CLUE Signaling
draft-kyzivat-clue-signaling-04
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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|---|---|---|---|
| Authors | Paul Kyzivat , Lennard Xiao , Christian Groves , Robert Hansen | ||
| Last updated | 2013-07-15 | ||
| Replaced by | draft-ietf-clue-signaling, draft-ietf-clue-signaling, RFC 8848 | ||
| RFC stream | (None) | ||
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| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
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draft-kyzivat-clue-signaling-04
Network Working Group P. Kyzivat
Internet-Draft L. Xiao
Intended status: Standards Track C. Groves
Expires: January 16, 2014 Huawei
R. Hansen
Cisco Systems
July 15, 2013
CLUE Signaling
draft-kyzivat-clue-signaling-04
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 January 16, 2014.
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
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include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. CLUE-Specific Signaling Protocol . . . . . . . . . . . . . . 3
3.1. Protocol Versioning, Options & Extensions . . . . . . . . 4
3.1.1. Versioning . . . . . . . . . . . . . . . . . . . . . 4
3.1.2. Options and/or Extensions . . . . . . . . . . . . . . 4
3.1.3. Negotiation . . . . . . . . . . . . . . . . . . . . . 4
3.1.4. Principles . . . . . . . . . . . . . . . . . . . . . 5
3.2. Acknowledging Messages . . . . . . . . . . . . . . . . . 5
3.2.1. Explicit Acknowledgment of Each Message . . . . . . . 5
3.2.2. Piggybacking ACK on Requests . . . . . . . . . . . . 6
3.2.3. Reporting Message Errors . . . . . . . . . . . . . . 7
3.3. Stand-alone messages or deltas? . . . . . . . . . . . . . 9
3.4. Message Sequencing . . . . . . . . . . . . . . . . . . . 9
3.4.1. Signaling Changes in Provider State . . . . . . . . . 10
3.4.2. Signaling Changes in Consumer State . . . . . . . . . 11
3.5. Message Transport . . . . . . . . . . . . . . . . . . . . 11
3.5.1. CLUE Channel Lifetime . . . . . . . . . . . . . . . . 11
3.5.2. Channel Error Handling . . . . . . . . . . . . . . . 12
3.6. CLUE Messages . . . . . . . . . . . . . . . . . . . . . . 12
3.6.1. ADVERTISEMENT Message . . . . . . . . . . . . . . . . 12
3.6.2. CONFIGURE Message . . . . . . . . . . . . . . . . . . 13
3.6.3. ACK Message . . . . . . . . . . . . . . . . . . . . . 13
3.6.4. NAK Message . . . . . . . . . . . . . . . . . . . . . 13
3.7. Message Syntax . . . . . . . . . . . . . . . . . . . . . 13
3.8. Message Framing . . . . . . . . . . . . . . . . . . . . . 16
3.9. other . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4. CLUE use of SDP O/A . . . . . . . . . . . . . . . . . . . . . 16
4.1. Establishing the CLUE channel . . . . . . . . . . . . . . 16
4.2. Representing CLUE Encodings in SDP . . . . . . . . . . . 16
4.3. Representing CLUE Encoding Groups in SDP . . . . . . . . 18
4.4. Signaling CLUE control of "m" lines . . . . . . . . . . . 18
4.5. Ensuring interoperability with non-CLUE devices . . . . . 19
5. Interaction of CLUE and SDP negotiations . . . . . . . . . . 19
5.1. Independence of SDP and CLUE negotiation . . . . . . . . 19
5.2. Recommendations for operating with non-atomic operations 19
5.3. Constraints on sending media . . . . . . . . . . . . . . 20
6. Example: A call between two CLUE-capable endpoints . . . . . 20
7. Example: A call between a CLUE and non-CLUE-capable endpoint 27
8. CLUE requirements on SDP O/A . . . . . . . . . . . . . . . . 29
9. SIP Signaling . . . . . . . . . . . . . . . . . . . . . . . . 29
10. Interoperation with Legacy SIP Devices . . . . . . . . . . . 29
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11. CLUE over RTCWEB . . . . . . . . . . . . . . . . . . . . . . 29
12. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 30
13. What else? . . . . . . . . . . . . . . . . . . . . . . . . . 30
14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 30
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30
16. Security Considerations . . . . . . . . . . . . . . . . . . . 30
17. Change History . . . . . . . . . . . . . . . . . . . . . . . 30
18. References . . . . . . . . . . . . . . . . . . . . . . . . . 31
18.1. Normative References . . . . . . . . . . . . . . . . . . 31
18.2. Informative References . . . . . . . . . . . . . . . . . 32
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 33
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.
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3.1. Protocol Versioning, Options & Extensions
3.1.1. Versioning
There must be some provision for identifying incompatible protocol
versions.
NOTE: We probably don't want to have incompatible versions.
Typically changes will be introduced in a backward compatible way.
But a time may come when this isn't possible, and we should be
prepared for that. This is more likely to occur before an RFC is
published. While it is probably unwise to deploy a product based on
a draft, there will certainly be prototypes developed for testing,
and those tests may lead to a need for incompatible change. So
whatever the mechanism is, it should be applicable to changes that
occur from draft to draft, as well as after an RFC has been
published.
3.1.2. Options and/or Extensions
There must be some provision for dealing with optional-to-implement
features in the specification, and/or for backward compatible
extensions to the protocol. These are superficially different, but
in practice they are more-or-less equivalent. To an implementation
of the base protocol and some extensions, those extensions must be
viewed as optional-to-implement features in peers.
One decision is whether extensions may be implemented mix-and-match,
or whether there is a sequence of extensions, and one extension may
only be supported if all the prior extensions have been supported.
3.1.3. Negotiation
Both version and options can be negotiated. Some mechanisms may work
for both, while others are only appropriate for one or the other.
Some possibilities:
o No negotiation at all. Instead, unrecognized syntax in certain
"extension points" is to be ignored. If it is recognized, then a
corresponding extension specification defines what to do.
o Negotiate via the SIP signaling.
o Negotiate as part of the O/A exchange that establishes the
channel. (E.g. it is likely that individual channels of the SCTP
association will be specified in SDP with a specific sub-protocol
type. There could be a separate sub-protocol for each new
version.)
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o Negotiate within the CLUE channel, via a special message exchange,
before exchanging "normal" CLUE messages.
o Declare versioning in every CLUE message. Define errors for
unsupported versions and fallback to earlier versions.
3.1.4. Principles
o CLUE SHOULD allow forwards and backwards compatibility through a
version and extension mechanism. Forward compatibility allows a
version of a protocol to communicate effectively with and
interwork with future versions of the protocol. A version should
not restrict the future protocol from providing extra
capabilities.
o Whenever possible backwards compatibility should be maintained.
Backward compatibility rules will be defined to ensure that
endpoints implementing future versions of CLUE will be able to
send protocol messages of the previous versions which will be
understood and fully processed by the remote endpoint.
o Existing protocol elements should not be changed unless a protocol
error needs to be corrected.
o The semantics of existing elements and values should not be
changed.
o Established rules for formatting and encoding messages and
elements should not be changed.
o When information elements are found to be obsolete they can be
marked as not used. However, the identifier for that information
element will be marked as reserved. In that way it cannot be used
in future versions.
3.2. Acknowledging Messages
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 NAK messages. Another
possibility is to add a confirmation element to each CLUE message, so
that confirmation can be piggybacked on the basic messages. Some
alternatives follow. [OTHER PROPOSALS WELCOME.]
3.2.1. Explicit Acknowledgment of Each Message
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The characteristics of this approach are:
o There are separate request and response messages. (This is
similar to SIP.)
o Every request message expects exactly one response message.
o Every request message carries a sequence number that identifies
it.
o Each end of the connection assigns sequential sequence numbers to
the requests it sends.
o Every response message carries the sequence number of the message
to which it responds.
o Responses are to be sent promptly upon the receipt of a request.
(Needs more detail.)
o Responses are either ACK or NAK. NAK responses also carry info
describing the error.
o Each CONFIGURE message is to be understood in the context of the
most recent ACKed ADVERTISEMENT message. A CONFIGURE message may
be rejected if there is an outstanding ADVERTISEMENT for which no
response has been received. (Or it may be accepted if the
advertiser is able to do so meaningfully.)
3.2.2. Piggybacking ACK on Requests
The characteristics of this approach are:
o Every message carries a sequence number that identifies it.
o Each end of the connection assigns sequential sequence numbers to
the messages it sends.
o Every message carries the sequence number of the last message
received and found valid.
o If a message is received and found invalid, then a NAK message is
sent that refers to it and indicates what is wrong with it.
o If a valid message is received and a new message needs to be sent
in response, then the responding message implicitly acknowledges
the prior message.
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o If a valid message is received and there is no need to immediately
send another message, then a NO-OP message is sent to acknowledge
the received message. But a NO-OP message is never sent in
response to a NO-OP message.
o Each CONFIGURE message is to be understood in the context of the
most recent *acknowledged* ADVERTISEMENT message. A CONFIGURE
message may be rejected if it doesn't acknowledge the most
recently sent ADVERTISEMENT. (Or it may be accepted if the
advertiser is able to do so meaningfully.)
The general format of every message is:
o sequence # of this message
o sequence # of most recently *received* and *valid* message
o message type (ADVERTISEMENT, CONFIG, NO-OP, NAK)
o body of the message, according to type
(The exact representation is TBD - by XML experts.)
There are loose ends to resolve here. In particular, how to
acknowledge messages after NAKing one.
3.2.3. Reporting Message Errors
There needs to be a mechanism to report errors with other messages.
The details of form, content, and usage still need to be specified,
and need to be tuned to the details of the protocol. This could use
distinct messages or be incorporated into the other messages. Errors
this message must be able to report include:
Syntax error in message: The message has been disregarded due to a
syntax error detected at the message level. The message does not
conform to the productions of messages in [Protocol Document].
Used when the message cannot be parsed.
Sequencing Error: Sequence number has already been used, or is
greater than the expected number. (Details of possible errors
depend upon the specific sequence numbering mechanism.)
Version not supported: This indicates a lack of support for the
protocol version indicated in the message header of the message.
In the case of the version number being indicated in the message
header, the message contents are disregarded.
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Option not supported: This indicates a lack of support for the
protocol option the used in the message. The message contents are
disregarded.
Unknown capture identity: The received Configure message contains an
unknown capture identity not previously declared by an
Advertisement. The message contents are disregarded.
Invalid identity: The received message contains an invalid capture
identity. For example a duplicated Capture scene identity or some
other semantically incorrect usage. The message contents are
disregarded.
Invalid value: The received message contains an invalid parameter
value. The value is not according to the protocol definition in
[protocol document] or according the extension documentation.
Missing element: The received message is missing an element.
Certain parameters require multiple values, e.g. Point of capture
requires X,Y,Z co-ordinates if one or more elements are missing
this error code is used.
Conflicting parameters or values: The received message contains
multiple values that may not be used together.
Invalid capture area: The received message defines a capture area
that cannot be rendered in a sensible manner. For example the
capture area does not define a quadrilateral region.
Invalid point of line of capture: The indicated co-ordinate for the
point on line of capture is invalid. For example: does not lie
between the point of capture and the area of capture or it is the
same as the point of capture.
Invalid capture scene entry: The message contains an invalid capture
scene entry. For example the capture scene entry contains more
than one media type.
Invalid Simultaneous Set: The simultaneous set contained in the
message is invalid. For example the simultaneous set refers to an
undefined capture set or does not match the specified capture
scene entries.
Invalid Configuration: The Configure message requests a
configuration that the provider cannot support.
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Invalid Advertisement reference: The Configure message refers to an
invalid Advertisement. The message refers-to/depends-upon out-of-
date ADVERTISEMENT message or provides an invalid reference.
3.3. 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.]
3.4. Message Sequencing
There is a very basic introduction to this topic in section 4
(Overview) of the CLUE Framework [I-D.ietf-clue-framework]. After
removing extraneous material it would look like:
+-----------+ +-----------+
| Endpoint1 | | Endpoint2 |
+----+------+ +-----+-----+
| |
| ADVERTISEMENT 1 |
|*********************************>|
| ADVERTISEMENT 2 |
|<*********************************|
| |
| CONFIGURE 1 |
|<*********************************|
| CONFIGURE 2 |
|*********************************>|
| |
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.
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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.
3.4.1. Signaling Changes in Provider State
Once a CLUE session has been established, ADVERTISEMENTs and
CONFIGUREs exchanged, and media is flowing, a provider may experience
a change in state that has an effect on what it wishes or is able to
provide. In this case it may need to alter what it is sending and/or
send a new ADVERTISEMENT. In some cases it will be necessary to
alter what is being sent without first sending a new ADVERTISEMENT
and waiting for a CONFIGURE conforming to it.
The following is a non-exhaustive list of situations and recommended
actions:
o An advertised capture, that is not currently configured, is no
longer available.
To recover from this: Send a new ADVERTISEMENT that omits this
capture.
o An advertised capture, that has been configured, is no longer
available.
To recover from this: (1) stop transmitting the configured
encoding of this capture. (2) Send a new ADVERTISEMENT that omits
this capture.
o The provider loses some resource and must reduce the frame rate,
frame size, or resolution of a capture encoding.
If the reduced values still fall within the advertised values for
the capture then the change may be made without any further
signaling.
If the change must be outside the range of what was advertised,
then the provider must cease transmitting the capture encoding.
It then must send a new ADVERTISEMENT reflecting what it is now
capable of delivering.
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o New or changed scenes or scene geometry. For instance, the
addition of a new scene containing presentation captures. Also,
an MCU may make significant changes in what it advertises as new
endpoints join a conference.
o [Add more]
3.4.2. Signaling Changes in Consumer State
If the Consumer for some reason looses the CLUE state information how
does it ask for an Advertisement from the provider? There could be
multiple possibilities. A error code approach? However error codes
would typically be associated with a NACK so it may not be good for a
Config message. Maybe send a message which means "send me a complete
update". An alternative may be to release the connection or just do
new signaling to establish a new CLUE session.
3.5. Message Transport
CLUE messages are transported over a bidirectional CLUE channel. 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.)
3.5.1. CLUE Channel Lifetime
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.
The CLUE channel will usually be offered during the initial SIP
INVITE, and remain connected for the duration of the CLUE/SIP
session. However this need not be the case. The CLUE channel may be
established mid-session after desire and capability for CLUE have
been determined, and the CLUE channel may be dropped mid-call if the
desire and/or capability to support it is lost.
There may be cases when it becomes necessary to "reset" the CLUE
channel. This by be as a result of an error on the underlying SCTP
association, a need to change the endpoint address of the SCTP
association, loss of CLUE protocol state, or something else TBD.
The precise mechanisms used to determine when a reset is required,
and how to accomplish it and return to a well defined state are TBS.
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3.5.2. Channel Error Handling
We will need to specify behavior in the face of transport errors that
are so severe that they can't be managed via CLUE messaging within
the CLUE channel. Some errors of this sort are:
o Unable to establish the SCTP association after signaling it in
SDP.
o CLUE channel setup rejected by peer.
o Error reported by transport while writing message to CLUE channel.
o Error reported by transport while reading message from CLUE
channel.
o Timeout - overdue acknowledgement of a CLUE message.
(Requirements for now soon a message must be responded to are
TBD.)
o Application fault. CLUE protocol state lost.
The worst case is to drop the entire CLUE call. Another possibility
is to fall back to legacy compatibility mode. Or perhaps a "reset"
can be done on the protocol. E.g. this might be accomplished by
sending a new O/A and establishing a replacement SCTP association.
Or a new CLUE channel might be established within the existing SCTP
association.
3.6. 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. This document specifies an
XML schema that contains an element definition for each CLUE message,
with much of the content of those elements being drawn from the Data
Model.
3.6.1. ADVERTISEMENT Message
This message contains XML representations of captures, capture
scenes, encoding groups, and simultaneous sets using the types
defined for those in the Data Model
[I-D.presta-clue-data-model-schema].
The XML definition for this is element <advertisement> in section
Section 3.7
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[[ Currently this does not contain any representation of encodings.
It assumes those will be defined in SDP. ]]
3.6.2. CONFIGURE Message
This message optionally contains an XML representations of
captureEncodings using the type defined in the Data Model
[I-D.presta-clue-data-model-schema]. A configure message with no
captureEncodings indicates that no captures are requested.
[[ It currently also contains a reference to the request number of
the advertisement it is based upon. Whether this should be present,
or if it should implicitly reference the most recently acknowledged
advertisement is TBD. ]]
The XML definition for this is element <configure> in section
Section 3.7
3.6.3. ACK Message
Need for, and details of, the ACK message are TBD.
The XML element <response> in section Section 3.7 could serve as the
representation, either with no reason element, or a reason element
with a special value.
3.6.4. NAK Message
Need for, and details of, the NACK message are TBD.
The XML element <response> in section Section 3.7 could serve to as
the representation, with the reason element providing the details.
Then the code value in the reason element should map to the errors in
section Section 3.2.3.
3.7. Message Syntax
[[ The following is a first cut at a schema for the actual messages
in the clue protocol. It uses <encodingGroups> from the data model
but not <encodings>. Rather, it assumes that encodings are described
in SDP as m-lines with a text identifier, and that the identifier has
the same value as the encodingIDs embedded in the <encodingGroups>.
If we stick with this the data model should be adjusted to agree, but
until then it should "work". The SDP encoding of the identifier is
proposed to be 'a=label:ID', though 'a=mid:ID' is another candidate.
]]
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For now there only <advertisement> and <configure> are defined. More
messages will be needed for acknowledgment.
<?xml version="1.0" encoding="UTF-8" ?>
<xs:schema
targetNamespace="urn:ietf:params:xml:ns:clue-message"
xmlns:tns="urn:ietf:params:xml:ns:clue-message"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:dm="urn:ietf:params:xml:ns:clue-info"
xmlns="urn:ietf:params:xml:ns:clue-message"
elementFormDefault="qualified"
attributeFormDefault="unqualified">
<!-- Import data model schema -->
<xs:import namespace="urn:ietf:params:xml:ns:clue-info"
schemaLocation="clue-data-model-04-wip.xsd"/>
<!-- ELEMENT DEFINITIONS -->
<xs:element name="advertisement" type="advertisementMessageType"/>
<xs:element name="configure" type="configureMessageType"/>
<xs:element name="response" type="responseMessageType"/>
<!-- CLUE MESSAGE TYPE -->
<xs:complexType name="clueMessageType" abstract="true">
<xs:sequence>
<!-- mandatory fields -->
<!-- TBS: version info -->
</xs:sequence>
</xs:complexType>
<!-- CLUE REQUEST MESSAGE TYPE -->
<xs:complexType name="clueRequestMessageType" abstract="true">
<xs:complexContent>
<xs:extension base="clueMessageType">
<xs:sequence>
<!-- mandatory fields -->
<xs:element name="requestNumber" type="xs:integer"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<!-- CLUE RESPONSE MESSAGE TYPE -->
<xs:complexType name="clueResponseMessageType">
<xs:complexContent>
<xs:extension base="clueMessageType">
<xs:sequence>
<!-- mandatory fields -->
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<xs:element name="requestNumber" type="xs:integer"/>
<!-- optional fields -->
<xs:element name="reason" type="reasonType" minOccurs="0"/>
<xs:any namespace="##other"
processContents="lax" minOccurs="0"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<!-- CLUE ADVERTISEMENT MESSAGE TYPE -->
<xs:complexType name="advertisementMessageType">
<xs:complexContent>
<xs:extension base="clueRequestMessageType">
<xs:sequence>
<!-- mandatory fields -->
<xs:element name="mediaCaptures"
type="dm:mediaCapturesType"/>
<xs:element name="encodingGroups"
type="dm:encodingGroupsType"/>
<!-- The encodings are defined via identifiers in the SDP,
referenced in encodingGroups -->
<xs:element name="captureScenes"
type="dm:captureScenesType"/>
<!-- optional fields -->
<xs:element name="simultaneousSets"
type="dm:simultaneousSetsType" minOccurs="0"/>
<xs:any namespace="##other"
processContents="lax" minOccurs="0"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<!-- CLUE CONFIGURE MESSAGE TYPE -->
<xs:complexType name="configureMessageType">
<xs:complexContent>
<xs:extension base="clueRequestMessageType">
<xs:sequence>
<!-- mandatory fields -->
<xs:element name="advertisementNumber" type="xs:integer"/>
<!-- advertisementNumber is requestNumber
of the advertisement-->
<!-- optional fields -->
<xs:element name="captureEncodings"
type="dm:captureEncodingsType" minOccurs="0"/>
<xs:any namespace="##other"
processContents="lax" minOccurs="0"/>
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</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<!-- REASON TYPE -->
<xs:complexType name="reasonType">
<xs:simpleContent>
<xs:extension base="xs:string">
<xs:attribute type="xs:short" name="code" use="required"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:schema>
3.8. Message Framing
Message framing is provided by the SCTP transport protocol. Each
CLUE message is carried in one SCTP message.
3.9. other
4. CLUE use of SDP O/A
4.1. Establishing the CLUE channel
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
specific pair of SCTP streams that comprise the CLUE channel.
The presence of an active m-line for the CLUE channel in an SDP offer
is an indication that the offer that the sender is CLUE-capable and
hence can understand CLUE-specific syntax.
4.2. Representing CLUE Encodings in SDP
Many CLUE constructs have no good analog in SDP. Entities such as
'captures', which describe spatial and other properties of a capture
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source such as a camera, are not tied directly to RTP streams, do not
have negotiated properties and would prove a significant challenge to
represent in SDP syntax (while also greatly increasing the size of
the SDP).
However, two entities defined in the CLUE Framework
[I-D.ietf-clue-framework] are a much closer fit for SDP: Encodings
and Encoding Groups. Both describe RTP media properties and
limitations, though unlike most SDP usage they describe the sender's
capabilities, not the receiver's. Representing encodings in CLUE
splits media limitations across two protocols, and risks duplicated
and potentially contradictory information being sent in CLUE and SDP.
As such we are exploring representing this information in SDP, with
the decision to convey them in the CLUE messages only to be made if
the SDP approach proves impractical.
This draft presents an attempt to describe CLUE encodings in SDP. As
a decision has not yet been reached on how multiplexed RTP streams
are to be expressed in SDP, at this stage the draft does so without
multiplexing, using existing SDP attributes, with a seperate "m" line
and hence port per unidirectional RTP stream. This is done with the
understanding that when a decision is reached on new syntax for
multiplexing RTP streams in SDP the CLUE SDP signaling will be
modified to use it. Further, the framework document states that the
multiplexing of streams by an implementation is optional, and in the
case of a disaggregated system, with media streams going to different
addresses, may not be possible.
With the current scheme of using existing syntax, an encoding is
specified in SDP as a unicast "m" line, which MUST be marked as
sendonly with the "a=sendonly" attribute or as inactive with the
"a=inactive" attribute. The encoder capabilities of the stream are
defined here using existing syntax; for instance, for H.264 see Table
6 in [RFC6184] for a list of valid parameters for representing
encoder sender stream limits.
Every "m" line representing a CLUE encoding SHOULD contain a "label"
attribute as defined in [RFC4574]. This label is used to identify
the encoding by the sender in CLUE Advertisement messages and by the
receiver in CLUE Configure messages.
A receiver who wishes to receive a CLUE stream via this encoding
requires a matching "a=recvonly" "m" line. As well as the normal
restrictions defined in [RFC3264] media MUST NOT be sent on this
stream until the sender has received a valid CLUE Configure message
specifying the capture to be used for this stream.
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4.3. Representing CLUE Encoding Groups in SDP
As per the previous section, there would be advantages to conveying
encoding group information in SDP. However, with current SDP syntax
there is no way to express the encoding group limits defined in the
Data Model [I-D.presta-clue-data-model-schema]. As such the current
draft keeps encoding groups as part of the Advertisement message for
the time being.
4.4. Signaling CLUE control of "m" lines
In many cases an implementation may wish to mix media channels that
are under CLUE control with those that are not. It may want to
ensure that there are non-CLUE streams for purposes of
interoperability, or that can provide media from the start of the
call before CLUE negotiation completes, or because the implementation
wants CLUE-controlled video but traditional audio, or for any other
reasons.
Which "m" lines in an SDP body are under control of the CLUE channel
is signalled via the SDP Grouping Framework [RFC5888]. Devices that
wish to negotiate CLUE MUST support the grouping framework.
A new semantic for the "group" session-level attribute, "CLUE", is
used to signal which "m" lines are under the control of a CLUE
channel. As per the framework, all of the "m" lines of a session
description that uses "group" MUST be identified with a "mid"
attribute whether they are controlled by CLUE or not. The "mid" id
of any "m" lines controlled by a CLUE channel MUST be included in the
"CLUE" group attribute alongside the "mid" id of the CLUE channel
controlling them.
The CLUE group MUST NOT include more than one "m" line for a CLUE
channel. If a CLUE channel is part of the CLUE group attribute other
media "m" lines included in the group are under the control of that
CLUE channel; media MUST NOT be sent or received on these "m" lines
until the CLUE channel has been negotiated and negotiation has taken
place as defined in this document. If no CLUE channel is part of the
CLUE group attribute then media MUST NOT be sent or received on these
"m" lines.
"m" lines not specified as under CLUE control follow normal rules for
media streams negotiated in SDP as defined in documents such as
[RFC3264].
An SDP MAY include more than one group attribute with the "CLUE"
semantic. An "mid" id for a given "m" line MUST NOT be included in
more than one CLUE group.
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4.5. Ensuring interoperability with non-CLUE devices
A CLUE-capable device sending an initial SDP offer SHOULD include an
"m" line for the CLUE channel, but SHOULD NOT include any other CLUE-
controlled "m" lines. Once each side of the call is aware that the
other side is CLUE-capable a new O/A exchange MAY be used to add
CLUE-controlled "m" lines.
5. Interaction of CLUE and SDP negotiations
Information about media streams in CLUE is split between two message
types: SDP, which defines media addresses and limits, and the CLUE
channel, which defines properties of capture devices available, scene
information and additional constraints. As a result certain
operations, such as advertising support for a new transmissible
capture with associated stream, cannot be performed atomically, as
they require changes to both SDP and CLUE messaging.
This section defines how the negotiation of the two protocols
interact, provides some recommendations on dealing with intermediary
stages in non-atomic operations, and mandates additional constraints
on when CLUE-configured media can be sent.
5.1. Independence of SDP and CLUE negotiation
To avoid complicated state machines with the potential to reach
invalid states if messages were to be lost, or be rewritten en-route
by middle boxes, the current proposal is that SDP and CLUE messages
are independent. The state of the CLUE channel does not restrict
when an implementation may send a new SDP offer or answer, and
likewise the implementation's ability to send a new CLUE
Advertisement or Configure message is not restricted by the results
of or the state of the most recent SDP negotiation.
The primary implication of this is that a device may receive an SDP
with a CLUE encoding it does not yet have capture information for, or
receive a CLUE Configure message specifying a capture encoding for
which the far end has not negotiated a media stream in SDP.
CLUE messages contain an EncodingID which is used to identify a
specific encoding in SDP. The non-atomic nature of CLUE negotiation
means that a sender may wish to send a new Advertisement before the
corresponding SDP message. As such the sender of the CLUE message
MAY include an EncodingID which does not currently match an extant id
in SDP.
5.2. Recommendations for operating with non-atomic operations
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Generally, implementations that receive messages for which they have
incomplete information SHOULD wait until they have the corresponding
information they lack before sending messages to make changes related
to that information. For instance, an implementation that receives a
new SDP offer with three new "a=sendonly" CLUE "m" lines that has not
received the corresponding CLUE Advertisement providing the capture
information for those streams SHOULD NOT include corresponding
"a=recvonly" lines in its answer, but instead should make a new SDP
offer when and if a new Advertisement arrives with captures relevant
to those encodings.
Because of the constraints of offer/answer and because new SDP
negotiations are generally more 'costly' than sending a new CLUE
message, implementations needing to make changes to both channels
SHOULD prioritize sending the updated CLUE message over sending the
new SDP message. The aim is for the recipient to receive the CLUE
changes before the SDP changes, allowing the recipient to send their
SDP answers without incomplete information, reducing the number of
new SDP offers required.
5.3. Constraints on sending media
While SDP and CLUE message states do not impose constraints on each
other, both impose constraints on the sending of media - media MUST
NOT be sent unless it has been negotiated in both CLUE and SDP: an
implementation MUST NOT send a specific CLUE capture encoding unless
its most recent SDP exchange contains an active media channel for
that encoding AND the far end has sent a CLUE Configure message
specifying a valid capture for that encoding.
6. Example: A call between two CLUE-capable endpoints
This example illustrates a call between two CLUE-capable endpoints.
Alice, initiating the call, is a system with three cameras and three
screens. Bob, receiving the call, is a system with two cameras and
two screens. A call-flow diagram is presented, followed by an
summary of each message.
To manage the size of this section only video is considered, and SDP
snippets only illustrate video 'm' lines. ACKs are not discussed.
+----------+ +-----------+
| Alice | | Bob |
| | | |
+----+-----+ +-----+-----+
| |
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| |
| INVITE 1 (BASIC SDP+COMEDIA) |
|--------------------------------->|
| |
| |
| 200 OK 2 (BASIC SDP+COMEDIA) |
|<---------------------------------|
| |
| |
| ACK 1 |
|--------------------------------->|
| |
| |
| |
|<########### MEDIA 1 ############>|
| 1 video A->B, 1 video B->A |
|<################################>|
| |
| |
| |
|<================================>|
| CLUE CTRL CHANNEL ESTABLISHED |
|<================================>|
| |
| |
| ADVERTISEMENT 1 |
|*********************************>|
| |
| |
| ADVERTISEMENT 2 |
|<*********************************|
| |
| |
| INVITE 2 (+3 sendonly) |
|--------------------------------->|
| |
| |
| CONFIGURE 1 |
|<*********************************|
| |
| |
| 200 OK 2 (+2 recvonly) |
|<---------------------------------|
| |
| |
| ACK 2 |
|--------------------------------->|
| |
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| |
| |
|<########### MEDIA 2 ############>|
| 2 video A->B, 1 video B->A |
|<################################>|
| |
| |
| INVITE 3 (+2 sendonly) |
|<---------------------------------|
| |
| |
| CONFIGURE 3 |
|*********************************>|
| |
| |
| 200 OK 3 (+2 recvonly) |
|--------------------------------->|
| |
| |
| |
| ACK 3 |
|<---------------------------------|
| |
| |
| |
|<########### MEDIA 3 ############>|
| 2 video A->B, 2 video B->A |
|<################################>|
| |
| |
| |
v v
In INVITE 1, Alice sends Bob 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]. A snippet of the SDP showing the
grouping attribute and the video m-line are shown below (mid 3
represents the CLUE channel):
...
a=group:CLUE 3
...
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m=video 6002 RTP/AVP 96
a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42e016;max-mbps=108000;max-fs=3600
a=sendrecv
a=mid:2
Bob responds with a similar SDP (200 OK 1); due to their similiarity
no SDP snippet is shown here. Alice and Bob are each able to send a
single audio and video stream (whether they choose to send this
initial media before CLUE has been negotiated is implementation-
dependent). This is illustrated as MEDIA 1.
With the successful initial O/A Alice and Bob are also free to
negotiate the CLUE channel. Once this is successfully established
CLUE negotiation can begin. This is illustrated as CLUE CHANNEL
ESTABLISHED.
Alice now sends her CLUE Advertisement (ADVERTISEMENT 1). She
advertises three static captures representing her three cameras. She
also includes switched captures suitable for two- and one-screen
systems. All of these captures are in a single capture scene, with
suitable capture scene entries to tell Bob that he should either
subscribe to the three static captures, the two switched capture view
or the one switched capture view. Alice has no simultaneity
constraints, so includes all six captures in one simultaneous set.
Finally, Alice includes an encoding group with three encoding IDs:
"enc1", "enc2" and "enc3". These encoding ids aren't currently
valid, but will match the next SDP offer she sends.
Bob received ADVERTISEMENT 1 but does not yet send a Configure
message, because he has not yet received Alice's encoding
information, so as yet he does not know if she will have sufficient
resources to send him the two streams he ideally wants at a quality
he is happy with.
Bob also sends his CLUE Advertisement (ADVERTISEMENT 2). He
advertises two static captures representing his cameras. He also
includes a single composed capture for single-screen systems, in
which he will composite the two camera views into a single video
stream. All three captures are in a single capture scene, with
suitable capture scene entries to tell Alice that she should either
subscribe to the two static captures, or the single composed capture.
Bob also has no simultaneity constraints, so includes all three
captures in one simultaneous set. Bob also includes a single
encoding group with two encoding IDs: "foo" and "bar".
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Similarly, Alices receives ADVERTISEMENT 2 but does not yet send a
Configure message, because she has not yet received Bob's encoding
information.
Alice now sends INVITE 2. She maintains the sendrecv audio, video
and CLUE m-lines, and she adds three new sendonly m-lines to
represents the maximum three encodings she can send. Each of these
m-lines has a label corresponding to one of the encoding ids from
ADVERTISEMENT 1. Each also has its mid added to the grouping
attribute to show they are controlled by the CLUE channel. A snippet
of the SDP showing the grouping attribute and the video m-lines are
shown below (mid 3 represents the CLUE channel):
...
a=group:CLUE 3 4 5 6
...
m=video 6002 RTP/AVP 96
a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42e016;max-mbps=108000;max-fs=3600
a=sendrecv
a=mid:2
...
m=video 6004 RTP/AVP 96
a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42e016
a=sendonly
a=mid:4
a=label:enc1
m=video 6006 RTP/AVP 96
a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42e016
a=sendonly
a=mid:5
a=label:enc2
m=video 6008 RTP/AVP 96
a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42e016
a=sendonly
a=mid:6
a=label:enc3
Bob now has all the information he needs to decide which streams to
configure. As such he now sends CONFIGURE 1. This requests the pair
of switched captures that represent Alice's scene, and he configures
them with encoder ids "enc1" and "enc2".
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Alice receives Bob's message CONFIGURE 1 but does not yet send the
capture encodings specified, because at this stage Bob hasn't
negotiated the ability to receive these streams in SDP.
Bob now sends his SDP answer as part of 200 OK 2. Alongside his
original audio, video and CLUE m-lines he includes two active
recvonly m-lines and a zeroed m-line for the third. He adds their
mid values to the grouping attribute to show they are controlled by
the CLUE channel. A snippet of the SDP showing the grouping
attribute and the video m-lines are shown below (mid 100 represents
the CLUE channel):
...
a=group:CLUE 11 12 100
...
m=video 58722 RTP/AVP 96
a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42e016;max-mbps=108000;max-fs=3600
a=sendrecv
a=mid:10
...
m=video 58724 RTP/AVP 96
a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42e016;max-mbps=108000;max-fs=3600
a=recvonly
a=mid:11
m=video 58726 RTP/AVP 96
a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42e016;max-mbps=108000;max-fs=3600
a=recvonly
a=mid:12
m=video 0 RTP/AVP 96
On receiving 200 OK 2 from Bob Alice is now able to send the two
streams of video Bob requested - this is illustrated as MEDIA 2.
The constraints of offer/answer meant that Bob could not include his
encoder information as new m-lines in 200 OK 2. As such Bob now
sends INVITE 3 to generate a new offer. Along with all the streams
from 200 OK 2 Bob also includes two new sendonly streams. Each
stream has a label corresponding to the encoding ids in his
ADVERTISEMENT 2 message. He also adds their mid values to the
grouping attribute to show they are controlled by the CLUE channel.
A snippet of the SDP showing the grouping attribute and the video
m-lines are shown below (mid 100 represents the CLUE channel):
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...
a=group:CLUE 11 12 13 14 100
...
m=video 58722 RTP/AVP 96
a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42e016;max-mbps=108000;max-fs=3600
a=sendrecv
a=mid:10
...
m=video 58724 RTP/AVP 96
a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42e016;max-mbps=108000;max-fs=3600
a=recvonly
a=mid:11
m=video 58726 RTP/AVP 96
a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42e016;max-mbps=108000;max-fs=3600
a=recvonly
a=mid:12
m=video 0 RTP/AVP 96
m=video 58728 RTP/AVP 96
a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42e016
a=sendonly
a=label:foo
a=mid:13
m=video 58730 RTP/AVP 96
a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42e016
a=sendonly
a=label:bar
a=mid:14
Having received this Alice now has all the information she needs to
send CONFIGURE 2. She requests the two static captures from Bob, to
be sent on encodings "foo" and "bar".
Bob receives Alice's message CONFIGURE 2 but does not yet send the
capture encodings specified, because Alice hasn't yet negotiated the
ability to receive these streams in SDP.
Alice now sends 200 OK 3, matching two recvonly m-lines to Bob's new
sendonly lines. She includes their mid values in the grouping
attribute to show they are controlled by the CLUE channel. A snippet
of the SDP showing the grouping attribute and the video m-lines are
shown below (mid 3 represents the CLUE channel):
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...
a=group:CLUE 3 4 5 7 8
...
m=video 6002 RTP/AVP 96
a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42e016;max-mbps=108000;max-fs=3600
a=sendrecv
a=mid:2
...
m=video 6004 RTP/AVP 96
a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42e016
a=sendonly
a=mid:4
a=label:enc1
m=video 6006 RTP/AVP 96
a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42e016
a=sendonly
a=mid:5
a=label:enc2
m=video 0 RTP/AVP 96
m=video 6010 RTP/AVP 96
a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42e016;max-mbps=108000;max-fs=3600
a=recvonly
a=mid:7
m=video 6012 RTP/AVP 96
a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42e016;max-mbps=108000;max-fs=3600
a=recvonly
a=mid:8
Finally, on receiving 200 OK 3 Bob is now able to send the two
streams of video Alice requested - this is illustrated as MEDIA 3.
Both sides of the call are now sending multiple video streams with
their sources defined via CLUE negotiation. As the call progresses
either side can send new Advertisement or Configure or new SDP
negotiation to add, remove or change what they have available or want
to receive.
7. Example: A call between a CLUE and non-CLUE-capable endpoint
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In this brief example Alice is a CLUE-capable endpoint making a call
to Bob, who is not CLUE-capable, i.e., it is not able to use the CLUE
protocol.
+----------+ +-----------+
| EP1 | | EP2 |
| | | |
+----+-----+ +-----+-----+
| |
| |
| INVITE 1 (BASIC SDP+COMEDIA) |
|--------------------------------->|
| |
| |
| 200 0K 1 (BASIC SDP+*NO*COMEDIA) |
|<---------------------------------|
| |
| |
| ACK 1 |
|--------------------------------->|
| |
| |
| |
|<########### MEDIA 1 ############>|
| 1 video A->B, 1 video B->A |
|<################################>|
| |
| |
| |
| |
v v
In INVITE 1, Alice sends Bob 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]. A snippet of the SDP showing the
grouping attribute and the video m-line are shown below (mid 3
represents the CLUE channel):
...
a=group:CLUE 3
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...
m=video 6002 RTP/AVP 96
a=rtpmap:96 H264/90000
a=fmtp:96 profile-level-id=42e016;max-mbps=108000;max-fs=3600
a=sendrecv
a=mid:2
Bob is not CLUE capable, and hence does not recognize the "CLUE"
semantic for the grouping attribute, not does he support the CLUE
channel. He responds with an answer with audio and video, but with
the CLUE channel zeroed.
From the lack of the CLUE channel Alice understands that Bob does not
support CLUE, or does not wish to use it. Both sides are now able to
send a single audio and video stream to each other. Alice at this
point begins to send her fallback video: in this case likely a
switched view from whichever camera shows the current loudest
participant on her side.
8. CLUE requirements on SDP O/A
The current proposal calls for a new "CLUE" semantic for the SDP
Grouping Framework [RFC5888].
Any other SDP extensions required to support CLUE signaling should
also 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.
NOTE: The RTP mapping document [I-D.even-clue-rtp-mapping] is also
likely to call for SDP extensions. We will have to reconcile how to
coordinate these two documents.
9. SIP Signaling
(Placeholder) This may be unremarkable. If so we can drop it.
10. 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.
11. CLUE over RTCWEB
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We may want to rule this out of scope for now. But we should be
thinking about this.
12. 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.
o The current method for expressing encodings in SDP limits the
parameters available when describing H264 encoder capabilities to
those defined in Table 6 in [RFC6184]
13. What else?
14. Acknowledgements
The team focusing on this draft consists of: Roni Even, Rob Hansen,
Christer Holmberg, Paul Kyzivat, Simon Pietro-Romano, Roberta Presta.
Christian Groves has contributed detailed comments and suggestions.
The author list should be updated as people contribute substantial
text to this document.
15. IANA Considerations
TBD
16. Security Considerations
TBD
17. Change History
-03:
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Internet-Draft CLUE Signaling July 2013
* Added a syntax section with an XML schema for CLUE messages.
This is a strawhorse, and is very incomplete, but it
establishes a template for doing this based on elements defined
in the data model. (Thanks to Roberta for help with this!)
* Did some rewording to fit the syntax section in and reference
it.
* Did some relatively minor restructuring of the document to make
it flow better in a logical way.
-02: A bunch of revisions by pkyzivat:
* Moved roberta's call flows to a more appropriate place in the
document.
* New section on versioning.
* New section on NAK.
* A couple of possible alternatives for message acknowledgment.
* Some discussion of when/how to signal changes in provider
state.
* Some discussion about the handling of transport errors.
* Added a change history section.
These were developed by Lennard Xiao, Christian Groves and Paul,
so added Lennard and Christian as authors.
-01: Updated by roberta to include some sample call flows.
-00: Initial version by pkyzivat. Established general outline for
the document, and specified a few things thought to represent wg
consensus.
18. References
18.1. 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]
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Internet-Draft CLUE Signaling July 2013
Duckworth, M., Pepperell, A., and S. Wenger, "Framework
for Telepresence Multi-Streams", draft-ietf-clue-
framework-11 (work in progress), July 2013.
[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-03 (work in
progress), March 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-04
(work in progress), June 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.
[RFC4574] Levin, O. and G. Camarillo, "The Session Description
Protocol (SDP) Label Attribute", RFC 4574, August 2006.
[RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description
Protocol (SDP) Grouping Framework", RFC 5888, June 2010.
18.2. Informative References
[RFC4353] Rosenberg, J., "A Framework for Conferencing with the
Session Initiation Protocol (SIP)", RFC 4353, February
2006.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264, June
2002.
[RFC6184] Wang, Y., Even, R., Kristensen, T., and R. Jesup, "RTP
Payload Format for H.264 Video", RFC 6184, May 2011.
[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.
[I-D.even-clue-rtp-mapping]
Even, R. and J. Lennox, "Mapping RTP streams to CLUE media
captures", draft-even-clue-rtp-mapping-05 (work in
progress), February 2013.
Kyzivat, et al. Expires January 16, 2014 [Page 32]
Internet-Draft CLUE Signaling July 2013
[I-D.hansen-clue-sdp-interaction]
Hansen, R., "SDP and CLUE message interactions", draft-
hansen-clue-sdp-interaction-01 (work in progress),
February 2013.
Authors' Addresses
Paul Kyzivat
Huawei
Email: pkyzivat@alum.mit.edu
Lennard Xiao
Huawei
Email: lennard.xiao@huawei.com
Christian Groves
Huawei
Email: Christian.Groves@nteczone.com
Robert Hansen
Cisco Systems
Email: rohanse2@cisco.com
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