Internet Engineering Task Force J. Manner
Internet-Draft X. Fu
Expires: June, 2005 December, 2004
Analysis of Existing Quality of Service Signaling Protocols
<draft-ietf-nsis-signalling-analysis-05.txt>
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Abstract
This document reviews some of the existing QoS signaling protocols
for an IP network. The goal here is to learn from them and to avoid
common misconceptions. Further, we need to avoid the mistakes during
the design and the implementation of any new protocol in this area.
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Table of Contents
1 Background ................................................... 3
2 RSVP and RSVP Extensions ..................................... 4
2.1 Basic Design ............................................... 4
2.1.1 Signaling Model .......................................... 4
2.1.2 Soft State ............................................... 5
2.1.3 Two-pass Signaling Message Exchanges ..................... 5
2.1.4 Receiver-based Resource Reservation ...................... 5
2.1.5 Separation of QoS Signaling from Routing ................. 5
2.2 RSVP Extensions ............................................ 6
2.2.1 Simple Tunneling ......................................... 6
2.2.2 IPsec Interface .......................................... 6
2.2.3 Policy Interface ......................................... 6
2.2.4 Refresh Reduction ........................................ 7
2.2.5 RSVP over RSVP ........................................... 7
2.2.6 IEEE 802-style LAN Interface ............................. 8
2.2.7 ATM Interface ............................................ 8
2.2.8 DiffServ Interface ....................................... 9
2.2.9 Null Service Type ........................................ 9
2.2.10 MPLS Traffic Engineering ................................ 9
2.2.11 GMPLS and RSVP-TE ....................................... 10
2.2.12 GMPLS Operation at UNI and E-NNI Reference Points ....... 11
2.2.13 MPLS and GMPLS Future Extensions ........................ 11
2.2.14 ITU-T H.323 Interface ................................... 12
2.2.15 3GPP Interface .......................................... 12
2.3 Extensions For New Deployment Scenarios .................... 13
2.4 Conclusion ................................................. 14
3 RSVP Transport Mechanism Issues .............................. 15
3.1 Messaging Reliability ...................................... 15
3.2 Message Packing ............................................ 15
3.3 MTU Problem ................................................ 16
3.4 RSVP-TE vs. Signaling Protocol for RT Applications ......... 16
3.5 What will be a better alternative? ........................ 17
4 RSVP Protocol Performance Issues ............................. 17
4.1 Processing Overhead ........................................ 17
4.2 Bandwidth Consumption ...................................... 18
5 RSVP Security and Mobility ................................... 19
5.1 Security ................................................... 19
5.2 Mobility Support ........................................... 19
6 Other QoS Signaling Proposals ................................ 20
6.1 Tenet and ST-II ............................................ 20
6.2 YESSIR ..................................................... 21
6.2.1 Reservation Functionality ................................ 21
6.2.2 Conclusion ............................................... 22
6.3 Boomerang .................................................. 22
6.3.1 Reservation Functionality ................................ 22
6.3.2 Conclusions .............................................. 23
6.4 INSIGNIA ................................................... 23
7 Inter-domain Signaling ....................................... 24
7.1 BGRP ....................................................... 24
7.2 SICAP ...................................................... 24
7.3 DARIS ...................................................... 25
8 Security Considerations ...................................... 27
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9 IANA Considerations .......................................... 27
10 Summary ..................................................... 27
11 Contributors ................................................ 27
12 Acknowledgment .............................................. 28
13 Normative References ........................................ 28
14 Non-Normative References .................................... 28
15 Authors' Information ........................................ 32
16 Appendix A - Comparison of RSVP to the NSIS Requirements
1. Background
This document reviews some of the existing QoS signaling protocols
for an IP network. The goal here is to learn from them and to avoid
common misconceptions. Further, we need to avoid the mistakes during
the design and the implementation of any new protocol in this area.
There have been a number of historic attempts in delivering QoS or
generic signaling into the Internet. In the early years, multicast
was believed to be going to be popular for the majority of
communications, hence, both RSVP and earlier ST-II were designed in a
way which is multicast-oriented.
ST-II was developed as a reservation protocol for point-to-multipoint
communication. However, since it is sender-initiated, it does not
scale with the number of receivers in a multicast group. Its
processing is fairly complex. Since every sender needs to set up its
own reservation, the total amount of reservation states is large.
RSVP was then designed to provide support for multipoint-to-
multipoint reservation setup in a more efficient way, however its
complexity, scalability and ability to meet new requirements have
been criticized.
YESSIR [PS98] and Boomerang [FNM+99] are examples of protocols
designed after RSVP. Both protocols were meant to be simpler than
RSVP. YESSIR is an extension to RTCP, while Boomerang is used with
ICMP.
Previously, there has been a lot of work targeted at creating a new
signaling protocol for resource control. Istvan Cselenyi suggested to
have a QoSSIG BOF in IETF47, for identifying problems in QoS
signaling, but failed to get enough support [URL1]. Some people
argued, "in many ways, RSVP improved upon ST-2, and it did start out
simpler, but resulting a design with complexity and scalability",
while some others thought it is "new knowledge and requirements" that
made RSVP insufficient, and there is no simpler way to handle the
same problem as RSVP.
Michael Welzl organized a special session "ABR to the Internet" in
SCI 2001, and gathered some inputs for requesting an "ABR to the
Internet" BOF in IETF#51, which was intended to introduce explicit
rate feedback related mechanisms for the Internet (e2e, edge2edge)
but failed because of "missing community interest".
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OPENSIG [URL2] has been involved in the Internet signaling for years.
Ping Pan initiated a SIGLITE [URL3] BOF mailing list to investigate
light-weight Internet signaling. Finally, NSIS BOF was successful and
the NSIS WG was formed.
The most mature and original protocols are presented in their own
sections and other QoS signaling protocols are presented in later
subsections. The presented protocols are chosen based on relevance to
the work within NSIS. The aim is not to review every existing
protocol.
2. RSVP and RSVP Extensions
RSVP (the Resource Reservation Protocol) [ZDSZ93] [RFC2205] [BEBH96]
has evolved from ST-II to provide end-to-end QoS signaling services
for application data streams. Hosts use RSVP to request a specific
quality of service (QoS) from the network for particular application
flows. Routers use RSVP to deliver QoS requests to all routers along
the data path. RSVP also can maintain and refresh states for a
requested QoS application flow.
By original design, RSVP fits well into the framework of the
Integrated Services (IntServ) [RFC2210] [BEBH96] with certain
modularity and scalability.
RSVP carries QoS signaling messages through the network, visiting
each node along the data path. To make a resource reservation at a
node, the RSVP module communicates with two local decision modules,
admission control and policy control. Admission control determines
whether the node has sufficient available resources to supply the
requested QoS. Policy control provides authorization for the QoS
request. If either check fails, the RSVP module returns an error
notification to the application process that originated the request.
If both checks succeed, the RSVP module sets parameters in a packet
classifier and packet scheduler to obtain the desired QoS.
2.1. Basic Design
The design of RSVP distinguished itself by a number of fundamental
ways, particularly, soft state management, two-pass signaling message
exchanges, receiver-based resource reservation and separation of QoS
signaling from routing.
2.1.1. Signaling Model
The RSVP signaling model is based on a special handling of multicast.
The sender of a multicast flow advertises the traffic characteristics
periodically to the receivers via "Path" messages. On receipt of an
advertisement, a receiver may generate a "Resv" message to reserve
resources along the flow path from the sender. Receiver reservations
may be heterogeneous. To accommodate the multipoint-to-multipoint
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multicast applications, RSVP was designed to support a vector of
reservation attributes called the "style". A style describes whether
all senders of a multicast group share a single reservation and which
receiver is applied. The "Scope" object additionally provides the
explicit list of senders.
2.1.2. Soft State
Because the number of receivers in a multicast flow is likely to
change, and the flow of delivery paths might change during the life
of an application flow, RSVP takes a soft-state approach in its
design, creating and removing the protocol states (Path and Resv
states) in routers and hosts incrementally over time. RSVP sends
periodic refresh messages (Path and Resv) to maintain its states and
to recover from occasional lost messages. In the absence of refresh
messages, the RSVP states automatically time out and are deleted.
States may also be deleted explicitly by PathTear, PathErr with
Path_State_Removed flag, or ResvTear Message.
2.1.3. Two-pass Signaling Message Exchanges
The receiver in an application flow is responsible for requesting the
desired QoS from the sender. To do this, the receiver issues an RSVP
QoS request on behalf of the local application. The request
propagates to all routers in reverse direction of the data paths
toward the sender. In this process, RSVP requests might be merged,
resulting in a protocol that scales well when there are a large
number of receivers.
2.1.4. Receiver-based Resource Reservation
Receiver-initiation is critical for RSVP to setup multicast sessions
with a large number of heterogeneous receivers. A receiver initiates
a reservation request at a leaf of the multicast distribution tree,
traveling toward the sender. Whenever a reservation is found to
already exist in a node in the distribution tree, the new request
will be merged with the existing reservation. This could result in
fewer signaling operations for the RSVP nodes in the multicast tree
close to the sender, but introduce a restriction to receiver-
initiation.
2.1.5. Separation of QoS Signaling from Routing
RSVP messages follow normal IP routing. RSVP is not a routing
protocol, but rather is designed to operate with current and future
unicast and multicast routing protocols. The routing protocols are
responsible for choosing the routes to use to forward packets, and
RSVP consults local routing tables to obtain routes. RSVP is
responsible only for reservation setup along a data path.
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A number of messages and objects have been defined for the protocol.
A detailed description is given in [RFC2205].
2.2. RSVP Extensions
RSVP [RFC2205] was originally designed to support real-time
applications over the Internet. Over the past several years, the
demand for multicast-capable real-time teleconferencing, which many
people had envisioned to be one of the key Internet applications that
could benefit from network-wide deployment of RSVP, has never
materialized. Instead, RSVP-TE [RFC3209], a RSVP extension for
traffic engineering, has been widely deployed by a large number of
network providers to support MPLS applications.
There are a large number of protocol extensions based on RSVP. Some
provide additional features, such as security and scalability, to the
original protocol. Some introduce additional interfaces to other
services, such as DiffServ. And some simply define new applications,
such as MPLS and GMPLS, that are completely irrelevant from
protocol's original intent.
In this section, we list only IETF-based RFCs and a limited set of
other organizations' specifications. Informational RFCs (e.g.,
RFC2998 [RFC2998]) and work-in-progress I-Ds (e.g., proxy) are not
covered here.
2.2.1. Simple Tunneling
[RFC2746] describes an IP tunneling enhancement mechanism that allows
RSVP to make reservations across all IP-in-IP tunnels, basically, by
way of recursively applying RSVP over the tunnel portion of the path.
2.2.2. IPsec Interface
RSVP can support IPsec on a per address, per protocol basis instead
of on a per flow basis. [RFC2207] extends RSVP by using the IPsec
Security Parameter Index (SPI) in place of the UDP/TCP-like ports.
This introduces a new FILTER_SPEC object, which contains the IPsec
SPI, and a new SESSION object.
2.2.3. Policy Interface
[RFC2750] specifies the format of POLICY_DATA objects and RSVP
handling of policy events. It introduces objects which are
interpreted only by policy aware nodes (PEPs) which interact with
policy decision points (PDPs). Nodes which are unable to interpret
the POLICY_DATA objects are called policy ignorant nodes (PINs). The
content of the POLICY_DATA object itself is protected only between
PEPs and therefore provides end-to-middle or middle-to-middle
security.
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[RFC2749] specifies the usage of COPS policy services in RSVP
environments. [RFC3181] specifies a preemption priority policy
element (PREEMPTION_PRI) for use by RSVP POLICY_DATA Object.
[RFC3520] describes how authorization provided by a separate protocol
(such as SIP) can be reused with the help of an authorization token
within RSVP. The token might therefore contain either the authorized
information itself (e.g. QoS parameters) or a reference to those
values. The token might be unprotected (which is strongly
discouraged) or protected based on symmetric or asymmetric
cryptography. Moreover, the document describes how to provide the
host with encoded session authorization information as a POLICY_DATA
object.
2.2.4. Refresh Reduction
[RFC2961] describes mechanisms to reduce processing overhead
requirements of refresh messages, eliminate the state synchronization
latency incurred when an RSVP message is lost and, refreshing state
without the transmission of whole refresh messages. It defines the
following objects: MESSAGE_ID, MESSAGE_ID_ACK, MESSAGE_ID_NACK,
MESSAGE_ID LIST, MESSAGE_ID SRC_LIST and MESSAGE_ID MCAST_LIST
objects. Three new RSVP message types are defined:
1) Bundle message, which consists of a bundle header followed by a
body consisting one or more standard RSVP messages. Bundle messages
help in scaling RSVP in reducing processing overhead and bandwidth
consumption.
2) ACK message, which carries one or more MESSAGE_ID_ACK or
MESSAGE_ID_NACK objects. ACK messages are sent between neighboring
RSVP nodes to detect message loss and support reliable RSVP message
delivery on a per hop basis.
3) Srefresh message, which carries one or more MESSAGE_ID LIST,
MESSAGE_ID SRC_LIST and MESSAGE_ID MCAST_LIST objects. correspondent
to Path and Resv messages that establish the states. Srefresh
messages are used to refresh RSVP states without transmitting
standard Path or Resv messages.
2.2.5. RSVP over RSVP
[RFC3175] allows to install one or more aggregated reservations in an
aggregation region, thus the number of individual RSVP sessions can
be reduced. The protocol type is swapped from RSVP to RSVP-E2E-IGNORE
in E2E (standard) Path, PathTear and ResvConf messages when they
enter the aggregation region, and swapped back when they leave. In
addition to a new PathErr code (NEW_AGGREGATE_NEEDED), three new
objects are introduced:
1) SESSION object, which contains two values: the IP Address of the
aggregate session destination, and the DSCP that it will use on the
E2E data the reservation contains.
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2) SENDER_TEMPLATE object, which identifies the aggregating router
for the aggregate reservation.
3) FILTER_SPEC object, which identifies the aggregating router for
the aggregate reservation, and is syntactically identical to the
SENDER_TEMPLATE object.
From the perspective of RSVP signaling and the handling of data
packets in the aggregation region, these cases are equivalent to the
case of aggregating E2E RSVP reservations. The only difference is
that E2E RSVP signaling does not take place and cannot therefore be
used as a trigger, so some additional knowledge is required in
setting up the aggregate reservation.
2.2.6. IEEE 802-style LAN Interface
[RFC2814] introduces an RSVP LAN_NHOP address object that keeps track
of the next L3 hop as the PATH message traverses an L2 domain between
two L3 entities (RSVP PHOP and NHOP nodes). Both layer-2 and layer-3
addresses are included in the LAN_NHOP; the RSVP_HOP_L2 object is
used to include the Layer 2 address (L2ADDR) of the previous hop,
complementing the L3 address information included in the RSVP_HOP
object (RSVP_HOP_L3 address).
To provide sufficient information for debugging or resource
management, RSVP diagnostic messages (DREQ and DREP) are defined in
[RFC2745] to collect and report RSVP state information along the path
from a receiver to a specific sender.
2.2.7. ATM Interface
[RFC2379] and [RFC2380] define RSVP over ATM implementation
guidelines and requirements to interwork with the ATM (Forum) UNI
3.x/4.0. [RFC2380] states that the RSVP (control) messages and RSVP
associated data packets must not be sent on the same VCs, and an
explicit release of RSVP associated QoS VCs must be performed once
the VC for forwarding RSVP control messages terminates. While a
separate control VC is also possible for forwarding RSVP control
messages, [RFC2379] recommends to create a best-effort short-cut (a
short-cut is a point-to-point VC where the two end-points locate in
different IP subnets) first (if not exist), which can allow setting
up RSVP triggered VCs to use the best-effort end-point. For data
flows, the subnet senders must establish all QoS VCs and the RSVP
enabled subnet receiver must be able to accept incoming QoS VCs. RSVP
must request the configurable inactivity timers of VCs be set to
"infinite", and if it is too complex to do this at the VC receiver,
RSVP over ATM implementations are required not to use an inactivity
timer to clear any received connections. In case of dynamic QoS, the
replacement of VC should be done gracefully.
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2.2.8. DiffServ Interface
RFC2996 [RFC2996] introduces a DCLASS Object to carry Differentiated
Services Code Points (DSCPs) in RSVP message objects. If the network
element determines that the RSVP request is admissible to the
DiffServ network, one or more DSCPs corresponding to the behavior
aggregate are determined, and will be carried by the DCLASS Object
added to the RESV message upstream toward the RSVP sender.
2.2.9. Null Service Type
For some applications, service parameters are specified by the
network, not by the application, e.g., enterprise resource planning
(ERP) applications. The Null Service [RFC2997] allows applications to
identify themselves to network QoS policy agents using RSVP
signaling, but does not require them to specify resource
requirements. QoS policy agents in the network respond by applying
QoS policies appropriate for the application (as determined by the
network administrator). The RSVP sender offers the new service type,
'Null Service Type' in the ADSPEC that is included with the PATH
message. A new TSPEC corresponding to the new service type is added
to the SENDER_TSPEC. In addition, the RSVP sender will typically
include with the PATH message policy objects identifying the user,
application and sub-flow, which will be used for network nodes to
manage the correspondent traffic flow.
2.2.10. MPLS Traffic Engineering
RSVP-TE [RFC3209] specifies the core extensions to RSVP for
establishing constraint-based explicitly routed LSPs in MPLS networks
using RSVP as a signaling protocol. RSVP-TE is intended for use by
label switching routers (as well as hosts) to establish and maintain
LSP-tunnels and to reserve network resources for such LSP-tunnels.
RFC3209 defines a new Hello message (for rapid node failure
detection).
RFC3209 also defines new C-Types (LSP_TUNNEL_IPv4 and
LSP_TUNNEL_IPv6) for the SESSION, SENDER_TEMPLATE, and FILTER_SPEC
objects. Here a session is the association of LSPs that support the
LSP-tunnel. The traffic on an LSP can be classified as the set of
packets that are assigned the same MPLS label value at the
originating node of an LSP-tunnel.
The following 5 new objects are also defined.
1) EXPLICIT_ROUTE object (ERO), which is incorporated into RSVP Path
messages, encapsulating a concatenation of hops which constitutes the
explicitly routed path. Using this object, the paths taken by label-
switched RSVP-MPLS flows can be pre-determined, independent of
conventional IP routing.
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2) LABEL_REQUEST object. To establish an LSP tunnel, the sender can
create a Path message with a LABEL_REQUEST object. A node that sends
a LABEL_REQUEST object MUST be ready to accept and correctly process
a LABEL object in the corresponding Resv messages.
3) LABEL object. Each node that receives a Resv message containing a
LABEL object uses that label for outgoing traffic associated with
this LSP tunnel.
4) SESSION_ATTRIBUTE object, which can be added to Path messages to
aid in session identification and diagnostics. Additional control
information, such as setup and holding priorities, resource
affinities and local-protection, are also included in this object.
5) RECORD_ROUTE object (RRO). The RECORD_ROUTE object may appear in
both Path and Resv messages. It is used to collect detailed path
information and is useful for loop detection and for diagnostics.
Section 5 of [RFC3270] further specifies the extensions to RSVP to
establish LSPs supporting DiffServ in MPLS networks, introducing a
new DIFFSERV Object (applicable in the Path messages) and using pre-
configured or (e.g. RFC3270) signaled "EXP<-->PHB mapping".
RSVP-TE provides a way to indicate an unnumbered link in its Explicit
Route and Record Route Objects through [RFC3477]. This specifies the
following extensions.
- An Unnumbered Interface ID Subobject, which is a subobject of the
Explicit Route Object (ERO) used to specify unnumbered links;
- An LSP_TUNNEL_INTERFACE_ID Object, to allow the adjacent LSR to
form or use an identifier for an unnumbered Forwarding Adjacency;
- A new subobject of the Record Route Object, used to record that the
LSP path traversed an unnumbered link.
2.2.11. GMPLS and RSVP-TE
GMPLS RSVP-TE [RFC3473] is an extension of RSVP-TE. It enables the
provisioning of data-paths within networks supporting a variety of
switching types including packet and cell switching networks, layer
two networks, TDM networks and photonic networks.
It defines the new Notify message (for general event notification),
which may contain notifications being sent, with respect to each
listed LSP, both upstream and downstream. Notify messages can be used
for expedited notification of failures and other events to nodes
responsible for restoring failed LSPs. A Notify message is sent
without the router alert option.
A number of new RSVP-TE (sub)objects are defined in GMPLS RSVP-TE for
general uses of MPLS:
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- a Generalized Label Request Object;
- a Generalized Label Object;
- a Suggested Label Object;
- a Label Set Object; (to restrict label choice)
- an Upstream_Label object; (to support bi-directional LSPs)
- a Label ERO subobject;
- IF_ID RSVP_HOP objects (IPv4 & IPv6; to identify interfaces in
out of band signaling or in bundled links);
- IF_ID ERROR_SPEC objects (IPv4 & IPv6; to identify interfaces in
out of band signaling or in bundled links);
- an Acceptable Label Set object (to support negotiation of label
values in particular for bidirecitonal LSPs)
- a Notify Request object (may be inserted in a Path or Resv message
to indicate to where a notification of LSP failure is to be sent)
- a Restart_Cap Object (used on Hello messages to identify recovery
capabilities)
- an Admin Status Object (to notify each node along the path of the
status of the LSP, and to control that state).
2.2.12. GMPLS Operation at UNI and E-NNI Reference Points
The ITU-T defines network reference points that separate
administrative or operational parts of the network. The reference
points are designated as:
- User to Network Interfaces (UNIs) if they lie between the user
or user network and the core network.
- External Network to Network Interfaces (E-NNIs) if they lie
between peer networks, network domains, or subnetworks.
GMPLS is applicable to the UNI and E-NNI without further
modification, and no new messages, objects or C-Types are required.
See [OVERLAY].
2.2.13. MPLS and GMPLS Future Extensions
At the time of writing MPLS and GMPLS are being extended by the MPLS
and CCAMP Working Groups to support additional sophisticated
functions. This will inevitably lead to the introduction of new C-
Types for existing objects, and to the requirement for new objects
(CNums). It is possible that new messages will also be introduced.
Some of the key features and functions being introduced include:
- Protection and restoration. Features will be developed to provide
- end-to-end protection
- segment protection
- various protection schemes (1+1, 1:1, 1:n)
- support of extra traffic on backup LSPs
- Diverse path establishment for protection and load sharing
- Establishment of point-to-multipoint paths
- Inter-area and inter-AS path establishment
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- with explicit path control
- with bandwidth reservation
- with path diversity
- Support for the requirements of ASON signaling as defined by the
ITU-T, including call and connection separation
- Crankback during LSP setup.
2.2.14. ITU-T H.323 Interface
ITU-T H.323 ([H.323]) recommends the IntServ resource reservation
procedure using RSVP. The information whether an endpoint supports
RSVP should be conveyed during the H.245 [H.245] capability exchange
phase, by setting appropriate qOSMode fields. If both endpoints are
RSVP-capable, when opening an H.245 logical channel, a receiver port
ID should be conveyed to the sender by the openLogicalChannelAck
message. Only after that, can a "Path - Resv - ResvConf" process
take place. The timer of waiting for ResvConf message will be set by
the endpoint. The action in case of this timer expires, as well as
RSVP reservation fails in any point during an H.323 call, is up to
the vendor to take. Once a ResvConf message is sent or received, the
endpoints should stop reservation timers and resume with the H.323
call procedures. Only explicit release of reservations are supported
in [H.323]: before sending a closeLogicalChannel message for a
stream, a sender should send a PathTear message if an RSVP session
has been previous created for that stream; after receiving a
closeLogicalChannel, a receiver should send a ResvTear similarly.
Only the FF style is supported, even for point-to-multipoint calls.
2.2.15. 3GPP Interface
3GPP TS 23.207 ([3GPP-TS23207]) specifies the QoS signaling procedure
with policy control within the UMTS end-to-end QoS architecture. When
using RSVP, the signaling source and/or destination are the User
Equipments (UEs, devices that allow users access to network services)
that locate in the Mobile Originating (MO) side and the Mobile
Terminating (MT) side, and an RSVP signaling process can either
trigger or be triggered by the (COPS) PDP Context
establishment/modification process. The operation of refreshing
states is not specified in [3GPP-TS23207]. If a bidirectional
reservation is needed, the RSVP signaling exchange must be performed
twice between the end-points. The authorization token and flow
identifier(s) in a policy data object should be included in the RSVP
messages sent by the UE, if the token is available in the UE. When
both RSVP and Service-based Local Policy are used, the Gateway GPRS
Support Node (GGSN, the access point of the network) should use the
policy information to decide whether to accept and forward Path/Resv
messages.
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2.3. Extensions For New Deployment Scenarios
As a well-acknowledged protocol in the Internet, RSVP is being more
and more expected to provide a more generic service for various
signaling applications. However, RSVP messages were designed in a way
to optimally support end-to-end QoS signaling. To meet with the
increasing demand for a signaling protocol to also operate in host-
to-edge and edge-to-edge ways, and serve for some other signaling
purposes in addition to end-to-end QoS signaling, RSVP needs to be
developed more flexible and applicable for more generic signaling.
RSVP proxies [BEGD02] extends RSVP by being able to originate or
receive the RSVP message on behalf of the end node(s), so that
applications may still benefit from reservations that are not truly
end-to-end. However, there are certainly scenarios where an
application would want to explicitly convey its non-QoS purposed (as
well as QoS) data from a host into the network, or from an ingress
node to an egress node of an administrative domain, but it must do so
without burdening the network with excess messaging overhead. Typical
examples are an end host desiring a firewall service from its
provider's network and MPLS label setup within an MPLS domain.
RSVP requires support from network routers and user space
applications. Domains not supporting RSVP are traversed
transparently. Unfortunately, like other IP options, RSVP messages
implemented by way of IP alert option may result in themselves being
dropped by some routers [FJ02]. Although applications need to be
built with RSVP libraries, one article presents a mechanism that
would allow any host to benefit from RSVP mechanisms without
applications awareness [MHS02].
A somewhat similar deployment benefit can be gained from the
Localized RSVP (LRSVP) [JR03] [MSK+04]. The documents present the
concept of local RSVP-based reservation that can be used to trigger
reservation within an access network alone. In those cases, an end-
host may request QoS from its own access network without the co-
operation of a correspondent node outside the access network - this
would be especially helpful when the correspondent node is unaware of
RSVP. A proxy node responds to the messages sent by the end host and
enables both upstream and downstream reservations. Furthermore, the
scheme allows for faster reservation repairs following a handover by
triggering the proxy to assist in an RSVP local repair.
Still, in end-hosts which are low in processing power and
functionality, having an RSVP daemon running and taking care of the
signaling may introduce unnecessary overhead. One article [Kars01]
proposes to create a remote API so that the daemon would in fact be
running on the end-host's default router and the end-host application
would send its requests to that daemon.
Another potential problem lies in the limited sized of signaled data
due to the limitation of message size. RSVP message must fit entirely
into a single non-fragmented IP datagram. Bundle messages [RFC2961]
can aggregate multiple RSVP messages within a single PDU, but still
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only occupy one IP datagram (i.e., approximately 64K); if it exceeds
the MTU, the datagram is fragmented by IP and reassembled at the
recipient node.
2.4. Conclusion
A good signaling protocol should be transparent to the applications.
RSVP has proven to be a very well designed protocol. However, it has
a number of fundamental protocol design issues that requires more
careful re-evaluation.
The design of RSVP was originally targeted at multicast applications.
The result has been that the message processing within nodes is
somewhat heavy, mainly due to flow merging. Still, merging rules
should not appear in the specification as they are QoS-specific.
RSVP has a comprehensive set of filtering rules (WF, FF, shared) and
is not tied to certain QoS objects (RSVP is not tied to IntServ GS/CL
specifications). Objects were designed to be modular, but Xspecs
(TSPEC, etc) are more or less QoS-specific and should be more
generalized; there is no clear layering/separation between the
signaled data and signaling protocol.
RSVP uses a soft state mechanism to maintain states and allows each
node to define its own refresh timer. The protocol is also
independent of underlying routing protocols. Still, in mobile
networks the movement of the mobile nodes may not properly trigger a
reservation refresh for the new path and therefore a mobile node may
be left without a reservation up to the length of the refresh timer.
Furthermore, RSVP does not work properly with changing end-point
identifiers, that is, if one of the IP addresses of a mobile node
changes, the filters may not be able to identify the flow that had a
reservation.
From the security point of view, RSVP does provide the basic building
blocks for deploying the protocol in various environments to protect
its messages from forgery and modification. Hop-by-hop protection is
provided. However, current RSVP security mechanism does not provide
non-repudiation and protection against message deletion; the two-way
peer authentication and key management procedures are still missing.
Finally, since the publication of the RSVP standard, tens of
extensions have emerged that allow for much wider deployment than
RSVP was originally designed for, as for instance, the Subnet
Bandwidth Manager, the NULL service type, aggregation, operation over
tunneling and MPLS as well as diagnostic messages.
Domains not supporting RSVP are traversed transparently by default.
Unfortunately, like other IP options, RSVP messages implemented by
way of IP alert option may result in themselves being dropped by some
routers. Also, the maximal size of RSVP message is limited.
The transport mechanisms, performance, security and mobility issues
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are detailed in the following sections.
3. RSVP Transport Mechanism Issues
3.1. Messaging Reliability
RSVP messages are defined as a new IP protocol (that is, a new ptype
in the IP header). RSVP Path messages must be delivered end-to-end.
In order for the transit routers to intercept the Path messages, a
new IP Router Alert option [RFC2113] was introduced. This design is
simple to implement and efficient to run. As shown from the
experiments in [PS00], IP option processing introduces very little
overhead on a Free BSD box with minor kernel changes.
However, RSVP does not have a good message delivery mechanism. If a
message is lost on the wire, the next re-transmit cycle by the
network would be one soft-state refresh interval later. By default,
a soft-state refresh interval is 30 seconds.
To overcome this problem, [PS97] introduced a staged refresh timer
mechanism, which has been defined as a RSVP extension in [RFC2961].
The staged refresh timer mechanism retransmits RSVP messages until
the receiving node acknowledges. It can address the reliability
problem in RSVP.
However, during its implementation, a lot of effort had to be spent
on per-session timer maintenance, message retransmission (e.g., avoid
message bursts) and message sequencing. In addition, we have to make
an effort to try to separate the transport functions from protocol
processing. For example, if a protocol extension requires a natural
RSVP session time-out (such as RSVP-TE one-to-one fast-reroute [FAST-
REROUTE]), we have to turn off the staged refresh timers.
3.2. Message Packing
According to RSVP [RFC2205], each RSVP message can only contain
information for one session. In a network that has a reasonably large
number of RSVP sessions, this constraint imposes a heavy processing
burden on the routers. Many router OS is based on UNIX. [PS00] showed
that the UNIX socket I/O processing is not very sensitive to packet
size. In fact, processing small packets takes almost as much CPU
overhead as processing large ones. However, processing too many
individual messages can easily cause congestion at socket I/O
interfaces.
To overcome this problem, RFC2961 introduced the message bundling
mechanism. The bundling mechanism packs multiple RSVP messages
between two adjacent nodes into a single packet. In one deployed
router platform, the bundling mechanism has improved the number of
RSVP sessions that a router can handle from 2,000 to over 7,000.
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3.3. MTU Problem
RSVP does not support message fragmentation and reassembly at
protocol level. If the size of a RSVP message is larger than the
link MTU, the message will be fragmented. And the routers simply
cannot detect and process RSVP message fragments.
There is no solution for the MTU problem. Fortunately, at places
where RSVP-TE has been used, either the amount of per-session RSVP
data is never too large, or the link MTU is adjustable - PPP and
Frame Relay can always increase or decrease the MTU sizes. For
example, on some routers, a Frame Relay interface can support the
link MTU size up to 9600 bytes. Currently, the RSVP MTU problem is
not a realistic concern in MPLS networks.
However, when and if RSVP is used for end-user applications, where
network security is an essential and critical concern, it is possible
that the size of RSVP messages can be larger than the link MTU. It is
important to notice that end-users are most likely to have to deal
with a small 1500-byte Ethernet MTU.
3.4. RSVP-TE vs. Signaling Protocol for RT Applications
RSVP-TE works in an environment that is different from what the
original RSVP has been designed for: in MPLS networks, the RSVP
sessions that are used to support Label-Switched-Paths (LSP's) do not
change frequently.
In fact, the network operators typically set up the MPLS LSP's in
such a way that they cannot switch too quickly. For example, the
operators often regulate the CSPF (Constraint-based Shortest Path
First, a routing algorithm operates from the network edge to compute
the "most" optimal routes for the LSP's) computation interval to
prevent or delay large volume of user traffic to shift from one
session to the other during LSP path optimization. As a result, RSVP-
TE does not have to handle a large amount of "triggered" (new or
modified) messages. Most of the messages are refresh messages, which
can be handled by the mechanisms introduced in RFC2961. In
particular, in the Summary Refresh extension [RFC2961], each RSVP
refresh message can be represented as a 4-byte ID. The routers can
simply exchange the ID's to refresh RSVP sessions. With the full
implementation of RFC2961, MPLS routers do not have any RSVP scaling
issue. On one deployed router platform, it can support over 50,000
RSVP sessions in a stable backbone network.
On the other hand, in many of the new applications where a signaling
protocol is required, the user session duration can be relatively
short. The dynamics of adding/dropping user sessions could introduce
a large number of "triggered" messages in the network. This can
clearly introduce a substantial amount of processing overhead to the
routers. This is one area where a new signaling protocol may be
needed to reduce the processing complexity in the resource
reservation process.
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3.5. What will be a better alternative?
A good signaling protocol should be transparent to the applications.
On the other hand, the design of a signaling protocol must take the
intended and potential applications into consideration.
With the addition of RFC2961, RSVP-TE is sufficient to support its
intended application, MPLS, within the backbone. There is no
significant transport-layer problem that needs to be solved.
In the last several years, a number of new applications have emerged
that are proposed to need IP signaling, beyond the traditional ones
associated with quality of service and resource allocation. On-path
firewall control/nat traversal (synergistic with the midcom design of
[RFC3303]) is one of these. There are far-out applications such as
depositing active network code in network devices. Next-generation
signaling protocols dealing with novel applications, with network
security requirements, and with the MTU problems described above,
will prevent the re-use of the existing RSVP transport mechanism.
If a new transport protocol is needed, the protocol must be able to
handle the following:
- reliable messaging;
- message packing;
- the MTU problem;
- small triggered message volume.
4. RSVP Protocol Performance Issues
4.1. Processing Overhead
By processing overhead we mean the amount of processing required to
handle messages belonging to a reservation session. This is the
processing required in addition to the processing needed for routing
an (ordinary) IP packet. The processing overhead of RSVP originates
from two major issues:
1) Complexity of the protocol elements. First, RSVP itself is
per-flow based, thus the number of states is proportional to RSVP
session number. Path and Resv states have to be maintained in each
RSVP router for each session (and Path state also record the
reverse route for the correspondent Resv message). Second, being
receiver-initiated, RSVP optimizes various merging operations for
multicast reservations while the Resv message is processed. To
handle multicast, other mechanisms like reservation styles, scope
object, and blockade state, are also required to present in the
basic protocol. This not only adds sources of failures and errors,
but also complicates the state machine [Fu02]. Third, the same RSVP
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signaling messages are not only used for maintaining the state, but
also dealing with recovery of signaling message loss and discovery
of route change. Thus, although protocol elements that represent
the actual data (e.g., QoS parameters) specification are separated
from signaling elements, the processing overhead needed for all
RSVP messages is not marginal. Finally, the possible variations of
the order and existence of objects increases the complexity of
message parsing and internal message and state representation.
2) Implementation-specific Overhead. There are two ways to send and
receive RSVP messages, either as "raw" IP datagrams with protocol
number 46, or as encapsulated UDP datagrams, the latter of which
increase the efficiency of RSVP processing. Typical RSVP
implementations are user-space daemons interacting with the
kernel, hence state management, message sending and reception
would affect the efficiency of the protocol processing. For
example, in the recent version of the implementation described in
[KSS01], the relative execution costs for message
sending/reception system calls "sendto", "select", "recvmsg" were
14-16%, 6-7%, 9-10%, individually, of the total execution cost;
[KSS01] also found that state (memory) management can use up to
17-18% of the total execution cost, but it is possible to decrease
that cost to 6-7%, if appropriate action is taken to replace the
standard memory management with dedicated memory management for
state information. RSVP/routing, RSVP/policy control, and
RSVP/traffic control interfaces can also pose different overhead
dependent on implementation. For example, the RSVP/routing
overhead has been measured to be approximately 11-12% of the total
execution cost [KSS01].
4.2. Bandwidth Consumption
By bandwidth consumption we mean the amount of bandwidth used to
during the lifetime of a session: set up a reservation session, keep
the session alive, and finally close it.
RSVP messages are sent either to trigger a new reservation or refresh
an existing reservation. In standard RSVP, Path/Resv messages are
used for triggering and refreshing/recovering reservations,
identically, which results in an increased size of refresh messages.
The hop-by-hop refreshment may reduce the bandwidth consumption for
RSVP, but could result in more sources of error/failure events.
[RFC2961] presents a way to bundle standard RSVP messages and reduces
the refreshment redundancy by Srefresh message.
Thus, the signaling for an RSVP session uses for a session lasting n
seconds:
F(n) = (bP + bR) + ((n/Ri) * (bP + bR)) + bPt ,where
bP IP payload size of Path message
bR IP payload size of Resv message
bPt IP payload size of Path Tear message
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Ri refresh interval
For example, for a simple Controlled Load reservation without
security and identification requirements the bandwidth consumption
would be (bP is 172 bytes, bR is 92, and bPt is 44 bytes and Ri is 30
seconds):
F(n): (172 + 92) + (n/30) * (172 + 92)) + 44 = 308 + (264n/30) bytes
5. RSVP Security and Mobility
5.1. Security
To allow a process on a system to securely identify the owner and the
application of the communicating process (e.g. user id) and convey
this information in RSVP messages (PATH or RESV) in a secure manner,
[RFC3182] specifies the encoding of identities as RSVP POLICY_DATA
Object. However, to provide iron-clad security protection
cryptographic authentication combined with authorization has to be
provided. Such a functionality is typically offered by authentication
and key exchange protocols. Solely including a user identifier is
insufficient.
To provide hop-by-hop integrity and authentication of RSVP messages,
RSVP message may contain an INTEGRITY object ([RFC2747]) using a
keyed message digest. Since intermediate routers need to modify and
process the content of the signaling message a hop-by-hop security
architecture based on a chain-of-trust is used. However, with the
different usage of RSVP as described throughout this document and
with new requirements a re-evaluation of the original assumptions
might be necessary.
RFC2747 provides protection against forgery and message modification.
However this does not provide non-repudiation and protect against
message deletion. In current RSVP security scheme, the two-way peer
authentication and key management procedures are still missing.
The security issues have been well analyzed in [Tsch03].
5.2. Mobility Support
Two issues raise concern when RSVP is used by a mobile node (MN): the
flow identifier and reservation refresh. When an MN changes
locations, it may need to change one of its assigned IP address. An
MN may have an IP address by which it is reachable by nodes outside
the access network and an IP address used to support local mobility
management. Depending on the mobility management mechanism, a
handover may force a change in any of these addresses. As a
consequence the filters associated with a reservation may not
identify the flow anymore and the resource reservation is
ineffective, until a refresh with a new set of filters is
initialized.
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The second issue is about following the movement of a mobile node.
RFC2205 defines that Path messages can perform a local repair of
reservation paths. When the route between the communicating end hosts
changes, a Path message will set the state of the reservation on the
new route and a subsequent Resv message will make the resource
reservation. Therefore, by sending a Resv message a host cannot alone
update the reservation, and thus perform a local repair, before a
Path message has passed. Also, in order to provide fast adaptation to
routing changes without the overhead of short refresh periods, the
local routing protocol module can notify the RSVP process of route
changes for particular destinations. The RSVP process should use this
information to trigger a quick refresh of state for these
destinations, using the new route (Chapter 3.6, RFC2205). However,
not all local mobility protocols, or even Mobile IP, affect routing
directly in routers, and thus mobility may not be noticed at RSVP
routers. Thus, it may take a relatively long time before a
reservation is refreshed following a handover.
There have been several designs for extensions to RSVP to allow for
more seamless mobility. One solution is presented in [MSK+04], which
discusses in one section the coupling of RSVP and the mobility
management mechanisms and proposes small extensions to RSVP to better
handle the handover event, among other things. The extension allows
the mobile host to request a Path for the downstream reservation when
a handover has happened.
Another example is Mobile RSVP (MRSVP) [TBA01], which is an extension
to standard RSVP. It is based on advance reservations, where
neighboring access points keep resources reserved for mobile nodes
moving to their coverage area. When a mobile node requests resources,
the neighboring access points are checked too and a passive
reservation is done around the mobile nodes current location.
The problem with the various 'advance reservation' schemes is that
they require topological information of the access network and
usually advance knowledge of the handover event. Furthermore, the way
the resource reserved in advance are used in the neighboring service
areas is an open issue. A good overview of these different schemes
can be found in [MA01].
The interactions of RSVP and Mobile IP have been well documented in
[Thom02].
6. Other QoS Signaling Proposals
6.1. Tenet and ST-II
Tenet and ST-II are two original QoS signaling protocols for the
Internet.
In the original Tenet architecture [BFM+96], the receiver sends a
reservation request toward the source. Each network node along the
way makes the reservation. Upon arriving at the source, the source
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sends another Relax message back toward to the receiver, and has the
option to modify the previous reservation at each node.
ST-II [RFC1819] basically works as the following: a sender originates
a Connect message to a set of receivers. Each intermediate node
determines the next hop subnets, and makes reservations on the links
going to these next hops. Upon receiving a Connect indication, a
receiver must send back either an Accept or a Refuse message to the
sender. In the case of an Accept, the receiver may further reduce
the resource request by updating the returned flow specifications.
ST-II consists of two protocols: ST for the data transport and SCMP,
the Stream Control Message Protocol, for all control functions. ST
is simple and contains only a single PDU format that is designed for
fast and efficient data forwarding in order to achieve low
communication delays. SCMP packets are transferred within ST packets.
ST-II has no built-in soft states, thus requires that the network be
responsible for correctness. It is sender-initiated, and the overhead
for ST-II to handle group membership dynamics is higher than RSVP
[MESZ94]. ST-II does not provide security but RFC 1819 describes
some objects related to charging.
6.2. YESSIR
YESSIR (YEt another Sender Session Internet Reservations) [PS98] is a
resource reservation protocol that seeks to simplify the process of
establishing reserved flows while preserving many unique features
introduced in RSVP. Simplicity is measured in terms of control
message processing, data packet processing, and user-level
flexibility. Features such as robustness, advertising network service
availability and resource sharing among multiple senders are also
supported in the proposal.
The proposed mechanism generates reservation requests by senders to
reduce the processing overhead. It is built as an extension to the
Real-Time Transport Control Protocol (RTCP), taking advantages of
Real-Time Protocol (RTP). YESSIR also introduces a concept called
partial reservation, where, for certain types of applications, the
reservation requests can be passed to the next hop, even though there
is not enough resources on a local node. The local node can rely on
optimized retries to complete the reservations.
6.2.1. Reservation Functionality
YESSIR [PS98] was designed for one-way, sender-initiated end-to-end
resource reservation. It also uses soft state to maintain states. It
supports resource query (similar to RSVP diagnosis message),
advertising (similar to RSVP ADSPEC), shared reservation, partial
reservations and flow merging.
To support multicast, YESSIR simplifies the reservation styles to
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individual and shared reservation styles. Individual reservations are
made separately for each sender, whereas shared reservations allocate
resources that can be used by all senders in an RTP session. While
RSVP supports shared reservation (SE and WF styles) from the
receiver's direction, YESSIR handles the shared reservation style
from the sender's direction, thus new receivers can re-use the
existing reservation of the previous sender.
It has been shown that the YESSIR one-pass reservation model has
better performance and lower processing cost, comparing with a
regular two-way signaling protocol, such as RSVP [PS98]. The
bandwidth consumption of YESSIR is somewhat lower than that of, for
example, RSVP, because it does not require additional IP and
transport headers. Bandwidth consumption is limited to the extension
header size.
YESSIR does not have any particular support for mobility and the
security of YESSIR relies on RTP/RTCP security measures.
6.2.2. Conclusion
YESSIR requires support in applications since it is an integral part
of RTCP. Similarly, it requires network routers to inspect RTCP
packets to identify reservation requests and refreshes. Routers
unaware of YESSIR forward the RTCP packets transparently.
6.3. Boomerang
Boomerang [FNM+99] is a another resource reservation protocol for IP
networks. The protocol has only one message type and a single
signaling loop for reservation set-up and tear-down, has no
requirements on the far end node, but, instead, concentrates the
intelligence in the Initiating Node (IN).
In addition, the Boomerang protocol allows for sender- or receiver-
oriented reservations and resource query. Flows are identified with
the common 5-tuple and the QoS can be specified with various means,
e.g.. service class and bit rate. Boomerang messages are in the
initial implementation transported in ICMP ECHO / REPLY messages.
6.3.1. Reservation Functionality
Boomerang can only be used for unicast sessions, no support for
multicast exists. The requested QoS can be specified with various
methods and both ends of a communication session can make a
reservation for their transmitted flow.
The authors of Boomerang show in [FNS02] that the processing of the
protocol is considerably lower than with the ISI RSVP daemon
implementation. However, this is mainly due to the limited
functionality provided by the protocol compared to RSVP.
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Boomerang messages are quite short and consume a relatively low
amount of link bandwidth. This is due to the limited functionality of
the protocol, for example, no security specific information or
policy-based interaction are provided. Being sender oriented, the
bandwidth consumption mostly affects the downstream direction, from
the sender to the receiver.
As Boomerang is sender oriented, there is no need to store backward
information. This reduces the signaling required. The rest of the
issues that were identified with RSVP apply with Boomerang. No
security mechanism is specified for Boomerang.
The Boomerang protocol has similar deployment issues as any host-
network-host protocol. It requires an implementation at both
communicating nodes and in routers. Boomerang-unaware routers should
be able to forward Boomerang messages transparently. Still, often
firewalls drop ICMP packets making the protocol useless.
6.3.2. Conclusions
Boomerang seems to be a very lightweight protocol and efficient in
its own scenarios. Still, the apparent low processing overhead and
bandwidth consumption results from the limited functionality. No
support for multicast or any security features are present which
allows for a different functionality than RSVP, which the authors
like to compare Boomerang to.
6.4. INSIGNIA
INSIGNIA [LGZC00] is proposed as a very simple signaling mechanism
for supporting QoS in mobile ad-hoc networks. It avoids the need for
separate signaling by carrying the QoS signaling data along with the
normal data in IP packets using IP packet header options. This
approach, known as "in-band signaling" is proposed as more suitable
in the rapidly changing environment of mobile networks since the
signaled QoS information is not tied to a particular path. It also
allows the flows to be rapidly established and, thus, is suitable for
short lived and dynamic flows.
INSIGNIA aims to minimize signaling by reducing the number of
parameters that are provided to the network. It assumes that real-
time flows may tolerate some loss, but are very delay sensitive so
that the only QoS information needed is the required minimum and
maximum bandwidth.
The INSIGNIA protocol operates at the network layer and assumes that
link status sensing and access schemes are provided by lower layer
entities. The usefulness of the scheme depends upon the MAC layers
but this is undefined so that INSIGNIA can run over any MAC layer.
The protocol requires that each router maintains per-flow state.
The INSIGNIA system implicitly supports mobility. A near-minimal
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amount of information is exchanged with the network. To achieve this,
INSIGNIA makes many assumptions about the nature of traffic that a
source will send. This may also simplify admission control and buffer
allocation. The system basically assumes that "real-time" will be
defined as a maximum delay and the user can simply request real-time
service for a particular quantity of traffic.
After handover, data that was transmitted to the old base station can
be forwarded to the new base station so that no data loss should
occur. However, there is no way to differentiate between re-routed
and new traffic so priority cannot be given to handover traffic, for
example.
INSIGNIA, however, (completely) lacks a security framework and does
not investigate how to secure signaled QoS data in ad-hoc network
where relatively weak trust or even no trust exists between the
participating nodes. Hence authorization and charging especially
might be a challenge. The security protection of in-band signaling is
costly since the data delivery itself experiences increased latency
if security processing is done hop-by-hop. Since the QoS signaling
information is encoded into the flow label and end-to-end addressing
is used, it is very difficult to provide security other than IPsec in
tunnel mode.
7. Inter-domain Signaling
This section gives a short overview of protocols designed for inter-
domain signaling.
7.1. BGRP
Border Gateway Reservation Protocol (BGRP) [BGRP] is a signaling
protocol for inter-domain aggregated resource reservation for unicast
traffic. BGRP builds a sink tree for each of the stub domains. Each
sink tree aggregates bandwidth reservations from all data sources in
the network. BGRP maintains these aggregated reservations using soft
state and relies on Differentiated Services for data forwarding.
BGRP scales in terms of message processing load, state storage and
bandwidth. Since backbone routers only maintain the sink tree
information, the total number of reservations at each router scales
linearly with the number of Internet domains.
7.2. SICAP
SICAP (Shared-segment Inter-domain Control Aggregation protocol)
[SGV03] is an inter-domain signaling solution that performs shared-
segment aggregation [SGV02] on the Autonomous System (AS) level with
the purpose of reducing state required at Boundary Routers (BRs).
SICAP performs aggregation based on path segments that different
reservations share. Thus, reservations may be merged into aggregates
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that do not extend necessarily all the way until the reservation's
destination. The motivation for creating "shorter" aggregates is, on
the one hand, their ability to more easily accommodate future
requests, and on the other hand, the minimization of aggregates
created and consequently, the reduction of state required to manage
established reservations. However, and in contrast to the sink-tree
approach (used by BGRP [BGRP]), the shared-segment approach
introduces intermediate de-aggregation locations: these are ASes
where aggregates may experience "re-aggregation". At these locations,
routers that perform aggregation (AS egress routers) have to keep
track of the mapping between reservations and aggregates. One
possible way of doing this is to keep each reservation identifier and
corresponding resources stored at each aggregator. However, this
solution incurs a high state penalty on state. SICAP avoids this
state penalty by keeping track of the mapping between aggregates and
reservations at the level of destination domains rather than
explicitly mapping individual reservations to aggregates. In other
words, SICAP maintains per aggregate a list of the destination
prefixes advertised by the destination AS an aggregate provides
access to.
Pan et al. show that BGRP scales well in terms of control state,
message processing, and bandwidth efficiency, when compared to RSVP
without aggregation. However, and partially given that it was the
first approach to explore in detail the issue of inter-domain control
aggregation, they did not provide a comparison with other aggregation
protocols.
SICAP and BGRP messaging sequences are similar and consequently,
these protocols attain the same signaling load. Such load is exactly
the same attained by proposals that do not perform aggregation, given
that SICAP and BGRP exchange messages per individual reservation. In
terms of bandwidth, both protocols provision aggregates with the
exact bandwidth required by their merged reservations. Therefore, the
major difference between SICAP and BGRP is state maintained at BRs,
which is significantly reduced by SICAP. We consider this to be of
importance not so much to offer a better performing alternative to
BGRP, but to quantify the performance improvements that might still
be available in the research field of control path aggregation.
Finally, to deal with the possible problem of the signaling load,
SICAP uses an over-reservation mechanism[SGV03b], whose design took
into consideration a possible support for BGRP.
7.3. DARIS
Dynamic Aggregation of Reservations for Internet Services (DARIS)
[Bless02] [Bless04] defines an inter-domain aggregation scheme for
resource reservations. Basically, it aggregates reservations along
Autonomous System (AS) paths (or parts thereof). A set of
reservations whose data paths share a common sequence of ASes are
integrated into a joint reservation aggregate along that shared sub-
path. All entities within the aggregate, except aggregate starting
and end point, can remove state information of the included
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individual reservations, thereby saving states. They just need to
hold the necessary information about the encompassing aggregate.
Moreover, these intermediate ASes are no longer involved in signaling
that is related to the aggregated reservations. If more aggregate
resources are reserved than were actually required, the capacity of
the aggregate does not need to be adapted with every new or released
reservation (thereby reducing the number of message exchanges).
An aggregate between two ASes is created as soon as a threshold k is
exceeded that describes the active number of unidirectional
reservations between them. It is, however, possible to apply
different aggregation triggers. Furthermore, DARIS allows to nest
aggregates hierarchically. Therefore, the existence of shorter
aggregates does not prevent the creation of longer (and thus more
efficient) aggregates and vice versa. An evaluation of recent BGP
routing information in [Bless02] showed that 92% of all end-to-end
paths contain at least four ASes. Consequently, an aggregate from
edge AS to edge AS can span four or more ASes, thus saving states and
signaling message processing in at least two ASes.
There is, however, a small chance that a reservation cannot be
included into a new aggregate, because it was already aggregated
elsewhere. This so-called "aggregation conflict" is caused by the
fact that state information related to individual reservations was
already removed within intermediate ASes of the encompassing
aggregate. This may also bring difficulties in case that reservations
or aggregates are re-routed between ASes. One must be careful when
considering to define sophisticated adaptation techniques for these
special cases, because they seem to become very complex.
The signaling protocol DMSP (Domain Manager Signaling Protocol)
supports aggregation by special extensions which reduce the
reservation setup time for more than one round-trip time in some
cases (e.g., if an aggregate's capacity must be increased before a
new reservation can be included). Details can be found in [Bless02].
The DARIS concept was evaluated by using a simulation with a topology
that was derived from real BGP routing table information and
comprised more than 5500 ASes. In comparison to a non-aggregated
scenario the number of saved states lay in the range of one to two
orders of magnitude and similar results were obtained with respect to
the number of signaling messages. Though [Bless02] describes DARIS in
the context of distributed Domain Management entities (similar to a
bandwidth broker) it can be applied in a router-based resource
management environment, too. This will achieve a higher degree of
distribution which is beneficial for large ASes which are highly
interconnected.
A general issue with aggregation is that not the aggregating and de-
aggregating ASes profit from their initiated aggregates, but all
intermediate ASes within an aggregate. Therefore, some incentive for
aggregate creation has to be given. This may lead to novel cost
models that have to be developed for aggregation concepts in the
future.
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8. Security Considerations
This document does not present new technology or protocols, thus,
there are no explicit security issues. Still, individual protocols
include different levels of security issues and those are highlighted
in the relevant sections and references.
9. IANA Considerations
This draft presents and analyzes RSVP and other QoS signaling
protocols. No new protocol or technology is defined, thus, there are
no actions for IANA.
10. Summary
Supporting flow-based soft state reservations has been proven useful.
Still, there have been different ways of improving the performance,
including refresh reduction and aggregation. However, some of the
main concerns with these signaling protocols are the complexity of
the protocol, which affects implementations and processing overhead,
and the security of the signaling. Especially, a proper scheme to
handle authentication, authorization of QoS resource requests and a
framework for providing signaling message security seems to be
missing from most protocols. RSVP has a mechanism to protect
signaling messages based on manually distributed keys and concepts
for authorization but they seem to be insufficient for a dynamic and
mobile environment. [Tsch03] provides more details on security
properties provided by RSVP. Moreover, secure and efficient signaling
to and from mobile nodes has been one of the critical challenges not
fully met by existing protocols.
Moving QoS signaling protocols into a generic messenger can provide
much adoption. It is expected that the development of future
protocols should learn from the lessons of existing ones.
Nevertheless, the tradeoffs between the expected functionality,
protocol complexity/performance would still be taken into account.
For example, RSVP uses the two-way signaling mechanism, where as
YESSIR employs only one-pass signaling. Both can be shown to out-
perform the other in specific carefully chosen signaling scenarios.
11. Contributors
This document is part of the work done in the NSIS Working Group. The
draft was initially written by Jukka Manner and Xiaoming Fu. Since
the first version, Martin Karsten has provided text about the
processing overhead of RSVP and Hannes Tschofenig has provided text
about various security issues in the protocols. Henning Schulzrinne
and Ping Pan have provided more information on RSVP transportation
after the second revision. Kireeti Kompella and Adrian Farrel
provided a review and updates to the discussion on RSVP-TE and GMPLS.
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12. Acknowledgment
We would like to acknowledge Bob Braden and Vlora Rexhepi for their
useful comments.
13. Normative References
[RFC3726] M. Brunner, "Requirements for Signaling Protocols", RFC
3726, April 2004.
14. Non-Normative References
[3GPP-TS23207] 3GPP TS 23.207 V5.6.0, End-to-end Quality of Service
(QoS) Concept and Architecture, Release 5, Dec. 2002.
[BEBH96] Braden, R., Estrin, D., Berson, S., Herzog, and D. Zappala,
"The Design of the RSVP Protocol", ISI Final Technical Report, Jul
1996.
[BEGD02] Y. Bernet, N. Elfassy, S. Gai, and D. Dutt, "RSVP Proxy",
draft-ietf-rsvp-proxy-03 (work in progress), March 2002.
[BFM+96] A. Banerjea, D. Ferrari, B. Mah, M. Moran, D. Verma, and H.
Zhang, "The Tenet Real-Time Protocol Suite: Design, Implementation,
and Experiences", IEEE/ACM Transactions on Networking, Volume 4,
Issue 1, February 1996, pp. 1-10.
[BGP4] Y. Rekhter, T. Li, and S. Hares, "A Border Gateway Protocol 4
(BGP-4)", Internet Draft, Work in Progress, November 2003 (draft-
ietf-idr-bgp4-23.txt).
[BGRP] P. Pan, E, Hahne, and H. Schulzrinne, "BGRP: A Tree-Based
Aggregation Protocol for Inter-domain Reservations", Journal of
Communications and Networks, Vol. 2, No. 2, June 2000, pp. 157-167.
[Bless02] R. Bless, "Dynamic Aggregation of Reservations for Internet
Services", Proceedings of the Tenth International Conference on
Telecommunication Systems - Modeling and Analysis (ICTSM 10), Vol. 1,
pp. 26-38, October 3-6 2002, Monterey California, slightly revised
version available under http://www.tm.uka.de/doc/2003/ictsm-daris-
journal-crc-web.pdf
[Bless04] R. Bless, "Towards Scalable Management of QoS-based End-to-
End Services" (PDF), Proceedings of NOMS 2004 (IEEE/IFIP 2004 Network
Operations and Management Symposium), April 2004, Seoul, Korea.
[FAST-REROUTE] P. Pan, G. Swallow, and A. Atlas, "Fast Reroute
Extensions to RSVP-TE for LSP Tunnels", Internet Draft, Work in
Progress, January 2004 (draft-ietf-mpls-rsvp-lsp-fastreroute-01.txt).
[FNM+99] G. Feher, K. Nemeth, M. Maliosz, I. Cselenyi, J. Bergkvist,
D. Ahlard, T. Engborg, "Boomerang A Simple Protocol for Resource
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Reservation in IP Networks", IEEE RTAS, 1999.
[FNS02] G. Feher, K. Nemeth, and I. Cselenyi, "Performance evaluation
framework for IP resource reservation signalling". Performance
Evaluation 48 (2002), pp. 131-156.
[FJ02] P. Fransson and A. Jonsson, "The need for an alternative to
IPv4-options", in RVK (RadioVetenskap och Kommunikation), Stockholm,
Sweden, pp. 162-166, June 2002.
[Fu02] X. Fu, C. Kappler, and H. Tschofenig, "Analysis on RSVP
Regarding Multicast". Technical Report No. IFI-TB-2002-001, ISSN
1611-1044, Institute for Informatics, University of Goettingen, Oct
2002.
[H.245] ITU-T Recommendation H.245, Control Protocol for Multimedia
Communication, July 2000.
[H.323] ITU-T Recommendation H.323, Packet-based Multimedia
Communications Systems, Nov. 2000.
[JR03] Jukka Manner, Kimmo Raatikainen, "Localized QoS Management for
Multimedia Applications in Wireless Access Networks". IASTED
International Conference on Internet and Multimedia Systems and
Applications (IMSA 2003), August, 2003, pp. 193 - 200.
[Kars01] M. Karsten, "Experimental Extensions to RSVP -- Remote
Client and One-Pass Signalling". IWQoS 2001, Karlsruhe, Germany, June
2001.
[KSS01] M. Karsten, Jens Schmitt, Ralf Steinmetz, "Implementation and
Evaluation of the KOM RSVP Engine". IEEE Infocom 2001.
[LGZC00] S. Lee, A. Gahng-Seop, X. Zhang, A. Campbell,"INSIGNIA: An
IP-Based Quality of Service Framework for Mobile Ad Hoc Networks".
Journal of Parallel and Distributed Computing (Academic Press),
Special issue on Wireless and Mobile Computing and Communications,
Vol. 60, Number 4, April, 2000, pp. 374-406.
[MA01] B. Moon, and H. Aghvami, "RSVP Extensions for Real-Time
Services in Wireless Mobile Networks". IEEE Communications Magazine,
December 2001, pp. 52-59.
[MESZ94] D. Mitzel, D. Estrin, S. Shenker, and L. Zhang, "An
Architectural Comparison of ST-II and RSVP", INFOCOM'94.
[MHS02] Y Miao, W. Hwang, and C. Shieh, "A transparent deployment
method of RSVP-aware applications on UNIX". Computer Networks, 40
(2002), pp. 45-56.
[MSK+04] J. Manner, T. Suihko, M. Kojo, M. Liljeberg, K. Raatikainen,
"Localized RSVP". Internet Draft, Work in Progress, September 2004
(draft-manner-lrsvp-04.txt).
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[OVERLAY] G. Swallow, J. Drake, H. Ishimatsu, and Y. Rekhter, "GMPLS
UNI: RSVP Support for the Overlay Model", Internet Draft, work in
progress, February 2004 (draft-ietf-ccamp-gmpls-overlay- 03.txt).
[PS97] P. Pan, and H. Schulzrinne, "Staged refresh timers for RSVP",
Global Internet, Phoenix, Arizona, Nov. 1997.
[PS98] P. Pan, and H. Schulzrinne, "YESSIR: A Simple Reservation
Mechanism for the Internet". Proceedings of NOSSDAV, Cambridge, UK,
July 1998.
[PS00] P. Pan, and H. Schulzrinne, "PF_IPOPTION: A kernel extension
for IP option packet processing", Technical Memorandum 10009669-02TM,
Bell Labs, Lucent Technologies, Murray Hill, NJ, June 2000.
[RFC1819] L. Delgrossi, and L. Berger, "Internet Stream Protocol
Version 2 (ST2) Protocol Specification - Version ST2+", RFC 1819,
August 1995.
[RFC2113] D. Katz, "IP Router Alert Option", RFC 2113, February 1997.
[RFC2205] R. Braden, L. Zhang, S. Berson, S. Herzog, and S. Jamin,
"Resource ReSerVation Protocol (RSVP) -- Version 1 Functional
Specification", RFC 2205, Sep 1997.
[RFC2207] L. Berger, and T. O'Malley, "RSVP Extensions for IPsec Data
Flows", RFC 2207, September 1997.
[RFC2210] J. Wroclawski, "The Use of RSVP with IETF Integrated
Services", RFC 2210, September 1997.
[RFC2379] L. Berger, "RSVP over ATM Implementation Guidelines", RFC
2379, August 1998.
[RFC2380] L. Berger, "RSVP over ATM Implementation Requirements", RFC
2380, August 1998.
[RFC2745] A. Terzis, B. Braden, S. Vincent, and L. Zhang, "RSVP
Diagnostic Messages", RFC 2745, January 2000.
[RFC2746] A. Terzis, J. Krawczyk, J. Wroclawski, and L. Zhang, "RSVP
Operation Over IP Tunnels", RFC 2746, January 2000.
[RFC2747] F. Baker, B. Lindell, and M. Talwar, "RSVP Cryptographic
Authentication", RFC 2747, January 2000.
[RFC2749] J. Boyle, R. Cohen, D. Durham, S. Herzog, R. Raja, and A.
Sastry, "COPS usage for RSVP", RFC 2749, January 2000.
[RFC2750] S. Herzog, "RSVP Extensions for Policy Control", RFC 2750,
January 2000.
[RFC3182] S. Yadav, R. Yavatkar, R. Pabbati, P. Ford, T. Moore, S.
Herzog, R. Hess, "Identity Representation for RSVP", RFC 3182,
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October 2001.
[RFC2814] R. Yavatkar, D. Hoffman, Y. Bernet, F. Baker, and M. Speer,
"SBM (Subnet Bandwidth Manager): A Protocol for Admission Control
over IEEE 802-style Networks", RFC 2814, May 2000.
[RFC2961] L. Berger, D. Gan, G. Swallow, P. Pan, F. Tommasi, and S.
Molendini, "RSVP refresh overhead reduction extensions", RFC 2961,
April 2001.
[RFC2996] Y. Bernet, "Format of the RSVP DCLASS Object", RFC 2996,
November 2000.
[RFC2997] Y. Bernet, A. Smith, and B. Davie, "Specification of the
Null Service Type", RFC 2997, November 2000.
[RFC2998] Y. Bernet, R. Yavatkar, P. Ford, F. Baker, L. Zhang, M.
Speer, R. Braden, and B. Davie, "Integrated Services Operation over
Diffserv Networks", RFC 2998, November 2000.
[RFC3036] L. Andersson, P. Doolan, N. Feldman, A. Fredette, and B.
Thomas, "LDP Specification", RFC 3036, January 2001.
[RFC3175] F. Baker, C. Iturralde, F. Le Faucheur, and B. Davie,
"Aggregation of RSVP for IPv4 and IPv6 Reservations", RFC 3175,
September 2001.
[RFC3181] S. Herzog, "Signaled Preemption Priority Policy Element",
RFC 3181, October 2001.
[RFC3209] D. Awduche, L. Berger, D. Gan, T. Li, V. Srinivasan, and G.
Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC 3209,
December 2001.
[RFC3270] F. Le Faucheur (ed), "Multi-Protocol Label Switching (MPLS)
Support of Differentiated Services", RFC 3270, May 2002.
[RFC3303] P. Srisuresh, J. Kuthan, J. Rosenberg, A. Molitor, A.
Rayhan, "Middlebox communication architecture and framework",
RFC3303, August 2002.
[RFC3473] L. Berger (ed), "Generalized MPLS Signaling - RSVP-TE
Extensions". RFC 3473, January 2003.
[RFC3474] Z. Lin, and D. Pendarakis, "Documentation of IANA
assignments for Generalized MultiProtocol Label Switching (GMPLS)
Resource Reservation Protocol - Traffic Engineering (RSVP-TE) Usage
and Extensions for Automatically Switched Optical Network (ASON)",
RFC3474, March 2003.
[RFC3477] K. Kompella, and Y. Rekhter, "Signalling Unnumbered Links
in Resource Reservation Protocol - Traffic Engineering (RSVP-TE)",
RFC 3477, January 2003.
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[RFC3520] L-N. Hamer, B. Gage, B. Kosinski, and H. Shieh, "Session
Authorization Policy Element", RFC 3520, April 2003.
[SGV02] R. Sofia, R. Gurin, and P. Veiga, "An Investigation of
Inter-Domain Control Aggregation Procedures", International
Conference on Networking Protocols, ICNP'02, Paris, France, November
2002.
[SGV03] R. Sofia, R. Gurin, and P. Veiga. SICAP, a Shared-segment
Inter-domain Control Aggregation Protocol. High Performance Switching
and Routing, HPSR 2003, Turin, Italy, June 2003.
[SGV03b] R. Sofia, R. Gurin, and P. Veiga. A Study of Over-
reservation for Inter-Domain Control Aggregation Protocols. Technical
report (short version under submission), University of Pennsylvania,
May 2003. Available at
http://einstein.seas.upenn.edu/mnlab/publications.html.
[TBA01] A. Talukdar, B. Badrinath, and A. Acharya, "MRSVP: A Resource
Reservation Protocol for an Integrated Services Network with Mobile
Hosts", Wireless Networks, vol. 7, no. 1, pp. 5-19. 2001.
[Thom02] M. Thomas, "Analysis of Mobile IP and RSVP Interactions".
Internet draft, Work in Progress, October 2002 (draft-thomas-nsis-
rsvp-analysis-00.txt).
[Tsch03] H. Tschofenig, "RSVP Security Properties". Internet Draft,
Work in Progress, February 2004 (draft-ietf-nsis-rsvp-sec-
properties-04.txt).
[ZDSZ93] L. Zhang, S. Deering, D. Estrin, and D. Zappala, "RSVP: A
New Resource Reservation Protocol", IEEE Network, Volume 7, Pages
8-18, Sep 1993.
URL links, checked Nov 26 2004:
[URL1] http://www.atm.tut.fi/list-archive/diffserv/thrd3.html
[URL2] OPENSIG http://comet.columbia.edu/opensig/
[URL3] SIGLITE
http://www.cs.columbia.edu/~pingpan/projects/siglite.html
15. Authors' Information
Jukka Manner
Department of Computer Science
University of Helsinki
P.O. Box 68 (Gustav Hallstrominkatu 2b)
FIN-00014 HELSINKI
Finland
Voice: +358-9-191-51298
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Fax: +358-9-191-51120
E-Mail: jmanner@cs.helsinki.fi
Xiaoming Fu
Institute for Informatics
Georg-August-University of Goettingen
Lotzestrasse 16-18
37083 Goettingen
Germany
Voice: +49-551-39-14411
Fax: +49-551-39-14403
E-Mail: fu@cs.uni-goettingen.de
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16. Appendix A - Comparison of RSVP to the NSIS Requirements
This section provides a comparison of RSVP to the requirements
identified as part of the work in NSIS [RFC3726]. The numbering
follows the division in the requirements document.
5.1 Architecture and Design Goals
5.1.1 NSIS SHOULD provide availability information on request
RSVP itself does not support query-type of operations. However,
the RSVP diagnosis messages extension [RFC2745] provides a means
to query resource availability.
5.1.2 NSIS MUST be designed modularly
RSVP was designed to be modular by way of TLV objects, however
it is regarded being lack of sufficient extensibility in various
kind of signalling applications.
5.1.3 NSIS MUST decouple protocol and information
RSVP is decoupled from the IntServ QoS specifications. Still,
the concept of sessions in RSVP are somewhat coupled to the
information it carries.
5.1.4 NSIS MUST support independence of signaling and network
control paradigm
The IntServ information carried by RSVP does not tie the QoS
provisioning mechanisms.
5.1.5 NSIS SHOULD be able to carry opaque objects
RSVP supports this.
5.2 Signaling Flows
5.2.1 The placement of NSIS Initiator, Forwarder, and Responder
anywhere in the network MUST be allowed
Standard RSVP works only end-to-end, although the RSVP proxy
[BEGD02] and the Localized RSVP [MSK+04] have relaxed this
assumption. RSVP relies on receiver-initiation way to perform
QoS reservations.
5.2.2 NSIS MUST support path-coupled and MAY support path-
decoupled signaling
Standard RSVP is path-coupled, but the SBM work makes RSVP
somewhat path-decoupled.
5.2.3 Concealment of topology and technology information SHOULD be
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possible
RSVP itself does not provide such capability.
5.2.4 Transparent signaling through networks SHOULD be possible
RSVP messages are intecepted and evaluated in each RSVP router,
and thus they may not cross certain RSVP-routers unnoticed.
Still, the message processing rules allow unknown RSVP messages
to be forwarded unharmed.
5.3 Messaging
5.3.1 Explicit erasure of state MUST be possible
Supported by the PathTear and ResvTear messages.
5.3.2 Automatic release of state after failure MUST be possible
On error reservation states are torn down with PathTear
messages.
5.3.3 NSIS SHOULD allow for sending notifications upstream
There are two notifications in RSVP, confirm of a reservation
set-up and tear down of reservation states as a result of
errors.
5.3.4 Establishment and refusal to set up state MUST be notified
PathErr and ResvErr messages provide refusal to set up state in
RSVP.
5.3.5 NSIS MUST allow for local information exchange
RSVP NULL service type [RFC2997] provides such a feature.
5.4 Control Information
5.4.1 Mutability information on parameters SHOULD be possible
Rspec and Adspec are mutable; Tspec is (generally) end-to-end
not mutable.
5.4.2 It SHOULD be possible to add and remove local domain
information
RSVP aggregation [RFC3175] and NULL service type [RFC2997] can
provide such a feature.
5.4.3 State MUST be addressed independent of flow identification
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RSVP states are tied to the flows, thus this requirement is not
met.
5.4.4 Modification of already established state SHOULD be seamless
Modifications of a reservation is possible with RSVP.
5.4.5 Grouping of signaling for several micro-flows MAY be
provided
Aggregated RSVP and RFC2961 allow this.
5.5 Performance
5.5.1 Scalability
RSVP scales linearly to the number of reservation states.
5.5.2 NSIS SHOULD allow for low latency in setup
Setting up an RSVP reservation takes one round-trip time and the
processing times are each RSVP router.
5.5.3 NSIS MUST allow for low bandwidth consumption for the
signaling protocol
The initial reservations messages can not be compressed, but the
refresh interval can be adjusted to consume less bandwidth, at
the expense of possible inefficient resource usage.
5.5.4 NSIS SHOULD allow to constrain load on devices
See discussions on RSVP performance (section 4).
5.5.5 NSIS SHOULD target the highest possible network utilization
This dedends on the IntServ service types, Controlled Load can
provide better overall utilization than Guaranteed Service.
5.6 Flexibility
5.6.1 Flow aggregation
Aggregated RSVP and RFC2961 allow this.
5.6.2 Flexibility in the placement of the NSIS Initiator/Responder
RSVP allows receiver as initiator of reservations.
5.6.3 Flexibility in the initiation of state change
RSVP receivers can initiate the state change during its
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refreshment.
5.6.4 SHOULD support network-initiated state change
As RSVP supports hop-by-hop refreshment, this is made possible.
5.6.5 Uni / bi-directional state setup
RSVP is only uni-directional.
5.7 Security
5.7.1 Authentication of signaling requests
Authentication is available in RSVP.
5.7.2 Request Authorization
Authorization with a PDP is possible in RSVP.
5.7.3 Integrity protection
The INTEGRITY Object is available in RSVP.
5.7.4 Replay protection
The INTEGRITY Object to replay protect the content of the
signaling messages between two RSVP nodes.
5.7.5 Hop-by-hop security
The RSVP security model works only hop-by-hop.
5.7.6 Identity confidentiality and network topology hiding
The INTEGRITY Object can be used for this purpose.
5.7.7 Denial-of-service attacks
Challenging with RSVP.
5.7.8 Confidentiality of signaling messages
Not supported by RSVP.
5.7.9 Ownership of state
Challenging with RSVP.
5.8 Mobility
5.8.1 Allow efficient service re-establishment after handover
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Works for upstream but may not be achieved for the downstream
if mobility is not noticed at the cross-over router.
5.9 Interworking with other protocols and techniques
5.9.1 MUST interwork with IP tunneling
RFC 2746 discusses these issues.
5.9.2 MUST NOT constrain either to IPv4 or IPv6
RSVP supports both IP versions.
5.9.3 MUST be independent from charging model
RSVP does not discuss this.
5.9.4 SHOULD provide hooks for AAA protocols
COPS and RSVP work together.
5.9.5 SHOULD work with seamless handoff protocols
Not supported by RSVP. Still, RFC2205 suggests that route
changes should be indicated to the local RSVP daemon, which can
then initiate state refresh.
5.9.6 MUST work with traditional routing
RSVP expects traditional routing.
5.10 Operational
5.10.1 Ability to assign transport quality to signaling messages
This is a network design issue, but is possible with DiffServ.
5.10.2 Graceful fail over
RSVP supports this.
5.10.3 Graceful handling of NSIS entity problems
RSVP itself does not supports this.
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Manner et al Expires June, 2005 [Page 39]
