Network Working Group P. Kyzivat
Internet-Draft L. Xiao
Intended status: Standards Track C. Groves
Expires: February 6, 2016 Huawei
R. Hansen
Cisco Systems
August 5, 2015
CLUE Signaling
draft-ietf-clue-signaling-06
Abstract
This document specifies how CLUE-specific signaling such as the CLUE
protocol [I-D.ietf-clue-protocol] and the CLUE data channel
[I-D.ietf-clue-datachannel] are used with each other and with
existing signaling mechanisms such as SIP and SDP to produce a
telepresence call.
Status of This Memo
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This Internet-Draft will expire on February 6, 2016.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Media Feature Tag Definition . . . . . . . . . . . . . . . . 4
4. SDP Grouping Framework CLUE Extension Semantics . . . . . . . 4
4.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.2. The CLUE data channel and the CLUE grouping semantic . . 4
4.3. CLUE-controlled media and the CLUE grouping semantic . . 5
4.4. SDP semantics for CLUE-controlled media . . . . . . . . . 5
4.4.1. Signalling CLUE Encodings . . . . . . . . . . . . . . 5
4.4.1.1. Referencing Encodings in the CLUE protocol . . . 6
4.4.1.2. Media line directionality . . . . . . . . . . . . 7
4.4.2. Negotiating receipt of CLUE Capture Encodings in SDP 7
4.5. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . 7
4.5.1. Generating the Initial Offer . . . . . . . . . . . . 7
4.5.2. Generating the Answer . . . . . . . . . . . . . . . . 8
4.5.2.1. Negotiating use of CLUE and the CLUE data channel 8
4.5.2.2. Negotiating CLUE-controlled media . . . . . . . . 8
4.5.2.3. Negotiating non-CLUE controlled media . . . . . . 9
4.5.3. Processing the initial Offer/Answer negotiation . . . 9
4.5.3.1. Successful CLUE negotiation . . . . . . . . . . . 9
4.5.3.2. CLUE negotiation failure . . . . . . . . . . . . 10
4.5.4. Modifying the session . . . . . . . . . . . . . . . . 10
4.5.4.1. Adding and removing CLUE-controlled media . . . . 10
4.5.4.2. Enabling CLUE mid-call . . . . . . . . . . . . . 10
4.5.4.3. Disabling CLUE mid-call . . . . . . . . . . . . . 11
5. Interaction of CLUE protocol and SDP negotiations . . . . . . 11
5.1. Independence of SDP and CLUE negotiation . . . . . . . . 11
5.2. Constraints on sending media . . . . . . . . . . . . . . 12
5.3. Recommendations for operating with non-atomic operations 12
6. Interaction of CLUE protocol and RTP/RTCP CaptureID . . . . . 13
6.1. CaptureID reception during MCC redefinition . . . . . . . 14
7. Multiplexing of CLUE-controlled media using BUNDLE . . . . . 14
7.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 14
7.2. Usage of BUNDLE with CLUE . . . . . . . . . . . . . . . . 15
7.2.1. Generating the Initial Offer . . . . . . . . . . . . 15
7.2.2. Bundle Address Synchronization . . . . . . . . . . . 15
7.2.3. Multiplexing of the data channel and RTP media . . . 15
8. Example: A call between two CLUE-capable Endpoints . . . . . 16
9. Example: A call between a CLUE-capable and non-CLUE Endpoint 24
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 25
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
11.1. New SDP Grouping Framework Attribute . . . . . . . . . . 25
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11.2. New SIP Media Feature Tag . . . . . . . . . . . . . . . 26
12. Security Considerations . . . . . . . . . . . . . . . . . . . 26
13. Change History . . . . . . . . . . . . . . . . . . . . . . . 27
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 32
14.1. Normative References . . . . . . . . . . . . . . . . . . 32
14.2. Informative References . . . . . . . . . . . . . . . . . 33
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34
1. Introduction
To enable devices to participate in a telepresence call, selecting
the sources they wish to view, receiving those media sources and
displaying them in an optimal fashion, CLUE involves two principal
and inter-related protocol negotiations. SDP, conveyed via SIP, is
used to negotiate the specific media capabilities that can be
delivered to specific addresses on a device. Meanwhile, a CLUE
protocol [I-D.ietf-clue-protocol], transported via a CLUE data
channel [I-D.ietf-clue-datachannel], is used to negotiate the Capture
Sources available, their attributes and any constraints in their use,
along with which Captures the far end provides a device wishes to
receive.
Beyond negotiating the CLUE channel, SDP is also used to negotiate
the details of supported media streams and the maximum capability of
each of those streams. As the CLUE Framework
[I-D.ietf-clue-framework] defines a manner in which the Media
Provider expresses their maximum encoding capabilities, SDP is also
used to express the encoding limits for each potential Encoding.
Backwards-compatibility is an important consideration of the
document: it is vital that a CLUE-capable device contacting a device
that does not support CLUE is able to fall back to a fully functional
non-CLUE call. The document also defines how a non-CLUE call may be
upgraded to CLUE in mid-call, and similarly how CLUE functionality
can be removed mid-call to return to a standard non-CLUE call.
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 uses terminology defined in the CLUE Framework
[I-D.ietf-clue-framework].
A few additional terms specific to this document are defined as
follows:
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non-CLUE device: A device that supports standard SIP and SDP, but
either does not support CLUE, or that does but does not currently
wish to invoke CLUE capabilities.
CLUE-controlled media: A media "m" line that is under CLUE control;
the Capture Source that provides the media on this "m" line is
negotiated in CLUE. See Section 4 for details of how this control
is signalled in SDP. There is a corresponding "non-CLUE-
controlled" media term.
3. Media Feature Tag Definition
The "sip.clue" media feature tag indicates support for CLUE. A CLUE-
capable device SHOULD include this media feature tag in its REGISTER
requests and OPTION responses. It SHOULD also include the media
feature tag in INVITE and UPDATE [RFC3311] requests and responses.
Presence of the media feature tag in the contact field of a request
or response can be used to determine that the far end supports CLUE.
4. SDP Grouping Framework CLUE Extension Semantics
4.1. General
This section defines a new SDP Grouping Framework extension, CLUE.
The CLUE extension can be indicated using an SDP session-level
'group' attribute. Each SDP media "m" line that is included in this
group, using SDP media-level mid attributes, is CLUE-controlled, by a
CLUE data channel also included in this CLUE group.
Currently only support for a single CLUE group is specified; support
for multiple CLUE groups in a single session is beyond the scope of
this document. A device MUST NOT include more than one CLUE group in
its SDP unless it is following a specification that defines how
multiple CLUE channels are signalled, and is either able to determine
that the other side of the SDP exchange supports multiple CLUE
channels, or is able to fail gracefully in the event it does not.
4.2. The CLUE data channel and the CLUE grouping semantic
The CLUE data channel [I-D.ietf-clue-datachannel] is a bidirectional
SCTP over DTLS channel used for the transport of CLUE messages. This
channel must be established before CLUE protocol messages can be
exchanged and CLUE-controlled media can be sent.
The data channel is negotiated over SDP as described in the relevant
document. A CLUE-capable device wishing to negotiate CLUE MUST also
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include a CLUE group in the SDP and include the "mid" of the "m" line
for the data channel in that group. A CLUE group MUST include the
"mid" of the "m" line for one (and only one) data channel.
Presence of the data channel in a CLUE group in an SDP offer or
answer also serves, along with the "sip.clue" media feature tag, as
an indication that the device supports CLUE and wishes to upgrade the
call to include CLUE-controlled media. A CLUE-capable device SHOULD
include a data channel "m" line in offers and, when allowed by
[RFC3264], answers.
4.3. CLUE-controlled media and the CLUE grouping semantic
CLUE-controlled media lines in an SDP are "m" lines in which the
content of the media streams to be sent is negotiated via the CLUE
protocol [I-D.ietf-clue-protocol]. For an "m" line to be CLUE-
controlled, its "mid" value MUST be included in a CLUE group. CLUE-
controlled media is controlled by the CLUE protocol as negotiated on
the CLUE data channel with an "mid" included in the CLUE group.
"m" lines not specified as under CLUE control follow normal rules for
media streams negotiated in SDP as defined in documents such as
[RFC3264].
The restrictions on CLUE-controlled media always apply to "m" lines
in an SDP offer or answer, even if negotiation of the data channel in
SDP failed due to lack of CLUE support by the remote device or for
any other reason, or in an offer if the recipient does not include
the "mid" of the corresponding "m" line in their CLUE group.
4.4. SDP semantics for CLUE-controlled media
4.4.1. Signalling CLUE Encodings
The CLUE Framework [I-D.ietf-clue-framework] defines the concept of
"Encodings", which represent the sender's encode ability. Each
Encoding the Media Provider wishes to signal is signalled via an "m"
line of the appropriate media type, which MUST be marked as sendonly
with the "a=sendonly" attribute or as inactive with the "a=inactive"
attribute.
The encoder limits of active (eg, "a=sendonly") Encodings can then be
expressed using existing SDP syntax. For instance, for H.264 see
Table 6 in [RFC6184] for a list of valid parameters for representing
encoder sender stream limits.
These Encodings are CLUE-controlled and hence MUST include an "mid"
in a CLUE group as defined above.
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As well as the normal restrictions defined in [RFC3264] the stream
MUST be treated as if the "m" line direction attribute had been set
to "a=inactive" until the Media Provider has received a valid CLUE
Configure message specifying the Capture to be used for this stream.
This means that media packets MUST NOT be sent until configuration is
complete, while non-media packets such as STUN and DTLS MUST be sent
as normal if negotiated.
Every "m" line representing a CLUE Encoding MUST 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. Each label used for a CLUE-
controlled "m" line MUST be different from the label on all other "m"
lines in the same CLUE group in the SDP message, unless an "m" line
represents a dependent stream related to another "m" line (such as a
FEC stream), in which case it MUST have the same label value as the
"m" line on which it is dependent.
4.4.1.1. Referencing Encodings in the CLUE protocol
CLUE Encodings are defined in SDP, but can be referenced from CLUE
protocol messages - this is how the protocol defines which Encodings
are part of an Encoding group (in Advertisement messages) and which
Encoding with which to encode a specific Capture (in Configure
messages). The labels on the CLUE-controlled "m" lines are the
references that are used in the CLUE protocol.
Each <encID> (in encodingIDListType) in a CLUE Advertisement message
SHOULD represent an Encoding defined in SDP; the specific Encoding
referenced is a CLUE-controlled "m" line in the most recent SDP sent
by the sender of the Advertisement message with a label value
corresponding to the text content of the <encID>.
Similarly, each <encodingID> (in captureEncodingType) in a CLUE
Configure message SHOULD represent an Encoding defined in SDP; the
specific Encoding referenced is a CLUE-controlled "m" line in the
most recent SDP received by the sender of the Configure message with
a label value corresponding to the text content of the <encodingID>.
Note that the non-atomic nature of SDP/CLUE protocol interaction may
mean that there are temporary periods where an <encID>/<encodingID>
in a CLUE message does not reference an SDP "m" line, or where an
Encoding represented in SDP is not referenced in a CLUE protocol
message. See Section 5 for specifics.
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4.4.1.2. Media line directionality
Presently, this specification mandates that CLUE-controlled "m" lines
must be unidirectional. This is because setting "m" lines to
"a=sendonly" allows the encoder limits to be expressed, whereas in
other cases codec attributes express the receive capabilities of a
media line.
It is possible that in future versions of this draft or its successor
this restriction will be relaxed. If a device does not feel there is
a benefit to expressing encode limitations, or if there are no
meaningful codec-specific limitations to express (such as with many
audio codecs) there are benefits to allowing bidirectional "m" lines.
With bidirectional media lines recipients do not always need to
create a new offer to add their own "m" lines to express their send
capabilities; if they can produce an equal or lesser number of
streams to send then they may not need additional "m" lines.
However, at present the need to express encode limitations and the
wish to simplify the offer/answer procedure means that for the time
being only unidirectional media lines are allowed for CLUE-controlled
media. The highly asymmetric nature of CLUE means that the
probability of the recipient of the initial offer needing to make
their own offer to add additional "m" lines is significantly higher
than it is for most other SIP call scenarios, in which there is a
tendancy for both sides to have similar numbers of potential audio
and video streams they can send.
4.4.2. Negotiating receipt of CLUE Capture Encodings in SDP
A receiver who wishes to receive a CLUE stream via a specific
Encoding requires an "a=recvonly" "m" line that matches the
"a=sendonly" Encoding.
These "m" lines are CLUE-controlled and hence MUST include their
"mid" in the CLUE group corresponding to the CLUE group of the
Encoding they wish to receive.
4.5. SDP Offer/Answer Procedures
4.5.1. Generating the Initial Offer
A CLUE-capable device sending an initial SDP offer of a SIP session
SHOULD include an "m" line for the data channel to convey the CLUE
protocol, along with a CLUE group containing the "mid" of the data
channel "m" line.
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For interoperability with non-CLUE devices a CLUE-capable device
sending an initial SDP offer SHOULD NOT include any "m" line for
CLUE-controlled media beyond the "m" line for the CLUE data channel,
and SHOULD include at least one non-CLUE-controlled media "m" line.
If the device has evidence that the receiver is also CLUE-capable,
for instance due to receiving an initial INVITE with no SDP but
including a "sip.clue" media feature tag, the above recommendation is
waived, and the initial offer MAY contain "m" lines for CLUE-
controlled media.
With the same interoperability recommendations as for Encodings, the
sender of the initial SDP offer MAY also include "a=recvonly" media
lines to preallocate "m" lines to receive media. Alternatively, it
MAY wait until CLUE protocol negotiation has completed before
including these lines in a new offer/answer exchange - see Section 5
for recommendations.
4.5.2. Generating the Answer
4.5.2.1. Negotiating use of CLUE and the CLUE data channel
If the recipient is CLUE-capable and the initial offer contains both
an "m" line for a data channel and a CLUE group containing the "mid"
for that "m" line, they SHOULD negotiate data channel support for an
"m" line, and include the "mid" of that "m" line in a corresponding
CLUE group.
A CLUE-capable recipient that receives an "m" line for a data channel
but no corresponding CLUE group containing the "mid" of that "m" line
MAY still include a corresponding data channel "m" line if there are
any other non-CLUE protocols it can convey over that channel, but
MUST NOT negotiate use of the CLUE protocol on this channel.
4.5.2.2. Negotiating CLUE-controlled media
If the initial offer contained "a=recvonly" CLUE-controlled media
lines the recipient SHOULD include corresponding "a=sendonly" CLUE-
controlled media lines, up to the maximum number of Encodings it
wishes to advertise. As CLUE-controlled media, the "mid" of these
"m" lines must be included in the corresponding CLUE group.
If the initial offer contained "a=sendonly" CLUE-controlled media
lines the recipient MAY include corresponding "a=recvonly" CLUE-
controlled media lines, up to the maximum number of Capture Encodings
it wishes to receive. Alternatively, it MAY wait until CLUE protocol
negotiation has completed before including these lines in a new
offer/answer exchange - see Section 5 for recommendations.
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4.5.2.3. Negotiating non-CLUE controlled media
A CLUE-controlled device implementation may prefer to render initial,
single-stream audio and/or video for the user as rapidly as possible,
transitioning to CLUE-controlled media once that has been negotiated.
Alternatively, an implementation may wish to suppress initial media,
only providing media once the final, CLUE-controlled streams have
been negotiated.
The receiver of the initial offer, if making the call CLUE-enabled
with their SDP answer, can make their preference clear by their
action in accepting or rejecting non-CLUE-controlled media lines.
Rejecting these "m" lines will ensure that no non-CLUE-controlled
media flows before the CLUe-controlled media is negotiated. In
contrast, accepting one or more non-CLUE-controlled "m" lines in this
initial answer will enable initial media to flow.
If the answerer chooses to send initial non-CLUE-controlled media in
a CLUE-enabled call, Section 4.5.4.1 addresses the need to disable it
once CLUE-controlled media is fully negotiated.
4.5.3. Processing the initial Offer/Answer negotiation
In the event that both offer and answer include a data channel "m"
line with a mid value included in corresponding CLUE groups CLUE has
been successfully negotiated and the call is now CLUE-enabled,
otherwise the call is not CLUE-enabled.
4.5.3.1. Successful CLUE negotiation
In the event of successful CLUE-enablement of the call, devices MUST
now begin negotiation of the CLUE channel, see
[I-D.ietf-clue-datachannel] for negotiation details. If negotiation
is successful, sending of CLUE protocol [I-D.ietf-clue-protocol]
messages can begin.
A CLUE-capable device MAY choose not to send media on the non-CLUE-
controlled channels during the period in which control of the CLUE-
controlled media lines is being negotiated. However, a CLUE-capable
device MUST still be prepared to receive media on non-CLUE-controlled
media lines that have been successfully negotiated as defined in
[RFC3264].
If either side of the call wishes to add additional CLUE-controlled
"m" line to send or receive CLUE-controlled media they MAY now send a
SIP request with a new SDP offer. Note that if BUNDLE has been
successfully negotiated and a Bundle Address Synchronization offer is
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required, the device to receive that offer SHOULD NOT generate a new
SDP offer until it has received that BAS offer.
4.5.3.2. CLUE negotiation failure
In the event that the negotiation of CLUE fails and the call is not
CLUE-enabled in the initial offer/answer then CLUE is not in use in
the call, and the CLUE-capable devices MUST either revert to non-CLUE
behaviour or terminate the call.
4.5.4. Modifying the session
4.5.4.1. Adding and removing CLUE-controlled media
Subsequent offer/answer exchanges MAY add additional "m" lines for
CLUE-controlled media; in most cases at least one additional exchange
will be required before both sides have added all the Encodings and
ability to receive Encodings that they desire. Devices MAY delay
adding "a=recvonly" CLUE-controlled m-lines until after CLUE protocol
negotiation completes - see Section 5 for recommendations.
Subsequent offer/answer exchanges MAY also deactive "m" lines for
CLUE-controlled media.
Once CLUE media has been successfully negotiated devices SHOULD
ensure that non-CLUE-controlled media is deactived in cases where it
corresponds to the media type of CLUE-controlled media that has been
successfully negotiated. This deactivate may require an additional
SDP exchange, or may be incorporated into one that is part of the
CLUE negotiation.
4.5.4.2. Enabling CLUE mid-call
A CLUE-capable device that receives an initial SDP offer from a non-
CLUE device SHOULD include a new data channel "m" line and
corresponding CLUE group in any subsequent offers it sends, to
indicate that it is CLUE-capable.
If, in an ongoing non-CLUE call, an SDP offer/answer exchange
completes with both sides having included a data channel "m" line in
their SDP and with the "mid" for that channel in corresponding CLUE
groups then the call is now CLUE-enabled; negotiation of the data
channel and subsequently the CLUE protocol begin.
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4.5.4.3. Disabling CLUE mid-call
If, in an ongoing CLUE-enabled call, an SDP offer-answer negotiation
completes in a fashion in which either the CLUE data channel was not
successfully negotiated or one side did not include the data channel
in a matching CLUE group then CLUE for this channel is disabled. In
the event that this occurs, CLUE is no longer enabled and sending of
all CLUE-controlled media associated with the corresponding CLUE
group MUST stop. If the data channel is still present but not
included in the CLUE group semantic CLUE protocol messages MUST no
longer be sent.
Note that this is distinct to cases where the CLUE data channel fails
or an error occurs on the CLUE protocol; see [I-D.ietf-clue-protocol]
for details of media and state preservation in this circumstance.
5. Interaction of CLUE protocol 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 the need to implement interlocking state machines with the
potential to reach invalid states if messages were to be lost, or be
rewritten en-route by middle boxes, the state machines in SDP and
CLUE operate independently. 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 (unless the SDP
negotiation has removed the CLUE channel).
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.
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CLUE messages contain an <encID> (in encodingIDListType) or
<encodingID> (in captureEncodingType), which is used to identify a
specific encoding or captureEncoding in SDP; see
[I-D.ietf-clue-data-model-schema] for specifcs. 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 <encID> which does not
currently match a CLUE-controlled "m" line label in SDP; A CLUE-
capable implementation MUST NOT reject a CLUE protocol messages
solely because it contains <encID> elements that do not match an id
in SDP.
The current state of the CLUE participant or Media Provider/Consumer
state machines do not affect compliance with any of the normative
language of [RFC3264]. That is, they MUST NOT delay an ongoing SDP
exchange as part of a SIP server or client transaction; an
implementation MUST NOT delay an SDP exchange while waiting for CLUE
negotiation to complete or for a Configure message to arrive.
Similarly, a device in a CLUE-enabled call MUST NOT delay any
mandatory state transitions in the CLUE Participant or Media
Provider/Consumer state machines due to the presence or absence of an
ongoing SDP exchange.
A device with the CLUE Participant state machine in the ACTIVE state
MAY choose not to move from ESTABLISHED to ADV (Media Provider state
machine) or from ESTABLISHED to WAIT FOR CONF RESPONSE (Media
Consumer state machine) based on the SDP state. See
[I-D.ietf-clue-protocol] for CLUE state machine specifics.
Similarly, a device MAY choose to delay initiating a new SDP exchange
based on the state of their CLUE state machines.
5.2. 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 - CLUE-
controlled 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.
5.3. Recommendations for operating with non-atomic operations
CLUE-capable devices MUST be able to handle states in which CLUE
messages make reference to EncodingIDs that do not match the most
recently received SDP, irrespective of the order in which SDP and
CLUE messages are received. While these mis-matches will usually be
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transitory a device MUST be able to cope with such mismatches
remaining indefinitely. However, this document makes some
recommendations on message ordering for these non-atomic transitions.
CLUE-capable devices SHOULD ensure that any inconsistencies between
SDP and CLUE signalling are temporary by sending updated SDP or CLUE
messages as soon as the relevant state machines and other constraints
permit.
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.
6. Interaction of CLUE protocol and RTP/RTCP CaptureID
[I-D.ietf-clue-framework] allows for Multiple Content Captures MCCs):
Captures which contain multiple source Captures, whether composited
into a single stream or switched based on some metric.
The Captures that constitute these MCCs may or may not be defined in
the Advertisement message. If they are defined and the MCC is
providing them in a switched format the recipient may wish to
determine which originating source Capture is currently being
provided, so that they can apply geometric corrections based on that
Capture's geometry, or take some other action based on the original
Capture information.
To do this, [I-D.ietf-clue-rtp-mapping] allows for the CaptureID of
the originating Capture to be conveyed via RTP or RTCP. A Media
Provider sending switched media from an MCC with defined originating
sources MUST send the CaptureID in both RTP and RTCP, as described in
the mapping document.
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6.1. CaptureID reception during MCC redefinition
Because the RTP/RTCP CaptureID is delivered via a different channel
to the Advertisement in which in the contents of the MCC are defined
there is an intrinsic race condition in cases in which the contents
of an MCC are redefined.
When a Media Provider redefines an MCC which involves CaptureIDs, the
reception of the relevant CaptureIDs by the recipient will either
lead or lag reception and processing of the new Advertisement by the
recipient. As such, a media recipient MUST not be disrupted by any
of the following in any CLUE- controlled media stream it is
receiving, whether that stream is for a static Capture or for an MCC
(as any static Capture may be redefined to an MCC in a later
Advertisement):
o Receiving RTP or RTCP containing a CaptureID when the most
recently processed Advertisement means that none are expected.
o Receiving RTP or RTCP without CaptureIDs when the most recently
processed Advertisement means that media CaptureIDs are expected.
o Receiving a CaptureID in RTP or RTCP for a Capture defined in the
most recently processed Advertisement, but which the same
Advertisement does not include in the MCC.
o Receiving a CaptureID in RTP or RTCP for a Capture not defined in
the most recently processed Advertisement.
7. Multiplexing of CLUE-controlled media using BUNDLE
7.1. Overview
A CLUE call may involve sending and/or receiving significant numbers
of media streams. Conventionally, media streams are sent and
received on unique ports. However, each seperate port used for this
purpose may impose costs that a device wishes to avoid, such as the
need to open that port on firewalls and NATs, the need to collect ICE
candidates [RFC5245], etc.
The BUNDLE [I-D.ietf-mmusic-sdp-bundle-negotiation] extension can be
used to negotiate the multiplexing of multiple media lines onto a
single 5-tuple for sending and receiving media, allowing devices in
calls to another BUNDLE-supporting device to potentially avoid some
of the above costs.
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While CLUE-capable devices MAY support the BUNDLE extension for this
purpose supporting the extension is not mandatory for a device to be
CLUE-compliant.
7.2. Usage of BUNDLE with CLUE
This specification imposes no additional requirements or restrictions
on the usage of BUNDLE when used with CLUE. There is no restriction
on combining CLUE-controlled media lines and non-CLUE-controlled
media lines in the same BUNDLE group or in multiple such groups.
However, there are several steps an implementation may wish to
ameliorate the cost and time requirements of extra SDP offer/answer
exchanges between CLUE and BUNDLE.
7.2.1. Generating the Initial Offer
BUNDLE mandates that the initial SDP offer MUST use a unique address
for each m-line with a non-zero port. Because CLUE implementations
generarlly will not include CLUE-controlled media lines with the
exception of the data channel CLUE devices that support large numbers
of streams can avoid ever having to open large numbers of ports if
they successfully negotiate BUNDLE.
7.2.2. Bundle Address Synchronization
When using BUNDLE the initial offerer may be mandated to send a
Bundle Address Synchronisation offer. If the initial offerer also
followed the recommendation of not including CLUE-controlled media
lines in their offer, they MAY choose to include them in this
subsequent offer. In this circumstance the BUNDLE specification
recommends that the offerer does not "modify SDP parameters that
could get the answerer to reject the BAS offer". Including new CLUE-
controlled media lines using codecs and other attributes used in
existing media lines should not increase the chance of the answerer
rejecting the BAS offer; implementations should consider carefully
before including new codecs or other new SDP attributes in these
CLUE-controlled media lines.
7.2.3. Multiplexing of the data channel and RTP media
BUNDLE-supporting CLUE-capable devices MAY include the data channel
in the same BUNDLE group as RTP media. In this case the device MUST
be able to demultiplex the various transports - see section 7.2 of
the BUNDLE draft [I-D.ietf-mmusic-sdp-bundle-negotiation]. If the
BUNDLE group includes other protocols than the data channel
transported via DTLS the device MUST also be able to differentiate
the various protocols.
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8. 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 SDP snippet only illustrate video
'm' lines. ACKs are not discussed. Note that BUNDLE is not in use.
+----------+ +-----------+
| Alice | | Bob |
| | | |
+----+-----+ +-----+-----+
| |
| |
| SIP INVITE 1 |
|--------------------------------->|
| |
| |
| SIP 200 OK 1 |
|<---------------------------------|
| |
| |
| SIP ACK 1 |
|--------------------------------->|
| |
| |
| |
|<########### MEDIA 1 ############>|
| 1 video A->B, 1 video B->A |
|<################################>|
| |
| |
| |
|<================================>|
| CLUE CTRL CHANNEL ESTABLISHED |
|<================================>|
| |
| |
| CLUE ADVERTISEMENT 1 |
|*********************************>|
| |
| |
| CLUE ADVERTISEMENT 2 |
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|<*********************************|
| |
| |
| SIP INVITE 2 (+3 sendonly) |
|--------------------------------->|
| |
| |
| CLUE CONFIGURE 1 |
|<*********************************|
| |
| |
| CLUE RESPONSE 1 |
|*********************************>|
| |
| |
| SIP 200 OK 2 (+2 recvonly) |
|<---------------------------------|
| |
| |
| SIP ACK 2 |
|--------------------------------->|
| |
| |
| |
|<########### MEDIA 2 ############>|
| 2 video A->B, 1 video B->A |
|<################################>|
| |
| |
| SIP INVITE 3 (+2 sendonly) |
|<---------------------------------|
| |
| |
| CLUE CONFIGURE 2 |
|*********************************>|
| |
| |
| CLUE RESPONSE 2 |
|<*********************************|
| |
| |
| SIP 200 OK 3 (+2 recvonly) |
|--------------------------------->|
| |
| |
| |
| SIP ACK 3 |
|<---------------------------------|
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| |
| |
| |
|<########### 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 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 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.
Alice has included a "CLUE" group, and included the mid corresponding
to a data channel in the group (3). Note that Alice has chosen not
to include any CLUE-controlled media in the initial offer - the mid
value of the video line is not included in the "CLUE" group.
...
a=group:CLUE 3
...
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=application 6100 UDP/DTLS/SCTP webrtc-datachannel
a=sctp-port: 5000
a=dcmap:2 subprotocol="CLUE";ordered=true
a=mid:3
Bob responds with a similar SDP (200 OK 1), which also has a "CLUE"
group including the mid value of a data channel; due to their
similiarity no SDP snippet is shown here. Bob wishes to receive
initial media, and so includes corresponding non-CLUE-controlled
audio and video lines. Alice and Bob are each now able to send a
single audio and video stream. 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
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CLUE negotiation can begin. This is illustrated as CLUE CTRL 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 Captures or
the one switched Capture. 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".
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 three CLUE-controlled 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, data channel and the video
"m" lines are shown below:
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...
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=application 6100 UDP/DTLS/SCTP webrtc-datachannel
a=sctp-port: 5000
a=dcmap:2 subprotocol="CLUE";ordered=true
a=mid:3
...
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". This also serves as an ack
for Alice's ADVERTISEMENT 1.
Alice receives Bob's message CONFIGURE 1 and sends RESPONSE 1 to ack
its receptions. She 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
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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, not shown):
...
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, not
shown):
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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 and sends RESPONSE 2 to ack
its receptions. Bob 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. Alice
also now deactivates the initial non-CLUE-controlled media, as
bidirectional CLUE-controlled media is now available. A snippet of
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the SDP showing the grouping attribute and the video m-lines are
shown below (mid 3 represents the data channel, not shown):
...
a=group:CLUE 3 4 5 7 8
...
m=video 0 RTP/AVP 96
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 message or new
SDP negotiation to add, remove or change what they have available or
want to receive.
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9. Example: A call between a CLUE-capable and non-CLUE Endpoint
In this brief example Alice is a CLUE-capable Endpoint making a call
to Bob, who is not CLUE-capable ((i.e. is not able to use the CLUE
protocol).
+----------+ +-----------+
| EP1 | | EP2 |
| | | |
+----+-----+ +-----+-----+
| |
| |
| SIP INVITE 1 |
|--------------------------------->|
| |
| |
| 200 0K 1 |
|<---------------------------------|
| |
| |
| 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 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 for
a DTLS/SCTP channel [I-D.ietf-mmusic-sctp-sdp]. A snippet of the SDP
showing the grouping attribute, data channel and the video m-line are
shown below:
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...
a=group:CLUE 3
...
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=application 6100 UDP/DTLS/SCTP webrtc-datachannel
a=sctp-port: 5000
a=dcmap:2 subprotocol="CLUE";ordered=true
a=mid:3
Bob is not CLUE-capable, and hence does not recognize the "CLUE"
semantic for grouping attribute, nor does he support the data
channel. He responds with an answer with audio and video, but with
the data channel zeroed.
From the lack of the data channel and grouping framework 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.
10. Acknowledgements
The team focusing on this draft consists of: Roni Even, Rob Hansen,
Christer Holmberg, Paul Kyzivat, Simon Pietro-Romano, Roberta Presta.
Christian Groves and Jonathon Lennox have contributed detailed
comments and suggestions.
11. IANA Considerations
11.1. New SDP Grouping Framework Attribute
This document registers the following semantics with IANA in the
"Semantics for the "group" SDP Attribute" subregistry (under the
"Session Description Protocol (SDP) Parameters" registry: Semantics
Token Reference ------------------------------------- ------
--------- CLUE controlled m-line CLUE [this draft]
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11.2. New SIP Media Feature Tag
This specification registers a new media feature tag in the SIP
[RFC3264] tree per the procedures defined in [RFC2506] and [RFC3840].
Media feature tag name: sip.clue ASN.1 Identifier: 1.3.6.1.8.4.26
Summary of the media feature indicated by this tag: This feature tag
indicates that the device supports CLUE controlled media. Values
appropriate for use with this feature tag: Boolean. The feature tag
is intended primarily for use in the following applications,
protocols, services, or negotiation mechanisms: This feature tag is
most useful in a communications application for describing the
capabilities of a device which uses multiple media streams.
12. Security Considerations
CLUE makes use of a number of protocols and mechanism, either defined
by CLUE or long-standing. The security considerations section of the
CLUE Framework [I-D.ietf-clue-framework] addresses the need to secure
these mechanisms by following the recommendations of the individual
protocols.
Beyond the need to secure the consistuent protocols, the use of CLUE
does impose additional security concerns. One area of increased risk
involves the potential for a malicious party to subvert a CLUE-
capable device to attack a third party by driving large volumes of
media (particularly video) traffic at them by establishing a
connection to the CLUE-capable device and directing the media to the
victim. While this is a risk for all media devices, a CLUE-capable
device may allow the attacker to configure multiple media streams to
be sent, significantly increasing the volume of traffic directed at
the victim.
This attack can be prevented by ensuring that the media recipient
intends to receive the media packets. As such all CLUE-capable
devices MUST support key negotiation and receiver intent assurance
via DTLS [RFC5763] on CLUE-controlled RTP "m" lines. All CLUE-
controlled RTP "m" lines must be secured and implemented using
mechanisms such as SRTP [RFC3711]; no specific security mechanisms
are made mandatory to use due to the issues addressed in [RFC7202].
Due to the requirements of backwards compatibility, these is not a
mandatory requirement for non-CLUE-controlled "m" lines.
CLUE also defines a new media feature tag that indicates CLUE
support. This tag may be present even in non-CLUE calls, which
increases the metadata available about the sending device, which can
help an attacker differentiate between multiple devices and help them
identify otherwise anonymised users via the fingerprint of features
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their device supports. To prevent this, SIP signalling SHOULD always
be encrypted using TLS [RFC5630].
13. Change History
Revision by Rob Hansen
o State machine interactions updated to match versions in -04 of
protocol doc.
o Section on encoding updated to specify both encID and encodingID
from data model doc.
o Removed the limitations on describing H264 encoding limits using
SDP syntax as an open issue.
o Previous draft had SRTP and DTLS mandatory to implement and to use
on CLUE- controlled m lines. Current version has DTLS mandatory
to implement, and 'security' mandatory to use but does not define
what that security is.
o Terminology reference to framework doc reinforced. All
terminology that duplicates framework removed. All text updated
with capitalisation that matches framework document's terminology.
o SDP example syntax updated to match that of ietf-clue-datachannel
and hence ietf-mmusic-data-channel-sdpneg.
Revision by Rob Hansen
o SRTP/DTLS made mandatory for CLUE-controlled media lines.
o IANA consideration section added (text as proposed by Christian
Groves).
o Includes provision for dependent streams on seperate "m" lines
having the same encID as their parent "m" line.
o References to putting CLUE-controlled media and data channels in
more than one CLUE group removed, since the document no longer
supports using more than one CLUE group.
o Section on CLUE controlled media restrictions still applying even
if the call does not end up being CLUE enabled being rewritten to
hopefully be clearer.
o Other minor syntax improvements.
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Revision by Rob Hansen
o Updated DTLS/SCTP channel syntax in examples to fix errors and
match latest format defined in draft-ietf-mmusic-sctp-sdp-07.
o Clarified the behaviour if an SDP offer includes a CLUE-controlled
"m" line and the answer accepts that "m" line but without CLUE
control of that line.
o Added a new section on the sending and receiving of CaptureIDs in
RTP and RTCP. Includes a section on the necessity of the receiver
coping with unexpected CaptureIDs (or the lack thereof) due to
MCCs being redefined in new Advertisement messages.
o Added reminder on IANA section on registering grouping semantic
and media feature tag, removed the less formal sections that did
the same job.
o Fixed and clarified issues raised by Christian's document review.
o Added a number of security considerations.
Revision by Rob Hansen
o Clarified text on not rejecting messages because they contain
unknown encIDs.
o Removed normative language in section on accepting/rejecting non-
CLUE-controlled media in the initial answer.
o Example SDP updated to include the data channel "m" lines.
o Example call flow updated to show disablement of non-CLUE-
controlled media once CLUE-controlled media is flowing.
-02: Revision by Rob Hansen
* Added section on not accepting non-CLUE-controlled "m" lines in
the initial answer when CLUE is to be negotiated.
* Removed previous language attempting to describe media
restrictions for CLUE-controlled "m" lines that had not been
configured, and replaced it with much more accurate 'treat as
"a=inactive" was set'.
* Made label element mandatory for CLUE-controlled media (was
previously "SHOULD include", but there didn't seem a good
reason for this - anyone wishing to include the "m" line but
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not immediately use it in CLUE can simply leave it out of the
<encodingIDList>.)
* Added a section on the specifics of relating encodings in SDP
to <encID> elements in the CLUE protocol, including the fact
that both Advertisement and Configure messages reference the
*encoding* (eg, in the Configure case the sender of the
Configure message includes the labels of the recipient's "m"
lines as their <encID> contents).
* Minor revisions to the section on complying with normative SDP/
CLUEstate machine language to clarify that these were not new
normative language, merely that existing normative language
still applies.
* Removed appendices which previously contained information to be
transferred to the protocol and data channel drafts. Removed
other text that discussed alternatives to the current approach.
* Cleaned up some 'todo' text.
-01: Revision by Rob Hansen
* Revised terminology - removed the term 'CLUE-enabled' device as
insufficiently distinct from 'CLUE-capable' and instead added a
term for 'CLUE-enabled' calls.
* Removed text forbidding RTCP and instead added text that ICE/
DTLS negotiation for CLUE controlled media must be done as
normal irrespective of CLUE negotiation.
* Changed 'sip.telepresence' to 'sip.clue' and 'TELEPRESENCE'
grouping semantic back to CLUE.
* Made it mandatory to have exactly one mid corresponding to a
data channel in a CLUE group
* Forbade having multiple CLUE groups unless a specification for
doing so is published.
* Refactored SDP-related text; previously the encoding
information had been in the "initial offer" section despite the
fact that we recommend that the initial offer doesn't actually
include any encodings. I moved the specifications of encodings
and how they're received to an earlier, seperate section.
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* Added text on how the state machines in CLUE and SDP are
allowed to affect one another, and further recommendations on
how a device should handle the sending of CLUE and SDP changes.
-00: Revision by Rob Hansen
* Submitted as -00 working group document
draft-kyzivat-08: Revisions by Rob Hansen
* Added media feature tag for CLUE support ('sip.telepresence')
* Changed grouping semantic from 'CLUE' to 'TELEPRESENCE'
* Restructured document to be more centred on the grouping
semantic and its use with O/A
* Lots of additional text on usage of the grouping semantic
* Stricter definition of CLUE-controlled m lines and how they
work
* Some additional text on defining what happens when CLUE
supports is added or removed
* Added details on when to not send RTCP for CLUE-controlled "m"
lines.
* Added a section on using BUNDLE with CLUE
* Updated data channel references to point at new WG document
rather than indivual draft
draft-kyzivat-07: Revisions by Rob Hansen
* Removed the text providing arguments for encoding limits being
in SDP and encoding groups in the CLUE protocol in favor of the
specifics of how to negotiate encodings in SDP
* Added normative language on the setting up of a CLUE call, and
added sections on mid-call changes to the CLUE status.
* Added references to [I-D.ietf-clue-datachannel] where
appropriate.
* Added some terminology for various types of CLUE and non-CLUE
states of operation.
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* Moved language related to topics that should be in
[I-D.ietf-clue-datachannel] and [I-D.ietf-clue-protocol], but
that has not yet been resolved in those documents, into an
appendix.
draft-kyzivat-06: Revisions by Rob Hansen
* Removed CLUE message XML schema and details that are now in
draft-presta-clue-protocol
* Encoding limits in SDP section updated to note that this has
been investigated and discussed and is the current working
assumption of the WG, though consensus has not been fully
achieved.
* A section has also been added on the current mandation of
unidirectional "m" lines.
* Updated CLUE messaging in example call flow to match draft-
presta-clue-protocol-03
draft-kyzivat-05: Revisions by pkyzivat:
* Specified versioning model and mechanism.
* Added explicit response to all messages.
* Rearranged text to work with the above changes. (Which
rendered diff almost useless.)
draft-kyzivat-04: Revisions by Rob Hansen: ???
draft-kyzivat-03: Revisions by pkyzivat:
* 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.
draft-kyzivat-02: A bunch of revisions by pkyzivat:
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* 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.
draft-kyzivat-01: Updated by roberta to include some sample call
flows.
draft-kyzivat-00: Initial version by pkyzivat. Established general
outline for the document, and specified a few things thought to
represent wg consensus.
14. References
14.1. Normative References
[I-D.ietf-clue-framework]
Duckworth, M., Pepperell, A., and S. Wenger, "Framework
for Telepresence Multi-Streams", draft-ietf-clue-
framework-22 (work in progress), April 2015.
[I-D.ietf-clue-data-model-schema]
Presta, R. and S. Romano, "An XML Schema for the CLUE data
model", draft-ietf-clue-data-model-schema-10 (work in
progress), June 2015.
[I-D.ietf-clue-protocol]
Presta, R. and S. Romano, "CLUE protocol", draft-ietf-
clue-protocol-04 (work in progress), April 2015.
[I-D.ietf-clue-datachannel]
Holmberg, C., "CLUE Protocol data channel", draft-ietf-
clue-datachannel-09 (work in progress), March 2015.
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Internet-Draft CLUE Signaling August 2015
[I-D.ietf-clue-rtp-mapping]
Even, R. and J. Lennox, "Mapping RTP streams to CLUE media
captures", draft-ietf-clue-rtp-mapping-04 (work in
progress), March 2015.
[I-D.ietf-mmusic-sctp-sdp]
Holmberg, C., Loreto, S., and G. Camarillo, "Stream
Control Transmission Protocol (SCTP)-Based Media Transport
in the Session Description Protocol (SDP)", draft-ietf-
mmusic-sctp-sdp-14 (work in progress), March 2015.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, DOI 10.17487/RFC3711, March 2004,
<http://www.rfc-editor.org/info/rfc3711>.
[RFC4574] Levin, O. and G. Camarillo, "The Session Description
Protocol (SDP) Label Attribute", RFC 4574,
DOI 10.17487/RFC4574, August 2006,
<http://www.rfc-editor.org/info/rfc4574>.
[RFC5763] Fischl, J., Tschofenig, H., and E. Rescorla, "Framework
for Establishing a Secure Real-time Transport Protocol
(SRTP) Security Context Using Datagram Transport Layer
Security (DTLS)", RFC 5763, DOI 10.17487/RFC5763, May
2010, <http://www.rfc-editor.org/info/rfc5763>.
14.2. Informative References
[RFC2506] Holtman, K., Mutz, A., and T. Hardie, "Media Feature Tag
Registration Procedure", BCP 31, RFC 2506,
DOI 10.17487/RFC2506, March 1999,
<http://www.rfc-editor.org/info/rfc2506>.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264,
DOI 10.17487/RFC3264, June 2002,
<http://www.rfc-editor.org/info/rfc3264>.
[RFC3311] Rosenberg, J., "The Session Initiation Protocol (SIP)
UPDATE Method", RFC 3311, DOI 10.17487/RFC3311, October
2002, <http://www.rfc-editor.org/info/rfc3311>.
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[RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat,
"Indicating User Agent Capabilities in the Session
Initiation Protocol (SIP)", RFC 3840,
DOI 10.17487/RFC3840, August 2004,
<http://www.rfc-editor.org/info/rfc3840>.
[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols", RFC 5245,
DOI 10.17487/RFC5245, April 2010,
<http://www.rfc-editor.org/info/rfc5245>.
[RFC5630] Audet, F., "The Use of the SIPS URI Scheme in the Session
Initiation Protocol (SIP)", RFC 5630,
DOI 10.17487/RFC5630, October 2009,
<http://www.rfc-editor.org/info/rfc5630>.
[RFC6184] Wang, Y., Even, R., Kristensen, T., and R. Jesup, "RTP
Payload Format for H.264 Video", RFC 6184,
DOI 10.17487/RFC6184, May 2011,
<http://www.rfc-editor.org/info/rfc6184>.
[RFC7202] Perkins, C. and M. Westerlund, "Securing the RTP
Framework: Why RTP Does Not Mandate a Single Media
Security Solution", RFC 7202, DOI 10.17487/RFC7202, April
2014, <http://www.rfc-editor.org/info/rfc7202>.
[I-D.ietf-mmusic-sdp-bundle-negotiation]
Holmberg, C., Alvestrand, H., and C. Jennings,
"Negotiating Media Multiplexing Using the Session
Description Protocol (SDP)", draft-ietf-mmusic-sdp-bundle-
negotiation-23 (work in progress), July 2015.
Authors' Addresses
Paul Kyzivat
Huawei
Email: pkyzivat@alum.mit.edu
Lennard Xiao
Huawei
Email: lennard.xiao@huawei.com
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Christian Groves
Huawei
Email: Christian.Groves@nteczone.com
Robert Hansen
Cisco Systems
Email: rohanse2@cisco.com
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