TSVWG F. Le Faucheur
Internet-Draft Cisco
Intended status: Informational J. Manner
Expires: April 29, 2010 TKK
D. Wing
Cisco
A. Guillou
SFR
October 26, 2009
RSVP Proxy Approaches
draft-ietf-tsvwg-rsvp-proxy-approaches-08.txt
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Abstract
The Resource ReSerVation Protocol (RSVP) can be used to make end-to-
end resource reservations in an IP network in order to guarantee the
quality of service required by certain flows. RSVP assumes that both
the data sender and receiver of a given flow take part in RSVP
signaling. Yet, there are use cases where resource reservation is
required, but the receiver, the sender, or both, is not RSVP-capable.
This document presents RSVP Proxy behaviors allowing RSVP routers to
initiate or terminate RSVP signaling on behalf of a receiver or a
sender that is not RSVP-capable. This allows resource reservations
to be established on a critical subset of the end-to-end path. This
document reviews conceptual approaches for deploying RSVP Proxies and
discusses how RSVP reservations can be synchronized with application
requirements, despite the sender, receiver, or both not participating
in RSVP. This document also points out where extensions to RSVP (or
to other protocols) may be needed for deployment of a given RSVP
Proxy approach. However, such extensions are outside the scope of
this document. Finally, practical use cases for RSVP Proxy are
described.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. RSVP Proxy Behaviors . . . . . . . . . . . . . . . . . . . . . 6
2.1. RSVP Receiver Proxy . . . . . . . . . . . . . . . . . . . 6
2.2. RSVP Sender Proxy . . . . . . . . . . . . . . . . . . . . 7
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 8
4. RSVP Proxy Approaches . . . . . . . . . . . . . . . . . . . . 9
4.1. Path-Triggered Receiver Proxy . . . . . . . . . . . . . . 9
4.1.1. Mechanisms for Maximizing the Reservation Span . . . . 12
4.2. Path-Triggered Sender Proxy for Reverse Direction . . . . 15
4.3. Inspection-Triggered Proxy . . . . . . . . . . . . . . . . 18
4.4. STUN-Triggered Proxy . . . . . . . . . . . . . . . . . . . 21
4.5. Application_Entity-Controlled Proxy . . . . . . . . . . . 23
4.5.1. Application_Entity-Controlled Sender Proxy using
"RSVP over GRE" . . . . . . . . . . . . . . . . . . . 26
4.5.2. Application_Entity-Controlled Proxy via Co-Location . 28
4.6. Policy_Server-Controlled Proxy . . . . . . . . . . . . . . 29
4.7. RSVP-Signaling-Triggered Proxy . . . . . . . . . . . . . . 32
4.8. Reachability Considerations . . . . . . . . . . . . . . . 33
5. Security Considerations . . . . . . . . . . . . . . . . . . . 34
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 36
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 36
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 36
8.1. Normative References . . . . . . . . . . . . . . . . . . . 36
8.2. Informative References . . . . . . . . . . . . . . . . . . 37
Appendix A. Use Cases for RSVP Proxies . . . . . . . . . . . . . 39
A.1. RSVP-based VoD Admission Control in Broadband
Aggregation Networks . . . . . . . . . . . . . . . . . . . 39
A.2. RSVP-based Voice/Video CAC in Enterprise WAN . . . . . . . 43
A.3. RSVP Proxies for Mobile Access Networks . . . . . . . . . 44
A.4. RSVP Proxies for Reservations in the presence of IPsec
Gateways . . . . . . . . . . . . . . . . . . . . . . . . . 46
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 49
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1. Introduction
Guaranteed Quality of Service (QoS) for some applications with tight
requirements (such as voice or video) 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 (for example from the sender to the network edge,
or from edge to edge, or from the network edge to the receiver).
Since the data sender or receiver may be unaware of RSVP, there are
two types of RSVP Proxies. When the sender is not using RSVP, an
entity in the network must operate on behalf of the data sender, and
in particular, generate RSVP Path messages, and eventually receive,
process and sink Resv messages. We refer to this entity as the RSVP
Sender Proxy. When the receiver is not using RSVP, an entity in the
network must receive Path messages sent by a data sender (or by an
RSVP Sender Proxy), sink those, and return Resv messages on behalf of
the data receiver(s). We refer to this entity as the RSVP Receiver
Proxy. The RSVP Proxies need to be on the data path in order to
establish the RSVP reservation; Note, however, that some of the
approaches described in this document allow the RSVP Proxies to be
controlled/triggered by an off-path entity.
The flow sender and receiver generally have at least some (if not
full) awareness of the application producing or consuming that flow.
Hence, the sender and receiver are in a natural position to
synchronize the establishment, maintenance and tear down of the RSVP
reservation with the application requirements. Similarly they are in
a natural position to determine the characteristics of the
reservation (bandwidth, QoS service,...) which best match the
application requirements. For example, before completing the
establishment of a multimedia session, the endpoints may decide to
establish RSVP reservations for the corresponding flows. Similarly,
when the multimedia session is torn down, the endpoints may decide to
tear down the corresponding RSVP reservations. For instance,
[RFC3312] discusses how RSVP reservations can be very tightly
synchronized by endpoints that uses the [RFC3261] Session Initiation
Protocol (SIP) for session control.
When RSVP reservation establishment, maintenance and tearing down is
to be handled by RSVP Proxies on behalf of an RSVP sender or
receiver, a key challenge for the RSVP Proxy is to determine when the
RSVP reservations need to be established, maintained and torn down
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and to determine what are the characteristics (bandwidth, QoS
Service,...) of the required RSVP reservations matching the
application requirements. We refer to this problem as the
synchronization of RSVP reservations with application level
requirements.
The IETF Next Steps in Signaling (NSIS) working group is specifying a
new QoS signaling protocol: the QoS NSIS Signaling Layer Protocol
(NSLP) ([I-D.ietf-nsis-qos-nslp]). This protocol also includes the
notion of proxy operation, and terminating QoS signaling on nodes
that are not the actual data senders or receivers (see section "4.8
Proxy Mode" of [I-D.ietf-nsis-qos-nslp]. This is the same concept as
the proxy operation for RSVP discussed in this document. One
difference though is that the NSIS framework does not consider
multicast resource reservations, which RSVP provides today.
Section 2 introduces the notion of RSVP Sender Proxy and RSVP
Receiver Proxy. Section 3 defines useful terminology. Section 4
then presents several fundamental RSVP Proxy approaches discussing
how they achieve the necessary synchronization of RSVP reservations
with application level requirements. Appendix A includes more
detailed use cases for the proxies in various real life deployment
environments.
It is important to keep in mind that the strongly recommended RSVP
deployment model remains end to end as assumed in [RFC2205] with RSVP
support on the sender and the receiver. The end to end model allows
the most effective synchronization between the reservation and
application requirements. Also, when compared to the end to end RSVP
model, the use of RSVP Proxies involves additional operational burden
and/or impose some topological constraints. The additional
operational burden comes in particular from additional configuration
needed to activate the RSVP Proxies and to help them identify for
which senders/receivers a Proxy behavior is required and for which
senders/receivers it is not (so that an RSVP Proxy does not perform
establishment of reservations on behalf of devices that are capable
of doing so themselves but would then be prevented -without
notification- from doing so by the RSVP Proxy). The additional
topological constraints come in particular from the requirement to
have one RSVP Receiver Proxy on the path from any sender to every
non-RSVP capable device (so that a non-RSVP capable device is always
taken care of by an RSVP Proxy) and the objective to have only one
such Receiver Proxy on the path from any sender to every non-RSVP
capable device (so that an RSVP Receiver Proxy does not short-circuit
another RSVP Receiver Proxy closer to the non-RSVP capable device,
thereby reducing the span of the RSVP reservation and the associated
benefits). In the case of the Path-triggered Receiver Proxy
approach, the operational burden and topological constraints can be
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significantly alleviated using the mechanisms discussed in
Section 4.1.1.
It is also worth noting that RSVP operations on endsystems is
considerably simpler than on a router, and consequently that RSVP
implementations on endsystems are very lightweight (particularly
considering modern endsystems capabilities, including mobile and
portable devices). For example, endsystem RSVP implementations are
reported to only consume low tens of kilobytes of code space. Hence,
the present document should not be seen as an encouragement to depart
from the end to end RSVP model. Its purpose is only to allow RSVP
deployment in special environments where RSVP just cannot be used on
some senders and/or some receivers for reasons specific to the
environment.
2. RSVP Proxy Behaviors
This section discusses the two types of proxies; the RSVP Sender
Proxy operating on behalf of data senders, and the RSVP Receiver
Proxy operating for data receivers. The concepts presented in this
document are not meant to deprecate the traditional [RFC2205] RSVP
end-to-end model: end-to-end RSVP reservations are still expected to
be used whenever possible. However, RSVP Proxies are intended to
facilitate RSVP deployment where end-to-end RSVP signaling is not
possible.
2.1. RSVP Receiver Proxy
With conventional end-to-end RSVP operations, RSVP reservations are
controlled by receivers of data. After a data sender has sent an
RSVP Path message towards the intended recipient(s), each recipient
that requires a reservation generates a Resv message. If, however, a
data receiver is not running the RSVP protocol, the last hop RSVP
router will still send the Path message to the data receiver, which
will silently drop this message as an IP packet with an unknown
protocol number.
In order for reservations to be made in such a scenario, one of the
RSVP routers on the data path determines that the data receiver will
not be participating in the resource reservation signaling and
performs RSVP Receiver Proxy functionality on behalf of the data
receiver. This is illustrated in Figure 1. Various mechanisms by
which the RSVP proxy router can gain the required information are
discussed later in the document.
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|----| *** *** |----------| |----|
| S |---------*r*----------*r*---------| RSVP |----------| R |
|----| *** *** | Receiver | |----|
| Proxy |
|----------|
===================RSVP==============>
***********************************************************>
|----| RSVP-capable |----| non-RSVP-capable ***
| S | Sender | R | Receiver *r* regular RSVP
|----| |----| *** router
***> unidirectional media flow
==> segment of flow path protected by RSVP reservation
Figure 1: RSVP Receiver Proxy
2.2. RSVP Sender Proxy
With conventional end-to-end RSVP operations, if a data sender is not
running the RSVP protocol, a resource reservation can not be set up;
a data receiver can not alone reserve resources without Path messages
first being received. Thus, even if the data receiver is running
RSVP, it still needs some node on the data path to send a Path
message towards the data receiver.
In that case, an RSVP node on the data path determines that it should
generate Path messages to allow the receiver to set up the resource
reservation. This node is referred to as the RSVP Sender Proxy and
is illustrated in Figure 2. This case presents additional challenges
over the Receiver Proxy case, since the RSVP Sender Proxy must be
able to generate all the information in the Path message (such as the
Sender TSpec) without the benefit of having previously received any
RSVP message. An RSVP Receiver Proxy, by contrast only needs to
formulate an appropriate Resv message in response to an incoming Path
message. Mechanisms to operate an RSVP Sender Proxy are discussed
later in this document.
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|----| |----------| *** *** |----|
| S |---------| RSVP |---------*r*----------*r*----------| R |
|----| | Sender | *** *** |----|
| Proxy |
|----------|
================RSVP==================>
***********************************************************>
|----| non-RSVP-capable |----| RSVP-capable ***
| S | Sender | R | Receiver *r* regular RSVP
|----| |----| *** router
***> unidirectional media flow
==> segment of flow path protected by RSVP reservation
Figure 2: RSVP Sender Proxy
3. Terminology
o On-Path: located on the datapath of the actual flow of application
data (regardless of where it is located with respect to the
application level signaling path).
o Off-Path: not On-Path.
o RSVP-capable (or RSVP-aware): which supports the RSVP protocol as
per [RFC2205].
o 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.
o 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.
o Regular RSVP Router: an RSVP-capable router which is not behaving
as a RSVP Receiver Proxy nor as a RSVP Sender Proxy.
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o Application level signaling: signaling between entities operating
above the IP layer and which are aware of the QoS requirements for
actual media flows. SIP ([RFC3261]) and RTSP ([RFC2326]) are
examples of application level signaling protocol. SDP ([RFC4566])
is an example of session description protocol that can be used by
the application level signaling protocol and from which some of
the RSVP reservation parameters (addresses, ports and bandwidth)
might be derived. RSVP is clearly not an application level
signaling.
The roles of RSVP Receiver Proxy, RSVP Sender Proxy, Regular RSVP
Router are all relative to a given 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.
Some application level signaling protocols support negotiation of QoS
reservations for a media stream. For example, with [RFC3312],
resource reservation requirements are explicitly signaled during
session establishment using SIP and SDP. Also, [RFC5432] defines a
mechanism to negotiate which resource reservation mechanism is to be
used for a particular media stream. Clearly, these reservation
negotiation mechanisms can be invoked and operate effectively when
both ends support RSVP (and obviously RSVP Proxies are not used).
When both ends do not support RSVP (and RSVP proxies are used at both
ends) these mechanisms will simply not be invoked. In the case where
one end supports RSVP and the other does not (and is helped by an
RSVP Proxy), the application level signaling entity supporting the
non RSVP capable end might use the reservation negotiation mechanisms
in such a way that the non RSVP capable end (helped by an RSVP Proxy)
appears to the remote end as an RSVP capable device. This will
ensure that the RSVP capable end is not discouraged to use RSVP
because the remote end is not RSVP capable. In the case of SIP, the
application level entity may achieve this by taking advantage of the
"segmented" Status Type of [RFC3312] and/or by taking advantage of a
SIP [RFC3261] Back-to-Back User Agent (B2BUA).
4. RSVP Proxy Approaches
This section discusses fundamental RSVP Proxy approaches.
4.1. Path-Triggered Receiver Proxy
In this approach, it is assumed that the sender is RSVP capable and
takes full care of the synchronization between application
requirements and RSVP reservations. With this approach, the RSVP
Receiver Proxy uses the RSVP Path messages generated by the sender as
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the cue for establishing the RSVP reservation on behalf of the
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.
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.
In order to build the Resv message, the RSVP Receiver Proxy can take
into account information received in the Path message. For example,
the RSVP Receiver Proxy may compose a FLOWSPEC object for the Resv
message which mirrors the SENDER_TSPEC object in the received Path
message (as an RSVP-capable receiver would typically do).
Operation of the Path-Triggered Receiver Proxy in the case of a
successful reservation is illustrated in Figure 3.
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|----| *** *** |----------| |----|
| S |---------*r*----------*r*---------| RSVP |----------| R |
|----| *** *** | Receiver | |----|
| Proxy |
|----------|
---Path---> ----Path----> ---Path---->
<--Resv---> <---Resv----- <--Resv----
==================RSVP===============>
**********************************************************>
|----| RSVP-capable |----| Non-RSVP-capable ***
| S | Sender | R | Receiver *r* regular RSVP
|----| |----| *** router
***> media flow
==> segment of flow path protected by RSVP reservation
Figure 3: Path-Triggered RSVP Receiver Proxy
In case the reservation establishment is rejected (for example
because of an admission control failure on a regular RSVP router on
the path between the RSVP-capable sender and the RSVP Receiver
Proxy), a ResvErr message will be generated as per conventional RSVP
operations and will travel downstream towards the RSVP Receiver
Proxy. While this ensures that the RSVP Receiver Proxy is aware of
the reservation failure, conventional RSVP procedures do not cater
for notification of the sender of the reservation failure. Operation
of the Path-Triggered RSVP Receiver Proxy in the case of an admission
control failure is illustrated in Figure 4.
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|----| *** *** |----------| |----|
| S |---------*r*----------*r*---------| RSVP |----------| R |
|----| *** *** | Receiver | |----|
| Proxy |
|----------|
---Path---> ----Path----> ---Path---->
<---Resv----- <--Resv------
---ResvErr---> --ResvErr--->
===================RSVP===============>
**********************************************************>
|----| RSVP-capable |----| Non-RSVP-capable ***
| S | Sender | R | Receiver *r* regular RSVP
|----| |----| *** router
***> media flow
==> segment of flow path protected by RSVP reservation
Figure 4: Path-Triggered RSVP Receiver Proxy with Failure
Since, as explained above, in this scenario involving the RSVP
Receiver Proxy, synchronization between application and RSVP
reservation is generally performed by the sender, notifying the
sender of reservation failure is needed.
[I-D.ietf-tsvwg-rsvp-proxy-proto] specifies RSVP extensions allowing
such sender notification in case of reservation failure in the
presence of a Path-Triggered RSVP Receiver Proxy.
4.1.1. Mechanisms for Maximizing the Reservation Span
The presence in the flow path of a Path-triggered RSVP Receiver Proxy
(for a given flow) that strictly behaves as described previously
would cause the Path message to be terminated and a Resv message to
be generated towards the sender. When the receiver is indeed not
RSVP capable and there is no other RSVP Receiver Proxy downstream on
the flow path, this achieves the best achievable result of
establishing an RSVP reservation as far downstream as the RSVP
Receiver Proxy.
However, if the eventual receiver was in fact RSVP capable, it would
be prevented from participating in RSVP signalling since it does not
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receive any Path message. As a result, the RSVP reservation would
only span a subset of the path it could actually span. A similar
suboptimality would exist with multiple Receiver Proxies in the path
of the flow: the first Receiver Proxy may prevent the Path message
from reaching the second one and therefore prevent the reservation
from extending down to the second Receiver Proxy.
It is desirable that, in the presence of Path-triggered RSVP Receiver
Proxies and of a mix of RSVP-capable and non-RSVP-capable receivers,
the RSVP reservation spans as much of the flow path as possible.
This can be achieved dynamically (avoiding tedious specific
configuration), using the mechanisms described in Section 4.1.1.1 and
in Section 4.1.1.2.
4.1.1.1. Dynamic Discovery of Downstream RSVP Functionality
When generating a proxy Resv message upstream, a Receiver Proxy may
be configured to perform dynamic discovery of downstream RSVP
functionality. To that end, when generating the proxy Resv message
upstream, the Receiver Proxy forwards the Path message downstream
instead of terminating it. This allows an RSVP capable receiver (or
a downstream Receiver Proxy) to respond to the Path with an upstream
Resv message. On receipt of a Resv message, the Receiver Proxy
internally converts its state from a proxied reservation to a regular
midpoint RSVP behavior. From then on, everything proceeds as if the
RSVP router had behaved as a regular RSVP router at reservation
establishment (as opposed to having behaved as an RSVP receiver proxy
for that flow).
The RSVP Receiver Proxy behavior for dynamic discovery of downstream
RSVP functionality is also discussed in section 4.1 of
[I-D.ietf-tsvwg-rsvp-proxy-proto].
This dynamic discovery mechanism has the benefit that new (or
upgraded) RSVP endpoints will automatically and seamlessly be able to
take advantage of end-to-end reservations, without impacting the
ability of a Receiver Proxy to proxy RSVP for other, non-RSVP-capable
endpoints. This mechanism also achieves the goal of automatically
discovering the longest possible RSVP-supporting segment in a network
with multiple Receiver Proxies along the path. This mechanism
dynamically adjusts to any topology and routing change. Also, this
mechanism dynamically handles the situation where a receiver was
RSVP-capable and for some reason (e.g. Software downgrade) no longer
is. Finally, this approach requires no new RSVP protocol extensions
and no configuration changes to the Receiver Proxy as new RSVP-
capable endpoints come and go.
The only identified drawbacks to this approach are:
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o If admission control fails on the segment between the Receiver
Proxy and the RSVP-capable receiver, the receiver will get a
ResvError and can take application-level signalling steps to
terminate the call. However, the receiver proxy has already sent
a Resv upstream for this flow, so the sender will see a "false"
reservation which is not truly end-to-end. The actual admission
control status will resolve itself in a short while, but the
sender will need to roll back any permanent action (such as
billing) that may have been taken on receipt of the phantom Resv.
Note that if the second receiver is also a Receiver Proxy which is
not participating in application signalling, it will convert the
received ResvError into a PathError which will be received by the
sender.
o If there is no RSVP-capable receiver (or other Receiver Proxy)
downstream of the Receiver Proxy, then the Path messages sent by
the Receiver Proxy every RSVP refresh interval (e.g. 30 seconds by
default) will never be responded to. However, these messages
consume a small amount of bandwidth, and in addition would install
some RSVP state on RSVP-capable midpoint nodes downstream of the
first Receiver Proxy. This is seen as a very minor sub-
optimality. We also observe that such resources would be consumed
anyways if the receiver was RSVP capable. Still, if deemed
necessary, to mitigate this, the receiver proxy can tear down any
unanswered downstream Path state after a predetermined time, and
stop sending Path messages for the flow (or only send them at much
lower frequency).
4.1.1.2. Selective Receiver Proxy and Sender Control of Receiver Proxy
An RSVP Receiver Proxy can be selective about the sessions that it
terminates, based on local policy decision. For example, an edge
router functioning as a Receiver Proxy may behave as a proxy only for
Path messages that are actually going to exit the domain in question,
not for Path messages that are transiting through it but stay within
the domain. As another example, the receiver proxy may be
configurable to only proxy for flows addressed to a given destination
address or destination address ranges (for which end devices are
known to not be RSVP capable).
The decision to proxy a Resv for a Path may also be based on
information signalled from the sender in the Path message. For
example, the sender may identify the type of application or flow in
the Application Identity Policy Element ([RFC2872]) in the Path, and
the Receiver Proxy may be configured to proxy for only certain types
of flows. Or, if the sender knows (for example through application
signalling) that the receiver is RSVP capable, the sender can include
an indication in a Policy Element to any Receiver Proxy that it ought
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not to terminate the Path (or conversely, if the receiver is known
not to support RSVP, the sender could include an indication to
Receiver Proxies that they ought to generate a proxy Resv message).
The Receiver Proxy Control Policy Element specified in section 4.2 of
[I-D.ietf-tsvwg-rsvp-proxy-proto] can be used for that purpose.
4.2. Path-Triggered Sender Proxy for Reverse Direction
In this approach, it is assumed that one endpoint is RSVP capable and
takes full care of the synchronization between application
requirements and RSVP reservations. This endpoint is the sender for
one flow direction (which we refer to as the "forward" direction) and
is the receiver for the flow in the opposite direction (which we
refer to as the "reverse" direction).
With the Path-Triggered Sender Proxy for Reverse Direction approach,
the RSVP Proxy uses the RSVP signaling generated by the receiver (for
the reverse direction) as the cue for initiating RSVP signaling for
the reservation in the reverse direction. More precisely, the RSVP
Proxy can take the creation (respectively, maintenance and teardown)
of a Path state by the receiver as the cue to create (respectively,
maintain and teardown) a Path state towards the receiver. Thus, the
RSVP Proxy is effectively acting as a Sender Proxy for the reverse
direction under the control of the receiver (for the reverse
direction). Note that this assumes a degree of symmetry for example
in terms of bandwidth for the two directions of the flow (as is
currently typical for IP telephony, for example).
The signaling flow for the Path-Triggered Sender Proxy for Reverse
Direction is illustrated in Figure 5.
Path messages generated by the receiver need to transit via the RSVP
Sender Proxy that is on the path from the sender to the receiver. In
some topologies, this will always be the case: for example where the
sender is on a stub network hanging off the RSVP Sender Proxy or
where there is no asymmetric routing (such that if a RSVP Sender
Proxy is on the path from receiver to sender, then it is also on the
path from sender to receiver). In some topologies (such as those
involving asymmetric routing), this may not always happen naturally.
Measures to ensure this does happen in these topologies are outside
the scope of this document.
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|----| *** *** |----------| |----|
| R |---------*r*----------*r*---------| RSVP |----------| S |
|----| *** *** | Sender | |----|
| Proxy |
|----------|
---Path---> ----Path----> ---Path---->
<--Path---> <---Path----- <--Path----
---Resv---> ----Resv----> ---Resv---->
<================RSVP==================
<**********************************************************
|----| RSVP-capable |----| Non-RSVP-capable ***
| R | Receiver for | S | Sender for *r* regular RSVP
|----| reverse direction |----| reverse direction *** router
***> media flow
==> segment of flow path protected by RSVP reservation
in reverse direction
Figure 5: Path-Triggered Sender Proxy for Reverse Direction
Of course, the RSVP Proxy may simultaneously (and typically will)
also act as the Path-Triggered Receiver Proxy for the forward
direction, as defined in Section 4.1. Such an approach is most
useful in situations involving RSVP reservations in both directions
for symmetric flows. This is illustrated in Figure 6.
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|----| *** *** |----------| |----|
|S/R |---------*r*----------*r*---------| RSVP |----------|S/R&|
|----| *** *** | Receiver | |----|
| & Sender |
| Proxy |
|----------|
---Path---> ----Path----> ---Path---->
<--Resv---> <---Resv----- <--Resv----
<--Path---> <---Path----- <--Path----
---Resv---> ----Resv----> ---Resv---->
================RSVP==================>
<================RSVP==================
**********************************************************>
<**********************************************************
|----| RSVP-capable |----| Non-RSVP-capable ***
|S/R | Sender and |S/R&| Sender and *r* regular RSVP
|----| Receiver |----| Receiver *** router
***> media flow
==> segment of flow path protected by RSVP reservation
in forward and in reverse direction
Figure 6: Path Triggered Receiver & Sender Proxy
With the Path-Triggered Sender Proxy for Reverse Direction approach,
the RSVP router may be configurable to use receipt of a regular RSVP
Path message as the trigger for Sender Proxy for Reverse Direction
behavior.
On receipt of the RSVP Path message for the forward direction, the
RSVP Sender Receiver Proxy :
1. sinks the Path message
2. behaves as if a Path message for reverse direction (whose details
are discussed below) had been received by the Sender Proxy. This
includes establishing the corresponding Path state, forwarding
the Path message downstream, sending periodic refreshes of the
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Path message and tearing down the Path in reverse direction when
the Path state in forward direction is torn down.
In order to build the Path message for the reverse direction, the
RSVP Sender Proxy can take into account information in the received
Path message for the forward direction. For example, the RSVP Sender
Proxy may mirror the SENDER_TSPEC object in the received Path
message.
We observe that this approach does not require any extensions to the
existing RSVP protocol.
In the case where reservations are required in both directions (as
shown in Figure 6), the RSVP-capable device simply needs to behave as
a regular RSVP sender and RSVP receiver. It needs not be aware that
an RSVP Proxy happens to be used and the Path message it sent for the
forward reservation also acts as the trigger for establishment of the
reverse reservation. However, in the case where a reservation is
only required in the reverse direction (as shown in Figure 5), the
RSVP-capable device has to generate Path messages in order to trigger
the reverse direction reservation even if no reservation is required
in the forward direction. Although this is not in violation with
[RFC2205], it may not be the default behavior of an RSVP-capable
device and therefore may need a behavioral change specifically to
facilitate operation of the Path-Triggered Sender Proxy for Reverse
Direction.
4.3. Inspection-Triggered Proxy
In this approach, it is assumed that the RSVP Proxy is on the
datapath of "packets of interest", that it can inspect such packets
on the fly as they transit through it, and that it can infer
information from these packets of interest to determine what RSVP
reservations need to be established, when and with what
characteristics (possibly also using some configured information).
One example of "packets of interest" could be application level
signaling. An RSVP Proxy capable of inspecting SIP signaling for
multimedia session or RTSP signaling for Video streaming, can obtain
from such signaling information about when a multimedia session is up
or when a Video is going to be streamed. It can also identify the
addresses and ports of senders and receivers and can determine the
bandwidth of the corresponding flows. It can also determine when the
reservation is no longer needed and tear it down. Thus, such an RSVP
Proxy can determine all necessary information to synchronize RSVP
reservations to application requirements. This is illustrated in
Figure 7.
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|-------------|
| Application |
| Signaling |
| Entity |
|-------------|
/ \
/ \
/ \
</////////////////////// \\\\\\\\\\\\\\\\\\\\\\\\>
|----| |--------| *** |--------| |----|
| S |--------| RSVP |------*r*--------| RSVP |----------| R |
|----| | Proxy | *** | Proxy | |----|
|--------| |--------|
=======RSVP=======>
********************************************************>
|----| Non-RSVP-capable |----| Non-RSVP-capable ***
| S | Sender | R | Receiver *r* regular RSVP
|----| |----| *** router
</\> application level signaling
***> media flow
==> segment of flow path protected by RSVP reservation
Figure 7: Inspection-Triggered RSVP Proxy
Another example of "packets of interest" could be transport control
messages (e.g. RTCP [RFC3550]) traveling alongside the application
flow itself (i.e. Media packets). An RSVP Proxy capable of
detecting the transit of packets from a particular flow, can attempt
to establish a reservation corresponding to that flow.
Characteristics of the reservation may be derived by various methods
such as from configuration, flow measurement or a combination of
those. However, these methods usually come with their respective
operational drawbacks: configuration involves an operational cost and
may hinder introduction of new applications, measurement is reactive
so that accurate reservation may lag actual traffic.
In case of reservation failure, the inspection-triggered RSVP Proxy
does not have a direct mechanism for notifying the application (since
it is not participating itself actively in application signaling) so
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that the application is not in a position to take appropriate action
(for example terminate the corresponding session). To mitigate this
problem, the inspection-triggered RSVP Proxy may mark differently the
Differentiated Services codepoint (DSCP) ([RFC2474]) of flows for
which an RSVP reservation has been successfully proxied from the
flows for which a reservation is not in place. In some situations,
the Inspection-Triggered Proxy might be able to modify the "packets
of interest" (e.g. Application signaling messages) to convey some
hint to applications that the corresponding flows cannot be
guaranteed by RSVP reservations.
With the inspection-triggered Proxy approach, the RSVP Proxy is
effectively required to attempt to build application awareness by
traffic inspection and then is somewhat limited in the actions it can
take in case of reservation failure. Depending on the "packets of
interest" used by the RSVP Proxy to trigger the reservation, there is
a risk that the RSVP Proxy ends up establishing a reservation for a
media flow that actually never starts. However, this can be
mitigated by timing out and tearing down of an unnecessary
reservation by the RSVP Proxy when no corresponding media flow is
observed. This flow observation and time out approach can also be
used to tear down reservation that were rightfully established for a
flow but are no longer needed because the flow stopped.
The inspection-triggered approach is also subject to the general
limitations associated with data inspection. This includes being
impeded by encryption or tunnelling, or being dependent on some
topology constraints such as relying on the fact that both the
packets of interest and the corresponding flow packets always transit
through the same RSVP Proxy.
Nonetheless, this may be a useful approach in specific environments.
Note also that this approach does not require any change to the RSVP
protocol.
With the "Inspection-Triggered" RSVP Proxy approach, the RSVP router
may be configurable to use and interpret some specific "packets of
interest" as the trigger for RSVP Receiver Proxy behavior.
When operating off signaling traffic, the "Inspection-Triggered" RSVP
Proxy may be able to detect from the signaling that the endpoint is
capable of establishing an RSVP reservation (e.g. In the case of SIP
via inspection of the [RFC3312]/[RFC4032] Precondition), in which
case it would not behave as a Proxy for that endpoint . Also, the
"Inspection-Triggered" RSVP proxy may inspect RSVP signaling and if
it sees RSVP signaling for the flow of interest, it can disable its
sender proxy behavior for that flow (or that sender). Optionally,
through RSVP signaling inspection, the sender proxy might also
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gradually "learn" (possibly with some timeout) which sender is RSVP
capable of not. These mechanisms can facilitate gradual and dynamic
migration from the Proxy model towards the end-to-end RSVP model as
more and more endpoints become RSVP capable.
4.4. STUN-Triggered Proxy
In this approach, the RSVP Proxy takes advantage of the application
awareness provided by the STUN ([RFC5389]) signaling to synchronize
RSVP reservations with application requirements. The STUN signaling
is sent from endpoint to endpoint. This is illustrated in Figure 8.
In this approach, a STUN message triggers the RSVP Proxy.
|----| |--------| *** |--------| |----|
| S |--------| RSVP |------*r*--------| RSVP |----------| R |
|----| | Proxy | *** | Proxy | |----|
|--------| |--------|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^>
=======RSVP=======>
********************************************************>
|----| Non-RSVP-capable |----| Non-RSVP-capable ***
| S | Sender | R | Receiver *r* regular RSVP
|----| |----| *** router
^^^> STUN message flow (over same UDP ports as media flow)
==> segment of flow path protected by RSVP reservation
***> RTP media flow
Figure 8: STUN-Triggered Proxy
For unicast flows, [I-D.ietf-mmusic-ice] is a widely-adopted approach
for NAT traversal. For our purposes of triggering RSVP Proxy
behavior, we rely on ICE's connectivity check which is based on the
exchange of STUN Binding Request messages between hosts to verify
connectivity (see section 2.2 of [I-D.ietf-mmusic-ice]). The STUN
message could also include (yet to be specified) STUN attributes to
indicate information such as the bandwidth and application requesting
the flow, which would allow the RSVP proxy agent to create an
appropriately-sized reservation for each flow. Including such new
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STUN attributes in the ICE connectivity check messages would
facilitates operation of the RSVP Proxy. To ensure RSVP reservations
are only established when needed, the RSVP Proxy needs to
distinguish, among all the STUN messages, the ones that reflect (with
high likelihood) an actual upcoming media flow. This can be achieved
by identifying the STUN messages associated with an ICE connectivity
check. In turn, this can be achieved through (some combination of)
the following checks:
o if, as discussed above, new STUN attributes (e.g. Conveying the
flow bandwidth) are indeed defined in the future in view of
facilitating STUN-Triggered reservations, then the presence of
these attributes would reveal that the STUN message is part of an
ICE connectivity check.
o the presence of the PRIORITY, USE-CANDIDATE, ICE-CONTROLLED or
ICE-CONTROLLING attributes reveals that the STUN message is part
of an ICE connectivity check
o the RSVP Proxy may wait for a STUN message containing the USE-
CANDIDATE attribute indicating the selected ICE "path" to trigger
reservation only for the selected "path". This allows the RSVP
Proxy to only trigger a reservation for the "path" actually
selected and therefore for the media flow that will actually be
established (for example when ICE is being used for v4/v6 path
selection).
o the RSVP Proxy configuration could contain some information
facilitating determination of when to perform RSVP Proxy
reservation and not. For example, the RSVP Proxy configuration
could contain the IP addresses of the STUN servers such that STUN
messages to/from those addresses are known to not be part of an
ICE connectivity check. As another example, the RSVP Proxy
configuration could contain information identifying the set of
Differentiated Services codepoint (DSCP) values that the media
flows requiring reservation use, so that STUN messages not using
one of these DSCP values are known to not be part of an ICE
connectivity check.
Despite these checks, there is always a potential risk that the RSVP
Proxy ends up establishing a reservation for a media flow that
actually never starts. However, this is limited to situations where
the end-systems is interested enough in establishing connectivity for
a flow but yet never transmit. Also, this can be mitigated by timing
out and tear down of an unnecessary reservations by the RSVP Proxy
when no corresponding media flow is observed.
The RSVP Proxy agent can inform endpoints of an RSVP reservation
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failure implicitly by dropping the ICE connectivity check message or
explicitly by sending ICMP messages back to the endpoint. This
allows reasonably effective synchronisation between RSVP reservations
handled by the RSVP Proxies and the application running on non RSVP-
capable endpoints. It also has the benefits of operating through
NATs.
For multicast flows (or certain kinds of unicast flows that don't or
can't use ICE), a STUN Indication message [RFC5389] could be used to
carry the (yet to be defined) STUN attributes mentioned earlier to
indicate the flow bandwidth, thereby providing a benefit similar to
the ICE connectivity check. STUN Indication messages are not
acknowledged by the receiver and have the same scalability as the
underlying multicast flow.
The corresponding extensions to ICE and STUN for such a STUN-
triggered RSVP Proxy approach are beyond the scope of this document.
They may be defined in the future in a separate document. As the
STUN-triggered RSVP Proxy approach uses STUN in a way (i.e. To
trigger reservations) that is beyond its initial intended purpose,
the potential security implications need to be considered by the
operator.
ICE connectivity checks is not always used for all flows. When the
STUN-triggered RSVP Proxy approach is used, it can establish RSVP
reservations for flows for which ICE connectivity is performed.
However, the STUN-triggered RSVP Proxy will not establish a
reservation for flows for which ICE connectivity check is not
performed. Those flows will either not benefit from an RSVP
reservation or can benefit from an RSVP reservation established
through other means (end-to-end RSVP, other forms of RSVP Proxy).
The STUN-triggered approach relies on interception and inspection of
STUN messages. Thus, this approach may be impeded by encryption or
tunneling.
4.5. Application_Entity-Controlled Proxy
In this approach, it is assumed that an entity involved in the
application level signaling controls an RSVP Proxy which is located
in the datapath of the application flows (i.e. "on-path"). With this
approach, the RSVP Proxy does not attempt to determine itself the
application reservation requirements. Instead the RSVP Proxy is
instructed by the entity participating in application level signaling
to establish, maintain and tear down reservations as needed by the
application flows. In other words, with this approach, the solution
for synchronizing RSVP signaling with application level requirements
is to rely on an application-level signaling entity that controls an
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RSVP Proxy function that sits in the flow datapath. This approach
allows control of an RSVP Sender Proxy, an RSVP Receiver Proxy or
both.
Operation of the Application_Entity-Controlled Proxy is illustrated
in Figure 9.
|---------| |---------|
/////////| App |////\\\\| App |\\\\\\\\
/ | Entity | | Entity | \
/ |---------| |---------| \
/ // \\ \
/ // \\ \
/ // \\ \
/ // \\ \
/ // \\ \
|----| |--------| *** |---------| |----|
| S |----------| |------*r*-------| |---------| R |
|----| | RSVP | *** | RSVP | |----|
| Sender | | Receiver|
| Proxy | | Proxy |
|--------| |---------|
=======RSVP=======>
********************************************************>
|----| Non-RSVP-capable |----| Non-RSVP-capable ***
| S | Sender | R | Receiver *r* regular RSVP
|----| |----| *** router
***> media flow
==> segment of flow path protected by RSVP reservation
/\ Application signaling (e.g. SIP)
// RSVP Proxy control interface
Figure 9: Application_Entity-Controlled Proxy
As an example, the Application_Entity-Controlled Proxy may be used in
the context of SIP Servers ([RFC3261]) or Session Border Controllers
(SBCs) (see [I-D.ietf-sipping-sbc-funcs] for description of SBCs) to
establish RSVP reservations for multimedia sessions. In that case,
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the Application Entity may be the signaling component of the SBC.
This RSVP Proxy approach does not require any extension to the RSVP
protocol. However, it relies on an RSVP Proxy control interface
allowing control of the RSVP Proxy by an application signaling
entity. This RSVP Proxy control interface is beyond the scope of the
present document. Candidate protocols for realizing such interface
include the IETF NETCONF configuration protocol
([RFC4741],[RFC5277]), Web Services protocol ([W3C]), QPIM
([RFC3644]) and DIAMETER ([RFC3588]). This interface can rely on
soft states or hard states. Clearly, when hard states are used,
those need to be converted appropriately by the RSVP Proxy entities
into the corresponding RSVP soft states. As an example,
[I-D.ietf-dime-diameter-qos] is intended to allow control of RSVP
Proxy via DIAMETER.
In general, the Application Entity is not expected to maintain
awareness of which RSVP Receiver Proxy is on the path to which
destination. However, in the particular cases where it does so
reliably, we observe that the Application Entity could control the
RSVP Sender Proxy and Receiver Proxy so that aggregate RSVP
reservations are used between those, instead of one reservation per
flow. For example, these aggregate reservations could be of RSVP-
AGGREGATE type as specified in [RFC3175] or of GENERIC-AGGREGATE type
as specified in [RFC4860]. Such aggregate reservations could be used
so that a single reservation can be used for multiple (possibly all)
application flows transiting via the same RSVP Sender Proxy and the
same RSVP Receiver Proxy.
For situations where only the RSVP Sender Proxy has to be controlled
by this interface, the interface may be realized through the simple
use of RSVP itself, over a GRE tunnel from the application entity to
the RSVP Sender Proxy. This particular case is further discussed in
Section 4.5.1. Another particular case of interest is where the
application signaling entity resides on the same device as the RSVP
Proxy. In that case, this interface may be trivially realized as an
internal API. An example environment based on this particular case
is illustrated in Section 4.5.2.
The application entity controlling the RSVP Proxy (e.g. a SIP Call
Agent) would often be aware of a number of endpoint capabilities and
it has to be aware about which endpoint can be best "served" by which
RSVP Proxy anyways. So it is reasonable to assume that such an
application is aware of whether a given endpoint is RSVP-capable or
not. The application may also consider the QoS preconditions and QoS
mechanisms signaled by an endpoint as per [RFC3312]/[RFC4032] and
[RFC5432]. The information about endpoint RSVP capability can then
be used by the application to decide whether to trigger Proxy
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behavior or not for a given endpoint. This can facilitate gradual
and dynamic migration from the Proxy model towards the end-to-end
RSVP model as more and more endpoints become RSVP capable.
In some environments, the application entities (e.g. SIP Back-to-
Back User Agents) that need to control the RSVP Proxies would already
be deployed independently of the use, or not, of the
Application_Entity-Controlled Proxy approach. In this case, the
activation of the RSVP Proxy approach should not introduce
significant disruption in the application signaling path. In some
environments, additional application entities may need to be deployed
to control the RSVP Proxies. In this case, the network operator
needs to consider the associated risks of disruption to the
application signaling path.
4.5.1. Application_Entity-Controlled Sender Proxy using "RSVP over GRE"
This approach is simply a particular case of the more general
Application_Entity-Controlled Proxy, but where only RSVP Sender
Proxies need to be controlled by the application, and where RSVP is
effectively used as the control protocol between the application
signaling entity and the RSVP Sender Proxy.
In this approach, the RSVP messages (e.g. RSVP Path message) are
effectively generated by the application entity and logically
"tunnelled" to the RSVP Sender Proxy via GRE tunneling. This is to
ensure that the RSVP messages follow the exact same path as the flow
they protect (as required by RSVP operations) on the segment of the
end-to-end path which is to be subject to RSVP reservations.
Figure 10 illustrates such an environment.
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|-------------|
////////////| Application |\\\\\\\\\
/ | Entity | \
/ |-------------| \
/ /=/ \
/ /=/ \
/ /=/ \
/ /=/ \
/ /=/ \
/ /=/ \
/ /=/ \
/ /=/ \
|----| |--------| *** |----|
| S |-----------| RSVP |-----------*r*-----------------| R |
|----| | Sender | *** |----|
| Proxy |
|--------|
=========RSVP====================>
*****************************************************>
|----| non-RSVP-capable |----| RSVP-capable ***
| S | Sender | R | Receiver *r* regular RSVP
|----| |----| *** router
***> media flow
==> segment of flow path protected by RSVP reservation
/\ Application level signaling
/=/ GRE-tunnelled RSVP (Path messages)
Figure 10: Application-Entity-Controlled Sender Proxy via "RSVP over
GRE"
With the Application_Entity-Controlled Sender Proxy using "RSVP Over
GRE", the application entity :
o generates a Path message on behalf of the sender, corresponding to
the reservation needed by the application and maintains the
corresponding Path state. The Path message built by the
application entity is exactly the same as would be built by the
actual sender (if it was RSVP-capable), with one single exception
which is that the Application Entity puts its own IP address as
the RSVP Previous Hop. In particular, it is recommended that the
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source address of the Path message built by the application entity
be set to the IP address of the sender (not of the application
entity). This helps ensuring that, in the presence of non-RSVP
routers and of load-balancing in the network where the load-
balancing algorithm takes into account the source IP address, the
Path message generated by the application entity follows the exact
same path that the actual stream sourced by the sender.
o encapsulates the Path message into a GRE tunnel whose destination
address is the RSVP Sender Proxy i.e. An RSVP Router sitting on
the datapath for the flow (and upstream of the segment which
requires QoS guarantees via RSVP reservation).
o processes the corresponding received RSVP messages (including Resv
messages) as per regular RSVP.
o synchronizes the RSVP reservation state with application level
requirements and signaling.
Note that since the application entity encodes its own IP address as
the previous RSVP hop inside the [RFC2205] RSVP_HOP object of the
Path message, the RSVP Router terminating the GRE tunnel naturally
addresses all the RSVP messages travelling upstream hop-by-hop (such
as Resv messages) to the application entity (without having to
encapsulate those in a reverse-direction GRE tunnel towards the
application entity).
4.5.2. Application_Entity-Controlled Proxy via Co-Location
This approach is simply a particular case of the more general
Application_Entity-Controlled Proxy, but where the application entity
is co-located with the RSVP Proxy. As an example, Session Border
Controllers (SBC) with on-board SIP agents could implement RSVP Proxy
functions and make use of such an approach to achieve session
admission control over the SBC-to-SBC segment using RSVP signaling.
Figure 11 illustrates operations of the Application_Entity-Controlled
RSVP Proxy via Co-location.
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|---------| |---------|
////////| App |////////\\\\\\\| App |\\\\\\\\\
/ | Entity | | Entity | \
/ | | | | \
|----| |---------| *** |---------| |----|
| S |--------| RSVP |------*r*------| RSVP |---------| R |
|----| | Sender | *** | Receiver| |----|
| Proxy | | Proxy |
|---------| |---------|
=======RSVP======>
*******************************************************>
|----| Non-RSVP-capable |----| Non-RSVP-capable ***
| S | Sender | R | Receiver *r* regular RSVP
|----| |----| *** router
***> media flow
==> segment of flow path protected by RSVP reservation
/\ Application level signaling
Figure 11: Application_Entity-Controlled Proxy via Co-Location
This RSVP Proxy approach does not require any protocol extensions.
We also observe that when multiple sessions are to be established on
paths sharing the same RSVP Sender Proxy and the same RSVP Receiver
Proxy, the RSVP Proxies have the option to establish aggregate RSVP
reservations (as defined in ([RFC3175] or [RFC4860]) for a group of
sessions, instead of establishing one RSVP reservation per session.
4.6. Policy_Server-Controlled Proxy
In this approach, it is assumed that a Policy Server, which is
located in the control plane of the network, controls an RSVP Proxy
which is located in the datapath of the application flows (i.e. "on-
path"). In turn, the Policy server is triggered by an entity
involved in the application level signaling. With this approach, the
RSVP Proxy does not attempt to determine itself the application
reservation requirements, but instead is instructed by the Policy
Server to establish, maintain and tear down reservations as needed by
the application flows. Moreover, the entity participating in
application level signaling does not attempt to understand the
specific reservation mechanism (i.e. RSVP) or the topology of the
network layer, but instead it simply asks the policy server to
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perform (or tear down) a reservation. In other words, with this
approach, the solution for synchronizing RSVP signaling with
application level requirements is to rely on an application level
entity that controls a policy server that, in turn, controls an RSVP
Proxy function that sits in the flow datapath. This approach allows
control of an RSVP Sender Proxy, an RSVP Receiver Proxy or both.
Operation of the Policy_Server-Controlled Proxy is illustrated
Figure 12.
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|---------|
/////////////| App |\\\\\\\\\\\\\\
/ | Entity | \
/ |---------| \
/ I \
/ I \
/ |----------| \
/ | Policy | \
/ | Server | \
/ |----------| \
/ // \\ \
/ // \\ \
/ // \\ \
|----| |--------| *** |---------| |----|
| S |-----------| |------*r*-----| |----------| R |
|----| | RSVP | *** | RSVP | |----|
| Sender | | Receiver|
| Proxy | | Proxy |
|--------| |---------|
=====RSVP========>
**********************************************************>
|----| Non-RSVP-capable |----| Non-RSVP-capable ***
| S | Sender | R | Receiver *r* regular RSVP
|----| |----| *** router
***> media flow
==> segment of flow path protected by RSVP reservation
/\ Application signaling (e.g. SIP)
// RSVP Proxy control interface
I Interface between Application Entity and Policy Server
Figure 12: Policy_Server-Controlled Proxy
This RSVP Proxy approach does not require any extension to the RSVP
protocol. However, as with the Application_Entity-Controlled Proxy
approach presented in Figure 9, this approach relies on an RSVP Proxy
control interface allowing control of the RSVP Proxy (by the Policy
Server in this case). This RSVP Proxy control interface is beyond
the scope of the present document. Considerations about candidate
protocols for realizing such interface can be found in Section 4.5.
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Again, for situations where only the RSVP Sender Proxy has to be
controlled by this interface, the interface may be realized through
the simple use of RSVP Itself, over a GRE tunnel from the Policy
Server to the RSVP Sender Proxy. This is similar to what is
presented in Section 4.5.1 except that the "RSVP over GRE" interface
is used in this case by the Policy Server (instead of the application
entity).
The interface between the Application Entity and the Policy Server is
beyond the scope of this document.
4.7. RSVP-Signaling-Triggered Proxy
An RSVP Proxy can also be triggered and controlled through extended
RSVP signaling from the remote end that is RSVP-capable (and supports
these RSVP extensions for Proxy control). For example, an RSVP
capable sender could send a new or extended RSVP message explicitly
requesting an RSVP Proxy on the path towards the receiver to behave
as an RSVP Receiver Proxy and also to trigger a reverse direction
reservation thus also behaving as a RSVP Sender Proxy. The new or
extended RSVP message sent by the sender could also include
attributes (e.g. Bandwidth) for the reservations to be signaled by
the RSVP Proxy.
The challenges in these explicit signaling schemes include:
o How can the nodes determine when a reservation request ought to be
proxied and when it should not, and accordingly invoke appropriate
signaling procedures?
o How does the node sending the messages explicitly triggering the
Proxy know where the Proxy is located, e.g., determine an IP
address of the proxy that should reply to the signaling?
o How is all the information needed by a Sender Proxy to generate a
Path message actually communicated to the Proxy?
An example of such a mechanism is presented in
[I-D.manner-tsvwg-rsvp-proxy-sig]. This scheme is primarily targeted
to local access network reservations whereby an end host can request
resource reservations for both incoming and outgoing flows only over
the access network. This may be useful in environments where the
access network is typically the bottleneck while the core is
comparatively over-provisioned, as may be the case with a number of
radio access technologies. In this proposal, messages targeted to
the Proxy are flagged with one bit in all RSVP messages. Similarly,
all RSVP messages sent back by the Proxy are also flagged. The use
of such a flag allows differentiating between proxied and end-to-end
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reservations. For triggering an RSVP Receiver Proxy, the sender of
the data sends a Path message which is marked with the mentioned
flag. The Receiver Proxy is located on the signaling and data path,
eventually gets the Path message, and replies back with a Resv
message. A node triggers an RSVP Sender Proxy with a newly defined
Path_Request message, which instructs the proxy to send Path messages
towards the triggering node. The node then replies back with a Resv.
More details can be found in [I-D.manner-tsvwg-rsvp-proxy-sig].
Such an RSVP-Signaling-Triggered Proxy approach would require RSVP
signaling extensions (that are outside the scope of the present
document). However it could provide more flexibility in the control
of the Proxy behavior (e.g. Control of reverse reservation
parameters) than provided by the Path-Triggered approaches defined in
Section 4.1 and Section 4.2.
Through potential corresponding protocol extensions, an RSVP-
Signaling-Triggered Proxy approach could facilitate operation (e.g.
Reduce or avoid the need for associated configuration) in hybrid
environments involving both reservations established end-to-end and
reservations established via RSVP Proxies. For
example,[I-D.manner-tsvwg-rsvp-proxy-sig] proposed a mechanism
allowing an end-system to control whether a reservation can be
handled by an RSVP Proxy on the path or is to be established end-to-
end.
4.8. Reachability Considerations
There may be situations where the RSVP Receiver Proxy is reachable by
the sender, while the receiver itself is not. In such situations, it
is possible that the RSVP Receiver Proxy is not always aware that the
receiver is unreachable, and consequently may accept to establish an
RSVP reservation on behalf of that receiver. This would result in
unnecessary reservation establishment and unnecessary network
resource consumption.
This is not considered a significant practical concern for a number
of reasons. First, in many cases, if the receiver is not reachable
from the sender, it will not be reachable either for application
signaling so that application level session establishment will not be
possible in the first place. Secondly, where the receiver is
unreachable from the sender but is reachable for application level
signaling (say because session establishment is performed through an
off-path SIP agent that uses a different logical topology to
communicate with the receiver), then the sender may detect that the
receiver is unreachable before attempting reservation establishment.
This may be achieved through mechanisms such as ICE's connectivity
check ( [I-D.ietf-mmusic-ice]). Finally, even if the sender does not
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detect that the receiver is unreachable before triggering the RSVP
reservation establishment, it is very likely that the application
will quickly realise this lack of connectivity (e.g. The human
accepting the phone call on the receiver side will not hear the
human's voice on the sender side) and therefore tear down the session
(e.g. Hang up the phone) which in turn will trigger RSVP reservation
release.
Nonetheless, it is recommended that network administrators consider
the above in light of their particular environment when deploying
RSVP Proxys.
The mirror considerations apply for situations involving an RSVP
Sender Proxy and where the sender cannot reach the destination while
the RSVP Sender Proxy can.
5. Security Considerations
In the environments of concern for this document, RSVP messages are
used to control resource reservations on a segment of the end-to-end
path of flows. The general security considerations associated with
[RFC2205] apply. To ensure the integrity of the associated
reservation and admission control mechanisms, the RSVP cryptographic
authentication mechanisms defined in [RFC2747]] and [RFC3097] can be
used. Those protect RSVP messages integrity hop-by-hop and provide
node authentication, thereby protecting against corruption, spoofing
of RSVP messages and replay.
[I-D.ietf-tsvwg-rsvp-security-groupkeying] discusses key types and
key provisioning methods as well as their respective applicability to
RSVP authentication.
[I-D.ietf-tsvwg-rsvp-security-groupkeying] also discusses
applicability of IPsec mechanisms ([RFC4303], [RFC4303]) and
associated key provisioning methods for security protection of RSVP.
This discusion applies to the protection of RSVP in the presence of
RSVP Proxies as defined in the present document.
A subset of RSVP messages are signaled with the router alert option
([RFC2113],[RFC2711]). Based on the current security concerns
associated with the use of the IP router alert option, the
applicability of RSVP (and therefore of the RSVP Proxy approaches
discussed in the present document) is limited to controlled
environments (i.e. Environments where the security risks associated
with the use of the router alert option are understood and protected
against). The security aspects and common practices around the use
of the current IP router alert option and consequences of using the
IP router alert option by applications such as RSVP are discussed in
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details in [I-D.rahman-rtg-router-alert-considerations].
A number of additional security considerations apply to the use of
RSVP proxies and are discussed below.
With some RSVP Proxy approaches, the RSVP proxy operates autonomously
inside an RSVP router. This is the case for the Path-Triggered Proxy
approaches defined in Section 4.1 and in Section 4.2, for the
Inspection-Triggered Proxy approach defined in Section 4.3, for the
STUN-Triggered Proxy approach defined in Section 4.4 and for the
RSVP-Signaling-Triggered approach defined in Section 4.7. Proper
reservation operation assumes that the RSVP proxy can be trusted to
behave correctly in order to control the RSVP reservation as required
and expected by the end systems. Since, the basic RSVP operation
already assumes a trust model where end-systems trust RSVP nodes to
appropriately perform RSVP reservations, the use of RSVP proxy that
behave autonomously within an RSVP router is not seen as introducing
any significant additional security threat or as fundamentally
modifying the RSVP trust model.
With some RSVP Proxy approaches, the RSVP proxy operates under the
control of another entity. This is the case for the
Application_Entity-Controlled Proxy approach defined in Section 4.5
and for the Policy_Server-Controlled Proxy approach defined in
Section 4.6. This introduces additional security risks since the
entity controlling the RSVP Proxy needs to be trusted for proper
reservation operation and also introduces additional authentication
and confidentiality requirements. The exact mechanisms to establish
such trust, authentication and confidentiality are beyond the scope
of this document, but they may include security mechanisms inside the
protocol used as the control interface between the RSVP Proxy and the
entity controlling it, as well as security mechanisms for all the
interfaces involved in the reservation control chain (e.g. Inside
the application signaling protocol between the end systems and the
application entity, and, in the case of the Policy_Server-Controlled
Proxy approach, in the protocol between the application entity and
the policy server).
In some situations, the use of RSVP Proxy to control reservations on
behalf of end-systems may actually reduce the security risk (at least
from the network operator viewpoint). This could be the case, for
example, because the routers where the RSVP Proxy functionality runs
are less exposed to tampering than end-systems. Such a case is
further discussed in section 4 of [I-D.ietf-tsvwg-rsvp-proxy-proto].
This could also be the case because the use of RSVP Proxy allows
localization of RSVP operation within the boundaries of a given
administrative domain (thus easily operating as a controlled
environment) while the end-to-end flow path spans multiple
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administrative domains.
6. IANA Considerations
This document does not make any request to IANA registration.
7. Acknowledgments
This document benefited from earlier work on the concept of RSVP
Proxy including the one documented by Silvano Gai, Dinesh Dutt,
Nitsan Elfassy and Yoram Bernet. It also benefited from discussions
with Pratik Bose, Chris Christou and Michael Davenport. Tullio
Loffredo and Massimo Sassi provided the base material for
Section 4.6. Thanks to James Polk, Magnus Westerlund, Dan Romascanu,
Ross Callon, Cullen Jennings and Jari Arkko for their thorough review
and comments.
8. References
8.1. Normative References
[I-D.ietf-mmusic-ice]
Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols",
draft-ietf-mmusic-ice-19 (work in progress), October 2007.
[I-D.ietf-tsvwg-rsvp-security-groupkeying]
Behringer, M. and F. Faucheur, "Applicability of Keying
Methods for RSVP Security",
draft-ietf-tsvwg-rsvp-security-groupkeying-05 (work in
progress), June 2009.
[RFC2205] Braden, B., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205, September 1997.
[RFC2210] Wroclawski, J., "The Use of RSVP with IETF Integrated
Services", RFC 2210, September 1997.
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
and W. Weiss, "An Architecture for Differentiated
Services", RFC 2475, December 1998.
[RFC2747] Baker, F., Lindell, B., and M. Talwar, "RSVP Cryptographic
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Authentication", RFC 2747, January 2000.
[RFC3097] Braden, R. and L. Zhang, "RSVP Cryptographic
Authentication -- Updated Message Type Value", RFC 3097,
April 2001.
[RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for NAT (STUN)", RFC 5389,
October 2008.
8.2. Informative References
[I-D.ietf-dime-diameter-qos]
Zorn, G., "Protocol for Diameter Quality of Service
Application", November 2007.
[I-D.ietf-nsis-qos-nslp]
Manner, J., Karagiannis, G., and A. McDonald, "NSLP for
Quality-of-Service Signaling", draft-ietf-nsis-qos-nslp-16
(work in progress), February 2008.
[I-D.ietf-sipping-sbc-funcs]
Hautakorpi, J., Camarillo, G., Penfield, R., Hawrylyshen,
A., and M. Bhatia, "Requirements from SIP (Session
Initiation Protocol) Session Border Control Deployments",
April 2007.
[I-D.ietf-tsvwg-rsvp-proxy-proto]
Faucheur, F., Malik, H., Manner, J., Narayanan, A.,
Guillou, A., and L. Faucheur, "RSVP Extensions for Path-
Triggered RSVP Receiver Proxy",
draft-ietf-tsvwg-rsvp-proxy-proto-09 (work in progress),
May 2009.
[I-D.manner-tsvwg-rsvp-proxy-sig]
Manner, J., "Localized RSVP for Controlling RSVP Proxies",
October 2006.
[I-D.rahman-rtg-router-alert-considerations]
Faucheur, F., "IP Router Alert Considerations and Usage",
draft-rahman-rtg-router-alert-considerations-02 (work in
progress), July 2009.
[RFC1633] Braden, B., Clark, D., and S. Shenker, "Integrated
Services in the Internet Architecture: an Overview",
RFC 1633, June 1994.
[RFC2113] Katz, D., "IP Router Alert Option", RFC 2113,
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February 1997.
[RFC2326] Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time
Streaming Protocol (RTSP)", RFC 2326, April 1998.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474,
December 1998.
[RFC2711] Partridge, C. and A. Jackson, "IPv6 Router Alert Option",
RFC 2711, October 1999.
[RFC2872] Bernet, Y. and R. Pabbati, "Application and Sub
Application Identity Policy Element for Use with RSVP",
RFC 2872, June 2000.
[RFC2961] Berger, L., Gan, D., Swallow, G., Pan, P., Tommasi, F.,
and S. Molendini, "RSVP Refresh Overhead Reduction
Extensions", RFC 2961, April 2001.
[RFC3175] Baker, F., Iturralde, C., Le Faucheur, F., and B. Davie,
"Aggregation of RSVP for IPv4 and IPv6 Reservations",
RFC 3175, September 2001.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[RFC3312] Camarillo, G., Marshall, W., and J. Rosenberg,
"Integration of Resource Management and Session Initiation
Protocol (SIP)", RFC 3312, October 2002.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.
[RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.
Arkko, "Diameter Base Protocol", RFC 3588, September 2003.
[RFC3644] Snir, Y., Ramberg, Y., Strassner, J., Cohen, R., and B.
Moore, "Policy Quality of Service (QoS) Information
Model", RFC 3644, November 2003.
[RFC4032] Camarillo, G. and P. Kyzivat, "Update to the Session
Initiation Protocol (SIP) Preconditions Framework",
RFC 4032, March 2005.
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[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, December 2005.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
[RFC4741] Enns, R., "NETCONF Configuration Protocol", RFC 4741,
December 2006.
[RFC4860] Le Faucheur, F., Davie, B., Bose, P., Christou, C., and M.
Davenport, "Generic Aggregate Resource ReSerVation
Protocol (RSVP) Reservations", RFC 4860, May 2007.
[RFC4923] Baker, F. and P. Bose, "Quality of Service (QoS) Signaling
in a Nested Virtual Private Network", RFC 4923,
August 2007.
[RFC5277] Chisholm, S. and H. Trevino, "NETCONF Event
Notifications", RFC 5277, July 2008.
[RFC5432] Polk, J., Dhesikan, S., and G. Camarillo, "Quality of
Service (QoS) Mechanism Selection in the Session
Description Protocol (SDP)", RFC 5432, March 2009.
[W3C] "World Wide Web Consortium (W3C) - Web Services
Architecture", <http://www.w3.org/TR/ws-arch/>.
Appendix A. Use Cases for RSVP Proxies
A.1. RSVP-based VoD Admission Control in Broadband Aggregation Networks
As broadband services for residential are becoming more and more
prevalent, next generation aggregation networks are being deployed in
order to aggregate traffic from broadband users (whether attached via
Digital Subscriber Line technology aka DSL, Fiber To The Home/Curb
aka FTTx, Cable or other broadband access technology). Video on
Demand (VoD) services which may be offered to broadband users present
significant capacity planning challenges for the aggregation network
for a number of reasons. First each VoD stream requires significant
dedicated sustained bandwidth (typically 2-4 Mb/s in Standard
Definition TV and 6-12 Mb/s in High Definition TV). Secondly, the
VoD codec algorithms are very sensitive to packet loss. Finally, the
load resulting from such services is very hard to predict (e.g. It
can vary very suddenly with block-buster titles made available as
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well as with promotional offerings). As a result, transport of VoD
streams on the aggregation network usually translate into a strong
requirement for admission control. The admission control solution
protects the quality of established VoD sessions by rejecting the
additional excessive session attempts during unpredictable peaks,
during link or node failures, or combination of those factors.
RSVP can be used in the aggregation network for admission control of
the VoD sessions. However, since Customer Premises equipment such as
Set Top Boxes (which behave as the receiver for VoD streams) often do
not support RSVP, the last IP hop in the aggregation network can
behave as an RSVP Receiver Proxy. This way, RSVP can be used between
VoD Pumps and the last IP hop in the Aggregation network to perform
accurate admission control of VoD streams over the resources set
aside for VoD in the aggregation network (typically a certain
percentage of the bandwidth of any link). As VoD streams are
unidirectional, a simple "Path-Triggered" RSVP Receiver Proxy (as
described in Section 4.1) is all that is required in this use case.
The Figure below illustrates operation of RSVP-based admission
control of VoD sessions in an Aggregation network involving RSVP
support on the VoD Pump (the senders) and RSVP Receiver Proxy on the
last IP hop of the aggregation network. All the customer premises
equipment remain RSVP unaware.
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|-------------|
| VoD SRM |
| |
////////| |\\\\\\\\\\\\\\\
/ |-------------| \
/ \
/ \
/ \
/ \
/ \
|----| |------| *** *** |--------| |-----| |---|
| VoD|--|RSVP |----*r*--*r*--|RSVP |--|DSLAM|~~~~|STB|--TV
|Pump| |Router| *** *** |Receiver| |-----| |---|
|----| |------| |Proxy |
|--------|
<---Aggregation Net------------->
******************************************************>
============RSVP====================>
SRM Session Resource Manager
*** |---|
*r* regular RSVP |STB| Set Top Box
*** router |---|
***> VoD media flow
==> segment of flow path protected by RSVP reservation
/\ VoD Application level signaling (e.g. RTSP)
Figure 13: VoD Use Case with Receiver Proxy
In the case where the VoD Pumps are not RSVP-capable, an
Application_Entity-Controlled Sender Proxy via "RSVP over GRE"
approach (as described in Section 4.5.1) can also be implemented on
the VoD Controller or Session Resource Manager (SRM) devices
typically involved in VoD deployments. Figure 14 illustrates
operation of RSVP-based admission control of VoD sessions in an
Aggregation network involving such Application_Entity-Controlled
Source Proxy combined with an RSVP Receiver Proxy on the last IP hop
of the aggregation network. All the customer premises equipment, as
well as the VoD pumps, remain RSVP unaware.
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|-------------|
////| VoD SRM |\\\\\\\\\\\
/ | | \
/ | + | \
/ | RSVP Sender | \
/ |Proxy Control| \
/ |-------------| \
/ /=/ \
/ /=/ \
/ /=/ \
/ /=/ \
/ /=/ \
|----| |------| *** *** |--------| |-----| |---|
| VoD|--|RSVP |----*r*--*r*--|RSVP |--|DSLAM|~~~~|STB|--TV
|Pump| |Sender| *** *** |Receiver| |-----| |---|
|----| |Proxy | |Proxy |
|------| |--------|
<---Aggregation Net------------->
******************************************************>
=========RSVP==============>
SRM Systems Resource Manager
*** |---|
*r* regular RSVP |STB| Set Top Box
*** router |---|
***> VoD media flow
==> segment of flow path protected by RSVP reservation
/ VoD Application level signaling (e.g. RTSP)
/=/ GRE-tunnelled RSVP (Path messages)
Figure 14: VoD Use Case with Receiver Proxy and SRM-based Sender
Proxy
The RSVP Proxy entities specified in this document play a significant
role here since they allow immediate deployment of an RSVP-based
admission control solution for VoD without requiring any upgrade to
the huge installed base of non-RSVP-capable customer premises
equipment. In one mode described above, they also avoid upgrade of
non-RSVP-capable VoD pumps. In turn, this means that the benefits of
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on-path admission control can be offered to VoD services over
broadband aggregation networks without network or VoD Pump upgrade.
Those include accurate bandwidth accounting regardless of topology
(hub-and-spoke, ring, mesh, star, arbitrary combinations) and dynamic
adjustment to any change in topology (such as failure, routing
change, additional links...).
A.2. RSVP-based Voice/Video CAC in Enterprise WAN
More and more enterprises are migrating their telephony and
videoconferencing applications onto IP. When doing so, there is a
need for retaining admission control capabilities of existing TDM-
based systems to ensure the QoS of these applications is maintained
even when transiting through the enterprise's Wide Area Network
(WAN). Since many of the endpoints already deployed (such as IP
Phones or Videoconferencing terminals) are not RSVP capable, RSVP
Proxy approaches are very useful: they allow deployment of an RSVP-
based admission control solution over the WAN without requiring
upgrade of the existing terminals.
A common deployment architecture for such environments relies on the
Application_Entity-Controlled Proxy approach as defined in
Section 4.5. Routers sitting at the edges of the WAN network and
naturally "on-path" for all inter-campus calls (or sessions) and
behave as RSVP Proxies. The RSVP Proxies establish, maintain and
tear-down RSVP reservations over the WAN segment for the calls (or
sessions) under the control of the SIP Server/Proxy. The SIP Server/
Proxy synchronizes the RSVP reservation status with the status of
end-to-end calls. For example, the called IP phone will only be
instructed to play a ring tone if the RSVP reservations over the
corresponding WAN segment has been successfully established.
This architecture allowing RSVP-based admission control of voice and
video on the Enterprise WAN is illustrated in Figure 15.
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|---------|
//////////////| SIP |\\\\\\\\\\\\
/ | Server/ | \
/ | Proxy | \
/ |---------| \
/ // \\ \
/ // \\ \
/ // \\ \
/ // \\ \
/ // \\ \
|-----| |--------| *** *** |--------| |-----|
| IP |------| Media |---*r*---*r*---| Media |-------|IP |
|Phone| | Relay | *** *** | Relay | |Phone|
|-----| | + | | + | |-----|
| RSVP | | RSVP |
| Proxy | | Proxy |
|--------| |--------|
<--campus--> <--campus-->
network network
<---------WAN----------->
<*************> <***********************> <**************>
<=========RSVP===========>
***
*r* Regular RSVP router
***
<***> media flow
<==> segment of flow path protected by RSVP reservation
/\ SIP signaling
// control interface between the SIP Server/Proxy and
RSVP Proxy
Figure 15: CAC on Enterprise WAN Use Case
A.3. RSVP Proxies for Mobile Access Networks
Mobile access networks are increasingly based on IP technology. This
implies that, on the network layer, all traffic, both traditional
data and streamed data like audio or video, is transmitted as
packets. Increasingly popular multimedia applications would benefit
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from better than best-effort service from the network, a forwarding
service with strict Quality of Service (QoS) with guaranteed minimum
bandwidth and bounded delay. Other applications, such as electronic
commerce, network control and management, and remote login
applications, would also benefit from a differentiated treatment.
The IETF has two main models for providing differentiated treatment
of packets in routers. The Integrated Services (IntServ) model
[RFC1633] together with the Resource Reservation Protocol (RSVP)
[RFC2205] [RFC2210] [RFC2961] provides per-flow guaranteed end-to-end
transmission service. The Differentiated Services (DiffServ)
framework [RFC2475] provides non-signaled flow differentiation that
usually provides, but does not guarantee, proper transmission
service.
However, these architectures have potential weaknesses for deployment
in Mobile Access Networks. For example, RSVP requires support from
both communication end points, and the protocol may have potential
performance issues in mobile environments. DiffServ can only provide
statistical guarantees and is not well suited for dynamic
environments.
Let us consider a scenario, where a fixed network correspondent node
(CN) would be sending a multimedia stream to an end host behind a
wireless link. If the correspondent node does not support RSVP it
cannot signal its traffic characteristics to the network and request
specific forwarding services. Likewise, if the correspondent node is
not able to mark its traffic with a proper Differentiated Services
codepoint (DSCP) to trigger service differentiation, the multimedia
stream will get only best-effort service which may result in poor
visual and audio quality in the receiving application. Even if the
connecting wired network is over-provisioned, an end host would still
benefit from local resource reservations, especially in wireless
access networks, where the bottleneck resource is most probably the
wireless link.
RSVP proxies would be a very beneficial solution to this problem. It
would allow distinguishing local network reservations from the end-
to-end reservations. The end host does not need to know the access
network topology or the nodes that will reserve the local resources.
The access network would do resource reservations for both incoming
and outgoing flows based on certain criterion, e.g., filters based on
application protocols. Another option is that the mobile end host
makes an explicit reservation that identifies the intention and the
access network will find the correct local access network node(s) to
respond to the reservation. RSVP proxies would, thus, allow resource
reservation over the segment which is the most likely bottleneck, the
wireless connectivity. If the wireless access network uses a local
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mobility management mechanism, where the IP address of the mobile
node does not change during handover, RSVP reservations would follow
the mobile node movement.
A.4. RSVP Proxies for Reservations in the presence of IPsec Gateways
[RFC4923] discusses how resource reservation can be supported end-to-
end in a nested VPN environment. At each VPN level, VPN Routers
behave as [RFC4301] security gateways between a plaintext domain and
a cyphertext domain. To achieve end-to-end resource reservation, the
VPN Routers process RSVP signaling on the plaintext side, perform
aggregation of plaintext reservations, and maintain the corresponding
aggregate RSVP reservations on the cyphertext side. Each aggregate
reservation is established on behalf of multiple encrypted end-to-end
sessions sharing the same ingress and egress VPN Routers. These
aggregate reservations can be as specified in [RFC3175] or [RFC4860].
Section 3 of [RFC4923] discusses the necessary data flows within a
VPN Router to achieve the behavior described in the previous
paragraph. Two mechanisms are described to achieve such data flows.
Section 3.1 presents the case where the VPN Router carries data
across the cryptographic boundary. Section 3.2 discusses the case
where the VPN router uses a Network-Guard.
Where such mechanisms are not supported by the VPN Routers, the
approach for end-to-end reservation presented in [RFC4923] cannot be
deployed. An alternative approach to support resource reservations
within the cyphertext core is to use the "Application_Entity-
Controlled Proxy" approach (as defined in Section 4.5) in the
following way:
o the RSVP Proxies are located inside the cyphertext domain and use
aggregate RSVP reservations,
o the Application Entity exchange application level signaling with
the end systems in the plaintext domain,
o the Application Entity controls the RSVP Proxies in the cyphertext
domain via an RSVP Proxy control interface
This is illustrated in Figure 16 in the case where the application is
SIP-based multimedia communications.
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|-------| |-------|
|SIP |///////////////////\\\\\\\\\\\\\\\\\|SIP |
/|Server/| |Server/|\
/ |Proxy | |Proxy | \
/ |-------| |-------| \
/ ^ \\ // ^ \
/ ^ \\ // ^ \
/ ^ \\ // ^ \
|---| |------| |--------| *** *** |--------| |------| |---|
| S |---|IPsec |--| ARSVP |---*r*---*r*---| ARSVP |--|IPsec |---| R |
|---| | GW | | Sender | *** *** |Receiver| | GW | |---|
|------| | Proxy | | Proxy | |------|
|--------| |--------|
***PT*****> **********************CT****************> ****PT***>
=====> =====>
=====ARSVP======>
|----| RSVP-capable |----| RSVP-capable ***
| S | Sender | R | Receiver *r* regular RSVP
|----| |----| *** router
|------|
|IPsec | IPsec security gateway
| GW |
|------|
ARSVP Aggregate RSVP
***> media flow
==> segment of flow path protected by RSVP reservation
/ \ SIP signaling
^ Network management interface between SIP Server/Proxy
and IPsec security gateway
// control interface between SIP Server/Proxy and ARSVP Proxy
PT Plaintext network
CT Cyphertext network
Figure 16: RSVP Proxies for Reservations in the Presence of IPsec
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Gateways
Where the sender and receiver are RSVP capable, they may also use
RSVP signaling. This achieves resource reservation on the plaintext
segments of the end-to-end i.e. :
o from the sender to the ingress IPsec gateway and
o from the egress IPsec gateway to the receiver.
In this use case, because the VPN Routers do not support any RSVP
specific mechanism, the end-to-end RSVP signaling is effectively
hidden by the IPsec gateways on the cyphertext segment of the end-to-
end path.
As with the "Application_Entity-Controlled Proxy" approach (defined
in Section 4.5), the solution here for synchronizing RSVP signaling
with application-level signaling is to rely on an application-level
signaling device that controls an on-path RSVP Proxy function.
However, in the present use case, the RSVP Proxies are a component of
a cyphertext network where all user (bearer) traffic is IPsec
encrypted. This has a number of implications including the
following:
1. encrypted flows can not be identified in the cyphertext domain so
that network nodes can only classify traffic based on IP address
and Differentiated Services codepoints (DSCPs). As a result,
only aggregate RSVP reservations (such as those specified in
[RFC3175] or [RFC4860] ) can be used. This is similar to
[RFC4923].
2. Determining the RSVP Sender proxy and RSVP receiver Proxy to be
used for aggregation of a given flow from sender to receiver
creates a number of challenges. Details on how this may be
achieved are beyond the scope of this document. We observe that,
as illustrated in Figure 16, this may be facilitated by a network
management interface between the application entity and the IPsec
gateways. For example, this interface may be used by the
application entity to obtain information about which IPsec
gateway is on the path of a given end-to-end flow. Then, the
application entity may maintain awareness of which RSVP Proxy is
on the cyphertext path between a given pair of IPsec gateways.
How such awareness is achieved is beyond the scope of this
document. We simply observe that such awareness can be easily
achieved through simple configuration in the particular case
where a single (physical or logical) RSVP Proxy is fronting a
given IPsec gateway. We also observe that when awareness of the
RSVP Receiver Proxy for a particular egress IPsec gateway (or
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end-to-end flow) is not available, the aggregate reservation may
be signaled by the RSVP Sender Proxy to the destination address
of the egress IPsec gateway and then proxied by the RSVP Receiver
Proxy.
Different flavors of operations are possible in terms of aggregate
reservation sizing. For example, the application entity can initiate
an aggregate reservation of fixed size a priori and then simply keep
count of the bandwidth used by sessions and reject sessions that
would result in excess usage of an aggregate reservation. The
application entity could also re-size the aggregate reservations on a
session by session basis. Alternatively, the application entity
could re-size the aggregate reservations in step increments typically
corresponding to the bandwidth requirement of multiple sessions.
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
Helsinki University of Technology (TKK)
P.O. Box 3000
Espoo FIN-02015 TKK
Finland
Phone: +358 9 451 2481
Email: jukka.manner@tkk.fi
URI: http://www.netlab.tkk.fi/~jmanner/
Dan Wing
Cisco Systems
170 West Tasman Drive
San Jose, CA 95134
United States
Email: dwing@cisco.com
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Allan Guillou
SFR
40-42 Quai du Point du Jour
Boulogne-Billancourt, 92659
France
Phone:
Fax:
Email: allan.guillou@sfr.com
URI:
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