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rfc:rfc6597

Internet Engineering Task Force (IETF) J. Downs, Ed. Request for Comments: 6597 PAR Government Systems Corp. Category: Standards Track J. Arbeiter, Ed. ISSN: 2070-1721 April 2012

                       RTP Payload Format for
     Society of Motion Picture and Television Engineers (SMPTE)
                        ST 336 Encoded Data

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 ST 336, into the
 Real-time Transport Protocol (RTP).

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc6597.

Copyright Notice

 Copyright (c) 2012 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.

Downs & Arbeiter Standards Track [Page 1] RFC 6597 RTP Format for SMPTE ST 336 Data April 2012

Table of Contents

 1. Introduction ....................................................2
 2. Conventions, Definitions, and Acronyms ..........................3
 3. Media Format Background .........................................3
 4. Payload Format ..................................................4
    4.1. RTP Header Usage ...........................................5
    4.2. Payload Data ...............................................5
         4.2.1. The KLVunit .........................................5
         4.2.2. KLVunit Mapping to RTP Packet Payload ...............6
    4.3. Implementation Considerations ..............................6
         4.3.1. Loss of Data ........................................6
                4.3.1.1. Damaged KLVunits ...........................7
                4.3.1.2. Treatment of Damaged KLVunits ..............9
 5. Congestion Control ..............................................9
 6. Payload Format Parameters .......................................9
    6.1. Media Type Definition ......................................9
    6.2. Mapping to SDP ............................................10
         6.2.1. Offer/Answer Model and Declarative Considerations ..10
 7. IANA Considerations ............................................11
 8. Security Considerations ........................................11
 9. References .....................................................12
    9.1. Normative References ......................................12
    9.2. Informative References ....................................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 [SMPTE-ST336], 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 ST 336, "Data Encoding Protocol Using
 Key-Length-Value", 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.

Downs & Arbeiter Standards Track [Page 2] RFC 6597 RTP Format for SMPTE ST 336 Data April 2012

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
 [SMPTE-ST298]) 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 Label Key, length, and value triplet encoded as described
 in [SMPTE-ST336].
 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

 [SMPTE-ST336], "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 ST 336 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 ST 336 encoded metadata in conjunction
 with video has enabled improvements in multimedia presentations,
 content management and distribution, archival and retrieval, and
 production workflow.
 The SMPTE ST 336 standard defines a 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.
 [SMPTE-ST298] further details the structure of 16-byte SMPTE-
 administered Universal Labels.  Universal Label Keys are maintained
 in registries published by SMPTE (see, for example, [SMPTE-ST335] and
 [SMPTE-RP210]).

Downs & Arbeiter Standards Track [Page 3] RFC 6597 RTP Format for SMPTE ST 336 Data April 2012

 The standard also provides methods for combining associated KLV
 triplets in data sets where the set of KLV triplets is itself coded
 with the KLV data coding protocol.  Such sets can be coded in either
 full form (Universal Sets) or 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.
 Additionally, the standard defines the use of KLV coding to provide a
 means to carry information that is registered with a non-SMPTE
 external agency.

4. Payload Format

 The main goal of the payload format design for SMPTE ST 336 data is
 to provide carriage of SMPTE ST 336 data over RTP in a simple, yet
 robust manner.  All forms of SMPTE ST 336 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 ST 336 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.

Downs & Arbeiter Standards Track [Page 4] RFC 6597 RTP Format for SMPTE ST 336 Data April 2012

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 is        |
 |           | defined as a parameter to the payload format          |
 |           | (Section 6).                                          |
 |           |                                                       |
 | M-bit     | The RTP header marker bit (M) is used to demarcate    |
 |           | KLVunits.  Senders MUST set the marker bit to '1' for |
 |           | any RTP packet that contains the final byte of a      |
 |           | KLVunit.  For all other packets, senders MUST set the |
 |           | RTP header marker bit 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
 [SMPTE-ST336], 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.

Downs & Arbeiter Standards Track [Page 5] RFC 6597 RTP Format for SMPTE ST 336 Data April 2012

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 the 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 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).

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.

Downs & Arbeiter Standards Track [Page 6] RFC 6597 RTP Format for SMPTE ST 336 Data April 2012

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  MUST consider the KLVunit partially received before a lost packet
    as damaged.  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 in the RTP
    header was set to '1'.
 o  MUST consider 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 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 is the KLVunit comprised of packets received
 subsequent to the lost packet (up to and including the next received
 packet with the M-bit set to '1').

Downs & Arbeiter Standards Track [Page 7] RFC 6597 RTP Format for SMPTE ST 336 Data April 2012

 The example below illustrates how a receiver would handle a lost
 packet in 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 a 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.

Downs & Arbeiter Standards Track [Page 8] RFC 6597 RTP Format for SMPTE ST 336 Data April 2012

4.3.1.2. Treatment of Damaged KLVunits

 SMPTE ST 336 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 [RFC3551].
 Further, SMPTE ST 336 data can be encoded in different schemes that
 reduce the overhead associated with individual data items within the
 overall stream.  SMPTE ST 336 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 RFC 6597.

Downs & Arbeiter Standards Track [Page 9] RFC 6597 RTP Format for SMPTE ST 336 Data April 2012

 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: RFC 6597
 Applications that use this media type: Streaming of metadata
    associated with simultaneously streamed video and transmission of
    [SMPTE-ST336]-based media formats (e.g., Material Exchange Format
    (MXF) [SMPTE-ST377]).
 Additional Information: none
 Person & email address to contact for further information: J. Downs
    <jeff_downs@partech.com>; IETF Payload Working Group
    <payload@ietf.org>
 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. Downs <jeff_downs@partech.com>
    J. Arbeiter <jimsgti@gmail.com>
 Change controller: IETF Payload 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].

6.2.1. Offer/Answer Model and Declarative Considerations

 This payload format has no configuration or optional format
 parameters.  Thus, when offering SMPTE ST 336 Encoded Data over RTP
 using the 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.

Downs & Arbeiter Standards Track [Page 10] RFC 6597 RTP Format for SMPTE ST 336 Data April 2012

7. IANA Considerations

 IANA has registered application/smpte336m as specified in
 Section 6.1.  The media type has been added to the IANA registry for
 "RTP Payload Format media 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
 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 is achieved through a
 suitable cryptographic integrity protection mechanism.  Cryptographic
 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 whether or not an RTP
 packet is from a member of the RTP session.
 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 signaling protocol employed.
 Therefore, a single mechanism is not sufficient, although if suitable
 the usage of the Secure Real-time Transport Protocol (SRTP) [RFC3711]
 is recommended.  Other mechanisms that may be used are IPsec
 [RFC4301] and Transport Layer Security (TLS) [RFC5246] (RTP over
 TCP), but other alternatives may exist as well.
 This RTP payload format presents the possibility for significant
 non-uniformity in the receiver-side computational complexity during
 processing of SMPTE ST 336 payload data.  Because the length of SMPTE
 ST 336 encoded data items is essentially unbounded, receivers must
 take care when allocating resources used in processing.  It is easy
 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 inherently active
 content.  However, individual SMPTE ST 336 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

Downs & Arbeiter Standards Track [Page 11] RFC 6597 RTP Format for SMPTE ST 336 Data April 2012

 integrity protection mechanisms places a receiver at risk 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 ST 336 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.

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.

Downs & Arbeiter Standards Track [Page 12] RFC 6597 RTP Format for SMPTE ST 336 Data April 2012

 [RFC5246]      Dierks, T. and E. Rescorla, "The Transport Layer
                Security (TLS) Protocol Version 1.2", RFC 5246,
                August 2008.
 [SMPTE-RP210]  Society of Motion Picture and Television Engineers,
                "SMPTE RP 210v12:2010 Data Element Dictionary", 2010,
                <http://www.smpte-ra.org/mdd/>.
 [SMPTE-ST298]  Society of Motion Picture and Television Engineers,
                "SMPTE ST 298:2009 Universal Labels for Unique
                Identification of Digital Data", 2009,
                <http://www.smpte.org>.
 [SMPTE-ST335]  Society of Motion Picture and Television Engineers,
                "SMPTE ST 335:2012 Metadata Element Dictionary
                Structure", 2012, <http://www.smpte.org>.
 [SMPTE-ST336]  Society of Motion Picture and Television Engineers,
                "SMPTE ST 336:2007 Data Encoding Protocol Using Key-
                Length-Value", 2007, <http://www.smpte.org>.
 [SMPTE-ST377]  Society of Motion Picture and Television Engineers,
                "SMPTE ST 377-1:2011 Material Exchange Format (MXF) -
                File Format Specification", 2011,
                <http://www.smpte.org>.

Authors' Addresses

 J. Downs (editor)
 PAR Government Systems Corp.
 US
 EMail: jeff_downs@partech.com
 J. Arbeiter (editor)
 US
 EMail: jimsgti@gmail.com

Downs & Arbeiter Standards Track [Page 13]

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