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Versions: (draft-holmberg-mmusic-sdp-bundle-negotiation) 00 01 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19

MMUSIC Working Group                                         C. Holmberg
Internet-Draft                                                  Ericsson
Updates: 3264 (if approved)                                H. Alvestrand
Intended status: Standards Track                                  Google
Expires: September 27, 2015                                  C. Jennings
                                                                   Cisco
                                                          March 26, 2015


 Negotiating Media Multiplexing Using the Session Description Protocol
                                 (SDP)
            draft-ietf-mmusic-sdp-bundle-negotiation-19.txt

Abstract

   This specification defines a new Session Description Protocol (SDP)
   Grouping Framework extension, 'BUNDLE'.  The extension can be used
   with the SDP Offer/Answer mechanism to negotiate the usage of a
   single address:port combination (BUNDLE address) for receiving media,
   referred to as bundled media, associated with multiple SDP media
   descriptions ("m=" lines).

   To assist endpoints in negotiating the use of bundle this
   specification defines a new SDP attribute, 'bundle-only', which can
   be used to request that specific media is only used if bundled.  This
   specification also updates sections 5.1, 8.1 and 8.2 of RFC 3264 to
   allow an answerer to assign a non-zero port value to an "m=" line in
   an SDP answer, even if the "m=" line in the associated SDP offer
   contained a zero port value.

   There are multiple ways to correlate the bundled RTP packets with the
   appropriate media descriptions.  This specification defines a new
   RTCP source description (SDES) item and a new RTP header extension
   that provides an additional way to do this correlation by using them
   to carry a value that associates the RTP/RTCP packets with a specific
   media description.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.





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

   This Internet-Draft will expire on September 27, 2015.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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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  . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   6
   4.  Applicability Statement . . . . . . . . . . . . . . . . . . .   7
   5.  SDP Grouping Framework BUNDLE Extension . . . . . . . . . . .   7
   6.  SDP 'bundle-only' Attribute . . . . . . . . . . . . . . . . .   7
   7.  SDP Information Considerations  . . . . . . . . . . . . . . .   8
     7.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .   8
     7.2.  Connection Data (c=)  . . . . . . . . . . . . . . . . . .   9
     7.3.  Bandwidth (b=)  . . . . . . . . . . . . . . . . . . . . .   9
     7.4.  Attributes (a=) . . . . . . . . . . . . . . . . . . . . .   9
   8.  SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . .   9
     8.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .   9
     8.2.  Generating the Initial SDP Offer  . . . . . . . . . . . .  10
       8.2.1.  General . . . . . . . . . . . . . . . . . . . . . . .  10
       8.2.2.  Suggesting the offerer BUNDLE address . . . . . . . .  11
     8.3.  Generating the SDP Answer . . . . . . . . . . . . . . . .  11
       8.3.1.  General . . . . . . . . . . . . . . . . . . . . . . .  11
       8.3.2.  Answerer Selection of Offerer Bundle Address  . . . .  12
       8.3.3.  Answerer Selection of Answerer BUNDLE Address . . . .  13
       8.3.4.  Moving A Media Description Out Of A BUNDLE Group  . .  13
       8.3.5.  Rejecting A Media Description In A BUNDLE Group . . .  13
     8.4.  Offerer Processing of the SDP Answer  . . . . . . . . . .  14
       8.4.1.  General . . . . . . . . . . . . . . . . . . . . . . .  14



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     8.5.  Modifying the Session . . . . . . . . . . . . . . . . . .  14
       8.5.1.  General . . . . . . . . . . . . . . . . . . . . . . .  14
       8.5.2.  Suggesting a new offerer BUNDLE address . . . . . . .  14
       8.5.3.  Adding a media description to a BUNDLE group  . . . .  15
       8.5.4.  Moving A Media Description Out Of A BUNDLE Group  . .  16
       8.5.5.  Disabling A Media Description In A BUNDLE Group . . .  16
   9.  Protocol Identification . . . . . . . . . . . . . . . . . . .  16
     9.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .  16
     9.2.  STUN, DTLS, SRTP  . . . . . . . . . . . . . . . . . . . .  17
   10. RTP Considerations  . . . . . . . . . . . . . . . . . . . . .  17
     10.1.  Single RTP Session . . . . . . . . . . . . . . . . . . .  17
       10.1.1.  General  . . . . . . . . . . . . . . . . . . . . . .  17
       10.1.2.  Payload Type (PT) Value Reuse  . . . . . . . . . . .  18
     10.2.  Associating RTP/RTCP Packets With Correct SDP Media
            Description  . . . . . . . . . . . . . . . . . . . . . .  18
     10.3.  RTP/RTCP Multiplexing  . . . . . . . . . . . . . . . . .  19
       10.3.1.  General  . . . . . . . . . . . . . . . . . . . . . .  19
       10.3.2.  SDP Offer/Answer Procedures  . . . . . . . . . . . .  19
   11. ICE Considerations  . . . . . . . . . . . . . . . . . . . . .  22
     11.1.  General  . . . . . . . . . . . . . . . . . . . . . . . .  22
     11.2.  SDP Offer/Answer Procedures  . . . . . . . . . . . . . .  22
       11.2.1.  General  . . . . . . . . . . . . . . . . . . . . . .  22
       11.2.2.  Generating the Initial SDP Offer . . . . . . . . . .  23
       11.2.3.  Generating the SDP Answer  . . . . . . . . . . . . .  23
       11.2.4.  Offerer Processing of the SDP Answer . . . . . . . .  23
       11.2.5.  Modifying the Session  . . . . . . . . . . . . . . .  23
   12. Update to RFC 3264  . . . . . . . . . . . . . . . . . . . . .  23
     12.1.  General  . . . . . . . . . . . . . . . . . . . . . . . .  23
     12.2.  Original text of section 5.1 (2nd paragraph) of RFC 3264  24
     12.3.  New text replacing section 5.1 (2nd paragraph) of RFC
            3264 . . . . . . . . . . . . . . . . . . . . . . . . . .  24
     12.4.  Original text of section 8.2 (2nd paragraph) of RFC 3264  24
     12.5.  New text replacing section 8.2 (2nd paragraph) of RFC
            3264 . . . . . . . . . . . . . . . . . . . . . . . . . .  24
     12.6.  Original text of section 8.4 (6th paragraph) of RFC 3264  25
     12.7.  New text replacing section 8.4 (6th paragraph) of RFC
            3264 . . . . . . . . . . . . . . . . . . . . . . . . . .  25
   13. RTP/RTCP extensions for identification-tag transport  . . . .  25
     13.1.  General  . . . . . . . . . . . . . . . . . . . . . . . .  25
     13.2.  RTCP MID SDES Item . . . . . . . . . . . . . . . . . . .  26
     13.3.  RTP MID Header Extension . . . . . . . . . . . . . . . .  27
   14. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  27
     14.1.  New SDES item  . . . . . . . . . . . . . . . . . . . . .  27
     14.2.  New RTP Header Extension URI . . . . . . . . . . . . . .  28
     14.3.  New SDP Attribute  . . . . . . . . . . . . . . . . . . .  28
   15. Security Considerations . . . . . . . . . . . . . . . . . . .  28
   16. Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  29
     16.1.  Example: Bundle Address Selection  . . . . . . . . . . .  29



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     16.2.  Example: BUNDLE Extension Rejected . . . . . . . . . . .  31
     16.3.  Example: Offerer Adds A Media Description To A BUNDLE
            Group  . . . . . . . . . . . . . . . . . . . . . . . . .  32
     16.4.  Example: Offerer Moves A Media Description Out Of A
            BUNDLE Group . . . . . . . . . . . . . . . . . . . . . .  34
     16.5.  Example: Offerer Disables A Media Description Within A
            BUNDLE Group . . . . . . . . . . . . . . . . . . . . . .  35
   17. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  37
   18. Change Log  . . . . . . . . . . . . . . . . . . . . . . . . .  37
   19. References  . . . . . . . . . . . . . . . . . . . . . . . . .  42
     19.1.  Normative References . . . . . . . . . . . . . . . . . .  42
     19.2.  Informative References . . . . . . . . . . . . . . . . .  43
   Appendix A.  Design Considerations  . . . . . . . . . . . . . . .  44
     A.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .  44
     A.2.  UA Interoperability . . . . . . . . . . . . . . . . . . .  44
     A.3.  Usage of port number value zero . . . . . . . . . . . . .  46
     A.4.  B2BUA And Proxy Interoperability  . . . . . . . . . . . .  46
       A.4.1.  Traffic Policing  . . . . . . . . . . . . . . . . . .  47
       A.4.2.  Bandwidth Allocation  . . . . . . . . . . . . . . . .  47
     A.5.  Candidate Gathering . . . . . . . . . . . . . . . . . . .  47
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  48

1.  Introduction

   This specification defines a way to use a single address:port
   combination (BUNDLE address) for receiving media associated with
   multiple SDP media descriptions ("m=" lines).

   This specification defines a new SDP Grouping Framework [RFC5888]
   extension called 'BUNDLE'.  The extension can be used with the
   Session Description Protocol (SDP) Offer/Answer mechanism [RFC3264]
   to negotiate the usage of a BUNDLE group.  Within the BUNDLE group, a
   BUNDLE address is used for receiving media associated with multiple
   "m=" lines.  This is referred to as bundled media.

   The offerer and answerer [RFC3264] use the BUNDLE extension to
   negotiate the BUNDLE addresses, one for the offerer (offerer BUNDLE
   address) and one for the answerer (answerer BUNDLE address), to be
   used for receiving the bundled media associated with a BUNDLE group.
   Once the offerer and the answerer have negotiated a BUNDLE group,
   they assign their respective BUNDLE address to each "m=" line in the
   BUNDLE group.  The BUNDLE addresses are used to receive all media
   associated with the BUNDLE group.

   The use of a BUNDLE group and a BUNDLE address also allows the usage
   of a single set of Interactive Connectivity Establishment (ICE)
   [RFC5245] candidates for multiple "m=" lines.




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   This specification also defines a new SDP attribute, 'bundle-only',
   which can be used to request that specific media is only used if kept
   within a BUNDLE group.

   As defined in RFC 4566 [RFC4566], the semantics of assigning the same
   port value to multiple "m=" lines are undefined, and there is no
   grouping defined by such means.  Instead, an explicit grouping
   mechanism needs to be used to express the intended semantics.  This
   specification provides such an extension.

   This specification also updates sections 5.1, 8.1 and 8.2 of RFC 3264
   [RFC3264].  The update allows an answerer to assign a non-zero port
   value to an "m=" line in an SDP answer, even if the "m=" line in the
   associated SDP offer contained a zero port value.

   This specification also defines a new Real-time Transport Protocol
   (RTP) [RFC3550] SDES item and a new RTP header extension that can be
   used to carry a value that associates RTP/RTCP packets with a
   specific media description.  This can be used to correlate a RTP
   packet with the correct media.

   SDP bodies can contain multiple BUNDLE groups.  A given BUNDLE
   address MUST only be associated with a single BUNDLE group.  The
   procedures in this specification apply independently to a given
   BUNDLE group.  All RTP based media flows associated with a single
   BUNDLE group belong to a single RTP session [RFC3550].

   The BUNDLE extension is backward compatible.  Endpoints that do not
   support the extension are expected to generate offers and answers
   without an SDP 'group:BUNDLE' attribute, and are expected to assign a
   unique address to each "m=" line within an offer and answer,
   according to the procedures in [RFC4566] and [RFC3264]

2.  Terminology

   5-tuple: A collection of the following values: source address, source
   port, destination address, destination port, and transport-layer
   protocol.

   Unique address: An IP address and port combination that is assigned
   to only one "m=" line in an offer or answer.

   Shared address: An IP address and port combination that is assigned
   to multiple "m=" lines within an offer or answer.

   Offerer BUNDLE-tag: The first identification-tag in a given SDP
   'group:BUNDLE' attribute identification-tag list in an offer.




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   Answerer BUNDLE-tag: The first identification-tag in a given SDP
   'group:BUNDLE' attribute identification-tag list in an answer.

   Offerer BUNDLE address: Within a given BUNDLE group, an IP address
   and port combination used by an offerer to receive all media
   associated with each "m=" line within the BUNDLE group.

   Answerer BUNDLE address: Within a given BUNDLE group, an IP address
   and port combination used by an answerer to receive all media
   associated with each "m=" line within the BUNDLE group.

   BUNDLE group: A set of "m=" lines, created using an SDP Offer/Answer
   exchange, which uses the same BUNDLE address for receiving media.

   Bundled "m=" line: An "m=" line, whose identification-tag is placed
   in an SDP 'group:BUNDLE' attribute identification-tag list in an
   offer or answer.

   Bundle-only "m=" line: A bundled "m=" line with an associated SDP
   'bundle-only' attribute.

   Bundled media: All media associated with a given BUNDLE group.

   Initial offer: The first offer, within an SDP session (e.g. a SIP
   dialog when the Session Initiation Protocol (SIP) [RFC3261] is used
   to carry SDP), in which the offerer indicates that it wants to create
   a given BUNDLE group.

   Subsequent offer: An offer which contains a BUNDLE group that has
   been created as part of a previous offer/answer exchange.

   Identification-tag: A unique token value that is used to identify an
   "m=" line.  The SDP 'mid' attribute [RFC5888], associated with an
   "m=" line, carries an unique identification-tag.  The session-level
   SDP 'group' attribute [RFC5888] carries a list of identification-
   tags, identifying the "m=" lines associated with that particular
   'group' attribute.

3.  Conventions

   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 BCP 14, RFC 2119
   [RFC2119].







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4.  Applicability Statement

   The mechanism in this specification only applies to the Session
   Description Protocol (SDP) [RFC4566], when used together with the SDP
   offer/answer mechanism [RFC3264].  Declarative usage of SDP is out of
   scope of this document, and is thus undefined.

5.  SDP Grouping Framework BUNDLE Extension

   This section defines a new SDP Grouping Framework extension
   [RFC5888], 'BUNDLE'.  The BUNDLE extension can be used with the SDP
   Offer/Answer mechanism to negotiate the usage of a single
   address:port combination (BUNDLE address) for receiving bundled
   media.

   A single address:port combination is also used for sending bundled
   media.  The address:port combination used for sending bundled media
   MAY be the same as the BUNDLE address, used to receive bundled media,
   depending on whether symmetric RTP is used.  A given address:port
   combination MUST NOT be used for sending media associated with
   multiple BUNDLE groups.

   All media associated with a BUNDLE group share a single 5-tuple, i.e.
   in addition to using a single address:port combination all bundled
   media MUST be transported using the same transport-layer protocol
   (e.g.  UDP or TCP).

   The BUNDLE extension is indicated using an SDP 'group' attribute with
   a "BUNDLE" semantics value [RFC5888].  An identification-tag is
   assigned to each bundled "m=" line, and each identification-tag is
   listed in the SDP 'group:BUNDLE' attribute identification-tag list.
   Each "m=" line, whose identification-tag is listed in the
   identification-tag list, is associated with a given BUNDLE group.

   SDP bodies can contain multiple BUNDLE groups.  Any given bundled
   "m=" line MUST NOT be associated with more than one BUNDLE group.

   Section 8 defines the detailed SDP Offer/Answer procedures for the
   BUNDLE extension.

6.  SDP 'bundle-only' Attribute

   This section defines a new SDP media-level attribute [RFC4566],
   'bundle-only'.







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      Name: bundle-only

      Value:

      Usage Level: media

      Charset Dependent: no

      Example:

         a=bundle-only


   In order to ensure that an answerer that does not supports the BUNDLE
   extension always rejects a bundled "m=" line, the offerer can assign
   a zero port value to the "m=" line.  According to [RFC4566] an
   answerer will reject such "m=" line.  By associating an SDP 'bundle-
   only' attribute with such "m=" line, the offerer can request that the
   answerer accepts the "m=" line if the answerer supports the Bundle
   extension, and if the answerer keeps the "m=" line within the
   associated BUNDLE group.

   NOTE: Once an offerer BUNDLE address has been selected, the offerer
   can ensure that an bundled "m=" line is accepted by the answerer only
   if the answerer keeps the "m=" line within the associated BUNDLE
   group by assigning the offerer BUNDLE address to the "m=" line.  If
   the answerer does not keep that "m=" line within the BUNDLE group,
   the answerer will reject it.  Therefore, the SDP 'bundle-only'
   attribute is not needed in such cases

   The usage of the 'bundle-only' attribute is only defined for a
   bundled "m=" line with a zero port value, within an offer.  Other
   usage is unspecified.

   Section 8 defines the detailed SDP Offer/Answer procedures for the
   'bundle-only' attribute.

7.  SDP Information Considerations

7.1.  General

   This section describes restrictions associated with the usage of SDP
   parameters within a BUNDLE group.  It also describes, when parameter
   and attribute values have been associated with each bundled "m="
   line, how to calculate a value for the whole BUNDLE group.






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7.2.  Connection Data (c=)

   The "c=" line nettype value [RFC4566] associated with a bundled "m="
   line MUST be 'IN'.

   The "c=" line addrtype value [RFC4566] associated with a bundled "m="
   line MUST be 'IP4' or 'IP6'.  The same value MUST be associated with
   each "m=" line.

   NOTE: Extensions to this specification can specify usage of the
   BUNDLE mechanism for other nettype and addrtype values than the ones
   listed above.

7.3.  Bandwidth (b=)

   An offerer and answerer MUST use the rules and restrictions defined
   in [I-D.mmusic-sdp-mux-attributes] for when associating the SDP
   bandwidth (b=) line with bundled "m=" lines.

7.4.  Attributes (a=)

   An offerer and answerer MUST use the rules and restrictions defined
   in [I-D.mmusic-sdp-mux-attributes] for when associating SDP
   attributes with bundled "m=" lines.

8.  SDP Offer/Answer Procedures

8.1.  General

   This section describes the SDP Offer/Answer [RFC3264] procedures for:

   o  Negotiating and creating of a BUNDLE group;

   o  Selecting the BUNDLE addresses (offerer BUNDLE address and
      answerer BUNDLE address);

   o  Adding an "m=" line to a BUNDLE group;

   o  Moving an "m=" line out of a BUNDLE group; and

   o  Disabling an "m=" line within a BUNDLE group.

   The generic rules and procedures defined in [RFC3264] and [RFC5888]
   also apply to the BUNDLE extension.  For example, if an offer is
   rejected by the answerer, the previously negotiated SDP parameters
   and characteristics (including those associated with a BUNDLE group)
   apply.  Hence, if an offerer generates an offer in which the offerer




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   wants to create a BUNDLE group, and the answerer rejects the offer,
   the BUNDLE group is not created.

   The procedures in this section are independent of the media type or
   "m=" line proto value represented by a bundled "m=" line.  Section 10
   defines additional considerations for RTP based media.  Section 6
   defines additional considerations for the usage of the SDP 'bundle-
   only' attribute.  Section 11 defines additional considerations for
   the usage of Interactive Connectivity Establishment (ICE) [RFC5245]
   mechanism .

   The offerer and answerer MUST follow the rules and restrictions
   defined in Section 7 when creating offers and answers.

   SDP offers and answers can contain multiple BUNDLE groups.  The
   procedures in this section apply independently to a given BUNDLE
   group.

8.2.  Generating the Initial SDP Offer

8.2.1.  General

   When an offerer generates an initial offer, in order to create a
   BUNDLE group, it MUST:

   o  Assign a unique address to each "m=" line within the offer,
      following the procedures in [RFC3264], unless the media line is a
      'bundle-only' "m=" line (see below);

   o  Add an SDP 'group:BUNDLE' attribute to the offer;

   o  Place the identification-tag of each bundled "m=" line in the SDP
      'group:BUNDLE' attribute identification-tag list; and

   o  Indicate which unique address the offerer suggests as the offerer
      BUNDLE address [Section 8.2.2].

   If the offerer wants to request that the answerer accepts a given
   bundled "m=" line only if the answerer keeps the "m=" line within the
   BUNDLE group, the offerer MUST:

   o  Associate an SDP 'bundle-only' attribute [Section 8.2.2] with the
      "m=" line; and

   o  Assign a zero port value to the "m=" line.

   NOTE: If the offerer assigns a zero port value to an "m=" line, but
   does not also associate an SDP 'bundle-only' attribute with the "m="



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   line, it is an indication that the offerer wants to disable the "m="
   line [Section 8.5.5].

   [Section 16.1] shows an example of an initial offer.

8.2.2.  Suggesting the offerer BUNDLE address

   In the offer, the address assigned to the "m=" line associated with
   the offerer BUNDLE-tag indicates the address that the offerer
   suggests as the offerer BUNDLE address.

8.3.  Generating the SDP Answer

8.3.1.  General

   When an answerer generates an answer, which contains a BUNDLE group,
   the following general SDP grouping framework restrictions, defined in
   [RFC5888], also apply to the BUNDLE group:

   o  The answerer MUST NOT include a BUNDLE group in the answer, unless
      the offerer requested the BUNDLE group to be created in the
      associated offer; and

   o  The answerer MUST NOT include an "m=" line within a BUNDLE group,
      unless the offerer requested the "m=" line to be within that
      BUNDLE group in the associated offer.

   If the answer contains a BUNDLE group, the answerer MUST:

   o  Select an Offerer BUNDLE Address [Section 8.3.2]; and

   o  Select an Answerer BUNDLE Address [Section 8.3.3];

   The answerer is allowed to select a new Answerer BUNDLE address each
   time it generates an answer to an offer.

   If the answerer does not want to keep an "m=" line within a BUNDLE
   group, it MUST:

   o  Move the "m=" line out of the BUNDLE group [Section 8.3.4]; or

   o  Reject the "m=" line [Section 8.3.5];

   If the answerer keeps a bundle-only "m=" line within the BUNDLE
   group, it follows the procedures (assigns the answerer BUNDLE address
   to the "m=" line etc) for any other "m=" line kept within the BUNDLE
   group.




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   If the answerer does not want to keep a bundle-only "m=" line within
   the BUNDLE group, it MUST reject the "m=" line [Section 8.3.5].

   The answerer MUST NOT associate an SDP 'bundle-only' attribute with
   any "m=" line in an answer.

   NOTE: If a bundled "m=" line in an offer contains a zero port value,
   but the "m=" line does not contain an SDP 'bundle-only' attribute, it
   is an indication that the offerer wants to disable the "m=" line
   [Section 8.5.5].

8.3.2.  Answerer Selection of Offerer Bundle Address

   In an offer, the address (unique or shared) assigned to the bundled
   "m=" line associated with the offerer BUNDLE-tag indicates the
   address that the offerer suggests as the offerer BUNDLE address
   [Section 8.2.2].  The answerer MUST check whether that "m=" line
   fulfills the following criteria:

   o  The answerer will not move the "m=" line out of the BUNDLE group
      [Section 8.3.4];

   o  The answerer will not reject the "m=" line [Section 8.3.5]; and

   o  The "m=" line does not contain a zero port value.

   If all of the criteria above are fulfilled, the answerer MUST select
   the address associated with the "m=" line as the offerer BUNDLE
   address.  In the answer, the answerer BUNDLE-tag represents the "m="
   line, and the address associated with the "m=" line in the offer
   becomes the offerer BUNDLE address.

   If one or more of the criteria are not fulfilled, the answerer MUST
   select the next identification-tag in the identification-tag list,
   and perform the same criteria check for the "m=" line associated with
   that identification-tag.  If there are no more identification-tags in
   the identification-tag list, the answerer MUST NOT create the BUNDLE
   group.  In addition, unless the answerer rejects the whole offer, the
   answerer MUST apply the answerer procedures for moving an "m=" line
   out of a BUNDLE group [Section 8.3.4] to each bundled "m=" line in
   the offer when creating the answer.

   [Section 16.1] shows an example of an offerer BUNDLE address
   selection.







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8.3.3.  Answerer Selection of Answerer BUNDLE Address

   When the answerer selects a BUNDLE address for itself, referred to as
   the answerer BUNDLE address, it MUST assign that address to each
   bundled "m=" line within the created BUNDLE group in the answer.

   The answerer MUST NOT assign the answerer BUNDLE address to an "m="
   line that is not within the BUNDLE group, or to an "m=" line that is
   within another BUNDLE group.

   [Section 16.1] shows an example of an answerer BUNDLE address
   selection.

8.3.4.  Moving A Media Description Out Of A BUNDLE Group

   When an answerer moves a "m=" line out of a BUNDLE group, it assigns
   an address to the "m=" line in the answer based on the following
   rules:

   o  In the associated offer, if the "m=" line contains a shared
      address (e.g. a previously selected offerer BUNDLE address), the
      answerer MUST reject the moved "m=" line [Section 8.3.5];

   o  In the associated offer, if the "m=" line contains a unique
      address, the answerer MUST assign a unique address also to the
      "m=" line in the answer; or

   o  In the associated offer, if an SDP 'bundle-only' attribute is
      associated with the "m=" line, and if the "m=" line contains a
      zero port value, the answerer MUST reject the "m=" line
      [Section 8.3.5].

   In addition, in either case above, the answerer MUST NOT place the
   identification-tag, associated with the moved "m=" line, in the SDP
   'group' attribute identification-tag list associated with the BUNDLE
   group.

8.3.5.  Rejecting A Media Description In A BUNDLE Group

   When an answerer rejects an "m=" line, it MUST assign an address with
   a zero port value to the "m=" line in the answer, according to the
   procedures in [RFC4566].

   In addition, the answerer MUST NOT place the identification-tag,
   associated with the rejected "m=" line, in the SDP 'group' attribute
   identification-tag list associated with the BUNDLE group.





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8.4.  Offerer Processing of the SDP Answer

8.4.1.  General

   When an offerer receives an answer, if the answer contains a BUNDLE
   group, the offerer MUST check that any bundled "m=" line in the
   answer was indicated as bundled in the associated offer.  If there is
   no mismatch, the offerer MUST use the offerer BUNDLE address,
   selected by the answerer [Section 8.3.2], as the address for each
   bundled "m=" line.

   NOTE: As the answerer might reject one or more bundled "m=" lines, or
   move a bundled "m=" line out of a BUNDLE group, each bundled "m="
   line in the offer might not be indicated as bundled in the answer.

   If the answer does not contain a BUNDLE group, the offerer MUST
   process the answer as a normal answer.

8.5.  Modifying the Session

8.5.1.  General

   When an offerer generates a subsequent offer, it MUST assign the
   previously selected offerer BUNDLE address [Section 8.3.2], to each
   bundled "m=" line (including any bundle-only "m=" line), except if:

   o  The offerer suggests a new offerer BUNDLE address [Section 8.5.2];

   o  The offerer wants to add a bundled "m=" line to the BUNDLE group
      [Section 8.5.3];

   o  The offerer wants to move a bundled "m=" line out of the BUNDLE
      group [Section 8.5.4]; or

   o  The offerer wants to disable the bundled "m=" line
      [Section 8.5.5].

   In addition, the offerer MUST select an offerer BUNDLE-tag
   [Section 8.2.2] associated with the previously selected offerer
   BUNDLE address, unless the offerer suggests a new offerer BUNDLE
   address.

8.5.2.  Suggesting a new offerer BUNDLE address

   When an offerer generates an offer, in which it suggests a new
   offerer BUNDLE address [Section 8.2.2], the offerer MUST:





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   o  Assign the address (shared address) to each "m=" line within the
      BUNDLE group; or

   o  Assign the address (unique address) to one bundled "m=" line.

   In addition, the offerer MUST indicate that the address is the new
   suggested offerer BUNDLE address [Section 8.2.2].

   NOTE: Unless the offerer assigns the new suggested offerer BUNDLE
   address to each bundled "m=" line, it can assign unique addresses to
   any number of bundled "m=" lines (and the previously selected offerer
   BUNDLE address to any remaining bundled "m=" line) if it wants to
   suggest multiple alternatives for the new offerer BUNDLE address.

8.5.3.  Adding a media description to a BUNDLE group

   When an offerer generates an offer, in which it wants to add a
   bundled "m=" line to a BUNDLE group, the offerer MUST:

   o  Assign a unique address to the "m=" line;

   o  Assign the previously selected offerer BUNDLE address to the "m="
      line; or

   o  If the offerer assigns a new (shared address) suggested offerer
      BUNDLE address to each bundled "m=" line [Section 8.5.2], also
      assign that address to the added "m=" line.

   In addition, the offerer MUST extend the SDP 'group:BUNDLE' attribute
   identification-tag list with the BUNDLE group [Section 8.2.2] by
   adding the identification-tag associated with the added "m=" line to
   the list.

   NOTE: Assigning a unique address to the "m=" line allows the answerer
   to move the "m=" line out of the BUNDLE group [Section 8.3.4],
   without having to reject the "m=" line.

   If the offerer assigns a unique address to the added "m=" line, and
   if the offerer suggests that address as the new offerer BUNDLE
   address [Section 8.5.2], the offerer BUNDLE-tag MUST represent the
   added "m=" line [Section 8.2.2].

   If the offerer assigns a new suggested offerer BUNDLE address to each
   bundled "m=" line [Section 8.5.2], including the added "m=" line, the
   offerer BUNDLE-tag MAY represent the added "m=" line [Section 8.2.2].

   [Section 16.3] shows an example where an offerer sends an offer in
   order to add a bundled "m=" line to a BUNDLE group.



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8.5.4.  Moving A Media Description Out Of A BUNDLE Group

   When an offerer generates an offer, in which it wants to move a
   bundled "m=" line out of a BUNDLE group it was added to in a previous
   offer/answer transaction, the offerer:

   o  MUST assign a unique address to the "m=" line; and

   o  MUST NOT place the identification-tag associated with the "m="
      line in the SDP 'group:BUNDLE' attribute identification-tag list
      associated with the BUNDLE group.

   NOTE: If an "m=" line, when being moved out of a BUNDLE group, is
   added to another BUNDLE group, the offerer applies the procedures in
   [Section 8.5.3] to the "m=" line.

   [Section 16.4] shows an example of an offer for moving an "m=" line
   out of a BUNDLE group.

8.5.5.  Disabling A Media Description In A BUNDLE Group

   When an offerer generates an offer, in which it wants to disable a
   bundled "m=" line (added to the BUNDLE group in a previous offer/
   answer transaction), the offerer:

   o  MUST assign an address with a zero port value to the "m=" line,
      following the procedures in [RFC4566]; and

   o  MUST NOT place the identification-tag associated with the "m="
      line in the SDP 'group:BUNDLE' attribute identification-tag list
      associated with the BUNDLE group.

   [Section 16.5] shows an example of an offer for disabling an "m="
   line within a BUNDLE group.

9.  Protocol Identification

9.1.  General

   Each "m=" line within a BUNDLE group MUST use the same transport-
   layer protocol.  If bundled "m=" lines use different protocols on top
   of the transport-layer protocol, there MUST exist a publicly
   available specification which describes a mechanism, for this
   particular protocol combination, how to associate a received packet
   with the correct protocol.

   In addition, if a received packet can be associated with more than
   one bundled "m=" line, there MUST exist a publically available



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   specification which describes a mechanism for associating the
   received packet with the correct "m=" line.

9.2.  STUN, DTLS, SRTP

   Section 5.1.2 of [RFC5764] describes a mechanism to identify the
   protocol of a received packet among the STUN, DTLS and SRTP protocols
   (in any combination).  If an offer or answer includes bundled "m="
   lines that represent these protocols, the offerer or answerer MUST
   support the mechanism described in [RFC5764], and no explicit
   negotiation is required in order to indicate support and usage of the
   mechanism.

   [RFC5764] does not describe how to identify different protocols
   transported on DTLS, only how to identify the DTLS protocol itself.
   If multiple protocols are transported on DTLS, there MUST exist a
   specification describing a mechanism for identifying each individual
   protocol.  In addition, if a received DTLS packet can be associated
   with more than one "m=" line, there MUST exist a specification which
   describes a mechanism for associating the received DTLS packet with
   the correct "m=" line.

   [Section 10.2] describes how to associate a received (S)RTP packet
   with the correct "m=" line.

10.  RTP Considerations

10.1.  Single RTP Session

10.1.1.  General

   All RTP-based media within a single BUNDLE group belong to a single
   RTP session [RFC3550].  Disjoint BUNDLE groups will form multiple RTP
   sessions, one per BUNDLE group.

   Since a single RTP session is used for each bundle group, all "m="
   lines representing RTP-based media in a bundle group will share a
   single SSRC numbering space [RFC3550].

   The following rules and restrictions apply for a single RTP session:

   o  A specific payload type value can be used in multiple bundled "m="
      lines if each codec associated with the payload type number shares
      an identical codec configuration [Section 10.1.2].

   o  The proto value in each bundled RTP-based "m=" line MUST be
      identical (e.g.  RTP/AVPF).




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   o  The RTP MID header extension MUST be enabled, by associating an
      SDP 'extmap' attribute [RFC5285], with a 'urn:ietf:params:rtp-
      hdrext:sdes:mid' URI value, with each bundled RTP-based "m=" line
      in every offer and answer.

   o  A given SSRC MUST NOT transmit RTP packets using payload types
      that originate from different bundled "m=" lines.

   NOTE: The last bullet above is to avoid sending multiple media types
   from the same SSRC.  If transmission of multiple media types are done
   with time overlap, RTP and RTCP fail to function.  Even if done in
   proper sequence this causes RTP Timestamp rate switching issues
   [RFC7160].  However, once an SSRC has left the RTP session (by
   sending an RTCP BYE packet), that SSRC value can later be reused by
   another source(possible associated with a different bundled "m="
   line.

10.1.2.  Payload Type (PT) Value Reuse

   Multiple bundled "m=" lines might represent RTP based media.  As all
   RTP based media associated with a BUNDLE group belong to the same RTP
   session, in order for a given payload type value to be used inside
   more than one bundled "m=" line, all codecs associated with the
   payload type number MUST share an identical codec configuration.
   This means that the codecs MUST share the same media type, encoding
   name, clock rate and any parameter that can affect the codec
   configuration and packetization.  [I-D.mmusic-sdp-mux-attributes]
   lists SDP attributes, whose attribute values must be identical for
   all codecs that use the same payload type value.

10.2.  Associating RTP/RTCP Packets With Correct SDP Media Description

   There are multiple mechanisms that can be used by an endpoint in
   order to associate received RTP/RTCP packets with a bundled "m="
   line.  Such mechanisms include using the payload type value carried
   inside the RTP packets, the SSRC values carried inside the RTP
   packets, and other "m=" line specific information carried inside the
   RTP packets.

   As all RTP/RTCP packets associated with a BUNDLE group are received
   (and sent) using single address:port combinations, the local
   address:port combination cannot be used to associate received RTP
   packets with the correct "m=" line.

   As described in [Section 10.1.2], the same payload type value might
   be used inside RTP packets described by multiple "m=" lines.  In such
   cases, the payload type value cannot be used to associate received
   RTP packets with the correct "m=" line.



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   An offerer and answerer can in an offer and answer inform each other
   which SSRC values they will use inside sent RTP/RTCP packets, by
   associating one or more SDP 'ssrc' attributes [RFC5576] with each
   bundled "m=" line which contains a payload type value that is also
   used inside another bundled "m=" line.  As the SSRC values will be
   carried inside the RTP/RTCP packets, the offerer and answerer can
   then use that information to associate received RTP packets with the
   correct "m=" line.  However, an offerer will not know which SSRC
   values the answerer will use until it has received the answer
   providing that information.  Due to this, before the offerer has
   received the answer, the offerer will not be able to associate
   received RTP/RTCP packets with the correct "m=" line using the SSRC
   values.

   In order for an offerer and answerer to always be able to associate
   received RTP and RTCP packets with the correct "m=" line, an offerer
   and answerer using the BUNDLE extension MUST support the mechanism
   defined in Section 13, where the remote endpoint inserts the
   identification-tag associated with an "m=" line in RTP and RTCP
   packets associated with that "m=" line.

10.3.  RTP/RTCP Multiplexing

10.3.1.  General

   When a BUNDLE group, which contains RTP based media, is created, the
   offerer and answerer MUST negotiate whether to enable RTP/RTCP
   multiplexing for the RTP based media associated with the BUNDLE group
   [RFC5761].

   If RTP/RTCP multiplexing is not enabled, separate address:port
   combinations will be used for receiving (and sending) the RTP packets
   and the RTCP packets.

10.3.2.  SDP Offer/Answer Procedures

10.3.2.1.  General

   This section describes how an offerer and answerer can use the SDP
   'rtcp-mux' attribute [RFC5761] and the SDP 'rtcp' attribute [RFC3605]
   to negotiate usage of RTP/RTCP multiplexing for RTP based media
   associated with a BUNDLE group.

10.3.2.2.  Generating the Initial SDP Offer

   When an offerer generates an initial offer, if the offerer wants to
   negotiate usage of RTP/RTCP multiplexing within a BUNDLE group, the
   offerer MUST associate an SDP 'rtcp-mux' attribute [RFC5761] with



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   each bundled RTP-based "m=" line (including any bundle-only "m="
   line) in the offer.

   If the offerer does not want to negotiate usage of RTP/RTCP
   multiplexing, it MUST NOT associate an SDP 'rtcp-mux' attribute with
   any bundled "m=" line in the offer.

   In addition, the offerer can associate an SDP 'rtcp' attribute
   [RFC3605] with one or more bundled RTP-based "m=" lines (including
   any bundle-only "m=" line) in the offer, in order to provide a port
   for receiving RTCP packets (if the answerer does not accept usage of
   RTP/RTCP multiplexing, or if the offerer does not want to negotiate
   usage of RTP/RTCP multiplexing).

   In the initial offer, the IP address and port combination for RTCP
   MUST be unique in each bundled RTP-based "m=" line, similar to RTP.

   NOTE: In case the offer wants to receive RTCP packets on the next
   higher port value, the SDP 'rtcp' attribute is not needed.

10.3.2.3.  Generating the SDP Answer

   When an answerer generates an answer, if the offerer indicated
   support of RTP/RTCP multiplexing [RFC5761] within a BUNDLE group in
   the associated offer, the answerer MUST either accept or reject the
   usage of RTP/RTCP multiplexing for the whole BUNDLE group in the
   answer.

   If the answerer accepts the usage of RTP/RTCP multiplexing within the
   BUNDLE group, it MUST associate an SDP 'rtcp-mux' attribute with each
   bundled RTP-based "m=" line in the answer.  The answerer MUST NOT
   associate an SDP 'rtcp' attribute with any bundled "m=" line in the
   answer.  The answerer will use the port value of the selected offerer
   BUNDLE address for sending RTP and RTCP packets associated with each
   RTP-based bundled "m=" line towards the offerer.

   If the answerer does not accept the usage of RTP/RTCP multiplexing
   within the BUNDLE group, it MUST NOT associate an SDP 'rtcp-mux'
   attribute with any bundled "m=" line in the answer.  The answerer
   will use the RTP and RTCP port values associated with the selected
   offerer BUNDLE address for sending RTP and RTCP packets associated
   with each RTP-based bundled "m=" line towards the offerer.

   In addition, if the answerer rejects the usage of RTP/RTCP
   multiplexing within the BUNDLE group, it MAY associate an SDP 'rtcp'
   attribute, with identical attribute values, with each RTP-based
   bundled "m=" line in the answer, in order to provide a port value for
   receiving RTCP packets from the offerer.



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   NOTE: In case the answerer wants to receive RTCP packets on the next
   higher port value, the SDP 'rtcp' attribute is not needed.

   If the usage of RTP/RTCP multiplexing within a BUNDLE group has been
   negotiated in a previous offer/answer transaction, and if the offerer
   indicates that it wants to continue using RTP/RTCP multiplexing in a
   subsequent offer, the answerer MUST associate an SDP 'rtcp-mux'
   attribute with each bundled "m=" line in the answer.  I.e. the
   answerer MUST NOT disable the usage of RTP/RTCP multiplexing.

   If the usage of RTP/RTCP multiplexing within a BUNDLE group has not
   been negotiated in a previous offer/answer transaction, and if the
   offerer indicates that it wants to use RTP/RTCP multiplexing in a
   subsequent offer, the answerer either accepts or rejects the usage,
   using the procedures above.

10.3.2.4.  Offerer Processing of the SDP Answer

   When an offerer receives an answer, if the answerer has accepted the
   usage of RTP/RTCP multiplexing (see Section 10.3.2.3), the answerer
   follows the procedures for RTP/RTCP multiplexing defined in
   [RFC5761].  The offerer will use the port value associated with the
   answerer BUNDLE address for sending RTP and RTCP packets associated
   with each RTP-based bundled "m=" line towards the answerer.

   If the answerer did not accept the usage of RTP/RTCP multiplexing
   (see Section 10.3.2.3), the offerer will use separate address:port
   combinations for sending RTP and RTCP packets towards the answerer.
   If the answerer associated an SDP 'rtcp' attribute with the "m=" line
   representing the answerer BUNDLE address, the offerer will use the
   attribute port value for sending RTCP packets associated with each
   bundled RTP-based "m=" line towards the answerer.  Otherwise the
   offerer will use the next higher port value associated with the
   answerer BUNDLE address for sending RTCP packets towards the
   answerer.

10.3.2.5.  Modifying the Session

   When an offerer generates a subsequent offer, if it wants to
   negotiate the usage of RTP/RTCP multiplexing within a BUNDLE group,
   or if it wants to continue the use of previously negotiated RTP/RTCP
   multiplexing, it MUST associate an SDP 'rtcp-mux' attribute with each
   RTP-based bundled "m=" line (including any bundled "m=" line that the
   offerer wants to add to the BUNDLE group), unless the offerer wants
   to disable or remove the "m=" line from the BUNDLE group.

   If the offerer does not want to negotiate the usage of RTP/RTCP
   multiplexing within the BUNDLE group, or if it wants to disable



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   previously negotiated usage of RTP/RTCP multiplexing, it MUST NOT
   associate an SDP 'rtcp-mux' and attribute with any bundled "m=" line
   in the subsequent offer.

   In addition, if the offerer does not indicate support of RTP/RTCP
   multiplexing within the subsequent offer, it MAY associate an SDP
   'rtcp' attribute, with identical attribute values, with each RTP-
   based bundled "m=" line (including any bundled "m=" line that the
   offerer wants to add to the BUNDLE group), in order to provide a port
   for receiving RTCP packets.

   NOTE: It is RECOMMENDED that, once the usage of RTP/RTCP multiplexing
   has been negotiated within a BUNDLE group, that the usage is not
   disabled.  Disabling RTP/RTCP multiplexing means that the offerer and
   answerer need to reserve new ports, to be used for sending and
   receiving RTCP packets.  Similar, if the usage of a specific RTCP
   port has been negotiated within a BUNDLE group, it is RECOMMENDED
   that the port value is not modified.

11.  ICE Considerations

11.1.  General

   This section describes how to use the BUNDLE grouping extension
   together with the Interactive Connectivity Establishment (ICE)
   mechanism [RFC5245].

   The procedures defined in [RFC5245] also apply to usage of ICE with
   BUNDLE, with the following exception:

   o  When BUNDLE addresses for a BUNDLE group have been selected for
      both endpoints, ICE connectivity checks and keep-alives only need
      to be performed for the whole BUNDLE group, instead of per bundled
      "m=" line.

   Support and usage of ICE mechanism together with the BUNDLE extension
   is OPTIONAL.

11.2.  SDP Offer/Answer Procedures

11.2.1.  General

   When an offerer assigns a unique address to a bundled "m=" line
   (excluding any bundle-only "m=" line), it MUST also associate unique
   ICE candidates [RFC5245] to the "m=" line.

   An offerer MUST NOT assign ICE candidates to a bundle-only "m=" line
   with a zero port value.



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   NOTE: The bundle-only "m=" line, if accepted by the answerer, will
   inherit the candidates associated with the selected offerer BUNDLE
   address.  An answerer that does not support BUNDLE would not accept a
   bundle-only "m=" line.

   When an offerer or answerer assigns a shared address (i.e. a
   previously selected BUNDLE address) to one or more bundled "m="
   lines, it MUST associate identical ICE candidates (referred to as
   shared ICE candidates) to each of those "m=" lines.

11.2.2.  Generating the Initial SDP Offer

   When an offerer generates an initial offer, it assigns unique or
   shared ICE candidates to the bundled "m=" lines, according to
   Section 11.1.

11.2.3.  Generating the SDP Answer

   When an answerer generates an answer, which contains a BUNDLE group,
   the answerer MUST assign shared ICE candidates to each bundled "m="
   line (including "m=" lines that were indicated as bundle-only in the
   associated offer) in the answer.

11.2.4.  Offerer Processing of the SDP Answer

   When an offerer receives an answer, if the answerer supports and uses
   the ICE mechanism and the BUNDLE extension, the offerer MUST assign
   the same ICE candidates, associated with the "m=" line representing
   the offerer BUNDLE address (selected by the answerer), to each
   bundled "m=" line.

11.2.5.  Modifying the Session

   When an offerer generates a subsequent offer, it assigns unique or
   shared ICE candidates to the bundled "m=" lines, according to
   (Section 11.1).

12.  Update to RFC 3264

12.1.  General

   This section replaces the text of the following sections of RFC 3264:

   o  Section 5.1 (Unicast Streams).

   o  Section 8.2 (Removing a Media Stream).

   o  Section 8.4 (Putting a Unicast Media Stream on Hold).



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12.2.  Original text of section 5.1 (2nd paragraph) of RFC 3264

   For recvonly and sendrecv streams, the port number and address in the
   offer indicate where the offerer would like to receive the media
   stream.  For sendonly RTP streams, the address and port number
   indirectly indicate where the offerer wants to receive RTCP reports.
   Unless there is an explicit indication otherwise, reports are sent to
   the port number one higher than the number indicated.  The IP address
   and port present in the offer indicate nothing about the source IP
   address and source port of RTP and RTCP packets that will be sent by
   the offerer.  A port number of zero in the offer indicates that the
   stream is offered but MUST NOT be used.  This has no useful semantics
   in an initial offer, but is allowed for reasons of completeness,
   since the answer can contain a zero port indicating a rejected stream
   (Section 6).  Furthermore, existing streams can be terminated by
   setting the port to zero (Section 8).  In general, a port number of
   zero indicates that the media stream is not wanted.

12.3.  New text replacing section 5.1 (2nd paragraph) of RFC 3264

   For recvonly and sendrecv streams, the port number and address in the
   offer indicate where the offerer would like to receive the media
   stream.  For sendonly RTP streams, the address and port number
   indirectly indicate where the offerer wants to receive RTCP reports.
   Unless there is an explicit indication otherwise, reports are sent to
   the port number one higher than the number indicated.  The IP address
   and port present in the offer indicate nothing about the source IP
   address and source port of RTP and RTCP packets that will be sent by
   the offerer.  A port number of zero in the offer by default indicates
   that the stream is offered but MUST NOT be used, but an extension
   mechanism might specify different semantics for the usage of a zero
   port value.  Furthermore, existing streams can be terminated by
   setting the port to zero (Section 8).  In general, a port number of
   zero by default indicates that the media stream is not wanted.

12.4.  Original text of section 8.2 (2nd paragraph) of RFC 3264

   A stream that is offered with a port of zero MUST be marked with port
   zero in the answer.  Like the offer, the answer MAY omit all
   attributes present previously, and MAY list just a single media
   format from amongst those in the offer.

12.5.  New text replacing section 8.2 (2nd paragraph) of RFC 3264

   A stream that is offered with a port of zero MUST by default be
   marked with port zero in the answer, unless an extension mechanism,
   which specifies semantics for the usage of a non-zero port value, is
   used.  If the stream is marked with port zero in the answer, the



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   answer MAY omit all attributes present previously, and MAY list just
   a single media format from amongst those in the offer."

12.6.  Original text of section 8.4 (6th paragraph) of RFC 3264

   RFC 2543 [10] specified that placing a user on hold was accomplished
   by setting the connection address to 0.0.0.0.  Its usage for putting
   a call on hold is no longer recommended, since it doesn't allow for
   RTCP to be used with held streams, doesn't work with IPv6, and breaks
   with connection oriented media.  However, it can be useful in an
   initial offer when the offerer knows it wants to use a particular set
   of media streams and formats, but doesn't know the addresses and
   ports at the time of the offer.  Of course, when used, the port
   number MUST NOT be zero, which would specify that the stream has been
   disabled.  An agent MUST be capable of receiving SDP with a
   connection address of 0.0.0.0, in which case it means that neither
   RTP nor RTCP should be sent to the peer.

12.7.  New text replacing section 8.4 (6th paragraph) of RFC 3264

   RFC 2543 [10] specified that placing a user on hold was accomplished
   by setting the connection address to 0.0.0.0.  Its usage for putting
   a call on hold is no longer recommended, since it doesn't allow for
   RTCP to be used with held streams, doesn't work with IPv6, and breaks
   with connection oriented media.  However, it can be useful in an
   initial offer when the offerer knows it wants to use a particular set
   of media streams and formats, but doesn't know the addresses and
   ports at the time of the offer.  Of course, when used, the port
   number MUST NOT be zero, if it would specify that the stream has been
   disabled.  However, an extension mechanism might specify different
   semantics of the zero port number usage.  An agent MUST be capable of
   receiving SDP with a connection address of 0.0.0.0, in which case it
   means that neither RTP nor RTCP should be sent to the peer.

13.  RTP/RTCP extensions for identification-tag transport

13.1.  General

   SDP Offerers and Answerers [RFC3264] can associate identification-
   tags with "m=" lines within SDP Offers and Answers, using the
   procedures in [RFC5888].  Each identification-tag uniquely represents
   an "m=" line.

   This section defines a new RTCP SDES item [RFC3550], 'MID', which is
   used to carry identification-tags within RTCP SDES packets.  This
   section also defines a new RTP header extension [RFC5285], which is
   used to carry identification-tags in RTP packets.




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   The SDES item and RTP header extension make it possible for a
   receiver to associate received RTCP- and RTP packets with a specific
   "m=" line, to which the receiver has assigned an identification-tag,
   even if those "m=" lines are part of the same RTP session.  The
   endpoint informs the remote endpoint about the identification-tag
   using the procedures in [RFC5888], and the remote endpoint then
   inserts the identification-tag in RTCP- and RTP packets sent towards
   the other endpoint.

   NOTE: This text above defines how identification-tags are carried in
   SDP Offers and Answers.  The usage of other signalling protocols for
   carrying identification-tags is not prevented, but the usage of such
   protocols is outside the scope of this document.

   [RFC3550] defines general procedures regarding the RTCP transmission
   interval.  The RTCP MID SDES item SHOULD be sent in the first few
   RTCP packets sent on joining the session, and SHOULD be sent
   regularly thereafter.  The exact number of RTCP packets in which this
   SDES item is sent is intentionally not specified here, as it will
   depend on the expected packet loss rate, the RTCP reporting interval,
   and the allowable overhead.

   The RTP MID header extension SHOULD be included in some RTP packets
   at the start of the session and whenever the SSRC changes.  It might
   also be useful to include the header extension in RTP packets that
   comprise random access points in the media (e.g., with video
   I-frames).  The exact number of RTP packets in which this header
   extension is sent is intentionally not specified here, as it will
   depend on expected packet loss rate and loss patterns, the overhead
   the application can tolerate, and the importance of immediate receipt
   of the identification-tag.

   For robustness purpose, endpoints need to be prepared for situations
   where the reception of the identification-tag is delayed, and SHOULD
   NOT terminate sessions in such cases, as the identification-tag is
   likely to arrive soon.

13.2.  RTCP MID SDES Item


       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      MID=TBD  |     length    | identification-tag          ...
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   The identification-tag payload is UTF-8 encoded, as in SDP.



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   The identification-tag is not zero terminated.

   [RFC EDITOR NOTE: Please replace TBD with the assigned SDES
   identifier value.]

13.3.  RTP MID Header Extension

   The payload, containing the identification-tag, of the RTP MID header
   extension element can be encoded using either the one-byte or two-
   byte header [RFC5285].  The identification-tag payload is UTF-8
   encoded, as in SDP.

   The identification-tag is not zero terminated.  Note, that set of
   header extensions included in the packet needs to be padded to the
   next 32-bit boundary using zero bytes [RFC5285].

   As the identification-tag is included in either an RTCP SDES item or
   an RTP header extension, or both, there should be some consideration
   about the packet expansion caused by the identification-tag.  To
   avoid Maximum Transmission Unit (MTU) issues for the RTP packets, the
   header extension's size needs to be taken into account when the
   encoding media.

   It is recommended that the identification-tag is kept short.  Due to
   the properties of the RTP header extension mechanism, when using the
   one-byte header, a tag that is 1-3 bytes will result in that a
   minimal number of 32-bit words are used for the RTP header extension,
   in case no other header extensions are included at the same time.
   Note, do take into account that some single characters when UTF-8
   encoded will result in multiple octets.

14.  IANA Considerations

14.1.  New SDES item

   [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this
   document.]

   [RFC EDITOR NOTE: Please replace TBD with the assigned SDES
   identifier value.]

   This document adds the MID SDES item to the IANA "RTCP SDES item
   types" registry as follows:








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           Value:          TBD
           Abbrev.:        MID
           Name:           Media Identification
           Reference:      RFCXXXX


14.2.  New RTP Header Extension URI

   [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this
   document.]

   This document defines a new extension URI in the RTP Compact Header
   Extensions subregistry of the Real-Time Transport Protocol (RTP)
   Parameters registry, according to the following data:


       Extension URI: urn:ietf:params:rtp-hdrext:sdes:mid
       Description:   Media identification
       Contact:       christer.holmberg@ericsson.com
       Reference:     RFCXXXX


14.3.  New SDP Attribute

   [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this
   document.]

   This document defines a new SDP media-level attribute, 'bundle-only',
   according to the following data:


          Attribute name:     bundle-only
          Type of attribute:  media
          Subject to charset: No
          Purpose:            Request a media description to be accepted
                          in the answer only if kept within a BUNDLE
                          group by the answerer.
          Appropriate values: N/A
          Contact name:       Christer Holmberg
          Contact e-mail:     christer.holmberg@ericsson.com
          Reference:          RFCXXXX


15.  Security Considerations

   The security considerations defined in [RFC3264] and [RFC5888] apply
   to the BUNDLE extension.  Bundle does not change which information
   flows over the network but only changes which ports that information



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   is flowing on and thus has very little impact on the security of the
   RTP sessions.

   When the BUNDLE extension is used, a single set of security
   credentials might be used for all media streams associated with a
   BUNDLE group.

   When the BUNDLE extension is used, the number of SSRC values within a
   single RTP session increases, which increases the risk of SSRC
   collision.  [RFC4568] describes how SSRC collision may weaken SRTP
   and SRTCP encryption in certain situations.

16.  Examples

16.1.  Example: Bundle Address Selection

   The example below shows:

   o  1.  An offer, in which the offerer assigns a unique address to
      each bundled "m=" line within the BUNDLE group.

   o  2.  An answer, in which the answerer selects the offerer BUNDLE
      address, and in which selects its own BUNDLE address (the answerer
      BUNDLE address) and assigns it each bundled "m=" line within the
      BUNDLE group.


























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   SDP Offer (1)

       v=0
       o=alice 2890844526 2890844526 IN IP4 atlanta.example.com
       s=
       c=IN IP4 atlanta.example.com
       t=0 0
       a=group:BUNDLE foo bar
       m=audio 10000 RTP/AVP 0 8 97
       b=AS:200
       a=mid:foo
       a=rtpmap:0 PCMU/8000
       a=rtpmap:8 PCMA/8000
       a=rtpmap:97 iLBC/8000
       a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
       m=video 10002 RTP/AVP 31 32
       b=AS:1000
       a=mid:bar
       a=rtpmap:31 H261/90000
       a=rtpmap:32 MPV/90000
       a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid


   SDP Answer (2)

       v=0
       o=bob 2808844564 2808844564 IN IP4 biloxi.example.com
       s=
       c=IN IP4 biloxi.example.com
       t=0 0
       a=group:BUNDLE foo bar
       m=audio 20000 RTP/AVP 0
       b=AS:200
       a=mid:foo
       a=rtpmap:0 PCMU/8000
       a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
       m=video 20000 RTP/AVP 32
       b=AS:1000
       a=mid:bar
       a=rtpmap:32 MPV/90000
       a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid










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16.2.  Example: BUNDLE Extension Rejected

   The example below shows:

   o  1.  An offer, in which the offerer assigns a unique address to
      each bundled "m=" line within the BUNDLE group.

   o  2.  An answer, in which the answerer rejects the offered BUNDLE
      group, and assigns a unique addresses to each "m=" line (following
      normal RFC 3264 procedures).









































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   SDP Offer (1)

       v=0
       o=alice 2890844526 2890844526 IN IP4 atlanta.example.com
       s=
       c=IN IP4 atlanta.example.com
       t=0 0
       a=group:BUNDLE foo bar
       m=audio 10000 RTP/AVP 0 8 97
       b=AS:200
       a=mid:foo
       a=rtpmap:0 PCMU/8000
       a=rtpmap:8 PCMA/8000
       a=rtpmap:97 iLBC/8000
       a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
       m=video 10002 RTP/AVP 31 32
       b=AS:1000
       a=mid:bar
       a=rtpmap:31 H261/90000
       a=rtpmap:32 MPV/90000
       a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid


   SDP Answer (2)

       v=0
       o=bob 2808844564 2808844564 IN IP4 biloxi.example.com
       s=
       c=IN IP4 biloxi.example.com
       t=0 0
       m=audio 20000 RTP/AVP 0
       b=AS:200
       a=rtpmap:0 PCMU/8000
       m=video 30000 RTP/AVP 32
       b=AS:1000
       a=rtpmap:32 MPV/90000



16.3.  Example: Offerer Adds A Media Description To A BUNDLE Group

   The example below shows:

   o  1.  A subsequent offer (the BUNDLE group has been created as part
      of a previous offer/answer transaction), in which the offerer adds
      a new "m=" line, represented by the "zen" identification-tag, to a
      previously negotiated BUNDLE group, assigns a unique address to
      the added "m=" line, and assigns the previously selected offerer



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      BUNDLE address to each of the other bundled "m=" lines within the
      BUNDLE group.

   o  2.  An answer, in which the answerer assigns the answerer BUNDLE
      address to each bundled "m=" line (including the newly added "m="
      line) within the BUNDLE group.


   SDP Offer (1)

       v=0
       o=alice 2890844526 2890844526 IN IP4 atlanta.example.com
       s=
       c=IN IP4 atlanta.example.com
       t=0 0
       a=group:BUNDLE foo bar zen
       m=audio 10000 RTP/AVP 0 8 97
       b=AS:200
       a=mid:foo
       a=rtpmap:0 PCMU/8000
       a=rtpmap:8 PCMA/8000
       a=rtpmap:97 iLBC/8000
       a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
       m=video 10000 RTP/AVP 31 32
       b=AS:1000
       a=mid:bar
       a=rtpmap:31 H261/90000
       a=rtpmap:32 MPV/90000
       a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
       m=video 20000 RTP/AVP 66
       b=AS:1000
       a=mid:zen
       a=rtpmap:66 H261/90000
       a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid


   SDP Answer (2)

       v=0
       o=bob 2808844564 2808844564 IN IP4 biloxi.example.com
       s=
       c=IN IP4 biloxi.example.com
       t=0 0
       a=group:BUNDLE foo bar zen
       m=audio 20000 RTP/AVP 0
       b=AS:200
       a=mid:foo
       a=rtpmap:0 PCMU/8000



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       a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
       m=video 20000 RTP/AVP 32
       b=AS:1000
       a=mid:bar
       a=rtpmap:32 MPV/90000
       a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
       m=video 20000 RTP/AVP 66
       b=AS:1000
       a=mid:zen
       a=rtpmap:66 H261/90000
       a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid



16.4.  Example: Offerer Moves A Media Description Out Of A BUNDLE Group

   The example below shows:

   o  1.  A subsequent offer (the BUNDLE group has been created as part
      of a previous offer/answer transaction), in which the offerer
      moves a bundled "m=" line out of a BUNDLE group, assigns a unique
      address to the moved "m=" line, and assigns the offerer BUNDLE
      address to each other bundled "m=" line within the BUNDLE group.

   o  2.  An answer, in which the answerer moves the "m=" line out of
      the BUNDLE group, assigns unique address to the moved "m=" line,
      and assigns the answerer BUNDLE address to each of the remaining
      bundled "m=" line within the BUNDLE group.


   SDP Offer (1)

       v=0
       o=alice 2890844526 2890844526 IN IP4 atlanta.example.com
       s=
       c=IN IP4 atlanta.example.com
       t=0 0
       a=group:BUNDLE foo bar
       m=audio 10000 RTP/AVP 0 8 97
       b=AS:200
       a=mid:foo
       a=rtpmap:0 PCMU/8000
       a=rtpmap:8 PCMA/8000
       a=rtpmap:97 iLBC/8000
       a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
       m=video 10000 RTP/AVP 31 32
       b=AS:1000
       a=mid:bar



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       a=rtpmap:31 H261/90000
       a=rtpmap:32 MPV/90000
       a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
       m=video 50000 RTP/AVP 66
       b=AS:1000
       a=mid:zen
       a=rtpmap:66 H261/90000


   SDP Answer (2)

       v=0
       o=bob 2808844564 2808844564 IN IP4 biloxi.example.com
       s=
       c=IN IP4 biloxi.example.com
       t=0 0
       a=group:BUNDLE foo bar
       m=audio 20000 RTP/AVP 0
       b=AS:200
       a=mid:foo
       a=rtpmap:0 PCMU/8000
       a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
       m=video 20000 RTP/AVP 32
       b=AS:1000
       a=mid:bar
       a=rtpmap:32 MPV/90000
       a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
       m=video 60000 RTP/AVP 66
       b=AS:1000
       a=mid:zen
       a=rtpmap:66 H261/90000



16.5.  Example: Offerer Disables A Media Description Within A BUNDLE
       Group

   The example below shows:

   o  1.  A subsequent offer (the BUNDLE group has been created as part
      of a previous offer/answer transaction), in which the offerer
      disables a bundled "m=" line within BUNDLE group, assigns a zero
      port number to the disabled "m=" line, and assigns the offerer
      BUNDLE address to each of the other bundled "m=" lines within the
      BUNDLE group.

   o  2.  An answer, in which the answerer moves the disabled "m=" line
      out of the BUNDLE group, assigns a zero port value to the disabled



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      "m=" line, and assigns the answerer BUNDLE address to each of the
      remaining bundled "m=" line within the BUNDLE group.


   SDP Offer (1)

       v=0
       o=alice 2890844526 2890844526 IN IP4 atlanta.example.com
       s=
       c=IN IP4 atlanta.example.com
       t=0 0
       a=group:BUNDLE foo bar
       m=audio 10000 RTP/AVP 0 8 97
       b=AS:200
       a=mid:foo
       a=rtpmap:0 PCMU/8000
       a=rtpmap:8 PCMA/8000
       a=rtpmap:97 iLBC/8000
       a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
       m=video 10000 RTP/AVP 31 32
       b=AS:1000
       a=mid:bar
       a=rtpmap:31 H261/90000
       a=rtpmap:32 MPV/90000
       a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
       m=video 0 RTP/AVP 66
       a=mid:zen
       a=rtpmap:66 H261/90000


   SDP Answer (2)

       v=0
       o=bob 2808844564 2808844564 IN IP4 biloxi.example.com
       s=
       c=IN IP4 biloxi.example.com
       t=0 0
       a=group:BUNDLE foo bar
       m=audio 20000 RTP/AVP 0
       b=AS:200
       a=mid:foo
       a=rtpmap:0 PCMU/8000
       a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid
       m=video 20000 RTP/AVP 32
       b=AS:1000
       a=mid:bar
       a=rtpmap:32 MPV/90000
       a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid



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       m=video 0 RTP/AVP 66
       a=mid:zen
       a=rtpmap:66 H261/90000



17.  Acknowledgements

   The usage of the SDP grouping extension for negotiating bundled media
   is based on a similar alternatives proposed by Harald Alvestrand and
   Cullen Jennings.  The BUNDLE extension described in this document is
   based on the different alternative proposals, and text (e.g.  SDP
   examples) have been borrowed (and, in some cases, modified) from
   those alternative proposals.

   The SDP examples are also modified versions from the ones in the
   Alvestrand proposal.

   Thanks to Paul Kyzivat, Martin Thomson, Flemming Andreasen, Thomas
   Stach and Ari Keraenen for taking the time to read the text along the
   way, and providing useful feedback.

18.  Change Log

   [RFC EDITOR NOTE: Please remove this section when publishing]

   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-18

   o  - Changes based on agreements at IETF#92

   o  -- BAS Offer removed, based on agreement at IETF#92.

   o  -- Procedures regarding usage of SDP "b=" line is replaced with a
      reference to to draft-ietf-mmusic-sdp-mux-attributes.

   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-17

   o  - Editorial changes based on comments from Magnus Westerlund.

   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-16

   o  - Modification of RTP/RTCP multiplexing section, based on comments
      from Magnus Westerlund.

   o  - Reference updates.

   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-15




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   o  - Editorial fix.

   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-14

   o  - Editorial changes.

   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-13

   o  Changes to allow a new suggested offerer BUNDLE address to be
      assigned to each bundled m- line.

   o  Changes based on WGLC comments from Paul Kyzivat

   o  - Editorial fixes

   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-12

   o  Usage of SDP 'extmap' attribute added

   o  SDP 'bundle-only' attribute scoped with "m=" lines with a zero
      port value

   o  Changes based on WGLC comments from Thomas Stach

   o  - ICE candidates not assigned to bundle-only m- lines with a zero
      port value

   o  - Editorial changes

   o  Changes based on WGLC comments from Colin Perkins

   o  - Editorial changes:

   o  -- "RTP SDES item" -> "RTCP SDES item"

   o  -- "RTP MID SDES item" -> "RTCP MID SDES item"

   o  - Changes in section 10.1.1:

   o  -- "SHOULD NOT" -> "MUST NOT"

   o  -- Additional text added to the Note

   o  - Change to section 13.2:

   o  -- Clarify that mid value is not zero terminated

   o  - Change to section 13.3:



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   o  -- Clarify that mid value is not zero terminated

   o  -- Clarify padding

   o  Changes based on WGLC comments from Paul Kyzivat

   o  - Editorial changes:

   o  Changes based on WGLC comments from Jonathan Lennox

   o  - Editorial changes:

   o  - Defintion of SDP bundle-only attribute alligned with structure
      in 4566bis draft

   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-11

   o  Editorial corrections based on comments from Harald Alvestrand.

   o  Editorial corrections based on comments from Cullen Jennings.

   o  Reference update (RFC 7160).

   o  Clarification about RTCP packet sending when RTP/RTCP multiplexing
      is not used (http://www.ietf.org/mail-archive/web/mmusic/current/
      msg13765.html).

   o  Additional text added to the Security Considerations.

   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-10

   o  SDP bundle-only attribute added to IANA Considerations.

   o  SDES item and RTP header extension added to Abstract and
      Introduction.

   o  Modification to text updating section 8.2 of RFC 3264.

   o  Reference corrections.

   o  Editorial corrections.

   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-09

   o  Terminology change: "bundle-only attribute assigned to m= line" to
      "bundle-only attribute associated with m= line".

   o  Editorial corrections.



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   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-08

   o  Editorial corrections.

   o  - "of"->"if" (8.3.2.5).

   o  - "optional"->"OPTIONAL" (9.1).

   o  - Syntax/ABNF for 'bundle-only' attribute added.

   o  - SDP Offer/Answer sections merged.

   o  - 'Request new offerer BUNDLE address' section added

   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-07

   o  OPEN ISSUE regarding Receiver-ID closed.

   o  - RTP MID SDES Item.

   o  - RTP MID Header Extension.

   o  OPEN ISSUE regarding insertion of SDP 'rtcp' attribute in answers
      closed.

   o  - Indicating that, when rtcp-mux is used, the answerer MUST NOT
      include an 'rtcp' attribute in the answer, based on the procedures
      in section 5.1.3 of RFC 5761.

   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-06

   o  Draft title changed.

   o  Added "SDP" to section names containing "Offer" or "Answer".

   o  Editorial fixes based on comments from Paul Kyzivat
      (http://www.ietf.org/mail-archive/web/mmusic/current/
      msg13314.html).

   o  Editorial fixed based on comments from Colin Perkins
      (http://www.ietf.org/mail-archive/web/mmusic/current/
      msg13318.html).

   o  - Removed text about extending BUNDLE to allow multiple RTP
      sessions within a BUNDLE group.

   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-05




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   o  Major re-structure of SDP Offer/Answer sections, to align with RFC
      3264 structure.

   o  Additional definitions added.

   o  - Shared address.

   o  - Bundled "m=" line.

   o  - Bundle-only "m=" line.

   o  - Offerer suggested BUNDLE mid.

   o  - Answerer selected BUNDLE mid.

   o  Q6 Closed (IETF#88): An Offerer MUST NOT assign a shared address
      to multiple "m=" lines until it has received an SDP Answer
      indicating support of the BUNDLE extension.

   o  Q8 Closed (IETF#88): An Offerer can, before it knows whether the
      Answerer supports the BUNDLE extension, assign a zero port value
      to a 'bundle-only' "m=" line.

   o  SDP 'bundle-only' attribute section added.

   o  Connection data nettype/addrtype restrictions added.

   o  RFC 3264 update section added.

   o  Indicating that a specific payload type value can be used in
      multiple "m=" lines, if the value represents the same codec
      configuration in each "m=" line.

   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-04

   o  Updated Offerer procedures (http://www.ietf.org/mail-
      archive/web/mmusic/current/msg12293.html).

   o  Updated Answerer procedures (http://www.ietf.org/mail-
      archive/web/mmusic/current/msg12333.html).

   o  Usage of SDP 'bundle-only' attribute added.

   o  Reference to Trickle ICE document added.

   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-02





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   o  Mechanism modified, to be based on usage of SDP Offers with both
      different and identical port number values, depending on whether
      it is known if the remote endpoint supports the extension.

   o  Cullen Jennings added as co-author.

   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-01

   o  No changes.  New version due to expiration.

   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-00

   o  No changes.  New version due to expiration.

   Changes from draft-holmberg-mmusic-sdp-multiplex-negotiation-00

   o  Draft name changed.

   o  Harald Alvestrand added as co-author.

   o  "Multiplex" terminology changed to "bundle".

   o  Added text about single versus multiple RTP Sessions.

   o  Added reference to RFC 3550.

19.  References

19.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
              with Session Description Protocol (SDP)", RFC 3264, June
              2002.

   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, July 2006.

   [RFC5285]  Singer, D. and H. Desineni, "A General Mechanism for RTP
              Header Extensions", RFC 5285, July 2008.

   [RFC5761]  Perkins, C. and M. Westerlund, "Multiplexing RTP Data and
              Control Packets on a Single Port", RFC 5761, April 2010.

   [RFC5888]  Camarillo, G. and H. Schulzrinne, "The Session Description
              Protocol (SDP) Grouping Framework", RFC 5888, June 2010.



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   [I-D.mmusic-sdp-mux-attributes]
              Nandakumar, S., "A Framework for SDP Attributes when
              Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-08
              (work in progress), January 2015.

19.2.  Informative References

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              June 2002.

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, July 2003.

   [RFC3605]  Huitema, C., "Real Time Control Protocol (RTCP) attribute
              in Session Description Protocol (SDP)", RFC 3605, October
              2003.

   [RFC4568]  Andreasen, F., Baugher, M., and D. Wing, "Session
              Description Protocol (SDP) Security Descriptions for Media
              Streams", RFC 4568, July 2006.

   [RFC5245]  Rosenberg, J., "Interactive Connectivity Establishment
              (ICE): A Protocol for Network Address Translator (NAT)
              Traversal for Offer/Answer Protocols", RFC 5245, April
              2010.

   [RFC5576]  Lennox, J., Ott, J., and T. Schierl, "Source-Specific
              Media Attributes in the Session Description Protocol
              (SDP)", RFC 5576, June 2009.

   [RFC5764]  McGrew, D. and E. Rescorla, "Datagram Transport Layer
              Security (DTLS) Extension to Establish Keys for the Secure
              Real-time Transport Protocol (SRTP)", RFC 5764, May 2010.

   [RFC7160]  Petit-Huguenin, M. and G. Zorn, "Support for Multiple
              Clock Rates in an RTP Session", RFC 7160, April 2014.

   [I-D.ietf-mmusic-trickle-ice]
              Ivov, E., Rescorla, E., and J. Uberti, "Trickle ICE:
              Incremental Provisioning of Candidates for the Interactive
              Connectivity Establishment (ICE) Protocol", draft-ietf-
              mmusic-trickle-ice-02 (work in progress), January 2015.






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Appendix A.  Design Considerations

A.1.  General

   One of the main issues regarding the BUNDLE grouping extensions has
   been whether, in SDP Offers and SDP Answers, the same port value
   should be inserted in "m=" lines associated with a BUNDLE group, as
   the purpose of the extension is to negotiate the usage of a single
   address:port combination for media associated with the "m=" lines.
   Issues with both approaches, discussed in the Appendix have been
   raised.  The outcome was to specify a mechanism which uses SDP Offers
   with both different and identical port values.

   Below are the primary issues that have been considered when defining
   the "BUNDLE" grouping extension:

   o  1) Interoperability with existing UAs.

   o  2) Interoperability with intermediary B2BUA- and proxy entities.

   o  3) Time to gather, and the number of, ICE candidates.

   o  4) Different error scenarios, and when they occur.

   o  5) SDP Offer/Answer impacts, including usage of port number value
      zero.

   NOTE: Before this document is published as an RFC, this
   Appendix might be removed.

A.2.  UA Interoperability

   Consider the following SDP Offer/Answer exchange, where Alice sends
   an SDP Offer to Bob:

















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   SDP Offer

       v=0
       o=alice 2890844526 2890844526 IN IP4 atlanta.example.com
       s=
       c=IN IP4 atlanta.example.com
       t=0 0
       m=audio 10000 RTP/AVP 97
       a=rtpmap:97 iLBC/8000
       m=video 10002 RTP/AVP 97
       a=rtpmap:97 H261/90000




   SDP Answer

       v=0
       o=bob 2808844564 2808844564 IN IP4 biloxi.example.com
       s=
       c=IN IP4 biloxi.example.com
       t=0 0
       m=audio 20000 RTP/AVP 97
       a=rtpmap:97 iLBC/8000
       m=video 20002 RTP/AVP 97
       a=rtpmap:97 H261/90000


   RFC 4961 specifies a way of doing symmetric RTP but that is an a
   later invention to RTP and Bob can not assume that Alice supports RFC
   4961.  This means that Alice may be sending RTP from a different port
   than 10000 or 10002 - some implementation simply send the RTP from an
   ephemeral port.  When Bob's endpoint receives an RTP packet, the only
   way that Bob know if it should be passed to the video or audio codec
   is by looking at the port it was received on.  This lead some SDP
   implementations to use the fact that each "m=" line had a different
   port number to use that port number as an index to find the correct m
   line in the SDP.  As a result, some implementations that do support
   symmetric RTP and ICE still use a SDP data structure where SDP with
   "m=" lines with the same port such as:











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   SDP Offer

       v=0
       o=alice 2890844526 2890844526 IN IP4 atlanta.example.com
       s=
       c=IN IP4 atlanta.example.com
       t=0 0
       m=audio 10000 RTP/AVP 97
       a=rtpmap:97 iLBC/8000
       m=video 10000 RTP/AVP 98
       a=rtpmap:98 H261/90000



   will result in the second "m=" line being considered an SDP error
   because it has the same port as the first line.

A.3.  Usage of port number value zero

   In an SDP Offer or SDP Answer, the media associated with an "m=" line
   can be disabled/rejected by setting the port number value to zero.
   This is different from e.g. using the SDP direction attributes, where
   RTCP traffic will continue even if the SDP "inactive" attribute is
   indicated for the associated "m=" line.

   If each "m=" line associated with a BUNDLE group would contain
   different port values, and one of those port values would be used for
   a BUNDLE address associated with the BUNDLE group, problems would
   occur if an endpoint wants to disable/reject the "m=" line associated
   with that port, by setting the port value to zero.  After that, no
   "m=" line would contain the port value which is used for the BUNDLE
   address.  In addition, it is unclear what would happen to the ICE
   candidates associated with the "m=" line, as they are also used for
   the BUNDLE address.

A.4.  B2BUA And Proxy Interoperability

   Some back to back user agents may be configured in a mode where if
   the incoming call leg contains an SDP attribute the B2BUA does not
   understand, the B2BUS still generates that SDP attribute in the Offer
   for the outgoing call leg.  Consider an B2BUA that did not understand
   the SDP "rtcp" attribute, defined in RFC 3605, yet acted this way.
   Further assume that the B2BUA was configured to tear down any call
   where it did not see any RTCP for 5 minutes.  In this cases, if the
   B2BUA received an Offer like:






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   SDP Offer

       v=0
       o=alice 2890844526 2890844526 IN IP4 atlanta.example.com
       s=
       c=IN IP4 atlanta.example.com
       t=0 0
       m=audio 49170 RTP/AVP 0
       a=rtcp:53020



   It would be looking for RTCP on port 49172 but would not see any
   because the RTCP would be on port 53020 and after five minutes, it
   would tear down the call.  Similarly, an SBC that did not understand
   BUNDLE yet put BUNDLE in it's offer may be looking for media on the
   wrong port and tear down the call.  It is worth noting that a B2BUA
   that generated an Offer with capabilities it does not understand is
   not compliant with the specifications.

A.4.1.  Traffic Policing

   Sometimes intermediaries do not act as B2BUA, in the sense that they
   don't modify SDP bodies, nor do they terminate SIP dialogs.  Still,
   however, they may use SDP information (e.g.  IP address and port) in
   order to control traffic gating functions, and to set traffic
   policing rules.  There might be rules which will trigger a session to
   be terminated in case media is not sent or received on the ports
   retrieved from the SDP.  This typically occurs once the session is
   already established and ongoing.

A.4.2.  Bandwidth Allocation

   Sometimes intermediaries do not act as B2BUA, in the sense that they
   don't modify SDP bodies, nor do they terminate SIP dialogs.  Still,
   however, they may use SDP information (e.g. codecs and media types)
   in order to control bandwidth allocation functions.  The bandwidth
   allocation is done per "m=" line, which means that it might not be
   enough if media associated with all "m=" lines try to use that
   bandwidth.  That may either simply lead to bad user experience, or to
   termination of the call.

A.5.  Candidate Gathering

   When using ICE, an candidate needs to be gathered for each port.
   This takes approximately 20 ms extra for each extra "m=" line due to
   the NAT pacing requirements.  All of this gather can be overlapped
   with other things while the page is loading to minimize the impact.



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   If the client only wants to generate TURN or STUN ICE candidates for
   one of the "m=" lines and then use trickle ICE
   [I-D.ietf-mmusic-trickle-ice] to get the non host ICE candidates for
   the rest of the "m=" lines, it MAY do that and will not need any
   additional gathering time.

   Some people have suggested a TURN extension to get a bunch of TURN
   allocation at once.  This would only provide a single STUN result so
   in cases where the other end did not support BUNDLE, may cause more
   use of the TURN server but would be quick in the cases where both
   sides supported BUNDLE and would fall back to a successful call in
   the other cases.

Authors' Addresses

   Christer Holmberg
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   Email: christer.holmberg@ericsson.com


   Harald Tveit Alvestrand
   Google
   Kungsbron 2
   Stockholm  11122
   Sweden

   Email: harald@alvestrand.no


   Cullen Jennings
   Cisco
   400 3rd Avenue SW, Suite 350
   Calgary, AB  T2P 4H2
   Canada

   Email: fluffy@iii.ca











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