILTER_SPECs (for SE style), a single FILTER_SPEC (FF
style), or empty (WF style). We use the symbol "FILTER_SPEC*"
to indicate such a FILTER_SPEC list.
RSB contents include:
- The outgoing (logical) interface OI on which the
reservation is to be made or has been made (required).
- FLOWSPEC*, list of FLOWSPEC objects (required)
- The style (required)
- A POLICY_DATA object (optional)
- A SCOPE object (optional, depending on style)
- A RESV_CONFIRM object (optional)
o TCSB -- Traffic Control State Block
TCSB's hold the reservation specifications that have been handed
to traffic control for specific outgoing interfaces. In
general, information in TCSB's is derived from RSB's for the
same outgoing interface. Each TCSB defines a single reservation
for a particular triple: (session, OI, filter_spec_list). TCSB
contents include:
- TC_Flowspec, the effective flowspec, i.e., the maximum over
the corresponding FLOWSPEC values from matching RSB's.
TC_Flowspec is passed to traffic control to make the actual
reservation. The Tspec part of TC_Flowspec is the
effective reservation Tspec Resv_Te (Section 2.3).
- TC_Tspec, equal to the effective sender Tspec Path_Te.
- Police Flags
The flags E_Police_Flag, M_Police_Flag,and B_Police_Flag
are defined in Section 3.6.
- Rhandle, F_Handle_list
Handles returned by the traffic control interface,
corresponding to the reservation (flowspec) and to the list
of filter specs.
Boolean flags Path_Refresh_Needed, Resv_Refresh_Needed, and
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Tear_Needed will also be used in this section.
[LZ: It might be very helpful to have a short section to summarize
the management of all the timers.]
MESSAGE ARRIVES
Verify version number and checksum fields of common header, and
discard message if any mismatch is found.
Reassemble a fragmented message.
Parse the sequence of objects in the message to verify the length
field of the common header; discard message if there is a mismatch.
If the message type is not PATH or PTEAR and if the IP destination
address does not match any of the addresses of the local interfaces,
then forward the message to IP destination address and return.
Verify the INTEGRITY object, if any. If the check fails, discard the
message and return.
Further processing depends upon message type.
PATH MESSAGE ARRIVES
Process the sender descriptor object sequence in the message as
follows. The flags Path_Refresh_Needed and Resv_Refresh_Needed
flags are initially off.
o If there is a POLICY_DATA object, verify it; if it is
unacceptable, build and send a "Administrative Rejection"
PERR message, drop the PATH message, and return.
o If the DstPort in the SESSION object is zero but the
SrcPort in the SENDER_TEMPLATE object is non-zero, build a
send a "Conflicting Src Port" PERR message, drop the PATH
message, and return.
o Search for a path state block (PSB) whose (SESSION,
SENDER_TEMPLATE) pair matches the corresponding objects in
the message, considering any wildcard ports.
o If, during the PSB search, a PSB is found whose session
matches the DestAddress and Protocol Id fields of the
received SESSION object, but the DstPorts differ and one is
zero, then build and send a "Conflicting Dst Port" PERR
message, drop the PATH message, and return.
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o If, during the PSB search, a PSB is found with a matching
sender host (in SENDER_TEMPLATE) but the SrcPorts differ
and one is zero, then build and send a "Ambiguous Path"
PERR message, drop the PATH message, and return.
o If there was no matching PSB, then:
1. Create a new PSB.
2. Call the appropriate Route_Query routine, using
DestAddress from SESSION and (for multicast routing)
SrcAddress from SENDER_TEMPLATE. Store the values of
OutInterface_list and IncInterface into the PSB.
However, if the sender is from the local API, then
instead of invoking routing, set OutInterface_List to
the single interface whose address matches the sender
address; IncInterface is undefined in this case.
3. If IncInterface is defined and if a multicast message
arrived on an interface different from IncInterface,
drop the message and return.
4. Set a cleanup timer for the PSB. If this is the first
PSB for the session, set a refresh timer for the
session.
5. Copy contents of the SESSION, SENDER_TEMPLATE,
SENDER_TSPEC, and PHOP (IP address and LIH) objects
into the PSB. Store the received TTL into the PSB.
Copy into the PSB either of the following objects that
are present: POLICY_DATA and ADSPEC.
6. Turn on the Path_Refresh_Needed flag.
o Otherwise (there is a matching PSB and there is no dest
port conflict):
1. If there is no route change notification in place,
call the appropriate Route_Query routine using
DestAddress from SESSION and (for multicast routing)
SrcAddress from SENDER_TEMPLATE.
- If the OutInterface_list that is returned differs
from that in the PSB, execute the PATH LOCAL
REPAIR event sequence below.
- If a multicast message arrived on an interface
different from IncInterface, drop the message and
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return.
2. If the PHOP IP address, the LIH, or SENDER_TSPEC
differs between the message and the PSB, copy the new
value into the PSB, execute the RESV REFRESH event
sequence for the sender defined by the PSB, and turn
on the Path_Refresh_Needed flag.
[LZ: [When] should ADSPEC change trigger a refresh?]
However, if the PATH message being processed came from
a local application and if there is reservation state
for this session, then make a Resv Event upcall to
that application instead of executing the RESV REFRESH
sequence.
Call: <Upcall_Proc>( session-id, Resv Event, 1,
{Flowspec}, NULL, NULL, NULL )
3. Restart the cleanup timer.
o If the message arrived with a TTL different from Send_TTL
in the RSVP common header, set the Non_RSVP flag on in the
PSB.
o If the Path_Refresh_Needed flag is now set then:
1. If this PATH message came from a network interface and
not from a local application, make a Path Event upcall
for each local application for this session:
Call: <Upcall_Proc>( session-id, Path Event, 1,
{SENDER_TSPEC}, {SENDER_TEMPLATE},
{ADSPEC}, {POLICY_DATA} )
2. Execute the PATH REFRESH event sequence (below) for
the sender defined by the PSB.
PATH TEAR MESSAGE ARRIVES
o Search for a PSB whose (SESSION, SENDER_TEMPLATE) pair
matches the corresponding objects in the message. If no
matching PSB is found, drop the PTEAR message and return.
o Forward a copy of the PTEAR message to each outgoing
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interface listed in OutInterface_list of the PSB.
o Find each RSB that matches this PSB, i.e., whose
FILTER_SPEC object matches the SENDER_TEMPLATE in the PSB
and whose OI is included in OutInterface_list.
If this RSB matches no other PSB, then tear down the RSB,
as described below under RESV TEAR MESSAGE ARRIVES.
o Delete the PSB.
o Drop the PTEAR message and return.
PATH ERROR MESSAGE ARRIVES
o Search for a PSB whose (SESSION, SENDER_TEMPLATE) pair
matches the corresponding objects in the message. If no
matching PSB is found, drop the PERR message and return.
o If the previous hop address in the PSB is the local API,
make an error upcall to the application:
Call: <Upcall_Proc>( session-id, Path Error,
Error_code, Error_value, Node_Addr,
0, 1, NULL, SENDER_TEMPLATE,
NULL, Policy_Data)
Any POLICY_DATA, SENDER_TSPEC, or ADSPEC object in the
message is ignored. [LZ: Why we don't send these objects
up to application? They might of some help to understand
the errors.] Drop the PERR message and return.
o Otherwise, send a copy of the PERR message to the PHOP IP
address, drop the PERR message, and return.
RESV MESSAGE ARRIVES
Initially, the Resv_Refresh_PHOP* list is empty and the
Resv_Refresh_Needed flag is off. These variables are used to
control immediate reservation refreshes.
o Process the NHOP object
The logical outgoing interface OI is taken from the LIH in
the NHOP object. (If the physical interface is not implied
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by the LIH, it can be learned from the interface matching
the IP destination address).
o Check the SESSION object.
If there are no existing PSB's for SESSION then build and
send a RERR message (as described later) specifying "No
path information", drop the RESV message, and return.
However, do not send the RERR message if the style has
wildcard reservation scope and this is the receiver host
itself.
[LZ: Explain this?]
o Check the S_POLICY_DATA object.
If there is an S_POLICY_DATA object in the message, check
permission to create a reservation for the session. If the
check fails, build and send an "Administrative rejection"
RERR message, drop the RESV message, and return.
Otherwise, copy the S_POLICY_DATA object into the RSB.
Now process the STYLE object and the flow descriptor list to
make reservations, as follows.
For FF style, execute the following steps independently for each
b flow descriptor, i.e., for each (FLOWSPEC, FILTER_SPEC) pair.
For FF style, FILTER_SPEC* consists of the single FILTER_SPEC
from the flow descriptor.
For SE style, execute the following steps once, with
FILTER_SPEC* consisting of the list of FILTER_SPEC objects from
the flow descriptor.
For WF style, execute the following steps once, with
FILTER_SPEC* consisting of a single internal placeholder
"WILD_FILTER".
o If the DstPort in the SESSION object is zero but the
SrcPort in the FILTER_SPEC object is non-zero, build a send
a "Conflicting Src Port" RERR message, drop the RESV
message, and return.
o Find or create a reservation state block (RSB) for the
triple: (SESSION, NHOP, FILTER_SPEC*). Call this the
"active RSB".
o If the RSB is not new and if its style is incompatible with
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the STYLE object in the message, build and send a RERR
message specifying "Conflicting Style", drop the RESV
message, and return.
o Start or restart the cleanup timer on the the active RSB.
o If the active RSB is not new, check whether FLOWSPEC or
SCOPE objects have changed. If not, continue with the next
flow descriptor in the RESV message, if any.
o If the active RSB is new, set its OI and style, and copy
any FLOWSPEC, POLICY_DATA, and/or SCOPE objects into it.
o If there is a RESV_CONFIRM in the message, turn on
Resv_Refresh_Needed and save the object in the RSB.
o The active RSB must be new or changed. Compute the traffic
control parameters, using the following steps.
1. Locate the set of PSBs (senders) whose
SENDER_TEMPLATEs match FILTER_SPEC* in the active RSB
and whose OutInterface_list includes OI.
If this set is empty, build and send an error message
specifying "No sender information", and continue with
the next flow descriptor in the RESV message.
2. If this set contains more than one PSB and if the
style has explicit sender selection (e.g., FF or SE),
build and send an error message specifying "Ambiguous
filter spec" and continue with the next flow
descriptor.
3. Add the PHOP from the PSB to the Resv_Refresh_PHOP*
list, if the PHOP is not already on the list.
4. Set TC_E_Police_flag on if any of these PSBs have
their E_Police flag on. Set TC_M_Police_flag on if it
is a shared style and there is more than one PSB in
the set.
5. Compute Path_Te as the sum of the SENDER_TSPEC objects
in this set of PSBs.
6. Scan all RSB's matching the SESSION and
Filter_Spec_list from the message.
- If any of these RSB's has a style that is
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incompatible with the specifying "Conflicting
Style", drop the RESV message, delete the RSB if
it has just been created, and return.
- Set TC_B_Police_flag on if TC_Flowspec is smaller
than, or incomparable to, any FLOWSPEC in those
RSB's.
7. Consider the set of RSB's for the same (SESSION, OI,
Filter_Spec_list) triple from the message.
- Compute the effective kernel flowspec,
TC_Flowspec, as the maximum of the FLOWSPEC
values in these RSB's.
- Compute the effective kernel filter spec (list),
TC_Filter*. by merging the FILTER_SPEC* object
(lists) from these RSB's.
o Search for a TCSB matching the triple (SESSION, OI,
FILTER_SPEC*), taken from the RSB.
1. If none is found but style is SE, search for a TCSB
matching (SESSION, OI). If find one and if TCSB's
TC_Flowspec, Path_Te, and police flags match the
computed values, then
- Make an appropriate set of TC_DelFilter and
TC_AddFilter calls to transform the
Filter_Spec_list in the TCSB into the
Filter_Spec_list from the message.
- Set Resv_Refresh_Needed on, drop the RESV
message, and return.
2. Otherwise, if none is found:
- Create a new TCSB.
- Store TC_Flowspec, Filter_Spec_list, Path_Te, and
the police flags into TCSB.
[SCOPE?]
- Set Resv_Refresh_Needed on.
- Make the traffic control call:
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Rhandle = TC_AddFlowspec( OI, TC_flowspec, Path_Te,
TC_E_Police_flag, TC_M_Police_flag,
TC_B_Police_flag )
If this call fails, build and send a RERR message
specifying "Admission control failed", and
continue with the next flow descriptor.
Otherwise, record Rhandle in the TCSB.
- For each filter_spec F in Filter_Spec_list, call:
Fhandle = TC_AddFilter( Rhandle, SESSION, F)
and record the returned Fhandle in the TCSB.
- Continue with the next flow descriptor.
3. Otherwise (found existing TCSB), check whether
TC_Flowspec, Path_Te, and/or any of the police flags
has changed, and if so:
- Store TC_Flowspec, Filter_Spec_list, Path_Te, and
the police flags into it.
[SCOPE?]
- Set Resv_Refresh_Needed on.
- Make the traffic control call:
TC_ModFlowspec( Rhandle, K_Flowspec, Path_Te,
TC_E_Police_flag, TC_M_Police_flag,
TC_B_Police_flag )
4. Continue with the next flow descriptor.
o If the Resv_Refresh_Needed flag is now on, execute the RESV
REFRESH sequence (below) for each PHOP in the
Resv_Refresh_PHOP* set.
If processing a RESV message finds an error, a RERR message is
created containing flow descriptor and an ERRORS object. The
Error Node field of the ERRORS object (see Appendix A) is set to
the IP address of OI, and the message is sent unicast to NHOP.
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RESV TEAR MESSAGE ARRIVES
A RTEAR message arrives with an IP destination address matching
outgoing interface OI. Flags Tear_Needed and
Resv_Refresh_Needed are initially off and Resv_Refresh_PHOP*
list is empty.
o Process the STYLE object and the flow descriptor list in
the RTEAR message to tear down local reservation state, as
follows.
For FF style, execute the following steps for each b flow
descriptor, i.e., for each (FLOWSPEC, FILTER_SPEC) pair
independently, with Filter_Spec_list consisting of a single
FILTER_SPEC object.
For SE style, execute the following steps once, with
Filter_Spec_list consisting of a list of FILTER_SPEC
objects.
For WF style, execute the following steps once, with
Filter_Spec_list consisting of a single internal
placeholder "WILD_FILTER".
1. Find matching RSB for the 4-tuple: (SESSION, NHOP,
style, Filter_Spec_list); call this the active RSB.
If no active RSB is found, continue with next flow
descriptor.
2. Delete the active RSB.
3. Find TCSB for the triple: (SESSION, OI,
Filter_Spec_list).
4. Consider the set of RSB's matching this TCSB. If
there are none:
- Call the traffic control interface routine:
TC_DelFlowspec( Rhandle )
- Delete the TCSB and set Tear_Needed flag on.
- Continue with the next flow descriptor.
5. Otherwise (there are other RSB's for the same TCSB),
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recompute TC_Flowspec and Path_Te (see RESV MESSAGE
ARRIVES). (This also adds the appropriate PHOP
addresses to the Resv_Refresh_PHOP* list>) If either
changed, update the TCSB, set flag Resv_Refresh_Needed
on, and call the traffic control interface module:
TC_ModFlowspec( Rhandle, TC_Flowspec, Path_Te)
TC_E_Police_flag, TC_M_Police_flag,
TC_B_Police_flag )
This kernel call should not fail, since the
reservation can only be reduced.
[LZ: Suppose receiver R has the credential to make the
reservation and others took a ride on top of R's
credential. Now R tears down its request, what should
happen? Shouldn't TEAR take policy data as input?]
o If Tear_Needed and Resv_Refresh_Needed flags are both off,
then drop the RTEAR message and return.
o If Tear_Needed is off but Resv_Refresh_Needed is on, then
execute the RESV REFRESH sequence for each PHOP in the
Resv_Refresh_PHOP* set, drop the RTEAR message, and return.
o Otherwise (Tear_Needed is on), need to forward RTEAR and/or
RESV refresh messages.
Do the following for each PSB whose OutInterface_list
includes the outgoing interface OI:
1. Pick each flow descriptor Fj in the RTEAR message
whose FILTER_SPEC matches the PSB, and do the
following.
- If there is no RSB whose FILTER_SPEC matches the
PSB, then add Fj to the new RTEAR message being
built.
- Otherwise (there is a matching RSB), note the PSB
as needing a RESV refresh message and set the
Resv_Refresh_Needed flag True.
2. If the new RTEAR message contains any flow
descriptors, send it to PHOP in the PSB.
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o If the Resv_Refresh_Needed flag is now on, execute the RESV
REFRESH sequence (below) for each PHOP in the
Resv_Refresh_PHOP* set.
If the Refresh_Needed flag is true, then execute the RESV
REFRESH sequence for the PSB's that have been noted.
o Drop the RTEAR message and return.
RESV ERROR MESSAGE ARRIVES
A RERR message arrives through the (real) incoming interface
In_If.
o If there is no path state for SESSION, drop the RERR
message and return.
o Do the following with each RSB for this SESSION whose OI
does not match In_If and whose FILTER_SPEC matches that in
the RERR message.
1. Copy the error flow descriptor from the incoming RERR
message.
2. Compare the FLOWSPEC in the RERR message with the
FLOWSPEC in the RSB. If they don't match along any
coordinate (i.e., if the RSB FLOWSPEC is strictly
`smaller'), continue with the next RSB.
If they agree on some but not all coordinates, turn on
the LUB-used flag.
3. If NHOP in RSB is the local API, deliver an error
upcall to application:
Call: <Upcall_Proc>( session-id, Resv Error,
Error_code, Error_value, Node_Addr,
LUB-Used,
Flowspec, Filter_Spec_List,
NULL, NULL)
and continue with the next RSB. Here k,
Filter_Spec_List, and Flowspec_List are constructed
from the error flow descriptor.
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4. If the RESV message has wildcard sender selection, use
its SCOPE object SC.In to construct a SCOPE object
SC.Out to be forwarded. SC.Out should contain those
sender addresses that appeared in SC.In and that route
to OI [LIH?], as determined by scanning the PSB's. If
SC.Out is empty, continue with the next RSB.
5. Create a new RERR message containing the error flow
descriptor and send to the NHOP address specified by
the RSB. Include SC.Out if the sender selection is
wildcard.
6. Continue with the next RSB.
o Drop the RERR message and return.
RESV CONFIRMATION ARRIVES
If the (unicast) IP address found in its RESV_CONFIRM object
matches an interface of the node, a confirmation upcall is made
to the matching application:
Call: <Upcall_Proc>( session-id, Resv Confirm,
Error_code, Error_value, Node_Addr,
LUB-Used, nlist, Flowspec,
Filter_Spec_List, NULL, NULL )
Otherwise, the RACK message is forwarded immediately to the
address in the IP address in its RESV_CONFIRM object.
PATH REFRESH
This sequence sends a path refresh for a particular sender,
i.e., a PSB. This sequence may be entered by either the
expiration of the path refresh timer or directly as the result
of the Path_Refresh_Needed flag being turned on during the
processing of a received PATH message.
o Compute the IP TTL for the PATH message as one less than
the maximum of the TTL values from the senders included in
the message. However, if the result is zero, return
without sending the PATH message.
o Insert TIME_VALUES and PHOP objects into the PATH message
being built.
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o Create a sender descriptor containing the SENDER_TEMPLATE,
SENDER_TSPEC, and POLICY_DATA objects, if present in the
PSB, and pack it into the PATH message being built.
o Pass any ADSPEC and SENDER_TSPEC objects present in the PSB
to the traffic control call TC_Advertise. Insert the
modified ADSPEC object that is returned into the PATH
message being built.
o If the PSB has the E_Police flag on and if interface OI is
not capable of policing, turn the E_Police flag on in the
PATH message being built.
o Send a copy of the PATH message to each interface in
OutInterfact_list. Before sending each copy, insert into
its PHOP object the interface address and the LIH for the
interface.
RESV REFRESH
This sequence sends a reservation refresh towards a particular
previous hop with IP address PH. This sequence may be entered
by either the expiration of a reservation refresh timer or
directly as the result of the Resv_Refresh_Needed flag being
turned on as the result of processing a RESV or RTEAR message.
In general, this sequence considers each of the PSB's with PHOP
address PH. For a given PSB, it scans the RSBs for matching
reservations and merges the styles, FLOWSPECs and FILTER_SPEC*'s
appropriately. It then builds a RESV message and sends it to
PH. The details depend upon the attributes of the style(s)
included in the reservations.
o If there are PSB's from more than one PHOP and if the
multicast routing protocol does not use shared trees, set
the Need_Scope flag on, otherwise set it off.
o Create an output message containing SESSION, RSVP_HOP,
INTEGRITY, and TIME_VALUES objects.
o Select each sender PSB whose PHOP has address PH.
1. Select all RSB's whose FILTER_SPEC*'s match the
SENDER_TEMPLATE object in the PSB and whose OI appears
in the OutInterface_list of the PSB.
2. Get a STYLE object from the first RSB and move it into
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the output message. (Note that the present set of
styles are never themselves merged; if future styles
can be merged, these rules will become more complex).
3. Compute the maximum/LUB over the FLOWSPEC objects of
this set of RSB's.
4. While computing the maximum/LUB, check for a
RESV_CONFIRM object in each RSB. If a RESV_CONFIRM
object is found and if the FLOWSPEC in that RSB is
larger than all other flowspecs being compared, then
save this RESV_CONFIRM object. If a RESV_CONFIRM
object is found but the corresponding FLOWSPEC is
equal or smaller than the largest, or if the result of
merging was a LUB, then create and send a RACK message
to the address in the RESV_CONFIRM object.
- Include the RESV_CONFIRM object in the RACK
message.
- Build a confirmation ERROR_SPEC object and
include it in the RACK message. The Error_Node
parameter in this object should be the IP address
of OI from the RSB.
Then delete the RESV_CONFIRM object from the RSB.
5. Merge the matching FILTER_SPEC objects from this set
of RSB's. The merging rule depend upon the style:
Explicit sender selection (FF, SE) styles:
Use the SENDER_TEMPLATE as the merged
FILTER_SPEC.
Wildcard sender selection (WF) style:
There is no filter spec to merge.
6. If the Need_Scope flag is on, compute a new SCOPE
object as the union of the SCOPE objects found in the
RSB's.
7. Merge the F_POLICY_DATA objects from the RSB's.
8. (All matching RSB's have been processed). The next
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step depends upon the style attributes.
Distinct reservation (FF) style
Pack the merged (FLOWSPEC, FILTER_SPEC,
F_POLICY_DATA) triplet into the message as a flow
descriptor.
Shared reservation (SE, WF) styles
Merge (take the maximum) across all PSB's the
merged FLOWSPECS from the RSB's.
If the sender selection is not wildcard (i.e., if
it is SE), form the union of the FILTER_SPECs
obtained from the RSB's. For Wildcard sender
selection (WF) style, there is not filter spec to
merge.
9. If the Need_Scope flag is on, remove from the merged
SCOPE object all sender addresses that do not match
the set of PSB's for PH, and all senders addresses
that are local. If the resulting set is empty, no
RESV should be forwarded to this PHOP; return;
otherwise (set is not empty), move the new SCOPE
object into the message.
o (All PSB's have been processed). If a shared reservation
style is being built, move the final merged FLOWSPEC,
F_POLICY_DATA, and FILTER_SPEC (if SE) objects into the
message.
o If a RESV_CONFIRM object was saved earlier, copy it into
the new RESV message and delete it from the RSB in which it
was found.
o Set the RSVP_HOP object in the message to contain the
IncInterface address through which it will be sent and the
LIH from (one of) the PSB's.
o Send the message to the address PH.
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APPENDIX A. Object Definitions
C-Types are defined for the two Internet address families IPv4 and
IP6. To accommodate other address families, additional C-Types could
easily be defined. These definitions are contained as an Appendix,
to ease updating.
All unused fields should be sent as zero and ignored on receipt.
A.1 SESSION Class
SESSION Class = 1.
o IPv4/UDP SESSION object: Class = 1, C-Type = 1
+-------------+-------------+-------------+-------------+
| IPv4 DestAddress (4 bytes) |
+-------------+-------------+-------------+-------------+
| Protocol Id | Flags | DstPort |
+-------------+-------------+-------------+-------------+
o IP/UDP SESSION object: Class = 1, C-Type = 2
+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ IP6 DestAddress (16 bytes) +
| |
+ +
| |
+-------------+-------------+-------------+-------------+
| Protocol Id | Flags | DstPort |
+-------------+-------------+-------------+-------------+
DestAddress
The IP unicast or multicast destination address of the
session. This parameter must be supplied.
Protocol Id
The IP Protocol Identifier for the data flow. This parameter
must be supplied.
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Flags
0x01 = E_Police flag
The E_Police flag is used in PATH messages to determine
the effective "edge" of the network, to control traffic
policing. If the sender host is not itself capable of
traffic policing, it will set this bit on in PATH
messages it sends. The first node whose RSVP is capable
of traffic policing will do so (if appropriate to the
service) and turn the flag off.
[It might make more sense to include this flag in ADSPEC
object.]
DstPort
The UDP/TCP destination port for the session. Zero may be
used to indicate a `wildcard', i.e., any port.
Other SESSION C-Types could be defined in the future to
support other demultiplexing conventions in the transport-
layer or application layer.
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A.2 RSVP_HOP Class
RSVP_HOP class = 3.
o IPv4 RSVP_HOP object: Class = 3, C-Type = 1
+-------------+-------------+-------------+-------------+
| IPv4 Next/Previous Hop Address |
+-------------+-------------+-------------+-------------+
| Logical Interface Handle |
+-------------+-------------+-------------+-------------+
o IP6 RSVP_HOP object: Class = 3, C-Type = 2
+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ IP6 Next/Previous Hop Address +
| |
+ +
| |
+-------------+-------------+-------------+-------------+
| Logical Interface Handle |
+-------------+-------------+-------------+-------------+
This object provides the IP address of the interface through which
the last RSVP-knowledgeable hop forwarded this message. The
Logical Interface Handle is a 32-bit number which may be used to
distinguish logical outgoing interfaces as described in Section
3.2; it should be identically zero if there is no logical
interface handle.
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A.3 INTEGRITY Class
INTEGRITY class = 4.
See draft-ietf-rsvp-md5-00.txt.
A.4 TIME_VALUES Class
TIME_VALUES class = 5.
o TIME_VALUES Object: Class = 5, C-Type = 1
+-------------+-------------+-------------+-------------+
| Refresh Period |
+-------------+-------------+-------------+-------------+
Refresh Period
The refresh timeout period R used to generate this message;
in milliseconds.
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A.5 ERROR_SPEC Class
ERROR_SPEC class = 6.
o IPv4 ERROR_SPEC object: Class = 6, C-Type = 1
+-------------+-------------+-------------+-------------+
| IP4 Error Node Address (4 bytes) |
+-------------+-------------+-------------+-------------+
| Flags | Error Code | Error Value |
+-------------+-------------+-------------+-------------+
o IP6 ERROR_SPEC object: Class = 6, C-Type = 2
+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ IP6 Error Node Address (16 bytes) +
| |
+ +
| |
+-------------+-------------+-------------+-------------+
| Flags | Error Code | Error Value |
+-------------+-------------+-------------+-------------+
Error Node Address
The IP address of the node in which the error was detected.
Flags
0x01 = LUB-Used
The use of this flag is described in section 3.1.5.
Error Code
A one-octet error description.
Error Value
A two-octet field containing additional information about the
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error. Its contents depend upon the Error Type.
The values for Error Code and Error Value are defined in Appendix
B.
A.6 SCOPE Class
SCOPE class = 7.
This object contains a list of IP addresses, used for routing
messages with wildcard scope without loops. The addresses must be
listed in ascending numerical order.
o IPv4 SCOPE List object: Class = 7, C-Type = 1
+-------------+-------------+-------------+-------------+
| IP4 Src Address (4 bytes) |
+-------------+-------------+-------------+-------------+
// //
+-------------+-------------+-------------+-------------+
| IP4 Src Address (4 bytes) |
+-------------+-------------+-------------+-------------+
o IP6 SCOPE list object: Class = 7, C-Type = 2
+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ IP6 Src Address (16 bytes) +
| |
+ +
| |
+-------------+-------------+-------------+-------------+
// //
+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ IP6 Src Address (16 bytes) +
| |
+ +
| |
+-------------+-------------+-------------+-------------+
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A.7 STYLE Class
STYLE class = 8.
o STYLE object: Class = 8, C-Type = 1
+-------------+-------------+-------------+-------------+
| Option Vector |
+-------------+-------------+-------------+-------------+
Option Vector
A set of bit fields giving values for the reservation
options. If new options are added in the future,
corresponding fields in the option vector will be assigned
from the least-significant end. If a node does not recognize
a style ID, it may interpret as much of the option vector as
it can, ignoring new fields that may have been defined.
The option vector bits are assigned (from the left) as
follows:
27 bits: Reserved
2 bits: Sharing control
00b: Reserved
01b: Distinct reservations
10b: Shared reservations
11b: Reserved
3 bits: Sender selection control
000b: Reserved
001b: Wildcard
010b: Explicit
011b - 111b: Reserved
The low order bits of the option vector are determined by the
style, as follows:
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WF 10001b
FF 01010b
SE 10010b
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A.8 FLOWSPEC Class
FLOWSPEC class = 9.
o Class = 9, C-Type = 1: int-serv flowspec
The contents of this object will be specified in documents
prepared by the int-serv working group.
o Class = 9, C-Type = 254: Unmerged Flowspec List
+-------------+-------------+-------------+-------------+
| |
// FLOWSPEC object 1 //
| |
+-------------+-------------+-------------+-------------+
| |
// FLOWSPEC object 2 //
| |
+-------------+-------------+-------------+-------------+
// //
// //
+-------------+-------------+-------------+-------------+
| |
// FLOWSPEC object k //
| |
+-------------+-------------+-------------+-------------+
This is a container C-Type, used to enclose a set of FLOWSPEC
objects that could not be merged at the next hop downstream
because they include unrecognized C-Types. The node that
receives this object may merge those it recognizes and
forward the rest in another Unmerged Flowspec List object.
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A.9 FILTER_SPEC Class
FILTER_SPEC class = 10.
o IPv4 FILTER_SPEC object: Class = 10, C-Type = 1
+-------------+-------------+-------------+-------------+
| IPv4 SrcAddress (4 bytes) |
+-------------+-------------+-------------+-------------+
| ////// | ////// | SrcPort |
+-------------+-------------+-------------+-------------+
o IP6 FILTER_SPEC object: Class = 10, C-Type = 2
+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ IP6 SrcAddress (16 bytes) +
| |
+ +
| |
+-------------+-------------+-------------+-------------+
| ////// | ////// | SrcPort |
+-------------+-------------+-------------+-------------+
o IP6 Flow-label FILTER_SPEC object: Class = 10, C-Type = 3
+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ IP6 SrcAddress (16 bytes) +
| |
+ +
| |
+-------------+-------------+-------------+-------------+
| /////// | Flow Label (24 bits) |
+-------------+-------------+-------------+-------------+
SrcAddress
The IP source address for a sender host, or zero to indicate
a `wildcard'.
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SrcPort
The UDP/TCP source port for a sender, or zero to indicate a
`wildcard' (i.e., any port).
Flow Label
A 24-bit Flow Label, defined in IP6. This value may be used
by the packet classifier to efficiently identify the packets
belonging to a particular (sender->destination) data flow.
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A.10 SENDER_TEMPLATE Class
SENDER_TEMPLATE class = 11.
o IPv4/UDP SENDER_TEMPLATE object: Class = 11, C-Type = 1
Definition same as IPv4/UDP FILTER_SPEC object.
o IP6/UDP SENDER_TEMPLATE object: Class = 11, C-Type = 2
Definition same as IP6/UDP FILTER_SPEC object.
A.11 SENDER_TSPEC Class
SENDER_TSPEC class = 12.
o Token Bucket SENDER_TSPEC object: Class = 12, C-Type = 1
The contents of this object will be specified in documents
prepared by the int-serv working group.
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A.12 ADSPEC Class
ADSPEC class = 13.
The contents of this object will be specified in documents
prepared by the int-serv working group.
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A.13 POLICY_DATA Class
POLICY_DATA class = 14.
o Type 1 POLICY_DATA object: Class = 14, C-Type = 1
The contents of this object are for further study.
o Unmerged POLICY_DATA object: Class = 14, C-Type = 254
This object is a container for a list of POLICY_DATA objects
(none of which may have C-Type = 254). The contained objects
have not yet been merged.
+-------------+-------------+-------------+-------------+
| |
// POLICY_DATA object 1 //
| |
+-------------+-------------+-------------+-------------+
| |
// POLICY_DATA object 2 //
| |
+-------------+-------------+-------------+-------------+
// //
// //
+-------------+-------------+-------------+-------------+
| |
// POLICY_DATA object k //
| |
+-------------+-------------+-------------+-------------+
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A.14 RESV_CONFIRM Class
RESV_CONFIRM class = 15.
o IPv4 RESV_CONFIRM object: Class = 15, C-Type = 1
+-------------+-------------+-------------+-------------+
| IPv4 Receiver Address (4 bytes) |
+-------------+-------------+-------------+-------------+
o IP6 RESV_CONFIRM object: Class = 15, C-Type = 2
+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ IP6 Receiver Address (16 bytes) +
| |
+ +
| |
+-------------+-------------+-------------+-------------+
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APPENDIX B. Error Codes and Values
The following Error Codes are defined.
o Error Code = 01: Admission failure
Reservation rejected by admission control.
For this Error Code, the 16 bits of the Error Value field are:
ussr cccc cccc cccc
where the bits are:
u = 0: RSVP rejects the message without updating local state.
u = 1: RSVP may use message to update local state and forward
the message.
ss = 00: Low order 12 bits contain a globally-defined sub-code
(values listed below).
ss = 10: Low order 12 bits contain a sub-code that is specific
to local organization. RSVP is not expected to be able to
interpret this except as a numeric value.
ss = 11: Low order 12 bits contain a sub-code that is specific
to the service. RSVP is not expected to be able to
interpret this except as a numeric value. Since the
traffic control mechanism might substitute a different
service, this encoding may include some representation of
the service in use.
r: Reserved bit, should be zero.
cccc cccc cccc: 12 bit code.
The following globally-defined sub-codes may appear in the low-
order 12 bits when ss = 00:
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- Sub-code = 1: Delay bound cannot be met
- Sub-code = 2: Requested bandwidth unavailable
- Sub-code = 11: Service conflict
- Sub-code = 12: Service unsupported
Traffic control can provide neither the requested service
nor an acceptable replacement.
- Sub-code = 13: Bad Flowspec or Tspec value
Unreasonable request. High order bit u = 0, i.e., RSVP
will reject the message.
- Sub-code = 14: Rmax value too small.
Rmax would result in excessive refresh overhead.
o Error Code = 02: Administrative rejection
Reservation has been rejected for administrative reasons.
The high order 4 bits of the Error Value field are assigned as
for Error Code = 01 (above). For Error Code = 02, the following
global sub-codes are defined:
- Sub-code = 1: Required credential(s) not presented.
- Sub-code = 2: Request too large
Reservation request exceeds allowed value for this user
class.
- Sub-code = 3: Insufficient quota or balance.
- Sub-code = 4: Administrative preemption
o Error Code = 03: No path information for this Resv
RSVP should reject the message.
o Error Code = 04: No sender information for this Resv
There is path information, but it does not include the sender
specified in one of the Filterspecs listed in the Resv message.
RSVP should reject the message.
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o Error Code = 05: Ambiguous path
Sender port appears both zero and non-zero in same session.
RSVP should reject the message.
o Error Code = 06: Ambiguous filter spec
Filter spec matches more than one sender, in a style that
requires a unique match. RSVP should reject the message.
o Error Code = 07: Conflicting or unknown style
Reservation style conflicts with style(s) of existing
reservation state, or it is unknown. If the high-order bit of
Error Value is zero, RSVP should reject the message.
o Error Code = 08: Conflicting dest port
Sessions for same destination address and protocol have appeared
with both zero and non-zero dest port fields.
o Error Code = 09: Conflicting source port
The source port is non-zero in a filter spec or sender template
for a session with destination port zero.
o Error Code = 11: Missing required object
RSVP was unable to find or construct required object data from
message. Error Value will be Class-Num that is missing. RSVP
should reject the message.
o Error Code = 12: Unknown object class
Error Value will contain 16-bit value composed of (Class-Num,
C-Type) of unknown object. This error should be sent only if
RSVP is going to reject the message.
o Error Code = 13: Unknown object C-Type
Error Value will contain 16-bit value composed of (Class-Num,
C-Type) of object. This error should be sent only if RSVP is
going to reject the message.
o Error Code = 14: Object error
A non-specific error indicating bad format or contents of an
object. The Error Value will contain 16-bits value (Class-Num,
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C-Type) from header of bad object. RSVP should reject the
message.
o Error Code = 21: Traffic Control error
Some system error was detected and reported by the traffic
control modules. The Error Value will contain a system-specific
value giving more information about the error. RSVP is not
expected to be able to interpret this value.
o Error Code = 22: RSVP System error
The Error Value field will provide implementation-dependent
information on the error. RSVP is not expected to be able to
interpret this value.
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APPENDIX C. UDP Encapsulation
An RSVP implementation will generally require the ability to perform
"raw" network I/O, i.e., to send and receive IP datagrams using
protocol 46. However, some important classes of host systems may not
support raw network I/O. To use RSVP, such hosts must encapsulate
RSVP messages in UDP.
The basic UDP encapsulation scheme makes two assumptions:
1. All hosts are capable of sending and receiving multicast
packets.
2. The first/last-hop routers are RSVP-capable.
A method of relaxing the second assumption is given later.
Let Hu be a "UDP-only" host that requires UDP encapsulation, and Hr a
host that can do raw network I/O. The UDP encapsulation scheme must
allow RSVP interoperation among an arbitrary topology of Hr hosts, Hu
hosts, and routers.
RESV, RERR, RTEAR, and PERR messages are sent to unicast addresses
learned from the path or reservation state in the node. If the node
keeps track of which previous hops and which interfaces need UDP
encapsulation, these messages message can be sent using UDP
encapsulation when necessary.
On the other hand, PATH and PTEAR messages are send to the unicast or
multicast destination address for the session. The table in Figure
12 shows the basic rules for UDP encapsulation of such messages.
Under the `Send' column, the notation is `mode(destaddr, destport,
TTL)', where TTL is the IP-layer hop count. The `Receive' column
shows the group that is joined and, where relevant, the UDP Listen
port. The following symbols are also used:
o D is the DestAddress for the particular session.
o G* is a well-known group address of the form 224.0.0.x, i.e., a
group that is limited to the local connected network. [TO BE
DEFINED]
o Pu is the well-known UDP port for UDP encapsulation of RSVP:
3455.
o Ra is the IP address of the router interface `a'.
o Tr is the TTL value of the specific PATH message.
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o Router interface `a' is on the local network connected to Hu and
Hr, while interface `b' is connected only to another router.
RSVP RSVP
Node Node Type Send Receive
___ __________ _____________ _______________
Hu UDP-only host UDP(G*,Pu,1) UDP(G*,Pu)
or UDP(Ra,Pu,1) and UDP(D,Pu)
[Note 1] [Note 3]
Hr Raw-mode host UDP(G*,Pu,1) UDP(G*,Pu)
and Raw(D,,Tr) and Raw()
R Router
Interface a: UDP(D,Pu,Tr) UDP(G*,Pu) [Note 2]
and Raw(D,,Tr) and UDP(Ra,Pu)
and Raw()
Interface b: Raw(D,,Tr) Raw()
Figure 12: UDP Encapsulation Rules for Path Messages
[Note 1] Hu sends a PATH message to Ra only if session destination
address D is unicast.
[Note 2] R ignores PATH messages addressed to G* if D is unicast.
(This is necessary to prevent routing and reservation anomalies).
[Note 3] The DestAddress D is the IP address of Hu in this case.
R and Hr send their PATH messages twice, once with UDP encapsulation
and once in raw mode. In two cases (Hr -> R and Hr -> Hr), each PATH
message will be delivered twice. The destination may take steps to
ignore the duplicates, although this redundancy has no ill effect
other than overhead for processing the extra messages.
A router may determine if its interface X needs UDP encapsulation by
listening for UDP-encapsulated PATH messages that were sent to either
G* (multicast D) or to the address of interface X (unicast D). There
is one failure mode for this scheme: if no host on the connected
network acts as an RSVP sender, there will be no PATH messages to
trigger UDP encapsulation. In this (unlikely) case, it will be
necessary to explicitly configure UDP encapsulation on the local
network interface of the router.
A UDP-only host Hu supporting unicast RSVP sessions must somehow know
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the address Ra, presumably by configuration.
When a UDP-encapsulated packet is received, the IP TTL is not
available to the application on most systems. The RSVP daemon that
receives a UDP-encapsulated PATH or PTEAR message should therefore
use the Send_TTL field of the RSVP common header as the effective
receive TTL.
We have assumed that the first-hop RSVP-capable router R is on the
directly-connected network. There are several possible approaches if
this is not the case.
1. Hu can send both unicast and multicast sessions to
UDP(Ra,Pu,Ta).
Here Ta must be the TTL to exactly reach R. If Ta is too small,
the PATH message will not reach R. If Ta is too large,
multicast routing in R will forward the UDP packet into the
Internet until its hop count expires. This will turn on UDP
encapsulation between routers within the Internet, causing bogus
UDP traffic. The host Hu must be explicitly configured with Ra
and Ta.
2. A particular host on the LAN connected to Hu could be designated
as an "RSVP relay host". A relay host would listen on (G*,Pu)
and forward any PATH messages directly to R, although it would
not be in the data path. The relay host would have to be
configured with Ra and Ta.
APPENDIX D. Experimental and Open Issues
D.1 Reservation Compatibility
How strong is the requirement for compatibility of reservations in
different directions? For example, see Figure 10; should it be
possible to have incompatible reservation styles on the two
interfaces? If R1 requests a WF reservation and R2 requests a FF
reservation, it is logically possible to make the corresponding
reservations on the two different interfaces. The current
implementation does NOT allow this; instead, it prevents mixing of
incompatible styles in the same session on a node, even if they
are on different interfaces.
D.2 Session Groups (Experimental)
Section 1.2 explained that a distinct destination address, and
therefore a distinct session, will be used for each of the
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subflows in a hierarchically encoded flow. However, these
separate sessions are logically related. For example it may be
necessary to pass reservations for all subflows to Admission
Control at the same time (since it would be nonsense to admit high
frequency components but reject the baseband component of the
session data). Such a logical grouping is indicated in RSVP by
defining a "session group", an ordered set of sessions.
To declare that a set of sessions form a session group, a receiver
includes a data structure we call a SESSION_GROUP object in the
RESV message for each of the sessions. A SESSION_GROUP object
contains four fields: a reference address, a session group ID, a
count, and a rank.
o The reference address is an agreed-upon choice from among the
DestAddress values of the sessions in the group, for example
the smallest numerically.
o The session group ID is used to distinguish different groups
with the same reference address.
o The count is the number of members in the group.
o The rank, an integer between 1 and count, is different in
each session of the session group.
The SESSION_GROUP objects for all sessions in the group will
contain the same values of the reference address, the session
group ID, and the count value. The rank values establishes the
desired order among them.
If RSVP at a given node receives a RESV message containing a
SESSION_GROUP object, it should wait until RESV messages for all
`count' sessions have appeared (or until the end of the refresh
cycle) and then pass the RESV requests to Admission Control as a
group. It is normally expected that all sessions in the group
will be routed through the same nodes. However, if not, only a
subset of the session group reservations may appear at a given
node; in this case, the RSVP should wait until the end of the
refresh cycle and then perform Admission Control on the subset of
the session group that it has received. The rank values will
identify which are missing.
Note that routing different sessions of the session group
differently will generally result in delays in establishing or
rejecting the desired QoS. A "bundling" facility could be added
to multicast routing, to force all sessions in a session group to
be routed along the same path.
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D.2.1 Resv Messages
Add:
[ <SESSION_GROUP> ]
after the SESSION object.
D.2.2 SESSION_GROUP Class
SESSION_GROUP class = 2.
o IPv4 SESSION_GROUP Object: Class = 2, C-Type = 1:
+-------------+-------------+-------------+-------------+
| IPv4 Reference DestAddress |
+-------------+-------------+-------------+-------------+
| Session_Group ID | Count | Rank |
+-------------+-------------+-------------+-------------+
o IP6 SESSION_GROUP Object: Class = 2, C-Type = 2:
+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ IP6 Reference DestAddress +
| |
+ +
| |
+-------------+-------------+-------------+-------------+
| Session-Group ID | Count | Rank |
+-------------+-------------+-------------+-------------+
The variables are defined in above.
D.3 DF Style (Experimental)
In addition to the WF and FF styles defined in this specification,
a Dynamic Filter (DF) style has also been proposed. The following
describes this style and gives examples of its usage. At this
time, DF style is experimental.
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D.3.1 Reservation Styles
A Dynamic-Filter (DF) style reservation makes "distinct"
reservations with "wildcard" scope, but it decouples
reservations from filters.
o Each DF reservation request specifies a number D of
distinct reservations using the same specified flowspec.
These reservations are distributed with wildcard scope,
i.e., to all senders.
The number of reservations that are actually made in a
particular node is D' = min(D,Ns), where Ns is the total
number of senders upstream of the node.
o In addition to D and the flowspec, a DF style reservation
may also specify a list of K filterspecs, for some K in
the range: 0 <= K <= D'. These filterspecs define
particular senders to use the D' reservations, and this
list establishes the scope for the filter specs.
Once a DF reservation has been established, the receiver
may change the set of filterspecs to specify a different
selection of senders, without a new admission control
check (assuming D' and the common flowspec remain
unchanged). This is known as "channel switching", in
analogy with a television set.
In order to provide assured channel switching, each node along
the path must reserve enough bandwidth for all D' channels,
even though some of this bandwidth may be unused at any one
time. If D' changes (because the receiver changed D or because
the number Ns of upstream sources changed), or if the common
flowspec changes, the refresh message is treated as a new
reservation that is subject to admission control and may fail.
The DF style allows a receiver to switch channels without
danger of an admission denial due to limited resources (unless
a topology change reroutes traffic along a lower-capacity path
or new senders appear), once the initial reservations have been
made. This in turn implies that the DF style creates
reservations that may not be in use at any given time.
The DF style is compatible with the FF style but not the WF or
SE style.
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D.3.2 Examples
To give an example of the DF style, we use the following
notation:
o DF Style
DF( n, {r} ; ) or DF( n, {r} ; S1, S2, ...)
This message carries the count n of channels to be reserved,
each using common flowspec r. It also carries a list, perhaps
empty, of filterspecs defining senders.
Figure 13 shows an example of Dynamic-Filter reservations. The
receivers downstream from interface (d) have requested two
reserved channels, but selected only one sender, S1. The node
reserves min(2,3) = 2 channels of size B on interface (d), and
it then applies any specified filters to these channels. Since
only one sender was specified, one channel has no corresponding
filter, as shown by `?'.
Similarly, the receivers downstream of interface (c) have
requested two channels and selected senders S1 and S2. The two
channels might have been one channel each from R1 and R2, or
two channels requested by one of them, for example.
|
Send | Reserve Receive
|
| ________
DF( 1,{B}; S1) <- (a) | (c) | S1{B} | (c) <- DF( 2,{B}; S1, S2)
| |________|
| | S2{B} |
| |________|
|
------------------------|-------------------------------------------
| ________
DF( 2,{B}; S2) <- (b) | (d) | S1{B} | (d) <- DF( 2,{B}; S1)
| |________|
| | ?{B} |
| |________|
Figure 13: Dynamic-Filter Reservation Example
A router should not reserve more Dynamic-Filter channels than
the number of upstream sources (three, in the router of Figure
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Internet Draft RSVP Specification November 1995
13).
Since there is only one source upstream from previous hop (a),
the first parameter of the DF message (the count of channels to
be reserved) was decreased to 1 in the forwarded reservations.
However, this is unnecessary, because the routers upstream will
reserve only one channel, regardless.
When a DF reservation is received, it is labeled with the IP
address of the next hop (RSVP-capable) router, downstream from
the current node. Since the outgoing interface may be directly
connected to a shared medium network or to a non-RSVP-capable
router, there may be more than one next-hop node downstream; if
so, each sends independent DF RESV messages for a given
session. The number N' of DF channels reserved on an outgoing
interface is given by the formula:
N' = min( D1+D2+...Dn, Ns),
where Di is the D value (channel reservation count) in a RESV
from the ith next-hop node.
For a DF reservation request with a Dynamic Reservation Count =
C, RSVP should call TC_AddFlowspec C times.
D.3.3 Resv Messages
Add the following sequence:
<flow descriptor list> ::=
<FLOWSPEC> <filter spec list>
D.3.4 STYLE Class
o STYLE-DF object: Class = 8, C-Type = 2
+-------------+-------------+-------------+-------------+
| Style ID=4 | Attribute Vector 0...0101001b |
+-------------+-------------+-------------+-------------+
| ////// /////// | Dynamic Resv Count |
+-------------+-------------+---------------------------+
Style ID
4 = Dynamic-Filter (DF)
Attribute Vector
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18 bits: Reserved
1 bit: Decoupled if 1.
2 bits: Sharing control (as before)
3 bits: Scope control (as before)
Dynamic Resv Count
The number of channels to be reserved for a Dynamic
Filter style reservation. This integer value must
not less than the number of FILTER_SPEC objects in
filter spec list.
References
[CSZ92] Clark, D., Shenker, S., and L. Zhang, "Supporting Real-Time
Applications in an Integrated Services Packet Network: Architecture
and Mechanisms", Proc. SIGCOMM '92, Baltimore, MD, August 1992.
[FJ94] Floyd, S. and V. Jacobson, "Synchronization of Periodic Routing
Messages", IEEE/ACM Transactions on Networking, Vol. 2, No. 2,
April, 1994.
[ISInt93] Braden, R., Clark, D., and S. Shenker, "Integrated Services
in the Internet Architecture: an Overview", RFC 1633, ISI, MIT, and
PARC, June 1994.
[IServ93] Shenker, S., Clark, D., and L. Zhang, "A Service Model for an
Integrated Services Internet", Work in Progress, October 1993.
[Katz95] Katz, D., "IP Router Alert Option", Internet Draft draft-
katz-router-alert-01.txt, Cisco Systems, November 16, 1995.
[Partridge92] Partridge, C., "A Proposed Flow Specification", RFC 1363,
BBN, September 1992.
[RSVP93] Zhang, L., Deering, S., Estrin, D., Shenker, S., and D.
Zappala, "RSVP: A New Resource ReSerVation Protocol", IEEE Network,
September 1993.
[ServTempl95a] Shenker, S., "Network Element Service Specification
Template", Internet Draft draft-ietf-intserv-svc-template-00.txt,
Integrated Services Working Group, March 1995.
[Shenker94] Shenker, S., "Two-Pass or Not Two-Pass", Current Meeting
Braden, Zhang, et al. Expiration: May 1996 [Page 109]
Internet Draft RSVP Specification November 1995
Report, RSVP Working Group, Proceedings of the Thirtieth Internet
Engineering Task Force, Toronto, Canada, July 1994.
Security Considerations
See Section 2.7.
Authors' Addresses
Lixia Zhang
Xerox Palo Alto Research Center
3333 Coyote Hill Road
Palo Alto, CA 94304
Phone: (415) 812-4415
EMail: Lixia@PARC.XEROX.COM
Bob Braden
USC Information Sciences Institute
4676 Admiralty Way
Marina del Rey, CA 90292
Phone: (310) 822-1511
EMail: Braden@ISI.EDU
Deborah Estrin
Computer Science Department
University of Southern California
Los Angeles, CA 90089-0871
Phone: (213) 740-4524
EMail: estrin@USC.EDU
Shai Herzog
USC Information Sciences Institute
4676 Admiralty Way
Marina del Rey, CA 90292
Palo Alto, CA 94304
Phone: (310) 822 1511
EMail: Herzog@ISI.EDU
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Sugih Jamin
Computer Science Department
University of Southern California
Los Angeles, CA 90089-0871
Phone: (213) 740-6578
EMail: jamin@catarina.usc.edu
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