[Docs] [txt|pdf] [Tracker] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01

Internet Draft                                            Luca Veltri
October 2002                                                  CoRiTeL
Expiration: April 2003                                Stefano Salsano
                                          Univ. of Rome "Tor Vergata"
                                                      Donald Papalilo
                                                              CoRiTeL
File: <draft-veltri-sip-qsip-01.txt>


                SIP Extensions for QoS support


     Status of this Memo

This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.

Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups.  Note that
other groups may also distribute working documents as Internet-
Drafts.

Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other
documents at any time.  It is inappropriate to use Internet-Drafts
as reference material or to cite them other than as "work in
progress."


The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt

The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.

Distribution of this memo is unlimited.

Copyright (C) The Internet Society (2002).  All Rights Reserved.



     Abstract

This work describes an enhancement to SIP protocol for the interworking
with QoS enabled IP networks. The proposed mechanism is simple and it
fully preserves backward compatibility and interoperability with current
SIP applications. The draft describes also, as an example, the
application of this mechanism to a particular QoS enabled IP network,
which implements Diffserv as transport mechanisms and COPS as protocol
for QoS requests and for admission control.




Veltri et al.             Expires April 2003                         1

                  SIP Extensions for QoS support                Oct-02




     Table of Contents

Abstract........................................................1
Glossary........................................................2
1. Introduction.................................................3
2. QoS SIP: Overview............................................5
2.1 QoS reservation modes.......................................7
2.2 QoS models..................................................8
3. Q-SIP signaling mechanism....................................8
3.1 Q-SIP message flow..........................................9
3.1.1 Q-SIP message flow - unidirectional QoS reservation.......9
3.1.2 Q-SIP message flow - bidirectional QoS reservation........11
3.2 Q-SIP protocol..............................................12
3.2.1 Stateful variant of Q-SIP protocol........................13
3.2.2 Stateless variant of the Q-SIP protocol...................15
4. Q-SIP syntax and rules.......................................17
4.1 Syntax......................................................17
4.2 Rules.......................................................18
5. Use of INFO method for robust tear-down procedure............19
6. SIP Terminals................................................19
7. Q-SIP Servers................................................20
8. Security Considerations......................................20
9. Change log and prototype implementation......................20
Appendix A: QoS-Enabled vs. QoS-Assured.........................21
A.1  Q-SIP using unidirectional QoS Network reservation.........21
A.1.1  Bidirectional e2e reservation sender initiated...........21
A.1.2  Unidirectional e2e reservation sender initiated..........23
A.1.3  Bidirectional e2e reservation receiver initiated.........24
A.1.4  Unidirectional e2e reservation receiver initiated........26
A.2  Q-SIP using bidirectional QoS Network reservation..........27
A.2.1  Bidirectional e2e reservation sender initiated...........27
A.2.2  Bidirectional e2e reservation receiver initiated.........29
Appendix B - Description of the QoS State.......................30
Appendix C - Payload type vs. bandwidth.........................31
Appendix D - Examples of Q-SIP messages.........................32
Appendix E......................................................36
References......................................................41
Author Information and Acknoledgements..........................42















Veltri et al.             Expires April 2003                         2

                  SIP Extensions for QoS support                Oct-02




Glossary

SIP      Session Initiation Protocol
RSVP     Resource Reservation Protocol
Intserv  Integrated Services
Diffserv Differentiated Services
BB       Bandwidth Broker
ER       Edge Router
COPS     Common Open Policy Service
PDP      Policy Decision Point
PEP      Policy Enforcement Point
Q-SIP    QoS enabled SIP
NSIS     Next Steps in Signaling
UA       User Agent







1. Introduction

Basically, SIP is an end-to-end session setup protocol. In order to
provide an adequate quality of services for audio and video
communications, a form of resource reservation may be needed. In the
current view [1][3], the SIP user agents should rely on existing QoS
protocols (e.g. RSVP) for the support of such resource reservation.
This fact has two main drawbacks: i) the user applications must be aware
of the QoS mechanism used in the access network and the relative QoS
signaling protocol (e.g. RSVP, COPS, or other), ii) user applications
must implement such QoS protocol, with the increase of the complexity.
Moreover, if RSVP is used as signaling protocol, both user terminals
should implement the RSVP protocol.
Currently two main approaches have been proposed in the IETF for the
support of QoS in an IP network: the Integrated Services (Intserv) model
(strictly based on the use of RSVP), and the Differentiated Services
(Diffserv) model.
An IP telephony (SIP based) architecture with end-to-end QoS support
which can rely on the Intserv model is described in [1]. Although the
Intserv model seems to be suitable for services that requires strict QoS
guarantees, as for the IP telephony, it is more complex and suffers of
scalability problems. For this reason the Diffserv model has been chosen
as QoS model in this work.
The NSIS IETF WG [2] is currently elaborating the signaling aspects that
could support IP QoS. The reference model it is still under a discussion
phase, and it is not completely defined. However, the architecture here
presented seems to be quite aligned with the drafts under discussion
within NSIS.

Figure 1 shows the reference scenario considered in this draft.


Veltri et al.             Expires April 2003                         3

                  SIP Extensions for QoS support                Oct-02



The SIP terminals are connected through access networks to a core
network with QoS support. The QoS provided in the core network is
accessed via some QoS Access Points at the border of such network;
without no loss of generality, we suppose that the QoS Access Points
coincide with the network Edge Routers (ERs) (as in Figure 1). The QoS
in the access networks depends on the QoS model used by the ISP for the
access, but it is outside the scope of the mechanisms described in this
document.
                              /------\
                           __/        \__
.-----.        .-----.    /     CORE     \    .-----.        .-----.
| SIP |        |Edge +---(     NETWORK    )---+Edge |        | SIP |
|phone|        |Router    \__          __/    |Router        |phone|
'--+--' Access '--+--'       \        /       '--+--' Access '--+--'
   |    Network   |           \------/           |    Network   |
 --+--------------|--                          --+--------------|--

Figure 1 - Reference QoS scenario

In this draft we propose a very simple solution for QoS call setup that
is based on the enhancement of the SIP protocol to convey end-to-end QoS
related information. We will refer to such QoS aware SIP implementation
as Q-SIP.
The proposed QoS architecture (see Figure 2) eliminates the need of QoS
supports on the user terminals since all the QoS related functions can
be moved to (local) SIP servers that will control both call setup and
resource reservation, thus relieving the terminals from unneeded
complexity.
Basically, when a call setup is initiated, the caller SIP UA can start a
SIP call setup session through an outbound SIP proxy server. If needed,
the server (a Q-SIP server) starts a QoS session interacting with a
remote Q-SIP server and with the QoS provider (a QoS Access Point). When
the QoS provider responds, the call setup can continue and finally the
data session starts.
The requirements at the basis of the Q-SIP proposal are:
  i) it should be possible to use existing SIP UAs; no
enhancements/modifications are needed in the SIP UA applications,
  ii) it should be possible to have a seamless interaction with other
parties which do not intend or are not able to use QoS,
  iii) the protocol enhancements should preserve backward compatibility
with standardized SIP protocol,
  iv) the resulting architecture should be as simple and scalable as
possible,
  v) the architecture should be extendible to new models of QoS support
for IP networks.

The QoS setup procedure is dealt entirely by QoS aware agents, generally
on SIP servers, and all protocol extensions needed for the QoS setup are
hidden from not-QoS-aware SIP agents. Hence the solution preserves
backward compatibility with current SIP applications and it de-couples
as much as possible the SIP signaling from the handling of QoS.
Note that, it is reasonable that in a Diffserv QoS scenario there will
be servers dedicated to policy control, accounting and billing aspects.

Veltri et al.             Expires April 2003                         4

                  SIP Extensions for QoS support                Oct-02



A solution based on a SIP server is really suited to this QoS scenario.
In the light of the current discussion in NSIS, the proposed Q-SIP
server would act as a QoS Initiator interacting with a QoS Controller.
The end-to-end SIP signaling can interact with the reservation of
resource using "out of band" NSIS signaling.


2. QoS SIP: Overview

The basic idea is that SIP UAs use a default SIP proxy server in their
domains for both outgoing and incoming calls. The UA sends SIP messages
to its proxy server and receives the messages from its server. The SIP
servers are therefore involved in the message exchange between the UAs
and can add (and read) QoS related information in the SIP messages. This
QoS information exchange is made transparent for the UAs. The SIP server
will extract from SIP signaling QoS parameters among them and will
interact with the network QoS mechanisms. The enhanced SIP server will
be called Q-SIP server (QoS enabled SIP server).
The originating Q-SIP server adds QoS information in the SIP messages.
This is meant as an offer to terminating SIP server, or as a hint that
the originating side is capable of QoS and is willing to exploit it. If
the terminating SIP server is able to handle QoS in a compatible way and
it is willing to exploit it, it will answer positively with proper
information in the response SIP messages. A legacy SIP server on the
terminating side will not understand the QoS information in the SIP
message and will silently ignore it. Obviously, the SIP session will be
setup with no QoS.

The reference architecture for the proposed SIP QoS scenario is depicted
in Figure 2 and Figure 3. The involved actors are the two SIP UAs, the
two SIP servers and a QoS enabled network. The QoS provided by the QoS
enabled network is accessed by QoS Access Point(s) located at the border
of the network in the ERs. Depending on the mechanism implemented inside
the core network in order to handle the reservation, there can be two
logical types of QoS Access Points distinguished by the type of
reservation offered: unidirectional and bidirectional from an ingress to
an egress point (ER).

             .--------.                        .--------.
             | Q-SIP  |    QoS enhanced SIP    | Q-SIP  |
             | server |<---------------------->| server |
             '--------'                        '--------'
              A      A                          A      A
              |      |                          |      |
          SIP/       |  <- COPS/NSIS/other ->   |       \SIP
            /        V                          V        \
.------.   /     .-------.                  .-------.     \   .------.
| SIP  |<-/      |  QoS  |                  |  QoS  |      \->| SIP  |
|  UA  |         | Access|                  | Access|         |  UA  |
'------'         | Point |                  | Point |         '------'
                 '-------'                  '-------'
Figure 2 - Q-SIP architecture based on the use of Q-SIP servers on QoS
IP networks that offer unidirectional flow reservation.

Veltri et al.             Expires April 2003                         5

                  SIP Extensions for QoS support                Oct-02




             .--------.                        .--------.
             | Q-SIP  |    QoS enhanced SIP    | Q-SIP  |
             | server |<---------------------->| server |
             '--------'                        '--------'
                A    A                               A
                |    |                               |
            SIP/     |COPS/NSIS/other                 \SIP
              /      V                                 \
.--------.   /   .-------.                              \   .--------.
|  SIP   |<-/    |  QoS  |                               \->|   SIP  |
|   UA   |       | Access|                                  |   UA   |
|(caller)|       | Point |                                  |(callee)|
'--------'       '-------'                                  '--------'
Figure 3 - Q-SIP architecture based on the use of Q-SIP servers on QoS
IP networks that offer bidirectional flow reservation.

The setup of QoS sessions in such scenario is logically composed of two
aspects: the end-to-end signaling mechanism to exchange QoS information
and the QoS negotiation between the SIP agents and the QoS network.
In order to design a clean and flexible solution it is important to de-
couple these two aspects as much as possible. Therefore the SIP protocol
mechanism to exchange QoS information should be generic and independent
from the actual QoS mechanisms.
Although the proposed QoS architecture will be kept very general with
respect to the used QoS mechanism, for completeness we will consider a
particular scenario in which the QoS aspects in the Diffserv core
network are dealt via the COPS protocol [4], with specific extension as
proposed in [5].
In our scenarios, the QoS enabled network can provide unidirectional or
bidirectional QoS reservations. In the first case, two different
reservations have to be requested to the QoS network (also RSVP QoS
model works in this way). When considering a QoS IP network that can
provide bidirectional reservations, the difference is that we have a
single QoS Access Point and a single reservation request made by the Q-
SIP.
Note that we mainly refer to a scenario where the SIP UAs are un-aware
of QoS aspects and the local SIP servers do all the QoS job. Actually,
the proposed SIP QoS mechanism can be applied also to a scenario where
the SIP user applications are enhanced in order to handle the QoS
aspects by themselves. The resulting scenario is depicted in Figure 4.













Veltri et al.             Expires April 2003                         6

                  SIP Extensions for QoS support                Oct-02



             .--------.                        .--------.
             |  SIP   |           Q-SIP        |  SIP   |
             | server |<---------------------->| server |
             '--------'                        '--------'
              A                                        A
              |                                        |
        Q-SIP/                                          \Q-SIP
            /                                            \
.------.   /     .-------.                  .-------.     \   .------.
|Q-SIP |<-/      |  QoS  |                  |  QoS  |      \->|Q-SIP |
|  UA  |<------->| Access|                  | Access|<------->|  UA  |
'------'  COPS/  | Point |                  | Point |  COPS/  '------'
          NSIS/  '-------'                  '-------'  NSIS/
          OTHER                                        OTHER
Figure 4 _ Q-SIP architecture with Q-SIP agents on user terminals.

Compared to Figure 2, note that SIP UAs become Q-SIP UAs and Q-SIP
servers become SIP servers. There can even be asymmetric scenarios where
one side is using a server and the other side uses a SIP application
based solution (see Figure 5).

             .--------.                        .--------.
             |  SIP   |          Q-SIP         | Q-SIP  |
             | server |<---------------------->| server |
             '--------'                        '--------'
              A                                 A      A
              |                                 |      |
        Q-SIP/                   COPS/NSIS/OTHER|       \Q-SIP
            /                                   V        \
.------.   /     .-------.                  .-------.     \   .------.
|Q-SIP |<-/      |  QoS  |                  |  QoS  |      \->| SIP  |
|  UA  |<------->| Access|                  | Access|         |  UA  |
'------'  COPS/  | Point |                  | Point |         '------'
          NSIS/  '-------'                  '-------'
          OTHER
Figure 5 _ Asymmetric Q-SIP architecture.


2.1 QoS reservation modes

As far as the reservation procedure is concerned, two different models
are possible: i) unidirectional reservations and ii) bidirectional
reservations. In the unidirectional reservation mode, the caller-side Q-
SIP server makes reservation for the caller-to-callee traffic flow,
while the callee-side Q-SIP server reserves resources for the callee-to-
caller flow; two reservations are hence needed for bidirectional flows.
Instead, in the bidirectional reservation mode, it is the caller-side Q-
SIP server that performs resource reservation for both directions. The
choice between the two models can be done on the basis of a pre-
configured mode or through the exchange of specific parameters ("qos-
mode" parameters) between the Q-SIP servers during the call setup phase.



Veltri et al.             Expires April 2003                         7

                  SIP Extensions for QoS support                Oct-02



2.2 QoS models

When the requested resource needed for a QoS call is not available, two
options are possible: i) the call is setup without QoS, ii) the call is
rejected. These two options are at the basis of the following two QoS
models:
i) "QoS-Assured", that is the session should not be established if
resources are not available; in this case the QoS should be setup before
alerting the user avoiding that a user may respond to a call when
resources are not available.
ii) "QoS-Enabled", that is the session is established regardless of the
availability of QoS resources; eventually the user may be signaled about
the presence of QoS.
In [1] the "QoS-Assured" model is considered. A possible interaction
between SIP and resource management and a precondition framework is
described.
On the contrary, the present proposal starts from the analysis of a
"QoS-Enabled" model, where the reservation of resources is not a
mandatory precondition and can be executed in parallel with normal
session setup. The extension of our proposal to a "QoS-Assured" model
(conforming to [1]) is reported in Appendix A.


3. Q-SIP signaling mechanism

This section provides the detailed description of the signaling
mechanisms of the proposed SIP based reservation architecture (Q-SIP).
We consider a QoS scenario in which a Diffserv backbone network serves
different access networks (Figure 1). The QoS requests are handled at
the border of the core network by the QoS Access Point(s). In the
following we assume that the Edge Router(s) act as QoS Access Point and
implement all the mechanisms needed to perform admission control
decisions (possibly with the aid of a Bandwidth Broker (BB)) and
policing function. As an example, the QoS scenario will be based on COPS
as the protocol for QoS reservations.
The IP phones/terminals are located on the access networks; standard SIP
UAs can be used and explicit SIP proxying configuration is set. When a
call setup is initiated, the caller SIP UA starts a SIP call setup
session through the SIP proxy server. If a Q-SIP server is encountered,
this will start a QoS session interacting with a remote Q-SIP server and
with the QoS provider for the backbone network (i.e. the access ER).
According to the direction of the call, the two Q-SIP servers are named
caller-side Q-SIP server and callee-side Q-SIP server. The reference
architecture is shown in Figure 2.
The basic goal of the Q-SIP signaling mechanism is to let the two parts
(i.e. the Q-SIP servers) that are willing to setup a QoS session to
interact each other and to exchange the needed information (e.g. IP
addresses of ingress and egress QoS elements). A new SIP header (QoS-
Info) will be defined for this purpose. We defined two variants of the
procedure depending on the state information that is kept in the Q-SIP
server during the session setup. One of the design goal of the SIP
protocol is that a SIP proxy server should operate in a stateless way
whenever possible, i.e. it should not be required for it to record any

Veltri et al.             Expires April 2003                         8

                  SIP Extensions for QoS support                Oct-02



session state. If we want to keep this principle for our Q-SIP server
operation, some information will be recorded in the SIP request messages
in a special way so that the servers will find this information in the
SIP response messages. This will be the "stateless" variant of the Q-SIP
protocol. Anyway, considering that the Q-SIP server is probably
interested to store a QoS state for the call session after its
establishment, it can be reasonable to store some state also during the
session setup. Relying on this state, the information that will be
transported in SIP messages will be simpler ("stateful" variant of the
Q-SIP protocol).


3.1 Q-SIP message flow

In this section the description of the Q-SIP procedure is given, for the
two types of reservations offered by the QoS enabled network:
unidirectional or bidirectional modes. Note that the Q-SIP server must
be aware (e.g. by configuration) of the type of reservation offered by
the QoS enabled network.

3.1.1   Q-SIP message flow - unidirectional QoS reservation

With reference to Figure 6, the call setup starts with a standard SIP
INVITE message sent by the caller to the local Q-SIP server (caller-side
Q-SIP server). The message carries the callee URI in the SIP header and
the session specification within the body SDP (media, codecs, source
ports, etc). The Q-SIP server is seen by the caller as a standard SIP
proxy server. The Q-SIP server, based on the caller identity and on
session information, decides whether a QoS session has to be started or
not. Note that the service admission decision can be handled locally
relying in a user profile or demanded to another external admission
control entity, but this is outside the scope of this work.
If a QoS session has to be setup, the Q-SIP server extracts the required
information from the message, inserts the additional Q-SIP header and
the Record-Route header information (to assure that all the messages for
this session will pass through itself) within the INVITE message.
If the stateful variant is used, some information is stored by the Q-SIP
server in order to maintain trace of the current QoS session. We will
refer to such information as "provisional QoS state".
If the stateless variant is used, the required information is stored as
additional fields in the Record Route header.
Then the Q-SIP forwards the INVITE message towards the invited callee;
the INVITE messages can be relayed by both standard SIP proxy servers
and Q-SIP servers. When the Q-SIP server on the callee side (callee-side
Q-SIP server) receives an INVITE message that contains the SIP QoS
extensions, it understands that a session with QoS has to be setup.
Therefore it extracts the needed information from the message, removes
the Q-SIP extension and inserts Record-Route header. In case of the
stateful variant, it initializes the "provisional QoS state", like the
caller-side Q-SIP. In case of the stateless variant, it adds additional
information in the Record-Route header.
When the callee responds with a 200 OK message, it is passed back to the
last Q-SIP server that is the Q-SIP server that controls the access

Veltri et al.             Expires April 2003                         9

                  SIP Extensions for QoS support                Oct-02



network of the callee. At this point the Q-SIP server on the callee side
has all the information to request a specific QoS reservation to the ER
on the callee access network for the callee-to-caller traffic flow. When
the callee-side Q-SIP receive a positive response for the QoS
reservation request, it stores such QoS information completing the QoS
state and sends the extension information for the callee side within the
200 OK message toward the caller. The QoS information data is stored by
the Q-SIP server. In case of the stateful variant, this QoS information
complete the QoS state previously stored. If the response for the
reservation is negative, the Q-SIP server update the QoS state and it
still inserts in the 200 OK response the extension header field needed
for the caller-to-callee reservation in order to give the possibility to
the caller-side Q-SIP server to make the reservation. The update of the
QoS state reports the failure of the reservation so retransmissions of
the 200 OK does not trigger QoS reservation request and only the
extension header field is inserted to handle correctly the message
retransmission. Actually, the handling of these reservations refusals is
different depending on QoS service model (i.e. QoS-Assured or QoS-
Enabled). Assuming a QoS-Enabled service, the Q-SIP server will simply
continue with the signaling.
When the caller-side Q-SIP server receives the 200 OK message with the
complete QoS session indicators, it completes the QoS session setup by
performing the QoS request to the ER on the caller access network for
the caller-to-callee traffic flow. If the response for this flow is
negative, the caller-to-callee flow will not have QoS support and the
QoS state previously installed is treated as in the callee-side Q-SIP
server in order to handle correctly retransmissions. If the response is
positive, the QoS state is completed.
When a call is terminated all resources that have been reserved must be
released. This action is triggered by the BYE messages; when a BYE
matching an installed QoS state is received, the Q-SIP server sends a
release request to the QoS provider and removes the QoS state. Another
way to assure the release of the resources, based on the use of time-
outs and the INFO method, is described in section 5.

It is important to note that the proposed architecture keeps the
compatibility with standard SIP UAs and standard SIP servers. As we will
see in the rest of this section, all the information needed by the Q-SIP
servers to perform the QoS session setup is inserted within the SIP
messages in such a way that non Q-SIP aware agents can transparently
manage the messages.













Veltri et al.             Expires April 2003                        10

                  SIP Extensions for QoS support                Oct-02



   SIP        SIP        Edge       Edge       SIP        SIP
Terminal     Server     Router     Router     Server    Terminal
    |          |          |          |          |          |
    |  INVITE  |  INVITE  |          |          |  INVITE  |
    |--------->|------------------------------->|--------->|
    |          |          |          |          |          |
    |180ringing|          |          |180ringing|180ringing|
    |<---------|<-------------------------------|<---------|
    |          |          |          |          |          |
    |          |          |          |          |  200 OK  |
    |          |          |          |   COPS   |<---------|
    |          |          |          |<---------|          |
    |          |          |          |   COPS   |          |
    |          |          |          |--------->|          |
    |          |          |          |  200 OK  |          |
    |          |<-------------------------------|          |
    |          |   COPS   |          |          |          |
    |          |--------->|          |          |          |
    |          |   COPS   |          |          |          |
    |  200 OK  |<---------|          |          |          |
    |<---------|          |          |          |          |
    |          |          |          |          |          |
    |   ACK    |   ACK    |          |          |   ACK    |
    |--------->|------------------------------->|--------->|
    |          |          |          |          |          |
    | Traffic  |          |          |          | Traffic  |
    |<====================================================>|
    |          |          |          |          |          |

Figure 6 _ Q-SIP call signaling flow - unidirectional QoS mode



3.1.2   Q-SIP message flow - bidirectional QoS reservation

The fundamental difference from the QoS unidirectional reservation mode
is that now there is only one interaction with the QoS provider, as
depicted in Figure 3. In this case when the caller-side Q-SIP receives a
200 OK response message for a QoS call, it starts a "bidirectional" QoS
reservation with the local QoS provider. The callee-side SIP server
still participates to Q-SIP signaling but does not talk with a QoS
provider. Analogously to the unidirectional case, the caller-side Q-SIP
server reads the needed information from the first INVITE and inserts
the Q-SIP extension header.  The caller-side Q-SIP also keeps the
"provisional QoS state", adds the Record-Route header (to remain along
the path of the successive requests) and forwards the message. When the
first INVITE reaches the callee-side Q-SIP, it installs the "provisional
QoS state". When the callee-side Q-SIP receives a 200 OK matching a
previously installed "provisional QoS state" it adds the QoS extensions
(ER IP address etc) and forwards the 200 OK message. Note that the
"provisional QoS state" on the callee-side Q-SIP is removed only when
ACK message from the caller is received, in order to handle possible 200
OK retransmissions. When caller-side Q-SIP receives the 200 OK it acts

Veltri et al.             Expires April 2003                        11

                  SIP Extensions for QoS support                Oct-02



in the same way as for the unidirectional case, but asking the QoS
provider for bi-directional reservation.

   SIP        SIP        Edge       Edge       SIP        SIP
Terminal     Server     Router     Router     Server    Terminal
    |          |          |          |          |          |
    |  INVITE  |  INVITE  |          |          |  INVITE  |
    |--------->|------------------------------->|--------->|
    |          |          |          |          |          |
    |180ringing|          |          |180ringing|180ringing|
    |<---------|<-------------------------------|<---------|
    |          |          |          |          |          |
    |          |          |          |  200 OK  |  200 OK  |
    |          |<-------------------------------|<---------|
    |          |   COPS   |          |          |          |
    |          |--------->|          |          |          |
    |          |   COPS   |          |          |          |
    |  200 OK  |<---------|          |          |          |
    |<---------|          |          |          |          |
    |          |          |          |          |          |
    |   ACK    |   ACK    |          |          |   ACK    |
    |--------->|------------------------------->|--------->|
    |          |          |          |          |          |
    | Traffic  |          |          |          | Traffic  |
    |<====================================================>|
    |          |          |          |          |          |

Figure 7 _ Q-SIP call signaling flow - bidirectional QoS mode


3.2 Q-SIP protocol

Regarding the management of QoS SIP sessions within Q-SIP servers, as
introduced in the previous sections, two different approaches are
considered:
i) the Q-SIP servers maintain a "provisional QoS state" during the
session setup (stateful Q-SIP),
ii) the Q-SIP servers are stateless respect to the QoS sessions during
the session setups (stateless Q-SIP).
The latter approach will lead to a lighter server implementation, but
more information has to be carried in the SIP messages.
Note that, considering that it is reasonable that a Q-SIP server will be
stateful after the session is setup (to keep track of QoS reservations),
we think that the stateful version can be preferred.
The next two sections describe separately the two variants.
The two variants differ on the manner in which the initial transaction
QoS information is kept by Q-SIP servers; in case of "stateful" Q-SIP
variant, such initial information is maintained within the server by a
"provisional QoS state", while in the "stateless" Q-SIP variant, this
information is inserted as parameter in the Record-Route header within
the request messages and read from response messages.  The latter option
is used according to the "RFC 3261" [3], stating that the Record Route
parameters can be used as a solution for keeping state in the messages

Veltri et al.             Expires April 2003                        12

                  SIP Extensions for QoS support                Oct-02



rather than within the proxies. For this reason all parameters included
must be echoed by the user agents (server side) within response
messages.

3.2.1   Stateful variant of Q-SIP protocol

In this variant a "provisional QoS state" is kept in the Q-SIP proxy
servers during session setup.
When the first Q-SIP server (i.e. the caller-side Q-SIP server) receives
a new INVITE message, it inserts the following new field :

QoS-Info: <qos-param> *(;<qos-param>)
Wherein <qos-param> can be some of:
<qos-mode> | <er-ingress> | <er-egress> | <qos-domain> | <caller-media-
addr> | caller-media-port> | <other>

example:

      QoS-Info: qos-domain=coritel.it;er-ingress=192.168.77.5;
                qos-mode=unidirectional

By means of the "er-ingress" field the caller-side Q-SIP informs the
callee-side Q-SIP server about the IP address of the caller-side ER;
instead the "er-egress" field is inserted by the callee-side Q-SIP
server for similar reason. This information is used by the Q-SIP servers
to specify to the corresponding Q-SIP server the remote endpoint of the
reservation. Note that we have assumed the "caller to callee" as an
"ingress to egress" reference direction. The "qos-domain" field is used
to identify the QoS enabled domain that the reservation has to be
accomplished. These wouldn't be strictly required in a intra-domain
scenario (one QoS enabled domain); however it could be useful for
possible interdomain extensions.
The Q-SIP server that initiates the QoS session sets also the "qos-mode"
field according to the type of QoS provider it supports (unidirectional
or bidirectional) and according to user profiles (in a scenario where
unidirectional and bidirectional QoS providers are both possible).
A Q-SIP server that receives a message and recognizes that it is for a
QoS session, according to a stateful Q-SIP implementation, it may also
decide to maintain a per-session provisional QoS state. The last Q-SIP
server that stores QoS for that request message will play as callee-side
Q-SIP server.
When the INVITE message reaches the invited callee, the UA processes the
call and if the call is accepted, generates a 200 OK response.











Veltri et al.             Expires April 2003                        13

                  SIP Extensions for QoS support                Oct-02



When the 200 OK reaches the callee-side Q-SIP server, the server
associates the response to the previously stored provisional QoS state.
The registered "qos-mode" specifies the kind of reservation to be
applied. In case of unidirectional reservations, it starts the QoS
reservation with the QoS provider (i.e. the egress ER). In order to make
the QoS request, it needs to retrieve some information (i.e. ingress ER
address, media port) from the stored provisional QoS info. When this QoS
reservation request/response phase is concluded, the 200 OK messages is
opportunely extended with a new "QoS-Info" header as follows:
      QoS-Info: qos-domain=coritel.it;er-egress=192.168.90.3;
                qos-mode=unidirectional
In case of bidirectional reservations, the callee-side Q-SIP server will
not start any QoS reservation and will forward the 200 OK message
including the QoS-Info header as shown above, where obviously qos-
mode=bidirectional.


Even if the QoS reservation for the callee-to-caller flow was not
successful, the extension is still inserted to make possible to reserve
the QoS for the caller-to-callee flow in a "QoS-Enabled" scenario;
however, in this case, the "provisional QoS state" is removed at the
receipt of the ACK for the same session. For a "QoS-Assured" model see
Appendix A.
If there are additional SIP servers handling this response in the path
between the callee-side Q-SIP and caller-side Q-SIP servers, they will
process it according to standard SIP rules. If they had previously
stored some QoS information for that session, they simply remove it.
When the message reaches the caller-side Q-SIP server, it associates the
message to the stored provisional QoS state and retrieves has all the
information to start a QoS reservation (uni- or bi-directional) with the
local QoS provider (the ingress ER). Finally, the SIP response is
forwarded to the caller.

In the Q-SIP mechanism, a key rule is played by the capacity of the Q-
SIP servers (both the caller and the callee servers) to gather the
necessary information from SIP messages in order to select the
appropriate QoS reservation. Particularly the Q-SIP servers have to
specify the bandwidth/QoS parameters and the flow characterization
parameters (i.e. for traffic policing) for the QoS reservation requests.
The Q-SIP servers have to select the appropriate level of bandwidth or
service classes, the ingress and egress ERs, and the session
identification parameters (i.e. the port number to identify the media
flows). This information can be obtained by the Q-SIP directly from the
incoming SIP messages.


As for the bandwidth or service class that has to be specified to the
QoS provider, this is selected on the basis of the type of media and
codecs specified by the end UAs (within the SDP body) and/or according
to the particular user profile. For most audio codecs it can be
relatively easy to prepare a mapping table of codecs and required
bandwidths, for RTP streams. For video codecs this is not so simple
therefore one could have to rely on user profiles. In Appendix C, it is

Veltri et al.             Expires April 2003                        14

                  SIP Extensions for QoS support                Oct-02



reported an example of mapping table for well known audio codecs. It
reports both the payload bit rates and the required bandwidths (taking
into account the IPv4 and IPv6 headers).

As for the session identification, in general different filters can be
used. For example, RSVP defines for basic flow filtering the destination
IP address, the transport protocol identifier and (optionally) a
transport address, i.e., in case of UDP/TCP, the destination port.
In our architecture we use a three-fields filter composed by the source
address, the destination address and the destination port. This
information can be extracted from the INVITE/200 OK messages directly by
the caller-side/callee-side Q-SIP servers.
Note that the caller address and port information needed to setup the
QoS for both directions are found within INVITE messages. Instead, the
reservation is made by the caller-side and callee-side Q-SIP servers
when they receive the 200 OK message. The callee media address and port
is extracted directly from the 200 OK message (the callee address from
the callee-side Q-SIP server and the callee address and port from the
caller-side Q-SIP server).

The Q-SIP call setup flow is shown in Figure 6 and Figure 7.

The tear down procedure is triggered by the receiving of the BYE and 200
OK messages at the caller-side /callee-side Q-SIP servers. When a Q-SIP
server receives the BYE request associated to a session with QoS, it
requests the releasing of the bandwidth for that session to the QoS
provider. If required, the resource details could be retrieved from a
stored "QoS state". In Appendix B there is an example of "provisional
QoS state" that can be associated to a new QoS setup transaction and the
"QoS state" that can be associated to the active QoS call.
When a BYE request matches one of the stored call-leg, the Q-SIP server
releases the resources by interacting with the QoS provider and frees
the QoS state. If a BYE message gets lost due to a terminal failure, the
session tear-down should be initiated (automatically) by the other SIP
terminal as a result of a session time-out. Another possibility to force
a resource release procedure is based on the use of time-outs and INFO
method ([7]) by the Q-SIP servers, as described in section 5. Note that
this mechanism can be used only if the UA supports the INFO method.
In order to ensure that the SIP signaling will cross the Q-SIP servers,
the Record-Route and Route headers are used. For this reason, the Q-SIP
server inserts the Record-Route header within requests for all QoS SIP
sessions.

Appendix D reports an example of Q-SIP messages using the stateful Q-SIP
variant.


3.2.2   Stateless variant of the Q-SIP protocol

Let us consider the stateless Q-SIP specification, i.e. the Q-SIP
variant that let the server stateless during the call setups. For this
reason, a mechanism is needed in order to allow a Q-SIP server that
receives a 200 OK message to retrieve all the information needed to

Veltri et al.             Expires April 2003                        15

                  SIP Extensions for QoS support                Oct-02



setup a reservation. Instead of maintaining a provisional QoS state
within the Q-SIP server, the QoS information is included in the SIP
request messages and retrieved when intercepting the responses.  The
insertion mechanism has been defined in such a way that does not require
the collaboration of SIP UAs (in order to allow the use of QoS-unaware
SIP UAs). For such objective, the Q-SIP makes use of the Route/Record-
Route SIP mechanism. According to the SIP specification, the Record-
Route header is returned opaquely by the called UA within the response
messages. Such functionality allows the Q-SIP server to "store" the QoS
information as Record-Route header parameter and to obtain it back in
the response messages.
When the caller-side Q-SIP receives an INVITE request, as specified for
a stateful Q-SIP server, it appends the previously defined QoS-Info
header and the Record-Route header.
The Record-Route header is now extended with the following Q-SIP
parameters:
      Record-Route: "<" <server-uri>;<qos-info>*(;<next_param>) ">"

Wherein <qos-info> can be of the form of:
                    <qos-param> *(;< qos-param>)

example:
Record-Route: <sip:qsip1.coritel.it;lr;
               qos-mode=unidirectional;
               qos-domain=coritel.it;
               er-ingress=192.168.77.5;
               caller-media-addr=192.168.10.44;
               caller-media-port=3220>

Note that, although it could appear redundant, both the qos-info Record-
Route parameter and the QoS-Info header is inserted by the Q-SIP.
In the same way, the callee-side Q-SIP server appends its Record-Route
header, that becomes:

Record-Route: <sip:qsip1.coritel.it;lr;qos-mode=unidirectional;
              qos-domain=coritel.it;er-ingress=192.168.77.5;
              caller-media-addr=192.168.10.44;caller-media-port=3220>,
              <sip:qsip2.coritel.it;lr;er-egress=192.168.90.3;
              caller-media-addr=192.168.10.44;caller-media-port=3220>

When the INVITE message reaches the callee host, the UA processes the
call, and, at last, generates the 200 OK response (if the call is
accepted).
If the UA is not aware of Q-SIP it simply discards the Q-SIP header (the
QoS-Info header if it is not removed by the callee-side Q-SIP server)
when forming the new response message. According to the SIP protocol,
the fields that it has to copy from the INVITE message are the Via, To,
From, CSeq, Call-ID and Record-Route header.
When the 200 OK reaches the callee-side Q-SIP server, the Record-Route
field is read and the QoS session information are extracted. In case of
unidirectional reservation mode a QoS request for the callee-to-caller
direction is started. When this QoS reservation request/response phase


Veltri et al.             Expires April 2003                        16

                  SIP Extensions for QoS support                Oct-02



is concluded and the resource is reserved, a QoS state may be stored and
the 200 OK messages is relayed toward the caller.
As for the stateful Q-SIP variant, a new QoS-Info header in added to the
response.
Even if the QoS reservation for the callee-to-caller flow was not
successful, or a bidirectional reservation is handled, this field is
still inserted to inform the callee-side Q-SIP about the callee QoS end-
point. The complete procedure for a "QoS-Assured" model is described in
Appendix A.
It is very important to remember that the use of the previously defined
Record-Route parameters lets each Q-SIP server extract all information
needed for the QoS reservation directly from the SIP message that it is
processing. This mechanism allows the Q-SIP not to keep per session
information until a QoS call is completely installed and can be used in
light Q-SIP implementations.
This "QoS state" is instead needed when the call setup is completed for
a robust tear-down procedure, for accounting and for resource control.

Regarding the caller media end-point (caller address and port), although
it is extracted from INVITE messages, it is used for making the
reservation when receiving the 200 OK message. Since no state is
maintained within the servers, both caller-side and callee-side Q-SIP
servers also store caller media end-point information within the Record-
Route qos-param (see previous examples).


Appendix E reports an example of Q-SIP messages using the stateless Q-
SIP variant.




4. Q-SIP syntax and rules

4.1 Syntax

  QoS-Info Header  = "QoS-Info" HCOLON qos-param *(SEMI qos-param)
  qos-param        = qos-mode / er-ingress / er-egress /
                     qos-domain / other
  qos-domain       = "qos-domain=" domain-name
  er-ingress       = "er-ingress=" ingress-ER-address
  er-egress        = "er-egress=" egress-ER-address
  qos-mode         = "qos-mode=" qos-reservation
  qos-reservation  = "unidirectional" / "bidirectional"
  domain-name      = alphanum / alphanum *( alphanum / "-") alphanum
  caller-media-addr= "caller-media-addr=" caller-addr
  caller-media-port= "caller-media-port=" media-port
  other            = token [EQUAL alphanum]

Record-Route Header= "Record-Route" HCOLON "<"server-uri;
                     qos-info *(;next_param)">"
  qos-info         = qos-param *(;qos-param)


Veltri et al.             Expires April 2003                        17

                  SIP Extensions for QoS support                Oct-02




4.2 Rules

Every Q-SIP server MUST be able to act as both caller-side and callee-
side Q-SIP servers.

QoS-Info Header : it is inserted by the caller-side Q-SIP server when
processing INVITE messages, and by the callee-side Q-SIP server when
processing 200 OK response messages (referring to an INVITE method).
The QoS-Info Header may carry both mandatory and optional parameters.
Table I reports for each QoS-Info parameter, whether it is mandatory (m)
or optional (o) for caller-side and callee-side Q-SIP servers.
These rules apply for both stateful and stateless Q-SIP variants.
If no qos-mode is specified, the unidirectional reservation mode is
supposed.

| Parameter          | caller-side Q-SIP | callee-side Q-SIP |
|--------------------+-------------------+-------------------|
| qos-domain         |        o          |        o          |
| er-ingress         |        m          |        -          |
| er-egress          |        -          |        m          |
| qos-mode           |        o          |        o          |
| caller-media-addr  |        o          |        -          |
| caller-media-port  |        o          |        -          |
|                    |                   |                   |

Table I - Mandatory and optional QoS-Info Header parameters


Record-Route Header : it is inserted by both caller-side and callee-side
Q-SIP servers by both stateful or stateless Q-SIP variants. The Record-
Route guaranties that the Q-SIP remains along the SIP signaling path.
The "qos-info" Record-Route parameter is inserted only for the stateless
Q-SIP variant. The implementation of the stateless Q-SIP extension
variant is not mandatory for a Q-SIP server; however if it is
implemented, all stateless Q-SIP rules MUST be satisfied.
Both caller-side and callee-side Q-SIP servers MUST insert the "qos-
info" Record-Route parameter.
Table II reports for each QoS-Info parameter, whether it is mandatory
(m) or optional (o) for caller-side and callee-side Q-SIP servers.
These rules apply for both stateful and stateless Q-SIP variants.
If no qos-mode is specified, the unidirectional reservation mode is
supposed.

| Parameter          | caller-side Q-SIP | callee-side Q-SIP |
|--------------------+-------------------+-------------------|
| qos-domain         |        o          |        o          |
| er-ingress         |        m          |        -          |
| er-egress          |        -          |        m          |
| qos-mode           |        o          |        o          |
| caller-media-addr  |        m          |        m          |
| caller-media-port  |        m          |        m          |
|                    |                   |                   |

Veltri et al.             Expires April 2003                        18

                  SIP Extensions for QoS support                Oct-02




Table II - Mandatory and optional qos-info parameters for Record-Route
Header




5. Use of INFO method for robust tear-down procedure

The tear-down of resources must be robust with respect to events like
terminal failures or network failures that may prevent the Q-SIP server
to receive the BYE message closing the session. A way to assure the
correct release of the previously reserved resources is the use of time-
outs and INFO method ([7]).
A Q-SIP proxy can use timeouts associated with the call session. The
timeout expiration triggers the generation of an INFO request matching
the characteristics of the dialog ID associated to the call state and
directed to the controlled SIP terminal (User Agent). This request and
its associated responses can be used as a "ping" for the call session
activity.
The INFO request, generated by the client side of the proxy, is sent
only to the local UA for a call session that the outbound Q-SIP proxy
has reserved resources to, so only local additional signaling messages
are generated.
The server side of the UA can respond with several messages that are
interpreted and used by the Q-SIP proxy:

          UA response to INFO              Q-SIP Proxy action
-------------------------------------------------------------------
200OK : Call/transaction exists          renew timeout associated
481   : Call/transaction doesn't         release reserved resources
        exist
405   : Method not allowed/supported     don't use this mechanism for
                                         this call session
501   : Not implemented                  don't use this mechanism for
                                         this UA

The chose of the time-out value is left to vendor implementation.


6. SIP Terminals

Although it has been supposed that the SIP user UAs are not aware of the
Q-SIP reservation mechanism, Q-SIP aware UAs can be also considered
(Figure 4).
Q-SIP aware UAs should simply include Q-SIP as described in the previous
sections. In that case, the UAs could directly request QoS reservation
to the QoS providers and the Q-SIP signaling would transparently bypass
any SIP or Q-SIP proxy server. Moreover the architecture is fully
compatible also for calls starting from Q-SIP aware UAs and directed to
standard SIP UAs with Q-SIP proxy servers, and vice-versa (Figure 5).



Veltri et al.             Expires April 2003                        19

                  SIP Extensions for QoS support                Oct-02



7. Q-SIP Servers

A basic design choice in the design of a SIP proxy server is whether to
make it stateful or stateless. Being stateful means that it keeps a
record of active SIP session and the processing of SIP messages can
depend on the session status. Being stateless means that each message is
processed by itself with no relations with previous messages of the same
session. A stateful server of course is more powerful as it can better
handle additional aspects (like for example policy and accounting), but
the SIP protocol has been designed so that stateless server can work as
well.
Looking at the proposed approach, we note that the Q-SIP server handles
the QoS for a SIP session, by making a reservation in the QoS enabled
network. The Q-SIP server has to care about this reservation, for
example the resources must be properly released when the session is
closed. For this reason we believe that the Q-SIP server must be
stateful once the session has been established.
Nevertheless, we have designed our Q-SIP extensions preserving the SIP
design goals: is possible either to store state information in Q-SIP
server during the session establishment or to carry all the needed
information in the SIP messages.




8. Security Considerations

A proxy that performs resource reservations triggered by the reception
of unauthenticated requests can be an easy target of a DoS (Denial of
Service) attack. Requests for a possible QoS session SHOULD be
authenticated.
In order to assure the correct handling of the QoS service offered to
the UA by the outbound Q-SIP server, proxy authentication SHOULD be
used. In this way, the Q-SIP before initiates a QoS session and
reserving resources, can use the authorization/authentication mechanism
to assure the right access control and availability of the service in
accord to the user profile.
The user profile can contain user password and the type of service that
the user is enabled to, so it can be used as authentication and resource
reservation support.




9. Change log and prototype implementation

This version v1 is the second version of the Q-SIP draft. The changes
with respect to previous version v0 are:

  - QoS state information in SIP messages is now carried in Record
    Route headers instead of Via headers (according to the change in
    SIP specification of [3])
  - The stateful variant of the Q-SIP protocol has been specified.

Veltri et al.             Expires April 2003                        20

                  SIP Extensions for QoS support                Oct-02



  - The use of bidirectional reservation (according to 2.1.)is
    supported
  - The use of INFO messages to support robust tear-down of resources
    has bee specified
  - A discussion on QoS assured model (Appendix A) has been added

A prototype implementation of a Q-SIP server is available [6].

The messages reported in Appendix D are extracted from the current
implementation in a simple successful SIP call that involves two Q-SIP
servers.



Appendix A: QoS-Enabled vs. QoS-Assured

In the previous part of the document the QoS enabled resource
reservation is considered. In a QoS assured scenario [1] the QoS can be
a precondition to the establishment of the session indicated by SIP. An
UA can use the Q-SIP proxy reservation mechanism in order to reserve
resources before beginning the session. In this scenario a UA can be
preconfigured to use the mechanism here described. Various situations
depending on the type of reservation handled by the proxy are discussed.
The UAs involved in this scenario supports the qos preconditions as
specified in [1] and the reliable provisional responses [8]. A
precondition is an information written in the SDP describing the SIP
session. By means of this information the terminals can communicate each
other that they want a QoS reservation and then that the reservation has
been established.
The main idea is the following. A Q-SIP server receives a message for a
local UA containing preconditions (i.e. stating that QoS reservation is
needed). The Q-SIP server will take care of the resource reservation and
change the preconditions in the message according to the reservation
done. In other words the Q-SIP will ensure that preconditions are met
with no need for the UAs to setup the QoS reservations..
This can be considered an alternative scenario to those presented in [1]
that consider only UAs supporting RSVP.

In the following sections A.1 and A.2 the technical details of the
possible interaction of the QoS assured scenario described in [1] and
the Q-SIP architecture are provided.

Note that in the described scenarios the Q-SIP server needs to modify
the SDP inside the SIP message.  Another more elegant solution could be
to insert a new SIP header to report the result of the resource
reservation to the UA. The UA will then change the SDP as described in
[1]. The drawback in this case is that the UAs need to supports the new
defined header.

A.1  Q-SIP using unidirectional QoS Network reservation

A.1.1  Bidirectional e2e reservation sender initiated


Veltri et al.             Expires April 2003                        21

                  SIP Extensions for QoS support                Oct-02



Figure 8 reports the signaling flow with the most important
interactions.

   SIP         Q-SIP       Edge       Edge       Q-SIP         SIP
   UA(A)      Server A     Router     Router   Server B       UA(B)
    |            |          |          |          |             |
    |INVITE(SDP1)|          INVITE(SDP1)          |INVITE(SDP1) |
    |----------->|------------------------------->|------------>|
    |            |          |          |          |             |
    |            |          |          |          |  183(SDP2)  |
    |            |          |          |   COPS   |<------------|
    |            |          |          |<---------|             |
    |            |          |          |   COPS   |             |
    |            |          |          |--------->|             |
    |            |          |          |183(SDP3) |             |
    |            |<-------------------------------|             |
    |            |   COPS   |          |          |             |
    |            |--------->|          |          |             |
    |            |   COPS   |          |          |             |
    |  183(SDP4) |<---------|          |          |             |
    |<-----------|          |          |          |             |
    |   PRACK    |          PRACK                 |    PRACK    |
    |----------->|------------------------------->|------------>|
    |            |      200 OK (PRACK)            |             |
    |<-----------|<-------------------------------|<------------|
    |UPDATE(SDP5)|          UPDATE(SDP5)          | UPDATE(SDP5)|
    |----------->|------------------------------->|------------>|
    |            |      200 OK (UPDATE)           |             |
    |<-----------|<-------------------------------|<------------|
    |            |      180 Ringing               |             |
    |<-----------|<-------------------------------|<------------|
    |            |      200 OK (INVITE)           |             |
    |<-----------|<-------------------------------|<------------|
    |   Traffic  |          |          |          |   Traffic   |
    |<=========================================================>|
    |            |          |          |          |             |


Figure 8 _ Bidirectional e2e successful reservation using Q-SIP in the
QoS assured sender initiated case

When Q-SIP A receives an INVITE containing an offer from a UA that is
preconfigured (user profile defined) to use it for the resource
reservation in a QoS assured mode, it reads SDP1. If it contains the SDP
attribute "a=des:" with the "qos" precondition_type, "mandatory"
strength tag, "e2e" status type and "send" or "sendrecv" direction-tag
the Q-SIP starts a QoS session as described previously. Almost the same
for Q-SIP B, that relies in the user profile of the called UA (UA (B))
to start the QoS session. The difference is even in the direction-tag
that must be "recv" or "sendrecv" to initiate the QoS session.
UA (B) relies in Q-SIP proxy QoS handling (preconfigured for proxy
resource reservation) so it responds with a reliable 183(SDP2) if it
wants to set-up the call with QoS. If for any reason it does not want,

Veltri et al.             Expires April 2003                        22

                  SIP Extensions for QoS support                Oct-02



it responds with a 580 Failure that is used also by the Q-SIP proxies to
terminate the pending QoS session.
When the Q-SIP B receives the 183(SDP2), it has all the information to
perform the resource reservation and depending on the result it changes
the SDP: if reservation (callee to caller) fails it sends SDP2 (SDP not
changed), if is OK sends SDP3(SDP changed!!!).
If the Q-SIP A receives a 183(SDP2), it understands that the reservation
in the callee to caller direction is failed , terminates the initiated
QoS session and proxies the message to the UA(A). If the message
received is a 183(SDP3), it performs the resource reservation. If the
reservation is successful the Q-SIP changes SDP3 in SDP4, else it
terminates the QoS session and does not change the SDP3.
If the UA(A) receives a 183 with SDP4 it sends immediately the new offer
in SDP5 using the UPDATE message. In any other case it assumes that the
QoS session has failed so it sends SDP6 in the UPDATE message.
Q-SIP A and Q-SIP B do nothing in case of UPDATE with SDP5, in case of
SDP6 the Q-SIP B releases the resources previously reserved.
Hereafter the relevant parts of the SDPs are listed:

        SDP1:   a=curr: qos e2e none
                a=des: qos mandatory e2e sendrecv

      SDP2: a=curr: qos e2e none
            a=des: qos mandatory e2e sendrecv
            a=conf: qos e2e recv

      SDP3: a=curr: qos e2e send
            a=des: qos mandatory e2e sendrecv
            a=conf: qos e2e recv

      SDP4: a=curr: qos e2e sendrecv
            a=des: qos mandatory e2e sendrecv
            a=conf: qos e2e recv

      SDP5: a=curr: qos e2e sendrecv
            a=des: qos mandatory e2e sendrecv

      SDP6: a=curr: qos e2e ****
            a=des: qos failure e2e sendrecv



A.1.2  Unidirectional e2e reservation sender initiated

In these cases only one flow is required to have the QoS support as
reported on the SDP1 (the offer).

Caller to callee QoS e2e required:

      SDP1: a=curr: qos e2e none
            a=des: qos mandatory e2e send



Veltri et al.             Expires April 2003                        23

                  SIP Extensions for QoS support                Oct-02



Q-SIP A handles the reservation and if it successful it changes the SDP
of the answer: SDP2 in SDP3. Q-SIP B only use Q-SIP extensions to
transmit to Q-SIP A the callee-side ER.

      SDP2: a=curr: qos e2e none
            a=des: qos mandatory e2e recv

      SDP3: a=curr: qos e2e recv
            a=des: qos mandatory e2e recv

Callee to caller QoS e2e required:

      SDP1: a=curr: qos e2e none
            a=des: qos mandatory e2e recv

Q-SIP A only uses Q-SIP extensions to transmit to Q-SIP B the caller ER.
Q-SIP B handles the reservation and if it is successful it changes SDP2
in SDP3 as reported below.

      SDP2: a=curr: qos e2e none
            a=des: qos mandatory e2e send

      SDP3: a=curr: qos e2e send
            a=des: qos mandatory e2e send

In all cases if a failure situation occurs the UA(A) sends the UPDATE
with the new offer containing SDP4.

      SDP3: a=curr: qos e2e ****
            a=des: qos failure e2e ****

Note: **** mean send or recv.


A.1.3  Bidirectional e2e reservation receiver initiated

In this case the first INVITE does not contain an SDP so the Q-SIP
entities cannot distinguish at this point if the session is to be set or
not with QoS. Even in this case the outbound proxy for the caller and
the callee side may remain on the signaling path using the Record-Route
support. As reported in Figure 9 it is the UA(B) that initiates the
offer-answer exchange sending the reliable 183(SDP1).
When Q-SIP B receives the 183(SDP1) and an associated QoS session does
not exist, it initiates the QoS session and uses the Q-SIP extensions to
transmit the callee-side ER.
When Q-SIP A receives the 183(SDP1) reporting also the extensions, it
initiates the QoS session.
UA(A) knows that it is configured with the Q-SIP for supporting the QoS
so it can send immediately the PRACK(SDP2)[7][8].
In the Q-SIP A the receipt of the PRACK(SDP2) for a QoS session of a UA
that is configured to have the QoS assured support triggers the
reservation (now we have all the needed information). If the reservation
is successful this is reported inside SDP3 and Q-SIP A uses the Q-SIP

Veltri et al.             Expires April 2003                        24

                  SIP Extensions for QoS support                Oct-02



extensions to transmit to the callee-side Q-SIP proxy the caller-side
ER, if not the SDP is removed (compliant with [1]) and the QoS session
is terminated.
If the Q-SIP B receives PRACK without SDP2 and the extensions, it
removes the QoS session and simply proxies the message. If the message
received is PRACK(SDP3) with the extensions, it tries to reserve the
resources requested. If the reservation is successful this is reported
inside SDP4, if not the SDP is removed, the QoS session is terminated
and the message is forwarder to UA(B).
Hereafter the relevant parts of the SDPs involved are reported:

      SDP1: a=curr: qos e2e none
            a=des: qos mandatory e2e sendrecv
            a=conf: qos e2e recv

      SDP2: a=curr: qos e2e none
            a=des: qos mandatory e2e sendrecv

      SDP3: a=curr: qos e2e send
            a=des: qos mandatory e2e sendrecv
      SDP4: a=curr: qos e2e sendrecv
            a=des: qos mandatory e2e sendrecv

Note that the if UA(B) receives SDP4, it knows that the preconditions
are meet so it can immediately send 200 OK (of PRACK) and the 180
Ringing without the need of an UPDATE. The UA(A) receives the 180
Ringing that assures that the preconditions are met.



























Veltri et al.             Expires April 2003                        25

                  SIP Extensions for QoS support                Oct-02



   SIP         Q-SIP       Edge       Edge       Q-SIP         SIP
   UA(A)      Server A     Router     Router   Server B       UA(B)
    |            |          |          |          |             |
    |   INVITE   |            INVITE              |   INVITE    |
    |----------->|------------------------------->|------------>|
    |            |          |          |          |             |
    |            |          |          |          |  183(SDP1)  |
    |            |            183(SDP1)           |<------------|
    |  183(SDP1) |<-------------------------------|             |
    |<-----------|          |          |          |             |
    | PRACK(SDP2)|          |          |          |             |
    |----------->|   COPS   |          |          |             |
    |            |--------->|          |          |             |
    |            |   COPS   |          |          |             |
    |            |<---------|          |          |             |
    |            |          PRACK(SDP3)           |             |
    |            |------------------------------->|             |
    |            |          |          |   COPS   |             |
    |            |          |          |<---------|             |
    |            |          |          |   COPS   |             |
    |            |          |          |--------->| PRACK(SDP4) |
    |            |          |          |          |------------>|
    |            |         200 OK (PRACK)         |             |
    |<-----------|<-------------------------------|<------------|
    |            |      180 Ringing               |             |
    |<-----------|<-------------------------------|<------------|
    |            |      200 OK (INVITE)           |             |
    |<-----------|<-------------------------------|<------------|
    |   Traffic  |          |          |          |   Traffic   |
    |<=========================================================>|
    |            |          |          |          |             |


Figure 9 _ Bidirectional e2e successful reservation using Q-SIP in the
           QoS assured receiver initiated case

If the PRACK received by UA(B) does not contain SDP, we have the
precondition failure case that is handled according to [7].



A.1.4  Unidirectional e2e reservation receiver initiated

In these cases only one flow is required to have the QoS support as
reported on the SDP1 (the offer).

Callee to caller QoS e2e required:

      SDP1: a=curr: qos e2e none
            a=des: qos mandatory e2e send




Veltri et al.             Expires April 2003                        26

                  SIP Extensions for QoS support                Oct-02



Q-SIP A only uses Q-SIP extensions to transmit to Q-SIP B the callee-
side ER. Q-SIP B handles the reservation and if it successful change SDP
of the answer: SDP2 in SDP3. If not it removes the SDP from the PRACK.

      SDP2: a=curr: qos e2e none
            a=des: qos mandatory e2e recv

      SDP3: a=curr: qos e2e recv
            a=des: qos mandatory e2e recv

Caller to callee QoS e2e required:

      SDP1: a=curr: qos e2e none
            a=des: qos mandatory e2e recv
            a=conf: qos e2e recv

Q-SIP B only uses Q-SIP extensions to transmit to Q-SIP B the caller ER
using the 183(SDP1). Q-SIP A handles the reservation and if it is
successful, change SDP2 in SDP3 as reported below. If not removes the
SDP from the PRACK.

      SDP2: a=curr: qos e2e none
            a=des: qos mandatory e2e send

      SDP3: a=curr: qos e2e send
            a=des: qos mandatory e2e send



A.2  Q-SIP using bidirectional QoS Network reservation

A.2.1  Bidirectional e2e reservation sender initiated

In the Figure 10 is reported the signaling flow with the most important
entity interactions. The main differences are that only one of the Q-SIP
(the caller one) is involved in the network reservation and the other
one needs only as support to have the needed information. Here below are
listed the entity interactions:

Q-SIP A receives INVITE(SDP1) from an UA that is enabled to receive the
QoS assured support: Initiate an QoS session and proxy the message
containing the Q-SIP extensions for this case.
Q-SIP B receives INVITE(SDP1) with the Q-SIP extensions: It installs the
QoS session and proxy the message.
UA(B) receives INVITE(SDP1) and it is preconfigured to have the QoS
proxy support (if need), so it sends the 183(SDP2).
Q-SIP B receives 183(SDP2) for an existing QoS session: It inserts the
Q-SIP extensions and proxy the message.
Q-SIP A receives 183(SDP2) for an existing QoS session: It handle
reservation; if it is successful change SDP in SDP3, if not don't
change-it.
When UA(A) receives 183(SDP3) it sends PRACK and UPDATE(SDP4). In the
other cases (preconditions failure), it sends PRACK and UPDATE(SDP5).

Veltri et al.             Expires April 2003                        27

                  SIP Extensions for QoS support                Oct-02



The SDPs involved in the signaling flow:

      SDP1: a=curr: qos e2e none
            a=des: qos mandatory e2e sendrecv

      SDP2: a=curr: qos e2e none
            a=des: qos mandatory e2e sendrecv
            a=conf: qos e2e recv

      SDP3: a=curr: qos e2e sendrecv
            a=des: qos mandatory e2e sendrecv
            a=conf: qos e2e recv

      SDP4: a=curr: qos e2e sendrecv
            a=des: qos mandatory e2e sendrecv

      SDP5: a=curr: qos e2e none
            a=des: qos failure e2e sendrecv




































Veltri et al.             Expires April 2003                        28

                  SIP Extensions for QoS support                Oct-02



   SIP         Q-SIP       Edge       Edge       Q-SIP         SIP
   UA(A)      Server A     Router     Router   Server B       UA(B)
    |            |          |          |          |             |
    |INVITE(SDP1)|          INVITE(SDP1)          |INVITE(SDP1) |
    |----------->|------------------------------->|------------>|
    |            |          |          |          |             |
    |            |          |          |          |  183(SDP2)  |
    |            |          |          |          |<------------|
    |            |          |          |183(SDP2) |             |
    |            |<-------------------------------|             |
    |            |   COPS   |          |          |             |
    |            |--------->|          |          |             |
    |            |   COPS   |          |          |             |
    |  183(SDP3) |<---------|          |          |             |
    |<-----------|          |          |          |             |
    |   PRACK    |          PRACK                 |    PRACK    |
    |----------->|------------------------------->|------------>|
    |            |      200 OK (PRACK)            |             |
    |<-----------|<-------------------------------|<------------|
    |UPDATE(SDP4)|          UPDATE(SDP4)          | UPDATE(SDP4)|
    |----------->|------------------------------->|------------>|
    |            |      200 OK (UPDATE)           |             |
    |<-----------|<-------------------------------|<------------|
    |            |      180 Ringing               |             |
    |<-----------|<-------------------------------|<------------|
    |            |      200 OK (INVITE)           |             |
    |<-----------|<-------------------------------|<------------|
    |   Traffic  |          |          |          |   Traffic   |
    |<=========================================================>|
    |            |          |          |          |             |


Figure 10 _ Bidirectional e2e successful reservation using Q-SIP in the
QoS assured sender initiated case

Note that the QoS session on the Q-SIP B is removed when the PRACK for
the 183 is received.

A.2.2  Bidirectional e2e reservation receiver initiated

The difference from the 3.1.3 is that only one reservation is done by
the caller-side Q-SIP and the Q-SIP B only supports this reservation by
giving the callee-side ER.
Here after the SDP involved in the signaling messages (shown in the
Figure 11) are reported:

      SDP1: a=curr: qos e2e none
            a=des: qos mandatory e2e sendrecv
            a=conf: qos e2e recv

      SDP2: a=curr: qos e2e none
            a=des: qos mandatory e2e sendrecv


Veltri et al.             Expires April 2003                        29

                  SIP Extensions for QoS support                Oct-02



      SDP3: a=curr: qos e2e sendrecv
            a=des: qos mandatory e2e sendrecv



   SIP         Q-SIP       Edge       Edge       Q-SIP         SIP
   UA(A)      Server A     Router     Router   Server B       UA(B)
    |            |          |          |          |             |
    |   INVITE   |            INVITE              |   INVITE    |
    |----------->|------------------------------->|------------>|
    |            |          |          |          |             |
    |            |          |          |          |  183(SDP1)  |
    |            |            183(SDP1)           |<------------|
    |  183(SDP1) |<-------------------------------|             |
    |<-----------|          |          |          |             |
    | PRACK(SDP2)|          |          |          |             |
    |----------->|   COPS   |          |          |             |
    |            |--------->|          |          |             |
    |            |   COPS   |          |          |             |
    |            |<---------|          |          |             |
    |            |          PRACK(SDP3)           |             |
    |            |------------------------------->|------------>|
    |            |         200 OK (PRACK)         |             |
    |<-----------|<-------------------------------|<------------|
    |            |      180 Ringing               |             |
    |<-----------|<-------------------------------|<------------|
    |            |      200 OK (INVITE)           |             |
    |<-----------|<-------------------------------|<------------|
    |   Traffic  |          |          |          |   Traffic   |
    |<=========================================================>|
    |            |          |          |          |             |


Figure 11 _ Bidirectional e2e successful reservation using Q-SIP in the
QoS assured receiver initiated case




Appendix B - Description of the QoS State

A possible implementation of the QoS State :


<QoState> ::= <Call-Identification>
              <Type of state >
              <Scope of the reservation>
             <Type of the reservation>
             <Session identification filter>

The Call-Identification has the following format:

<Call-Identification> ::= <Call-ID>

Veltri et al.             Expires April 2003                        30

                  SIP Extensions for QoS support                Oct-02




The type of state has the following format:

< Type of state > ::= <Provisional/Call>

The scope of the reservation has the following format :

<Scope of the reservation> ::= <QoSdomainID>
                               <Ingress ER>
                               <Egress ER>
                               <Bandwidth>

The type of the reservation has the following format :

<Type of the reservation> ::= <Unidirectional/Bidirectional>

The Session identification filter has the following format:

<Session identification filter> ::= <Source address>
                                    [<Source port>]
                                    <Destination address>
                                    <Destination port>

Note that the source/destination port is to intend as the ingress ports
for the media flow (the port where the User Agent wait for the media
data). According to the assumptions made before, that the QoS state in
our scenario refers to a unidirectional or bidirectional flow inside the
core network.


Appendix C - Payload type vs. bandwidth

|---------|---------|---------|-----------------------|
|         | Payload | Payload |                       |
|  Code   |  Type   | Bit-Rate| Bandwidth (IPv4/IPv6) |
|         |         | (kbit/s)|       (kbit/s)        |
|---------|---------|---------|-----------------------|
|  PCMU   |    0    |   64    |      81.6 / 88        |
|  1016   |    1    |   16    |      33.6 / 40        |
|  G.721  |    2    |   32    |      49.6 / 56        |
|  GSM    |    3    |   13    |      30.6 / 37        |
|  G.723  |    4    |    6.3  |      23.9 / 30.3      |
|  DV14   |    5    |   32    |      49.6 / 56        |
| DV14(2) |    6    |   64    |      81.6 / 88        |
|  LPC    |    7    |    2.4  |        20 / 26.6      |
|  PCMA   |    8    |   64    |      81.6 / 88        |
|  G.722  |    9    |   64    |      81.6 / 88        |
|  MPA    |   14    |   32    |      49.6 / 56        |
|  G.728  |   15    |   16    |      33.6 / 40        |
|  G.729  |   18    |    8    |      25.6 / 32        |
|         |         |         |                       |
|---------|---------|---------|-----------------------|


Veltri et al.             Expires April 2003                        31

                  SIP Extensions for QoS support                Oct-02




Appendix D - Examples of Q-SIP messages

Examples of Q-SIP messages in the successful reservation scenario using
the "provisional QoS state" approach are depicted in the picture
hereafter. The messages are numbered from M1 to M18. Only the messages
sent by the proxy servers are reported in detail.


<sip:UserA@gauss.coritel.it>          <sip:UserB@maxwell.coritel.it>
 eulero.coritel.it                              galileo.coritel.it
               gauss.coritel.it  maxwell.coritel.it
   User A          Proxy 1          Proxy 2          User B
     |   INVITE M1    |                |                |
     |--------------->|   INVITE M2    |                |
     |                |--------------->|   INVITE M3    |
     |                |                |--------------->|
     |  180ringing M6 | 180ringing M5  |  180ringing M4 |
     |<---------------|<---------------|<---------------|
     |                |                |   200 OK M7    |
     |                |   200 OK M8    |<---------------|
     |    200 OK M9   |<---------------|                |
     |<---------------|                |                |
     |     ACK M10    |    ACK M11     |     ACK M12    |
     |--------------->|--------------->|--------------->|
     |                 RTP Media                        |
     |<================================================>|
     |                |                |     BYE M13    |
     |                |    BYE M14     |<---------------|
     |     BYE M15    |<---------------|                |
     |<---------------|                |                |
     |   200 OK M16   |   200 OK M17   |   200 OK M18   |
     |--------------->|--------------->|--------------->|





















Veltri et al.             Expires April 2003                        32

                  SIP Extensions for QoS support                Oct-02



Message M2 (INVITE from Proxy 1 to Proxy 2):

INVITE sip:UserB@maxwell.coritel.it SIP/2.0
Via: SIP/2.0/UDP gauss.coritel.it:5060;branch=z9hG4bKzksdfse3re
Via: SIP/2.0/UDP eulero.coritel.it:5060;branch=z9hG4bKzkdui3jfid
From: UserA<sip:UserA@gauss.coritel.it>;tag=938108741
To: UserB<sip:UserB@maxwell.coritel.it>
Server: Coritel SIP Server 1.0
Record-Route: <sip:gauss.coritel.it;lr>
QoS-Info: qos-domain=coritel.it;er-ingress=192.168.90.3;qos-mode=
unidirectional
Call-ID: 1234567001@eulero.coritel.it
Max-Forwards: 69
CSeq: 1 INVITE
Contact: <sip:UserA@151.100.37.131>
Content-Type: application/sdp
Content-Length: 148

v=0
o=UserA 2890844526 2890844526 IN IP4 eulero.coritel.it
s=Session SDP
c=IN IP4 151.100.37.131
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000

Message M3 (INVITE from Proxy 2 to User B):

INVITE sip:UserB@galileo.coritel.it:5060 SIP/2.0
Via: SIP/2.0/UDP maxwell.coritel.it:5060;branch=z9hG4bKkvjg1kk5gf
Via: SIP/2.0/UDP gauss.coritel.it:5060;branch=z9hG4bKzksdfse3re
Via: SIP/2.0/UDP eulero.coritel.it:5060;branch=z9hG4bKzkdui3jfid
From: UserA<sip:UserA@gauss.coritel.it>;tag=938108741
To: UserB<sip:UserB@maxwell.coritel.it>
Server: Coritel SIP Server 1.0
Server: Coritel SIP Server 1.0
Record-Route: <sip:gauss.coritel.it;lr>,<sip:maxwell.coritel.it;lr>
Call-ID: 1234567001@eulero.coritel.it
Max-Forwards: 68
CSeq: 1 INVITE
Contact: <sip:UserA@151.100.37.131>
Content-Type: application/sdp
Content-Length: 148

v=0
o=UserA 2890844526 2890844526 IN IP4 eulero.coritel.it
s=Session SDP
c=IN IP4 151.100.37.131
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000



Veltri et al.             Expires April 2003                        33

                  SIP Extensions for QoS support                Oct-02



Message M8 (200 OK from Proxy 2 to Proxy1):

SIP/2.0 200 OK
Via: SIP/2.0/UDP gauss.coritel.it:5060;branch=z9hG4bKzksdfse3re
Via: SIP/2.0/UDP eulero.coritel.it:5060;branch=z9hG4bKzkdui3jfid
From: UserA<sip:UserA@gauss.coritel.it>;tag=938108741
To: UserB<sip:UserB@maxwell.coritel.it>;tag=181046899
Record-Route: <sip:gauss.coritel.it;lr>,<sip:maxwell.coritel.it;lr>
QoS-Info: qos-domain=coritel.it;er-egress=192.168.90.9;qos-mode=
unidirectional
Call-ID: 1234567001@eulero.coritel.it
CSeq: 1 INVITE
Contact: <sip:UserB@151.100.37.143>
Content-Type: application/sdp
Content-Length: 148

v=0
o=UserB 2890844527 2890844527 IN IP4 galileo.coritel.it
s=Session SDP
c=IN IP4 151.100.37.143
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000































Veltri et al.             Expires April 2003                        34

                  SIP Extensions for QoS support                Oct-02



Message M9 (200 OK from Proxy 1 to User A):

SIP/2.0 200 OK
Via: SIP/2.0/UDP eulero.coritel.it:5060;branch=z9hG4bKzkdui3jfid
From: UserA<sip:UserA@gauss.coritel.it>;tag=938108741
To: UserB<sip:UserB@maxwell.coritel.it>;tag=181046899
Record-Route: <sip:gauss.coritel.it;lr>,<sip:maxwell.coritel.it;lr>
Call-ID: 1234567001@eulero.coritel.it
CSeq: 1 INVITE
Contact: <sip:UserB@151.100.37.143>
Content-Type: application/sdp
Content-Length: 148

v=0
o=UserB 2890844527 2890844527 IN IP4 galileo.coritel.it
s=Session SDP
c=IN IP4 151.100.37.143
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

Message M14 (BYE from Proxy 2 to Proxy 1):

BYE sip:UserA@gauss.coritel.it SIP/2.0
Via: SIP/2.0/UDP maxwell.coritel.it:5060;branch=z9hG4bKljfds7df8s
Via: SIP/2.0/UDP galileo.coritel.it:5060;branch=z9hG4bKpinfjd6h3h
Route: <sip:gauss.coritel.it;lr>
From: UserB<sip:UserB@maxwell.coritel.it>;tag=181046899
To: UserA<sip:UserA@gauss.coritel.it>;tag=938108741
Server: Coritel SIP Server 1.0
Call-ID: 1234567001@eulero.coritel.it
Max-Forwards: 69
CSeq: 1 BYE
Content-Length: 0


Message M15 (BYE from Proxy 1 to user A)

BYE sip:UserA@eulero.coritel.it:5060 SIP/2.0
Via: SIP/2.0/UDP gauss.coritel.it:5060;branch=z9hG4bKlj2kl4jdik
Via: SIP/2.0/UDP maxwell.coritel.it:5060;branch=z9hG4bKljfds7df8s
Via: SIP/2.0/UDP galileo.coritel.it:5060;branch=z9hG4bKpinfjd6h3h From:
UserB<sip:UserB@maxwell.coritel.it>;tag=181046899
To: UserA<sip:UserA@gauss.coritel.it>;tag=938108741
Server: Coritel SIP Server 1.0
Server: Coritel SIP Server 1.0
Call-ID: 1234567001@eulero.coritel.it
Max-Forwards: 68
CSeq: 1 BYE
Content-Length: 0




Veltri et al.             Expires April 2003                        35

                  SIP Extensions for QoS support                Oct-02












Appendix E


Examples of Q-SIP messages in the successful reservation scenario
keeping "provisional QoS state" in the messages are depicted in the
picture hereafter. The messages are numbered from M1 to M18. Only the
messages sent by the proxy servers are reported in detail.


<sip:UserA@gauss.coritel.it>          <sip:UserB@maxwell.coritel.it>
 eulero.coritel.it                              galileo.coritel.it
               gauss.coritel.it  maxwell.coritel.it
   User A          Proxy 1          Proxy 2          User B
     |   INVITE M1    |                |                |
     |--------------->|   INVITE M2    |                |
     |                |--------------->|   INVITE M3    |
     |                |                |--------------->|
     |  180ringing M6 | 180ringing M5  |  180ringing M4 |
     |<---------------|<---------------|<---------------|
     |                |                |   200 OK M7    |
     |                |   200 OK M8    |<---------------|
     |    200 OK M9   |<---------------|                |
     |<---------------|                |                |
     |     ACK M10    |    ACK M11     |     ACK M12    |
     |--------------->|--------------->|--------------->|
     |                 RTP Media                        |
     |<================================================>|
     |                |                |     BYE M13    |
     |                |    BYE M14     |<---------------|
     |     BYE M15    |<---------------|                |
     |<---------------|                |                |
     |   200 OK M16   |   200 OK M17   |   200 OK M18   |
     |--------------->|--------------->|--------------->|












Veltri et al.             Expires April 2003                        36

                  SIP Extensions for QoS support                Oct-02



Message M2 (INVITE from Proxy 1 to Proxy 2):

INVITE sip:UserB@maxwell.coritel.it SIP/2.0
Via: SIP/2.0/UDP gauss.coritel.it:5060;branch=z9hG4bKicd7op8ocx
Via: SIP/2.0/UDP eulero.coritel.it:5060;branch=z9hG4bKjasldjl2oi
From: UserA<sip:UserA@gauss.coritel.it>;tag=734578133
To: UserB<sip:UserB@maxwell.coritel.it>
Server: Coritel SIP Server 1.0
Record-Route: <sip: gauss.coritel.it;lr;qos-mode=unidirectional;qos-
domain=coritel.it;er-ingress=192.168.90.3;caller-media-
addr=151.100.37.131;caller-media-port=49172>
QoS-Info: qos-domain=coritel.it;er-ingress=192.168.90.3;qos-mode=
unidirectional
Call-ID: 1234567801@eulero.coritel.it
Max-Forwards: 69
CSeq: 1 INVITE
Contact: <sip:UserA@151.100.37.131>
Content-Type: application/sdp
Content-Length: 148

v=0
o=UserA 2890844526 2890844526 IN IP4 eulero.coritel.it
s=Session SDP
c=IN IP4 151.100.37.131
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000



























Veltri et al.             Expires April 2003                        37

                  SIP Extensions for QoS support                Oct-02



Message M3 (INVITE from Proxy 2 to User B):

INVITE sip:UserB@galileo.coritel.it:5060 SIP/2.0
Via: SIP/2.0/UDP maxwell.coritel.it:5060;branch=z9hG4bKsdfpogir4r
Via: SIP/2.0/UDP gauss.coritel.it:5060;branch=z9hG4bKicd7op8ocx
Via: SIP/2.0/UDP eulero.coritel.it:5060;branch=z9hG4bKjasldjl2oi
From: UserA<sip:UserA@gauss.coritel.it>;tag=734578133
To: UserB<sip:UserB@maxwell.coritel.it>
Server: Coritel SIP Server 1.0
Server: Coritel SIP Server 1.0
Record-Route: <sip:gauss.coritel.it;lr;qos-mode=unidirectional;qos-
domain=coritel.it;er-ingress=192.168.90.3;caller-media-
addr=151.100.37.131;caller-media-port=49172>,
<sip:maxwell.coritel.it;lr;er-ingress=192.168.90.3;caller-media-
addr=151.100.37.131;caller-media-port=49172>
Call-ID: 1234567801@eulero.coritel.it
Max-Forwards: 68
CSeq: 1 INVITE
Contact: <sip:UserA@151.100.37.131>
Content-Type: application/sdp
Content-Length: 148

v=0
o=UserA 2890844526 2890844526 IN IP4 eulero.coritel.it
s=Session SDP
c=IN IP4 151.100.37.131
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000

























Veltri et al.             Expires April 2003                        38

                  SIP Extensions for QoS support                Oct-02



Message M8 (200 OK from Proxy 2 to Proxy 1):

SIP/2.0 200 OK
Via: SIP/2.0/UDP gauss.coritel.it:5060;branch=z9hG4bKicd7op8ocx
Via: SIP/2.0/UDP eulero.coritel.it:5060;branch=z9hG4bKjasldjl2oi
From: UserA<sip:UserA@gauss.coritel.it>;tag=734578133
To: UserB<sip:UserB@maxwell.coritel.it>;tag=234857984
Record-Route: <sip:gauss.coritel.it;lr;qos-mode=unidirectional;qos-
domain=coritel.it;er-ingress=192.168.90.3;caller-media-
addr=151.100.37.131;caller-media-port=49172>,
<sip:maxwell.coritel.it;lr;er-ingress=192.168.90.3;caller-media-
addr=151.100.37.131;caller-media-port=49172>
QoS-Info: qos-domain=coritel.it;er-egress=192.168.90.9;qos-mode=
unidirectional
Call-ID: 1234567801@eulero.coritel.it
CSeq: 1 INVITE
Contact: <sip:UserB@151.100.37.143>
Content-Type: application/sdp
Content-Length: 148

v=0
o=UserB 2890844527 2890844527 IN IP4 galileo.coritel.it
s=Session SDP
c=IN IP4 151.100.37.143
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000



























Veltri et al.             Expires April 2003                        39

                  SIP Extensions for QoS support                Oct-02



Message M9 (200 OK from Proxy 1 to User A):

SIP/2.0 200 OK
Via: SIP/2.0/UDP eulero.coritel.it:5060;branch=z9hG4bKjasldjl2oi
From: UserA<sip:UserA@gauss.coritel.it>;tag=734578133
To: UserB<sip:UserB@maxwell.coritel.it>;tag=234857984
Record-Route: <sip:gauss.coritel.it;lr;qos-mode=unidirectional;qos-
domain=coritel.it;er-ingress=192.168.90.3;caller-media-
addr=151.100.37.131;caller-media-port=49172>,
<sip:maxwell.coritel.it;lr;er-ingress=192.168.90.3;caller-media-
addr=151.100.37.131;caller-media-port=49172>
Call-ID: 1234567801@eulero.coritel.it
CSeq: 1 INVITE
Contact: <sip:UserB@151.100.37.143>
Content-Type: application/sdp
Content-Length: 148

v=0
o=UserB 2890844527 2890844527 IN IP4 galileo.coritel.it
s=Session SDP
c=IN IP4 151.100.37.143
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

Message M14 (BYE from Proxy 2 to Proxy 1):

BYE sip:UserA@gauss.coritel.it SIP/2.0
Via: SIP/2.0/UDP maxwell.coritel.it:5060;branch=asdfhkjksdf3kjj2f
Via: SIP/2.0/UDP galileo.coritel.it:5060;branch=sdlfhk4f3gmpsdfo3
Route: <sip:gauss.coritel.it;lr;qos-mode=unidirectional;qos-
domain=coritel.it;er-ingress=192.168.90.3;caller-media-
addr=151.100.37.131;caller-media-port=49172>
From: UserB<sip:UserB@maxwell.coritel.it>;tag=234857984
To: UserA<sip:UserA@gauss.coritel.it>;tag=734578133
Server: Coritel SIP Server 1.0
Call-ID: 1234567801@eulero.coritel.it
Max-Forwards: 69
CSeq: 1 BYE
Content-Length: 0














Veltri et al.             Expires April 2003                        40

                  SIP Extensions for QoS support                Oct-02



Message M15 (BYE from Proxy 1 to user A)

BYE sip:UserA@eulero.coritel.it:5060 SIP/2.0
Via: SIP/2.0/UDP gauss.coritel.it:5060;branch=h2kerpuighber5d4l
Via: SIP/2.0/UDP maxwell.coritel.it:5060;branch=asdfhkjksdf3kjj2f
Via: SIP/2.0/UDP galileo.coritel.it:5060;branch=sdlfhk4f3gmpsdfo3
From: UserB<sip:UserB@maxwell.coritel.it>;tag=234857984
To: UserA<sip:UserA@gauss.coritel.it>;tag=734578133
Server: Coritel SIP Server 1.0
Server: Coritel SIP Server 1.0
Call-ID: 1234567801@eulero.coritel.it
Max-Forwards: 68
CSeq: 1 BYE
Content-Length: 0



References

[1]     G. Camarillo et al. "Integration of Resource Management and
SIP", IETF Internet Draft <draft-ietf-sip-manyfolks-resource-07.txt>,
April 2002, Work in Progress.
[2]     IETF WG NSIS - Next Step In Signaling
http://www.ietf.org/html.charters/nsis-charter.html
[3]     J. Rosenberg, H. Schulzrinne, G. Camarillo, A. Johnston, J.
Peterson, R. Sparks, M. Handley, E. Schooler, " SIP: Session Initiation
Protocol", IETF RFC 3261, June 2002.
[4]     D. Durham, Ed., J. Boyle, R. Cohen, S. Herzog, R. Rajan, A.
Sastry, "The COPS (Common Open Policy Service) Protocol", IETF RFC 2748,
January 2000.
[5]     S. Salsano " COPS Usage for Diffserv Resource Allocation (COPS-
DRA) ", draft-salsano-cops-dra-00.txt, October 2001, work in progress
[6]     CoRiTeL The Q-SIP project http://www.coritel.it/projects/qsip
[7]     S. Donovan, "The SIP INFO method", RFC 2976, October 2000.
[8]     J. Rosenberg, H. Schulzrinne, "Reliability of Provisional
Responses in the Session Initiation Protocol (SIP)", RFC 3262, June
2002.

















Veltri et al.             Expires April 2003                        41

                  SIP Extensions for QoS support                Oct-02



Author Information and Acknoledgements

Special thanks to Jocelyn Fiorina for his comments and suggestions and
for the work on the prototype implementation for the previous version of
the draft.

Luca Veltri
CoRiTeL - Consorzio di Ricerca sulle Telecomunicazioni
Via Anagnina, 203
00040 Roma - ITALY
email: veltri@coritel.it

Stefano Salsano
DIE - University of Rome "Tor Vergata"
Viale Politecnico, 1
00133 Roma - ITALY
email: stefano.salsano@uniroma2.it

Donald Papalilo
CoRiTeL - Consorzio di Ricerca sulle Telecomunicazioni
Via Anagnina, 203
00040 Roma - ITALY
email: papalilo@coritel.it































Veltri et al.             Expires April 2003                        42


Html markup produced by rfcmarkup 1.123, available from https://tools.ietf.org/tools/rfcmarkup/