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Versions: (draft-ietf-avt-rtp-klv) 00 01 02 03 04 RFC 6597

Payload Working Group                                   J. Arbeiter, Ed.
Internet-Draft                                        Harris Corporation
Intended status: Standards Track                           J. Downs, Ed.
Expires: December 3, 2011                   PAR Government Systems Corp.
                                                            June 1, 2011


             RTP Payload Format for SMPTE 336M Encoded Data
                     draft-ietf-payload-rtp-klv-00

Abstract

   This document specifies the payload format for packetization of KLV
   (Key-Length-Value) Encoded Data, as defined by the Society of Motion
   Picture and Television Engineers (SMPTE) in SMPTE 336M, into the
   Real-time Transport Protocol (RTP).

Status of this Memo

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

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

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

   This Internet-Draft will expire on December 3, 2011.

Copyright Notice

   Copyright (c) 2011 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
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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.



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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions, Definitions and Acronyms  . . . . . . . . . . . .  3
   3.  Media Format Background  . . . . . . . . . . . . . . . . . . .  3
   4.  Payload Format . . . . . . . . . . . . . . . . . . . . . . . .  4
     4.1.  RTP Header Usage . . . . . . . . . . . . . . . . . . . . .  4
     4.2.  Payload Data . . . . . . . . . . . . . . . . . . . . . . .  5
       4.2.1.  The KLVunit  . . . . . . . . . . . . . . . . . . . . .  5
       4.2.2.  KLVunit Mapping to RTP Packet Payload  . . . . . . . .  5
     4.3.  Implementation Considerations  . . . . . . . . . . . . . .  6
       4.3.1.  Loss of Data . . . . . . . . . . . . . . . . . . . . .  6
         4.3.1.1.  Damaged KLVunits . . . . . . . . . . . . . . . . .  6
         4.3.1.2.  Treatment of Damaged KLVunits  . . . . . . . . . .  7
   5.  Congestion Control . . . . . . . . . . . . . . . . . . . . . .  8
   6.  Payload Format Parameters  . . . . . . . . . . . . . . . . . .  8
     6.1.  Media Type Definition  . . . . . . . . . . . . . . . . . .  8
     6.2.  Mapping to SDP . . . . . . . . . . . . . . . . . . . . . .  9
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 10
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11



























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1.  Introduction

   This document specifies the payload format for packetization of KLV
   (Key-Length-Value) Encoded Data, as defined by the Society of Motion
   Picture and Television Engineers (SMPTE) in [SMPTE336M], into the
   Real-time Transport Protocol (RTP) [RFC3550].

   The payload format is defined in such a way that arbitrary KLV data
   can be carried.  No restrictions are placed on which KLV data keys
   can be used.

   A brief description of SMPTE 336M, KLV Encoded Data, is given.  The
   payload format itself, including use of the RTP header fields, is
   specified in Section 4.  The media type and IANA considerations are
   also described.  This document concludes with security considerations
   relevant to this payload format.


2.  Conventions, Definitions and Acronyms

   The term "KLV item" is used in this document to refer to one single
   universal key, length, and value triplet, or one single SMPTE
   Universal Label, encoded as described in [SMPTE336M].

   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 [RFC2119].


3.  Media Format Background

   [SMPTE336M], Data Encoding Protocol Using Key-Length-Value, defines a
   byte-level data encoding protocol for representing data items and
   data groups.  This encoding protocol definition is independent of the
   application or transportation method used.

   SMPTE 336M data encoding can be applied to a wide variety of binary
   data.  This encoding has been used to provide diverse and rich
   metadata sets that describe or enhance associated video
   presentations.  Use of SMPTE 336M encoded metadata in conjunction
   with video has enabled improvements in multimedia presentations,
   content management and distribution, archival and retrieval, and
   production workflow.

   The SMPTE 336M standard defines a Key-Length-Value (KLV) triplet as a
   data interchange protocol for data items or data groups where the Key
   identifies the data, the Length specifies the length of the data and
   the Value is the data itself.  The KLV protocol provides a common



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   interchange point for all compliant applications irrespective of the
   method of implementation or transport.

   The standard also provides methods for combining associated KLV
   triplets in data sets where the set of KLV triplets is itself coded
   with KLV data coding protocol.  Such sets can be coded in either full
   form (Universal Sets) or in one of four increasingly bit-efficient
   forms (Global Sets, Local Sets, Variable Length Packs and Defined
   Length Packs).  The standard provides a definition of each of these
   data constructs.

   The standard also describes implications of KLV coding including the
   use of a SMPTE Universal Label as a value within a KLV coding triplet
   or whose meaning is entirely conveyed by the SMPTE UL itself.  The
   two kinds of usage for such standalone SMPTE Universal Labels are a)
   as a value in a K L V construct and b) as a Key that has no Length
   and no Value.

   The standard also defines the use of KLV coding to provide a means to
   carry information that is registered with a non-SMPTE external
   agency.

   The encoding byte range (length of the payload) may accommodate
   unusually large volumes of data.  Consequently, a specific
   application of KLV encoding may require only a limited operating data
   range and those details shall be defined in a relevant application
   document.


4.  Payload Format

   The main goal of the payload format design for SMPTE 336M data is to
   provide carriage of SMPTE 336M data over RTP in a simple, yet robust
   manner.  All forms of SMPTE 336M data can be carried by the payload
   format.  The payload format maintains simplicity by using only the
   standard RTP headers and not defining any payload headers.

   SMPTE 336M KLV data is broken into KLVunits (see Section 4.2.1) based
   on source data timing.  Each KLVunit is then placed into one or more
   RTP packet payloads.  The RTP header marker bit is used to assist
   receivers in locating the boundaries of KLVunits.

4.1.  RTP Header Usage

   This payload format uses the RTP packet header fields as described in
   the table below:





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   +-----------+-------------------------------------------------------+
   | Field     | Usage                                                 |
   +-----------+-------------------------------------------------------+
   | Timestamp | The RTP Timestamp encodes the instant along a         |
   |           | presentation timeline that the entire KLVunit encoded |
   |           | in the packet payload is to be presented. When one    |
   |           | KLVunit is placed in multiple RTP packets, the RTP    |
   |           | timestamp of all packets comprising that KLVunit MUST |
   |           | be the same. The timestamp clock frequency SHALL be   |
   |           | defined as a parameter to the payload format          |
   |           | (Section 6).                                          |
   | M-bit     | The RTP header marker bit (M) SHALL be set to '1' for |
   |           | any RTP packet which contains the final byte of a     |
   |           | KLVunit. For all other packets, the RTP header marker |
   |           | bit SHALL be set to '0'. This allows receivers to     |
   |           | pass a KLVunit for parsing/decoding immediately upon  |
   |           | receipt of the last RTP packet comprising the         |
   |           | KLVunit. Without this, a receiver would need to wait  |
   |           | for the next RTP packet with a different timestamp to |
   |           | arrive, thus signaling the end of one KLVunit and the |
   |           | start of another.                                     |
   +-----------+-------------------------------------------------------+

   The remaining RTP header fields are used as specified in [RFC3550].

4.2.  Payload Data

4.2.1.  The KLVunit

   A KLVunit is a logical collection of all KLV items that are to be
   presented at a specific time.  A KLVunit is comprised of one or more
   KLV items.  Compound items (sets, packs) are allowed as per
   [SMPTE336M], but the contents of a compound item MUST NOT be split
   across two KLVunits.  Multiple KLV items in a KLVunit occur one after
   another with no padding or stuffing between items.

4.2.2.  KLVunit Mapping to RTP Packet Payload

   An RTP packet payload SHALL contain one, and only one, KLVunit or a
   fragment thereof.  KLVunits small enough to fit into a single RTP
   packet (RTP packet size is up to implementation but should consider
   underlying transport/network factors such as MTU limitations) are
   placed directly into the payload of the RTP packet, with the first
   byte of the KLVunit (which is the first byte of a KLV universal key)
   being the first byte of the RTP packet payload.

   KLVunits too large to fit into a single RTP packet payload MAY span
   multiple RTP packet payloads.  When this is done, the KLVunit data



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   MUST be sent in sequential byte order, such that when all RTP packets
   comprising the KLVunit are arranged in sequence number order,
   concatenating the payload data together exactly reproduces the
   original KLVunit.

   Additionally, when a KLVunit is fragmented across multiple RTP
   packets, all RTP packets transporting the fragments a KLVunit MUST
   have the same timestamp.

   KLVunits are bounded with changes in RTP packet timestamps.  The
   marker (M) bit in the RTP packet headers marks the last RTP packet
   comprising a KLVunit (see Section 4.1).

4.3.  Implementation Considerations

4.3.1.  Loss of Data

   RTP is generally deployed in network environments where packet loss
   may occur.  RTP header fields enable detection of lost packets, as
   described in [RFC3550].  When transmitting payload data described by
   this payload format, packet loss can cause the loss of whole KLVunits
   or portions thereof.

4.3.1.1.  Damaged KLVunits

   A damaged KLVunit is any KLVunit that was carried in one or more RTP
   packets that have been lost.  When a lost packet is detected (through
   use of the sequence number header field), the receiver:

   o  SHOULD consider the KLVunit carried in the prior packet (in
      sequence number order) as damaged unless that prior packet's M bit
      in the RTP header was set to '1'.

   o  SHOULD consider all subsequent packets (in sequence number order)
      up to and including the next one with the M-bit in the RTP header
      set to '1' as part of a damaged KLVunit.

   The example below illustrates how a receiver would handle a lost
   packet in one possible packet sequence:












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          +---------+-------------+    +--------------+
          | RTP Hdr | Data        |    |              |
          +---------+-------------+    +--------------+
     .... | ts = 30 | KLV KLV ... |    |              |  >---+
          | M = 1   |             |    |              |      |
          | seq = 5 | ... KLV KLV |    |              |      |
          +---------+-------------+    +--------------+      |
           Last RTP pkt for time 30      Lost RTP Pkt        |
                 For time 30               (seq = 6)         |
                                                             |
    +--------------------------------------------------------+
    |
    |     +---------+-------------+    +---------+-------------+
    |     | RTP Hdr |     Data    |    | RTP Hdr |     Data    |
    |     +---------+-------------+    +---------+-------------+
    +-->  | ts = 45 | KLV KLV ... |    | ts = 45 | ... KLV ... | >---+
          | M = 0   |             |    | M = 1   |             |     |
          | seq = 7 | ... KLV ... |    | seq = 8 | ... KLV KLV |     |
          +---------+-------------+    +---------+-------------+     |
             RTP pkt for time 45        Last RTP pkt for time 45     |
              KLVunit carried in these two packets is "damaged"      |
                                                                     |
    +----------------------------------------------------------------+
    |
    |     +---------+-------------+
    |     | RTP Hdr |     Data    |
    |     +---------+-------------+
    +-->  | ts = 55 | KLV KLV ... |   ....
          | M = 1   |             |
          | seq = 9 | ... KLV ... |
          +---------+-------------+
           Last and only RTP pkt
               for time 55


   In this example, the packets with sequence numbers 7 and 8 contain
   portions of a KLVunit with timestamp of 45.  This KLVunit is
   considered "damaged" due to the missing RTP packet with sequence
   number 6, which may have been part of this KLVunit.  The KLVunit for
   timestamp 30 (ended in packet with sequence number 5) is unaffected
   by the missing packet.  The KLVunit for timestamp 55, carried in the
   packet with sequence number 9, is also unaffected by the missing
   packet and is considered complete and intact.

4.3.1.2.  Treatment of Damaged KLVunits

   SMPTE 336M KLV data streams are built in such a way that it is
   possible to partially recover from errors or missing data in a



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   stream.  Exact specifics of how damaged KLVunits are handled are left
   to each implementation, as different implementations may have
   differing capabilities and robustness in their downstream KLV payload
   processing.  Because some implementations may be particularly limited
   in their capacity to handle damaged KLVunits, receivers MAY drop
   damaged KLVunits entirely.


5.  Congestion Control

   The general congestion control considerations for transporting RTP
   data apply; see RTP [RFC3550] and any applicable RTP profile like AVP
   [RFC3551].

   Further, SMPTE 336M data can be encoded in different schemes which
   reduce the overhead associated with individual data items within the
   overall stream.  SMPTE 336M grouping constructs, such as local sets
   and data packs, provide a mechanism to reduce bandwidth requirements.


6.  Payload Format Parameters

   This RTP payload format is identified using the application/smpte336m
   media type which is registered in accordance with [RFC4855] and using
   the template of [RFC4288].

6.1.  Media Type Definition

      Type name: application

      Subtype name: smpte336m

      Required parameters:

         rate: RTP timestamp clock rate.  Typically chosen based on
         sampling rate of metadata being transmitted, but other rates
         may be specified.

      Optional parameters:

      Encoding considerations: This media type is framed and binary; see
      Section 4.8 of [RFC4288].

      Security considerations: See Section 8 of RFCXXXX.

      Interoperability considerations: Data items in smpte336m can be
      very diverse.  Receivers may only be capable of interpreting a
      subset of the possible data items; unrecognized items are skipped.



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      Agreement on data items to be used out of band, via application
      profile or similar, is typical.

      Published specification: RFCXXXX

      Applications that use this media type: Audio and video streaming
      and conferencing tools

      Additional Information: none

      Person & email address to contact for further information: J.
      Arbeiter <jarbeite@harris.com>

      Intended usage: COMMON

      Restrictions on usage: This media type depends on RTP framing, and
      hence is only defined for transfer via RTP ([RFC3550]).  Transport
      within other framing protocols is not defined at this time.

      Author:

         J. Arbeiter <jarbeite@harris.com>

         J. Downs <jeff_downs@partech.com>

      Change controller: IETF Audio/Video Transport working group
      delegated from the IESG.

6.2.  Mapping to SDP

   The mapping of the above defined payload format media type and its
   parameters SHALL be done according to Section 3 of [RFC4855].


7.  IANA Considerations

   This memo requests that IANA registers application/smpte336m as
   specified in Section 6.1.  The media type is also requested to be
   added to the IANA registry for "RTP Payload Format MIME types"
   (http://www.iana.org/assignments/rtp-parameters).


8.  Security Considerations

   RTP packets using the payload format defined in this specification
   are subject to the security considerations discussed in the RTP
   specification [RFC3550], and in any applicable RTP profile.  The main
   security considerations for the RTP packet carrying the RTP payload



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   format defined within this memo are confidentiality, integrity and
   source authenticity.  Confidentiality is achieved by encryption of
   the RTP payload.  Integrity of the RTP packets through suitable
   cryptographic integrity protection mechanism.  Cryptographic system
   may also allow the authentication of the source of the payload.  A
   suitable security mechanism for this RTP payload format should
   provide confidentiality, integrity protection and at least source
   authentication capable of determining if an RTP packet is from a
   member of the RTP session or not.

   Note that the appropriate mechanism to provide security to RTP and
   payloads following this memo may vary.  It is dependent on the
   application, the transport, and the signalling protocol employed.
   Therefore a single mechanism is not sufficient, although if suitable
   the usage of SRTP [RFC3711] is recommended.  Other mechanism that may
   be used are IPsec [RFC4301] and TLS [RFC5246] (RTP over TCP), but
   also other alternatives may exist.

   This RTP payload format presents the possibility for significant non-
   uniformity in the receiver-side computational complexity during
   processing of SMPTE 336M payload data.  Because the length of SMPTE
   336M encoded data items is essentially unbounded, receivers must take
   care when allocating resources used in processing.  It is trivial to
   construct pathological data that would cause a naive decoder to
   allocate large amounts of resources, resulting in denial-of-service
   threats.  Receivers are encouraged to place limits on resource
   allocation that are within the bounds set forth by any application
   profile in use.

   This RTP payload format does not contain any inheritly active
   content.  However, individual SMPTE 336M KLV items could be defined
   to convey active content in a particular application.  Therefore,
   receivers capable of decoding and interpreting such data items should
   use appropriate caution and security practices.  Receivers not
   capable of decoding such data items are not at risk; unknown data
   items are skipped over and discarded according to SMPTE 336M
   processing rules.


9.  References

9.1.  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



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              Applications", STD 64, RFC 3550, July 2003.

   [RFC3551]  Schulzrinne, H. and S. Casner, "RTP Profile for Audio and
              Video Conferences with Minimal Control", STD 65, RFC 3551,
              July 2003.

   [RFC4288]  Freed, N. and J. Klensin, "Media Type Specifications and
              Registration Procedures", BCP 13, RFC 4288, December 2005.

   [RFC4855]  Casner, S., "Media Type Registration of RTP Payload
              Formats", RFC 4855, February 2007.

   [SMPTE336M]
              SMPTE, "SMPTE336M-2007: Data Encoding Protocol Using Key-
              Length-Value", 2007, <http://www.smpte.org>.

9.2.  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.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.


Authors' Addresses

   J. Arbeiter (editor)
   Harris Corporation
   US

   Phone:
   Email: jarbeite@harris.com


   J. Downs (editor)
   PAR Government Systems Corp.
   US

   Phone:
   Email: jeff_downs@partech.com






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