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Versions: (draft-holmberg-mmusic-sdp-bundle-negotiation) 00 01 03 04 05 06 07 08

MMUSIC Working Group                                         C. Holmberg
Internet-Draft                                                  Ericsson
Updates: 3264 (if approved)                                H. Alvestrand
Intended status: Standards Track                                  Google
Expires: February 23, 2015                                   C. Jennings
                                                                   Cisco
                                                         August 22, 2014


 Negotiating Media Multiplexing Using the Session Description Protocol
                                 (SDP)
            draft-ietf-mmusic-sdp-bundle-negotiation-08.txt

Abstract

   This specification defines a new SDP Grouping Framework extension,
   "BUNDLE", that can be used with the Session Description Protocol
   (SDP) Offer/Answer mechanism to negotiate the usage of bundled media,
   which refers to the usage of a single 5-tuple for sending and
   receiving media associated with multiple SDP media descriptions ("m="
   lines).

   This specification also updates sections 5.1, 8.1 and 8.2 of RFC
   3264, in order to allow an answerer to in an SDP answer assign a non-
   zero port value to an "m=" line, even if the offerer in the
   associated SDP offer had assigned a zero port value to the "m=" line.

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/.

   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 February 23, 2015.








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Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   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 . . . . . . . . . . . . . . . . . . .   6
   5.  SDP Grouping Framework BUNDLE Extension Semantics . . . . . .   6
     5.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .   6
     5.2.  SDP Offer/Answer Procedures . . . . . . . . . . . . . . .   6
       5.2.1.  General . . . . . . . . . . . . . . . . . . . . . . .   6
       5.2.2.  SDP Information Considerations  . . . . . . . . . . .   7
       5.2.3.  Generating the Initial SDP Offer  . . . . . . . . . .   8
       5.2.4.  Generating the SDP Answer . . . . . . . . . . . . . .   8
       5.2.5.  Offerer Processing of the SDP Answer  . . . . . . . .  10
       5.2.6.  Modifying the Session . . . . . . . . . . . . . . . .  11
   6.  SDP 'bundle-only' Attribute . . . . . . . . . . . . . . . . .  13
     6.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .  13
     6.2.  SDP Offer/Answer Procedures . . . . . . . . . . . . . . .  13
       6.2.1.  Generating the Initial SDP Offer  . . . . . . . . . .  13
       6.2.2.  Generating the SDP Answer . . . . . . . . . . . . . .  13
       6.2.3.  Offerer Processing of the SDP Answer  . . . . . . . .  14
       6.2.4.  Modifying the Session . . . . . . . . . . . . . . . .  14
   7.  Protocol Identification . . . . . . . . . . . . . . . . . . .  15
     7.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .  15
     7.2.  STUN, DTLS, SRTP  . . . . . . . . . . . . . . . . . . . .  15
   8.  RTP Considerations  . . . . . . . . . . . . . . . . . . . . .  15
     8.1.  Single RTP Session  . . . . . . . . . . . . . . . . . . .  15
       8.1.1.  General . . . . . . . . . . . . . . . . . . . . . . .  16
       8.1.2.  Payload Type (PT) Value Re-usage  . . . . . . . . . .  16
     8.2.  Associating RTP/RTCP Packets With Correct SDP Media
           Description . . . . . . . . . . . . . . . . . . . . . . .  16
     8.3.  RTP/RTCP Multiplexing . . . . . . . . . . . . . . . . . .  17
       8.3.1.  General . . . . . . . . . . . . . . . . . . . . . . .  17



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       8.3.2.  SDP Offer/Answer Procedures . . . . . . . . . . . . .  18
   9.  ICE Considerations  . . . . . . . . . . . . . . . . . . . . .  19
     9.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .  19
     9.2.  SDP Offer/Answer Procedures . . . . . . . . . . . . . . .  20
       9.2.1.  Generating the Initial SDP Offer  . . . . . . . . . .  20
       9.2.2.  Generating the SDP Answer . . . . . . . . . . . . . .  20
       9.2.3.  Offerer Processing of the SDP Answer  . . . . . . . .  20
       9.2.4.  Modifying the Session . . . . . . . . . . . . . . . .  20
       9.2.5.  Keep-alives . . . . . . . . . . . . . . . . . . . . .  20
   10. Update to RFC 3264  . . . . . . . . . . . . . . . . . . . . .  20
     10.1.  General  . . . . . . . . . . . . . . . . . . . . . . . .  20
     10.2.  Original text of section 5.1 (2nd paragraph) of RFC 3264  21
     10.3.  New text replacing section 5.1 (2nd paragraph) of RFC
            3264 . . . . . . . . . . . . . . . . . . . . . . . . . .  21
     10.4.  Original text of section 8.2 (2nd paragraph) of RFC 3264  21
     10.5.  New text replacing section 8.2 (2nd paragraph) of RFC
            3264 . . . . . . . . . . . . . . . . . . . . . . . . . .  22
     10.6.  Original text of section 8.4 (6th paragraph) of RFC 3264  22
     10.7.  New text replacing section 8.4 (6th paragraph) of RFC
            3264 . . . . . . . . . . . . . . . . . . . . . . . . . .  22
   11. RTP/RTCP extensions for mid value transport . . . . . . . . .  22
     11.1.  General  . . . . . . . . . . . . . . . . . . . . . . . .  22
     11.2.  RTP MID SDES Item  . . . . . . . . . . . . . . . . . . .  23
     11.3.  RTP MID Header Extension . . . . . . . . . . . . . . . .  24
     11.4.  IANA Considerations  . . . . . . . . . . . . . . . . . .  24
   12. Security Considerations . . . . . . . . . . . . . . . . . . .  24
   13. Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  25
     13.1.  Example: Bundle Address Selection  . . . . . . . . . . .  25
     13.2.  Example: Bundle Mechanism Rejected . . . . . . . . . . .  26
     13.3.  Example: Offerer Adds A Media Description To A BUNDLE
            Group  . . . . . . . . . . . . . . . . . . . . . . . . .  27
     13.4.  Example: Offerer Moves A Media Description Out Of A
            BUNDLE Group . . . . . . . . . . . . . . . . . . . . . .  29
     13.5.  Example: Offerer Disables A Media Description Within A
            BUNDLE Group . . . . . . . . . . . . . . . . . . . . . .  31
   14. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  33
   15. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  33
   16. Change Log  . . . . . . . . . . . . . . . . . . . . . . . . .  33
   17. References  . . . . . . . . . . . . . . . . . . . . . . . . .  35
     17.1.  Normative References . . . . . . . . . . . . . . . . . .  35
     17.2.  Informative References . . . . . . . . . . . . . . . . .  36
   Appendix A.  Design Considerations  . . . . . . . . . . . . . . .  36
     A.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .  37
     A.2.  UA Interoperability . . . . . . . . . . . . . . . . . . .  37
     A.3.  Usage of port number value zero . . . . . . . . . . . . .  39
     A.4.  B2BUA And Proxy Interoperability  . . . . . . . . . . . .  39
       A.4.1.  Traffic Policing  . . . . . . . . . . . . . . . . . .  40
       A.4.2.  Bandwidth Allocation  . . . . . . . . . . . . . . . .  40



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     A.5.  Candidate Gathering . . . . . . . . . . . . . . . . . . .  40
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  40

1.  Introduction

   In the IETF RTCWEB WG, a need to use a single 5-tuple for sending and
   receiving media associated with multiple SDP media descriptions ("m="
   lines) has been identified.  This would e.g. allow the usage of a
   single set of Interactive Connectivity Establishment (ICE) [RFC5245]
   candidates for multiple media descriptions.  Normally different media
   types (audio, video etc) will be described using different media
   descriptions.

   This specification defines a new SDP Grouping Framework [RFC5888]
   extension, "BUNDLE", that can be used with the Session Description
   Protocol (SDP) Offer/Answer mechanism [RFC3264] to negotiate the
   usage of bundled media, which refers to the usage of a single 5-tuple
   for sending and receiving media associated with multiple SDP media
   descriptions ("m=" lines).

   The offerer and answerer [RFC3264] use the BUNDLE mechanism to
   negotiate BUNDLE addresses, one for the offerer (offerer BUNDLE
   address) and one for the answerer (answerer BUNDLE address) to be
   used for the bundled media associated with a BUNDLE group.

   Once the offerer and the answerer have negotiated a BUNDLE group, and
   the associated BUNDLE addresses, each endpoint can assign its BUNDLE
   address to each "m=" line within, and use the address to send and
   receive all media associated with, the BUNDLE group.

   NOTE: 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.

   SDP bodies can contain multiple BUNDLE groups.  Each BUNDLE group
   MUST use a unique 5-tuple.  Any given "m=" line can only be
   associated with a single BUNDLE group.

   The procedures in this specification apply independently to a given
   BUNDLE group.

   All Real-time Transport Protocol (RTP) [RFC3550] based media flows
   associated with a single BUNDLE group belong to a single RTP session
   [RFC3550].





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

   This specification also updates sections 5.1, 8.1 and 8.2 of
   [RFC3264], in order to allow an answerer to assign a non-zero port
   value to an "m=" line in an SDP answer, even if the offerer in the
   associated SDP offer had assigned a zero port value to the "m=" line.

2.  Terminology

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

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

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

   Offerer suggested BUNDLE mid: The first mid value in a given SDP
   'group:BUNDLE' attribute mid list in an SDP offer.

   Answerer selected BUNDLE mid: The first mid value in a given SDP
   'group:BUNDLE' attribute mid list in an SDP answer.

   Offerer BUNDLE address: Within a given BUNDLE group, an IP address
   and IP 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 IP 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, for which a single 5-tuple is used to send and receive
   media.  Each endpoint uses its BUNDLE address, associated with the
   BUNDLE group, to send and receive the media.

   Bundled "m=" line: An "m=" line, in an SDP offer or SDP answer,
   associated with a BUNDLE group.

   Bundle-only "m=" line: An "m=" line, to which an SDP 'bundle-only'
   attribute has been assigned.

   Bundled media: All media associated with a BUNDLE group.



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   Initial SDP offer: The first SDP offer, within an SDP session, in
   which the offerer indicates that it wants to create a given BUNDLE
   group.

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

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].

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].

5.  SDP Grouping Framework BUNDLE Extension Semantics

5.1.  General

   This section defines a new SDP Grouping Framework extension, BUNDLE.

   The BUNDLE extension can be indicated using an SDP session-level
   'group' attribute.  Each SDP Media Description ("m=" line) that is
   grouped together, using SDP media-level mid attributes, belongs to a
   given BUNDLE group.

5.2.  SDP Offer/Answer Procedures

5.2.1.  General

   This section describes usage of the SDP offer/answer mechanism
   [RFC3264] for negotiating usage of the BUNDLE mechanism, for creating
   a BUNDLE group, for selecting the BUNDLE addresses (offerer BUNDLE
   address and answerer BUNDLE address), for adding an "m=" line to a
   BUNDLE group, for moving an "m=" line out of a BUNDLE group, and for
   disabling an "m=" line within a BUNDLE group.

   The generic rules and procedures defined in [RFC3264] and [RFC5888]
   also apply to the BUNDLE mechanism.  For example, if an SDP 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 SDP offer in which the




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

   The procedures in this section are independent of the media type or
   transport protocol represented by a bundled "m=" line.  [Section 8]
   defines additional considerations for RTP based media.  [Section 6]
   defines additional considerations for the usage of the SDP 'bundle-
   only' attribute.  [Section 9] defines additional considerations for
   the usage of Interactive Connectivity Establishment (ICE) mechanism
   [RFC5245].

5.2.2.  SDP Information Considerations

5.2.2.1.  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 assigned to each bundled "m=" line,
   how to calculate a value for the whole BUNDLE group.

5.2.2.2.  Connection Data (c=)

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

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

5.2.2.3.  Bandwidth (b=)

   The total proposed bandwidth is the sum of the proposed bandwidth for
   each bundled "m=" line.

5.2.2.4.  Attributes (a=)

   [I-D.nandakumar-mmusic-sdp-mux-attributes] defines rules and
   restrictions for assigning different types of SDP attributes to a
   bundled "m=" line.








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5.2.3.  Generating the Initial SDP Offer

5.2.3.1.  General

   When an offerer generates an initial SDP offer, in order to create a
   BUNDLE group, the offerer MUST in the SDP offer assign a unique
   address to each "m=" line with a non-zero port value, following the
   procedures in [RFC3264].

   The offerer MUST in the SDP offer insert an SDP session level
   'group:BUNDLE' attribute, associated with the BUNDLE group, and
   assign an SDP 'mid' attribute [RFC5888] to each "m=" line that the
   offerer wants to be within the BUNDLE group, and place the 'mid'
   attribute value in the 'group:BUNDLE' attribute mid list.

   [Section 13.1] shows an example of an initial SDP offer.

5.2.3.2.  Request offerer BUNDLE address selection

   When an offerer generates an initial SDP offer, in order to create a
   BUNDLE group, the offerer MUST in the SDP offer indicate which unique
   address, associated with one of the "m=" lines that the offerer wants
   to be within the BUNDLE group, that the offerer wants the answerer to
   select as the offerer BUNDLE address [Section 5.2.4.2].  In the SDP
   offer, the offerer BUNDLE mid value represents that address.

5.2.4.  Generating the SDP Answer

5.2.4.1.  RFC 5888 restrictions

   When an answerer generates an SDP answer, the following restrictions,
   defined in [RFC5888], also apply a BUNDLE group:

   o  1) The answerer MUST NOT in the SDP answer include a BUNDLE group,
      unless the offerer in the associated SDP offer requested the
      BUNDLE group to be created; and

   o  2) The answerer MUST NOT in the SDP answer include an "m=" line
      within a BUNDLE group, unless the offerer in the associated SDP
      offer requested the "m=" line to be within the BUNDLE group.

5.2.4.2.  Answerer Selection of Offerer Bundle Address

   When an answerer generates an SDP answer, it MUST select a BUNDLE
   address for the offerer, referred to as the offerer BUNDLE address.
   The answerer MUST select an address which the offerer in the
   associated SDP offer requested to be within the BUNDLE group.




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   In the SDP offer, the offerer suggested BUNDLE mid represents the
   "m=" line to which the offerer in the SDP offer has assigned the
   address that it wants the answerer to select as the offerer BUNDLE
   address [Section 5.2.3.2].  The answerer MUST first select the "m="
   line associated with the offerer suggested BUNDLE mid, and check
   whether it fulfils the following criteria:

   o  The answerer will in the SDP answer create the BUNDLE group;

   o  The answerer will not in the SDP answer move the "m=" line out of
      the BUNDLE group [Section 5.2.4.4];

   o  The answerer will not in the SDP answer reject the "m=" line
      [Section 5.2.4.5]; and

   o  The offerer did not in the associated SDP offer assign a zero port
      value to the "m=" line.

   If all of the criteria above is fulfilled, the answerer MUST select
   the address associated with the "m=" line as the offerer BUNDLE
   address.

   If all of the criteria is not fulfilled, the answerer MUST select the
   next mid value in the mid list, and perform the same criteria check
   for the "m=" line associated with the mid value.

   In the SDP answer, the answerer selected BUNDLE mid value represents
   the "m=" line which address (in the associated SDP offer) the
   answerer has selected as the offerer BUNDLE address.

   [Section 13.1] shows an example of an offerer BUNDLE address
   selection.

5.2.4.3.  Answerer Selection of Answerer BUNDLE Address

   When an answerer generates an SDP answer, the answerer MUST select a
   BUNDLE address for itself, referred to as the answerer BUNDLE
   address, and in the SDP answer assign the answerer BUNDLE address to
   each "m=" line within the created BUNDLE group.

   The answerer MUST NOT in the SDP answer assign the answerer BUNDLE
   address to an "m=" line that is not associated with the BUNDLE group,
   or to an "m=" line that is associated with another BUNDLE group.

   The answerer is allowed to select a new answerer BUNDLE address in
   every SDP answer that the answerer generates.





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   [Section 13.1] shows an example of an answerer BUNDLE address
   selection.

5.2.4.4.  Moving A Media Description Out Of A BUNDLE Group

   When an answerer generates an SDP answer, in which the answerer moves
   a bundled "m=" line out a BUNDLE group, the answerer assigns an
   address to the moved "m=" line based on the type of address that the
   offerer in the associated SDP offer assigned to the "m=" line.

   o  If the offerer in the SDP offer has assigned a shared address
      (e.g. a previously selected offerer BUNDLE address) to the "m="
      line, the answerer MUST in the SDP answer reject the moved "m="
      line, according to the procedures in [Section 5.2.4.5].

   o  If the offerer in the SDP offer assigned an SDP 'bundle-only'
      attribute to the "m=" line, the answerer MUST in the SDP answer
      reject the moved "m=" line, according to the procedures in
      [Section 5.2.4.5].

   o  If the offerer in the SDP offer assigned a unique address to the
      "m=" line, the answerer MUST in the SDP answer assign a unique
      address to the moved "m=" line.

   In addition, in either case above, the answerer MUST NOT in the SDP
   answer include a mid value, associated with the moved "m=" line, in
   the SDP 'group:BUNDLE' attribute mid list associated with the BUNDLE
   group.

5.2.4.5.  Rejecting A Media Description In A BUNDLE Group

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

   In addition, the answerer MUST NOT in the SDP answer include a mid
   value, associated with the rejected "m=" line, in the SDP
   'group:BUNDLE' attribute mid list associated with the BUNDLE group.

5.2.5.  Offerer Processing of the SDP Answer

5.2.5.1.  General

   When an offerer receives an SDP answer, the offerer MUST apply the
   selected offerer BUNDLE address to each bundled "m=" line.  If the
   offerer generates a subsequent SDP offer, the offerer MUST in the SDP




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   offer assign the offerer BUNDLE address to each bundled "m=" line
   (including any 'bundle-only' "m=" line) [Section 5.2.6].

   If the SDP answer does not contain a BUNDLE group, the offerer MUST
   cease to use any procedure associated with the BUNDLE mechanism.

5.2.5.2.  Bundle Address Synchronization (BAS)

   If the selected offerer BUNDLE address is different than the address
   that the offerer in the associated SDP offer assigned to a bundled
   "m=" line (including an "m=" line that the offerer in the SDP offer
   added to an existing BUNDLE group [Section 5.2.6.2]), and the bundled
   "m=" line was not rejected [Section 5.2.4.5], or moved out of the
   BUNDLE group [Section 5.2.4.4] by the answerer, the offerer SHOULD as
   soon as possible generate a subsequent SDP offer, in which the
   offerer assigns the offerer BUNDLE address to each bundled "m=" line.
   This procedure is referred to as Bundle Address Synchronization
   (BAS), and the SDP offer is referred to as a BAS Offer.

   The offerer MAY in the BAS offer modify any SDP parameter.

   NOTE: It is important that the BAS offer gets accepted by the
   answerer.  For that reason the offerer needs to consider the
   necessity to in the BAS offer modify SDP parameters that could get
   the answerer to reject the BAS offer.  Disabling "m=" lines, or
   reducing the number of codecs, in a BAS offer is considered to have a
   low risk of being rejected.

   NOTE: The main purpose of the BAS offer is to ensure that
   intermediaries, that might not support the BUNDLE mechanism, have
   correct information regarding the address is going to be used to
   transport the bundled media.

   [Section 13.1] shows an example where an offerer sends a BAS offer.

5.2.6.  Modifying the Session

5.2.6.1.  General

   When an offerer generates a subsequent SDP offer, the offerer MUST in
   the SDP offer assign the previously selected offerer BUNDLE address
   [Section 5.2.4.2] to each bundled "m=" line (including any bundle-
   only "m=" line), unless the offerer in the SDP offer moves the "m="
   line out of the BUNDLE group [Section 5.2.6.3], or disables the "m="
   line [Section 5.2.6.4].






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   If the SDP offerer in the SDP offer adds an "m=" line to the BUNDLE
   group [Section 5.2.6.2], the offerer MAY assign the previously
   selected offerer BUNDLE address to the added "m=" line.

   In addition, the offerer MUST in the SDP offer indicate which address
   (unique or previously selected offerer BUNDLE address) it wants the
   answerer to select as the offerer BUNDLE address, following the
   procedures in [Section 5.2.3.2].  The offerer MUST do this even if
   the offerer in the SDP offer assigns a previously selected offerer
   BUNDLE address to each bundled "m=" line.

5.2.6.2.  Adding a media description to a BUNDLE group

   When an offerer generates an SDP offer, in which the offerer wants to
   add an "m=" line to a BUNDLE group, the offerer assigns in the SDP
   offer an address (unique or previously selected offerer BUNDLE
   address) to the "m=" line, assigns an SDP 'mid' attribute to the "m="
   line, and places the mid value in the SDP 'group:BUNDLE' attribute
   mid list associated with the BUNDLE group [Section 5.2.3.2].

   NOTE: If the offerer wants the answerer to select the address
   associated with the added "m=" as the offerer BUNDLE address, the
   offerer suggested BUNDLE mid MUST represent the added "m=" line
   [Section 5.2.3.2].

   [Section 13.3] shows an example where an offerer sends an SDP offer
   in order to add an "m=" line to a BUNDLE group.

5.2.6.3.  Moving A Media Description Out Of A BUNDLE Group

   When an offerer generates an SDP offer, in which the offerer wants to
   move a bundled "m=" line out of a BUNDLE group, the offerer MUST
   assign a unique address to the "m=" line.  In addition, the offerer
   MUST NOT place a mid value associated with the "m=" line in the SDP
   'group:BUNDLE' attribute mid list associated with the BUNDLE group.

   NOTE: The offerer MAY keep a previously assigned SDP 'mid' attribute
   in an "m=" line that it wants to move out of a BUNDLE group, e.g. if
   the mid value is used for some other SDP grouping extension than
   BUNDLE.

   [Section 13.4] shows an example where an offerer sends an SDP offer
   in order to move an "m=" line out of a BUNDLE group.








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5.2.6.4.  Disabling A Media Description In A BUNDLE Group

   When an offerer generates an SDP offer, in which the offerer wants to
   disable a bundled "m=" line, the offerer MUST assign an address with
   a zero port alue to the "m=" line, following the procedures in
   [RFC4566].  In addition, the offerer MUST NOT place a mid value
   associated with the "m=" line in the SDP 'group:BUNDLE' attribute mid
   list associated with the BUNDLE group.

   NOTE: The offerer MAY assign an SDP 'mid' attribute to an "m=" line
   that it wants to disable, e.g. if the mid value is used for some
   other SDP grouping extension than BUNDLE.

   [Section 13.5] shows an example where an offerer sends an SDP offer
   in order to disable an "m=" line within a BUNDLE group.

6.  SDP 'bundle-only' Attribute

6.1.  General

   This section defines a new SDP media-level attribute [RFC4566],
   'bundle-only'.  An offerer can in an SDP offer assign a 'bundle-only'
   "m=" line to a bundled "m=" line (including an "m=" line that the
   offerer wants to add to the BUNDLE group [Section 5.2.6.2]), in order
   to ensure that the answerer only accepts the "m=" line if the
   answerer supports the BUNDLE mechanism, and if the answerer in the
   SDP answer keeps the "m=" line within the BUNDLE group.

6.2.  SDP Offer/Answer Procedures

6.2.1.  Generating the Initial SDP Offer

   When an offerer generates an initial SDP offer, in order to create a
   BUNDLE group, the offerer can in the SDP offer assign an SDP 'bundle-
   only' attribute to an "m=" line that the offerer wants to be within
   the BUNDLE group.

   The offerer MUST in the SDP offer assign a zero port value the
   bundle-only "m=" line.

6.2.2.  Generating the SDP Answer

   When the answerer selects the offerer BUNDLE address
   [Section 5.2.4.2], the answerer MUST also take a bundle-only "m="
   line with a non-zero port value into consideration.

   If the offerer in the SDP offer has assigned a zero port value to a
   bundle-only "m=" line, and if the answerer accepts the "m=" line, the



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   answerer will treat the "m=" line as any other bundle "m=" line when
   the answerer generates the SDP answer [Section 5.2.4].

   NOTE: If the offerer in the SDP offer has assigned a zero port value
   to a bundled "m=" line, but the offerer has not assigned a 'bundle-
   only' SDP attribute to the "m=" line, it is an indication that the
   offerer wants to disable the "m=" line [Section 5.2.6.4].

   If the answerer in the SDP answer does not keep the bundle-only "m="
   line within the BUNDLE group, the answerer MUST in the SDP answer
   reject the "m=" line [Section 5.2.4.5].

   The answerer MUST NOT in the SDP answer assign an SDP 'bundle-only'
   attribute to an "m=" line (even if the offerer in the associated SDP
   offer has assigned a 'bundle-only' attribute to the "m="line).

6.2.3.  Offerer Processing of the SDP Answer

   When the offerer receives an SDP answer, the offerer follows the
   procedures in [Section 5.2.5].  If the offerer in the associated SDP
   offer assigned an SDP 'bundle-only' attribute to an "m=" line, and
   the "m=" line was accepted (and was kept within the BUNDLE group) by
   the answerer, the selected offerer BUNDLE address also applies to the
   "m=" line.

6.2.4.  Modifying the Session

   When an offerer creates a subsequent SDP offer, the offerer follows
   the procedures in [Section 5.2.6].  If the offerer in the SDP offer
   assigns an SDP 'bundle-only' attribute to a bundled "m=" line, in
   order to ensure that the answerer accepts the "m=" line only if the
   answerer keeps the "m=" line within the BUNDLE group, the offerer
   MUST NOT assign a zero port value to the "m=" line.  Instead, the
   offerer MUST in the SDP offer assign the offerer BUNDLE address or,
   if the "m=" line is added to the BUNDLE group [Section 5.2.6.2],
   either the offerer BUNDLE address or a unique address, to the "m="
   line.

   NOTE: The offerer can in a subsequent SDP offer assign an SDP
   'bundle-only' attribute to a bundled "m=" line even if the offerer
   did not assign a 'bundle-only' attribute to the "m=" line in a
   previous SDP offer.

   If the offerer in the SDP offer wants to move a bundled "m=" line out
   of a BUNDLE group [Section 5.2.6.3], the offerer MUST NOT in the SDP
   offer assign a 'bundle-only' attribute to the "m=" line.





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   If the offerer in the SDP offer wants to disable a bundled "m=" line
   [Section 5.2.6.4], the offerer MUST NOT in the SDP offer assign a
   'bundle-only' attribute to the "m=" line.

7.  Protocol Identification

7.1.  General

   If bundled "m=" lines represent different transport protocols, there
   MUST exist a specification which describes a mechanism, for this
   specific transport protocol combination, how to associate a received
   packet with the correct transport protocol.

   In addition, if a received packet can be associated with more than
   one bundled "m=" line, there MUST exist a specification which
   describes a mechanism how to associated the received packet with the
   correct "m=" line.

7.2.  STUN, DTLS, SRTP

   Section 5.1.2 of [RFC5764] describes a mechanism how to identify the
   protocol among the STUN, DTLS and SRTP protocols (in any
   combination).  If an offer or answerer in SDP offers or answers
   include 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 how to identify 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 how to associate the received DTLS packet with
   the correct "m=" line.

   [Section 8.2] describes how to associate a received (S)RTP packet
   with the correct "m=" line.

8.  RTP Considerations

8.1.  Single RTP Session








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8.1.1.  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 8.1.2].

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

   o  A given SSRC SHOULD NOT transmit RTP packets using payload types
      that originates 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 fails to function.  Even if done in
   proper sequence this causes RTP Timestamp rate switching issues [ref
   to draft-ietf-avtext-multiple-clock-rates].

8.1.2.  Payload Type (PT) Value Re-usage

   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 used inside more
   than one bundled "m=" line, all codecs associated with the payload
   type numbers 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.nandakumar-mmusic-sdp-mux-attributes] lists SDP
   attributes, which attribute values must be identical for all codecs
   that use the same payload type value.

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

   In general, there are multiple mechanisms that can be used by an
   endpoint in order to associate received RTP/RTCP packets with the
   bundled "m=" line representing the RTP packets.  Such mechanisms
   include using the local address:port combination on which the RTP
   packets are received, the payload type value carried inside the RTP



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   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 sent and
   received using the same 5-tuple, the local address:port combination
   cannot be used to associate received RTP packets with the correct
   "m=" line.

   As described in [Section 8.1.2], 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.

   An offerer and answerer can in an SDP offer and answer inform each
   other which SSRC values they will use inside sent RTP/RTCP packets
   by, by assigning an SDP 'ssrc' attribute [RFC5576] to 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 SDP answer providing that
   information.  Due to this, before the offerer has received the SDP
   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 mechanism MUST use the mechanism
   defined in Section 11, where the remote endpoint inserts the SDP
   'mid' attribute value of an "m=" line in RTP and RTCP packets
   associated with that "m=" line.

8.3.  RTP/RTCP Multiplexing

8.3.1.  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 5-tuples will be
   used for sending and receiving the RTP packets and the RTCP packets.







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8.3.2.  SDP Offer/Answer Procedures

8.3.2.1.  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 associated
   with a BUNDLE group.

8.3.2.2.  Generating the Initial SDP Offer

   When an offerer generates an initial SDP offer, if the offerer wants
   to negotiate usage of RTP/RTCP multiplexing within a BUNDLE group,
   the offerer MUST in the SDP offer assign an SDP 'rtcp-mux' attribute
   [RFC5761] to each bundled "m=" line (including any bundle-only "m="
   line).  In addition, the offerer MUST in the SDP offer assign an SDP
   'rtcp' attribute [RFC3605] to each bundled "m=" line (including any
   bundle-only "m=" line), with an attribute value that is identical to
   the port value assigned to the "m=" line itself.

   If the offerer does not want to negotiate usage of RTP/RTCP
   multiplexing, the offerer MUST NOT assign the SDP attributes above to
   any bundled "m=" line.

8.3.2.3.  Generating the SDP Answer

8.3.2.3.1.  Generating the SDP Answer to an Initial SDP Offer

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

   If the answerer accepts usage of RTP/RTCP multiplexing within the
   BUNDLE group, the answerer MUST in the SDP answer assign an SDP
   'rtcp-mux' attribute to each bundled "m=" line.  The answerer MUST
   NOT in the SDP answer assign an SDP 'rtcp' attribute to any bundled
   "m=" line.

   If the answerer rejects usage of RTP/RTCP multiplexing within the
   BUNDLE group, the answerer MUST NOT in the SDP answer assign an SDP
   'rtcp-mux' or SDP 'rtcp' attribute to any bundled "m=" line.








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8.3.2.3.2.  Generating the SDP Answer to a Subsequent SDP Offer

   When the answerer generates an SDP answer to a subsequent SDP offer,
   if the offerer in the associated SDP offer indicated support of RTP/
   RTCP multiplexing [RFC5761] within a BUNDLE group, the answerer MUST
   in the SDP answer assign an SDP 'rtcp-mux' attribute and SDP 'rtcp'
   attribute to each bundled "m=" line.

   NOTE: The BUNDLE mechanism does not allow the answerer to, in a
   subsequent SDP answer, disable usage of RTP/RTCP multiplexing, if the
   offerer in the associated SDP offer indicates that it wants to
   continue using RTP/RTCP multiplexing.

8.3.2.4.  Offerer Processing of the SDP Answer

   When the offerer receives an SDP answer, it follows the procedures
   defined in [RFC5245].

8.3.2.5.  Modifying the Session

   When an offerer generates a subsequent SDP offer, if the offerer
   wants to negotiate usage of RTP/RTCP multiplexing within a BUNDLE
   group, or if the offerer wants to continue usage of previously
   negotiated RTP/RTCP multiplexing within the BUNDLE group, the offerer
   MUST in the SDP offer assign 'rtcp-mux' and 'rtcp' attributes to each
   bundled "m=" line (including bundle-only "m=" lines), unless the "m="
   line is disabled or removed from the BUNDLE group.

   If the offerer does not want to negotiate usage of RTP/RTCP
   multiplexing within the BUNDLE group, or if the offerer wants to
   disable previously negotiated usage of RTP/RTCP multiplexing within a
   BUNDLE group, the offerer MUST NOT in the SDP offer assign 'rtcp-mux'
   and 'rtcp' attributes to any bundled "m=" line.

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

9.  ICE Considerations

9.1.  General

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




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

9.2.  SDP Offer/Answer Procedures

9.2.1.  Generating the Initial SDP Offer

   When an offerer generates an initial SDP offer, which contains a
   BUNDLE group, the offerer MUST assign ICE candidates [RFC5245] to
   each bundled "m=" line, except to an "m=" line to which the offerer
   assigns a zero port value (e.g. a bundle-only "m=" line).  The
   offerer MUST assign unique ICE candidate values to each "m=" line.

9.2.2.  Generating the SDP Answer

   When an answerer generates and SDP Answer, which contains a BUNDLE
   group, the answerer MUST assign ICE candidates to each bundled "m="
   line.  The answerer MUST assign identical ICE candidate values to
   each bundled "m=" line.

9.2.3.  Offerer Processing of the SDP Answer

   When the offerer receives an SDP answer, it follows the procedures
   defined in [RFC5245].

9.2.4.  Modifying the Session

   When an offerer generates a subsequent SDP offer, for each bundled
   "m=" line to which the offerer assigns its BUNDLE address, the
   offerer MUST assign identical ICE candidate values.  The offerer MUST
   assign the ICE candidate values associated with the "m=" line that
   was used by the answerer to select the offerer BUNDLE address [ref-
   to-be-added].

9.2.5.  Keep-alives

   Once it is known that both endpoints support, and accept to use, the
   BUNDLE grouping extension, ICE connectivity checks and keep-alives
   only needs to be performed for the whole BUNDLE group, instead of for
   each bundled "m=" line.

10.  Update to RFC 3264

10.1.  General

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

   o  Section 5.1 (Unicast Streams).



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   o  Section 8.2 (Removing a Media Stream).

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

10.2.  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.

10.3.  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.

10.4.  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.






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10.5.  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.

10.6.  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.

10.7.  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.

11.  RTP/RTCP extensions for mid value transport

11.1.  General

   SDP Offerers and Answerers [RFC3264] can assign values, mid values,
   to SDP Media Descriptions (m= lines) within SDP Offers and Answers,
   using the procedures in [RFC5888].  Each mid value uniquely
   references an m= line.





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   This section defines a new RTP SDES item [RFC3550], 'MID', which is
   used to carry mid values within RTCP SDES packets.  This section also
   defines a new RTP header extension [RFC5285], which can be used to
   carry the mid value in RTP packets.

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

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

   The RTP 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 mid value.

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

11.2.  RTP 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    | mid value                   ...
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




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   The mid value payload is UTF-8 encoded, as in SDP.

11.3.  RTP MID Header Extension

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

11.4.  IANA Considerations

   [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 "RTP SDES item
   types" registry as follows:


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


   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


12.  Security Considerations

   This specification does not significantly change the security
   considerations of SDP which can be found in Section X of TBD.

   TODO: Think carefully about security analysis of reuse of same SDES
   key on multiple "m=" lines when the far end does not use BUNDLE and
   warn developers of any risks.





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13.  Examples

13.1.  Example: Bundle Address Selection

   The example below shows:

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

   o  2.  An SDP 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.

   o  3.  A subsequent SDP offer (BAS offer), which is used to perform a
      Bundle Address Synchronization (BAS).


   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
       a=mid:foo
       b=AS:200
       a=rtpmap:0 PCMU/8000
       a=rtpmap:8 PCMA/8000
       a=rtpmap:97 iLBC/8000
       m=video 10002 RTP/AVP 31 32
       a=mid:bar
       b=AS:1000
       a=rtpmap:31 H261/90000
       a=rtpmap:32 MPV/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



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       a=mid:foo
       b=AS:200
       a=rtpmap:0 PCMU/8000
       m=video 20000 RTP/AVP 32
       a=mid:bar
       b=AS:1000
       a=rtpmap:32 MPV/90000


   SDP Offer (3)

       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
       a=mid:foo
       b=AS:200
       a=rtpmap:0 PCMU/8000
       a=rtpmap:8 PCMA/8000
       a=rtpmap:97 iLBC/8000
       m=video 10000 RTP/AVP 31 32
       a=mid:bar
       b=AS:1000
       a=rtpmap:31 H261/90000
       a=rtpmap:32 MPV/90000


13.2.  Example: Bundle Mechanism Rejected

   The example below shows:

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

   o  2.  An SDP 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
       a=mid:foo
       b=AS:200
       a=rtpmap:0 PCMU/8000
       a=rtpmap:8 PCMA/8000
       a=rtpmap:97 iLBC/8000
       m=video 10002 RTP/AVP 31 32
       a=mid:bar
       b=AS:1000
       a=rtpmap:31 H261/90000
       a=rtpmap:32 MPV/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
       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



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

   The example below shows:

   o  1.  An SDP offer, in which the offerer adds a new "m=" line,
      represented by the "zen" mid value, to a previously negotiated
      BUNDLE group, assigns a unique address to the added "m=" line, and
      assigns the previously selected offerer BUNDLE address to each of
      the other bundled "m=" lines within the BUNDLE group.





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   o  2.  An SDP 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.

   o  3.  A subsequent SDP offer (BAS offer), which is used to perform a
      Bundle Address Synchronization (BAS).


   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
       a=mid:foo
       b=AS:200
       a=rtpmap:0 PCMU/8000
       a=rtpmap:8 PCMA/8000
       a=rtpmap:97 iLBC/8000
       m=video 10000 RTP/AVP 31 32
       a=mid:bar
       b=AS:1000
       a=rtpmap:31 H261/90000
       a=rtpmap:32 MPV/90000
       m=video 20000 RTP/AVP 66
       a=mid:zen
       b=AS:1000
       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 zen
       m=audio 20000 RTP/AVP 0
       a=mid:foo
       b=AS:200
       a=rtpmap:0 PCMU/8000
       m=video 20000 RTP/AVP 32
       a=mid:bar
       b=AS:1000



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       a=rtpmap:32 MPV/90000
       m=video 20000 RTP/AVP 66
       a=mid:zen
       b=AS:1000
       a=rtpmap:66 H261/90000


   SDP Offer (3)

       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
       a=mid:foo
       b=AS:200
       a=rtpmap:0 PCMU/8000
       a=rtpmap:8 PCMA/8000
       a=rtpmap:97 iLBC/8000
       m=video 10000 RTP/AVP 31 32
       a=mid:bar
       b=AS:1000
       a=rtpmap:31 H261/90000
       a=rtpmap:32 MPV/90000
       m=video 10000 RTP/AVP 66
       a=mid:zen
       b=AS:1000
       a=rtpmap:66 H261/90000



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

   The example below shows:

   o  1.  An SDP offer, 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 SDP 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 other
      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
       a=mid:foo
       b=AS:200
       a=rtpmap:0 PCMU/8000
       a=rtpmap:8 PCMA/8000
       a=rtpmap:97 iLBC/8000
       m=video 10000 RTP/AVP 31 32
       a=mid:bar
       b=AS:1000
       a=rtpmap:31 H261/90000
       a=rtpmap:32 MPV/90000
       m=video 50000 RTP/AVP 66
       b=AS:1000
       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
       a=mid:foo
       b=AS:200
       a=rtpmap:0 PCMU/8000
       m=video 20000 RTP/AVP 32
       a=mid:bar
       b=AS:1000
       a=rtpmap:32 MPV/90000
       m=video 60000 RTP/AVP 66
       b=AS:1000
       a=rtpmap:66 H261/90000








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

   The example below shows:

   o  1.  An SDP offer, in which the offerer disables a bundled "m="
      line within BUNDLE group, assigns a zero port number 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 SDP answer, in which the answerer moves the disabled "m="
      line out of the BUNDLE group, assigns a zero port value to the
      disabled "m=" line, and assigns the answerer BUNDLE address to
      each of the other bundled "m=" lines 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
       a=mid:foo
       b=AS:200
       a=rtpmap:0 PCMU/8000
       a=rtpmap:8 PCMA/8000
       a=rtpmap:97 iLBC/8000
       m=video 10000 RTP/AVP 31 32
       a=mid:bar
       b=AS:1000
       a=rtpmap:31 H261/90000
       a=rtpmap:32 MPV/90000
       m=video 0 RTP/AVP 66
       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
       a=mid:foo
       b=AS:200
       a=rtpmap:0 PCMU/8000
       m=video 20000 RTP/AVP 32
       a=mid:bar
       b=AS:1000
       a=rtpmap:32 MPV/90000
       m=video 0 RTP/AVP 66
       a=rtpmap:66 H261/90000










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14.  IANA Considerations

   This document requests IANA to register the new SDP Grouping semantic
   extension called BUNDLE.

15.  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 mechanism 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 and Martin Thompson for taking the the time to
   read the text along the way, and providing useful feedback.

16.  Change Log

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

   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 SDP
      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).



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   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

   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 mechanism.

   o  Q8 Closed (IETF#88): An Offerer can, before it knows whether the
      Answerer supports the BUNDLE mechanism, 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).





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   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

   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.

17.  References

17.1.  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.



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   [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.

   [I-D.nandakumar-mmusic-sdp-mux-attributes]
              Nandakumar, S., "A Framework for SDP Attributes when
              Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-01
              (work in progress), February 2014.

17.2.  Informative References

   [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.

   [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.

   [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-01 (work in progress), February 2014.

Appendix A.  Design Considerations







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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 number
   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 5-tuple 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 number 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:


   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






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   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:


   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.








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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 number values, and one of those port would be used for
   the 5-tuple, problems would occur if an endpoint wants to disable/
   reject the "m=" line associated with that port, by setting the port
   number value to zero.  After that, no "m=" line would contain the
   port number value which is used for the 5-tuple.  In addition, it is
   unclear what would happen to the ICE candidates associated with the
   "m=" line, as they are also used for the 5-tuple.

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:


   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.



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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.
   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









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   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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