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rfc:rfc6015

Internet Engineering Task Force (IETF) A. Begen Request for Comments: 6015 Cisco Category: Standards Track October 2010 ISSN: 2070-1721

           RTP Payload Format for 1-D Interleaved Parity
                   Forward Error Correction (FEC)

Abstract

 This document defines a new RTP payload format for the Forward Error
 Correction (FEC) that is generated by the 1-D interleaved parity code
 from a source media encapsulated in RTP.  The 1-D interleaved parity
 code is a systematic code, where a number of repair symbols are
 generated from a set of source symbols and sent in a repair flow
 separate from the source flow that carries the source symbols.  The
 1-D interleaved parity code offers a good protection against bursty
 packet losses at a cost of reasonable complexity.  The new payload
 format defined in this document should only be used (with some
 exceptions) as a part of the Digital Video Broadcasting-IPTV (DVB-
 IPTV) Application-layer FEC specification.

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/rfc6015.

Begen Standards Track [Page 1] RFC 6015 RTP Payload Format for Interleaved FEC October 2010

Copyright Notice

 Copyright (c) 2010 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.

Begen Standards Track [Page 2] RFC 6015 RTP Payload Format for Interleaved FEC October 2010

Table of Contents

 1. Introduction ....................................................4
    1.1. Use Cases ..................................................6
    1.2. Overhead Computation .......................................8
    1.3. Relation to Existing Specifications ........................8
         1.3.1. RFCs 2733 and 3009 ..................................8
         1.3.2. SMPTE 2022-1 ........................................8
         1.3.3. ETSI TS 102 034 .....................................9
    1.4. Scope of the Payload Format ...............................10
 2. Requirements Notation ..........................................10
 3. Definitions, Notations, and Abbreviations ......................10
    3.1. Definitions ...............................................10
    3.2. Notations .................................................11
 4. Packet Formats .................................................11
    4.1. Source Packets ............................................11
    4.2. Repair Packets ............................................11
 5. Payload Format Parameters ......................................15
    5.1. Media Type Registration ...................................15
         5.1.1. Registration of audio/1d-interleaved-parityfec .....15
         5.1.2. Registration of video/1d-interleaved-parityfec .....16
         5.1.3. Registration of text/1d-interleaved-parityfec ......18
         5.1.4. Registration of
                application/1d-interleaved-parityfec ...............19
    5.2. Mapping to SDP Parameters .................................20
         5.2.1. Offer-Answer Model Considerations ..................21
         5.2.2. Declarative Considerations .........................22
 6. Protection and Recovery Procedures .............................22
    6.1. Overview ..................................................22
    6.2. Repair Packet Construction ................................22
    6.3. Source Packet Reconstruction ..............................24
         6.3.1. Associating the Source and Repair Packets ..........25
         6.3.2. Recovering the RTP Header and Payload ..............25
 7. Session Description Protocol (SDP) Signaling ...................27
 8. Congestion Control Considerations ..............................27
 9. Security Considerations ........................................28
 10. IANA Considerations ...........................................29
 11. Acknowledgments ...............................................29
 12. References ....................................................29
    12.1. Normative References .....................................29
    12.2. Informative References ...................................30

Begen Standards Track [Page 3] RFC 6015 RTP Payload Format for Interleaved FEC October 2010

1. Introduction

 This document extends the Forward Error Correction (FEC) header
 defined in [RFC2733] and uses this new FEC header for the FEC that is
 generated by the 1-D interleaved parity code from a source media
 encapsulated in RTP [RFC3550].  The resulting new RTP payload format
 is registered by this document.
 The type of the source media protected by the 1-D interleaved parity
 code can be audio, video, text, or application.  The FEC data are
 generated according to the media type parameters that are
 communicated through out-of-band means.  The associations/
 relationships between the source and repair flows are also
 communicated through out-of-band means.
 The 1-D interleaved parity FEC uses the exclusive OR (XOR) operation
 to generate the repair symbols.  In a nutshell, the following steps
 take place:
 1.  The sender determines a set of source packets to be protected
     together based on the media type parameters.
 2.  The sender applies the XOR operation on the source symbols to
     generate the required number of repair symbols.
 3.  The sender packetizes the repair symbols and sends the repair
     packet(s) along with the source packets to the receiver(s) (in
     different flows).  The repair packets may be sent proactively or
     on demand.
 Note that the source and repair packets belong to different source
 and repair flows, and the sender needs to provide a way for the
 receivers to demultiplex them, even in the case in which they are
 sent in the same transport flow (i.e., same source/destination
 address/port with UDP).  This is required to offer backward
 compatibility (see Section 4).  At the receiver side, if all of the
 source packets are successfully received, there is no need for FEC
 recovery and the repair packets are discarded.  However, if there are
 missing source packets, the repair packets can be used to recover the
 missing information.  Block diagrams for the systematic parity FEC
 encoder and decoder are sketched in Figures 1 and 2, respectively.

Begen Standards Track [Page 4] RFC 6015 RTP Payload Format for Interleaved FEC October 2010

                             +------------+
  +--+  +--+  +--+  +--+ --> | Systematic | --> +--+  +--+  +--+  +--+
  +--+  +--+  +--+  +--+     | Parity FEC |     +--+  +--+  +--+  +--+
                             |  Encoder   |
                             |  (Sender)  | --> +==+  +==+
                             +------------+     +==+  +==+
  Source Packet: +--+    Repair Packet: +==+
                 +--+                   +==+
       Figure 1: Block diagram for systematic parity FEC encoder
                             +------------+
  +--+    X    X    +--+ --> | Systematic | --> +--+  +--+  +--+  +--+
  +--+              +--+     | Parity FEC |     +--+  +--+  +--+  +--+
                             |  Decoder   |
              +==+  +==+ --> | (Receiver) |
              +==+  +==+     +------------+
  Source Packet: +--+    Repair Packet: +==+    Lost Packet: X
                 +--+                   +==+
       Figure 2: Block diagram for systematic parity FEC decoder
 Suppose that we have a group of D x L source packets that have
 sequence numbers starting from 1 running to D x L.  If we apply the
 XOR operation to the group of the source packets whose sequence
 numbers are L apart from each other as sketched in Figure 3, we
 generate L repair packets.  This process is referred to as 1-D
 interleaved FEC protection, and the resulting L repair packets are
 referred to as interleaved (or column) FEC packets.

Begen Standards Track [Page 5] RFC 6015 RTP Payload Format for Interleaved FEC October 2010

     +-------------+ +-------------+ +-------------+     +-------+
     | S_1         | | S_2         | | S3          | ... | S_L   |
     | S_L+1       | | S_L+2       | | S_L+3       | ... | S_2xL |
     | .           | | .           | |             |     |       |
     | .           | | .           | |             |     |       |
     | .           | | .           | |             |     |       |
     | S_(D-1)xL+1 | | S_(D-1)xL+2 | | S_(D-1)xL+3 | ... | S_DxL |
     +-------------+ +-------------+ +-------------+     +-------+
            +               +               +                +
      -------------   -------------   -------------       -------
     |     XOR     | |     XOR     | |     XOR     | ... |  XOR  |
      -------------   -------------   -------------       -------
            =               =               =                =
          +===+           +===+           +===+            +===+
          |C_1|           |C_2|           |C_3|      ...   |C_L|
          +===+           +===+           +===+            +===+
         Figure 3: Generating interleaved (column) FEC packets
 In Figure 3, S_n and C_m denote the source packet with a sequence
 number n and the interleaved (column) FEC packet with a sequence
 number m, respectively.

1.1. Use Cases

 We generate one interleaved FEC packet out of D non-consecutive
 source packets.  This repair packet can provide a full recovery of
 the missing information if there is only one packet missing among the
 corresponding source packets.  This implies that 1-D interleaved FEC
 protection performs well under bursty loss conditions provided that a
 large enough value is chosen for L, i.e., L packet duration should
 not be shorter than the duration of the burst that is intended to be
 repaired.
 For example, consider the scenario depicted in Figure 4 in which the
 sender generates interleaved FEC packets and a bursty loss hits the
 source packets.  Since the number of columns is larger than the
 number of packets lost due to the bursty loss, the repair operation
 succeeds.

Begen Standards Track [Page 6] RFC 6015 RTP Payload Format for Interleaved FEC October 2010

                       +---+
                       | 1 |    X      X      X
                       +---+
                       +---+  +---+  +---+  +---+
                       | 5 |  | 6 |  | 7 |  | 8 |
                       +---+  +---+  +---+  +---+
                       +---+  +---+  +---+  +---+
                       | 9 |  | 10|  | 11|  | 12|
                       +---+  +---+  +---+  +---+
                       +===+  +===+  +===+  +===+
                       |C_1|  |C_2|  |C_3|  |C_4|
                       +===+  +===+  +===+  +===+
    Figure 4: Example scenario where 1-D interleaved FEC protection
                        succeeds error recovery
 The sender may generate interleaved FEC packets to combat the bursty
 packet losses.  However, two or more random packet losses may hit the
 source and repair packets in the same column.  In that case, the
 repair operation fails.  This is illustrated in Figure 5.  Note that
 it is possible that two or more bursty losses may occur in the same
 source block, in which case interleaved FEC packets may still fail to
 recover the lost data.
                       +---+         +---+  +---+
                       | 1 |    X    | 3 |  | 4 |
                       +---+         +---+  +---+
                       +---+         +---+  +---+
                       | 5 |    X    | 7 |  | 8 |
                       +---+         +---+  +---+
                       +---+  +---+  +---+  +---+
                       | 9 |  | 10|  | 11|  | 12|
                       +---+  +---+  +---+  +---+
                       +===+  +===+  +===+  +===+
                       |C_1|  |C_2|  |C_3|  |C_4|
                       +===+  +===+  +===+  +===+
 Figure 5: Example scenario where 1-D interleaved FEC protection fails
                            error recovery

Begen Standards Track [Page 7] RFC 6015 RTP Payload Format for Interleaved FEC October 2010

1.2. Overhead Computation

 The overhead is defined as the ratio of the number of bytes that
 belong to the repair packets to the number of bytes that belong to
 the protected source packets.
 Assuming that each repair packet carries an equal number of bytes
 carried by a source packet and ignoring the size of the FEC header,
 we can compute the overhead as follows:
      Overhead = 1/D
 where D is the number of rows in the source block.

1.3. Relation to Existing Specifications

 This section discusses the relation of the current specification to
 other existing specifications.

1.3.1. RFCs 2733 and 3009

 The current specification extends the FEC header defined in [RFC2733]
 and registers a new RTP payload format.  This new payload format is
 not backward compatible with the payload format that was registered
 by [RFC3009].

1.3.2. SMPTE 2022-1

 In 2007, the Society of Motion Picture and Television Engineers
 (SMPTE) - Technology Committee N26 on File Management and Networking
 Technology - decided to revise the Pro-MPEG Code of Practice (CoP) #3
 Release 2 specification (initially produced by the Pro-MPEG Forum in
 2004), which discussed several aspects of the transmission of MPEG-2
 transport streams over IP networks.  The new SMPTE specification is
 referred to as [SMPTE2022-1].
 The Pro-MPEG CoP #3 Release 2 document was originally based on
 [RFC2733].  SMPTE revised the document by extending the FEC header
 proposed in [RFC2733] (by setting the E bit).  This extended header
 offers some improvements.
 For example, instead of utilizing the bitmap field used in [RFC2733],
 [SMPTE2022-1] introduces separate fields to convey the number of rows
 (D) and columns (L) of the source block as well as the type of the
 repair packet (i.e., whether the repair packet is an interleaved FEC
 packet computed over a column or a non-interleaved FEC packet
 computed over a row).  These fields, plus the base sequence number,
 allow the receiver side to establish associations between the source

Begen Standards Track [Page 8] RFC 6015 RTP Payload Format for Interleaved FEC October 2010

 and repair packets.  Note that although the bitmap field is not
 utilized, the FEC header of [SMPTE2022-1] inherently carries over the
 bitmap field from [RFC2733].
 On the other hand, some parts of [SMPTE2022-1] are not in compliance
 with RTP [RFC3550].  For example, [SMPTE2022-1] sets the
 Synchronization Source (SSRC) field to zero and does not use the
 timestamp field in the RTP headers of the repair packets (receivers
 ignore the timestamps of the repair packets).  Furthermore,
 [SMPTE2022-1] also sets the CSRC Count (CC) field in the RTP header
 to zero and does not allow any Contributing Source (CSRC) entry in
 the RTP header.
 The current document adopts the extended FEC header of [SMPTE2022-1]
 and registers a new RTP payload format.  At the same time, this
 document fixes the parts of [SMPTE2022-1] that are not compliant with
 RTP [RFC3550], except the one discussed below.
 The baseline header format first proposed in [RFC2733] does not have
 fields to protect the P and X bits and the CC fields of the source
 packets associated with a repair packet.  Rather, the P bit, X bit,
 and CC field in the RTP header of the repair packet are used to
 protect those bits and fields.  This, however, may sometimes result
 in failures when doing the RTP header validity checks as specified in
 [RFC3550].  While this behavior has been fixed in [RFC5109], which
 obsoleted [RFC2733], the RTP payload format defined in this document
 still allows this behavior for legacy purposes.  Implementations
 following this specification must be aware of this potential issue
 when RTP header validity checks are applied.

1.3.3. ETSI TS 102 034

 In 2009, the Digital Video Broadcasting (DVB) consortium published a
 technical specification [ETSI-TS-102-034] through the European
 Telecommunications Standards Institute (ETSI).  This specification
 covers several areas related to the transmission of MPEG-2 transport
 stream-based services over IP networks.
 Annex E of [ETSI-TS-102-034] defines an optional protocol for
 Application-layer FEC (AL-FEC) protection of streaming media for
 DVB-IP services carried over RTP [RFC3550] transport.  The DVB-IPTV
 AL-FEC protocol uses two layers for protection: a base layer that is
 produced by a packet-based interleaved parity code, and an
 enhancement layer that is produced by a Raptor code [DVB-AL-FEC].
 While the use of the enhancement layer is optional, the use of the
 base layer is mandatory wherever AL-FEC is used.  The DVB-IPTV AL-FEC
 protocol is also described in [DVB-AL-FEC].

Begen Standards Track [Page 9] RFC 6015 RTP Payload Format for Interleaved FEC October 2010

 The interleaved parity code that is used in the base layer is a
 subset of [SMPTE2022-1].  In particular, the AL-FEC base layer uses
 only the 1-D interleaved FEC protection from [SMPTE2022-1].  The new
 RTP payload format that is defined and registered in this document
 (with some exceptions listed in [DVB-AL-FEC]) is used as the AL-FEC
 base layer.

1.4. Scope of the Payload Format

 The payload format specified in this document must only be used in
 legacy applications where the limitations explained in Section 1.3.2
 are known not to impact any system components or other RTP elements.
 Whenever possible, a payload format that is fully compliant with
 [RFC3550], such as [RFC5109] or other newer payload formats, must be
 used.

2. Requirements Notation

 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. Definitions, Notations, and Abbreviations

 The definitions and notations commonly used in this document are
 summarized in this section.

3.1. Definitions

 This document uses the following definitions:
 Source Flow: The packet flow(s) carrying the source data to which FEC
 protection is to be applied.
 Repair Flow: The packet flow(s) carrying the repair data.
 Symbol: A unit of data.  Its size, in bytes, is referred to as the
 symbol size.
 Source Symbol: The smallest unit of data used during the encoding
 process.
 Repair Symbol: Repair symbols are generated from the source symbols.
 Source Packet: Data packets that contain only source symbols.
 Repair Packet: Data packets that contain only repair symbols.

Begen Standards Track [Page 10] RFC 6015 RTP Payload Format for Interleaved FEC October 2010

 Source Block: A block of source symbols that are considered together
 in the encoding process.

3.2. Notations

 o  L: Number of columns of the source block.
 o  D: Number of rows of the source block.

4. Packet Formats

 This section defines the formats of the source and repair packets.

4.1. Source Packets

 The source packets need to contain information that identifies the
 source block and the position within the source block occupied by the
 packet.  Since the source packets that are carried within an RTP
 stream already contain unique sequence numbers in their RTP headers
 [RFC3550], we can identify the source packets in a straightforward
 manner, and there is no need to append additional field(s).  The
 primary advantage of not modifying the source packets in any way is
 that it provides backward compatibility for the receivers that do not
 support FEC at all.  In multicast scenarios, this backward
 compatibility becomes quite useful as it allows the non-FEC-capable
 and FEC-capable receivers to receive and interpret the same source
 packets sent in the same multicast session.

4.2. Repair Packets

 The repair packets MUST contain information that identifies the
 source block to which they pertain and the relationship between the
 contained repair symbols and the original source block.  For this
 purpose, we use the RTP header of the repair packets as well as
 another header within the RTP payload, which we refer to as the FEC
 header, as shown in Figure 6.

Begen Standards Track [Page 11] RFC 6015 RTP Payload Format for Interleaved FEC October 2010

           +------------------------------+
           |          IP Header           |
           +------------------------------+
           |       Transport Header       |
           +------------------------------+
           |          RTP Header          | __
           +------------------------------+   |
           |          FEC Header          |    \
           +------------------------------+     > RTP Payload
           |        Repair Symbols        |    /
           +------------------------------+ __|
                  Figure 6: Format of repair packets
 The RTP header is formatted according to [RFC3550] with some further
 clarifications listed below:
 o  Version: The version field is set to 2.
 o  Padding (P) Bit: This bit is equal to the XOR sum of the
    corresponding P bits from the RTP headers of the source packets
    protected by this repair packet.  However, padding octets are
    never present in a repair packet, independent of the value of the
    P bit.
 o  Extension (X) Bit: This bit is equal to the XOR sum of the
    corresponding X bits from the RTP headers of the source packets
    protected by this repair packet.  However, an RTP header extension
    is never present in a repair packet, independent of the value of
    the X bit.
 o  CSRC Count (CC): This field is equal to the XOR sum of the
    corresponding CC values from the RTP headers of the source packets
    protected by this repair packet.  However, a CSRC list is never
    present in a repair packet, independent of the value of the CC
    field.
 o  Marker (M) Bit: This bit is equal to the XOR sum of the
    corresponding M bits from the RTP headers of the source packets
    protected by this repair packet.
 o  Payload Type: The (dynamic) payload type for the repair packets is
    determined through out-of-band means.  Note that this document
    registers a new payload format for the repair packets (refer to
    Section 5 for details).  According to [RFC3550], an RTP receiver
    that cannot recognize a payload type must discard it.  This action
    provides backward compatibility.  The FEC mechanisms can then be
    used in a multicast group with mixed FEC-capable and non-FEC-

Begen Standards Track [Page 12] RFC 6015 RTP Payload Format for Interleaved FEC October 2010

    capable receivers.  If a non-FEC-capable receiver receives a
    repair packet, it will not recognize the payload type, and hence,
    discards the repair packet.
 o  Sequence Number (SN): The sequence number has the standard
    definition.  It MUST be one higher than the sequence number in the
    previously transmitted repair packet.  The initial value of the
    sequence number SHOULD be random (unpredictable) [RFC3550].
 o  Timestamp (TS): The timestamp SHALL be set to a time corresponding
    to the repair packet's transmission time.  Note that the timestamp
    value has no use in the actual FEC protection process and is
    usually useful for jitter calculations.
 o  Synchronization Source (SSRC): The SSRC value SHALL be randomly
    assigned as suggested by [RFC3550].  This allows the sender to
    multiplex the source and repair flows on the same port or
    multiplex multiple repair flows on a single port.  The repair
    flows SHOULD use the RTP Control Protocol (RTCP) CNAME field to
    associate themselves with the source flow.
    In some networks, the RTP Source (which produces the source
    packets) and the FEC Source (which generates the repair packets
    from the source packets) may not be the same host.  In such
    scenarios, using the same CNAME for the source and repair flows
    means that the RTP Source and the FEC Source MUST share the same
    CNAME (for this specific source-repair flow association).  A
    common CNAME may be produced based on an algorithm that is known
    both to the RTP and FEC Source.  This usage is compliant with
    [RFC3550].
    Note that due to the randomness of the SSRC assignments, there is
    a possibility of SSRC collision.  In such cases, the collisions
    MUST be resolved as described in [RFC3550].
 Note that the P bit, X bit, CC field, and M bit of the source packets
 are protected by the corresponding bits/fields in the RTP header of
 the repair packet.  On the other hand, the payload of a repair packet
 protects the concatenation of (if present) the CSRC list, RTP
 extension, payload, and padding of the source RTP packets associated
 with this repair packet.
 The FEC header is 16 octets.  The format of the FEC header is shown
 in Figure 7.

Begen Standards Track [Page 13] RFC 6015 RTP Payload Format for Interleaved FEC October 2010

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          SN base low          |        Length recovery        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |E| PT recovery |                     Mask                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          TS recovery                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |N|D|Type |Index|     Offset    |       NA      |  SN base ext  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                  Figure 7: Format of the FEC header
 The FEC header consists of the following fields:
 o  The SN base low field is used to indicate the lowest sequence
    number, taking wraparound into account, of those source packets
    protected by this repair packet.
 o  The Length recovery field is used to determine the length of any
    recovered packets.
 o  The E bit is the extension flag introduced in [RFC2733] and used
    to extend the [RFC2733] FEC header.
 o  The PT recovery field is used to determine the payload type of the
    recovered packets.
 o  The Mask field is not used.
 o  The TS recovery field is used to determine the timestamp of the
    recovered packets.
 o  The N bit is the extension flag that is reserved for future use.
 o  The D bit is not used.
 o  The Type field indicates the type of the error-correcting code
    used.  This document defines only one error-correcting code.
 o  The Index field is not used.
 o  The Offset and NA fields are used to indicate the number of
    columns (L) and rows (D) of the source block, respectively.
 o  The SN base ext field is not used.

Begen Standards Track [Page 14] RFC 6015 RTP Payload Format for Interleaved FEC October 2010

 The details on setting the fields in the FEC header are provided in
 Section 6.2.
 It should be noted that a Mask-based approach (similar to the one
 specified in [RFC2733]) may not be very efficient to indicate which
 source packets in the current source block are associated with a
 given repair packet.  In particular, for the applications that would
 like to use large source block sizes, the size of the Mask that is
 required to describe the source-repair packet associations may be
 prohibitively large.  Instead, a systematized approach is inherently
 more efficient.

5. Payload Format Parameters

 This section provides the media subtype registration for the 1-D
 interleaved parity FEC.  The parameters that are required to
 configure the FEC encoding and decoding operations are also defined
 in this section.

5.1. Media Type Registration

 This registration is done using the template defined in [RFC4288] and
 following the guidance provided in [RFC4855].

5.1.1. Registration of audio/1d-interleaved-parityfec

 Type name: audio
 Subtype name: 1d-interleaved-parityfec
 Required parameters:
 o  rate: The RTP timestamp (clock) rate in Hz.  The (integer) rate
    SHALL be larger than 1000 to provide sufficient resolution to RTCP
    operations.  However, it is RECOMMENDED to select the rate that
    matches the rate of the protected source RTP stream.
 o  L: Number of columns of the source block.  L is a positive integer
    that is less than or equal to 255.
 o  D: Number of rows of the source block.  D is a positive integer
    that is less than or equal to 255.
 o  repair-window: The time that spans the FEC block (i.e., source
    packets and the corresponding repair packets).  An FEC encoder
    processes a block of source packets and generates a number of
    repair packets, which are then transmitted within a certain
    duration not larger than the value of the repair window.  At the

Begen Standards Track [Page 15] RFC 6015 RTP Payload Format for Interleaved FEC October 2010

    receiver side, the FEC decoder should wait at least for the
    duration of the repair window after getting the first packet in an
    FEC block to allow all the repair packets to arrive (the waiting
    time can be adjusted if there are missing packets at the beginning
    of the FEC block).  The FEC decoder can start decoding the already
    received packets sooner; however, it SHOULD NOT register an FEC
    decoding failure until it waits at least for the repair-window
    duration.  The size of the repair window is specified in
    microseconds.
 Optional parameters: None.
 Encoding considerations: This media type is framed (see Section 4.8
 in the template document [RFC4288]) and contains binary data.
 Security considerations: See Section 9 of [RFC6015].
 Interoperability considerations: None.
 Published specification: [RFC6015].
 Applications that use this media type: Multimedia applications that
 want to improve resiliency against packet loss by sending redundant
 data in addition to the source media.
 Additional information: None.
 Person & email address to contact for further information: Ali Begen
 <abegen@cisco.com> and the IETF Audio/Video Transport Working Group.
 Intended usage: COMMON.
 Restriction on usage: This media type depends on RTP framing, and
 hence, is only defined for transport via RTP [RFC3550].
 Author: Ali Begen <abegen@cisco.com>.
 Change controller: IETF Audio/Video Transport Working Group delegated
 from the IESG.

5.1.2. Registration of video/1d-interleaved-parityfec

 Type name: video
 Subtype name: 1d-interleaved-parityfec
 Required parameters:

Begen Standards Track [Page 16] RFC 6015 RTP Payload Format for Interleaved FEC October 2010

 o  rate: The RTP timestamp (clock) rate in Hz.  The (integer) rate
    SHALL be larger than 1000 to provide sufficient resolution to RTCP
    operations.  However, it is RECOMMENDED to select the rate that
    matches the rate of the protected source RTP stream.
 o  L: Number of columns of the source block.  L is a positive integer
    that is less than or equal to 255.
 o  D: Number of rows of the source block.  D is a positive integer
    that is less than or equal to 255.
 o  repair-window: The time that spans the FEC block (i.e., source
    packets and the corresponding repair packets).  An FEC encoder
    processes a block of source packets and generates a number of
    repair packets, which are then transmitted within a certain
    duration not larger than the value of the repair window.  At the
    receiver side, the FEC decoder should wait at least for the
    duration of the repair window after getting the first packet in an
    FEC block to allow all the repair packets to arrive (the waiting
    time can be adjusted if there are missing packets at the beginning
    of the FEC block).  The FEC decoder can start decoding the already
    received packets sooner; however, it SHOULD NOT register an FEC
    decoding failure until it waits at least for the repair-window
    duration.  The size of the repair window is specified in
    microseconds.
 Optional parameters: None.
 Encoding considerations: This media type is framed (see Section 4.8
 in the template document [RFC4288]) and contains binary data.
 Security considerations: See Section 9 of [RFC6015].
 Interoperability considerations: None.
 Published specification: [RFC6015].
 Applications that use this media type: Multimedia applications that
 want to improve resiliency against packet loss by sending redundant
 data in addition to the source media.
 Additional information: None.
 Person & email address to contact for further information: Ali Begen
 <abegen@cisco.com> and the IETF Audio/Video Transport Working Group.
 Intended usage: COMMON.

Begen Standards Track [Page 17] RFC 6015 RTP Payload Format for Interleaved FEC October 2010

 Restriction on usage: This media type depends on RTP framing, and
 hence, is only defined for transport via RTP [RFC3550].
 Author: Ali Begen <abegen@cisco.com>.
 Change controller: IETF Audio/Video Transport Working Group delegated
 from the IESG.

5.1.3. Registration of text/1d-interleaved-parityfec

 Type name: text
 Subtype name: 1d-interleaved-parityfec
 Required parameters:
 o  rate: The RTP timestamp (clock) rate in Hz.  The (integer) rate
    SHALL be larger than 1000 to provide sufficient resolution to RTCP
    operations.  However, it is RECOMMENDED to select the rate that
    matches the rate of the protected source RTP stream.
 o  L: Number of columns of the source block.  L is a positive integer
    that is less than or equal to 255.
 o  D: Number of rows of the source block.  D is a positive integer
    that is less than or equal to 255.
 o  repair-window: The time that spans the FEC block (i.e., source
    packets and the corresponding repair packets).  An FEC encoder
    processes a block of source packets and generates a number of
    repair packets, which are then transmitted within a certain
    duration not larger than the value of the repair window.  At the
    receiver side, the FEC decoder should wait at least for the
    duration of the repair window after getting the first packet in an
    FEC block to allow all the repair packets to arrive (the waiting
    time can be adjusted if there are missing packets at the beginning
    of the FEC block).  The FEC decoder can start decoding the already
    received packets sooner; however, it SHOULD NOT register an FEC
    decoding failure until it waits at least for the repair-window
    duration.  The size of the repair window is specified in
    microseconds.
 Optional parameters: None.
 Encoding considerations: This media type is framed (see Section 4.8
 in the template document [RFC4288]) and contains binary data.
 Security considerations: See Section 9 of [RFC6015].

Begen Standards Track [Page 18] RFC 6015 RTP Payload Format for Interleaved FEC October 2010

 Interoperability considerations: None.
 Published specification: [RFC6015].
 Applications that use this media type: Multimedia applications that
 want to improve resiliency against packet loss by sending redundant
 data in addition to the source media.
 Additional information: None.
 Person & email address to contact for further information: Ali Begen
 <abegen@cisco.com> and the IETF Audio/Video Transport Working Group.
 Intended usage: COMMON.
 Restriction on usage: This media type depends on RTP framing, and
 hence, is only defined for transport via RTP [RFC3550].
 Author: Ali Begen <abegen@cisco.com>.
 Change controller: IETF Audio/Video Transport Working Group delegated
 from the IESG.

5.1.4. Registration of application/1d-interleaved-parityfec

 Type name: application
 Subtype name: 1d-interleaved-parityfec
 Required parameters:
 o  rate: The RTP timestamp (clock) rate in Hz.  The (integer) rate
    SHALL be larger than 1000 to provide sufficient resolution to RTCP
    operations.  However, it is RECOMMENDED to select the rate that
    matches the rate of the protected source RTP stream.
 o  L: Number of columns of the source block.  L is a positive integer
    that is less than or equal to 255.
 o  D: Number of rows of the source block.  D is a positive integer
    that is less than or equal to 255.
 o  repair-window: The time that spans the FEC block (i.e., source
    packets and the corresponding repair packets).  An FEC encoder
    processes a block of source packets and generates a number of
    repair packets, which are then transmitted within a certain
    duration not larger than the value of the repair window.  At the
    receiver side, the FEC decoder should wait at least for the

Begen Standards Track [Page 19] RFC 6015 RTP Payload Format for Interleaved FEC October 2010

    duration of the repair window after getting the first packet in an
    FEC block to allow all the repair packets to arrive (the waiting
    time can be adjusted if there are missing packets at the beginning
    of the FEC block).  The FEC decoder can start decoding the already
    received packets sooner; however, it SHOULD NOT register an FEC
    decoding failure until it waits at least for the repair-window
    duration.  The size of the repair window is specified in
    microseconds.
 Optional parameters: None.
 Encoding considerations: This media type is framed (see Section 4.8
 in the template document [RFC4288]) and contains binary data.
 Security considerations: See Section 9 of [RFC6015].
 Interoperability considerations: None.
 Published specification: [RFC6015].
 Applications that use this media type: Multimedia applications that
 want to improve resiliency against packet loss by sending redundant
 data in addition to the source media.
 Additional information: None.
 Person & email address to contact for further information: Ali Begen
 <abegen@cisco.com> and the IETF Audio/Video Transport Working Group.
 Intended usage: COMMON.
 Restriction on usage: This media type depends on RTP framing, and
 hence, is only defined for transport via RTP [RFC3550].
 Author: Ali Begen <abegen@cisco.com>.
 Change controller: IETF Audio/Video Transport Working Group delegated
 from the IESG.

5.2. Mapping to SDP Parameters

 Applications that use RTP transport commonly use Session Description
 Protocol (SDP) [RFC4566] to describe their RTP sessions.  The
 information that is used to specify the media types in an RTP session
 has specific mappings to the fields in an SDP description.  In this
 section, we provide these mappings for the media subtype registered
 by this document ("1d-interleaved-parityfec").  Note that if an
 application does not use SDP to describe the RTP sessions, an

Begen Standards Track [Page 20] RFC 6015 RTP Payload Format for Interleaved FEC October 2010

 appropriate mapping must be defined and used to specify the media
 types and their parameters for the control/description protocol
 employed by the application.
 The mapping of the media type specification for "1d-interleaved-
 parityfec" and its parameters in SDP is as follows:
 o  The media type (e.g., "application") goes into the "m=" line as
    the media name.
 o  The media subtype ("1d-interleaved-parityfec") goes into the
    "a=rtpmap" line as the encoding name.  The RTP clock rate
    parameter ("rate") also goes into the "a=rtpmap" line as the clock
    rate.
 o  The remaining required payload-format-specific parameters go into
    the "a=fmtp" line by copying them directly from the media type
    string as a semicolon-separated list of parameter=value pairs.
 SDP examples are provided in Section 7.

5.2.1. Offer-Answer Model Considerations

 When offering 1-D interleaved parity FEC over RTP using SDP in an
 Offer/Answer model [RFC3264], the following considerations apply:
 o  Each combination of the L and D parameters produces a different
    FEC data and is not compatible with any other combination.  A
    sender application may desire to offer multiple offers with
    different sets of L and D values as long as the parameter values
    are valid.  The receiver SHOULD normally choose the offer that has
    a sufficient amount of interleaving.  If multiple such offers
    exist, the receiver may choose the offer that has the lowest
    overhead or the one that requires the smallest amount of
    buffering.  The selection depends on the application requirements.
 o  The value for the repair-window parameter depends on the L and D
    values and cannot be chosen arbitrarily.  More specifically, L and
    D values determine the lower limit for the repair-window size.
    The upper limit of the repair-window size does not depend on the L
    and D values.
 o  Although combinations with the same L and D values but with
    different repair-window sizes produce the same FEC data, such
    combinations are still considered different offers.  The size of
    the repair-window is related to the maximum delay between the

Begen Standards Track [Page 21] RFC 6015 RTP Payload Format for Interleaved FEC October 2010

    transmission of a source packet and the associated repair packet.
    This directly impacts the buffering requirement on the receiver
    side, and the receiver must consider this when choosing an offer.
 o  There are no optional format parameters defined for this payload.
    Any unknown option in the offer MUST be ignored and deleted from
    the answer.  If FEC is not desired by the receiver, it can be
    deleted from the answer.

5.2.2. Declarative Considerations

 In declarative usage, like SDP in the Real-time Streaming Protocol
 (RTSP) [RFC2326] or the Session Announcement Protocol (SAP)
 [RFC2974], the following considerations apply:
 o  The payload format configuration parameters are all declarative
    and a participant MUST use the configuration that is provided for
    the session.
 o  More than one configuration may be provided (if desired) by
    declaring multiple RTP payload types.  In that case, the receivers
    should choose the repair flow that is best for them.

6. Protection and Recovery Procedures

 This section provides a complete specification of the 1-D interleaved
 parity code and its RTP payload format.

6.1. Overview

 The following sections specify the steps involved in generating the
 repair packets and reconstructing the missing source packets from the
 repair packets.

6.2. Repair Packet Construction

 The RTP header of a repair packet is formed based on the guidelines
 given in Section 4.2.
 The FEC header includes 16 octets.  It is constructed by applying the
 XOR operation on the bit strings that are generated from the
 individual source packets protected by this particular repair packet.
 The set of the source packets that are associated with a given repair
 packet can be computed by the formula given in Section 6.3.1.
 The bit string is formed for each source packet by concatenating the
 following fields together in the order specified:

Begen Standards Track [Page 22] RFC 6015 RTP Payload Format for Interleaved FEC October 2010

 o  Padding bit (1 bit) (This is the most significant bit of the bit
    string.)
 o  Extension bit (1 bit)
 o  CC field (4 bits)
 o  Marker bit (1 bit)
 o  PT field (7 bits)
 o  Timestamp (32 bits)
 o  Unsigned network-ordered 16-bit representation of the source
    packet length in bytes minus 12 (for the fixed RTP header), i.e.,
    the sum of the lengths of all the following if present: the CSRC
    list, header extension, RTP payload, and RTP padding (16 bits).
 o  If CC is nonzero, the CSRC list (variable length)
 o  If X is 1, the header extension (variable length)
 o  Payload (variable length)
 o  Padding, if present (variable length)
 Note that if the lengths of the source packets are not equal, each
 shorter packet MUST be padded to the length of the longest packet by
 adding octet(s) of 0 at the end.  Due to this possible padding and
 mandatory FEC header, a repair packet has a larger size than the
 source packets it protects.  This may cause problems if the resulting
 repair packet size exceeds the Maximum Transmission Unit (MTU) size
 of the path over which the repair flow is sent.
 By applying the parity operation on the bit strings produced from the
 source packets, we generate the FEC bit string.  Some parts of the
 RTP header and the FEC header of the repair packet are generated from
 the FEC bit string as follows:
 o  The first (most significant) bit in the FEC bit string is written
    into the Padding bit in the RTP header of the repair packet.
 o  The next bit in the FEC bit string is written into the Extension
    bit in the RTP header of the repair packet.
 o  The next 4 bits of the FEC bit string are written into the CC
    field in the RTP header of the repair packet.

Begen Standards Track [Page 23] RFC 6015 RTP Payload Format for Interleaved FEC October 2010

 o  The next bit of the FEC bit string is written into the Marker bit
    in the RTP header of the repair packet.
 o  The next 7 bits of the FEC bit string are written into the PT
    recovery field in the FEC header.
 o  The next 32 bits of the FEC bit string are written into the TS
    recovery field in the FEC header.
 o  The next 16 bits are written into the Length recovery field in the
    FEC header.  This allows the FEC procedure to be applied even when
    the lengths of the protected source packets are not identical.
 o  The remaining bits are set to be the payload of the repair packet.
 The remaining parts of the FEC header are set as follows:
 o  The SN base low field MUST be set to the lowest sequence number,
    taking wraparound into account, of those source packets protected
    by this repair packet.
 o  The E bit MUST be set to 1 to extend the [RFC2733] FEC header.
 o  The Mask field SHALL be set to 0 and ignored by the receiver.
 o  The N bit SHALL be set to 0 and ignored by the receiver.
 o  The D bit SHALL be set to 0 and ignored by the receiver.
 o  The Type field MUST be set to 0 and ignored by the receiver.
 o  The Index field SHALL be set to 0 and ignored by the receiver.
 o  The Offset field MUST be set to the number of columns of the
    source block (L).
 o  The NA field MUST be set to the number of rows of the source block
    (D).
 o  The SN base ext field SHALL be set to 0 and ignored by the
    receiver.

6.3. Source Packet Reconstruction

 This section describes the recovery procedures that are required to
 reconstruct the missing source packets.  The recovery process has two
 steps.  In the first step, the FEC decoder determines which source

Begen Standards Track [Page 24] RFC 6015 RTP Payload Format for Interleaved FEC October 2010

 and repair packets should be used in order to recover a missing
 packet.  In the second step, the decoder recovers the missing packet,
 which consists of an RTP header and RTP payload.
 In the following, we describe the RECOMMENDED algorithms for the
 first and second steps.  Based on the implementation, different
 algorithms MAY be adopted.  However, the end result MUST be identical
 to the one produced by the algorithms described below.

6.3.1. Associating the Source and Repair Packets

 The first step is to associate the source and repair packets.  The SN
 base low field in the FEC header shows the lowest sequence number of
 the source packets that form the particular column.  In addition, the
 information of how many source packets are available in each column
 and row is available from the media type parameters specified in the
 SDP description.  This set of information uniquely identifies all of
 the source packets associated with a given repair packet.
 Mathematically, for any received repair packet, p*, we can determine
 the sequence numbers of the source packets that are protected by this
 repair packet as follows:
                     p*_snb + i * L (modulo 65536)
 where p*_snb denotes the value in the SN base low field of the FEC
 header of the p*, L is the number of columns of the source block and
                               0 <= i < D
 where D is the number of rows of the source block.
 We denote the set of the source packets associated with repair packet
 p* by set T(p*).  Note that in a source block whose size is L columns
 by D rows, set T includes D source packets.  Recall that 1-D
 interleaved FEC protection can fully recover the missing information
 if there is only one source packet missing in set T.  If the repair
 packet that protects the source packets in set T is missing, or the
 repair packet is available but two or more source packets are
 missing, then missing source packets in set T cannot be recovered by
 1-D interleaved FEC protection.

6.3.2. Recovering the RTP Header and Payload

 For a given set T, the procedure for the recovery of the RTP header
 of the missing packet, whose sequence number is denoted by SEQNUM, is
 as follows:

Begen Standards Track [Page 25] RFC 6015 RTP Payload Format for Interleaved FEC October 2010

 1.   For each of the source packets that are successfully received in
      set T, compute the bit string as described in Section 6.2.
 2.   For the repair packet associated with set T, compute the bit
      string in the same fashion except use the PT recovery field
      instead of the PT field and TS recovery field instead of the
      Timestamp field, and set the CSRC list, header extension and
      padding to null regardless of the values of the CC field, X bit,
      and P bit.
 3.   If any of the bit strings generated from the source packets are
      shorter than the bit string generated from the repair packet,
      pad them to be the same length as the bit string generated from
      the repair packet.  For padding, the padding of octet 0 MUST be
      added at the end of the bit string.
 4.   Calculate the recovered bit string as the XOR of the bit strings
      generated from all source packets in set T and the FEC bit
      string generated from the repair packet associated with set T.
 5.   Create a new packet with the standard 12-byte RTP header and no
      payload.
 6.   Set the version of the new packet to 2.
 7.   Set the Padding bit in the new packet to the first bit in the
      recovered bit string.
 8.   Set the Extension bit in the new packet to the next bit in the
      recovered bit string.
 9.   Set the CC field to the next 4 bits in the recovered bit string.
 10.  Set the Marker bit in the new packet to the next bit in the
      recovered bit string.
 11.  Set the Payload type in the new packet to the next 7 bits in the
      recovered bit string.
 12.  Set the SN field in the new packet to SEQNUM.
 13.  Set the TS field in the new packet to the next 32 bits in the
      recovered bit string.
 14.  Take the next 16 bits of the recovered bit string and set the
      new variable Y to whatever unsigned integer this represents
      (assuming network order).  Convert Y to host order and then take
      Y bytes from the recovered bit string and append them to the new

Begen Standards Track [Page 26] RFC 6015 RTP Payload Format for Interleaved FEC October 2010

      packet.  Y represents the length of the new packet in bytes
      minus 12 (for the fixed RTP header), i.e., the sum of the
      lengths of all the following if present: the CSRC list, header
      extension, RTP payload, and RTP padding.
 15.  Set the SSRC of the new packet to the SSRC of the source RTP
      stream.
 This procedure completely recovers both the header and payload of an
 RTP packet.

7. Session Description Protocol (SDP) Signaling

 This section provides an SDP [RFC4566] example.  The following
 example uses the FEC grouping semantics [RFC5956].
 In this example, we have one source video stream (mid:S1) and one FEC
 repair stream (mid:R1).  We form one FEC group with the "a=group:
 FEC-FR S1 R1" line.  The source and repair streams are sent to the
 same port on different multicast groups.  The repair window is set to
 200 ms.
      v=0
      o=ali 1122334455 1122334466 IN IP4 fec.example.com
      s=Interleaved Parity FEC Example
      t=0 0
      a=group:FEC-FR S1 R1
      m=video 30000 RTP/AVP 100
      c=IN IP4 233.252.0.1/127
      a=rtpmap:100 MP2T/90000
      a=mid:S1
      m=application 30000 RTP/AVP 110
      c=IN IP4 233.252.0.2/127
      a=rtpmap:110 1d-interleaved-parityfec/90000
      a=fmtp:110 L=5; D=10; repair-window=200000
      a=mid:R1

8. Congestion Control Considerations

 FEC is an effective approach to provide applications with resiliency
 against packet losses.  However, in networks where the congestion is
 a major contributor to the packet loss, the potential impacts of
 using FEC SHOULD be considered carefully before injecting the repair
 flows into the network.  In particular, in bandwidth-limited
 networks, FEC repair flows may consume most or all of the available
 bandwidth and may consequently congest the network.  In such cases,
 the applications MUST NOT arbitrarily increase the amount of FEC

Begen Standards Track [Page 27] RFC 6015 RTP Payload Format for Interleaved FEC October 2010

 protection since doing so may lead to a congestion collapse.  If
 desired, stronger FEC protection MAY be applied only after the source
 rate has been reduced.
 In a network-friendly implementation, an application SHOULD NOT send/
 receive FEC repair flows if it knows that sending/receiving those FEC
 repair flows would not help at all in recovering the missing packets.
 Such a practice helps reduce the amount of wasted bandwidth.  It is
 RECOMMENDED that the amount of FEC protection is adjusted dynamically
 based on the packet loss rate observed by the applications.
 In multicast scenarios, it may be difficult to optimize the FEC
 protection per receiver.  If there is a large variation among the
 levels of FEC protection needed by different receivers, it is
 RECOMMENDED that the sender offers multiple repair flows with
 different levels of FEC protection and the receivers join the
 corresponding multicast sessions to receive the repair flow(s) that
 is best for them.

9. 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
 encrypting the RTP payload.  Altering the FEC packets can have a big
 impact on the reconstruction operation.  An attack that changes some
 bits in the FEC packets can have a significant effect on the
 calculation and the recovery of the source packets.  For example,
 changing the length recovery field can result in the recovery of a
 packet that is too long.  Depending on the application, it may be
 helpful to perform a sanity check on the received source and FEC
 packets before performing the recovery operation and to determine the
 validity of the recovered packets before using them.
 The integrity of the RTP packets is achieved through a suitable
 cryptographic integrity protection mechanism.  Such a cryptographic
 system may also allow the authentication of the source of the
 payload.  A suitable security mechanism for this RTP payload format
 should provide source authentication capable of determining if 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, transport and signaling protocol employed.  Therefore, a

Begen Standards Track [Page 28] RFC 6015 RTP Payload Format for Interleaved FEC October 2010

 single mechanism is not sufficient, although if suitable, using 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]; other alternatives may exist.
 If FEC protection is applied on already encrypted source packets,
 there is no need for additional encryption.  However, if the source
 packets are encrypted after FEC protection is applied, the FEC
 packets should be cryptographically as secure as the source packets.
 Failure to provide an equal level of confidentiality, integrity, and
 authentication to the FEC packets can compromise the source packets'
 confidentiality, integrity or authentication since the FEC packets
 are generated by applying XOR operation across the source packets.

10. IANA Considerations

 New media subtypes are subject to IANA registration.  For the
 registration of the payload format and its parameters introduced in
 this document, refer to Section 5.

11. Acknowledgments

 A major part of this document is borrowed from [RFC2733], [RFC5109],
 and [SMPTE2022-1].  Thus, the author would like to thank the authors
 and editors of these earlier specifications.  The author also thanks
 Colin Perkins for his constructive suggestions for this document.

12. References

12.1. 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.
 [RFC5956]          Begen, A., "Forward Error Correction Grouping
                    Semantics in Session Description Protocol",
                    RFC 5956, September 2010.

Begen Standards Track [Page 29] RFC 6015 RTP Payload Format for Interleaved FEC October 2010

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

12.2. Informative References

 [DVB-AL-FEC]       Begen, A. and T. Stockhammer, "Guidelines for
                    Implementing DVB-IPTV Application-Layer Hybrid FEC
                    Protection", Work in Progress, December 2009.
 [RFC2733]          Rosenberg, J. and H. Schulzrinne, "An RTP Payload
                    Format for Generic Forward Error Correction",
                    RFC 2733, December 1999.
 [RFC3009]          Rosenberg, J. and H. Schulzrinne, "Registration of
                    parityfec MIME types", RFC 3009, November 2000.
 [RFC5109]          Li, A., "RTP Payload Format for Generic Forward
                    Error Correction", RFC 5109, December 2007.
 [ETSI-TS-102-034]  ETSI TS 102 034 V1.4.1, "Transport of MPEG 2 TS
                    Based DVB Services over IP Based Networks",
                    August 2009.
 [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.
 [SMPTE2022-1]      SMPTE 2022-1-2007, "Forward Error Correction for
                    Real-Time Video/Audio Transport over IP Networks",
                    2007.
 [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.

Begen Standards Track [Page 30] RFC 6015 RTP Payload Format for Interleaved FEC October 2010

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

Author's Address

 Ali Begen
 Cisco
 181 Bay Street
 Toronto, ON  M5J 2T3
 Canada
 EMail: abegen@cisco.com

Begen Standards Track [Page 31]

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