Internet Draft R. Braden, Ed.
Expiration: January 1996 ISI
File: draft-ietf-rsvp-spec-07.txt L. Zhang
PARC
D. Estrin
ISI
S. Herzog
ISI
S. Jamin
USC
Resource ReSerVation Protocol (RSVP) --
Version 1 Functional Specification
July 7, 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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What's Changed Since Danvers IETF
The most important changes in this document from the rsvp-spec-05 draft
are:
o Added fields to common header for linear fragmentation, and
moved all references to semantic fragmentation to Appendix D.
o Added SE (Shared Explicit) style to all parts of the document.
o Further clarified reservation options and added table in Figure
3. Defined option vector in STYLE object.
o Renamed CREDENTIAL object class to POLICY_DATA object class, and
rewrote section 2.5 to more fully express its intended usage.
o Clarified the relationship between the wildcard scope
reservation option and wildcards in individual FILTER_SPEC
objects: wildcard is as wildcard does.
o Added SCOPE object definition and defined the rules for its use
to prevent looping of wildcard-scope messages.
o Added some mechanisms for handling backwards compatibility for
future protocol extensions: (1) High bit of object class number;
(2) unmerged FLOWSPEC C-Type; (3) unmerged POLICY_DATA C-Type.
o Rewrote Section 4.3 on preventing looping. Included rules for
SCOPE object.
o Specified rules for local repair upon route change notification
(Section 4.4).
o Specified for each error type whether or not the state
information in the erroneous packet is to be stored and
forwarded.
o Deleted the discussion of retransmitting a Teardown message Q
times; assume Q=1 is sufficient.
o Moved Session Groups to Appendix D, "Experimental and Open
Issues". Session Groups should be revisited as part of a larger
context of cross-session reservations.
o Changed common header format, removing Object Count (which was
redundant) and rearranging the remaining fields. Moved the two
common header flags into objects: Entry-Police into SESSION
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object and LUB-used into ERROR_SPEC object.
o Revised the rules for state timeout (Section 4.5) and redefined
the TIME_VALUES object format.
o Changed the error message format: (1) removed required RSVP_HOP
object from PERR and RERR messages; (2) specified more carefully
what may appear in flow descriptor list of RERR messages.
o Revised the definitions of error codes and error values, and
moved them into a separate Appendix B.
o No longer require CREDENTIAL (i.e., POLICY_DATA) match for
teardown.
o Revised routing of RERR messages to use SCOPE objects to avoid
wildcard-induced looping.
o Added LIH (logical interface handle) to RSVP_HOP object, for IP
multicast tunnels.
o Specified that addresses should be sorted in SCOPE object.
o Added two new upcall event types in the API: reservation event
and policy data event.
o Generalized the generic traffic control calls slightly to allow
multiple filter specs per flowspec, for SE style. This
introduced a new set of handles, called FHandle. Also added a
preemption upcall.
o Added route change notification to the generic interface to
routing.
o Updated the message processing rules (Section 5).
o Rewrote Appendix C on UDP encapsulation.
o Removed specification of FLOWSPEC object format (but int-serv
working group has since reneged on promise to specify it).
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1. Introduction
This document defines RSVP, a resource reservation setup protocol
designed for an integrated services Internet [RSVP93,ISInt93].
A host uses the RSVP protocol to request a specific quality of
service (QoS) from the network, on behalf of an application data
stream. RSVP is also used to deliver QoS requests to routers along
the path(s) of the data stream and to maintain router and host state
to provide the requested service. This will generally (but not
necessarily) require reserving resources along the data path.
RSVP reserves resources for simplex data streams, i.e., it reserves
resources in only one direction on a link, so that a sender is
logically distinct from a receiver. However, the same application
may act as both sender and receiver. RSVP operates on top of IP,
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. As shown in Figure 1, an implementation of RSVP, like the
implementations of routing and management protocols, will typically
execute in the background, not in the data forwarding path.
RSVP is not itself a routing protocol; the RSVP daemon consults the
local routing protocol(s) to obtain routes. Thus, a host sends IGMP
messages to join a multicast group, and it sends RSVP messages to
reserve resources along the delivery path(s) from that group. RSVP
is designed to operate with existing and future unicast and multicast
routing protocols.
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HOST ROUTER
_________________________ RSVP ______________________
| | .---------------. |
| _______ ______ | . | ________ . ______ |
| | | | | | . || | . | || RSVP
| |Applic-| | RSVP <----- ||Routing | -> RSVP <------>
| | App <----->daemon| | ||Protocol| |daemon||
| | | | | | || daemon <----> ||
| |_______| |___.__| | ||_ ._____| |__.___||
|===|===============v=====| |===v=============v====|
| data .......... | | . ............ |
| | ____v_ ____v____ | | _v__v_ _____v___ |
| | |Class-| | || data | |Class-| | || data
| |=> ifier|=> Packet =============> ifier|==> Packet |======>
| |______| |Scheduler|| | |______| |Scheduler||
| |_________|| | |_________||
|_________________________| |______________________|
Figure 1: RSVP in Hosts and Routers
Each router that is capable of resource reservation passes incoming
data packets to 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. The scheduler allocates resources
for transmission on the particular link-layer medium used by each
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. There are many possible ways this might be
accomplished, and the details will be medium-dependent. The
scheduler itself allocates packet transmission capacity on a QoS-
passive medium such as a leased line. 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 and to be consistent with IP multicast, RSVP
makes receivers responsible for requesting resource reservations
[RSVP93]. A QoS request, typically originating in a receiver host
application, will be passed to the local RSVP implementation, shown
as a user daemon in Figure 1. The RSVP protocol is then used to pass
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 program applies a local decision procedure,
called "admission control", to determine if it can supply the
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requested QoS. If admission control succeeds, the RSVP program sets
parameters to the packet classifier and scheduler to obtain the
desired QoS. If admission control fails at any node, the RSVP
program returns an error indication to the application 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 the membership of a large group will be constantly changing,
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, in addition to receiver-initiation.
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).
In summary, RSVP has the following attributes:
o RSVP supports multicast or unicast data delivery and adapts to
changing group membership as well as changing routes.
o RSVP is simplex.
o RSVP is receiver-oriented, i.e., the receiver of a data flow is
responsible for the initiation and maintenance of the resource
reservation used for that flow.
o RSVP maintains "soft state" in the routers, enabling it to
gracefully support dynamic membership changes and automatically
adapt to routing changes.
o RSVP provides several reservation models or "styles" (defined
below) to fit a variety of applications.
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
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services. Section 2 presents an overview of the RSVP protocol
mechanisms, while Section 3 gives examples of the services and
mechanism. Section 4 contains the functional specification of RSVP.
Section 5 presents explicit message processing rules.
1.1 Data Flows
The set of data flows with the same unicast or multicast
destination constitute a session. RSVP treats each session
independently. All data packets in a particular session are
directed to the same IP destination address DestAddress, and
perhaps to some further demultiplexing point defined in a higher
layer (transport or application). We refer to the latter as a
"generalized destination port".
DestAddress is the group address for multicast delivery, or the
unicast address of a single receiver. A generalized destination
port 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 uses 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
the multicast routing protocol. 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 correspond to a unique Internet host,
or a single host may contain multiple logical senders and/or
receivers, distinguished by generalized ports.
Senders Receivers
_____________________
( ) ===> R1
S1 ===> ( Multicast )
( ) ===> R2
( distribution )
S2 ===> ( )
( by Internet ) ===> R3
(_____________________)
Figure 2: Multicast Distribution Session
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Even if the destination address is unicast, there may be multiple
receivers, distinguished by the generalized port. There may also
be multiple senders for a unicast destination, i.e., RSVP can set
up reservations for multipoint-to-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 the DestAddress and the generalized
destination port defining the session) defines 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. Note that the action to control the QoS occurs at the
place where the data enters the medium, i.e., at the upstream end
of the link, although the RSVP reservation request originates from
receiver(s) downstream.
The flowspec in a reservation request will generally include a
service type and two sets of numeric parameters: (1) an "Rspec" (R
for `reserve'), which defines the desired per-hop reservation, and
(2) a "Tspec" (T for `traffic'), which defines the parameters that
may be used to police the data flow, i.e., to ensure it does not
exceed its promised traffic level.
The form and contents of Tspecs and Rspecs are determined by the
integrated service model [ServTempl95a], and are generally opaque
to RSVP. RSVP delivers the Tspec and Rspec, together with an
indication whether traffic policing is needed to the admission
control and packet scheduling components of traffic control. A
service that requires traffic policing might for example apply it
at the edge of the network and at data merge points; RSVP knows
when these occur and must so indicate to the traffic control
mechanism. On the other hand, RSVP cannot interpret the service
embodied in the flowspec and therefore does not know whether
policing will actually be applied in a particular case.
In the general RSVP reservation model [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
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the interest of simplicity (and to minimize layer violation), the
present RSVP version uses a much more restricted form of filter
spec: select only on sender IP address, on UDP/TCP port number,
and perhaps on IP protocol id.
RSVP can distinguish subflows of a hierarchically-encoded signal
if they are assigned distinct multicast destination addresses, or,
for a unicast destination, distinct destination ports. Data
packets that are addressed to a particular session but do not
match any of the filter specs for that session are expected to be
sent as best-effort traffic, and under congested conditions, such
packets are likely to experience long delays, and they may be
dropped. When a receiver does not wish to receive a particular
(sub-)flow, it can economize on network resources by explicitly
asking the network to drop unneeded the data packets; it does so
by leaving the multicast group(s) to which these packets are
addressed. Thus, determining where packets get delivered should
be a routing function; RSVP is concerned only with the QoS of
those packets that are delivered by routing.
RSVP reservation request messages originate at receivers and are
passed upstream towards the sender(s). (This document defines the
directional terms "upstream" vs. "downstream", "previous hop" vs.
"next hop", and "incoming interface" vs "outgoing interface" with
respect to the data flow direction.) When an elementary
reservation request is received at a node, the RSVP daemon takes
two primary actions:
1. Daemon makes 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. Daemon forwards the reservation 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, for two reasons. First, it is
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possible (in theory) for the traffic control mechanism to modify
the flowspec hop-by-hop, although currently no realtime services
do this. Second, reservations from different downstream branches
of the multicast distribution tree(s) must be "merged" as
reservations travel upstream. Merging reservations is a necessary
consequence of multicast distribution, which creates a single
stream of data packets in a particular router from any Si,
regardless of the set of receivers downstream. The reservation
for Si on a particular outgoing link L should be the "maximum" of
the individual flowspecs from the receivers Rj that are downstream
via link L. Merging is discussed further in Section 2.2.
The basic RSVP reservation model is "one pass": a receiver sends a
reservation request upstream, and each node in the path can only
accept or reject the request. This scheme provides no way to make
end-to-end service guarantees, since the QoS request must be
applied independently at each hop. RSVP also supports an optional
reservation model, known as "One Pass With Advertising" (OPWA)
[Shenker94]. In OPWA, RSVP control packets sent downstream,
following the data paths, are used to gather information on the
end-to-end service that would result from a variety of possible
reservation requests. The results ("advertisements") are
delivered by RSVP to the receiver host, and perhaps to the
receiver application. The information may then be used by the
receiver to construct 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 scope of the request: an
"explicit" sender specification, or a "wildcard" that implicitly
selects a group of senders. In an explicit-style reservation, the
filter spec must match exactly one sender, while the filter spec
in a wildcard reservation must match at least one sender but may
match any number.
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|| Reservations:
Scope || 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):
1. Wildcard-Filter (WF) Style
The WF style implies the options: "shared" reservation and "
wildcard" reservation scope. 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 for that link from all receivers,
independent of the number of senders using it. A WF-style
reservation has wildcard scope, i.e., the reservation is
propagated upstream towards all sender hosts. A WF-style
reservation automatically extends to new senders as they
appear.
2. Fixed-Filter (FF) Style
The FF style implies the options: "distinct" reservations and
"explicit" reservation scope. 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. It scope is
determined by an explicit list of senders.
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
necessarily be merged to share a single reservation in a
given node.
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3. Shared Explicit (SE) Style
The SE style implies the options: "shared" reservation and "
explicit" reservation scope. Thus, an SE-style reservation
creates a single reservation into which flows from all
upstream senders are mixed. However, like a FF reservation
the set of senders (and therefore its scope (and therefore
the scope) is specified explicitly by the receiver making the
reservation.
WF and SE are both shared reservations, appropriate for those
multicast applications whose application-specific constraints make
it unlikely that multiple data sources will transmit
simultaneously. One example is audio conferencing, where a limited
number of people talk at once; each receiver might issue a WF or
SE reservation request for twice one audio channel (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.
It is not possible to merge shared reservations with distinct
reservations. Therefore, WF and SE styles are incompatible with
FF, but are compatible with each other. Merging a WF style
reservation with an SE style reservation results in a WF
reservation.
Other reservation options and styles may be defined in the future
(see Appendix D.4, for example).
2. RSVP Protocol Mechanisms
2.1 RSVP Messages
There are two fundamental RSVP message types: RESV and PATH .
Each receiver host sends RSVP reservation request (RESV) messages
towards the senders. These reservation messages must follow in
reverse the routes the data packets will use, all the way upstream
to the sender hosts included in the scope. RESV messages must be
delivered to the sender hosts so that the hosts can set up
appropriate traffic control parameters for the first hop.
Also note that RSVP sends no positive acknowledgment messages to
indicate success (although the delivery of a reservation request
to a sender could be used to trigger an acknowledgement at a
higher level of protocol.)
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Sender Receiver
_____________________
Path --> ( )
Si =======> ( Multicast ) Path -->
<-- Resv ( ) =========> Rj
( distribution ) <-- Resv
(_____________________)
Figure 4: RSVP Messages
Each sender transmits RSVP PATH messages forward along the uni-
/multicast routes provided by the routing protocol(s); see Figure
4. These "Path" messages store path state in each node. Path
state is used by RSVP 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).
PATH messages may also carry the following information:
o Sender Template
The Sender Template 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 sender IP address,
UDP/TCP sender port, and protocol id. The port number
and/or protocol id can be wildcarded.
o Tspec
PATH message may optionally carry a Tspec that defines an
upper bound on the traffic level that the sender will
generate. This Tspec can be used by RSVP to prevent over-
reservation (and perhaps unnecessary Admission Control
failure) on the non-shared links starting at the sender.
o Adspec
The PATH message may 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 routines,
which return an updated Adspec; the updated version is
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forwarded downstream.
Previous Incoming Outgoing Next
Hops Interfaces Interfaces Hops
_____ _____________________ _____
| | data --> | | data --> | |
| A |-----------| a c |--------------| C |
|_____| <-- Resv | | <-- Resv |_____|
Path --> | | Path --> _____
_____ | ROUTER | | | |
| | | | | |--| D |
| B |--| data-->| | data --> | |_____|
|_____| |--------| b d |-----------|
|<-- Resv| | <-- Resv | _____
_____ | Path-->|_____________________| Path --> | | |
| | | |--| D' |
| B' |--| | |_____|
|_____| | |
Figure 5: Router Using RSVP
Figure 5 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 but the same
session).
As illustrated in Figure 5, there may be multiple previous hops
and/or next hops through a given physical interface. This may
result from the connected network being a shared medium or from
the existence of non-RSVP routers in the path to the next RSVP hop
(see Section 2.6). An RSVP daemon must preserve the next and
previous hop addresses in its reservation and path state,
respectively. A RESV message is sent with a unicast destination
address, the address of a previous hop. PATH messages, on the
other hand, are sent with the session destination address, unicast
or multicast.
Although multiple next hops may send reservation requests through
the same physical interface, the final effect should be to install
a reservation on that interface, which is defined by an effective
flowspec. This effective flowspec will be the "maximum" of the
flowspecs requested by the different next hops. In turn, a RESV
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message forwarded to a particular previous hop carries a flowspec
that is the "maximum" over the effective reservations on the
corresponding outgoing interfaces. Both cases represent merging,
which is discussed further below.
There are a number of ways for a syntactically valid reservation
request to fail in a given node:
1. The effective flowspec, computed using the new request, may
fail admission control.
2. Administrative policy or control may prevent the requested
reservation.
3. There may be no matching path state (i.e., the scope may be
empty), which would prevent the reservation being propagated
upstream.
4. A reservation style that requires a unique sender may have a
filter spec that matches more than one sender in the path
state, due to the use of wildcards.
5. The requested style may be incompatible with the style(s) of
existing reservations for the same session on the same
outgoing interface, so an effective flowspec cannot be
computed.
6. The requested style may be incompatible with the style(s) of
reservations that exist on other outgoing interfaces but will
be merged with this reservation to create a refresh message
for the previous hop.
In any of these cases, an error message is returned to the
receiver(s) responsible for the erroneous message. 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 was detected will persist until the
receiver(s) responsible cease attempting the reservation.
The erroneous message may or may not be propagated forward. In
general, if the error is likely to be repeated at every node
further along the path, it is best to drop the erroneous message
rather than generate a flood of error messages; this is the case
for the last four error classes listed above. The first two error
classes, admission control and administrative policy, may or may
not allow propagation of the message, depending upon the detailed
reason and perhaps on local administrative policy and/or the
particular service request. More complete rules are given in the
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error definitions in Appendix B.
An erroneous FILTER_SPEC object in a RESV message will normally be
detected at the first RSVP hop from the receiver application,
i.e., within the receiver host. However, an admission control
failure caused by a FLOWSPEC or a POLICY_DATA object may be
detected anywhere along the path(s) to the sender(s).
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).
A node may be allowed to preempt an established reservation, in
accordance with administrative policy; this will also trigger an
error message to all affected receivers.
2.2 Merging and Packing
A previous section explained that reservation requests in RESV
messages are necessarily merged, to match the multicast
distribution tree. As a result, only the essential (i.e., the
"largest") reservation requests are forwarded, once per refresh
period. A successful reservation request will propagate as far as
the closest point(s) along the sink tree to the sender(s) where a
reservation level equal or greater than that being requested has
been made. At that point, the merging process will drop it in
favor of another, equal or larger, reservation request.
For protocol efficiency, RSVP also allows multiple sets of path
(or reservation) information for the same session to be "packed"
into a single PATH (or RESV) message, respectively. (For
simplicity, the protocol currently prohibits packing different
sessions into the same RSVP message). Unlike merging, packing
preserves information.
In order to merge reservations, RSVP must be able to merge
flowspecs and to merge filterspecs. Merging flowspecs requires
calculating the the "largest" of a set of flowspecs, which are
otherwise opaque to RSVP. Merging flowspecs is required both to
calculate the effective flowspec to install on a given physical
interface (see the discussion in connection with Figure 5), and to
merge flowspecs when sending a refresh message upstream. Since
flowspecs are generally multi-dimensional vectors (they contain
both Tspec and Rspec components, each of which may itself be
multi-dimensional), they are not strictly ordered. When it cannot
take the larger of two flowspecs, RSVP must compute and use a
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third flowspec that is at least as large as each, i.e., a "least
upper bound" (LUB). It is also possible for two flowspecs to be
incomparable, which is treated as an error. The definition and
implementation of the rules for comparing flowspecs are outside
RSVP proper, but they are defined as part of the service templates
[ServTempl95a]
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 5.
o 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).
o The Tspecs supplied in PATH messages from different previous
hops which may send data packets to this reservation (e.g.,
some or all of A, B, and B' in Figure 5) are summed; call
this sum Path_Te.
o The maximum Tspec supplied in RESV messages from different
next hops (e.g., D and D') is calculated; call this Resv_Te.
o 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.
Two filter specs can be merged only they are identical or if one
contains the other through wild-carding. The result is the more
general of the two, i.e., the one with more wildcard fields.
2.3 Soft State
To maintain reservation state, RSVP keeps "soft state" in router
and host nodes. 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 as the result
of an explicit "teardown" message, described in the next section.
At the expiration of each "refresh timeout" period, RSVP scans its
state to build and forward PATH and RESV refresh messages to
succeeding hops.
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
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"new" or a "refresh" is determined separately at each node,
depending upon the existence of state at that node.
RSVP sends its messages as IP datagrams without reliability
enhancement. Periodic transmission of refresh messages by hosts
and routers is expected to replace any lost RSVP messages. To
tolerate K-1 successive packet losses, the effective cleanup
timeout must be at least K times the refresh timeout. In
addition, the traffic control mechanism in the network should be
statically configured to grant high-reliability service to RSVP
messages, to protect RSVP messages from congestion losses.
The "soft" state maintained by RSVP is dynamic; to change the set
of senders Si or receivers Rj 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 and
immediate propagation to all nodes along the path.
In steady state, refreshing is performed hop-by-hop, which allows
merging and packing as described in the previous section. If the
received state differs from the stored state, the stored state is
updated. Furthermore, if the result will be to modify the refresh
messages to be generated, these refresh messages must be generated
and forwarded immediately. This will result in state changes
propagating 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.
The RSVP state associated with a session in a particular node is
divided into atomic elements that are created, refreshed, and
timed out independently. The atomicity is determined by the
requirement that any sender or receiver may enter or leave the
session at any time, so its state should be created and timed out
independently.
2.4 Teardown
RSVP teardown messages remove path and reservation state without
waiting for the cleanup timeout period, as an optimization to
release resources quickly. It is not necessary to explicitly tear
down an old reservation, although it may be desirable in many
cases.
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 should be
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forwarded hop-by-hop without delay.
Teardown messages (like other RSVP messages) are not delivered
reliably. However, loss of a teardown message is not considered a
problem because the state will time out even if it is not
explicitly deleted. If one or more teardown message hops are
lost, the router that failed to receive a teardown 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.
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. A 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 message deletes the specified state in the node where
it is received. Like any other state change, this will be
propagated immediately to the next node, but only if it represents
a net change after merging. As a result, an RTEAR message will
prune the reservation state back (only) as far as possible.
2.5 Admission 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 will 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 as well as 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 neighboring RSVP-capable nodes. These
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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 not be possible or desirable to carry all the
receivers' policy data upstream to the sender(s). The policy data
will have to be administratively merged, near enough to 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.
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.
2.6 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, so service guarantees cannot be made.
However, if such a cloud has sufficient excess capacity, it may
provide acceptable and useful realtime service.
RSVP will automatically tunnel 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, the copies that emerge will carry as a Previous
Hop address the IP address of the last RSVP-capable router before
entering the cloud. This will effectively construct a tunnel
through the cloud for RESV messages, which will be forwarded
directly to the next RSVP-capable router on the path(s) back
towards the source.
Automatic tunneling is not perfect; in some circumstances it may
distribute path information to RSVP-capable routers not included
in the data distribution paths, which may create unused
reservations at these routers. This is because PATH messages
carry the IP source address of the previous hop, not of the
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original sender, and multicast routing may depend upon the source
as well as the destination address. This can be overcome by
manual configuration of the neighboring RSVP programs, when
necessary.
2.7 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, using RSVP.
H3 A receiver application receives a PATH message.
H4 A receiver starts sending appropriate RESV messages,
specifying the desired flow descriptors, using RSVP.
H5 A sender application receives a RESV message.
H6 A sender starts sending data packets.
There are several synchronization considerations.
o Suppose that a new sender starts sending data (H6) but no
receivers have joined the group (H1). Then there will be no
multicast routes beyond the host (or beyond the first RSVP-
capable router) along the path; the data will be dropped at
the first hop until receivers(s) do appear (assuming a
multicast routing protocol that "prunes off" or otherwise
avoids unnecessary paths).
o Suppose that a new sender starts sending PATH messages (H2)
and immediately starts sending data (H6), 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.
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o If a receiver starts sending RESV messages (H4) before any
PATH messages have reached it (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.
A specific application program interface (API) for RSVP is not
defined in this protocol spec, as it may be host system dependent.
However, Section 4.6.1 discusses the general requirements and
presents a generic API.
3. Examples
We use the following notation for a RESV message:
1. Wildcard-Filter (WF)
WF( *{Q})
Here "*{Q}" represents a Flow Descriptor with a "wildcard" scope
(choosing all senders) and a flowspec of quantity Q.
2. Fixed-Filter (FF)
FF( S1{Q1}, S2{Q2}, ...)
A list of (sender, flowspec) pairs, i.e., flow descriptors,
packed into a single RESV message.
3. Shared Explicit (SE)
SE( (S1,S2,...)Q1, (S3,S4,...)Q2, ...)
A list of shared reservations, each specified by a single
flowspec and a list of senders.
For simplicity we assume here that flowspecs are one-dimensional,
defining for example the average throughput, and state them as a
multiple of some unspecified base resource quantity B.
Figure 6 shows schematically a router with two previous hops labeled
(a) and (b) and two outgoing interfaces 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 and R2 (R3) are routed via
outgoing interface (c) ((d) respectively).
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In addition to the connectivity shown in 6, we must also specify the
multicast routing within this node. Assume first that data packets
(hence, PATH messages) from each Si shown in Figure 6 is routed to
both outgoing interfaces. Under this assumption, Figures 7, 8, and 9
illustrate Wildcard-Filter, Fixed-Filter, and Shared-Explicit
reservations, respectively.
________________
(a)| | (c)
( S1 ) ---------->| |----------> ( R1, R2)
| Router |
(b)| | (d)
( S2,S3 ) ------->| |----------> ( R3 )
|________________|
Figure 6: Router Configuration
In Figure 7, the "Receive" column shows the RESV messages received
over outgoing interfaces (c) and (d) and the "Reserve" column shows
the resulting reservation state for each interface. The "Send"
column shows the RESV messages forwarded to previous hops (a) and
(b). In the "Reserve" column, each box represents one reservation
"channel", with the corresponding filter. As a result of merging,
only the largest flowspec is forwarded upstream to each previous hop.
|
Send | Reserve Receive
|
| _______
WF( *{3B} ) <- (a) | (c) | * {B} | (c) <- WF( *{B} )
| |_______|
|
-----------------------|----------------------------------------
| _______
WF( *{3B} ) <- (b) | (d) | * {3B}| (d) <- WF( *{3B} )
| |_______|
Figure 7: Wildcard-Filter (WF) Reservation Example
Figure 8 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 message forwarded to previous hop b.
On the other hand, the two different flow descriptors for sender S1
are merged into the single message FF( S1{3B} ), which is sent to
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previous hop (a). For each outgoing interface, there is a private
reservation for each source that has been requested, but this private
reservation is shared among the receivers that made the request.
|
Send | Reserve Receive
|
| ________
FF( S1{3B} ) <- (a) | (c) | S1{B} | (c) <- FF( S1{B}, S2{5B} )
| |________|
| | S2{5B} |
| |________|
---------------------|---------------------------------------------
| ________
<- (b) | (d) | S1{3B} | (d) <- FF( S1{3B}, S3{B} )
FF( S2{5B}, S3{B} ) | |________|
| | S3{B} |
| |________|
Figure 8: Fixed-Filter (FF) Reservation Example
Figure 9 shows a simple example of Shared-Explicit (SE) style
reservations. Here each outgoing interface has a single reservation
that is shared by a list of senders.
|
Send | Reserve Receive
|
| ________
SE( S1{3B} ) <- (a) | (c) |(S1,S2) | (c) <- SE( (S1,S2){B} )
| | {B} |
| |________|
---------------------|---------------------------------------------
| ________
<- (b) | (d) |(S1,S3) | (d) <- SE( (S1,S3){3B} )
SE( (S2,S3){3B} ) | | {3B} |
| |________|
Figure 9: Shared-Explicit (SE) Reservation Example
The three examples just shown assume full routing, i.e., data packets
from S1, S2, and S3 are routed to both outgoing interfaces. The top
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part of Figure 10 shows another routing assumption: data packets
from S1 are not forwarded to interface (d), because the mesh topology
provides a shorter path for S1 -> R3 that does not traverse this
node. The bottom of Figure 10 shows WF style reservations under this
assumption. Since there is no route from (a) to (d), the reservation
forwarded out interface (a) considers only the reservation on
interface (c); no merging takes place in this case.
_______________
(a)| | (c)
( S1 ) ---------->| --------->--> |----------> ( R1, R2)
| / |
| / |
(b)| / | (d)
( S2,S3 ) ------->| ->----------> |----------> ( R3 )
|_______________|
Router Configuration
|
Send | Reserve Receive
|
| _______
WF( *{B} ) <- (a) | (c) | * {B} | (c) <- WF( *{B} )
| |_______|
|
-----------------------|----------------------------------------
| _______
WF( *{3B} ) <- (b) | (d) | * {3B}| (d) <- WF( * {3B} )
| |_______|
Figure 10: WF Reservation Example -- Partial Routing
Finally, we note that state that is received through a particular
interface I is never 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 11, 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)
are 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. These
result in independent reservations in the two directions.
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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 11: Independent Reservations
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4. RSVP Functional Specification
4.1 RSVP Message Formats
All RSVP messages consist 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 ordering and choice of object types. These rules are
specified using Backus-Naur Form (BNF) augmented with square
brackets surrounding optional sub-sequences.
4.1.1 Common Header
0 1 2 3
+-------------+-------------+-------------+-------------+
| Vers | Flags| Type | RSVP Checksum |
+-------------+-------------+-------------+-------------+
| RSVP Length | (Reserved) |
+-------------+-------------+-------------+-------------+
| 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
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.
Message ID: 32 bits
A label shared by all fragments of one message from a
given next/previous RSVP hop. An RSVP implementation
assignes 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.
4.1.2 Object Formats
An 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 |
+-------------+-------------+-------------+-------------+
| |
// (Object contents) //
| |
+-------------+-------------+-------------+-------------+
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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 will always be 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) and
possibly 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
If present, contains values for the refresh period R
and the state time-to-live T (see section 4.5), to
override the default values of R and T.
STYLE
Defines the reservation style plus style-specific
information that is not a FLOWSPEC or FILTER_SPEC
object, in a RESV message.
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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 an Adspec containing 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,
of this RSVP message.
SCOPE
An explicit specification of the scope for forwarding
a RESV message.
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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 (together with the 'Optional' flag bit)
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. If Class-Num < 128, then the node should
ignore the object but forward it (unmerged). If Class-Num >=
128, the message should be rejected and an "Unknown Object
Class" error returned. Note that merging cannot be performed
on unknown object types; as a result, unmerged objects may be
forwarded to the first node that does know how to merge them.
The scaling limitations that this imposes must be considered
when defining and deploying new object types.
4.1.3 Path Message
PATH messages carry information from senders to receivers along
the paths used by the data packets. The IP destination address
of a PATH message is the DestAddress for the session; the
source address is an address of the node that sent the message
(preferably the address of the interface through which it was
sent). The PHOP (i.e., the RSVP_HOP) object of each PATH
message must contain the address of the interface through which
the PATH message was sent.
The format of a PATH message is as follows:
<Path Message> ::= <Common Header> <SESSION> <RSVP_HOP>
[ <INTEGRITY> ] [ <TIME_VALUES> ]
<sender descriptor list>
<sender descriptor list> ::= <empty > |
<sender descriptor list> <sender descriptor>
<sender descriptor> ::= <SENDER_TEMPLATE> [ <SENDER_TSPEC> ]
[ <POLICY_DATA> ] [ <ADSPEC> ]
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Each sender descriptor defines a sender, and the sender
descriptor list allows multiple sender descriptors to be packed
into a PATH message. For each sender in the list, the
SENDER_TEMPLATE object defines the format of data packets; in
addition, a SENDER_TSPEC object may specify the traffic flow, a
POLICY_DATA object may specify user credential and accounting
information, and an ADSPEC object may carry advertising (OPWA)
data.
Each sender host must periodically send PATH message(s)
containing a sender descriptor for each its own data stream(s).
Each sender descriptor is forwarded and replicated as necessary
to follow the delivery path(s) for a data packet from the same
sender, finally reaching the applications on all receivers
(except that it is not looped back to a receiver included in
the same application process as the sender).
It is an error to send ambiguous path state, i.e., two or more
Sender Templates that are different but overlap, due to
wildcards. For example, if we represent a Sender Template as
(IP address, sender port, protocol id and use `*' to represent
a wildcard, then each of the following pairs of Sender
Templates would be an error:
(10.1.2.3, 34567, *) and (10.1.2.3, *, *)
(10.1.2.3, 34567, *) and (10.1.2.3, 34567, 17)
A PATH message received at a node is processed to create path
state for all senders defined by SENDER_TEMPLATE objects in the
sender descriptor list. If present, 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 all senders implied by the
SENDER_TEMPLATEs.
Periodically, the path state is scanned to create new PATH
messages to be forwarded downstream. A node must independently
compute the route for each sender descriptor being forwarded.
These routes, obtained from uni-/multicast routing, generally
depend upon the (sender host address, DestAddress) pairs and
consist of a list of outgoing interfaces. The descriptors
being forwarded through the same outgoing interface may be
packed into as few PATH messages as possible. Note that
multicast routing of path information is based on the sender
address(es) from the sender descriptors, not the IP source
address; this is necessary to prevent routing loops; see
Section 4.3.
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Multicast routing may also report the expected incoming
interface (i.e., the shortest path back to the sender). If so,
any PATH message that arrives on a different interface should
be discarded immediately.
It is possible that routing will report no routes for a
(sender, DestAddress) pair; path state for this sender should
be stored locally but not forwarded.
4.1.4 Resv Messages
RESV messages carry reservation requests hop-by-hop from
receivers to senders, along the reverse paths of data flow 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 NHOP (i.e., the RSVP_HOP) object
must contain the IP address of the (incoming) interface through
which the RESV message is sent.
The RESV message format is as follows:
<Resv Message> ::= <Common Header> <SESSION> <RSVP_HOP>
[ <INTEGRITY> ] [ <TIME_VALUES> ]
[ <S_POLICY_DATA> ] [ <SCOPE> ]
<STYLE> <flow descriptor list>
<S_POLICY_DATA> ::= <POLICY DATA>
<flow descriptor list> ::= <flow descriptor> |
<flow descriptor list> <flow descriptor>
Here the S_POLICY_DATA object is a POLICY_DATA object that is
associated with the session, i.e., with all the flows that may
be listed. 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 more exactly the composition of a valid flow descriptor
list.
o WF Style:
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<flow descriptor list> ::= <WF flow descriptor>
<WF flow descriptor> ::=
<FLOWSPEC> [ <F_POLICY_DATA> ] <FILTER_SPEC>
<F_POLICY_DATA> ::= <POLICY_DATA>
o FF style:
<flow descriptor list> ::= <FF flow descriptor> |
<flow descriptor list> <FF flow descriptor>
<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 or POLICY_DATA object can be
omitted if it is identical to the most recent such object
that appeared in the list.
o SE style:
<flow descriptor list> ::= <SE descriptor>
| <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, possibly a POLICY_DATA object, and a list of
FILTER_SPEC objects. Multiple elementary requests, each
representing an independent shared reservation, may be
packed into the flow descriptor list of a single RESV
message. A POLICY_DATA object may be omitted if it is
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identical to the most recent such object that appeared in
the list.
The reservation scope, i.e., the set of sender hosts towards
which a particular reservation is to be forwarded, is
determined as follows:
o For a style with explicit scope, match each FILTER_SPEC
object against the path state created from SENDER_TEMPLATE
objects to select a particular sender. It is an error if
a FILTER_SPEC matches more than one SENDER_TEMPLATE, due
to wildcarding. A SCOPE object, if present, should be
ignored.
o For a style with wildcard scope, a SCOPE object, if
present, defines the scope with an explicit list of sender
IP addresses (see Section 4.3 below). If there is no
SCOPE object, the scope is determined by the relevant set
of senders in the path state. A SCOPE object must be sent
in any wildcard scope RESV message that is forwarded to
more than one previous hop. See Section 4.3 below.
4.1.5 Error Messages
There are two types of RSVP error 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.
Errors encountered while processing error messages must not
create further error messages.
<PathErr message> ::= <Common Header> <SESSION>
[ <INTEGRITY> ] <ERROR_SPEC>
<sender descriptor>
<sender descriptor> ::= (see earlier definition)
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<ResvErr Message> ::= <Common Header> <SESSION>
[ <INTEGRITY> ] [S_POLICY_DATA]
<ERROR_SPEC>
<STYLE> <error flow descriptor>
The following style-dependent rules define the composition of a
valid error flow descriptor in terms of sequences defined
earlier:
o WF Style:
<error flow descriptor> ::= <WF flow descriptor>
o FF style:
<error flow descriptor> ::= <FF flow descriptor>
o SE style:
<error flow descriptor> ::= <SE flow descriptor>
POLICY_DATA objects need be included in error messages only for
information when they are relevant (i.e., when an
administrative failure is being reported).
The ERROR_SPEC object specifies the error and includes the IP
address of the node that detected the error (Error Node
Address).
When a PATH or RESV message has been "packed" with multiple
sets of elementary parameters, the RSVP implementation should
process each set independently and return a separate error
message for each that is in error.
In general, error messages should be delivered to the
applications on all the session nodes that (may have)
contributed to this error. A PERR message is forwarded to all
previous hops for all senders listed in the Sender Descriptor
List. A RERR message is generally forwarded towards all
receivers that may have caused the error being reported. More
specifically:
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o The node that detects an error in a reservation request
creates and sends an 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 4.3.
When the error is an admission control failure, a node is
allowed (but not required) to match the FLOWSPEC as well as the
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 `un-merging' the
filter spec).
When a RERR 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 `equal' to (but not
necessarily identical to) the FLOWSPEC originated by this
application; otherwise, they may differ.
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4.1.6 Teardown Messages
There are two types of RSVP Teardown message, PTEAR and RTEAR.
o A PTEAR message deletes path state (which may, in turn,
delete reservation state) 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 like 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>
[ <INTEGRITY> ]
<sender descriptor list>
<sender descriptor list> ::= (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 the RTEAR message will cease to be forwarded at the
same node where merging suppresses forwarding of the
corresponding RESV messages. The change will be propagated as
a new teardown message if the result has been to remove all
state for this session at this node; otherwise, it may result
in the immediate forwarding of a modified RESV refresh message.
Deletion of path state, whether as the result of a teardown
message or because of timeout, may force adjustments in related
reservation state to maintain consistency in the local node.
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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 distinct reservations (FF),
only reservations for sender S should be deleted; if the style
specifies shared reservations (WF or SE), delete the
reservation if this was the last filter spec. These
reservation changes should not trigger an immediate RESV
refresh message, since the teardown message will 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.
4.2 Sending RSVP Messages
RSVP messages are sent hop-by-hop between RSVP-capable routers as
"raw" IP datagrams with protocol number 46. Raw IP datagrams are
similarly intended to be used between an end system and the
first/last hop router; however, it is also possible to encapsulate
RSVP messages as UDP datagrams for end-system communication, as
described in Appendix C. UDP encapsulation may simplify
installation of RSVP on current end systems, particularly when
firewalls are in use.
Upon the arrival of an RSVP message M that changes the state, a
node must forward the modified state immediatly. If this is
implemented as an immediate refresh of all the state for the
session, then no refresh messages should be sent out the interface
through which M arrived. 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 is
appropriate as a ressembly timeout time.
Since RSVP messages are normally expected to be generated and sent
hop-by-hop, using the RSVP-level fragmentation mechanism should
result in no IP fragmentation. However, IP fragmentation may
occur through a non-RSVP cloud. For IP6, which does not support
router fragmentation, this case will require that the RSVP
implementation use Path MTU Discovery or hand configuration to
obtain an appropriate MTU.
Under overload conditions, lost RSVP control messages could cause
a failure of resource reservations. Routers should be configured
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to give a preferred class of service to RSVP packets. RSVP should
not use significant bandwidth, but queueing delay and dropping of
RSVP messages needs to be controlled. Loss of RSVP packets
through a congested non-RSVP cloud may still be a problem. The
simplest solution is to adopt a larger value for the timeout
factor K (see section 4.5 below). If this does not suffice,
neighboring RSVP routers could use a TCP connection to pass RSVP
messages through a non-RSVP cloud. The current protocol contains
no automatic mechanism to setting up such connections; hand
configuration is assumed.
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
physical interface. A multicast routing protocol that supports
tunnels will describe a route using a list of logical rather than
physical interfaces. RSVP can support 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. This information is carried (in the HOP
object) as a value called the "logical interface handle" or
LIH.
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 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'.
4.3 Avoiding RSVP Message Loops
We must ensure that the rules for forwarding RSVP control messages
avoid looping. In steady state, PATH and RESV messages are
forwarded only once per refresh period on each hop. This avoids
directly looping packets, but there is still the possibility of an
" auto-refresh" loop, clocked by the refresh period. The effect
of such a loop is to keep state active "forever", even if the end
nodes have ceased refreshing it (but the state will be deleted
when 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
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subject to direct looping.
o PATH Messages
PATH messages are forwarded using routes determined by the
appropriate routing protocol. For routing that is source-
dependent (e.g., some multicast routing algorithms), the RSVP
daemon must route each sender descriptor separately using the
source addresses found in the SENDER_TEMPLATE objects. This
should ensure that there will be no auto-refresh loops of
PATH messages, even in a topology with cycles.
Consider each message type.
o PTEAR Messages
PTEAR messages use the same routing as PATH messages and
therefore cannot loop.
o PERR Messages
Since PATH messages don't 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
Like PERR message, RESV messages directed to particular
senders (i.e., with explicit scope) cannot loop. However,
there is a potential for auto-refresh of RESV messages with
wildcard scope; the solution is presented below.
o RTEAR Messages
RTEAR messages are routed the same as RESV messages and have
an analogous looping problem for wildcard scope.
o RERR Messages
RERR messages for wildcard scope reservations have the same
potential for looping as the reservations themselves, and the
solution presented below is required.
If the topology has no loops, then looping of wildcard-scoped
messages 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
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topology does have cycles then further effort is needed to prevent
auto-refresh loops in wildcard-scope RESV, RTEAR, and RERR
messages. The solution is for such messages to carry an explicit
sender address list in a SCOPE object.
When a RESV or RTEAR message with wildcard scope is to be
forwarded to a particular previous hop, a new SCOPE object is
computed from the SCOPE objects that were received (in messages of
the same type). 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 or RTEAR message are as
follows:
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 wildcard scope (WF) message that arrived
on outgoing interface OI, the substitute list is the set of
senders that route to OI. For an explicit scope (SE)
message, it is the set of senders explicitly listed in the
message.
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 12 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 12: 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 scope.
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 wildcard-scoped
RERR messages:
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
4.1.5. 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
RERR message should not be sent out OI.
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4.4 Local Repair
When a route changes, the next PATH or RESV refresh 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 an immediate 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 sending PATH messages for destination G, RSVP
sends immediate PATH refreshes for all sessions G/* (i.e.,
for any session with destination G, regardless of destination
port). Such refresh messages are to be sent to at least the
new outgoing interfaces for these sessions.
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.
4.5 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
receiving successive refreshes for the state, and its 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 is used to determine the L when the state is
received and stored.
In more detail:
1. To avoid premature loss of state, we require that L >= (K +
0.5)* R, where K is a small integer. Then K-1 successive
messages may be lost without state being deleted. Currently
K = 3 is suggested.
2. Each message will generally carry a TIME_VALUES object
containing the R used to generate refreshes; the recipient
node uses this R to determine L of the stored state.
However, if a default R = Rdef is used, the TIME_VALUES
object may be omitted from a message. Rdef is currently
defined to be 30 seconds.
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3. This document does not specify the interval R to be used for
generating refresh messages. If the node does not implement
local repair of reservations disrupted by route changes, a
smaller R improves the speed of adapting to routing changes
(but increases 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 limit the overhead due to
refresh messages.
4. The TIME_VALUES object could contain, in addition to the
hop-by-hop R value, an end-to-end upper bound on R, called
Rmax. When Rmax is specified, a node cannot set R > Rmax.
However, a node is allowed to refuse an RSVP message (i.e.,
drop it and return an error) when it specifies an Rmax value
that is so small that it would create unacceptable overhead.
This refusal would look like a kind of admission control
failure.
5. However, 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
more often than R after a state change (including initial
state establishment).
7. A node should randomize its refresh timeouts to avoid
synchronization and burstiness of refreshes.
8. The values of Rdef, K, and Slew.Max used in an implementation
should be easily modifiable, as experience may lead to
different values. The possibility of dynamically changing K
and/or Slew.Max in response to measured loss rates is for
future study.
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4.6 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).
4.6.1 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
Call: REGISTER( DestAddress , DestPort
[ , SESSION_object ] , SND_flag , RCV_flag
[ , Source_Address ] [ , Source_Port ]
[ , Source_ProtID ] [ , Sender_Template ]
[ , Sender_Tspec ] [ , Data_TTL ]
[ , Sender_Policy_Data ]
[ , Upcall_Proc_addr ] ) -> Session-id
This call initiates RSVP processing for a session, defined
by DestAddress together with the TCP/UDP port number
DestPort. If successful, the REGISTER call returns
immediately with a local session identifier Session-id,
which may be used in subsequent calls.
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; if it is supplied, it should be an
appropriately-formatted representation of a SESSION
object.
SND_flag should be set true if the host will send data,
and RCV_flag should be set true if the host will receive
data. Setting neither true is an error. The optional
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parameters Source_Address, Source_Port, Sender_Template,
Sender_Tspec, Data_TTL, and Sender_Policy_Data are all
concerned with a data source, and they will be ignored
unless SND_flag is true.
If SND_FLAG is true, a successful REGISTER call will cause
RSVP to begin sending PATH messages for this session using
these parameters, which 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.
- Source_ProtID
This is the IP protocol ID for the sender data. If
it is omitted or zero, the protocol id is "wild" and
can match any protocol id 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; if it is supplied, it should be an
appropriately formatted representation of a
SENDER_TEMPLATE object.
- Sender_Tspec
This parameter is a Tspec describing 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
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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.
Finally, Upcall_Proc_addr is the address of an upcall
procedure to receive asynchronous error or event
notification; see below.
o Reserve
Call: RESERVE( session-id,
style, style-dependent-parms )
A receiver uses this call to make a resource reservation
for the session registered as `session-id'. 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 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 the reservations may result in
admission control failure, depending upon the style).
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 will terminate RSVP state for the session
specified by session-id. It may send appropriate teardown
messages and will cease sending refreshes for this
session-id.
o Error/Event Upcalls
Upcall: <Upcall_Proc>( ) -> session-id, Info_type,
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[ Error_code , Error_value , LUB-Used, ]
List_count, [ Flowspec_list,]
[ Filter_spec_list, ] [ Advert_list, ]
[ Policy_data ]
Here "Upcall_Proc" represents the upcall procedure whose
address was supplied in the REGISTER call.
This upcall may occur asynchronously at any time after a
REGISTER call and before a RELEASE call, to indicate an
error or an event. Currently there are three upcall
types, distinguished by the Info_type parameter:
1. Info_type = Path Event
A Path Event upcall indicates to a receiver
application that there is at least one active sender.
It results from receipt of the first PATH message for
this session.
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 indicates to a sender application
that a reservation for this session in place along
the entire path to at least one receiver. It is
triggered by the receipt of the first reservation
message or by modification of 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
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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 the REGISTER call.
The Error_code parameter will define the error, and
Error_value may supply some additional (perhaps
system-specific) data about the error. `List_count'
will be 1, and Filter_spec_list and Flowspec_list
will contain the Sender_Template supplied in the
REGISTER call; Sender_Tspec and Advert_list will each
contain one NULL object. The Policy_data parameter
will be undefined in this upcall.
4. Info_type = Resv Error
An Resv Error event indicates an error in processing
a reservation message to which this application
contributed. The Error_code parameter will define
the error, and Error_value may supply some additional
(perhaps system-specific) data on the error.
Filter_spec_list and Flowspec_list will contain the
FILTER_SPEC and FLOWSPEC objects from the error flow
descriptor (see Section 4.1.5). List_count will
specify the number of FILTER_SPECS in
Filter_spec_list, while there will be one FLOWSPEC in
Flowspec_list. The Policy_data parameter will be
undefined in this upcall.
5. Info_type = Policy Data
A Policy Information upcall passes a Policy_data
parameter containing policy information (accounting,
current costs, prices, quota, etc.) that arrived at
the receiver.
List_count will be zero, and the Error_code,
Error_value, and LUB-Used flag parameters will be
undefined in this upcall.
Although RSVP messages indicating path events or errors
may be received periodically, the API should make the
corresponding asynchronous upcall to the application only
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on the first occurrence, or when the information to be
reported changes.
4.6.2 RSVP/Traffic Control Interface
In each router and host, enhanced QoS is achieved by a group of
inter-related traffic control functions: a packet classifier,
an admission control module, and a packet scheduler. This
section describes a generic RSVP interface to traffic control.
1. Make a Reservation
Call: Rhandle = TC_AddFlowspec( Interface, Flowspec
[ , Sender_Tspec]
, E_Police_Flag , M_Police_Flag )
This call passes a Flowspec defining a desired QoS to
admission control. It may also pass Sender_Tspec, the
maximum traffic characteristics computed over the
SENDER_TSPECs of senders that will contribute data packets
to this reservation.
E_Police_Flag and M_Police_Flag are Boolean parameters.
E_Police_Flag is on if this is an entry node, while
M_Police is on if this node is an interior data merge
point for a shared reservation style. These flags are
used to enable traffic policing or shaping when
appropriate, in accordance with the service.
This 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.
2. Modify Reservation
Call: TC_ModFlowspec( Rhandle, new_Flowspec
[ , Sender_Tspec] , 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
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in force. The corresponding filter specs, if any, are not
affected.
3. Delete Flowspec
Call: TC_DelFlowspec( Rhandle )
This call will delete an existing reservation, including
the flowspec and all associated filter specs.
4. 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.
5. Delete Filter Spec
Call: TC_DelFilter( FHandle )
This call is used to remove a specific filter, specified
by FHandle.
6. OPWA Update
Call: TC_Advertise( interface, Adspec
[ ,Sender_TSpec ] ) -> New_Adspec
This call is used for OPWA to compute the outgoing
advertisement New_Adspec for a specified interface.
Sender_TSpec is also passed if it is available.
7. 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
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upcall to RSVP, passing the RHandle of the preempted
reservation, and some indication of the reason.
4.6.3 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 datagram received for IP protocol 46 must be diverted
to the RSVP program for processing, without being
forwarded. The identity of the interface on which it is
received should also be available to the RSVP daemon.
o Route Query
RSVP must be able to query the routing daemon for the
route(s) for forwarding a specific datagram.
Ucast_Route_Query( DestAddress, Notify_flag ) -> OutInterface
Mcast_Route_Query( SrcAddress, DestAddress, Notify_flag )
-> OutInterface_list
If the Notify_flag is True, routing will save state
necessary to issue unsolicited route change notification
callbacks whenever the specified route changes. This will
continue until routing receives a route query call with
the Notify_Flag set False.
o Route Change Notification
If requested by a route query with the Notify_flag True,
the routing daemon may provide an asynchronous callback to
RSVP that a specified route has changed.
Ucast_Route_Change( ) -> DestAddress, OutInterface
Mcast_Route_Change( )
-> SrcAddress, DestAddress, OutInterface_list
o Outgoing Link Specification
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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 because RSVP may send different
versions of outgoing PATH messages for the same source and
destination addresses on different interfaces. It is also
necessary in some cases to avoid routing loops.
o Discover Interface List
RSVP must be able to learn what real and virtual
interfaces are active, with their IP addresses.
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5. Message Processing Rules
This generic description of RSVP operation assumes the following data
structures. An actual implementation may use additional or different
structures to optimize processing.
o PSB -- Path State Block
Each PSB holds path state for a particular (session, sender)
pair, which are defined by SESSION and SENDER_TEMPLATE objects,
respectively. PSB contents include a PHOP object and possibly
SENDER_TSPEC, POLICY_DATA, and/or ADSPEC objects from PATH
messages.
o RSB -- Reservation State Block
Each RSB holds reservation state for a particular 4-tuple:
(session, next hop, style, filterspec), which are defined in
SESSION, NHOP, STYLE, and FILTER_SPEC objects, respectively.
RSB contents also include a FLOWSPEC object and may include a
POLICY_DATA object. We assume that RSB contents include the
outgoing interface OI that is implied by NHOP.
MESSAGE ARRIVES
Verify version number, checksum, and length fields of common header,
and discard message if any mismatch is found.
Further processing depends upon message type.
PATH MESSAGE ARRIVES
Each sender descriptor object sequence in the message defines a
sender. Process each sender as follows, starting the
Path_Refresh_Needed and Resv_Refresh_Needed flags off.
1. 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.
2. Call the appropriate Route_Query routine, using DestAddress
from SESSION and (for multicast routing) SrcAddress from
SENDER_TEMPLATE. This provides a routing bit mask
ROUTE_MASK and (for a multicast destination) an
EXPECTED_INTERFACE.
3. If the message arrived on an interface different from
EXPECTED_INTERFACE, drop it and return.
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4. Search for a path state block (PSB) whose (SESSION,
SENDER_TEMPLATE) pair matches the corresponding objects in
the message.
If there is a match considering wildcards in the
SENDER_TEMPLATE objects, but the two SENDER_TEMPLATEs
differ, build and send a "Ambiguous Path" PERR message,
drop the PATH message, and return.
5. If there is no matching PSB for the (SESSION,
SENDER_TEMPLATE) pair then:
o Create a new PSB.
o Set a cleanup timer for the PSB. If this is the first
PSB for the session, set a refresh timer for the
session.
o Copy the SESSION, TIME_VALUES, and PHOP objects into
the PSB. Copy into the PSB any of the following
objects that are present: POLICY_DATA, SENDER_TSPEC,
and ADSPEC.
o Store ROUTE_MASK and EXPECTED_INTERFACE in the PSB.
o Turn on the Path_Refresh_Needed flag.
6. Otherwise (there is a matching PSB):
o Restart cleanup timer.
o If the SENDER_TSPEC and/or ADSPEC values differ
between the message and the PSB, copy the new values
into the PSB and turn on the Path_Refresh_Needed flag.
Note that if SEND_TSPEC has changed, reservations
matching S may also change; this may be deferred until
a RESV refresh arrives.
o If the new ROUTE_MASK differs from that stored in the
PSB, turn on the Path_Refresh_Needed flag, and store
the new ROUTE_MASK into the PSB.
o If the new EXPECTED_INTERFACE differs from that stored
in the PSB, turn on the Resv_Refres_Needed flag and
store the new EXPECTED_INTERFACE value into the PSB.
7. Save the IP TTL with which the message arrived in the PSB .
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8. If the Path_Refresh_Needed flag is now set, execute the
PATH REFRESH event sequence (below); however, send no PATH
refresh messages out the interface through which the PATH
message arrived.
9. If the Resv_Needed flag is now set, execute the RESV
REFRESH event sequence (below).
PATH TEAR MESSAGE ARRIVES
o If there is no path state for this destination, drop the
message and return.
o Forward a copy of the PTEAR message using the same rules as
for a PATH message (see PATH REFRESH).
o Each sender descriptor in the PTEAR message contains a
SENDER_TEMPLATE object defining a sender S; process it as
follows.
1. Locate the PSB for the pair: (session, S). If none
exists, continue with next sender descriptor.
2. Examine the RSB's for this session and delete
reservation state that is associated with sender S and
no other sender.
3. Delete the PSB.
o Drop the PTEAR message and return.
PATH ERROR MESSAGE ARRIVES
o If there are no existing PSB's for SESSION then drop the
PERR message and return.
o Look up the PSB for (session, sender); sender is defined by
SENDER_TEMPLATE. If no PSB is found, drop PERR message and
return.
o If PHOP in PSB is local API, deliver error to application
via an upcall:
Call: <Upcall_Proc>( session-id, Path Error,
Error_code, Error_value, 0,
1, SENDER_TEMPLATE, NULL, NULL, NULL)
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Any POLICY_DATA, SENDER_TSPEC, or ADSPEC object in the
message is ignored.
o Otherwise (PHOP is not local API), forward a copy of the
PERR message to the PHOP node.
RESV MESSAGE ARRIVES
A RESV message arrives through outgoing interface OI.
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 not the receiver
host itself.
o Check the STYLE object.
If the style in the message conflicts with the style of any
reservation for this session in place on any interface,
reject the RESV message by building and sending a RERR
message specifying "Conflicting Style", drop the RESV
message, and return.
o Check the POLICY_DATA object.
Verify the POLICY_DATA field (if any) to check permission
to create a reservation. If it is unacceptable, build and
send an "Administrative rejection" RERR message, drop the
RESV message, and return.
o Make reservations
Process the STYLE object and the flow descriptor list.
For FF style, execute the following steps for each b flow
descriptor, i.e., for each (FLOWSPEC, FILTER_SPEC) pair.
For SE style, execute the following steps for each
FILTER_SPEC in the list, using the given FLOWSPEC. For WF
style, execute the following once, using an internal
placeholder "WILD_FILTER" for FILTERSPEC if it is omitted.
1. Find or create a reservation state block (RSB) for the
4-tuple: (SESSION, NHOP, style, FILTER_SPEC).
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2. Start or restart the cleanout timer on the RSB. Start
a refresh timer for this session if none was started.
3. If the RSB existed and contains state matching this
flow descriptor, continue with the next flow
descriptor. Otherwise (the state is new or modified),
continue processing the current flow descriptor with
the following steps.
4. Scan the set of PSBs (senders) whose SENDER_TSPECs
match FILTER_SPEC.
- If this set is empty, build and send an error
message specifying "No sender information", and
continue with the next flow descriptor.
- If this set contains more than one PSB and if the
style has the explicit option (e.g., FF or SE),
build and send an error message specifying
"Ambiguous filter spec" and continue with the
next flow descriptor.
- Set K_E_Police_flag on if any of these PSBs have
the E_Police flag on, otherwise set
K_E_Police_flag off. Set K_M_Police_flag on if
the style has wildcard scope and there is more
than one PSB in the scope, otherwise, set
K_M_Police_flag off.
- Compute K_Tspec as the sum of the SENDER_TSPEC
objects, if any, in this set of PSBs.
5. Compute the parameters for the effective reservation,
by considering all RSB's for the same (SESSION, OI,
FILTERSPEC) triple.
- Compute the effective kernel flowspec,
K_Flowspec, as the maximum of the FLOWSPEC values
in these RSB's
- Compute the effective kernel filter spec K_Filter
by merging the FILTER_SPEC objects in these
RSB's.
6. If this reservation has wildcard scope and this is not
the first flow descriptor in the message, one of the
filter specs must have changed; delete the old one and
install the new:
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TC_DelFilter( old_Fhandle );
Fhandle = TC_AddFilter( Rhandle, SESSION, K_filter)
Then continue with the next flow descriptor.
7. Otherwise, if there was no previous kernel reservation
in place for (SESSION, OI, FILTERSPEC), call the
kernel interface module:
Rhandle = TC_AddFlowspec( OI, K_flowspec, K_Tspec,
K_E_Police_flag, K_M_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 the
kernel handle Rhandle returned by the call in the
RSB(s). Then call:
TC_AddFilter( Rhandle, SESSION, K_Filter)
to set the filter, and continue with the next flow
descriptor.
However, if there was a previous kernel reservation
with handle Rhandle, and the flowspec has changed,
call:
TC_ModFlowspec( Rhandle, K_Flowspec, K_Tspec,
K_E_Police_flag, K_M_Police_flag )
If this call fails, build and send a RERR message
specifying "Admission control failed". In any case,
drop the RESV message and return.
If the flowspec is unchanged but the filter spec has
changed, install the new:
TC_DelFilter( old_Fhandle )
Fhandle = TC_AddFilter( Rhandle, SESSION, K_filter)
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Then continue with the next flow descriptor.
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.
RESV TEAR MESSAGE ARRIVES
A RTEAR message arrives on outgoing interface OI.
o Initialize flag Tear_Needed to False.
o Execute the following steps for each flow descriptor, i.e.,
each (FLOWSPEC, FILTERSPEC) pair, in the flow descriptor
list:
1. Find matching RSB for the 4-tuple: (SESSION, NHOP,
style, FILTER_SPEC). If no RSB is found, continue
with next flow descriptor.
2. Delete the RSB.
3. If there are no more RSBs for the same (SESSION, OI,
FILTER_SPEC) triple, call the kernel interface to
delete the reservation:
TC_DelFlowspec( K_handle )
and set Tear_Needed to True.
4. Otherwise (there are other RSB's for the same
reservation), recompute K_Flowspec and call the kernel
interface module:
TC_ModFlowspec( K_handle, K_Flowspec, Sender_Tspec)
to update the reservation. If this kernel call fails,
return; the prior reservation will remain in place.
o If Tear_Needed is False (the resulting merged state may
have changed but is still in place), then execute the RESV
REFRESH sequence below, drop RTEAR message, and return.
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o Otherwise, need to create new RTEAR message for each PHOP,
and perhaps some RESV refresh messages.
Set Refresh_Needed flag to False. Do the following for
each sender Si (in the path stat) whose ROUTE_MASK includes
the outgoing interface OI and for each PHOP:
1. Pick each flow descriptor Fj in the RTEAR message
whose FILTER_SPEC matches Si, and do the following.
- If there is no RSB whose FILTER_SPEC matches Si,
then add Fj to the new RTEAR message being built.
- Otherwise (there is a matching RSB), note the
incoming interface of Si as an interface needing
a RESV refresh message and set the Refresh_Needed
flag True.
2. If the new RTEAR message contains any flow
descriptors, forward it to PHOP.
If the scope is wildcard, include only a single flow
descriptor in the message.
o If the Refresh_Needed flag is true, then execute the
RESV_REFRESH sequence below, for the incoming interfaces
that have been noted.
RESV ERROR MESSAGE ARRIVES
o If there is no state for SESSION, then drop the RERR
mesasge and return.
o For each RSB, do the following. Note that an RSB implies
an outgoing interface OI and a next hop NHOP.
1. If OI differs from the incoming interface through
which the RERR message arrived, continue with the next
RSB.
2. Compare the FILTER_SPEC(s) in the error flow
descriptor with the FILTER_SPEC(s) in the RSB. If no
match, continue with the next RSB.
Otherwise, form a new error flow descriptor with the
subset of FILTER_SPECs that matched.
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3. 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.
4. If NHOP in PSB is local API, deliver error to
application via an upcall:
Call: <Upcall_Proc>( session-id, Resv Error, k,
Error_code, Error_value, LUB-Used,
Filter_Spec_List, Flowspec_List, NULL,
NULL)
and continue with the next RSB. Here k,
Filter_Spec_List, and Flowspec_List are constructed
from the new error flow descriptor.
5. If the RESV message has wildcard scope, 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.
6. Create a new RERR message containing the new error
flow descriptor and send to the NHOP address specified
by the RSB. Include SC.Out if the scope is wildcard.
7. Continue with the next RSB.
o Drop the RERR message and return.
PATH REFRESH
This sequence may be entered by either the expiration of the path
refresh timer for a particular session, or immediately as the result
of processing a PATH message turning on the Path_Refresh_Needed flag.
For each outgoing interface OI, build a PATH message and send it to
OI. To build the message, consider each PSB whose ROUTE_MASK
includes OI, and do the following:
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o Pass the ADSPEC and SENDER_TSPEC objects present in the PSB to
the kernel call TC_Advertise, and get back a modified ADSPEC
object. Pack this modified object into the PATH message being
built.
o Create a sender descriptor sequence containing the
SENDER_TEMPLATE, SENDER_TSPEC, and POLICY_DATA objects, if
present in the PSB. Pack the sender descriptor 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 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 If the maximum size of the PATH message is reached, send the
packet out interface OI and start packing a new one.
RESV REFRESH
This sequence may be entered by either the expiration of the
reservation refresh timer for a particular session, or immediately as
the result of processing a RESV or RTEAR message.
For each PHOP defined by the path state, scan the RSBs, merge the
style, FLOWSPECs and FILTER_SPECs appropriately, build a new RESV
message, and send it to PHOP. Each message carries a NHOP object
containing the local address of the interface through which it is
sent.
The details of building the RESV messages depend upon the
shared/distinct option of the style. For each PHOP, do the
following:
o Distinct style
Select each sender Si (PSB) for PHOP, and do the following:
1. Select all RSB's whose FILTER_SPECs match the
SENDER_TEMPLATE object for Si and whose OI matches a bit in
the ROUTE_MASK of the PSB for Si.
2. Compute the maximum over the FLOWSPEC objects of this set
of RSB's, and merge their FILTER_SPEC, STYLE, and
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POLICY_DATA objects.
3. Append the (FLOWSPEC, FILTER_SPEC pair) to the RESV message
being built for destination PHOP. When the packet fills,
or upon completion of all PSB's with the same PHOP, send
it.
o Shared style
1. Select each sender Si (PSB) for PHOP, and select all RSB's
that: (a) have an OI matching a bit in the ROUTE_MASK for
Si, and (b) contain at least one FILTER_SPEC that matches
the SENDER_TEMPLATE object for Si.
2. For all selected RSB's for all Si corresponding to a given
PHOP:
- Compute the maximum over the FLOWSPEC objects of this
set of RSB's.
- Merge the metching FILTER_SPEC objects; this will in
general result in a list of non-overlapping
FILTER_SPECs, but where there are overlaps due to
wildcards, use the `wildest'.
- Merge the STYLE and POLICY_DATA objects.
- Place the resulting merged objects into a RESV message
and send it to PHOP.
3. If the scope is wildcard, a forwarded RESV must contain a
SCOPE object. The set of IP addresses in the SCOPE object
sent to a given PHOP is formed as follows.
- Take the union of the senders listed in SCOPE objects
in all RSB's.
- Intersect that set with the set of sender hosts listed
in path state for PHOP.
- If the resulting set is empty, no RESV should be
forwarded to this PHOP.
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APPENDIX A. Object Definitions
C-Types are defined for the two Internet address families IPv4 and
IP6. To accomodate 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) |
+-------------+-------------+-------------+-------------+
| ////// | Flags | DestPort |
+-------------+-------------+-------------+-------------+
o IP/UDP SESSION object: Class = 1, C-Type = 2
+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ IP6 DestAddress (16 bytes) +
| |
+ +
| |
+-------------+-------------+-------------+-------------+
| /////// | Flags | DestPort |
+-------------+-------------+-------------+-------------+
DestAddress
The IP unicast or multicast destination address of the
session.
Flags
0x01 = E_Police flag
The E_Police flag is used in PATH messages to determine
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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.]
DestPort
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
4.2; 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 |
+-------------+-------------+-------------+-------------+
| Max Refresh Period |
+-------------+-------------+-------------+-------------+
Refresh Period
The refresh timeout period R used to generate this message;
in milliseconds.
Max Refresh Period
The largest R value that a node is allowed to apply to the
downstream state for this session. A node may refuse to
accept this requirement, by ignoring the message containing
this TIME_VALUES object and sending a "R too small" error
message.
If this value is zero, no limit is set.
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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 4.1.5.
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
+-------------+-------------+-------------+-------------+
| Style ID | Option Vector |
+-------------+-------------+-------------+-------------+
Style ID
An integer identifying the style, as follows:
0 = No ID assigned; use option vector.
1 = WF
2 = FF
3 = SE
Option Vector
A set of bit fields giving values for the reservation
options. If new options are added in the futre,
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:
19 bits: Reserved
2 bits: Sharing control
00b: Reserved
01b: Distinct reservations
10b: Shared reservations
11b: Reserved
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3 bits: Scope control
000b: Reserved
001b: Wildcard scope
010b: Explicit scope
011b - 111b: Reserved
The low order bits of the option vector are determined by the
style id, as follows:
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) |
+-------------+-------------+-------------+-------------+
| Protocol Id | ////// | SrcPort |
+-------------+-------------+-------------+-------------+
o IP6 FILTER_SPEC object: Class = 10, C-Type = 2
+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ IP6 SrcAddress (16 bytes) +
| |
+ +
| |
+-------------+-------------+-------------+-------------+
| Protocol Id | ////// | 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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Protocol Id
The IP protocol Identifier, or zero to indicate a `wildcard'.
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.
The only current form of Tspec is a token bucket.
o Token Bucket SENDER_TSPEC object: Class = 12, C-Type = 1
+-----------+-----------+-----------+-----------+
| b: Token Bucket Depth (bits) |
+-----------+-----------+-----------+-----------+
| r: Average data rate (bits/sec) |
+-----------+-----------+-----------+-----------+
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A.12 ADSPEC Class
ADSPEC class = 13.
[TBD]
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A.13 POLICY_DATA Class
POLICY_DATA class = 14.
o Type 1 POLICY_DATA object: Class = 14, C-Type = 1
[TBD]
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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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 should reject the message without updating local
state.
u = 1: RSVP may use message to update local state and forward
it.
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 uu = 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 substitute.
- Sub-code = 13: Bad Flowspec or Tspec value
Unreasonable request. High order 4 bits should be 000r, so
that 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.
For this Error Code, the high order 4 bits of the Error Value
field are assigned as for Code = 01 (above). For this case, the
following global sub-codes may be used:
- 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 any of the Filterspecs listed in the Resv message.
RSVP should reject the message.
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o Error Code = 05: Ambiguous path
Sender specification is ambiguous with existing path state.
RSVP should reject the message.
o Error Code = 06: Ambiguous filter spec
Filter spec matches more than one sender, in 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 = 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 should 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,
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.
o Error Code = 22: RSVP System error
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The Error Value field will provide implementation- dependent
information on the error.
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APPENDIX C. UDP Encapsulation
As described earlier, RSVP control messages are intended to be
carried directly within IP datagrams as "raw packets". Implementing
RSVP in a node will require an intercept in the packet forwarding
path for protocol 46, and the necessary kernel change is incorporated
in the recent releases of IP multicasting
There are particular circumstances where it may be desirable to
encapsulate RSVP messages in UDP packets, as a short-term measure.
1. UDP encapsulation can be used between hosts and the last- (or
first-) hop router(s). This may ease installing RSVP on some
host systems, by avoiding a kernel change for the RSVP
intercept.
2. UDP encapsulation may be useful for legal penetration of
firewalls.
3. UDP encapsulation might be used on each interface of an
intermediate RSVP router whose kernel supported multicast but
which did not have the RSVP intercept.
In the following discussion, we concentrate on (1) and (2).
Figure 13 shows a typical situation for a host running RSVP. Here
two RSVP-capable hosts Hu and Hr within a corporation are connected
to the Internet through some arbitrarily complex set of networks and
routers that is labelled the "Corporate cloud". The border router R
is assumed to be RSVP-capable, but the corporate cloud is not.
_ _ _ _
______ ( ) RSVP-capable
| | ( ) router
| Hu |-----( Corporate ) ______
|______| ( ) a| |b
( cloud )-----| R |---->Internet
______ ( ) |______|
| | ( )
| Hr |------( )
|______| (_ _ _ _ _)
Figure 13: End Host Situation
We assume that Hu is a "UDP-only" host that requires UDP
encapsulation, while Hr is a "raw-capable" host that can use raw RSVP
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packets. The UDP encapsulation scheme should allow RSVP
interoperation among an arbitrary topology of Hr hosts and Hu hosts
as well as routers R.
RESV messages are always sent unicast; once path state has been
established, the unicast destination address of each RESV message is
known. If the path state also indicates whether the next host node
needs UDP encapsulation, a RESV message can simply be sent to the
next-hop node, either in raw mode or with UDP encapsuation.
UDP encapsulation of PATH messages poses a more difficult problem.
To solve it, we define two new well-known multicast addresses G1 and
G2, and a well-known UDP port Pu. Then the table in Figure 14 shows
the rules. 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. T1 and T2 are configured IP TTL values used for
encapsulation, while Tr is the local TTL value of the specific PATH
message. Finally, D is the DestAddress for the particular session.
Node Node Type Send Receive
___ __________ _______________ _______________
Hu UDP-only host UDP(G1,Pu,T1) UDP(G1,Pu)
and UDP(G2,Pu)
Hr Raw-mode host UDP(G1,Pu,T1) UDP(G1,Pu)
and Raw(D,,Tr) and Raw()
R Router
Interface a: UDP(G2,Pu,T2) UDP(G1,Pu)
and Raw(D,,Tr) and Raw()
Interface b: Raw(D,,Tr) Raw()
Figure 14: UDP Encapsulation Rules for Path Messages
Note that R and Hr must 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 router may take
steps to ignore the duplicates, but this redundancy actually has no
ill effect other than overhead for processing the extra messages.
A router must keep track of which of its interfaces are using UDP
encapsulation and which are not. A node can always listen for
UDP(G1,Pu) on each interface, and if it receives a UDP-encapsulated
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PATH message, mark the corresponding path state as UDP-needed. Then
matching RESV messages will be correctly encapsulated.
Two provisions are necessary for this automatic determination of
encapsulation to work.
C1 A router must use different groups G1 and G2 for sending and
receiving, as already shown.
C2 The TTL value T1 used by a host must be exactly enough to reach
the router R.
If T1 is too small to pass through the corporate cloud, of course
PATH messages will not be forwarded. If T1 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. (Note that
UDP packets addressed to G2 by a router will not be received by a
neighboring router).
However, there are possible situations where it will be impossible to
find a value of T1 that meets condition C2. Within the corporate
cloud there might be a multicast tunnel with an outgoing threshold
larger than the hop count through the cloud. Another possibility is
that there might be more than one border router R, with different
TTL's. There are several possible ways that C2 might be satisfied in
such cases.
1. It might be possible to configure the hosts' RSVP daemons with
the IP address for R; the daemons could then "unicast" PATH
messages to this address. This solution will be feasible as
long as the number of Hr and Hu hosts is small.
2. A particular host on the LAN including Hu could be designated as
an "RSVP relay host". This system would listen on (G1,Pu) and
be configured with the IP address of R. It could then forward
any (PATH) messages it received directly to R, and T1 could be
set only large enough to reach local hosts and the relay.
Finally, manual configuration of T1 could be replaced by an expanding
ring search conducted by host RSVP daemons. This possibility is for
future study.
APPENDIX D. Experimental and Open Issues
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D.1 Reservation Compatability
How strong is the requirement for compatability of reservations in
different directions? For example, see Figure 11; 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
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
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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.
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:
+-------------+-------------+-------------+-------------+
| |
+ +
| |
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+ 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.
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,
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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.
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 15 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.
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|
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 15: 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
15). 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.
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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
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.
D.4 Semantic Fragmentation
Long RSVP messages are fragmented into MTU-sized packets when they
are sent and reassembled upon receipt. This is normally expected
to be done at the RSVP layer, but may also occur at the IP layer
(when fragmentation occurs within a non-RSVP cloud). It is well
known that such "linear fragmentation" amplifies the effect of
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packet loss. There is some concern that this could result in lost
RSVP state across congested paths through non-RSVP clouds.
One way to avoid this problem would be to use "semantic"
fragmentation, exploiting the structure of an RSVP message. With
semantic fragmentation, the state information that would have been
packed into one large message is sent in multiple packets, each of
which is constructed to be logically complete. Upon receipt, each
packet can be processed independently of the other packets, with
no explicit reassembly required.
Semantic fragmentation causes some redundancy of information; for
example, each packet of a RESV message must include SESSION,
NHOP/PHOP, TIME_VALUES, and STYLE objects. More importantly, the
rules for semantic fragmentation are complex, since a single RESV
message may contain two unbounded lists, and different styles
require different rules. Finally, the largest atomic message must
still fit into an MTU-sized packet, leading to a complex set of
limits on the sizes of individual objects. At present, most
objects are known to be small, but POLICY_DATA objects are
variable and may perhaps grow large.
The text of this section describes (some of) the rules for
semantic fragmentation. It has been removed from the main body of
the document, but is kept here for futur consideration.
D.4.1 Semantic Fragmentation of RESV Messages
An outgoing RESV message that is too large for the MTU of the
interface can be sent as multiple messages, as follows:
o For FF style, the flow descriptor list can be split as
required to fit; the rest of the message should be
replicated into each packet.
o For WF style, a SCOPE object containing an explicit list
of sender IP addresses can be split as required to fit;
the rest of the message should be replicated into each
packet.
o For SE style, the flow descriptor list can be split as
required to fit; the rest of the message should be
replicated into each packet.
If a single SE descriptor is too large to fit, its filter
spec list can similarly be split as required. However,
the subsets of a particular filter spec list must each be
enclosed in TAG objects carrying the same tag value, so
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Internet Draft RSVP Specification July 1995
the receiver will be able to match each FILTER_SPEC object
to the appropriate shared reservation.
D.4.2 TAG class
TAG class = 15.
o TAG object: Class = 15, C-Type = 1
+-------------+-------------+-------------+-------------+
| Tag Value |
+-------------+-------------+-------------+-------------+
| |
// Tagged Sublist //
| |
+-------------+-------------+-------------+-------------+
Tag Value
The value of the tag being attached to the objects in
the Tagged Sublist. The tag value is unique for each
session and next/previous hop.
Tagged Sublist
A list of objects with the same class-num (but not
necessarily the same C-Type).
A TAG object encloses a list of one or more objects and
attaches a logical name or "tag" value to them. The tag
value is unique to the next/previous hop and the session
(specified by HOP and SESSION objects, respectively). The
enclosed object list is the "tagged sublist", and the
objects in it said to be "tagged" with the tag value.
Objects in a particular tagged sublist must all have the
same class-num.
Tagged objects with the same tag value are declared to be
logically related, i.e., to be members of some larger
logical set of objects. Note that the tagged sublist
implies no ordering; it defines only a set of objects.
The meaning of the logical relationship depends upon the
class-num of the tagged objects.
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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.
[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.
[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
Report, RSVP Working Group, Proceedings of the Thirtieth Internet
Engineering Task Force, Toronto, Canada, July 1994.
Security Considerations
See Section 2.5.
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
Braden, Zhang, et al. Expiration: January 1996 [Page 95]
Internet Draft RSVP Specification July 1995
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
Sugih Jamin
Computer Science Department
University of Southern California
Los Angeles, CA 90089-0871
Phone: (213) 740-6578
EMail: jamin@catarina.usc.edu
Braden, Zhang, et al. Expiration: January 1996 [Page 96]
