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Versions: (draft-xia-avtext-splicing-notification) 00 01 02 03 04 05 06 07 08 09 RFC 8286

AVTEXT Working Group                                              J. Xia
INTERNET-DRAFT                                                   R. Even
Intended Status: Standards Track                                R. Huang
Expires: June 13, 2015                                            Huawei
                                                                 L. Deng
                                                            China Mobile
                                                       December 10, 2014


            RTP/RTCP extension for RTP Splicing Notification
               draft-ietf-avtext-splicing-notification-01


Abstract

   Content splicing is a process that replaces the content of a main
   multimedia stream with other multimedia content, and delivers the
   substitutive multimedia content to the receivers for a period of
   time. The splicer is designed to handle RTP splicing and needs to
   know when to start and end the splicing.

   This memo defines two RTP/RTCP extensions to indicate the splicing
   related information to the splicer: an RTP header extension that
   conveys the information in-band and an RTCP packet that conveys the
   information out-of-band.

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as
   Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
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   http://www.ietf.org/1id-abstracts.html

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html





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Copyright and License Notice

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

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document. Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document. Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.



Table of Contents

   1  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1  Terminology . . . . . . . . . . . . . . . . . . . . . . . .  3
   2  Overview of RTP Splicing Notification . . . . . . . . . . . . .  4
   3  Conveying Splicing Interval in RTP/RTCP extensions  . . . . . .  5
     3.1 RTP Header Extension . . . . . . . . . . . . . . . . . . . .  5
     3.2 RTCP Splicing Notification Message . . . . . . . . . . . . .  6
   4  Reducing Splicing Latency . . . . . . . . . . . . . . . . . . .  7
   5  Failure Cases . . . . . . . . . . . . . . . . . . . . . . . . .  8
   6 SDP Signaling  . . . . . . . . . . . . . . . . . . . . . . . . .  8
     6.1 Declarative SDP  . . . . . . . . . . . . . . . . . . . . . .  9
     6.2 Offer/Answer without BUNDLE  . . . . . . . . . . . . . . . .  9
     6.3 Offer/Answer with BUNDLE: All Media are spliced  . . . . . . 10
     6.4 Offer/Answer with BUNDLE: a Subset of Media are Spliced  . . 12
   7  Security Considerations . . . . . . . . . . . . . . . . . . . . 13
   8  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 14
     8.1  RTCP Control Packet Types . . . . . . . . . . . . . . . . . 14
     8.2  RTP Compact Header Extensions . . . . . . . . . . . . . . . 14
     8.3 SDP Grouping Semantic Extension  . . . . . . . . . . . . . . 14
   9 Acknowledges . . . . . . . . . . . . . . . . . . . . . . . . . . 15
   10  References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     10.1  Normative References . . . . . . . . . . . . . . . . . . . 15
     10.2  Informative References . . . . . . . . . . . . . . . . . . 15
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16









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1  Introduction

   Splicing is a process that replaces some multimedia content with
   other multimedia content and delivers the substitutive multimedia
   content to the receivers for a period of time. In some predictable
   splicing cases, e.g., advertisement insertion, the splicing duration
   MUST be inside of the specific, pre-designated time slot.  Certain
   timing information about when to start and end the splicing must be
   first acquired by the splicer in order to start the splicing. This
   document refers to this information as Splicing Interval.

   [SCTE35] provides a method that encapsulates the Splicing Interval
   inside the MPEG2-TS layer in cable TV systems. But in the RTP
   splicing scenario described in [RFC6828], the RTP mixer designed as
   the splicer has to decode the RTP packets and search for the Splicing
   Interval inside the payloads. The need for such processing increases
   the workload of the mixer and limits the number of RTP sessions the
   mixer can support.

   The document defines an RTP header extension [RFC5285] used by the
   main RTP sender to provide the Splicing Interval by including it in
   the RTP packets.

   Nevertheless, the Splicing Interval conveyed in the RTP header
   extension might not reach the mixer successfully, any splicing un-
   aware middlebox on the path between the RTP sender and the mixer
   might strip this RTP header extension.

   To increase robustness against such case, the document also defines a
   new RTCP packet type in a complementary fashion to carry the same
   Splicing Interval to the mixer.

1.1  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

   The terminology defined in "Content Splicing for RTP Sessions"
   [RFC6828] applies to this document and in addition, we define:

   Splicing Interval:

      The NTP timestamps for the Splicing-In point and Splicing-Out
      point per [RFC6828] allowing the mixer to know when to start and
      end the RTP splicing.





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2  Overview of RTP Splicing Notification

   According to RTP Splicing draft [RFC6828], a mixer is designed to
   handle splicing on the RTP layer at the reserved time slots set by
   the main RTP sender. This implies that the mixer must first know the
   Splicing Interval from the main RTP sender before it can start
   splicing.

   When a new splicing is forthcoming, the main RTP sender MUST send the
   Splicing Interval to the mixer. Usually, the Splicing Interval SHOULD
   be sent more than once to mitigate the possible packet loss. To
   enable the mixer to get the substitutive content before the splicing
   starts, the main RTP sender MUST send the Splicing Interval far
   ahead. For example, the main RTP sender can estimate when to send the
   Splicing Interval based on the round-trip time (RTT) following the
   mechanisms in section 6.4.1 of [RFC3550] when the mixer sends RTCP RR
   to the main sender.

   The substitutive sender also needs to learn the Splicing Interval
   from the main RTP sender in advance, and thus estimates when to
   transfer the substitutive content to the mixer. The Splicing Interval
   could be transmitted from the main RTP sender to the substitutive
   content using some out-of-band mechanisms, the details how to achieve
   that are beyond the scope of this memo. To ensure the Splicing
   Interval is valid for both the main RTP sender and the substitutive
   RTP sender, the two senders MUST share a common reference clock, so
   the mixer can achieve accurate splicing.

   In this document, the main RTP sender uses a couple of NTP-format
   timestamps, derived from the common reference clock, to indicate when
   to start and end the splicing to the mixer: the timestamp of the
   first substitutive RTP packet at the splicing in point, and the
   timestamp of the first main RTP packet at the splicing out point.

   When the substitutive RTP sender gets the Splicing Interval, it must
   prepare the substitutive stream. The mixer MUST ensure that the RTP
   timestamp of the first substitutive RTP packet that would be
   presented to the receivers corresponds to the same time instant as
   the former NTP timestamp in the Splicing Interval. To enable the
   mixer to know the first substitutive RTP packet it needs to send, the
   substitutive RTP sender MUST send the substitutive RTP packet ahead
   of the Splicing In point, sllowing the mixer to find out the
   timestamp of this first RTP packet in the substitutive RTP stream,
   e.g., using a prior RTCP SR message.

   When the splicing will end, the mixer MUST ensure that the RTP
   timestamp of the first main RTP packet that would be presented on the
   receivers corresponds to the same time instant as the latter NTP



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   timestamp in the Splicing Interval.


3  Conveying Splicing Interval in RTP/RTCP extensions

   This memo defines two backwards compatible RTP extensions to convey
   the Splicing Interval to the mixer: an RTP header extension and an
   RTCP splicing notification message.


3.1 RTP Header Extension

   The RTP header extension mechanism defined in [RFC5285] can be
   adapted to carry the Splicing Interval consisting of a couple of NTP-
   format timestamps.

   One variant is defined for this header extension. It carries the 7
   octets splicing-out NTP timestamp (lower 24-bit part of the Seconds
   of a NTP-format timestamp and the 32 bits of the Fraction of a NTP-
   format timestamp as defined in [RFC5905]), followed by the 8 octets
   splicing-in NTP timestamp (64-bit NTP-format timestamp as defined in
   [RFC5905]). The top 8 bits of the splicing-out NTP timestamp are
   referred from the top 8 bits of the splicing-in NTP timestamp. This
   is unambiguous, under the assumption that the splicing-out time is
   after the splicing-in time, and the splicing interval is less than
   2^25 seconds.

   The format is shown in Figures 1.

        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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |       0xBE    |    0xDE       |           length=4            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+E
      |   ID  | L=15  | OUT NTP timestamp format - Seconds (bit 8-31) |x
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+t
      |       OUT NTP timestamp format - Fraction (bit 0-31)          |e
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+n
      |       IN  NTP timestamp format - Seconds (bit 0-31)           |s
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+i
      |       IN  NTP timestamp format - Fraction (bit 0-31)          |o
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+n

                    Figure 1: Sample hybrid NTP Encoding Using
                           the One-Byte Header Format

   Note that the inclusion of an RTP header extension will reduce the
   efficiency of RTP header compression. It is RECOMMENDED that the main



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   sender begins to insert the RTP header extensions into a number of
   RTP packets prior to the splicing in, while leaving the remaining RTP
   packets unmarked.

   After the mixer intercepts the RTP header extension and derives the
   Splicing Interval, it will generate its own stream and SHOULD NOT
   include the RTP header extension in outgoing packets to reduce header
   overhead.

   Furthermore, whether the in-band NTP-format timestamps are included
   or not, RTCP splicing notification message, specified in the next
   section, MUST be sent to provide robustness in case of any splicing-
   unaware middlebox that might strip RTP header extensions.

3.2 RTCP Splicing Notification Message

   In addition to the RTP header extension, the main RTP sender includes
   the Splicing Interval in an RTCP splicing notification message.

   The RTCP splicing notification message is a new RTCP packet type. It
   has a fix header followed by a couple of NTP-format timestamps:


         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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |V=2|P|reserved |    PT=TBA   |              length             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                           SSRC                                |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |             IN NTP Timestamp (most significant word)          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |             IN NTP Timestamp (least significant word)         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |             OUT NTP Timestamp (most significant word)         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |             OUT NTP Timestamp (least significant word)        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 2: RTCP Splicing Notification Message

   The RSI packet includes the following fields:

   Length: 16 bits

      As defined in [RFC3550], the length of the RTCP packet in 32-bit
      words minus one, including the header and any padding.




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   SSRC: 32 bits

      The SSRC of the Main RTP Sender.

   Timestamp: 64 bits

      Indicates the wallclock time when this splicing starts and ends.
      The full-resolution NTP timestamp is used, which is a 64-bit,
      unsigned, fixed-point number with the integer part in the first 32
      bits and the fractional part in the last 32 bits.  This format is
      similar to RTCP Sender Report (Section 6.4.1 of [RFC3550]).

   The RTCP splicing notification message can be appended to RTCP SR the
   main RTP sender generates in compound RTCP packets, and hence follows
   the compound RTCP rules defined in Section 6.1 in [RFC3550].

   If the use of non-compound RTCP [RFC5506] was previously negotiated
   between the sender and the mixer, the RTCP splicing notification
   message may be sent as non-compound RTCP packets.

   When the mixer intercepts the RTCP splicing notification message, it
   MAY NOT forward the message to the receivers in order to reduce RTCP
   bandwidth consumption or to avoid downstream receivers from detecting
   splicing defined in Section 4.5 in [RFC6828].


4  Reducing Splicing Latency

   When splicing starts or ends, the mixer outputs the multimedia
   content from another sender to the receivers. Given that the
   receivers must first acquire certain information ([RFC6285] refers to
   this information as Reference Information) to start processing the
   multimedia data, either the main RTP sender or the substitutive
   sender SHOULD provide the Reference Information align with its
   multimedia content to reduce the delay caused by acquiring the
   Reference Information. The methods by which the Reference Information
   is distributed to the receivers is out of scope of this memo.

   Another latency element is synchronization caused delay. The
   receivers must receive enough synchronization metadata prior to
   synchronizing the separate components of the multimedia streams when
   splicing starts or ends. Either the main RTP sender or the
   substitutive sender SHOULD send the synchronization metadata early
   enough so that the receivers can play out the multimedia in a
   synchronized fashion. The mechanisms defined in [RFC6051] are
   RECOMMENDED to be adopted to reduce the possible synchronization
   delay.




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5  Failure Cases

   This section examines the implications of losing RTCP splicing
   notification message and other failure case, e.g., the RTP header
   extension is stripped on the path.

   Given that there may be splicing un-aware middlebox on the path
   between the main RTP sender and the mixer, one heuristics will be
   used to verify whether or not the Splicing Interval reaches the
   mixers.

   If the mixer does not get the Splicing Interval when the splicing
   starts, it will still output the main content to the downstream
   receivers and forward the RTCP RR packets sent from downstream
   receivers to the main RTP sender (see section 4.2 of [RFC6828]). In
   such case, the main RTP sender can learn that splicing failed.

   In a similar manner, the substitutive sender can learn that splicing
   failed if it does not receive any RTCP RR packets from downstream
   receivers when the splicing starts.

   Upon the detection of a failure, the main RTP sender or the
   substitutive sender SHOULD check the path to the failed mixer, or
   fallback to the payload specific mechanisms, e.g., MPEG-TS splicing
   solution defined in [SCTE35].


6 SDP Signaling

   This document defines the URI for declaring this header extension in
   an extmap attribute to be "urn:ietf:params:rtp-hdrext:splicing-
   interval".

   This document extended the standard semantics defined in SDP Grouping
   Framework [RFC5888] with a new semantic: SPLICE to represent the
   relationship between the main RTP stream and the substitutive RTP
   stream. The main RTP sender provides the information about both main
   and substitutive sources.

   The extended SDP attribute specified in this document is applicable
   for offer/answer content [RFC3264] and do not affect any rules when
   negotiating offer and answer. When used with multiple media,
   substitutive RTP MUST be applied only to the RTP packets whose SDP m-
   line is in the same group with the substitutive stream using FID and
   has the extended splicing extmap attribute. This semantics is to have
   splicing applicable for BUNDLE cases.

   The following examples show how SDP signaling could be used for



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   splicing in different cases.

6.1 Declarative SDP

              v=0
              o=xia 1122334455 1122334466 IN IP4 splicing.example.com
              s=RTP Splicing Example
              t=0 0
              a=group:SPLICE 1 2
              m=video 30000 RTP/AVP 100
              i=Main RTP Stream
              c=IN IP4 233.252.0.1/127
              a=rtpmap:100 MP2T/90000
              a=extmap:1 urn:ietf:params:rtp-hdrext:splicing-interval
              a=mid:1
              m=video 30002 RTP/AVP 100
              i=Substitutive RTP Stream
              c=IN IP4 233.252.0.2/127
              a=sendonly
              a=rtpmap:100 MP2T/90000
              a=mid:2

         Figure 3: Example SDP for a single-channel splicing scenario

   The mixer receiving the SDP message above receives one MPEG2-TS
   stream (payload 100) from the main RTP sender (with multicast
   destination address of 233.252.0.1) on port 30000, and/or receives
   another MPEG2-TS stream from the substitutive RTP sender (with
   multicast destination address of 233.252.0.2) on port 30002.  But at
   a particular point in time, the mixer only selects one stream and
   outputs the content from the chosen stream to the downstream
   receivers.

6.2 Offer/Answer without BUNDLE

   SDP Offer - from main RTP sender

            v=0
            o=xia 1122334455 1122334466 IN IP4 splicing.example.com
            s=RTP Splicing Example
            t=0 0
            a=group:SPLICE 1 2
            m=video 30000 RTP/AVP 31 100
            i=Main RTP Stream
            c=IN IP4 splicing.example.com
            a=rtpmap:31 H261/90000
            a=rtpmap:100 MP2T/90000
            a=extmap:1 urn:ietf:params:rtp-hdrext:splicing-interval



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            a=mid:1
            m=video 40000 RTP/AVP 31 100
            i=Substitutive RTP Stream
            c=IN IP4 substitutive.example.com
            a=rtpmap:31 H261/90000
            a=rtpmap:100 MP2T/90000
            a=sendonly
            a=mid:2

   SDP Answer - from splicer

            v=0
            o=xia 1122334455 1122334466 IN IP4 splicer.example.com
            s=RTP Splicing Example
            t=0 0
            a=group:SPLICE 1 2
            m=video 30000 RTP/AVP 100
            i=Main RTP Stream
            c=IN IP4 splicer.example.com
            a=rtpmap:100 MP2T/90000
            a=extmap:1 urn:ietf:params:rtp-hdrext:splicing-interval
            a=mid:1
            m=video 40000 RTP/AVP 100
            i=Substitutive RTP Stream
            c=IN IP4 splicer.example.com
            a=rtpmap:100 MP2T/90000
            a=recvonly
            a=mid:2


   Only codecs that are supported both by the main RTP stream and the
   substitutive RTP stream could be negotiated with SDP O/A. And the
   mixer MUST choose the same codec for both of these two streams.

6.3 Offer/Answer with BUNDLE: All Media are spliced

   In this example, the bundled audio and video media have their own
   substitutive media for splicing:

   1.  An Offer, in which the offerer assigns a unique address and a
   substitutive media to each bundled "m="line for splicing within the
   BUNDLE group.

   2.  An answer, in which the answerer selects its own BUNDLE address,
   and leave the substitutive media untouched.

   SDP Offer - from main RTP sender




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          v=0
          o=alice 1122334455 1122334466 IN IP4 splicing.example.com
          s=RTP Splicing Example
          c=IN IP4 splicing.example.com
          t=0 0
          a=group:SPLICE foo 1
          a=group:SPLICE bar 2
          a=group:BUNDLE foo bar
          m=audio 10000 RTP/AVP 0 8 97
          a=mid:foo
          b=AS:200
          a=rtpmap:0 PCMU/8000
          a=rtpmap:8 PCMA/8000
          a=rtpmap:97 iLBC/8000
          a=extmap:1 urn:ietf:params:rtp-hdrext:splicing-interval
          m=video 10002 RTP/AVP 31 32
          a=mid:bar
          b=AS:1000
          a=rtpmap:31 H261/90000
          a=rtpmap:32 MPV/90000
          a=extmap:2 urn:ietf:params:rtp-hdrext:splicing-interval
          m=audio 20000 RTP/AVP 0 8 97
          i=Substitutive audio RTP Stream
          c=IN IP4 substitive.example.com
          a=rtpmap:0 PCMU/8000
          a=rtpmap:8 PCMA/8000
          a=rtpmap:97 iLBC/8000
          a=sendonly
          a=mid:1
          m=video 20002 RTP/AVP 31 32
          i=Substitutive video RTP Stream
          c=IN IP4 substitive.example.com
          a=rtpmap:31 H261/90000
          a=rtpmap:32 MPV/90000
          a=mid:2

   SDP Answer - from the splicer

          v=0
          o=bob 2808844564 2808844564 IN IP4 splicer.example.com
          s=RTP Splicing Example
          c=IN IP4 splicer.example.com
          t=0 0
          a=group:SPLICE foo 1
          a=group:SPLICE bar 2
          a=group:BUNDLE foo bar
          m=audio 30000 RTP/AVP 0
          a=mid:foo



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          b=AS:200
          a=rtpmap:0 PCMU/8000
          a=extmap:1 urn:ietf:params:rtp-hdrext:splicing-interval
          m=video 30000 RTP/AVP 32
          a=mid:bar
          b=AS:1000
          a=rtpmap:32 MPV/90000
          a=extmap:2 urn:ietf:params:rtp-hdrext:splicing-interval
          m=audio 30002 RTP/AVP 0
          i=Substitutive audio RTP Stream
          c=IN IP4 splicer.example.com
          a=rtpmap:0 PCMU/8000
          a=sendonly
          a=mid:1
          m=video 30004 RTP/AVP 32
          i=Substitutive video RTP Stream
          c=IN IP4 splicer.example.com
          a=rtpmap:32 MPV/90000
          a=mid:2

6.4 Offer/Answer with BUNDLE: a Subset of Media are Spliced

   In this example, the substitutive media only applies for video when
   splicing:

   1. An Offer, in which the offerer assigns a unique address to each
   bundled "m="line within the BUNDLE group, and assigns a substitutive
   media to the bundled video "m=" line for splicing.

   2. An answer, in which the answerer selects its own BUNDLE address,
   and leave the substitutive media untouched.

   SDP Offer - from the main RTP sender:

          v=0
          o=alice 1122334455 1122334466 IN IP4 splicing.example.com
          s=RTP Splicing Example
          c=IN IP4 splicing.example.com
          t=0 0
          a=group:SPLICE bar 2
          a=group:BUNDLE foo bar
          m=audio 10000 RTP/AVP 0 8 97
          a=mid:foo
          b=AS:200
          a=rtpmap:0 PCMU/8000
          a=rtpmap:8 PCMA/8000
          a=rtpmap:97 iLBC/8000
          m=video 10002 RTP/AVP 31 32



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          a=mid:bar
          b=AS:1000
          a=rtpmap:31 H261/90000
          a=rtpmap:32 MPV/90000
          a=extmap:2 urn:ietf:params:rtp-hdrext:splicing-interval
          m=video 20000 RTP/AVP 31 32
          i=Substitutive video RTP Stream
          c=IN IP4 substitutive.example.com
          a=rtpmap:31 H261/90000
          a=rtpmap:32 MPV/90000
          a=mid:2

   SDP Answer - from the splicer:

          v=0
          o=bob 2808844564 2808844564 IN IP4 splicer.example.com
          s=RTP Splicing Example
          c=IN IP4 splicer.example.com
          t=0 0
          a=group:SPLICE bar 2
          a=group:BUNDLE foo bar
          m=audio 30000 RTP/AVP 0
          a=mid:foo
          b=AS:200
          a=rtpmap:0 PCMU/8000
          m=video 30000 RTP/AVP 32
          a=mid:bar
          b=AS:1000
          a=rtpmap:32 MPV/90000
          a=extmap:2 urn:ietf:params:rtp-hdrext:splicing-interval
          m=video 30004 RTP/AVP 32
          i=Substitutive video RTP Stream
          c=IN IP4 splicer.example.com
          a=rtpmap:32 MPV/90000
          a=mid:2

7  Security Considerations

   The security considerations of the RTP specification [RFC3550], the
   general mechanism for RTP header extensions [RFC5285] and the
   security considerations of the RTP splicing specification [RFC6828]
   apply.

   The RTP header extension defined in Section 4.1 include two NTP-
   format timestamps.  In the Secure Real-time Transport Protocol
   (SRTP)[RFC3711], RTP header extensions are authenticated but not
   encrypted.  A malicious endpoint possessing the SRTP key could choose
   to set the values in this header extension falsely, so as to falsely



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   claim the splicing time. Also, such a malicious endpoint could cause
   any arbitrary content it wishes spliced into the main RTP stream.

   In scenarios where this is a concern, additional mechanisms MUST be
   used to protect the confidentiality of the header extension.  This
   mechanism could be header extension encryption [SRTP-ENCR-HDR], or a
   lower-level security and authentication mechanism such as IPsec
   [RFC4301].


8  IANA Considerations

8.1  RTCP Control Packet Types

   Based on the guidelines suggested in [RFC5226], a new RTCP packet
   format has been registered with the RTCP Control Packet Type (PT)
   Registry:

         Name: SNM

         Long name: Splicing Notification Message

         Value: TBA

         Reference: This document

8.2  RTP Compact Header Extensions

   The IANA has also registered a new RTP Compact Header Extension
   [RFC5285], according to the following:

         Extension URI: urn:ietf:params:rtp-hdrext:splicing-interval

         Description: Splicing Interval

         Contact: Jinwei Xia <xiajinwei@huawei.com>

         Reference: This document

8.3 SDP Grouping Semantic Extension

   This document request IANA to register the new SDP grouping semantic
   extension called "SPLICE".

         Semantics: Splice

         Token:SPLICE




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         Reference: This document

         Contact: Jinwei Xia <xiajinwei@huawei.com>

9 Acknowledges

   TBD


10  References

10.1  Normative References

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

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

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

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

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

   [RFC5905]  Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
              "Network Time Protocol Version 4: Protocol and Algorithms
              Specification", RFC 5905, June 2010.

   [RFC6051]  Perkins, C. and T. Schierl, "Rapid Synchronisation of RTP
              Flows", RFC 6051, November 2010.

   [RFC6828]  Xia, J., "Content Splicing for RTP Sessions", RFC 6828,
              January 2013.

10.2  Informative References

   [RFC3711]  Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
              Norrman, "The Secure Real-time Transport Protocol (SRTP)",
              RFC 3711, March 2004.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005.




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   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC5506]  Johansson, I. and M. Westerlund, "Support for Reduced-Size
              Real-Time Transport Control Protocol (RTCP): Opportunities
              and Consequences", RFC 5506, April 2009.

   [RFC6285]  Ver Steeg, B., Begen, A., Van Caenegem, T., and Z. Vax,
              "Unicast-Based Rapid Acquisition of Multicast RTP
              Sessions", RFC 6285, June 2011.

   [RFC6904]  Lennox, J.,"Encryption of Header Extensions in the Secure
              Real-Time Transport Protocol (SRTP)", April 2013.

   [SCTE35]   Society of Cable Telecommunications Engineers (SCTE),
              "Digital Program Insertion Cueing Message for Cable",
              2011.


Authors' Addresses


   Jinwei Xia
   Huawei

   Email: xiajinwei@huawei.com



   Roni Even
   Huawei

   Email: ron.even.tlv@gmail.com


   Rachel Huang
   Huawei

   Email: rachel.huang@huawei.com


   Lingli Deng
   China Mobile

   Email: denglingli@chinamobile.com





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