Internet DRAFT - draft-jones-insipid-session-id
draft-jones-insipid-session-id
Network Working Group P. Jones
Internet Draft C. Pearce
Intended status: Standards Track J. Polk
Expires: August 20, 2013 G. Salgueiro
Cisco Systems
February 20, 2013
End-to-End Session Identification in IP-Based Multimedia
Communication Networks
draft-jones-insipid-session-id-02.txt
Abstract
This document describes an end-to-end Session Identifier for use in
IP-based Multimedia Communication systems that enables endpoints,
intermediate devices, and management systems to identify a session
end-to-end, associate multiple endpoints with a given multipoint
conference, track communication sessions when they are redirected,
and associate one or more media flows with a given communication
session.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
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
This Internet-Draft will expire on August 20, 2013.
Jones, et al. Expires August 20, 2013 [Page 1]
Internet-Draft End-To-End Session ID February 2013
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document.
Table of Contents
1. Introduction...................................................2
2. Conventions used in this document..............................3
3. Session Identifier Requirements and Use Cases..................3
4. Constructing the Session Identifier............................3
5. Transmitting the Session Identifier in SIP.....................4
6. Endpoint Behavior..............................................5
7. Processing by Intermediaries...................................6
8. Associating Endpoints in a Multipoint Conference...............7
9. Various Call Flow Operations Utilizing the Session ID..........7
9.1. Basic Session-ID Construction with 2 UUIDs................8
9.2. Basic Call Transfer using REFER...........................9
9.3. Basic Call Transfer using reINVITE.......................10
9.4. Single Focus Conferencing................................11
9.5. Single Focus Conferencing using WebEx....................13
9.6. Cascading Conference Bridge Support for the Session-ID...14
9.7. Basic 3PCC for two UAs...................................15
10. Compatibility with a Previous Implementation.................16
11. Security Considerations......................................17
12. IANA Considerations..........................................17
13. Acknowledgments..............................................18
14. References...................................................18
14.1. Normative References....................................18
Author's Addresses...............................................19
1. Introduction
IP-based multimedia communication systems like SIP [1] and H.323 [2]
have the concept of a "call identifier" that is globally unique. The
identifier is intended to represent an end-to-end communication
session from the originating device to the terminating device. Such
an identifier is useful for troubleshooting, session tracking, and so
forth.
Jones, et al. Expires August 20, 2013 [Page 2]
Internet-Draft End-To-End Session ID February 2013
Unfortunately, there are a number of factors that contribute to the
fact that the current call identifiers defined in SIP and H.323 are
not suitable for end-to-end session identification. A fundamental
issue in protocol interworking is the fact that the syntax for the
call identifier in SIP and H.323 is different between the two
protocols. This important fact makes it impossible for call
identifiers to be exchanged end-to-end when a network utilizes one or
more session protocols.
Another reason why the current call identifiers are not suitable to
identify the session end-to-end is that in real-world deployments
devices like session border controllers often change the session
signaling as it passes through the device, including the value of the
call identifier. While this is deliberate and useful, it makes it
very difficult to track sessions end-to-end.
This draft presents a new identifier, referred to as the Session
Identifier, or "Session ID", and associated syntax intended to
overcome the issues that exist with the currently defined call
identifiers. The proposal in this document attempts to comply with
the requirements specified in Error! Reference source not found..
This proposal also has capabilities not mentioned in [5], shown in
call flows in section 10. Additionally, this proposal attempts to
account for a previous, proprietary version of a SIP Session ID
header, proposing a backwards compatibility of sorts, described in
section 11.
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [3] when they
appear in ALL CAPS. These words may also appear in this document in
lower case as plain English words, absent their normative meanings.
3. Session Identifier Requirements and Use Cases
Requirements and Use Cases for the end-to-end Session Identifier can
be found in a separate memo titled "Requirements for an End-to-End
Session Identification in IP-Based Multimedia Communication Networks"
Error! Reference source not found..
4. Constructing the Session Identifier
The Session Identifier is comprised of two RFC 4122 defined UUIDs
[4], with each UUID representing one of the endpoints participating
in the session. The SIP user agent (UA) initially transmitting the
SIP request will create a UUID and transmit that to the ultimate
destination UA. Likewise, the responding UA will create a UUID and
Jones, et al. Expires August 20, 2013 [Page 3]
Internet-Draft End-To-End Session ID February 2013
transmit that to the first UA. These two distinct UUIDs form what is
referred to as the Session Identifier and is represented in this
document in set notation of the form {A,B}, where A is UUID value
from the UA transmitting a message and B is the UUID value from the
intended recipient of the message, i.e., not an intermediary server
along the signaling path. The set {A,B} is equal to the set {B,A},
and thus both represent the same Session Identifier.
In the case where only one UUID is known, such as when a UA first
initiates a SIP request, the Session ID would be {A}, where "A"
represents the single UUID value transmitted.
Since SIP sessions are subject to any number of service interactions,
SIP INVITE messages might be forked as sessions are established, and
since conferences might be established or expanded with endpoints
calling in or the conference focus calling out, the construction of
the Session Identifier from a set of UUIDs is important.
To understand this better, consider that a UA participating in a
communication session might be replaced with another, such as the
case where two "legs" of a call are joined together by a PBX.
Suppose that UA A and UA B both call UA C. Further suppose that UA C
uses a local PBX function to join the call between itself and UA A
with the call between itself and UA B. This merged call needs to be
identified and identification of such sessions is natural and easily
traceable when utilizing UUID values assigned by each entity in the
communication session.
In the case of forking, UA A might send an INVITE that gets forked to
five different UAs, as an example. Until one UA returns a 200 OK to
the initial INVITE, a means of identifying each of these separate
communication sessions is needed and allowing the set of {A, B1}, {A,
B2}, {A, B3}, {A, B4}, and {A, B5} makes this possible.
For conferencing scenarios, it is also useful to have a two-part
Session-ID where the conference focus specifies one UUID. This might
allow for correlation among the participants in a single conference,
for example.
How a device acting on Session Identifiers stores, processes, or
utilizes the Session Identifier is outside the scope of this
document.
5. Transmitting the Session Identifier in SIP
Each session initiated or accepted MUST have a local UA-generated
UUID associated with the session. This value MUST remain unchanged
throughout the duration of that session.
Jones, et al. Expires August 20, 2013 [Page 4]
Internet-Draft End-To-End Session ID February 2013
A SIP UA MUST convey its Session Identifier UUID in all transmitted
messages within the same session. To do this, each transmitted
message MUST include the "Session-ID" header. The Session-ID header
has the following ABNF [5] syntax:
session-id = "Session-ID" HCOLON local-uuid
*(SEMI sess-id-param)
local-uuid = sess-uuid
remote-uuid = sess-uuid
sess-uuid = 32(DIGIT / %x61-66) ;32 chars of [0-9a-f]
sess-id-param = remote-param / generic-param
remote-param = "remote" EQUAL remote-uuid
The productions "SEMI", "EQUAL", and "generic-param" production is
defined in RFC 3261. The production DIGIT is defined in RFC 5234.
The Session-ID header MUST NOT have more than one "remote" parameter.
The "local-uuid" in the Session-ID header represents the UUID value
of the UA transmitting the message. If the UA transmitting the
message previously received a UUID value from its peer endpoint, it
MUST include that UUID as the "remote" parameter. For example, using
the UUID values from the previous section, a Session-ID header might
appear like this:
Session-ID: aeffa652b22911dfa81f12313a006823;
remote=be11afc8b22911df86c412313a006823
The UUID values are presented as strings of lower-case hexadecimal
characters, with the most significant byte of the UUID appearing
first.
6. Endpoint Behavior
To comply with this specification, SIP UAs MUST include a Session-ID
header-value in all messages transmitted as a part of a communication
session.
A non-intermediary UAS that receives a Session-ID header MUST take
note of the first UUID value that it receives in the Session-ID
header and assume that that is the UUID of the peer endpoint within
that communications session. UAs MUST include this received UUID
Jones, et al. Expires August 20, 2013 [Page 5]
Internet-Draft End-To-End Session ID February 2013
value as the "remote" parameter when transmitting subsequent
messages.
It should be noted that messages received by a UA might contain a
"remote" parameter that does match the UAs UUID. This might happen
as a result of service interactions by intermediaries and MUST NOT be
regarded as an error.
For any purpose the UA has for the Session-ID, it MUST assume that
the Session-ID is {A,B} where "A" is the UUID value of this endpoint
and "B" is the UUID value of the peer endpoint, taken from the most
recently received message within this session.
An endpoint MUST assume that the UUID value of the peer UA MAY change
at any time due to service interactions. However, once an UA
allocates a UUID value for a communication session, the UA MUST NOT
change that UUID value for the duration of the session, including
when communication attempts are retried due to receipt of 4xx
messages, when the session is redirected in response to a 3xx
message, or when a session is transferred via a REFER message [6].
It is also important to note that if a session is forked by an
intermediary in the network, the initiating UA may receive multiple
responses back from different endpoints, each of which will contain a
different UUID value. UAs MUST take care to ensure that the correct
UUID value is returned in the "remote" parameter when responding to
those endpoints.
7. Processing by Intermediaries
Intermediaries that wish to utilize the Session-ID MAY extract the
UUID header-values from any SIP message. Alternatively,
intermediaries MAY observe the first UUID value in the Session-ID
header for messages sent in each direction and use those values to
locally construct the Session Identifier.
Intermediaries MUST NOT alter the UUID values found in the Session-ID
header, except as described in this section.
Intermediary devices that transfer a call, such as by joining
together two different "call legs", MUST properly construct a
Session-ID header that contains the correct UUID values and correct
placement of those values. As described above, the recipient of any
message initiated by the intermediary will assume that the first UUID
value belongs to the peer endpoint.
If a SIP message having no Session-ID header is received by an
intermediary, the intermediary MAY assign a "local-uuid" value to
represent the sending endpoint and insert that value into all
Jones, et al. Expires August 20, 2013 [Page 6]
Internet-Draft End-To-End Session ID February 2013
signaling messages on behalf of the sending endpoint. If the
intermediary is aware of a "remote" value that identifies the
receiving UA, it MUST insert that value if also inserting the "local-
uuid" value.
Devices that initiate communication sessions following the procedures
for third party call control MUST fabricate a UUID value that will be
utilized only temporarily. Once the responding endpoint provides a
UUID value in a response message, the temporary value MUST be
discarded and replaced with the endpoint-provided UUID value. Refer
to the third-party call control example for an illustration.
Whenever there is a UA that does not implement this specification
communicating through a B2BUA, the B2BUA MAY become dialog stateful
and insert a UUID value into the Session-ID header on behalf of the
UA according to the rules stated in Section 6.
8. Associating Endpoints in a Multipoint Conference
Multipoint Control Units (MCUs) group two or more sessions into a
single multipoint conference. The MCU should utilize the same UUID
value for each session that is grouped into the same conference. In
so doing, each individual session in the conference will have a
unique Session Identifier (since each endpoint will create a unique
UUID of its own), but will also have one UUID in common with all
other participants in the conference.
Intermediary devices, such as proxies or session border controllers,
or network diagnostics equipment might assume that when they see two
or more sessions with different Session Identifiers, but with one
UUID in common, that the sessions are part of the same conference.
Note, however, that this assumption of being part of the same
conference is not always true. For example, in a SIP forking
scenario, there might also be what appears to be multiple sessions
with a shared UUID value. This is actually desirable. What is
desired is to allow for the association of related sessions. Whether
sessions are related because of forking or because endpoints are
communicating as a part of a conference does not matter. They are
nonetheless related.
9. Various Call Flow Operations Utilizing the Session ID
Seeing something frequently makes understanding easier. With that in
mind, we include several call flows with the initial UUID and the
complete Session-ID indicated per message, as well as when the
Session-ID changes according to the rules within this document during
certain operations/functions.
Jones, et al. Expires August 20, 2013 [Page 7]
Internet-Draft End-To-End Session ID February 2013
9.1. Basic Session-ID Construction with 2 UUIDs
Session-ID
--- Alice B2BUA Bob Carol
{A} |----INVITE----->| |
{A} | |----INVITE----->|
{B,A} | |<---200 OK------|
{B,A} |<---200 OK------| |
{A,B} |------ACK------>| |
{A,B} | |------ACK------>|
|<==============RTP==============>|
Figure 1 - Session-ID Creation when Alice calls Bob
Operation/Rules:
o Transmitter of SIP message places its Session-ID UUID first in
order;
o UA-Alice sends its UUID in INVITE;
o B2BUA receives an INVITE with a Session-ID header-value from UA-
Alice, and transmits INVITE towards UA-Bob with an unchanged
Session-ID header-value;
o UA-Bob receives Session-ID and adds its UUID to construct the
whole/complete Session-ID header-value in the 200 OK;
o UA-Bob orders the UUIDs such that its UUID is first when UA-Bob
is transmitting the SIP message;
o B2BUA receives the 200 OK response with a complete Session-ID
header-value from UA-Bob, and transmits 200 OK towards UA-Alice
with an unchanged Session-ID header-value; while maintaining the
order of UUIDs in the Session-ID header-value;
o UA-Alice, upon reception of the 200 OK from the B2BUA, transmits
the ACK towards the B2BUA with its UUID positioned first, and
the UUID from UA-Bob positioned second in the Session-ID header-
value.
o B2BUA receives the ACK with a complete Session-ID header-value
from UA-Alice, and transmits ACK towards UA-Bob with an
unchanged Session-ID header-value; while maintaining the order
of UUIDs in the Session-ID header-value;
Jones, et al. Expires August 20, 2013 [Page 8]
Internet-Draft End-To-End Session ID February 2013
9.2. Basic Call Transfer using REFER
From the example built within Section 9.1 (the basic session-ID
establishment), we proceed to this 'Basic Call Transfer using REFER'
example.
Session-ID
--- Alice B2BUA Bob Carol
| | | |
|<==============RTP==============>| |
{B,A} | |<---reINVITE----| |
{B,A} |<---reINVITE----| (puts Alice on Hold) |
{A,B} |-----200 OK---->| | |
{A,B} | |-----200 OK---->| |
{B,A} | |<-----ACK-------| |
{B,A} |<-----ACK-------| | |
| | | |
{B,A} | |<----REFER------| |
{B,A} |<----REFER------| | |
{A,B} |-----200 OK---->| | |
{A,B} | |-----200 OK---->| |
{B,A} | |<-----ACK-------| |
{B,A} |<-----ACK-------| | |
{A,B} |-----NOTIFY---->| | |
{A,B} | |-----NOTIFY---->| |
{B,A} | |<----200 OK-----| |
{B,A} |<----200 OK-----| | |
| | | |
{A} |-----INVITE---->| |
{A} | |-----INVITE-------------------->|
{C,A} | |<----200 OK---------------------|
{C,A} |<----200 OK-----| |
{A,C} |------ACK------>| |
{A,C} | |------ACK---------------------->|
| | | |
|<======================RTP======================>|
| | | |
{A,B} |-----NOTIFY---->| | |
{A,B} | |-----NOTIFY---->| |
{B,A} | |<----200 OK-----| |
{B,A} |<----200 OK-----| | |
{B,A} | |<-----BYE-------| |
{B,A} |<-----BYE-------| | |
{A,B} |-----200 OK---->| | |
{A,B} | |-----200 OK---->| |
| | | |
Figure 2 - Call Transfer using REFER
Jones, et al. Expires August 20, 2013 [Page 9]
Internet-Draft End-To-End Session ID February 2013
Operation/Rules:
Starting from the existing Alice/Bob call described in Figure 1,
which established an existing Session-ID header-value...
o UA-Bob reINVITEs Alice to call Carol, using a REFER transaction,
as described in [RFC3515]. UA-Alice is initially put on hold,
then told in the REFER who to contact with a new INVITE, in this
case UA-Carol.
o UA-Alice retains her UUID from the Alice-to-Bob call {A} when
requesting a call with UA-Carol. This same UUID traverses the
B2BUA unchanged.
o UA-Carol receives the INVITE with a Session-ID UUID {A}, creates
its own UUID {C}, and combines them to form a full Session-ID
{C,A} in the 200 OK to the INVITE. This Session-ID header-value
traverses the B2BUA unchanged towards UA-Alice.
o UA-Alice receives the 200 OK with the Session-ID {C,A} and both
responses to UA-Carol with an ACK, generates a NOTIFY to Bob
with a Session-ID {A,B} indicating the call transfer was
successful.
o It does not matter which UA terminates the Alice-to-Bob call;
Figure 2 shows UA-Bob doing this transaction.
9.3. Basic Call Transfer using reINVITE
From the example built within Section 9.1 (the basic session-ID
establishment), we proceed to this 'Basic Call Transfer using
reINVITE' example.
Alice is talking to Bob. Bob pushes a button on his phone to transfer
Alice to Carol via the B2BUA (using reINVITE).
Session-ID
--- Alice B2BUA Bob Carol
| | | |
|<==============RTP==============>| |
| | | |
{B,A} | |<---reINVITE----| |
{A,B} | |-----200 OK---->| |
{B,A} | |<-----ACK-------| |
| | | |
{A} | |-----INVITE-------------------->|
{C,A} | |<----200 OK---------------------|
{A,C} | |------ACK---------------------->|
| | | |
Jones, et al. Expires August 20, 2013 [Page 10]
Internet-Draft End-To-End Session ID February 2013
|<======================RTP======================>|
| | | |
{B,A} | |<-----BYE-------| |
{B,A} |<-----BYE-------| | |
{A,B} |-----200 OK---->| | |
{A,B} | |-----200 OK---->| |
| | | |
Figure 3 - Call transfer using reINVITE
Operation/Rules:
o We assume the call between Alice and Bob from Section 9.1 is
operational with Session-ID {A,B}.
o Bob sends a reINVITE to Alice to transfer her to Carol.
o The B2BUA intercepts this reINVITE and sends a new INVITE with
Alice's UUID {A} to Carol.
o Carol receives the INVITE and accepts the request and adds her
UUID {C} to the Session-ID for this session {C,A}.
o Bob terminates the call (which Alice could too) with a BYE using
their Session-ID {B,A}.
9.4. Single Focus Conferencing
Multiple users call into a conference server (say, an MCU) to attend
one of many conferences hosted on or managed by that server. Each
user has to identify which conference they want to join, but this
information is not necessarily in the SIP messaging. It might be
done by having a dedicated address for the conference or via an IVR,
as assumed in this example. Each user in this example goes through a
two-step process of signaling to gain entry onto their conference
call.
Session-ID Conference
--- Alice Focus Bob Carol
| | | |
| | | |
{A} |----INVITE----->| | |
{M1,A} |<---200 OK------| | |
{A,M1} |-----ACK------->| | |
|<====RTP=======>| | |
{M',A} |<---reINVITE----| (to change the | |
{A||M'} |-----200 OK---->| UUID to M') | |
{M',A} |<-----ACK-------| | |
| | | |
Jones, et al. Expires August 20, 2013 [Page 11]
Internet-Draft End-To-End Session ID February 2013
| | | |
{B} | |<----INVITE-----| |
{M2,B} | |-----200 OK---->| |
{B,M2} | |<-----ACK-------| |
| |<=====RTP======>| |
{M'||B} | (to change the |----reINVITE--->| |
{B||M'} | UUID to M') |<----200 OK-----| |
{M'||B} | |------ACK------>| |
| | | |
| | | |
{C} | |<--------------------INVITE-----|
{M3,C} | |---------------------200 OK---->|
{C,M3} | |<---------------------ACK-------|
| |<=====================RTP======>|
{M'||C} | (to change the |--------------------reINVITE--->|
{C||M'} | UUID to M') |<--------------------200 OK-----|
{M'||C} | |----------------------ACK------>|
Figure 4 - Single Focus Conference Bridge
Operation/Rules:
Alice calls into a conference server to attend a certain conference.
This is a two-step operation since Alice cannot include the
conference ID and any passcode in the INVITE.
o Alice sends an INVITE to the conference server with her UUID
{A}.
o The conference server accepts using a generic, temporary UUID
{M1}.
o Once Alice, the user, gains access to the IVR for this
conference server, she enters a specific conference ID and
whatever passcode (if needed) to enter a specific conference
call.
o Once the conference server is satisfied Alice has identified
which conference she wants to attend (including any passcode
verification), the conference server reINVITEs Alice to the
specific conference and includes the UUID {M'} for that
conference. All valid participants in the same conference will
receive this same UUID for identification purposes and to better
enable monitoring, and tracking functions.
o Bob goes through this two-step process of an INVITE transaction,
followed by a reINVITE transaction to get this same UUID for
that conference.
Jones, et al. Expires August 20, 2013 [Page 12]
Internet-Draft End-To-End Session ID February 2013
o In this example, Carol (and each additional user) goes through
the same procedures and steps as Alice to get on this same
conference.
9.5. Single Focus Conferencing using WebEx
Alice, Bob and Carol call into same Webex conference.
Session-ID Conference
--- Alice Focus Bob Carol
| | | |
|<*** HTTPS ****>| | |
| Transaction | | |
| | | |
{M} |<----INVITE-----| | |
{A||M} |-----200 OK---->| | |
{M||A} |<-----ACK-------| | |
|<=====RTP======>| | |
| | | |
| |<** HTTPS *****>| |
| | Transaction | |
| | | |
{M} | |-----INVITE---->| |
{B||M} | |<----200 OK-----| |
{M||B} | |------ACK------>| |
| |<=====RTP======>| |
| | | |
| |<******************** HTTPS ***>|
| | Transaction |
| | | |
{M} | |--------------------INVITE----->|
{C||M} | |<-------------------200 OK------|
{M||C} | |---------------------ACK------->|
| |<====================RTP=======>|
Figure 5 - Single Focus Webex Conference
Operation/Rules:
o Alice communicates with Webex server with desire to join a
certain meeting, by meeting number; also includes UA-Alice's
contact information (phone number or URI).
o Conference Focus server sends INVITE to UA-Alice to start
session with the Session-ID of that server for this A/V
conference call.
o Bob and Carol perform same function to join this same A/V
conference call as Alice.
Jones, et al. Expires August 20, 2013 [Page 13]
Internet-Draft End-To-End Session ID February 2013
9.6. Cascading Conference Bridge Support for the Session-ID
To expand conferencing capabilities requires cascading conference
bridges. A conference bridge, or MCU, needs a way to identify itself
when contacting another MCU. RFC 4579 [6] defines the 'isfocus'
Contact: header parameter just for this purpose.
Cascading MCUs for the purpose of having each use the same UUID (aka
half the Session-ID), in its simplest form, is one MCU informing
another which UUID to use for joining UAs.
Session-ID
--- MCU-1 MCU-2 MCU-3 MCU-4
| | | |
{M'} |----INVITE----->| | |
{M'} |<---200 OK------| | |
{M'} |-----ACK------->| | |
Figure 6 - MCUs Communicating Session-ID UUID for Bridge
Regardless of which MCU (1 or 2) a UA contacts for this conference,
once the above exchange has been received and acknowledged, the UA
will get the same M' UUID from the MCU for the complete Session-ID.
A more complex form would be a series of MCUs all being informed of
the same UUID to use for a specific conference. This series of MCUs
can either be informed
o All by one MCU (that initially generates the UUID for the
conference),
o The one MCU that generates the UUID informs one or several MCUs
of this common UUID, and they inform downstream MCUs of this
common UUID each will be using for this one conference, or
Session-ID
--- MCU-1 MCU-2 MCU-3 MCU-4
| | | |
{M'} |----INVITE----->| | |
{M'} |<---200 OK------| | |
{M'} |-----ACK------->| | |
| | | |
{M'} |---------------------INVITE----->| |
{M'} |<--------------------200 OK------| |
{M'} |----------------------ACK------->| |
| | | |
{M'} |-------------------------------------INVITE----->|
{M'} |<------------------------------------200 OK------|
{M'} |--------------------------------------ACK------->|
Jones, et al. Expires August 20, 2013 [Page 14]
Internet-Draft End-To-End Session ID February 2013
Figure 7 - MCU Communicating Session-ID UUID to More than One
Operation/Rules:
o The MCU generating the Session-ID UUID communicates this in a
separate INVITE, having a Contact header with the 'isfocus'
header parameter. This will identify the MCU as what RFC 4579
conference-aware SIP entity.
o The MCU that is contacted, i.e., the UAS MCU, does not populate
or complete the Session-ID header value. The UAS MCU transmits a
200 OK response acknowledging it is to respond with this M' UUID
to all requests for the designated conference.
o An MCU that receives this M' UUID in an inter-MCU transaction,
can communicate the M' UUID in a manner in which it was received
(though this time this second MCU would be the UAC MCU), unless
local policy dictates otherwise.
9.7. Basic 3PCC for two UAs
External entity sets up call to both Alice and Bob for them to talk
to each other.
Session-ID
--- Alice B2BUA Bob Carol
| | |
{X} |<----INVITE-----| |
{A,X} |-----200 OK---->| |
{A} | |----INVITE----->|
{B,A} | |<---200 OK------|
{A,B} |<-----ACK-------| |
{A,B} | |------ACK------>|
|<==============RTP==============>|
Figure 8 - 3PCC initiated call between Alice and Bob
Operation/Rules:
o Some out of band procedure directs a B2BUA (or other SIP server)
to have Alice and Bob talk to each other.
o The SIP server INVITEs Alice to a session and uses a temporary
UUID {X}.
o Alice receives and accepts this call set-up and includes her
UUID {A} in the Session-ID, now {A,X}.
Jones, et al. Expires August 20, 2013 [Page 15]
Internet-Draft End-To-End Session ID February 2013
o The SIP server uses Alice's UUID {A}, and discards its own {X}
to INVITE Bob to the session as if this came from Alice
originally.
o Bob receives and accepts this INVITE and adds his own UUID {B}
to the Session-ID, now {B,A} for the response.
o And the session is established.
10. Compatibility with a Previous Implementation
There is a much earlier and proprietary document that specifies the
use of a Session-ID header that we will herewith attempt to achieve
backwards compatibility. Neither Session-ID has any versioning
information, so merely adding that this document describes "version
2" is insufficient. Here are the set of rules for compatibility
between the two specifications. For the purposes of this discussion,
we will label the proprietary specification of the Session-ID as the
"old" version and this specification as the "new" version of the
Session-ID.
The previous (i.e., "old") version only has a single value as a
Session-ID, but has a generic-parameter value that can be of use.
In order to have an "old" version talk to an "old" version
implementation, nothing needs to be done as far as the IETF is
concerned.
In order to have a "new" version talk to a "new" version
implementation, both implementations need to following this document
(to the letter) and everything should be just fine.
In order to have an "old" version talk to a "new" version
implementation, several aspects need to be looked at. They are:
o The "old" version UA will include a single UUID as its Session-
ID.
o The "new" version UA will respond by including a complete
Session-ID with two UUIDs, with the "new" version's UUID listed
first (because it cannot know it is talking with an "old"
version implementation at this point).
o The "old" version UA will have to ignore the first UUID, and
consider its singular "old" UUID as valid, as long as the value
does not change..
o During subsequent transactions within this session, the "new"
version may receive SIP requests without its UUID, but with the
Jones, et al. Expires August 20, 2013 [Page 16]
Internet-Draft End-To-End Session ID February 2013
"old" version's UUID. The "new" version UA MUST add its UUID to
the received Session-ID. The "old" version implementation will
merely disregard it each time it receives this "new" version
UUID (if it was not the first UUID).
In order to have a "new" version talk to an "old" Version
implementation, several aspects need to be looked at. They are:
o The "new" version UA will include a single UUID as its initial
Session-ID header always, not knowing which version of UA it is
communicating with.
o The "old" version UA will respond by seeing the UUID as a valid
and complete Session-ID and not include another UUID or generic-
param. Thus, the 200 OK will not include any Session-ID part of
its own from the "old" version implementation.
Rule: implementation supporting a "new" version of the Session-ID
MUST NOT error or otherwise reject receiving only its own UUID
back in any transaction. It MUST interpret this response to mean
that it is communicating with an "old" Session-ID
implementation.
o Open question - how do we want all intermediaries and/or
monitoring systems to interpret this single UUID complete
Session-ID?
11. Security Considerations
When creating a UUID value, endpoints SHOULD ensure that there is no
user or device-identifying information contained within the UUID. In
some environments, though, use of a MAC address, which is one option
when constructing a UUID, may be desirable, especially in some
enterprise environments. When communicating over the Internet,
though, the UUID value MUST utilize random values.
The Session-ID might be utilized for logging or troubleshooting, but
MUST NOT be used for billing purposes. { Why does this matter? }
Other considerations???
12. IANA Considerations
The following is the registration for the 'Session-ID' header field
to the "Header Name" registry at http://www.iana.org/assignments/sip-
parameters:
RFC number: [this document]
Jones, et al. Expires August 20, 2013 [Page 17]
Internet-Draft End-To-End Session ID February 2013
Header name: 'Session-ID'
Compact form: none
13. Acknowledgments
The authors would like to than Hadriel Kaplan, Christer Holmberg, and
Paul Kyzivat for their invaluable comments during the development of
this document.
This document was prepared using 2-Word-v2.0.template.dot.
14. References
14.1. Normative References
[1] Rosenberg, J., et al., "SIP: Session Initiation Protocol", RFC
3261, June 2002.
[2] Recommendation ITU-T H.323, "Packet-based multimedia
communications systems", December 2009.
[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[4] Leach, P., Mealling, M., Salz, R., "A Universally Unique
IDentifier (UUID) URN Namespace", RFC 4122, July 2005.
[5] Crocker, D., Overell, P, "Augmented BNF for Syntax
Specifications: ABNF", RFC 5234, January 2008.
[6] A. Johnston, O. Levin, "Session Initiation Protocol (SIP) Call
Control - Conferencing for User Agents", RFC 4579, August 2006
Informative References
[6] Sparks, R., "The Session Initiation Protocol (SIP) Refer
Method", RFC 3515, April 2003.
[7] Schulzrinne, H., et al., "RTP: A Transport Protocol for Real-
Time Applications", RFC 3550, July 2003.
[8] Jones, et al., "Requirements for an End-to-End Session
Identification in IP-Based Multimedia Communication Networks",
draft-jones-insipid-session-id-reqts-02.txt, October 2012.
Jones, et al. Expires August 20, 2013 [Page 18]
Internet-Draft End-To-End Session ID February 2013
Author's Addresses
Paul E. Jones
Cisco Systems, Inc.
7025 Kit Creek Rd.
Research Triangle Park, NC 27709
USA
Phone: +1 919 476 2048
Email: paulej@packetizer.com
IM: xmpp:paulej@packetizer.com
Chris Pearce
Cisco Systems, Inc.
2300 East President George Bush Highway
Richardson, TX 75082
USA
Phone: +1 972 813 5123
Email: chrep@cisco.com
IM: xmpp:chrep@cisco.com
James Polk
Cisco Systems, Inc.
3913 Treemont Circle
Colleyville, Texas
USA
Phone: +1 817 271 3552
Email: jmpolk@cisco.com
IM: xmpp:jmpolk@cisco.com
Gonzalo Salgueiro
Cisco Systems, Inc.
7025 Kit Creek Rd.
Research Triangle Park, NC 27709
USA
Phone: +1 919 392 3266
Email: gsalguei@cisco.com
IM: xmpp:gsalguei@cisco.com
Jones, et al. Expires August 20, 2013 [Page 19]
