Payload Working Group                                      J. Downs, Ed.
Internet-Draft                              PAR Government Systems Corp.
Intended status: Standards Track                        J. Arbeiter, Ed.
Expires: August 4, September 2, 2012                                 February                                 March 1, 2012

             RTP Payload Format for SMPTE 336M Encoded Data


   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

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on August 4, September 2, 2012.

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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  Damaged KLVunits . . . . . . . . . . . . . . . . .  6  Treatment of Damaged KLVunits  . . . . . . . . . .  7  8
   5.  Congestion Control . . . . . . . . . . . . . . . . . . . . . .  8
   6.  Payload Format Parameters  . . . . . . . . . . . . . . . . . .  8
     6.1.  Media Type Definition  . . . . . . . . . . . . . . . . . .  8
     6.2.  Mapping to SDP . . . . . . . . . . . . . . . . . . . . . .  9
       6.2.1.  Offer/Answer Model and Declarative Considerations  . .  9
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 11
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12

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 "Universal Label Key" is used in this document to refer to a
   fixed-length, 16-byte SMPTE-administered Universal Label (see
   [SMPTE298M]) that is used as an identifying key in a KLV item.

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

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   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
   interchange point for all compliant applications irrespective of the
   method of implementation or transport.

   The Key of a KLV triplet (a Universal Label Key) is coded using a
   fixed-length 16-byte SMPTE-administered Universal Label.  [SMPTE298M]
   further details the structure of 16-byte SMPTE-administered Universal
   Labels.  Universal Label Keys are maintained in registries published
   by SMPTE (see, for example, [SMPTE335M] and [SMPTERP210]).

   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 (UL) as a value within a KLV coding
   triplet or whose meaning is entirely conveyed by

   Additionally, the SMPTE UL itself.
   The two kinds of usage for such standalone SMPTE ULs are a) as a
   value in a KLV construct and b) as a Key that has no Length and no

   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) can accommodate
   unusually large volumes of data.  Consequently, a specific
   application of KLV encoding might 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.  A KLVunit is simply a
   logical grouping of otherwise unframed KLV data, grouped based on
   source data timing (see Section 4.2.1).  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:

   | 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 is defined |
   |           | defined as a parameter to the payload format          |
   |           | (Section 6).     |
   | M-bit     | The RTP header marker bit (M) SHALL be is used to demarcate    |
   |           | KLVunits. Senders MUST set the marker bit to '1' for  |
   |           | any RTP packet which contains the final byte of a     |
   |           | KLVunit. For all other packets, senders MUST set the RTP header marker  |
   |           | RTP header marker bit SHALL be set to '0'. This allows receivers to   |
   |           | to pass a KLVunit for parsing/decoding immediately upon    |
   |           | 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) Universal Label
   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
   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 of 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).  A receiver MUST consider a
   KLVunit to be completed when it receives either a packet with M=1 or
   a packet with a new timestamp.  In the former case, the packet
   payload is included in the completed KLVunit; in the latter case, it
   is not.

4.3.  Implementation Considerations

4.3.1.  Loss of Data

   RTP is generally deployed in network environments where packet loss
   might 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.  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  MUST consider any the KLVunit presently being partially received before a lost packet
      as damaged.
      The  This damaged KLVunit includes all packets prior to
      the lost one (in sequence number order) back to, but not
      including, the most recent packet in which the M bit M-bit in the RTP
      header was set to '1'.

   o  MUST consider all subsequent packets the first KLVunit received after a lost packet as
      damaged.  This damaged KLVunit includes the first packet after the
      lost one (in sequence number order) and, if the first packet has
      its M-bit in the RTP header is set to '0', all subsequent packets
      up to and including the next one with the M-bit in the RTP header
      set to '1'.

   The above applies regardless of the M-bit value in the RTP header of
   the lost packet itself.  This enables very basic receivers to look
   solely at the M-bit to determine the outer boundaries of damaged
   KLVunits.  For example, when a packet with the M-bit set to '1' is
   lost, the KLVunit that the lost packet would have terminated is
   considered damaged, as part is the KLVunit comprised of a damaged KLVunit. packets received
   subsequent to the lost packet (up to and including the next received
   packet with M-bit set to '1').

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

          +---------+-------------+    +--------------+
          | RTP Hdr | Data        |    |              |
          +---------+-------------+    +--------------+
     .... | ts = 30 | KLV KLV ... |    |              |  >---+
          | M = 1   |             |    |              |      |
          | seq = 5 | ... KLV KLV |    |              |      |
          +---------+-------------+    +--------------+      |
           Last RTP pkt for time 30      Lost RTP Pkt        |
                                           (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 might 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.  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
   stream.  Exact specifics of how damaged KLVunits are handled are left
   to each implementation, as different implementations can have
   differing capabilities and robustness in their downstream KLV payload
   processing.  Because some implementations can 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

   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
         can be specified.

      Optional parameters: None
      Encoding considerations: This media type is framed and binary; see
      Section 4.8 of [RFC4288].

      Security considerations: See Section 8 of RFCXXXX (note to RFC
      editor: please replace XXXX with the number assigned to this RFC).

      Interoperability considerations: Data items in smpte336m can be
      very diverse.  Receivers might only be capable of interpreting a
      subset of the possible data items; unrecognized items are skipped.
      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: Streaming of metadata
      associated with simultaneously streamed video and transmission of
      [SMPTE336M] based media formats (e.g.  MXF [SMPTE377M]).

      Additional Information: none

      Person & email address to contact for further information: J.
      Downs <>; IETF Payload Working Group

      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.


         J. Downs <>

         J. Arbeiter <>

      Change controller: IETF Payload working group delegated from the

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].

6.2.1.  Offer/Answer Model and Declarative Considerations

   This payload format has no configuration or optional format
   parameters.  Thus, when offering SMPTE 336M Encoded Data over RTP
   using SDP Session Description Protocol (SDP) in an Offer/Answer model
   [RFC3264] or in a declarative manner (e.g., SDP in the Real-time
   Streaming Protocol (RTSP) [RFC2326] or the Session Announcement
   Protocol (SAP) [RFC2974]), there are no specific considerations.

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"

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
   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 systems
   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 signaling protocol employed.
   Therefore a single mechanism is not sufficient, although if suitable
   the usage of SRTP [RFC3711] is recommended.  Other mechanism mechanisms 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 SHOULD 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 inherently 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.  In particular,
   accepting active content from streams that lack authenticity or
   integrity proteciton protection mechanisms places a receiver at risk to of attacks
   using spoofed packets.  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
              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.

              Society of Motion Picture and Television Engineers,
              "SMPTE336M-2007: Data Encoding Protocol Using Key-Length-
              Value", 2007, <>.

9.2.  Informative References

   [RFC2326]  Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time
              Streaming Protocol (RTSP)", RFC 2326, April 1998.

   [RFC2974]  Handley, M., Perkins, C., and E. Whelan, "Session
              Announcement Protocol", RFC 2974, October 2000.

   [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
              with Session Description Protocol (SDP)", RFC 3264,
              June 2002.

   [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.

              Society of Motion Picture and Television Engineers, "ANSI/
              SMPTE 298M-1997: Universal Labels for Unique
              Identification of Digital Data", 1997,

              Society of Motion Picture and Television Engineers, "SMPTE
              335M-2001: Metadata Dictionary Structure", 2001,

              Society of Motion Picture and Television Engineers,
              "SMPTE336M-2007: Data Encoding Protocol Using Key-Length-
              Value", 2007, <>.

              Society of Motion Picture and Television Engineers,
              "SMPTE377M-2004: "SMPTE
              377M-2004: Material Exchange Format (MXF) File Format
              Specification", 2004, <>.

              Society of Motion Picture and Television Engineers, "SMPTE
              RP 210v12: Metadata Dictionary Registry of Metadata
              Element Descriptions", 2010, <>.

Authors' Addresses

   J. Downs (editor)
   PAR Government Systems Corp.

   J. Arbeiter (editor)