TSVWG F. Le Faucheur
Internet-Draft Cisco
Intended status: Standards Track J. Manner
Expires: August 28, 2007 University of Helsinki
A. Narayanan
Cisco
February 24, 2007
RSVP Extensions for Path-Triggered RSVP Receiver Proxy
draft-ietf-tsvwg-rsvp-proxy-proto-00.txt
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Copyright (C) The IETF Trust (2007).
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Abstract
RSVP signaling can be used to make end-to-end resource reservations
in an IP network in order to guarantee the QoS required by certain
flows. With conventional RSVP, both the data sender and receiver of
a given flow take part in RSVP signaling. Yet, there are many use
cases where resource reservation is required, but the receiver, the
sender, or both, is not RSVP-capable. Where the receiver is not
RSVP-capable, an RSVP router may behave as an RSVP Receiver Proxy
thereby performing RSVP signaling on behalf of the receiver. This
allows resource reservations to be established on the segment of the
end-to-end path from the sender to the RSVP Receiver Proxy. However,
as discussed in the companion document presenting RSVP Proxy
Approaches, RSVP extensions are needed to facilitate operations with
an RSVP Receiver Proxy whose signaling is triggered by receipt of
RSVP Path messages from the sender. This document specifies these
extensions.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Conventions Used in This Document . . . . . . . . . . . . 5
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. RSVP Extensions for Sender Notification . . . . . . . . . . . 7
3.1. Sender Notification via PathErr Message . . . . . . . . . 9
3.1.1. Composition of SESSION and <Sender descriptor> . . . . 12
3.1.2. Composition of ERROR_SPEC . . . . . . . . . . . . . . 12
4. Security Considerations . . . . . . . . . . . . . . . . . . . 14
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16
7. Normative References . . . . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
Intellectual Property and Copyright Statements . . . . . . . . . . 19
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1. Introduction
Guaranteed QoS for some applications with tight Qos requirements may
be achieved by reserving resources in each node on the end-to-end
path. The main IETF protocol for these resource reservations is RSVP
specified in [RFC2205]. RSVP does not require that all intermediate
nodes support RSVP, however it assumes that both the sender and the
receiver of the data flow support RSVP. There are environments where
it would be useful to be able to reserve resources for a flow on at
least a subset of the flow path even when the sender or the receiver
(or both) is not RSVP-capable.
Since either the data sender or receiver may be unaware of RSVP,
there are two distinct use cases. In the first case, an entity in
the network must operate on behalf of the data sender, generate an
RSVP Path message, and eventually receive, process and sink a Resv
message. We refer to this entity as the RSVP Sender Proxy. In the
latter case, an entity in the network must receive a Path message
sent by a data sender (or by an RSVP Sender Proxy), and reply to it
with a Resv message on behalf of the data receiver(s). We refer to
this entity as the RSVP Receiver Proxy.
RSVP Proxy approaches are presented in
[I-D.ietf-tsvwg-rsvp-proxy-approaches]. That document also
discusses, for each approach, how the reservations controlled by the
RSVP Proxy can be synchronised with the application requirements
(e.g. when to establish, maintain, tear down the RSVP reservation to
satisfy application requirements).
One RSVP Proxy approach is referred to as the Path-Triggered RSVP
Receiver Proxy approach. With this approach, the RSVP Receiver Proxy
uses the RSVP Path messages generated by the sender as the cue for
establishing the RSVP reservation on behalf of the non-RSVP-capable
receiver. The RSVP Receiver Proxy is effectively acting as a slave
making reservations (on behalf of the receiver) under the sender's
control. This changes somewhat the usual RSVP reservation model
where reservations are normally controlled by receivers. Such a
change greatly facilitates operations in the scenario of interest
here, which is where the receiver is not RSVP-capable. Indeed it
allows the RSVP Receiver Proxy to remain application unaware by
taking advantage of the application awareness and RSVP awareness of
the sender.
Since the synchronisation between RSVP reservation and application
requirement is now effectively performed by the sender, it is
important that the sender is aware of the reservation state.
However, as conventional RSVP assumes that the reservation is to be
controlled by the receiver, some notifications about reservation
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state (notably the error message sent in case of admission control
rejection of the reservation) are only sent to the receiver. This
document specifies extension to RSVP procedures allowing such
notifications to be also conveyed to the sender. This facilitates
synchronization by the sender between RSVP reservation and
application requirements in scenarios involving a Path-Triggered RSVP
receiver Proxy.
1.1. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
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2. Terminology
RSVP-capable (or RSVP-aware): which supports the RSVP protocol as per
[RFC2205]
RSVP Receiver Proxy: an RSVP-capable router performing, on behalf of
a receiver, the RSVP operations which would normally be performed by
an RSVP-capable receiver if end-to-end RSVP signaling was used. Note
that while RSVP is used upstream of the RSVP Receiver Proxy, RSVP is
not used downstream of the RSVP Receiver Proxy.
RSVP Sender Proxy: an RSVP-capable router performing, on behalf of a
sender, the RSVP operations which would normally be performed by an
RSVP-capable sender if end-to-end RSVP signaling was used. Note that
while RSVP is used downstream of the RSVP Sender Proxy, RSVP is not
used upstream of the RSVP Sender Proxy.
Regular RSVP Router: an RSVP-capable router which is not behaving as
a RSVP Receiver Proxy nor as a RSVP Sender Proxy.
Note that the roles of RSVP Receiver Proxy, RSVP Sender Proxy,
Regular RSVP Router are all relative to one unidirectional flow. A
given router may act as the RSVP Receiver Proxy for a flow, as the
RSVP Sender Proxy for another flow and as a Regular RSVP router for
yet another flow.
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3. RSVP Extensions for Sender Notification
This section defines extensions to RSVP procedures allowing
notification of the sender of reservation failure. This facilitates
synchronization by the sender between RSVP reservation and
application requirements in scenarios involving a Path-Triggered RSVP
receiver Proxy.
As discussed in [I-D.ietf-tsvwg-rsvp-proxy-approaches], with the
Path-Triggered RSVP Receiver Proxy approach, the RSVP router may be
configured to use receipt of a regular RSVP Path message as the
trigger for RSVP Receiver Proxy behavior. On receipt of the RSVP
Path message, the RSVP Receiver Proxy:
1. establishes the RSVP Path state as per regular RSVP processing
2. identifies the downstream interface towards the receiver
3. sinks the Path message
4. behaves as if a Resv message (whose details are discussed below)
was received on the downstream interface. This includes
performing admission control on the downstream interface,
establishing a Resv state (in case of successful admission
control) and forwarding the Resv message upstream, sending
periodic refreshes of the Resv message and tearing down the
reservation if the Path state is torn down.
Operation of the Path-Triggered Receiver Proxy in the case of a
successful reservation is illustrated in Figure 1.
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|----| *** *** |----------| |----|
| S |---------*r*----------*r*---------| RSVP |----------| R |
|----| *** *** | Receiver | |----|
| Proxy |
|----------|
*************************************************************>
===================RSVP======================>
---Path---> ----Path----> ---Path---->
<--Resv---> <---Resv----- <--Resv----
|----| RSVP-capable |----| Non-RSCP-capable ***
| S | Sender | R | Receiver *r* regular RSVP
|----| |----| *** router
***> media flow
==> segment of flow path protected by RSVP reservation
Figure 1: Successful Reservation
We observe that, in the case of successful reservation, conventional
RSVP procedures ensure that the sender is notified of the successful
reservation establishment. Thus, no extensions are required in the
presence of a Path-Triggered RSVP Receiver Proxy in the case of
succesful reservation establishment.
However, in case of reservation failure, conventional RSVP procedures
only ensure that the receiver (or the RSVP Receiver Proxy) is
notified of the reservation failure. Specifically, in case of an
admission control rejection on a regular RSVP router, a ResvErr
message is sent downstream towards the receiver. In the presence of
an RSVP Receiver Proxy, if we simply follow conventional RSVP
procedures, this means that the RSVP Receiver Proxy is notified of
the reservation failure, but the sender does not. Operation of the
Path-Triggered RSVP Receiver Proxy in the case of an admission
control failure, assuming conventional RSVP procedures, is
illustrated in Figure 2.
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|----| *** *** |----------| |----|
| S |---------*r*----------*r*---------| RSVP |----------| R |
|----| *** *** | Receiver | |----|
| Proxy |
|----------|
*************************************************************>
===================RSVP======================>
---Path---> ----Path----> ---Path---->
<---Resv----- <--Resv------
---ResvErr---> --ResvErr--->
|----| |----| ***
| S | Sender | R | Receiver *r* regular RSVP
|----| |----| *** router
***> media flow
==> segment of flow path protected by RSVP reservation
Figure 2: Reservation Failure With Conventional RSVP
While the sender could infer reservation failure from the fact that
it has not received a Resv message after a certain time, there are
clear benefits in ensuring that the sender gets a prompt explicit
notification in case of reservation failure.
Section 3.1 defines a method which can be used to achieve sender
notification of reservation failure. An implementation of this
document MUST support the method defined in Section 3.1.
3.1. Sender Notification via PathErr Message
With this method, the RSVP Receiver Proxy MUST generate a PathErr
message whenever the two following conditions are met:
1. The reservation establishment has failed (or the previously
established reservation has been torn down)
2. The RSVP Receiver Proxy determines that it cannot re-establish
the reservation (e.g. by adapting its reservation request in
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reaction to the error code provided in the received ResvErr in
accordance with local policy)
Operation of the Path-Triggered RSVP Receiver Proxy in the case of an
admission control failure, using sender notification via PathErr
Message, is illustrated in Figure 3.
|----| *** *** |----------| |----|
| S |---------*r*----------*r*---------| RSVP |----------| R |
|----| *** *** | Receiver | |----|
| Proxy |
|----------|
*************************************************************>
===================RSVP======================>
---Path---> ----Path----> ---Path---->
<---Resv----- <--Resv------
---ResvErr---> --ResvErr--->
<--PathErr- <--PathErr--- <--PathErr---
|----| |----| ***
| S | Sender | R | Receiver *r* regular RSVP
|----| |----| *** router
***> media flow
==> segment of flow path protected by RSVP reservation
Figure 3: Reservation Failure With Sender Notification
The role of this PathErr is to notify the sender that the reservation
was not established or was torn down. This may be in the case of
receipt of a ResvErr, or because of local failure on the Receiver
Proxy. On receipt of a ResvErr, in all situations where the
reservation cannot be installed, the Receiver Proxy MUST generate a
PathErr towards the sender. For local failures on the Receiver Proxy
node, if a similar failure on an RSVP midpoint would cause the
generation of a ResvErr (for example, CAC failure), the Receiver
Proxy MUST generate a PathErr towards the sender. The Receiver Proxy
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MAY additionally generate a PathErr upon local failures which would
not ordinarily cause generation of a ResvErr message, such as
described in Appendix B of [RFC2205]. The PathErr generated by the
Receiver Proxy corresponds to the sender(s) which triggered
generation of Resv messages that failed. For Fixed-Filter (FF) style
reservations, the Receiver Proxy sends a PathErr towards the (single)
sender matching the failed reservation. For Shared-Explicit (SE)
style reservations, the Receiver Proxy sends the PathErr(s) towards
the set of senders which triggered reservations that failed. This
may be a subset of senders sharing the same reservation, in which
case the remaining senders would have their reservation intact and
would not receive a PathErr. In both cases, the rules described in
Section 3.1.8 of [RFC2205] for generating flow descriptors in
ResvErrs, also apply for generating sender descriptors in PathErrs.
For Wildcard-Filter (WF) style reservations, it is not possible for
the receiver to know which sender caused the reservation failure.
Therefore, the procedures described in this section do not apply to
WF-style reservations.
The procedures described in this section apply to both unicast and
multicast sessions. However, for a multicast session, it is possible
that reservation failure (e.g. admission control failure) in a node
close to a sender may cause ResvErr messages to be sent to a large
group of receivers. These receivers would, in turn, all send PathErr
messages back to the same sender, which could cause a scalability
issue in some environments. From the perspective of the sender,
errors that prevent a reservation from being set up can be classified
in two ways:
1. Errors which the sender can attempt to correct. The error code
for those errors should explicitly be communicated back to the
sender. An examples of this is "Class 1: Admission Control
Failure", because the sender could potentially resend a Path with
smaller traffic parameters.
2. Errors which the sender has no control over. For these errors,
it is sufficient to notify the sender that the reservation was
not set up successfully. An example of this is "Class 13:
Unknown Object", because the sender has no control over the
objects inserted into the reservation by the Receiver Proxy.
The PathErr message generated by the Receiver Proxy has the same
format as regular PathErr messages defined in [RFC2205]. The
SESSION, ERROR_SPEC and sender descriptor are composed by the
Receiver Proxy as specified in the following subsections. The
Receiver Proxy MAY reflect back to the sender in the PathErr any
POLICY_DATA objects received in the ResvErr.
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3.1.1. Composition of SESSION and <Sender descriptor>
The Receiver Proxy MUST insert the SESSION object corresponding to
the failed reservation, into the PathErr. For Fixed-Filter (FF)
style reservations, the Receiver Proxy MUST insert a <sender
descriptor> corresponding to the failed reservation, into the
PathErr. This is equal to the <flow descriptor> in the ResvErr
received by the Receiver Proxy. For Shared-Explicit (SE) style
reservations, the Receiver Proxy MUST insert a <sender descriptor>
corresponding to the sender triggering the failed reservation, into
the PathErr. This is equal to the <flow descriptor> in the ResvErr
received by the Receiver Proxy. If multiple <flow descriptors> could
not be admitted at a midpoint node, that node would generate multiple
ResvErrs towards the receiver as per Section 3.1.8 of [RFC2205].
Each ResvErr would contain a <flow descriptor> that matches a
specific sender. The Receiver Proxy MUST generate a PathErr for each
ResvErr received, towards the corresponding sender.
3.1.2. Composition of ERROR_SPEC
The Receiver Proxy MUST compose the ERROR_SPEC to be inserted into
the PathErr as follows:
1. If the Receiver Proxy receives a ResvErr with any of these error
codes: "Code 1 - Admission Control Failure" or "Code 2 - Policy
Control Failure" then the Receiver Proxy copies the error code
and value from the ERROR_SPEC in the ResvErr, into the ERROR_SPEC
of the PathErr message. The error node in the PathErr MUST be
set to the address of the Receiver Proxy. This procedure MUST
also be followed for a local error on the Receiver Proxy that
would ordinarily cause a midpoint to generate a ResvErr with one
of the above codes.
2. If the Receiver Proxy receives a ResvErr with any error code
other than the ones listed in 1. above, it composes a new
ERROR_SPEC with error code "<TBD>: Unrecoverable Receiver Proxy
error" and error value "<TBD>". The error node in the PathErr
MUST be set to the address of the Receiver Proxy. This procedure
MUST also be followed for a local error on the Receiver Proxy
that would ordinarily cause a midpoint to generate a ResvErr with
any error code except in 1) above, or if the Receiver Proxy
generates a PathErr for a local error which ordinarily would not
cause generation of a ResvErr. In some cases it may be
predetermined that the PathErr will not reach the sender. For
example, a node receiving a ResvErr with "Code 3: No Path for
Resv", knows a priori that the PathErr message it generates
cannot be forwarded by the same node which could not process the
Resv. Nevertheless, the procedures above MUST be followed. Use
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of extensions such as the Notify message defined in [RFC3473] may
be investigated in the future to address this issue.
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4. Security Considerations
To be added.
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5. IANA Considerations
This document requires that IANA allocates a new RSVP Error Code
"<TBD>: Unrecoverable Receiver Proxy error" as discussed in
Section 3.1.2.
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6. Acknowledgments
This document benefited from discussions with Carol Iturralde and
Amca Zamfir.
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7. Normative References
[I-D.ietf-tsvwg-rsvp-proxy-approaches]
Le Faucheur, L., "RSVP Proxy Approaches", February 2007.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2205] Braden, B., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205, September 1997.
[RFC3473] Berger, L., "Generalized Multi-Protocol Label Switching
(GMPLS) Signaling Resource ReserVation Protocol-Traffic
Engineering (RSVP-TE) Extensions", RFC 3473, January 2003.
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Authors' Addresses
Francois Le Faucheur
Cisco Systems
Greenside, 400 Avenue de Roumanille
Sophia Antipolis 06410
France
Phone: +33 4 97 23 26 19
Email: flefauch@cisco.com
Jukka Manner
University of Helsinki
P.O. Box 68
University of Helsinki FIN-00014 University of Helsinki
Finland
Phone: +358 9 191 51298
Email: jmanner@cs.helsinki.fi
URI: http://www.cs.helsinki.fi/u/jmanner/
Ashok Narayan
Cisco Systems
300 Beaver Brook Road
Boxborough, MAS 01719
United States
Email: ashokn@cisco.com
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