MMUSIC Working Group                                         C. HolmbergInternet-Draft                                                  EricssonUpdates: 3264 (if approved)                                H. AlvestrandIntended status: Standards Track                                  GoogleExpires: March 4, 2018                                       C. Jennings                                                                   Cisco                                                         August 31, 2017 Negotiating Media Multiplexing Using the Session Description Protocol                                 (SDP)            draft-ietf-mmusic-sdp-bundle-negotiation-39.txtAbstract   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, specified by 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.  The   specification also updates RFC 3264, to allow usage of zero port   values without meaning that media is rejected.   There are multiple ways to correlate the bundled RTP packets with the   appropriate media descriptions.  This specification defines a new   Real-time Transport Protocol (RTP) 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/.   Internet-Drafts are draft documents valid for a maximum of six months   and may be updated, replaced, or obsoleted by other documents at anyHolmberg, et al.          Expires March 4, 2018                 [Page 1]Internet-Draft                Bundled media                  August 2017   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 March 4, 2018.Copyright Notice   Copyright (c) 2017 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.   This document may contain material from IETF Documents or IETF   Contributions published or made publicly available before November   10, 2008.  The person(s) controlling the copyright in some of this   material may not have granted the IETF Trust the right to allow   modifications of such material outside the IETF Standards Process.   Without obtaining an adequate license from the person(s) controlling   the copyright in such materials, this document may not be modified   outside the IETF Standards Process, and derivative works of it may   not be created outside the IETF Standards Process, except to format   it for publication as an RFC or to translate it into languages other   than English.Table of Contents   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5   3.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   7   4.  Applicability Statement . . . . . . . . . . . . . . . . . . .   7   5.  SDP Grouping Framework BUNDLE Extension . . . . . . . . . . .   7   6.  SDP 'bundle-only' Attribute . . . . . . . . . . . . . . . . .   8   7.  SDP Information Considerations  . . . . . . . . . . . . . . .   9     7.1.  Connection Data (c=)  . . . . . . . . . . . . . . . . . .   9     7.2.  Bandwidth (b=)  . . . . . . . . . . . . . . . . . . . . .   9   8.  SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . .   9     8.1.  Mux Category Considerations . . . . . . . . . . . . . . .  10     8.2.  Generating the Initial SDP Offer  . . . . . . . . . . . .  10       8.2.1.  Suggesting the offerer BUNDLE address . . . . . . . .  11       8.2.2.  Example: Initial SDP Offer  . . . . . . . . . . . . .  11Holmberg, et al.          Expires March 4, 2018                 [Page 2]Internet-Draft                Bundled media                  August 2017     8.3.  Generating the SDP Answer . . . . . . . . . . . . . . . .  12       8.3.1.  Answerer Selection of Offerer Bundle Address  . . . .  13       8.3.2.  Answerer Selection of Answerer BUNDLE Address . . . .  14       8.3.3.  Moving A Media Description Out Of A BUNDLE Group  . .  14       8.3.4.  Rejecting A Media Description In A BUNDLE Group . . .  15       8.3.5.  Example: SDP Answer . . . . . . . . . . . . . . . . .  15     8.4.  Offerer Processing of the SDP Answer  . . . . . . . . . .  15     8.5.  Modifying the Session . . . . . . . . . . . . . . . . . .  16       8.5.1.  Suggesting a new offerer BUNDLE address . . . . . . .  16       8.5.2.  Adding a media description to a BUNDLE group  . . . .  17       8.5.3.  Moving A Media Description Out Of A BUNDLE Group  . .  17       8.5.4.  Disabling A Media Description In A BUNDLE Group . . .  18   9.  Protocol Identification . . . . . . . . . . . . . . . . . . .  18     9.1.  STUN, DTLS, SRTP  . . . . . . . . . . . . . . . . . . . .  19   10. RTP Considerations  . . . . . . . . . . . . . . . . . . . . .  19     10.1.  Single RTP Session . . . . . . . . . . . . . . . . . . .  19       10.1.1.  Payload Type (PT) Value Reuse  . . . . . . . . . . .  20     10.2.  Associating RTP/RTCP Streams With Correct SDP Media            Description  . . . . . . . . . . . . . . . . . . . . . .  20     10.3.  RTP/RTCP Multiplexing  . . . . . . . . . . . . . . . . .  26       10.3.1.  SDP Offer/Answer Procedures  . . . . . . . . . . . .  26   11. ICE Considerations  . . . . . . . . . . . . . . . . . . . . .  28     11.1.  SDP Offer/Answer Procedures  . . . . . . . . . . . . . .  29       11.1.1.  Generating the Initial SDP Offer . . . . . . . . . .  30       11.1.2.  Generating the SDP Answer  . . . . . . . . . . . . .  30       11.1.3.  Offerer Processing of the SDP Answer . . . . . . . .  30       11.1.4.  Modifying the Session  . . . . . . . . . . . . . . .  30   12. DTLS Considerations . . . . . . . . . . . . . . . . . . . . .  30   13. RTP Header Extensions Consideration . . . . . . . . . . . . .  31   14. Update to RFC 3264  . . . . . . . . . . . . . . . . . . . . .  31     14.1.  Original text of section 5.1 (2nd paragraph) of RFC 3264  31     14.2.  New text replacing section 5.1 (2nd paragraph) of RFC            3264 . . . . . . . . . . . . . . . . . . . . . . . . . .  32     14.3.  Original text of section 8.2 (2nd paragraph) of RFC 3264  32     14.4.  New text replacing section 8.2 (2nd paragraph) of RFC            3264 . . . . . . . . . . . . . . . . . . . . . . . . . .  32     14.5.  Original text of section 8.4 (6th paragraph) of RFC 3264  32     14.6.  New text replacing section 8.4 (6th paragraph) of RFC            3264 . . . . . . . . . . . . . . . . . . . . . . . . . .  33   15. RTP/RTCP extensions for identification-tag transport  . . . .  33     15.1.  RTCP MID SDES Item . . . . . . . . . . . . . . . . . . .  34     15.2.  RTP SDES Header Extension For MID  . . . . . . . . . . .  34   16. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  35     16.1.  New SDES item  . . . . . . . . . . . . . . . . . . . . .  35     16.2.  New RTP SDES Header Extension URI  . . . . . . . . . . .  35     16.3.  New SDP Attribute  . . . . . . . . . . . . . . . . . . .  36     16.4.  New SDP Group Semantics  . . . . . . . . . . . . . . . .  36   17. Security Considerations . . . . . . . . . . . . . . . . . . .  37Holmberg, et al.          Expires March 4, 2018                 [Page 3]Internet-Draft                Bundled media                  August 2017   18. Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  38     18.1.  Example: Bundle Address Selection  . . . . . . . . . . .  38     18.2.  Example: BUNDLE Extension Rejected . . . . . . . . . . .  40     18.3.  Example: Offerer Adds A Media Description To A BUNDLE            Group  . . . . . . . . . . . . . . . . . . . . . . . . .  41     18.4.  Example: Offerer Moves A Media Description Out Of A            BUNDLE Group . . . . . . . . . . . . . . . . . . . . . .  43     18.5.  Example: Offerer Disables A Media Description Within A            BUNDLE Group . . . . . . . . . . . . . . . . . . . . . .  45   19. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  46   20. Change Log  . . . . . . . . . . . . . . . . . . . . . . . . .  47   21. References  . . . . . . . . . . . . . . . . . . . . . . . . .  56     21.1.  Normative References . . . . . . . . . . . . . . . . . .  56     21.2.  Informative References . . . . . . . . . . . . . . . . .  58   Appendix A.  Design Considerations  . . . . . . . . . . . . . . .  59     A.1.  UA Interoperability . . . . . . . . . . . . . . . . . . .  59     A.2.  Usage of port number value zero . . . . . . . . . . . . .  61     A.3.  B2BUA And Proxy Interoperability  . . . . . . . . . . . .  61       A.3.1.  Traffic Policing  . . . . . . . . . . . . . . . . . .  62       A.3.2.  Bandwidth Allocation  . . . . . . . . . . . . . . . .  62     A.4.  Candidate Gathering . . . . . . . . . . . . . . . . . . .  62   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  631.  Introduction   When multimedia communications are established, each 5-tuple reserved   for an individual media stream consume additional resources   (especially when Interactive Connectivity Establishment (ICE)   [RFC5245] is used).  For this reason, it is attractive to use a   5-tuple for multiple media streams.   This specification defines a way to use a single address:port   combination (BUNDLE address) for receiving media specified by   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 specified by 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 specified by a BUNDLE group.   Once the offerer and the answerer have negotiated a BUNDLE group,   they associate their respective BUNDLE address with each "m=" line inHolmberg, et al.          Expires March 4, 2018                 [Page 4]Internet-Draft                Bundled media                  August 2017   the BUNDLE group.  The BUNDLE addresses are used to receive all media   specified by 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.   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.  The specification also updates RFC 3264, to   allow usage of zero port values without meaning that media is   rejected.   As defined in RFC 4566 [RFC4566], the semantics of assigning the same   transport address (IP address and port) 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] source description (SDES) item, 'MID', and a new RTP   SDES header extension that can be used to associate RTP streams with   media descriptions.   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 described by 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   associate a unique address with each "m=" line within an offer and   answer, according to the procedures in [RFC4566] and [RFC3264]2.  Terminology   "m=" line: SDP bodies contain one or more media descriptions.  Each   media description is identified by an SDP "m=" line.Holmberg, et al.          Expires March 4, 2018                 [Page 5]Internet-Draft                Bundled media                  August 2017   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 associated   with only one "m=" line in an offer or answer.   Shared address: An IP address and port combination that is associated   with 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.   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   specified by 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   specified by 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 specified by 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-Holmberg, et al.          Expires March 4, 2018                 [Page 6]Internet-Draft                Bundled media                  August 2017   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].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 [RFC4961] is used.   All media associated with a BUNDLE group MUST be transport 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   associated with 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.   NOTE: The order of the "m=" lines listed in the SDP 'group:BUNDLE'   attribute identification-tag list does not have to be the same as the   order in which the "m=" lines occur in the SDP.Holmberg, et al.          Expires March 4, 2018                 [Page 7]Internet-Draft                Bundled media                  August 2017   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'. 'bundle-only' is a property attribute [RFC4566], and   hence has no value.      Name: bundle-only      Value: N/A      Usage Level: media      Charset Dependent: no      Example:        a=bundle-only   In order to ensure that an answerer that does not support the BUNDLE   extension always rejects a bundled "m=" line, the offerer can assign   a zero port value to the "m=" line.  According to [RFC3264] 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 the offerer BUNDLE address has been selected, the offerer   does not need to include the 'bundle-only' attribute in subsequent   offers.  By associating the offerer BUNDLE address with an "m=" line   of a subsequent offer, the offerer will ensure that the answerer will   either keep the "m=" line within the BUNDLE group, or the answerer   will have to reject the "m=" line.   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.Holmberg, et al.          Expires March 4, 2018                 [Page 8]Internet-Draft                Bundled media                  August 20177.  SDP Information Considerations   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.7.1.  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.7.2.  Bandwidth (b=)   An offerer and answerer MUST use the rules and restrictions defined   in [I-D.ietf-mmusic-sdp-mux-attributes] for associating the SDP   bandwidth (b=) line with bundled "m=" lines.8.  SDP Offer/Answer Procedures   This section describes the SDP Offer/Answer [RFC3264] procedures for:   o  Negotiating and creating a BUNDLE group; and   o  Selecting the BUNDLE addresses (offerer BUNDLE address and      answerer BUNDLE address); and   o  Adding an "m=" line to a BUNDLE group; and   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   wants to create a BUNDLE group, and the answerer rejects the offer,   the BUNDLE group is not created.Holmberg, et al.          Expires March 4, 2018                 [Page 9]Internet-Draft                Bundled media                  August 2017   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)   [I-D.ietf-ice-rfc5245bis] mechanism.   SDP offers and answers can contain multiple BUNDLE groups.  The   procedures in this section apply independently to a given BUNDLE   group.8.1.  Mux Category Considerations   When an offerer or answerer associates SDP attributes with a bundled   "m=" line (including any bundle-only "m=" line) associated with a   shared address, IDENTICAL and TRANSPORT mux category SDP attributes   [I-D.ietf-mmusic-sdp-mux-attributes] are associated with the "m="   line only if the "m=" line is also associated with the offerer/   answerer BUNDLE-tag.  Otherwise the offerer/answerer MUST NOT   associate such SDP attributes with the "m=" line.  The rule above   does not apply to a bundled "m=" line associated with a unique   address.   NOTE: As bundled "m=" lines (including any bundle-only "m=" line)   associated with a shared address will share the same IDENTICAL and   TRANSPORT mux category SDP attributes, and attribute values, there is   no need to associate such SDP attributes with each "m=" line.  The   attributes and attribute values are implicitly applied to each "m="   line.   The semantics of some SDP attributes only apply to specific types of   media.  For example, the semantics of the SDP 'rtcp-mux' and SDP   'rtcp-mux-only' attributes only apply to "m=" lines describing RTP-   based media.  However, as described in Section 8.1, there are cases   where IDENTICAL and TRANSPORT mux category SDP attributes are only   associated with the "m=" line associated with the BUNDLE-tag.  That   means that media-specific IDENTICAL and TRANSPORT mux category   attributes can be associated with an "m=" line associated with   another type of media.8.2.  Generating the Initial SDP Offer   When an offerer generates an initial offer, in order to create a   BUNDLE group, it MUST:Holmberg, et al.          Expires March 4, 2018                [Page 10]Internet-Draft                Bundled media                  August 2017   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); and   o  Add an SDP 'group:BUNDLE' attribute to the offer; and   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 8.2.1].   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 8.2.1] 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="   line, it is an indication that the offerer wants to disable the "m="   line [Section 8.5.4].   [Section 18.1] shows an example of an initial offer.8.2.1.  Suggesting the offerer BUNDLE address   In the offer, the address associated with the "m=" line associated   with the offerer BUNDLE-tag indicates the address that the offerer   suggests as the offerer BUNDLE address.   The "m=" line associated with the offerer BUNDLE-tag MUST NOT contain   a zero port value or an SDP 'bundle-only' attribute.8.2.2.  Example: Initial SDP Offer   The example shows an initial SDP offer.  The offer includes two "m="   lines in the SDP, and suggests that both are included in a BUNDLE   group.  The audio "m=" line is associated with the offerer BUNDLE-tag   (placed first in the SDP group:BUNDLE attribute identificatoin-id   list).Holmberg, et al.          Expires March 4, 2018                [Page 11]Internet-Draft                Bundled media                  August 2017   SDP Offer     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=rtcp-mux     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:mid8.3.  Generating the SDP Answer   When an answerer generates an answer that 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      corresponding 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 corresponding offer.   If the answer contains a BUNDLE group, the answerer MUST:   o  Select an Offerer BUNDLE Address [Section 8.3.1]; and   o  Select an Answerer BUNDLE Address [Section 8.3.2];   The answerer is allowed to select a new Answerer BUNDLE address each   time it generates an answer to an offer.Holmberg, et al.          Expires March 4, 2018                [Page 12]Internet-Draft                Bundled media                  August 2017   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 8.3.3]; or   o  Reject the "m=" line [Section 8.3.4];   If the answerer keeps a bundle-only "m=" line within the BUNDLE   group, it follows the procedures (associates the answerer BUNDLE   address with the "m=" line etc) for any other "m=" line kept within   the BUNDLE group.   If the answerer does not want to keep a bundle-only "m=" line within   the BUNDLE group, it MUST reject the "m=" line [Section 8.3.4].   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 8.5.4].8.3.1.  Answerer Selection of Offerer Bundle Address   In an offer, the address (unique or shared) associated with the   bundled "m=" line associated with the offerer BUNDLE-tag indicates   the address that the offerer suggests as the offerer BUNDLE address   [Section 8.2.1].  The answerer MUST check whether that "m=" line   fulfils the following criteria:   o  The answerer will not move the "m=" line out of the BUNDLE group      [Section 8.3.3]; and   o  The answerer will not reject the "m=" line [Section 8.3.4]; 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 inHolmberg, et al.          Expires March 4, 2018                [Page 13]Internet-Draft                Bundled media                  August 2017   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 8.3.3] to each bundled "m=" line in   the offer when creating the answer.   [Section 18.1] shows an example of an offerer BUNDLE address   selection.8.3.2.  Answerer Selection of Answerer BUNDLE Address   When the answerer selects a BUNDLE address for itself, referred to as   the answerer BUNDLE address, it MUST associate that address with each   bundled "m=" line within the created BUNDLE group in the answer.   The answerer MUST NOT associate the answerer BUNDLE address with an   "m=" line that is not within the BUNDLE group, or to an "m=" line   that is within another BUNDLE group.   [Section 18.1] shows an example of an answerer BUNDLE address   selection.8.3.3.  Moving A Media Description Out Of A BUNDLE Group   When an answerer wants to move an "m=" line out of a BUNDLE group, it   MUST first check the following criteria:   o  In the corresponding offer, the "m=" line is associated with a      shared address (e.g. a previously selected offerer BUNDLE      address); or   o  In the corresponding offer, an SDP 'bundle-only' attribute is      associated with the "m=" line, and the "m=" line contains a zero      port value.   If either criteria above is fulfilled, the answerer MUST reject the   "m=" line [Section 8.3.4].   Otherwise, if in the corresponding offer the "m=" line is associated   with a unique address, the answerer MUST associate a unique address   with the "m=" line in the answer (the answerer does not reject the   "m=" line).   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.Holmberg, et al.          Expires March 4, 2018                [Page 14]Internet-Draft                Bundled media                  August 20178.3.4.  Rejecting A Media Description In A BUNDLE Group   When an answerer rejects an "m=" line, it MUST associate an address   with a zero port value with the "m=" line in the answer, according to   the procedures in [RFC3264].   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.8.3.5.  Example: SDP Answer   The example shows an SDP answer, based on the SDP offer in   [Section 8.2.2].  The answers acceppts both "m=" lines in the BUNDLE   group.   SDP Answer     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=rtcp-mux     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:mid8.4.  Offerer Processing of the SDP Answer   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 corresponding offer.  If there   is no mismatch, the offerer MUST use the offerer BUNDLE address,   selected by the answerer [Section 8.3.1], as the address for each   bundled "m=" line.Holmberg, et al.          Expires March 4, 2018                [Page 15]Internet-Draft                Bundled media                  August 2017   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   When an offerer generates a subsequent offer, it MUST associate the   previously selected offerer BUNDLE address [Section 8.3.1] with each   bundled "m=" line (including any bundle-only "m=" line), except if:   o  The offerer suggests a new offerer BUNDLE address [Section 8.5.1];      or   o  The offerer wants to add a bundled "m=" line to the BUNDLE group      [Section 8.5.2]; or   o  The offerer wants to move a bundled "m=" line out of the BUNDLE      group [Section 8.5.3]; or   o  The offerer wants to disable the bundled "m=" line      [Section 8.5.4].   In addition, the offerer MUST select an offerer BUNDLE-tag   [Section 8.2.1] associated with the previously selected offerer   BUNDLE address, unless the offerer suggests a new offerer BUNDLE   address.8.5.1.  Suggesting a new offerer BUNDLE address   When an offerer generates an offer, in which it suggests a new   offerer BUNDLE address [Section 8.2.1], the offerer MUST:   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 8.2.1].   NOTE: Unless the offerer associates the new suggested offerer BUNDLE   address with each bundled "m=" line, it can associate unique   addresses with any number of bundled "m=" lines (and the previously   selected offerer BUNDLE address to any remaining bundled "m=" line)Holmberg, et al.          Expires March 4, 2018                [Page 16]Internet-Draft                Bundled media                  August 2017   if it wants to suggest multiple alternatives for the new offerer   BUNDLE address.8.5.2.  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 added "m=" line; or   o  Assign the previously selected offerer BUNDLE address to the added      "m=" line; or   o  If the offerer associates a new (shared address) suggested offerer      BUNDLE address with each bundled "m=" line [Section 8.5.1], also      associate that address with the added "m=" line.   In addition, the offerer MUST add the identification-tag associated   with the added "m=" line to the SDP 'group:BUNDLE' attribute   identification-tag list with the BUNDLE group [Section 8.2.1].   NOTE: Assigning a unique address to the "m=" line allows the answerer   to move the "m=" line out of the BUNDLE group [Section 8.3.3],   without having to reject the "m=" line.   If the offerer associates a unique address with the added "m=" line,   and if the offerer suggests that address as the new offerer BUNDLE   address [Section 8.5.1], the offerer BUNDLE-tag MUST represent the   added "m=" line [Section 8.2.1].   If the offerer associates a new suggested offerer BUNDLE address with   each bundled "m=" line [Section 8.5.1], including the added "m="   line, the offerer BUNDLE-tag MAY represent the added "m=" line   [Section 8.2.1].   [Section 18.3] shows an example where an offerer sends an offer in   order to add a bundled "m=" line to a BUNDLE group.8.5.3.  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 associate a unique address with the "m=" line; andHolmberg, et al.          Expires March 4, 2018                [Page 17]Internet-Draft                Bundled media                  August 2017   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 the removed "m=" line is associated with the previously   selected BUNDLE-tag, the offerer needs to suggest a new BUNDLE-tag   [Section 8.2.1].   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 8.5.2] to the "m=" line.   [Section 18.4] shows an example of an offer for moving an "m=" line   out of a BUNDLE group.8.5.4.  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 associate an address with a zero port value with 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 18.5] shows an example of an offer for disabling an "m="   line within a BUNDLE group.9.  Protocol Identification   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 received data with   the correct protocol.   In addition, if received data can be associated with more than one   bundled "m=" line, there MUST exist a publicly available   specification which describes a mechanism for associating the   received data with the correct "m=" line.   This document describes a mechanism to identify the protocol of   received data among the STUN, DTLS and SRTP protocols (in any   combination), when UDP is used as transport-layer protocol, but doesHolmberg, et al.          Expires March 4, 2018                [Page 18]Internet-Draft                Bundled media                  August 2017   not describe how to identify different protocols transported on DTLS.   While the mechanism is generally applicable to other protocols and   transport-layer protocols, any such use requires further   specification around how to multiplex multiple protocols on a given   transport-layer protocol, and how to associate received data with the   correct protocols.9.1.  STUN, DTLS, SRTP   Section 5.1.2 of [RFC5764] describes a mechanism to identify the   protocol of a received packet among the STUN, Datagram Transport   Layer Security (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 the packets in a received   SRTP stream with the correct "m=" line.10.  RTP Considerations10.1.  Single RTP Session   All RTP-based media within a single BUNDLE group belong to a single   RTP session [RFC3550].   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 only if each codec associated with the payload type number      shares an identical codec configuration [Section 10.1.1].   o  The proto value in each bundled RTP-based "m=" line MUST be      identical (e.g.  RTP/AVPF).Holmberg, et al.          Expires March 4, 2018                [Page 19]Internet-Draft                Bundled media                  August 2017   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 can be reused by another   source (possibly associated with a different bundled "m=" line) after   a delay of 5 RTCP reporting intervals (the delay is to ensure the   SSRC has timed out, in case the RTCP BYE packet was lost [RFC3550]).10.1.1.  Payload Type (PT) Value Reuse   Multiple bundled "m=" lines might represent RTP based media.  As all   RTP based media specified by 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.ietf-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 Streams With Correct SDP Media Description   NOTE: The text in this section is copied from Appendix B of JSEP.   The community has not yet agreed on the text.   As described in [RFC3550], RTP packets are associated with RTP   streams [RFC7656].  Each RTP stream is identified by an SSRC value,   and each RTP packet includes an SSRC field that is used to associate   the packet with the correct RTP stream.  RTCP packets also use SSRCs   to identify which RTP streams the packet relates to.  However, a RTCP   packet can contain multiple SSRC fields, in the course of providing   feedback or reports on different RTP streams, and therefore can be   associated with multiple such streams.   In order to be able to process received RTP/RTCP packets correctly,   it must be possible to associate an RTP stream with the correct "m="Holmberg, et al.          Expires March 4, 2018                [Page 20]Internet-Draft                Bundled media                  August 2017   line, as the "m=" line and SDP attributes associated with the "m="   line contain information needed to process the packets.   As all RTP streams associated with a BUNDLE group use the same   address:port combination for sending and receiving RTP/RTCP packets,   the local address:port combination cannot be used to associate an RTP   stream with the correct "m=" line.  In addition, multiple RTP streams   might be associated with the same "m=" line.   An offerer and answerer can inform each other which SSRC values they   will use for an RTP stream by using the SDP 'ssrc' attribute   [RFC5576].  However, an offerer will not know which SSRC values the   answerer will use until the offerer 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 an RTP stream with   the correct "m=" line using the SSRC value associated with the RTP   stream.  In addition, the offerer and answerer may start using new   SSRC values mid-session, without informing each other using the SDP   'ssrc' attribute.   In order for an offerer and answerer to always be able to associate   an RTP stream with the correct "m=" line, the offerer and answerer   using the BUNDLE extension MUST support the mechanism defined in   Section 15, where the offerer and answerer insert the identification-   tag associated with an "m=" line (provided by the remote peer) into   RTP and RTCP packets associated with a BUNDLE group.   When using this mechanism, the mapping from an SSRC to an   identification-tag is carried in RTP header extensions or RTCP SDES   packets, as specified in Section 15.  Since a compound RTCP packet   can contain multiple RTCP SDES packets, and each RTCP SDES packet can   contain multiple chunks, a single RTCP packet can contain several   SSRC to identification-tag mappings.  The offerer and answerer   maintain tables used for routing that are updated each time an RTP/   RTCP packet contains new information that affects how packets should   be routed.   However, some implementations of may not include this identification-   tag in their RTP and RTCP traffic when using the BUNDLE mechanism,   and instead use a payload type based mechanism to associate RTP   streams with SDP m= lines.  In this situation, each "m=" line MUST   use unique payload type values, in order for the payload type to be a   reliable indicator of the relevant "m=" line for the RTP stream.   Note that when using the payload type to associate RTP streams with   m= lines an RTP stream, identified by SSRC, will be mapped to an "m="   line when the first packet of that RTP stream is received, and the   mapping will not be changed even if the payload type used by that RTPHolmberg, et al.          Expires March 4, 2018                [Page 21]Internet-Draft                Bundled media                  August 2017   stream changes.  In other words, the SSRC cannot to "move" to a   different "m=" line simply by changing the payload type.   Applications can implement RTP stacks in many different ways.  The   algorithm below details one way that RTP streams can be associated   with m= lines, but is not meant to be prescriptive about exactly how   an RTP stack needs to be implemented.  Applications MAY use any   algorithm that achieves equivalent results to those described in the   algorithm below.   To prepare to associate RTP streams with the correct "m=" line, the   following steps MUST be followed for each BUNDLE group.      Construct a table mapping MID to "m=" line for each "m=" line in      this BUNDLE group.  Note that an "m=" line may only have one MID.      Construct a table mapping SSRCs of incoming RTP streams to "m="      line for each "m=" line in this BUNDLE group and for each SSRC      configured for receiving in that "m=" line.      Construct a table mapping the SSRC of each outgoing RTP stream to      "m=line" for each "m=" line in this BUNDLE group and for each SSRC      configured for sending in that "m=" line.      Construct a table mapping payload type to "m=" line for each "m="      line in the BUNDLE group and for each payload type configured for      receiving in that "m=" line.  If any payload type is configured      for receiving in more than one "m=" line in the BUNDLE group, do      not it include it in the table, as it cannot be used to uniquely      identify a "m=" line.      Note that for each of these tables, there can only be one mapping      for any given key (MID, SSRC, or PT).  In other words, the tables      are not multimaps.   As "m=" lines are added or removed from the BUNDLE groups, or their   configurations are changed, the tables above MUST also be updated.   When an RTP packet is received, it MUST be delivered to the RTP   stream corresponding to its SSRC.  That RTP stream MUST then be   associated with the correct m= line within a BUNDLE group, for   additional processing, according to the following steps.      If the MID associated with the RTP stream is not in the table      mapping MID to a&#128;&#156;m=a&#128;&#156; line, then the RTP      stream is not decoded and the payload data is discarded.Holmberg, et al.          Expires March 4, 2018                [Page 22]Internet-Draft                Bundled media                  August 2017      If the packet has a MID, and the packet's extended sequence number      is greater than that of the last MID update, as discussed in      [RFC7941], Section 4.2.6, update the MID associated with the RTP      stream to match the MID carried in the RTP packet, then update the      mapping tables to include an entry that maps the SSRC of that RTP      stream to the a&#128;&#156;m=a&#128;&#156; line for that MID.      If the SSRC of the RTP stream is in the incoming SSRC mapping      table, check that the payload type used by the RTP stream matches      a payload type included on the matching      a&#128;&#156;m=a&#128;&#156; line.  If so, associate the RTP      stream with that a&#128;&#156;m=a&#128;&#156; line.  Otherwise,      the RTP stream is not decoded and the payload data is discarded.      If the payload type used by the RTP stream is in the payload type      table, update the incoming SSRC mapping table to include an entry      that maps the RTP streama&#128;&#153;s SSRC to the      a&#128;&#156;m=a&#128;&#156; line for that payload type.      Associate the RTP stream with the corresponding      a&#128;&#156;m=a&#128;&#156; line.      Otherwise, mark the RTP stream as not for decoding and discard the      payload.   If the RTP packet contains one of more contributing source (CSRC)   identifiers, then each CSRC is looked up in the incoming SSRC table   and a copy of the RTP packet is associated with the corresponding m=   line for additional processing.   For each RTCP packet received (including each RTCP packet that is   part of a compound RTCP packet), the packet is processed as usual by   the RTP layer, then is passed to the a&#128;&#156;m=a&#128;&#156;   lines corresponding to the RTP streams it contains information about   for additional processing.  This routing is type-dependent, as each   kind of RTCP packet has its own mechanism for associating it with the   relevant RTP streams.   RTCP packets for which no appropriate a&#128;&#156;m=a&#128;&#156;   line can be identified MUST be processed as usual by the RTP layer,   updating the metadata associated with the corresponding RTP streams,   but are not passed to any a&#128;&#156;m=a&#128;&#156; line.  This   situation can occur with certain multiparty RTP topologies, or when   RTCP packets are sent containing a subset of the SDES information.   Rules for additional processing of the various types of RTCP packets   are explained below.Holmberg, et al.          Expires March 4, 2018                [Page 23]Internet-Draft                Bundled media                  August 2017      If the RTCP packet is of type SDES, for each chunk in the packet      whose SSRC is found in the incoming SSRC table, deliver a copy of      the SDES packet to the "m=" line associated with that SSRC.  In      addition, for any SDES MID items contained in these chunks, if the      MID is found in the table mapping MID to "m=" line, update the      incoming SSRC table to include an entry that maps the RTP stream      associated with chunk's SSRC to the "m=" line associated with that      MID, unless the packet is older than the packet that most recently      updated the mapping for this SSRC, as discussed in [RFC7941],      Section 4.2.6.      Note that if an SDES packet is received as part of a compound RTCP      packet, the SSRC to "m=" line mapping may not exist until the SDES      packet is handled (e.g., in the case where RTCP for a source is      received before any RTP packets).  Therefore, when processing a      compound packet, any contained SDES packet MUST be handled first.      Note that this is a backwards change from [RFC3550] Section 6.1,      which states that "Each individual RTCP packet in the compound      packet may be processed independently with no requirements upon      the order or combination of packets".      If the RTCP packet is of type BYE, it indicates that the RTP      streams referenced in the packet are ending.  Therefore, for each      SSRC indicated in the packet that is found in the incoming SSRC      table, first deliver a copy of the BYE packet to the "m=" line      associated with that SSRC, but then remove the entry for that SSRC      from the incoming SSRC table after an appropriate delay to account      for "straggler packets", as specified in [RFC3550], Section 6.2.1.      If the RTCP packet is of type SR or RR, for each report block in      the report whose "SSRC of source" is found in the outgoing SSRC      table, deliver a copy of the SR or RR packet to the "m=" line      associated with that SSRC.  In addition, if the packet is of type      SR, and the sender SSRC for the packet is found in the incoming      SSRC table, deliver a copy of the SR packet to the "m=" line      associated with that SSRC.      If the implementation supports RTCP XR and the packet is of type      XR, as defined in [RFC3611], for each report block in the report      whose "SSRC of source" is is found in the outgoing SSRC table,      deliver a copy of the XR packet to the "m=" line associated with      that SSRC.  In addition, if the sender SSRC for the packet is      found in the incoming SSRC table, deliver a copy of the XR packet      to the "m=" line associated with that SSRC.      If the RTCP packet is a feedback message of type RTPFB or PSFB, as      defined in [RFC4585], it will contain a media source SSRC, and      this SSRC is used for routing certain subtypes of feedbackHolmberg, et al.          Expires March 4, 2018                [Page 24]Internet-Draft                Bundled media                  August 2017      messages.  However, several subtypes of PSFB messages include      target SSRC(s) in a section called Feedback Control Information      (FCI).  For these messages, the target SSRC(s) are used for      routing.      If the RTCP packet is a feedback packet that does not include      target SSRCs in its FCI section, and the media source SSRC is      found in the outgoing SSRC table, deliver the feedback packet to      the "m=" line associated with that SSRC.  RTPFB and PSFB types      that are handled in this way include:      Generic NACK:  [RFC4585] (PT=RTPFB, FMT=1).      Picture Loss Indication (PLI):  [RFC4585] (PT=PSFB, FMT=1).      Slice Loss Indication (SLI):  [RFC4585] (PT=PSFB, FMT=2).      Reference Picture Selection Indication (RPSI):  [RFC4585]         (PT=PSFB, FMT=3).      If the RTCP packet is a feedback message that does include target      SSRC(s) in its FCI section, it can either be a request or a      notification.  Requests reference a RTP stream that is being sent      by the message recipient, whereas notifications are responses to      an earlier request, and therefore reference a RTP stream that is      being received by the message recipient.      If the RTCP packet is a feedback request that includes target      SSRC(s), for each target SSRC that is found in the outgoing SSRC      table, deliver a copy of the RTCP packet to the "m=" line      associated with that SSRC.  PSFB types that are handled in this      way include:      Full Intra Request (FIR):  [RFC5104] (PT=PSFB, FMT=4).      Temporal-Spatial Trade-off Request (TSTR):  [RFC5104] (PT=PSFB,         FMT=5).      H.271 Video Back Channel Message (VBCM):  [RFC5104] (PT=PSFB,         FMT=7).      Layer Refresh Request (LRR):  [I-D.ietf-avtext-lrr] (PT=PSFB,         FMT=TBD).      If the RTCP packet is a feedback notification that include target      SSRC(s), for each target SSRC that is found in the incoming SSRC      table, deliver a copy of the RTCP packet to the "m=" lineHolmberg, et al.          Expires March 4, 2018                [Page 25]Internet-Draft                Bundled media                  August 2017      associated with the RTP stream with matching SSRC.  PSFB types      that are handled in this way include:      Temporal-Spatial Trade-off Notification (TSTN):  [RFC5104]         (PT=PSFB, FMT=6).  This message is a notification in response         to a prior TSTR.      If the RTCP packet is of type APP, then it is handled in an      application specific manner.  If the application does not      recognise the APP packet, then it MUST be discarded.10.3.  RTP/RTCP Multiplexing   Within a BUNDLE group, the offerer and answerer MUST enable RTP/RTCP   multiplexing [RFC5761] for the RTP-based media specified by the   BUNDLE group.   When RTP/RTCP multiplexing is enabled, the same address:port   combination will be used for sending all RTP packets and the RTCP   packets associated with the BUNDLE group.  Each endpoint will send   the packets towards the BUNDLE address of the other endpoint.  The   same address:port combination MAY be used for receiving RTP packets   and RTCP packets.10.3.1.  SDP Offer/Answer Procedures   This section describes how an offerer and answerer use the SDP 'rtcp-   mux' attribute [RFC5761] and the SDP 'rtcp-mux-only' attribute   [I-D.ietf-mmusic-mux-exclusive] to negotiate usage of RTP/RTCP   multiplexing for RTP-based media associated with a BUNDLE group.   The mux category [I-D.ietf-mmusic-sdp-mux-attributes] of the SDP   'rtcp-mux' and 'rtcp-mux-only' attributes is IDENTICAL.  Section 8.1   describes the details regarding which bundled "m=" lines an offerer   and answerer associates the attributes with.   RTP/RTCP multiplexing only applies to RTP-based media.  However, as   described in Section 8.1, within a BUNDLE group the SDP 'rtcp-mux'   and SDP 'rtcp-mux-only' attributes might be associated with a non-   RTP-based bundled "m=" line.10.3.1.1.  Generating the Initial SDP Offer   When an offerer generates an initial offer, if the offer contains one   or more RTP-based bundled "m=" lines (or, if there is a chance that   RTP-based "m=" lines will later be added to the BUNDLE group), the   offerer MUST associate an SDP 'rtcp-mux' attribute [RFC5761] with one   or more "m=" lines, following the procedures for IDENTICAL muxHolmberg, et al.          Expires March 4, 2018                [Page 26]Internet-Draft                Bundled media                  August 2017   category attributes in Section 8.1.  In addition, the offerer MAY   associate an SDP 'rtcp-mux-only' attribute   [I-D.ietf-mmusic-mux-exclusive] with the same "m=" lines.   NOTE: Whether the offerer associates the SDP 'rtcp-mux-only'   attribute depends on whether the offerer supports fallback to usage   of a separate port for RTCP in case the answerer moves one or more   RTP-based "m=" line out of the BUNDLE group in the answer.   NOTE: If the offerer associates an SDP 'rtcp-mux' attribute with one   or more bundled "m=" lines, but does not associate an SDP 'rtcp-mux-   only' attribute, the offerer can also associate an SDP 'rtcp'   attribute [RFC3605] with one or more RTP-based "m=" line in order to   provide a fallback port for RTCP, as described in [RFC5761].   However, the fallback port will only be used for RTP-based "m=" lines   moved out of the BUNDLE group by the answerer.   In the initial offer, the address:port combination for RTCP MUST be   unique in each bundled RTP-based "m=" line (excluding a bundle-only   "m=" line), similar to RTP.10.3.1.2.  Generating the SDP Answer   When an answerer generates an answer, if the answerer supports RTP-   based media, and if a bundled "m=" line in the offer contained an SDP   'rtcp-mux' attribute, the answerer MUST enable usage of RTP/RTCP   multiplexing, even if there currently are no RTP-based "m=" lines   within the BUNDLE group.  The answerer MUST associate an SDP 'rtcp-   mux' attribute with "m=" lines within the BUNDLE group in the answer   following the procedures for IDENTICAL mux category attributes in   Section 8.1.  In addition, if the "m=" line in the offer contained an   an SDP "rtcp-mux-only" attribute, the answerer MUST associate an SDP   "rtcp-mux-only" attribute with the "m=" line in the answer.   If the "m=" line associated with the offerer BUNDLE-tag in the offer   contained an SDP 'rtcp-mux-only' attribute, and if the answerer moves   an RTP-based "m=" line out of the BUNDLE group in the answer   Section 8.3.3, the answerer MUST either associate the attribute with   the moved "m=" line (and enable RTP/RTCP multiplexing for the media   associated with the "m=" line), or reject the "m=" line   Section 8.3.4.   The answerer MUST NOT associate an SDP 'rtcp' attribute with any "m="   line within the BUNDLE group 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.Holmberg, et al.          Expires March 4, 2018                [Page 27]Internet-Draft                Bundled media                  August 2017   If the usage of RTP/RTCP multiplexing within a BUNDLE group has been   negotiated in a previous offer/answer transaction, the answerer MUST   associate an SDP 'rtcp-mux' attribute with the "m=" line associated   with the answerer BUNDLE-tag in the answer.  It is not possible to   disable RTP/RTCP multiplexing within a BUNDLE group.10.3.1.3.  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 10.3.1.2), 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.   NOTE: It is considered a protocol error if the answerer has not   accepted the usage of RTP/RTCP multiplexing for RTP-based "m=" lines   that the answerer included in the BUNDLE group.10.3.1.4.  Modifying the Session   When an offerer generates a subsequent offer, the offerer MUST   associate an SDP 'rtcp-mux' attribute with a bundled "m=" line,   following the procedures for IDENTICAL mux category attributes in   Section 8.1.   If the offerer wants to add a bundled RTP-based "m=" line to the   BUNDLE group, it MAY also associate an SDP 'rtcp-mux-only' attribute   with a bundled "m=", following the procedures for IDENTICAL mux   category attributes in Section 8.1.  This allows the offerer to   mandate RTP/RTCP multiplexing for the added "m=" line (or the "m="   line to be rejected by the answerer) even if the answerer does not   accept the "m=" line within the BUNDLE group.11.  ICE Considerations   This section describes how to use the BUNDLE grouping extension   together with the Interactive Connectivity Establishment (ICE)   mechanism [I-D.ietf-ice-rfc5245bis].   The generic procedures for negotiating usage of ICE using SDP,   defined in [I-D.ietf-mmusic-ice-sip-sdp], also apply to usage of ICE   with BUNDLE, with the following exceptions:   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.Holmberg, et al.          Expires March 4, 2018                [Page 28]Internet-Draft                Bundled media                  August 2017   o  Among bundled "m=" lines (including any bundle-only "m=" line)      with which the offerer has associated a shared address, the      offerer only associates ICE-related media-level SDP attributes      with the "m=" line associated with the offerer BUNDLE-tag,      following the procedures in Section 8.1.   o  Among "m=" lines with which the answerer has associated a shared      address within a BUNDLE group, the answerer only associates ICE-      related media-level SDP attributes with the "m=" line associated      with the answerer BUNDLE-tag, following the procedures in      Section 8.1.   Support and usage of ICE mechanism together with the BUNDLE extension   is OPTIONAL.11.1.  SDP Offer/Answer Procedures   When an offerer associates a unique address with a bundled "m=" line   (excluding any bundle-only "m=" line), the offerer MUST associate SDP   'candidate' attributes (and other applicable ICE-related media-level   SDP attributes), containing unique ICE properties (candidates etc),   with the "m=" line, according to the procedures in   [I-D.ietf-mmusic-ice-sip-sdp].   When an offerer associates a shared address with a bundled "m=" line,   the offerer MUST associate SDP 'candidate' attributes (and other   applicable ICE-related media-level SDP attributes) with the "m=" line   following the procedures in Section 8.1.   When an answerer associates a shared address with an "m=" line within   a BUNDLE group, if the answerer MUST associate SDP 'candidate'   attributes (and other applicable ICE-related media-level SDP   attributes) with the "m=" line following the procedures in   Section 8.1.   NOTE: As most ICE-related media-level SDP attributes belong to the   TRANSPORT mux category [I-D.ietf-mmusic-sdp-mux-attributes], the   offerer and answerer follow the procedures in Section 8.1 when   deciding whether to associate an attribute with a bundled "m=" line.   However, in the case of ICE-related media-level attributes, the rules   apply to all attributes (see note below), even if they belong to a   different mux category.   NOTE: The following ICE-related media-level SDP attributes are   defined in [I-D.ietf-mmusic-ice-sip-sdp]: 'candidiate', 'remote-   candidates', 'ice-mismatch', 'ice-ufrag', 'ice-pwd', and 'ice-   pacing'.Holmberg, et al.          Expires March 4, 2018                [Page 29]Internet-Draft                Bundled media                  August 201711.1.1.  Generating the Initial SDP Offer   When an offerer generates an initial offer, the offerer MUST   associate ICE-related media-level SDP attributes with bundled "m="   lines forllowin the procedures in [Section 11.1].11.1.2.  Generating the SDP Answer   When an answerer generates an answer that contains a BUNDLE group,   the answer MUST associate ICE-related SDP attributes to "m=" lines   within the BUNDLE group according to [Section 11.1].11.1.3.  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   associate the ICE properties associated with the offerer BUNDLE   address, selected by the answerer [Section 8.3.1], with each bundled   "m=" line.11.1.4.  Modifying the Session   When an offerer generates a subsequent offer, it MUST associate ICE   properties to bundled "m=" lines following the procedures in   [Section 11.1].12.  DTLS Considerations   One or more media streams within a BUNDLE group might use the   Datagram Transport Layer Security (DTLS) protocol [RFC6347] in order   to encrypt the data, or to negotiate encryption keys if another   encryption mechanism is used to encrypt media.   When DTLS is used within a BUNDLE group, the following rules apply:   o  There can only be one DTLS association [RFC6347] associated with      the BUNDLE group; and   o  Each usage of the DTLS association within the BUNDLE group MUST      use the same mechanism for determining which endpoints (the      offerer or answerer) become DTLS client and DTLS server; and   o  Each usage of the DTLS association within the Bundle group MUST      use the same mechanism for determining whether an offer or answer      will trigger the establishment of a new DTLS association, or      whether an existing DTLS association will be used; andHolmberg, et al.          Expires March 4, 2018                [Page 30]Internet-Draft                Bundled media                  August 2017   o  If the DTLS client supports DTLS-SRTP [RFC5764] it MUST include      the 'use_srtp' extension [RFC5764] in the DTLS ClientHello message      [RFC5764], The client MUST include the extension even if the usage      of DTLS-SRTP is not negotiated as part of the multimedia session      (e.g., SIP session [RFC3261].   NOTE: The inclusion of the 'use_srtp' extension during the initial   DTLS handshake ensures that a DTLS renegotiation will not be required   in order to include the extension, in case DTLS-SRTP encrypted media   is added to the BUNDLE group later during the multimedia session.13.  RTP Header Extensions Consideration   When [RFC5285] RTP header extensions are used in the context of this   specification, the identifier used for a given extension MUST   identify the same extension across all the bundled media   descriptions.14.  Update to RFC 3264   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).14.1.  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.Holmberg, et al.          Expires March 4, 2018                [Page 31]Internet-Draft                Bundled media                  August 201714.2.  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.14.3.  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.14.4.  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   answer MAY omit all attributes present previously, and MAY list just   a single media format from amongst those in the offer."14.5.  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.Holmberg, et al.          Expires March 4, 2018                [Page 32]Internet-Draft                Bundled media                  August 201714.6.  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.15.  RTP/RTCP extensions for identification-tag transport   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 SDES header extension [RFC7941], which   is used to carry the 'MID' RTCP SDES item in RTP packets.   The SDES item and RTP SDES header extension make it possible for a   receiver to associate each RTP stream with with a specific "m=" line,   with which the receiver has associated an identification-tag, even if   those "m=" lines are part of the same RTP session.  The RTP SDES   header extension also ensures that the media recipient gets the   identification-tag upon receipt of the first decodable media and is   able to associate the media with the correct application.   A media recipient informs the media sender about the identification-   tag associated with an "m=" line through the use of an 'mid'   attribute [RFC5888].  The media sender then inserts the   identification-tag in RTCP and RTP packets sent to the media   recipient.   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.Holmberg, et al.          Expires March 4, 2018                [Page 33]Internet-Draft                Bundled media                  August 2017   [RFC3550] defines general procedures regarding the RTCP transmission   interval.  The RTCP MID SDES item SHOULD be sent in the first few   RTCP packets sent after 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 SDES header extension for carrying the 'MID' RTCP SDES 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 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.15.1.  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.   The identification-tag is not zero terminated.   [RFC EDITOR NOTE: Please replace TBD with the assigned SDES   identifier value.]15.2.  RTP SDES Header Extension For MID   The payload, containing the identification-tag, of the RTP SDES   header extension element can be encoded using either the one-byte or   two-byte header [RFC7941].  The identification-tag payload is UTF-8   encoded, as in SDP.Holmberg, et al.          Expires March 4, 2018                [Page 34]Internet-Draft                Bundled media                  August 2017   The identification-tag is not zero terminated.  Note, that the 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 SDES 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 encoding the 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 a minimal   number of 32-bit words used for the RTP SDES 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.  The identification-tag MUST NOT   contain any user information, and applications SHALL avoid generating   the identification-tag using a pattern that enables application   identification.16.  IANA Considerations16.1.  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 "RTP SDES item   types" registry as follows:     Value:     TBD     Abbrev.:   MID     Name:      Media Identification     Reference: RFCXXXX16.2.  New RTP SDES Header Extension URI   [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this   document.]Holmberg, et al.          Expires March 4, 2018                [Page 35]Internet-Draft                Bundled media                  August 2017   This document defines a new extension URI in the RTP SDES Compact   Header Extensions sub-registry of the RTP Compact Header Extensions   registry sub-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     The SDES item does not reveal privacy information about the users.     It is simply used to associate RTP-based media with the correct SDP     media description (m- line) in the SDP used to negotiate the media.     The purpose of the extension is for the offerer to be able to     associate received multiplexed RTP-based media before the offerer     receives the associated SDP answer.16.3.  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     Mux category:       NORMAL16.4.  New SDP Group Semantics   [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this   document.]Holmberg, et al.          Expires March 4, 2018                [Page 36]Internet-Draft                Bundled media                  August 2017   This document registers the following semantics with IANA in the   "Semantics for the "group" SDP Attribute" subregistry (under the   "Session Description Protocol (SDP) Parameters" registry:       Semantics                              Token   Reference       -------------------------------------  ------  ---------       Media bundling                         BUNDLE  [RFCXXXX]17.  Security Considerations   The security considerations defined in [RFC3264] and [RFC5888] apply   to the BUNDLE extension.  Bundle does not change which information,   e.g., RTP streams, flows over the network, with the exception of the   usage of the MID SDES item as discussed below.  Primarily it changes   which addresses and ports, and thus in which (RTP) sessions that the   information is flowing in.  This affects the security contexts being   used and can cause previously separated information flows to share   the same security context.  This has very little impact on the   performance of the security mechanism of the RTP sessions.  In cases   where one would have applied different security policies on the   different RTP streams being bundled, or where the parties having   access to the security contexts would have differed between the RTP   stream, additional analysis of the implications are needed before   selecting to apply BUNDLE.   The identification-tag, independent of transport, RTCP SDES packet or   RTP header extension, can expose the value to parties beyond the   signaling chain.  Therefore, the identification-tag values MUST be   generated in a fashion that does not leak user information, e.g.,   randomly or using a per-bundle group counter, and SHOULD be 3 bytes   or less, to allow them to efficiently fit into the MID RTP header   extension.  Note that if implementations use different methods for   generating identification-tags this could enable fingerprinting of   the implementation making it vulnerable to targeted attacks.  The   identification-tag is exposed on the RTP stream level when included   in the RTP header extensions, however what it reveals of the RTP   media stream structure of the endpoint and application was already   possible to deduce from the RTP streams without the MID SDES header   extensions.  As the identification-tag is also used to route the   media stream to the right application functionality it is also   important that the value received is the one intended by the sender,   thus integrity and the authenticity of the source are important to   prevent denial of service on the application.  Existing SRTP   configurations and other security mechanisms protecting the whole   RTP/RTCP packets will provide the necessary protection.Holmberg, et al.          Expires March 4, 2018                [Page 37]Internet-Draft                Bundled media                  August 2017   When the BUNDLE extension is used, the set of configurations of the   security mechanism used in all the bundled media descriptions will   need to be compatible so that they can simultaneously used in   parallel, at least per direction or endpoint.  When using SRTP this   will be the case, at least for the IETF defined key-management   solutions due to their SDP attributes (a=crypto, a=fingerprint,   a=mikey) and their classification in   [I-D.ietf-mmusic-sdp-mux-attributes].   The security considerations of "RTP Header Extension for the RTP   Control Protocol (RTCP) Source Description Items" [RFC7941] requires   that when RTCP is confidentiality protected that any SDES RTP header   extension carrying an SDES item, such as the MID RTP header   extension, is also protected using commensurate strength algorithms.   However, assuming the above requirements and recommendations are   followed there are no known significant security risks with leaving   the MID RTP header extension without confidentiality protection.   Thus, the requirements in RFC 7941 MAY be ignored for the MID RTP   header extension.  Security mechanisms for RTP/RTCP are discussed in   Options for Securing RTP Sessions [RFC7201], for example SRTP   [RFC3711] can provide the necessary security functions of ensuring   the integrity and source authenticity.18.  Examples18.1.  Example: Bundle Address Selection   The example below shows:   o  An offer, in which the offerer associates a unique address with      each bundled "m=" line within the BUNDLE group.   o  An answer, in which the answerer selects the offerer BUNDLE      address, and then selects its own BUNDLE address (the answerer      BUNDLE address) and associates it with each bundled "m=" line      within the BUNDLE group.Holmberg, et al.          Expires March 4, 2018                [Page 38]Internet-Draft                Bundled media                  August 2017   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=rtcp-mux       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=rtcp-mux       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=rtcp-mux       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:midHolmberg, et al.          Expires March 4, 2018                [Page 39]Internet-Draft                Bundled media                  August 201718.2.  Example: BUNDLE Extension Rejected   The example below shows:   o  An offer, in which the offerer associates a unique address with      each bundled "m=" line within the BUNDLE group.   o  An answer, in which the answerer rejects the offered BUNDLE group,      and associates a unique address with each "m=" line (following      normal RFC 3264 procedures).Holmberg, et al.          Expires March 4, 2018                [Page 40]Internet-Draft                Bundled media                  August 2017   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=rtcp-mux       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=rtcp-mux       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=rtcp-mux       a=rtpmap:0 PCMU/8000       m=video 30000 RTP/AVP 32       b=AS:1000       a=rtcp-mux       a=rtpmap:32 MPV/9000018.3.  Example: Offerer Adds A Media Description To A BUNDLE Group   The example below shows:Holmberg, et al.          Expires March 4, 2018                [Page 41]Internet-Draft                Bundled media                  August 2017   o  A subsequent offer (the BUNDLE group has been created as part of a      previous offer/answer exchange), in which the offerer adds a new      "m=" line, represented by the "zen" identification-tag, to a      previously negotiated BUNDLE group, associates a unique address      with the added "m=" line, and associates the previously selected      offerer BUNDLE address with each of the other bundled "m=" lines      within the BUNDLE group.   o  An answer, in which the answerer associates the answerer BUNDLE      address with 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=rtcp-mux       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=rtcp-mux       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=Holmberg, et al.          Expires March 4, 2018                [Page 42]Internet-Draft                Bundled media                  August 2017       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=rtcp-mux       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 20000 RTP/AVP 66       b=AS:1000       a=mid:zen       a=rtpmap:66 H261/90000       a=extmap 1 urn:ietf:params:rtp-hdrext:sdes:mid18.4.  Example: Offerer Moves A Media Description Out Of A BUNDLE Group   The example below shows:   o  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, associates a unique      address with the moved "m=" line, and associates the offerer      BUNDLE address with each other bundled "m=" line within the BUNDLE      group.   o  An answer, in which the answerer moves the "m=" line out of the      BUNDLE group, associates a unique address with the moved "m="      line, and associates the answerer BUNDLE address with 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 97Holmberg, et al.          Expires March 4, 2018                [Page 43]Internet-Draft                Bundled media                  August 2017       b=AS:200       a=mid:foo       a=rtcp-mux       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 50000 RTP/AVP 66       b=AS:1000       a=mid:zen       a=rtcp-mux       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=rtcp-mux       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=rtcp-mux       a=rtpmap:66 H261/90000Holmberg, et al.          Expires March 4, 2018                [Page 44]Internet-Draft                Bundled media                  August 201718.5.  Example: Offerer Disables A Media Description Within A BUNDLE       Group   The example below shows:   o  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 a BUNDLE group, assigns a zero port      number to the disabled "m=" line, and associates the offerer      BUNDLE address with each of the other bundled "m=" lines within      the BUNDLE group.   o  An 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 associates the answerer BUNDLE address with 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=rtcp-mux       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=0Holmberg, et al.          Expires March 4, 2018                [Page 45]Internet-Draft                Bundled media                  August 2017       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=rtcp-mux       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 0 RTP/AVP 66       a=mid:zen       a=rtpmap:66 H261/9000019.  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, Ari Keranen, Adam Roach, Christian Groves, Roman Shpount,   Suhas Nandakumar, Nils Ohlmeier, Jens Guballa, Raju Makaraju and   Justin Uberti for reading the text, and providing useful feedback.   Thanks to Bernard Aboba, Cullen Jennings, Peter Thatcher, Justin   Uberti, and Magnus Westerlund for providing the text for the section   on RTP/RTCP stream association.   Thanks to Magnus Westerlund, Colin Perkins and Jonathan Lennox for   providing help and text on the RTP/RTCP procedures.   Thanks to Spotify for providing music for the countless hours of   document editing.Holmberg, et al.          Expires March 4, 2018                [Page 46]Internet-Draft                Bundled media                  August 201720.  Change Log   [RFC EDITOR NOTE: Please remove this section when publishing]   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-38   o  Changes to RTP streaming mapping section based on text from Colin      Perkins.   o  The following GitHub pull requests were merged:   o  https://github.com/cdh4u/draft-sdp-bundle/pull/34   o  - Proposed updates to RTP processing   o  https://github.com/cdh4u/draft-sdp-bundle/pull/35   o  - fixed reference to receiver-id section   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-37   o  The following GitHub pull request was merged:   o  https://github.com/cdh4u/draft-sdp-bundle/pull/33   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-36   o  The following GitHub pull requests were merged:   o  https://github.com/cdh4u/draft-sdp-bundle/pull/32   o  - extmap handling in BUNDLE.   o  https://github.com/cdh4u/draft-sdp-bundle/pull/31   o  - Additional Acknowledgement text added.   o  https://github.com/cdh4u/draft-sdp-bundle/pull/30   o  - MID SDES item security procedures updated   o  https://github.com/cdh4u/draft-sdp-bundle/pull/29   o  - Appendix B of JSEP moved into BUNDLE.   o  - Associating RTP/RTCP packets with SDP m- lines.   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-35Holmberg, et al.          Expires March 4, 2018                [Page 47]Internet-Draft                Bundled media                  August 2017   o  Editorial changes on RTP streaming mapping section based on      comments from Colin Perkins.   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-34   o  RTP streams, instead of RTP packets, are associated with m- lines.   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-33   o  Editorial changes based on comments from Eric Rescorla and Cullen      Jennings:   o  - Changes regarding usage of RTP/RTCP multiplexing attributes.   o  - Additional text regarding associating RTP/RTCP packets with SDP      m- lines.   o  - Reference correction.   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-32   o  Editorial changes based on comments from Eric Rescorla and Cullen      Jennings:   o  - Justification for mechanism added to Introduction.   o  - Clarify that the order of m- lines in the group:BUNDLE attribute      does not have to be the same as the order in which the m- lines      are listed in the SDP.   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-31   o  Editorial changes based on GitHub Pull requests by Martin Thomson:   o  - https://github.com/cdh4u/draft-sdp-bundle/pull/2   o  - https://github.com/cdh4u/draft-sdp-bundle/pull/1   o  Editorial change based on comment from Diederick Huijbers (9th      July 2016).   o  Changes based on comments from Flemming Andreasen (21st June      2016):   o  - Mux category for SDP bundle-only attribute added.   o  - Mux category considerations editorial clarification.Holmberg, et al.          Expires March 4, 2018                [Page 48]Internet-Draft                Bundled media                  August 2017   o  - Editorial changes.   o  RTP SDES extension according to draft-ietf-avtext-sdes-hdr-ext.   o  Note whether Design Considerations appendix is to be kept removed:   o  - Appendix is kept within document.   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-30   o  Indicating in the Abstract and Introduction that the document      updates RFC 3264.   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-29   o  Change based on WGLC comment from Colin Perkins.   o  - Clarify that SSRC can be reused by another source after a delay      of 5 RTCP reporting intervals.   o  Change based on WGLC comment from Alissa Cooper.   o  - IANA registry name fix.   o  - Additional IANA registration information added.   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-28   o  - Alignment with exclusive mux procedures.   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-27   o  - Yet another terminology change.   o  - Mux category considerations added.   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-26   o  - ICE considerations modified: ICE-related SDP attributes only      added to the bundled m- line representing the selected BUNDLE      address.   o  - Reference to draft-ietf-mmusic-ice-sip-sdp added.   o  - Reference to RFC 5245 replaced with reference to draft-ietf-ice-      rfc5245bis.   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-25Holmberg, et al.          Expires March 4, 2018                [Page 49]Internet-Draft                Bundled media                  August 2017   o  - RTP/RTCP mux procedures updated with exclusive RTP/RTCP mux      considerations.   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-24   o  - Reference and procedures associated with exclusive RTP/RTCP mux      added   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-23   o  - RTCP-MUX mandatory for bundled RTP m- lines   o  - Editorial fixes based on comments from Flemming Andreasen   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-22   o  - Correction of Ari's family name   o  - Editorial fixes based on comments from Thomas Stach   o  - RTP/RTCP correction based on comment from Magnus Westerlund   o  -- http://www.ietf.org/mail-archive/web/mmusic/current/      msg14861.html   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-21   o  - Correct based on comment from Paul Kyzivat   o  -- 'received packets' replaced with 'received data'   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-20   o  - Clarification based on comment from James Guballa   o  - Clarification based on comment from Flemming Andreasen   Changes from draft-ietf-mmusic-sdp-bundle-negotiation-19   o  - DTLS Considerations section added.   o  - BUNDLE semantics added to the IANA Considerations   o  - Changes based on WGLC comments from Adam Roach   o  -- http://www.ietf.org/mail-archive/web/mmusic/current/      msg14673.htmlHolmberg, et al.          Expires March 4, 2018                [Page 50]Internet-Draft                Bundled media                  August 2017   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   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 valueHolmberg, et al.          Expires March 4, 2018                [Page 51]Internet-Draft                Bundled media                  August 2017   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:   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).Holmberg, et al.          Expires March 4, 2018                [Page 52]Internet-Draft                Bundled media                  August 2017   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.   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.Holmberg, et al.          Expires March 4, 2018                [Page 53]Internet-Draft                Bundled media                  August 2017   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   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.Holmberg, et al.          Expires March 4, 2018                [Page 54]Internet-Draft                Bundled media                  August 2017   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   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.Holmberg, et al.          Expires March 4, 2018                [Page 55]Internet-Draft                Bundled media                  August 201721.  References21.1.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels", BCP 14, RFC 2119,              DOI 10.17487/RFC2119, March 1997, <https://www.rfc-              editor.org/info/rfc2119>.   [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model              with Session Description Protocol (SDP)", RFC 3264,              DOI 10.17487/RFC3264, June 2002, <https://www.rfc-              editor.org/info/rfc3264>.   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.              Jacobson, "RTP: A Transport Protocol for Real-Time              Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,              July 2003, <https://www.rfc-editor.org/info/rfc3550>.   [RFC3605]  Huitema, C., "Real Time Control Protocol (RTCP) attribute              in Session Description Protocol (SDP)", RFC 3605,              DOI 10.17487/RFC3605, October 2003, <https://www.rfc-              editor.org/info/rfc3605>.   [RFC3711]  Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.              Norrman, "The Secure Real-time Transport Protocol (SRTP)",              RFC 3711, DOI 10.17487/RFC3711, March 2004,              <https://www.rfc-editor.org/info/rfc3711>.   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session              Description Protocol", RFC 4566, DOI 10.17487/RFC4566,              July 2006, <https://www.rfc-editor.org/info/rfc4566>.   [RFC4961]  Wing, D., "Symmetric RTP / RTP Control Protocol (RTCP)",              BCP 131, RFC 4961, DOI 10.17487/RFC4961, July 2007,              <https://www.rfc-editor.org/info/rfc4961>.   [RFC5245]  Rosenberg, J., "Interactive Connectivity Establishment              (ICE): A Protocol for Network Address Translator (NAT)              Traversal for Offer/Answer Protocols", RFC 5245,              DOI 10.17487/RFC5245, April 2010, <https://www.rfc-              editor.org/info/rfc5245>.   [RFC5285]  Singer, D. and H. Desineni, "A General Mechanism for RTP              Header Extensions", RFC 5285, DOI 10.17487/RFC5285, July              2008, <https://www.rfc-editor.org/info/rfc5285>.Holmberg, et al.          Expires March 4, 2018                [Page 56]Internet-Draft                Bundled media                  August 2017   [RFC5761]  Perkins, C. and M. Westerlund, "Multiplexing RTP Data and              Control Packets on a Single Port", RFC 5761,              DOI 10.17487/RFC5761, April 2010, <https://www.rfc-              editor.org/info/rfc5761>.   [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,              DOI 10.17487/RFC5764, May 2010, <https://www.rfc-              editor.org/info/rfc5764>.   [RFC5888]  Camarillo, G. and H. Schulzrinne, "The Session Description              Protocol (SDP) Grouping Framework", RFC 5888,              DOI 10.17487/RFC5888, June 2010, <https://www.rfc-              editor.org/info/rfc5888>.   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer              Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,              January 2012, <https://www.rfc-editor.org/info/rfc6347>.   [RFC7941]  Westerlund, M., Burman, B., Even, R., and M. Zanaty, "RTP              Header Extension for the RTP Control Protocol (RTCP)              Source Description Items", RFC 7941, DOI 10.17487/RFC7941,              August 2016, <https://www.rfc-editor.org/info/rfc7941>.   [I-D.ietf-ice-rfc5245bis]              Keranen, A., Holmberg, C., and J. Rosenberg, "Interactive              Connectivity Establishment (ICE): A Protocol for Network              Address Translator (NAT) Traversal", draft-ietf-ice-              rfc5245bis-10 (work in progress), May 2017.   [I-D.ietf-mmusic-sdp-mux-attributes]              Nandakumar, S., "A Framework for SDP Attributes when              Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-16              (work in progress), December 2016.   [I-D.ietf-mmusic-mux-exclusive]              Holmberg, C., "Indicating Exclusive Support of RTP/RTCP              Multiplexing using SDP", draft-ietf-mmusic-mux-              exclusive-12 (work in progress), May 2017.   [I-D.ietf-mmusic-ice-sip-sdp]              Petit-Huguenin, M., Keranen, A., and S. Nandakumar,              "Session Description Protocol (SDP) Offer/Answer              procedures for Interactive Connectivity Establishment              (ICE)", draft-ietf-mmusic-ice-sip-sdp-13 (work in              progress), June 2017.Holmberg, et al.          Expires March 4, 2018                [Page 57]Internet-Draft                Bundled media                  August 201721.2.  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,              DOI 10.17487/RFC3261, June 2002, <https://www.rfc-              editor.org/info/rfc3261>.   [RFC3611]  Friedman, T., Ed., Caceres, R., Ed., and A. Clark, Ed.,              "RTP Control Protocol Extended Reports (RTCP XR)",              RFC 3611, DOI 10.17487/RFC3611, November 2003,              <https://www.rfc-editor.org/info/rfc3611>.   [RFC5104]  Wenger, S., Chandra, U., Westerlund, M., and B. Burman,              "Codec Control Messages in the RTP Audio-Visual Profile              with Feedback (AVPF)", RFC 5104, DOI 10.17487/RFC5104,              February 2008, <https://www.rfc-editor.org/info/rfc5104>.   [RFC4585]  Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,              "Extended RTP Profile for Real-time Transport Control              Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585,              DOI 10.17487/RFC4585, July 2006, <https://www.rfc-              editor.org/info/rfc4585>.   [RFC5576]  Lennox, J., Ott, J., and T. Schierl, "Source-Specific              Media Attributes in the Session Description Protocol              (SDP)", RFC 5576, DOI 10.17487/RFC5576, June 2009,              <https://www.rfc-editor.org/info/rfc5576>.   [RFC7160]  Petit-Huguenin, M. and G. Zorn, Ed., "Support for Multiple              Clock Rates in an RTP Session", RFC 7160,              DOI 10.17487/RFC7160, April 2014, <https://www.rfc-              editor.org/info/rfc7160>.   [RFC7201]  Westerlund, M. and C. Perkins, "Options for Securing RTP              Sessions", RFC 7201, DOI 10.17487/RFC7201, April 2014,              <https://www.rfc-editor.org/info/rfc7201>.   [RFC7656]  Lennox, J., Gross, K., Nandakumar, S., Salgueiro, G., and              B. Burman, Ed., "A Taxonomy of Semantics and Mechanisms              for Real-Time Transport Protocol (RTP) Sources", RFC 7656,              DOI 10.17487/RFC7656, November 2015, <https://www.rfc-              editor.org/info/rfc7656>.Holmberg, et al.          Expires March 4, 2018                [Page 58]Internet-Draft                Bundled media                  August 2017   [I-D.ietf-ice-trickle]              Ivov, E., Rescorla, E., Uberti, J., and P. Saint-Andre,              "Trickle ICE: Incremental Provisioning of Candidates for              the Interactive Connectivity Establishment (ICE)              Protocol", draft-ietf-ice-trickle-13 (work in progress),              July 2017.   [I-D.ietf-avtext-lrr]              Lennox, J., Hong, D., Uberti, J., Holmer, S., and M.              Flodman, "The Layer Refresh Request (LRR) RTCP Feedback              Message", draft-ietf-avtext-lrr-07 (work in progress),              July 2017.Appendix A.  Design Considerations   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 specified by 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.A.1.  UA Interoperability   Consider the following SDP Offer/Answer exchange, where Alice sends   an SDP Offer to Bob:Holmberg, et al.          Expires March 4, 2018                [Page 59]Internet-Draft                Bundled media                  August 2017   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 knows 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:Holmberg, et al.          Expires March 4, 2018                [Page 60]Internet-Draft                Bundled media                  August 2017   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.2.  Usage of port number value zero   In an SDP Offer or SDP Answer, the media specified by 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.3.  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 B2BUA still generates that SDP attribute in the Offer   for the outgoing call leg.  Consider a 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 case, if the   B2BUA received an Offer like:Holmberg, et al.          Expires March 4, 2018                [Page 61]Internet-Draft                Bundled media                  August 2017   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, a B2BUA 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.3.1.  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.3.2.  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 specified by all "m=" lines try to use that   bandwidth.  That may either simply lead to bad user experience, or to   termination of the call.A.4.  Candidate Gathering   When using ICE, a 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 for exampe a web-page is loading to minimize theHolmberg, et al.          Expires March 4, 2018                [Page 62]Internet-Draft                Bundled media                  August 2017   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-ice-trickle] 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   allocations 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.caHolmberg, et al.          Expires March 4, 2018                [Page 63]