CLUE Signaling
draft-kyzivat-clue-signaling-01
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Replaced".
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|
|---|---|---|---|
| Author | Paul Kyzivat | ||
| Last updated | 2013-02-04 | ||
| Replaced by | draft-ietf-clue-signaling, draft-ietf-clue-signaling, RFC 8848 | ||
| RFC stream | (None) | ||
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| Consensus boilerplate | Unknown | ||
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draft-kyzivat-clue-signaling-01
Network Working Group P. Kyzivat
Internet-Draft Huawei
Updates: 5234 (if approved) February 4, 2013
Intended status: Standards Track
Expires: August 8, 2013
CLUE Signaling
draft-kyzivat-clue-signaling-01
Abstract
This document specifies how signaling is conducted in the course of
CLUE sessions. This includes how SIP/SDP signaling is applied to
CLUE sessions as well as defining a CLUE-specific signaling protocol
that complements SIP/SDP and supports negotiation of CLUE application
level data.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on August 8, 2013.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. CLUE-Specific Signaling Protocol . . . . . . . . . . . . . . . 3
3.1. CLUE Messages . . . . . . . . . . . . . . . . . . . . . . 3
3.1.1. ADVERTISEMENT Message . . . . . . . . . . . . . . . . 4
3.1.2. CONFIGURE Message . . . . . . . . . . . . . . . . . . 4
3.1.3. Stand-alone messages or deltas? . . . . . . . . . . . 4
3.1.4. other . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Message Acknowledgement . . . . . . . . . . . . . . . . . 4
3.3. Message Sequencing . . . . . . . . . . . . . . . . . . . . 5
3.3.1. Two CLUE-capable endpoints . . . . . . . . . . . . . . 5
3.3.2. A case with a non-CLUE-capable endpoint . . . . . . . 8
3.4. Message Transport . . . . . . . . . . . . . . . . . . . . 10
3.5. Message Framing . . . . . . . . . . . . . . . . . . . . . 10
3.6. other . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4. CLUE use of SDP O/A . . . . . . . . . . . . . . . . . . . . . 10
5. Coordination of CLUE protocol and SDP O/A . . . . . . . . . . 11
6. CLUE requirements on SDP O/A . . . . . . . . . . . . . . . . . 11
7. SIP Signaling . . . . . . . . . . . . . . . . . . . . . . . . 11
8. Interoperation with Legacy SIP Devices . . . . . . . . . . . . 11
9. CLUE over RTCWEB . . . . . . . . . . . . . . . . . . . . . . . 11
10. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 12
11. What else? . . . . . . . . . . . . . . . . . . . . . . . . . . 12
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
14. Security Considerations . . . . . . . . . . . . . . . . . . . 12
15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
15.1. Normative References . . . . . . . . . . . . . . . . . . . 13
15.2. Informative References . . . . . . . . . . . . . . . . . . 13
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 13
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1. Introduction
This document specifies how signaling is conducted in the course of
CLUE sessions. This includes how SIP/SDP signaling is applied to
CLUE sessions as well as defining a CLUE-specific signaling protocol
that complements SIP/SDP and supports negotiation of CLUE application
level data.
[Yes, this is a dup of the abstract for now. Eventually it should
say more.]
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
This document draws liberally from the terminology defined in the
CLUE Framework [I-D.ietf-clue-framework].
Other terms introduced here:
CLUE Channel: A reliable, bidirectional, transport mechanism used to
convey CLUE messages. A CLUE channel consists of one SCTP stream
in each direction over a DTLS/SCTP session.
3. CLUE-Specific Signaling Protocol
The CLUE Framework [I-D.ietf-clue-framework] mentions a CLUE-specific
protocol for the exchange of ADVERTISEMENT and CONFIGURE messages,
but gives little detail. The Data Model
[I-D.presta-clue-data-model-schema] specifies a model and XML
representation for CLUE-related data, but doesn't currently specify
exactly what data belongs in each message, or how messages are
sequenced. This document provides the detail missing from those
documents.
3.1. CLUE Messages
CLUE messages are encoded in XML. The Data Model
[I-D.presta-clue-data-model-schema] defines many/most of the elements
from which CLUE messages are composed. The content of each
individual CLUE message could be defined by reference to an XML
element type defined in the Data Model. Or this document could
itself define an XML element type for each message, with much of the
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content of those elements being drawn from the Data Model. Which
approach to follow is TBD.
3.1.1. ADVERTISEMENT Message
Most of the content needed for the ADVERTISEMENT message is already
defined in the Data Model. But the Data Model has't been constructed
with that in mind. So either the Data Model needs revision with a
focus on the needs of signaling, or else additional schema is needed
here.
3.1.2. CONFIGURE Message
The CONFIGURE message should probably also be based primarily on data
elements defined in the Data Model.
The CONFIGURE message must make reference (explicitly or implicitly)
to the ADVERTISEMENT message on which it is based. The mechanism for
doing this must be specified.
3.1.3. Stand-alone messages or deltas?
Each message exchanged within a CLUE session could contain a complete
description of the state it wishes to achieve. Or each message could
describe just the changes that it wishes to make to the current
state. Or the protocol could support both message forms. Which
direction to pursue is TBD.
[Paul: while this does need to be decided, it is fundamentally just
an optimization. IMO it does not have major impact on the other
parts of this document, so I would prefer to continue deferring it
until we are so far along with the remainder of the document that we
can no longer defer it.]
3.1.4. other
3.2. Message Acknowledgement
The CLUE channel is reliable, so there is no need for acknowledgement
to guarantee delivery. But there is still a need for application-to-
application acknowledgement to report that the message has been
received, parsed, and found to be of an acceptable format. One
possibility is to introduce separate ACK and/or NAK messages.
Another possibility is to add a confirmation element to each CLUE
message, so that confirmation can be piggybacked on the basic
messages. Something concrete needs to be proposed.
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3.3. Message Sequencing
There is a very basic introduction to this topic in section 9.4
(Message Flow) of the CLUE Framework [I-D.ietf-clue-framework]. That
still mentions the Consumer Capability message, which we have decided
to drop. Without that it would look like:
Media Consumer Media Provider
-------------- ------------
| |
|<----- ADVERTISEMENT message --------|
| |
| |
|-------- CONFIGURE message --------->|
| |
But we need much more than this, to show multiple CONFIGUREs per
ADVERTISEMENT, interleaving of ADVERTISEMENTs and CONFIGUREs in both
directions, etc.
Message sequencing needs to be described at two levels:
o Basic sequencing of the CLUE messages themselves, without regard
for the SIP/SDP signaling that may be going on at the same time.
This is useful to cover the basic concepts. That should be
covered in this section. It provides context for understanding
the more detailed treatment later.
This could include some simple state machines.
o In reality there is a complex dependency between CLUE signaling
and SDP Offer/Answer exchanges carried in SIP signaling. So there
is a need to describe the valid ways in which these two forms of
signaling interact. That is covered in Section 5.
3.3.1. Two CLUE-capable endpoints
This is the case where two CLUE-capable endpoints are willing to set
up a CLUE telepresence session. In the following, a possible
approach addressing the problem is illustrated.
+----------+ +-----------+
| EP1 | | EP2 |
| | | |
+----+-----+ +-----+-----+
| |
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| |
| INVITE (BASIC SDP+COMEDIA) |
|--------------------------------->|
| |
| |
| 200 0K (BASIC SDP+COMEDIA)|
|<---------------------------------|
| |
| |
| ACK |
|--------------------------------->|
| |
| |
| |
|<################################>|
| ?? BASIC SDP MEDIA SESSION ?? |
|<################################>|
| |
| |
| CLUE CTRL CHANNEL SETUP |
|<================================>|
| ... |
|<================================>|
| CLUE CTRL CHANNEL ESTABLISHED |
|<================================>|
| |
| |
| ADVERTISEMENT 1 |
|*********************************>|
| |
| |
| ADVERTISEMENT 2 |
|<*********************************|
| |
| |
| |
| CONFIGURE 1 |
|<*********************************|
| |
| |
| CONFIGURE 2 |
|*********************************>|
| |
| |
| |
| REINVITE (UPDATED SDP) |
|--------------------------------->|
| |
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| |
| 200 0K (UPDATED SDP)|
|<---------------------------------|
| |
| |
| ACK |
|--------------------------------->|
| |
|<################################>|
| UPDATED SDP MEDIA SESSION |
|<################################>|
| |
| |
| |
| |
| |
v v
First, endpoint EP1 sends to endpoint EP2 a SIP INVITE including in
the SDP body the basilar audio and video capabilities ("BASIC SDP")
and the information needed for opening a control channel to be used
for CLUE protocol messages exchange, according to what is envisioned
in the COMEDIA approach ("COMEDIA") for DTLS/SCTP channel
[I-D.ietf-mmusic-sctp-sdp].
After the successful SIP O/A phase, EP1 and EP2 are able to exchange
audio and video streams ("BASIC AUDIO AND VIDEO"). [RP: Is this
channel needed at this point of the call flow?] [RP: which streams
are sent on this channel in this moment?]
Moreover, another effect of the above successful SIP O/A phase, is
the opening of the control channel. After the setup phase, the
channel is established and CLUE protocol messages can flow above it.
CLUE protocol messages have not been formally defined yet. However,
up to now there is a common agreement on their names and their main
purposes, that should be following.
CLUE protocol ADVERTISEMENT messages are used to better describe the
media provider's available streams in order to make the media
consumer able to reproduce them in a more realistic fashion, as it is
the main purpose of a telepresence session. These messages are
needed since it is not possible in an agile fashion to describe
spatial information and several further metadata about media captures
via SDP.
In this document it is assumed that ADVERTISEMENT messages contain
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the full description of the sender's telepresence room in terms of
available media capture and encoding capabilities. [RP: open issue -
the mapping between what is described in the advertisement messages
and media streams exchanged in the eventual basic SDP session already
established]
CLUE protocol CONFIGURE messages are used to let the media consumer
indicate to the media provider which are the available streams it is
interested in, so that the media provider can send to the media
consumer what it desires.
In the following, it is considered one of the possible call flow that
can lead to the desired session configuration.
EP1 sends the ADVERTISEMENT message to EP2 (ADVERTISEMENT 1), which
replies with a CONFIGURE message (CONFIGURE 1). After receiving the
CONFIGURE message, EP1 assumes the CLUE offer/answer negotiation it
started is completed. EP1 then can issue a REINVITE to EP2 with an
SDP body updated accordingly to the CLUE messages exchange.
Similarly, EP2 sends its ADVERTISEMENT to EP1 (ADVERTISEMENT 2),
which replies with a CONFIGURE (CONFIGURE 2).
EP1 re-negotiates the media involved in the existent session via a
SIP REINVITE message to EP2. The SDP body within the REINVITE
message reflects the negotiation carried on by the CLUE message
exchange. In the case represented in figure, EP2 builds the 200 OK
response also according to the second CLUE O/A negotiation.
3.3.2. A case with a non-CLUE-capable endpoint
In this example, one of the two involved endpoint (EP2) is not CLUE-
capable, i.e., it is not able to use the CLUE protocol.
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+----------+ +-----------+
| EP1 | | EP2 |
| | | |
+----+-----+ +-----+-----+
| |
| |
| INVITE (BASIC SDP+COMEDIA) |
|--------------------------------->|
| |
| |
| 200 0K (BASIC SDP + *NO* COMEDIA)|
|<---------------------------------|
| |
| |
| ACK |
|--------------------------------->|
| |
| |
| |
|<################################>|
| ?? BASIC SDP MEDIA SESSION ?? |
|<################################>|
| |
| |
| |
| REINVITE (UPDATED SDP) |
|--------------------------------->|
| |
| |
| 200 0K (UPDATED SDP)|
|<---------------------------------|
| |
| |
| ACK |
|--------------------------------->|
| |
|<################################>|
| UPDATED SDP MEDIA SESSION |
|<################################>|
| |
| |
| |
| |
| |
v v
Endpoint EP1 sends to endpoint EP2 a SIP INVITE including in the SDP
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body the basilar audio and video capabilities ("BASIC SDP") and the
information needed for opening a control channel to be used for CLUE
protocol messages exchange, as envisioned by the COMEDIA approach
("COMEDIA") for DTLS/SCTP channel [I-D.ietf-mmusic-sctp-sdp].
Since EP2 is not CLUE-capable, it answers with a 200 OK in which
basic audio and video capabilities are accepted while the opening of
the CLUE channel is rejected.
From such a response, EP1 understands the peer is not CLUE-capable.
In this example, EP1 re-negotiates the session according to a pre-
determined bulk of media streams to be sent to non-CLUE-capable
endpoints.
3.4. Message Transport
CLUE messages are transported over CLUE channels. In a two-party
CLUE session, a CLUE channel connects the two endpoints. In a CLUE
conference, each endpoint has a CLUE channel connecting it to an MCU.
(In conferences with cascaded mixers [RFC4353], two MCUs will be
connected by a CLUE channel.)
The transport mechanism used for CLUE messages is DTLS/SCTP as
specified in [I-D.tuexen-tsvwg-sctp-dtls-encaps] and
[I-D.ietf-mmusic-sctp-sdp]. A CLUE channel consists of one SCTP
stream in each direction over a DTLS/SCTP session. The mechanism for
establishing the DTLS/SCTP session is described in Section 4.
3.5. Message Framing
Message framing is provided by the SCTP transport protocol. Each
CLUE message is carried in one SCTP message.
3.6. other
4. CLUE use of SDP O/A
The CLUE channel is usually offered in the first SIP O/A exchange
between two parties in an intended CLUE session. The offer of the
CLUE channel is the indicator that this SIP session is proposing to
establish a CLUE session.
(However it is also acceptable to start with a non-CLUE SIP session
and upgrade it to a CLUE session later.)
The mechanism for negotiating a DTLS/SCTP connection is specified in
[I-D.ietf-mmusic-sctp-sdp]. We need to specify how to select the
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specific pair of SCTP streams that comprise the CLUE channel.
Any specific usage/conventions required for coordination of SDP
offers and answers with the CLUE messages should also be described
here.
(We have a draft [I-D.even-clue-sdp-clue-relation] that can
contribute to this.)
5. Coordination of CLUE protocol and SDP O/A
This should include state machines and/or call flows. These will
illustrate, and then provide normative rules for valid sequences of
messages of both types. For instance this needs to show when SDP
offers and answers must occur relative to an ADVERTISEMENT or
CONFIGURE message that requires SDP changes.
[THIS IS A VERY IMPORTANT PART OF THIS DOCUMENT!]
6. CLUE requirements on SDP O/A
Any SDP extensions required by CLUE should be specified here. Then
we will need to take action within MMUSIC to make those happen. This
section should be empty and removed before this document becomes an
RFC.
7. SIP Signaling
(Placeholder) This may be unremarkable. If so we can drop it.
8. Interoperation with Legacy SIP Devices
This may just describe how the degenerate form of the general
mechanisms work for legacy devices. Or it may describe special case
handling that we mandate as part of CLUE. Or it may just discuss
non-normative things for implementors should consider.
9. CLUE over RTCWEB
We may want to rule this out of scope for now. But we should be
thinking about this.
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10. Open Issues
Here are issues pertinent to signaling that need resolution.
Resolution will probably result in changes somewhere in this
document, but may also impact other documents.
o While the preference is to multiplex multiple capture encodings
over a single RTP session, this will not always be desirable or
possible. The factors that prevent multiplexing may come from
either the provider or the consumer. So the extent of
multiplexing must be negotiated. The decision about how to
multiplex affects the number and grouping of m-lines in the SDP.
The endpoint of a CLUE session that sends an offer needs to know
the mapping of capture encodings to m-lines for both sides.
AFAIK this issue hasn't yet been considered at all.
11. What else?
12. Acknowledgements
The team focusing on this draft consists of: Roni Even, Rob Hansen,
Christer Holmberg, Paul Kyzivat, Simon Pietro-Romano, Roberta Presta.
Paul's contributions are supported by collaboration with colleague
Lennard Xiao on the study of CLUE signaling.
The author list should be updated as people contribute substantial
text to this document.
13. IANA Considerations
TBD
14. Security Considerations
TBD
15. References
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15.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[I-D.ietf-clue-framework]
Duckworth, M., Pepperell, A., and S. Wenger, "Framework
for Telepresence Multi-Streams",
draft-ietf-clue-framework-08 (work in progress),
December 2012.
[I-D.presta-clue-data-model-schema]
Presta, R. and S. Romano, "An XML Schema for the CLUE data
model", draft-presta-clue-data-model-schema-02 (work in
progress), February 2013.
[I-D.ietf-mmusic-sctp-sdp]
Loreto, S. and G. Camarillo, "Stream Control Transmission
Protocol (SCTP)-Based Media Transport in the Session
Description Protocol (SDP)", draft-ietf-mmusic-sctp-sdp-03
(work in progress), January 2013.
[I-D.tuexen-tsvwg-sctp-dtls-encaps]
Jesup, R., Loreto, S., Stewart, R., and M. Tuexen, "DTLS
Encapsulation of SCTP Packets for RTCWEB",
draft-tuexen-tsvwg-sctp-dtls-encaps-01 (work in progress),
July 2012.
15.2. Informative References
[RFC4353] Rosenberg, J., "A Framework for Conferencing with the
Session Initiation Protocol (SIP)", RFC 4353,
February 2006.
[I-D.even-clue-sdp-clue-relation]
Even, R., "Signalling of CLUE and SDP offer/answer",
draft-even-clue-sdp-clue-relation-01 (work in progress),
October 2012.
Author's Address
Paul Kyzivat
Huawei
Email: pkyzivat@alum.mit.edu
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