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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: January 30, 2015                                         Huawei
                                                                 L. Deng
                                                            China Mobile
                                                           July 29, 2014


            RTP/RTCP Extension for RTP Splicing Notification
               draft-ietf-avtext-splicing-notification-00


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 RTP mixer is designed to handle RTP splicing in [RFC6828],
   but how the RTP mixer knows when to start and end the splicing is
   still unspecified.

   This memo defines two RTP/RTCP extensions to indicate the splicing
   related information to the RTP mixer: 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
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   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
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.



Table of Contents

   1  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  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 Extention . . . . . . . . . . . . . . . . . . . .  5
     3.2 RTCP Splicing Notification Message . . . . . . . . . . . . .  6
   4  Reduing Splicing Latency  . . . . . . . . . . . . . . . . . . .  7
   5  Failure Cases . . . . . . . . . . . . . . . . . . . . . . . . .  7
   6 SDP Signaling  . . . . . . . . . . . . . . . . . . . . . . . . .  8
   7  Security Considerations . . . . . . . . . . . . . . . . . . . .  9
   8  IANA Considerations . . . . . . . . . . . . . . . . . . . . . .  9
     8.1  RTCP Control Packet Types . . . . . . . . . . . . . . . . .  9
     8.2  RTP Compact Header Extensions . . . . . . . . . . . . . . . 10
   9 Acknowledges . . . . . . . . . . . . . . . . . . . . . . . . . . 10
   10  References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     10.1  Normative References . . . . . . . . . . . . . . . . . . . 10
     10.2  Informative References . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11














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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 mixer 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 RTP splicing
   scenario described in [RFC6828], the mixer has to decode the RTP
   packets, search and solve the Splicing Interval inside the payloads.
   The need for such processing enhances the workload of the mixer and
   limits the size of RTP sessions the mixer can support.

   The document defines an RTP header extension [RFC5285] through which
   the main RTP sender can 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 the RTP header extension.

   To increase robustness against above case, the document also defines
   a new RTCP packet type in a complementary fashion to carry the
   Splicing Interval to the mixer even though RTCP is inherently
   unreliable too.

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].

   Most terminology defined in "Content Splicing for RTP Sessions"
   [RFC6828] applies to this document except the following one.

   Splicing Interval:

      A set of certain metadata that allows the mixer to know when to
      start and end the RTP splicing. The information consists of a
      couple of NTP-format timestamps on the splicing in point and on
      the splicing out point.




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2  Overview of RTP Splicing Notification

   According to RTP Splicing draft [RFC6828], a mixer is designed to do
   splicing on the RTP layer, but it cannot insert the substitutive
   content randomly but only do that at the reserved time slots set by
   the main RTP sender. This implies the mixer must first know the
   Splicing Interval from the main RTP sender before splicing starts.

   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 against 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 enough in
   advance. Alternatively, 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 to 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 on the splicing in point, and the
   timestamp of the first main RTP packet on the splicing out point.

   When the substitutive RTP sender gets the Splicing Interval, it must
   prepare the substitutive stream. The RTP timestamp of the first
   substitutive RTP packet that would be presented on the receivers MUST
   correspond to the same time instant as the former NTP timestamp in
   the Splicing Interval. To enable mixer to know the first substitutive
   RTP packet it begins to output, the substitutive RTP sender MUST
   enable the mixer to know above RTP timestamp in advance, e.g., from
   prior receipt of RTCP SR message.

   When the splicing will end, the RTP timestamp of the first main RTP
   packet that would be presented on the receivers MUST correspond to
   the same time instant as the latter NTP timestamp in the Splicing
   Interval.




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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 Extention

   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, under
   the consumption that the splicing-out time is after the splicing-in
   time, and the splicing interval is less than 2^25 seconds, this order
   allows full resolution for splicing-in NTP timestamp while keeping 4
   octets alignment.

   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
   sender begins to insert the RTP header extensions into a number of
   RTP packets in advance of the splicing starting, while leaving the



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   remain RTP packets unmarked.

   After the mixer intercepts the RTP header extension and derives the
   Splicing Interval, it will generate its own stream and could 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 in next section MUST be
   sent to provide robustness in the case of any splicing-unaware
   middlebox that might strip RTP header extensions.

3.2 RTCP Splicing Notification Message

   Besides 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.

   SSRC: 32 bits




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      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  Reduing 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 means 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.


5  Failure Cases



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   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 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. In such case, the main RTP sender
   can learn the splicing failed.

   In a similar manner, the substitutive sender can learn the 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 also reuses the Flow Identification (FID) semantics
   defined in SDP Grouping Framework [RFC5888] to represent the
   relationship between the main RTP stream and the substitutive RTP
   stream.

   The next example shows how the "group" attribute used with FID
   semantics can indicate RTP splicing support on RTP sender.

              v=0
              o=xia 1122334455 1122334466 IN IP4 splicing.example.com
              s=RTP Splicing Example
              t=0 0
              a=group:FID 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



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              a=mid: 1
              m= video 30001 RTP/AVP 100
              i=Substitutive RTP Stream
              c=IN IP4 233.252.0.2/127
              a=sendonly
              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 30001.  But at
   a particular point in time, the mixer only selects one stream and
   output the content from the chosen stream to the downstream
   receivers.


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 could choose to set the values in
   this header extension falsely, so as to falsely claim the splicing
   time.

   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:




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         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


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,



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              "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.

   [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






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   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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