Internet Draft                                             K. Hedayat
  Expires: October 8, 2010 January 27, 2011                                        EXFO
                                                               N. Venna
                                                                   EXFO
                                                               P. Jones
                                                    Cisco Systems, Inc.
                                                        A. Roychowdhury
                                                  Hughes Systique Corp.
                                                         C. SivaChelvan
                                                    Cisco Systems, Inc.
                                                            N. Stratton
                                                        BlinkMind, Inc.
                                                          April 8,
                                                          July 27, 2010

     An Extension to the Session Description Protocol (SDP) for Media
                                Loopback
                   draft-ietf-mmusic-media-loopback-13
                   draft-ietf-mmusic-media-loopback-14

 Status of this Memo

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    This Internet-Draft will expire on June 30, 2010. January 27, 2011.

 Copyright Notice

    Copyright (c) 2009 IETF Trust and the persons identified as the
    document authors.  All rights reserved.

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 Abstract

    The wide deployment of Voice over IP (VoIP), Real-time Text and
    Video over IP services has introduced new challenges in managing
    and maintaining voice/real-time Text/video quality, reliability,
    and overall performance.  In particular, media delivery is an area
    that needs attention.  One method of meeting these challenges is
    monitoring the media delivery performance by looping media back to
    the transmitter.  This is typically referred to as "active
    monitoring" of services.   Media loopback is especially popular in
    ensuring the quality of transport to the edge of a given VoIP,
    Real-time Text or Video over IP service.  Today in networks that
    deliver real-time media, short of running 'ping' and 'traceroute'
    to the edge, service providers are left without the necessary tools
    to actively monitor, manage, and diagnose quality issues with their
    service.  The extension defined herein adds new SDP media
    attributes which enables establishment of media sessions where the
    media is looped back to the transmitter. Such media sessions will
    serve as monitoring and troubleshooting tools by providing the
    means for measurement of more advanced VoIP, Real-time Text and
    Video over IP performance metrics.

 Table of Contents

    1. Introduction                     .................................................. 3
    2. Terminology                    ................................................... 4
    3. Offering Entity Behavior                                 ...................................... 4
    4. Answering Entity Behavior                                  ..................................... 4
    5. SDP Constructs Syntax                              ......................................... 5
       5.1 Loopback Type Attribute                                    ................................... 5
       5.2 Loopback Mode Attribute                                    ................................... 6
       5.3 Payload type mapping for loopback sessions                                                       ................ 6
       5.4 Generating the Offer for Loopback Session                                                      ................. 6
       5.4 7
       5.5 Generating the Answer for Loopback Session                                                       ................ 7
       5.5 8
       5.6 Offerer Processing of the Answer                                             .......................... 9
       5.6
       5.7 Modifying the Session                                  ..................................... 9
       5.7                                  .................................... 10
       5.8 Priming the loopback pump                                      ................................. 9                                      ................................ 10
    6. RTP Requirements                         ............................................. 10
    7. Payload formats for Packet loopback                                            .......................... 11
       7.1 Encapsulated Payload format                                        .............................. 11 12
       7.2 Direct loopback RTP payload format                                               ....................... 13 14
    8. Payload formats format for Priming the Loopback Pump                                                      ................                                                     ................. 15
       8.1 Usage of RTP Header fields                                       ............................... 15
       8.2 Usage of SDP                         ............................................. 15 16
    9. RTCP Requirements                          ............................................ 15 16
    10. Congestion Control                            .......................................... 16
    11. Examples                  .................................................... 16 17
       11.1 Offer for specific media loopback type                                                    .................. 16 17
       11.2 Offer for choice of media loopback type                                                     ................. 17
       11.3 Offer for choice of media loopback type with loopback
       primer               ....................................................... 18
       11.4 Response to INVITE request rejecting loopback media                                                                 ..... 19
       11.5 Response to INVITE request rejecting loopback media with
       loopback primer payload type                                     ................................. 20
    12. Security Considerations                                 ..................................... 20 21
    13. Implementation Considerations                                       ............................... 21
    14. IANA Considerations                             ......................................... 21 22
       14.1 SDP Attributes                            .......................................... 21 22
       14.2 MIME Types                        .............................................. 22 23
    15. Acknowledgements                          ............................................ 36
    16. Normative References                              ........................................ 36

 1.     Introduction

    The overall quality, reliability, and performance of VoIP,
    Real-time Text and Video over IP services rely on the performance
    and quality of the media path.  In order to assure the quality of
    the delivered media there is a need to monitor the performance of
    the media transport.  One method of monitoring and managing the
    overall quality of VoIP, Real-time Text and Video over IP Services
    is through monitoring the quality of the media in an active
    session.  This type of "active monitoring" of services is a method
    of proactively managing the performance and quality of VoIP based
    services.

    The goal of active monitoring is to measure the media quality of a
    VoIP, Real-time Text or Video over IP session.  A way to achieve
    this goal is to request an endpoint to loop media back to the other
    endpoint and to provide media statistics (e.g., RTCP and RTCP XR
    information).  Another method involves deployment of special
    endpoints that always loop incoming media back for sessions.
    Although the latter method has been used and is functional, it does
    not scale to support large networks and introduces new network
    management challenges.  Further, it does not offer the granularity
    of testing a specific endpoint that may be exhibiting problems.

    The extension defined in this memo introduces new SDP media
    attributes that enable establishment of media sessions where the
    media is looped back to the transmitter.  The offer/answer model
    [RFC3264] is used to establish a loopback connection.  Furthermore,
    this extension provides guidelines on handling RTP [RFC3550], as
    well as usage of RTCP [RFC3550] and RTCP XR [RFC3611] for reporting
    media related measurements.

 2.     Terminology

    The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
    "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
    this document are to be interpreted as described in RFC 2119.

 3.     Offering Entity Behavior

    An offering entity compliant to this memo and attempting to
    establish a media session with media loopback MUST include
    "loopback" media attributes for each individual media description
    in the offer message.  The offering entity MUST look for the
    "loopback" media attributes in the media description(s) of the
    response from the answering entity for confirmation that the
    request is accepted.

 4.     Answering Entity Behavior

    An answering entity compliant to this specification and receiving
    an offer containing media descriptions with the "loopback" media
    attributes, MUST acknowledge the request by including the received
    "loopback" media attributes for each media description in its
    response.  The server MAY reject the "loopback" request for
    specific media types as defined in section 5.4.1 5.5.1 of this
    specification.

    An answering entity that is not compliant to this specification and
    which receives an offer with the "loopback" media attributes MAY
    ignore the attribute and treat the incoming offer as a normal
    request.

 5.     SDP Constructs Syntax

    Two new media attributes are defined: one indicates the type of
    loopback and one the other indicates the mode of the loopback.

 5.1      Loopback Type Attribute

    The loopback type is a property media attribute with the following
    syntax:

       a=loopback:<loopback-type>

    Following is the Augmented BNF [RFC5234] for loopback-type:

    loopback-type          = loopback-choice [1*SP loopback-choice]
    loopback-choice        = loopback-type-pkt / loopback-type-media
    loopback-type-pkt      = "rtp-pkt-loopback"
    loopback-type-media    = "rtp-media-loopback"

    The loopback type is used to indicate the type of loopback.  The
    loopback-type values are rtp-pkt-loopback, and rtp-media-loopback.

    rtp-pkt-loopback: In this mode, the RTP packets are looped back to
    the sender at a point before the encoder/decoder function in the
    receive direction to a point after the encoder/decoder function in
    the send direction. This effectively re-encapsulates the RTP
    payload with the RTP/UDP/IP overheads appropriate for sending it in
    the reverse direction.  Any type of encoding related functions,
    such as packet loss concealment, MUST NOT be part of this type of
    loopback path. In this mode the RTP packets are looped back with a
    new payload type and format.  Section 7 describes the payload
    formats that MUST be used for this type of loopback.

    rtp-media-loopback: This loopback is activated as close as possible
    to the analog interface and after the decoder so that the RTP
    packets are subsequently re-encoded prior to transmission back to
    the sender.

 5.2      Loopback Mode Attribute

    The loopback mode is a value media attribute that is used to
    indicate the mode of the loopback.  These attributes are additional
    mode attributes like sendonly, recvonly, etc.  The syntax of the
    loopback mode media attribute is:

       a=<loopback-mode>:<fmt>...

    The loopback-mode values are loopback-source and loopback-mirror.

    loopback-source: This attribute specifies that the sender is the
    media source and expects the receiver to act as a loopback-mirror.

    loopback-mirror: This attribute specifies that the receiver will
    mirror (echo) all received media back to the sender of the RTP
    stream.  No media is generated locally by the receiver for
    transmission in the mirrored stream unless the loopback primer
    payload type (described in Section 8 of this document) is requested
    by the loopback-source or included in the response by
    loopback-mirror.

    <fmt> is a media format description. The format description has the
    semantics as defined in section 5.14 of RFC 4566[RFC4566]. When
    loopback-mode is specified as loopback-source, the media format
    corresponds to the RTP payload types the source is willing to send.
    When loopback-mode is specified as loopback-mirror, the media
    format corresponds to the RTP payload types the mirror is willing
    to receive. The payload types specified in m= "m=" line for a
    loopback-source specify the payloads the source is willing to
    receive. Similarly, for the loopback-mirror these payload types
    specify the payloads it is willing to send. This separation of
    payload types allow receivers that do not understand media loopback
    to reject the call.

 5.3      Payload type mapping for loopback sessions

    As specified in RFC 4566[RFC4566], the rtpmap attribute maps from
    an RTP payload type number (as used in an "m=" line) to an encoding
    name denoting the payload format to be used. For loopback sessions,
    media formats are specified both in the "m=" line and the loopback-
    mode attribute line as described in Section 5.2. This specification
    extends the usage of rtpmap attribute to media formats specified in
    the loopback-mode attribute line in addition to the "m=" line.

 5.4      Generating the Offer for Loopback Session

    If an offerer wishes to make a loopback request, it MUST include
    both the loopback-type and loopback-mode attribute in a valid SDP
    offer:

    Example:   m=audio 41352 RTP/AVP 0 8 100
               a=loopback:rtp-media-loopback
               a=loopback-source:0 8 100
               a=rtpmap:0 pcmu/8000
               a=rtpmap:8 pcma/8000
               a=rtpmap:100 G7221/16000/1

    Note: A loopback offer in a given media description MUST NOT
    contain the standard mode attributes sendonly, recvonly, sendrecv
    or inactive. The loopback-mode attributes (loopback-source and
    loopback-mirror) replace the standard attributes.

    The offerer may offer more than one loopback-type in the SDP offer.
    In this case the answer MUST include only one of the loopback types
    that are accepted by the answerer.  The answerer SHOULD give
    preference to the first loopback-type in the SDP offer.

    For loopback-source media (e.g. audio) streams, the port number and
    the address in the offer (m= line) indicate where the offerer would
    like to receive the media stream.  The payload type numbers
    indicate the value of the payload the offerer expects to receive.
    The RTP payload types indicated in the a=loopback-source line are
    the payload types for the codecs the offerer is willing to send.
    However, the answer might indicate a different payload type number
    for the same codec.  In that case, the offerer MUST send the
    payload type received in the answer.

    If loopback-type is rtp-pkt-loopback, the loopback-mirror MUST send
    and the loopback-source MUST receive the looped back packets
    encoded in one of the two payload formats (encapsulated RTP or
    payload loopback) as defined in section 7.

    Example:   m=audio 41352 RTP/AVP 112
               a=loopback:rtp-pkt-loopback
               a=loopback-source:0 8
               a=rtpmap:112 encaprtp/8000

    Example:   m=audio 41352 RTP/AVP 112
               a=loopback:rtp-pkt-loopback
               a=loopback-source:0 8
               a=rtpmap:112 rtploopback/8000

 5.4

 5.5      Generating the Answer for Loopback Session

    If an answerer wishes to accept the loopback request it MUST
    include both the loopback mode and loopback type attribute in the
    answer. When a stream is offered with the loopback-source
    attribute, the corresponding stream in the response MUST be
    loopback-mirror and vice versa, provided that answerer is capable
    of supporting the requested loopback-type.

    For example, if the offer contains the loopback-source attribute:

       m=audio 41352 RTP/AVP 0 8
       a=loopback:rtp-media-loopback
       a=loopback-source:0 8

    The answer that is capable of supporting the offer MUST contain the
    loopback-mirror attribute:

       m=audio 41352 RTP/AVP 0 8
       a=loopback:rtp-media-loopback
       a=loopback-mirror:0 8

    As previously stated if a stream is offered with multiple loopback
    type attributes, the corresponding stream MUST contain only one
    loopback type attribute selected by the answerer.

    For example, if the offer contains:

       m=audio 41352 RTP/AVP 0 8 112
       a=loopback:rtp-media-loopback rtp-pkt-loopback
       a=loopback-source:0 8
       a=rtpmap:112 encaprtp/8000

    The answer that is capable of supporting the offer and chooses to
    loopback the media using the rtp-media-loopback type MUST contain:

       m=audio 41352 RTP/AVP 0 8
       a=loopback:rtp-media-loopback
       a=loopback-mirror:0 8

    As specified in section 7, if the loopback-type is
    rtp-pkt-loopback, either the encapsulated RTP payload format or
    direct loopback RTP payload format MUST be used for looped back
    packets.

    For example, if the offer contains:

       m=audio 41352 RTP/AVP 112 113
       a=loopback:rtp-pkt-loopback
       a=loopback-source:0 8
       a=rtpmap:112 encaprtp/8000
       a=rtpmap:113 rtploopback/8000

    The answer that is capable of supporting the offer MUST contain one
    of the following:

       m=audio 41352 RTP/AVP 112
       a=loopback:rtp-pkt-loopback
       a=loopback-mirror:0 8
       a=rtpmap:112 encaprtp/8000

       m=audio 41352 RTP/AVP 113
       a=loopback:rtp-pkt-loopback
       a=loopback-mirror:0 8
       a=rtpmap:113 rtploopback/8000

 5.4.1

 5.5.1 Rejecting the Loopback Offer

    An offered stream with loopback-source MAY be rejected if the
    loopback-type is not specified, the specified loopback-type is not
    supported, or the endpoint cannot honor the offer for any other
    reason.  The Loopback request may be rejected by setting the media
    port number to zero in the answer as per RFC 3264 [RFC3264].

 5.5

 5.6      Offerer Processing of the Answer

    The answer to a loopback-source MUST be loopback-mirror.  The
    answer to a loopback-mirror MUST be loopback-source.  The
    loopback-mode line MUST contain at least one codec the answerer is
    willing to send or receive depending on whether it is the loopback-
    source or the loopback-mirror. In addition, the "m=" line MUST
    contain at least one codec that the answerer is willing to send or
    receive depending on whether it is the loopback-mirror or the
    loopback-source.

    If the answer does not contain a=loopback-mirror or
    a=loopback-source, it is assumed that the loopback extensions are
    not supported by the target UA.

 5.6

 5.7      Modifying the Session

    At any point during the loopback session, either participant may
    issue a new offer to modify the characteristics of the previous
    session.  In case of SIP this is defined in section 8 of RFC 3264
    [RFC3264].  This also includes transitioning from a normal media
    processing mode to loopback mode, and vice a versa.

 5.7

 5.8      Priming the loopback pump

    In certain scenarios it is possible that the media transmitted by
    the loopback-source is blocked by a network element until the
    loopback-mirror starts transmitting packets. One example of this
    scenario is the presence of an RTP relay in the path of the media.
    RTP relays exist in VoIP networks for purpose of NAT and Firewall
    traversal.  If an RTP relay is present, the loopback-source's
    packets are dropped by the RTP relay until the loopback-mirror has
    started transmitting media and the media state within the RTP relay
    is established.  This results in a chicken and egg scenario as the
    looback-mirror cannot transmit any media until it receives the
    media packets from the loopback-source but for the loopback-mirror
    to receive any packets it needs to send one first. In order to
    resolve this dilemma, Section 8 introduces a new payload type whose
    sole purpose is to establish the media state in the intermediate
    devices. In the presence of this payload type, the loopback-mirror
    will transmit media according to the payload description until it
    receives media from the loopback-source.  The loopback-mirror MAY
    include this payload type in the answer if it is not present in the
    offer.  This may be necessary if the loopback-mirror is aware of
    NAT's, firewalls, or RTP relays on the path of the call. In this
    case the loopback-source MUST accept media corresponding to this
    payload type.  After the first media packet is received from the
    loopback-source, the loopback-mirror MUST terminate the
    transmission of media for this payload type and MUST start looping
    back media as defined by the other loopback attributes present in
    the offer.

 6.     RTP Requirements
    An answering entity that is compliant to this specification and
    accepting a media with rtp-pkt-loopback loopback-type MUST loopback
    the incoming RTP packets using either the encapsulated RTP payload
    format or the direct loopback RTP payload format as defined in
    section 7 of this specification.

    An answering entity that is compliant to this specification and
    accepting a media with the loopback type rtp-media-loopback loopback-type MUST
    transmit all received media back to the sender. The incoming media
    MUST be treated as if it were to be played (e.g. the media stream
    MAY receive treatment from PLC algorithms).  The answering entity
    MUST re-generate all the RTP header fields as it would when
    transmitting media. The answering entity MAY choose to encode the
    loopback media according to any of the media descriptions supported
    by the offering entity. Furthermore, in cases where the same media
    type is looped back, the answering entity MAY choose to preserve
    number of frames/packet and bitrate of the encoded media according
    to the received media.

 7.     Payload formats for Packet loopback

    The payload formats described in this section MUST be used by a
    loopback-mirror when rtp-pkt-loopback is the specified
    loopback-type.  Two different formats are specified here - an
    encapsulated RTP payload format and a direct loopback RTP payload
    format.  The encapsulated RTP payload format should be used when
    the incoming RTP header information needs to be preserved during
    the loopback operation.  This is useful in cases where loopback
    source needs to measure performance metrics in both directions.
    However, this comes at the expense of increased packet size as
    described in section 7.1.  The direct loopback RTP payload format
    should be used when bandwidth requirement prevent prevents the use of
    encapsulated RTP payload format.

    To keep the implementation of loopback-mirrors simple it is
    mandated that no payload format other than encapsulated or direct
    loopback formats can be used in the packets generated by a
    loopback-mirror. As described in RFC 3550 [RFC3550], sequence
    numbers and timestamps in the RTP header are generated with initial
    random values for security reasons. If this were not mandated and
    the source payload is sequence number aware, the loopback-mirror
    will be required to understand that payload format to generate
    looped back packets that do not violate RFC 3550 [RFC3550].
    Requiring looped back packets to be in one of the two formats means
    loopback-mirror does not have to look into the actual payload
    received before generating the loopback packets.

 7.1      Encapsulated Payload format

    A received RTP packet is encapsulated in the payload section of the
    RTP packet generated by a loopback-mirror.  Each received packet
    MUST be encapsulated in a different packet, the encapsulated packet
    MAY be fragmented only if required (for example: due to MTU
    limitations).

 7.1.1 Usage of RTP Header fields

    Payload Type (PT): The assignment of an RTP payload type for this
    packet format is outside the scope of this document; it is either
    specified by the RTP profile under which this payload format is
    used or more likely signaled dynamically out-of-band (e.g., using
    SDP; section 7.1.3 defines the name binding).

    Marker (M) bit: If the received RTP packet is looped back in
    multiple RTP packets, the M bit is set to 1 in the last packet,
    otherwise it is set to 0.

    Extension (X) bit: Defined by the RTP Profile used.

    Sequence Number: The RTP sequence number SHOULD be generated by the
    loopback-mirror in the usual manner with a constant random offset
    as described in RFC 3550 [RFC3550].

    Timestamp: The RTP timestamp denotes the sampling instant for when
    the loopback-mirror is transmitting this packet to the loopback-
    source.  The RTP timestamp MUST use the same clock rate used by the
    loopback-source. The initial value of the timestamp SHOULD be
    random for security reasons (see Section 5.1 of RFC 3550
    [RFC3550]).

    SSRC: set as described in RFC 3550 [RFC3550].

    CC and CSRC fields are used as described in RFC 3550 [RFC3550].

 7.1.2 RTP Payload Structure

    The RTP header in the encapsulated packet MUST be followed by the
    payload header defined in this section. If the received RTP packet
    has to be looped back in multiple packets due to fragmentation, the
    RTP header in each packet MUST be followed by the payload header
    defined in this section.  The header is devised so that the
    loopback-source can decode looped back packets in the presence of
    moderate packet loss [RFC3550].

     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         receive timestamp                     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | F | R |  CC   |M|     PT      |       sequence number         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                           transmit timestamp                  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |           synchronization source (SSRC) identifier            |
    +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
    |            contributing source (CSRC) identifiers             |
    |                             ....                              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    The 12 octets after the receive timestamp are identical to the RTP
    header in the received packet except for the first 4 bits of the
    first octet.

    Receive Timestamp: 32 bits

    The Receive timestamp denotes the sampling instant for when the
    last octet of the received media packet that is being encapsulated
    by the loopback-mirror is received from the loopback-source.  The
    Receive timestamp MUST be based on the same clock used by the
    loopback-source.  The initial value of the timestamp SHOULD be
    random for security reasons (see Section 5.1 of RFC 3550
    [RFC3550]).

    Fragmentation (F): 2 bits

    First Fragment (00) /Last Fragment (01) /No Fragmentation(10)/
    Intermediate Fragment (11).  This field identifies how much of the
    received packet is encapsulated in this packet by the loopback-
    mirror.  If the received packet is not fragmented, this field is
    set to 10; otherwise the packet that contains the first fragments
    sets this field to 00, the packet that contains the last fragment
    sets this field to 01, all other packets set this field to 11.

    Reserved: 2 bits

    This field is reserved for future definition. In the absence of
    such a definition, the bits in this field MUST be set to zero and
    MUST be ignored by the receiver.

    Any padding octets in the original packet MUST not be included in
    the loopback packet generated by a loopback-mirror. The
    loopback-mirror MAY add padding octets if required.

 7.1.3 Usage of SDP

    The payload type number for the encapsulated stream can be
    negotiated using a mechanism like SDP. There is no static payload
    type assignment for the encapsulated stream, so dynamic payload
    type numbers MUST be used.  The binding to the name is indicated by
    an rtpmap attribute.  The name used in this binding is "encaprtp".

    The following is an example SDP fragment for encapsulated RTP.

    m=audio 41352 RTP/AVP 112
    a=rtpmap:112 encaprtp/8000

 7.2      Direct loopback RTP payload format

    The direct loopback RTP payload format can be used in scenarios
    where the 16 byte overhead of the encapsulated payload format is
    significant.  This payload format MUST not be used in cases where
    the MTU on the loopback path will cause fragmentation of looped
    back RTP packets.  When using this payload format, the receiver
    MUST loop back each received packet in a separate RTP packet.

 7.2.1 Usage of RTP Header fields

    Payload Type (PT): The assignment of an RTP payload type for this
    packet format is outside the scope of this document; it is either
    specified by the RTP profile under which this payload format is
    used or more likely signaled dynamically out-of-band (e.g., using
    SDP; section 7.2.3 defines the name binding).

    Marker (M) bit: Set to the value in the received packet.

    Extension (X) bit: Defined by the RTP Profile used.

    Sequence Number: The RTP sequence number SHOULD be generated by the
    loopback-mirror in the usual manner with a constant random offset.

    Timestamp: The RTP timestamp denotes the sampling instant for when
    the loopback-mirror is transmitting this packet to the
    loopback-source.  The RTP timestamp MUST be based on the same clock
    used by the loopback-source.  The initial value of the timestamp
    SHOULD be random for security reasons (see Section 5.1 of RFC 3550
    [RFC3550]).

    SSRC: set as described in RFC 3550 [RFC3550].

    CC and CSRC fields are used as described in RFC 3550 [RFC3550].

 7.2.2 RTP Payload Structure

    This payload format does not define any payload specific headers.
    The loopback-mirror simply copies the payload data from the payload
    portion of the packet received from the loopback-source.

 7.2.3 Usage of SDP

    The payload type number for the payload loopback stream can be
    negotiated using a mechanism like SDP. There is no static payload
    type assignment for the stream, so dynamic payload type numbers
    MUST be used. The binding to the name is indicated by an rtpmap
    attribute.  The name used in this binding is "rtploopback".

    The following is an example SDP fragment for direct loopback RTP
    format.

    m=audio 41352 RTP/AVP 112
    a=rtpmap:112 rtploopback/8000

 8.     Payload format for Priming the Loopback Pump

    The sole purpose of the payload format described in this section is
    to prime the loopback pump in cases where the loopback process
    cannot start because of intermediate devices in the network as
    described in Section 5.7.

 8.1      Usage of RTP Header fields

    Payload Type (PT): The assignment of an RTP payload type for this
    packet format is outside the scope of this document; it is either
    specified by the RTP profile under which this payload format is
    used or more likely signaled dynamically out-of-band (e.g., using
    SDP; section 8.2 defines the name binding).

    All other fields are set as described in RFC 3550 [RFC3550].

 8.2      Usage of SDP

    The payload type number for the loopback primer stream can be
    negotiated using a mechanism like SDP. There is no static payload
    type assignment for the loopback primer stream, so dynamic payload
    type numbers MUST be used.  The binding to the name is indicated by
    an rtpmap attribute.  The name used in this binding is
    "loopbkprimer".

    The following is an example SDP fragment for loopback primer RTP
    stream.

    m=audio 41352 RTP/AVP 112
    a=rtpmap:112 loopbkprimer/8000

 9.     RTCP Requirements

    The use of the loopback attribute is intended for monitoring of
    media quality of the session.  Consequently the media performance
    information should be exchanged between the offering and the
    answering entities.  An offering or answering entity that is
    compliant to this specification SHOULD support RTCP per [RFC3550]
    and RTCP-XR per RFC 3611 [RFC3611].  Furthermore, if the client or
    the server choose to support RTCP-XR,  they SHOULD support RTCP-XR
    Loss RLE report block, Duplicate RLE report block, Statistics
    Summary report block, and VoIP Metric Reports Block per sections
    4.1, 4.2, 4.6, and 4.7 of RFC 3611 [RFC3611].  The client and the
    server MAY support other RTCP-XR reporting blocks as defined by RFC
    3611 [RFC3611].

 10.      Congestion Control

    All the participants in a loopback session SHOULD implement
    congestion control mechanisms as defined by the RTP profile under
    which the loopback mechanism is implemented. For audio video
    profiles, implementations SHOULD conform to the mechanism defined
    in Section 2 of RFC 3551.

 11.      Examples

    This section provides examples for media descriptions using SDP for
    different scenarios.  The examples are given for SIP-based
    transactions and are abbreviated and do not show the complete
    signaling for convenience.

 11.1       Offer for specific media loopback type

    A client sends an INVITE request with SDP which looks like:

    v=0
    o=user1
    o=alice 2890844526 2890842807 IN IP4 192.0.2.11 host.atlanta.example.com
    s=Example
    i=An example session
    e=user@example.com
    e=alice@example.com
    c=IN IP4 192.0.2.12/127 host.atlanta.example.com
    t=0 0
    m=audio 49170 RTP/AVP 0
    a=loopback:rtp-media-loopback
    a=loopback-source:0
    a=rtpmap:0 pcmu/8000

    The client is offering to source the media and expects the server
    to mirror the RTP stream per rtp-media-loopback loopback type.

    A server sends a response with SDP which looks like:

    v=0
    o=user1
    o=bob 2890844526 2890842807 IN IP4 192.0.2.11 host.biloxi.example.com
    s=Example
    i=An example session
    e=user@example.com
    e=bob@example.com
    c=IN IP4 192.0.2.12/127 host.biloxi.example.com
    t=0 0
    m=audio 49270 RTP/AVP 0
    a=loopback:rtp-media-loopback
    a=loopback-mirror:0
    a=rtpmap:0 pcmu/8000

    The server is accepting to mirror the media from the client at the
    media level.

 11.2       Offer for choice of media loopback type
    A client sends an INVITE request with SDP which looks like:

    v=0
    o=user1
    o=alice 2890844526 2890842807 IN IP4 192.0.2.11 host.atlanta.example.com
    s=Example
    i=An example session
    e=user@example.com
    e=alice@example.com
    c=IN IP4 192.0.2.12/127 host.atlanta.example.com
    t=0 0
    m=audio 49170 RTP/AVP 0 112 113
    a=loopback:rtp-media-loopback rtp-pkt-loopback
    a=loopback-source:0
    a=rtpmap:0 pcum/8000
    a=rtpmap:112 encaprtp/8000
    a=rtpmap:113 rtploopback/8000

    The client is offering to source the media and expects the server
    to mirror the RTP stream at either the media or rtp level.

    A server sends a response with SDP which looks like:

    v=0
    o=user1
    o=box 2890844526 2890842807 IN IP4 192.0.2.11 host.biloxi.example.com
    s=Example
    i=An example session
    e=user@example.com
    e=bob@example.com
    c=IN IP4 192.0.2.12/127 host.biloxi.example.com
    t=0 0
    m=audio 49270 RTP/AVP 112
    a=loopback:rtp-pkt-loopback
    a=loopback-mirror:0
    a=rtpmap:0 pcmu/8000
    a=rtpmap:112 encaprtp/8000

    The server is accepting to mirror the media from the client at the
    packet level using the encapsulated RTP payload format.

 11.3       Offer for choice of media loopback type with loopback primer

    A client sends an INVITE request with SDP which looks like:

    v=0
    o=user1
    o=alice 2890844526 2890842807 IN IP4 192.0.2.11 host.atlanta.example.com
    s=Example
    i=An example session
    e=user@example.com
    e=alice@example.com
    c=IN IP4 192.0.2.12/127 host.atlanta.example.com
    t=0 0
    m=audio 49170 RTP/AVP 0 112 113 114
    a=loopback:rtp-media-loopback rtp-pkt-loopback
    a=loopback-source:0
    a=rtpmap:0 pcmu/8000
    a=rtpmap:112 encaprtp/8000
    a=rtpmap:113 rtploopback/8000
    a=rtpmap:114 loopbkprimer/8000

    The client is offering to source the media and expects the server
    to mirror the RTP stream at either the media or rtp level.  The
    client also expects the server to source media until it receives
    packets from the server per media described with the loopbkprimer
    payload type.

    A server sends a response with SDP which looks like:

    v=0
    o=user1
    o=bob 2890844526 2890842807 IN IP4 192.0.2.11 host.biloxi.example.com
    s=Example
    i=An example session
    e=user@example.com
    c=IN IP4 192.0.2.12/127 host.biloxi.example.com
    t=0 0
    m=audio 49270 RTP/AVP 113
    a=loopback:rtp-pkt-loopback
    a=loopback-mirror:0 114
    a=rtpmap:0 pcmu/8000
    a=rtpmap:113 rtploopback/8000
    a=rtmpa:114 loopbkprimer/8000

    The server is accepting to mirror the media from the client at the
    packet level using the direct loopback RTP payload format.  The
    server is also accepting to source media until it receives media
    packets from the client.

 11.4       Response to INVITE request rejecting loopback media

    A client sends an INVITE request with SDP which looks like:

    v=0
    o=user1
    o=alice 2890844526 2890842807 IN IP4 192.0.2.11 host.atlanta.example.com
    s=Example
    i=An example session
    e=user@example.com
    c=IN IP4 192.0.2.12/127 host.atlanta.example.com
    t=0 0
    m=audio 49170 RTP/AVP 0
    a=loopback:rtp-media-loopback
    a=loopback-source:0
    a=rtpmap:0 pcmu/8000

    The client is offering to source the media and expects the server
    to mirror the RTP stream at the media level.

    A server sends a response with SDP which looks like:

    v=0
    o=user1
    o=bob 2890844526 2890842807 IN IP4 192.0.2.11 host.biloxi.example.com
    s=Example
    i=An example session
    e=user@example.com
    c=IN IP4 192.0.2.12/127 host.biloxi.example.com
    t=0 0
    m=audio 0 RTP/AVP 0
    a=loopback:rtp-media-loopback
    a=loopback-mirror:0
    a=rtpmap:0 pcmu/8000

    NOTE: Loopback request may be rejected by either not including the
    loopback mode attribute (for backward compatibility) or setting the
    media port number to zero, or both, in the response.

 11.5       Response to INVITE request rejecting loopback media with loopback
     primer payload type

    A client sends an INVITE request with SDP which looks like:

    v=0
    o=user1
    o=alice 2890844526 2890842807 IN IP4 192.0.2.11 host.atlanta.example.com
    s=Example
    i=An example session
    e=user@example.com
    e=alice@example.com
    c=IN IP4 192.0.2.12/127 host.atlanta.example.com
    t=0 0
    m=audio 49170 RTP/AVP 0 100
    a=loopback:rtp-media-loopback
    a=loopback-source:0
    a=rtpmap:0 pcum/8000
    a=rtpmap:100 loopbkprimer/8000
    The client is offering to source the media and expects the server
    to mirror the RTP stream at the media level.  The client also
    expects the server to source media until it receives packets from
    the server using the loopbkprimer payload type.

    A server sends a response with SDP which looks like:

    v=0
    o=user1
    o=bob 2890844526 2890842807 IN IP4 192.0.2.11 host.biloxi.example.com
    s=Example
    i=An example session
    e=user@example.com
    e=bob@example.com
    c=IN IP4 192.0.2.12/127 host.biloxi.example.com
    t=0 0
    m=audio 0 RTP/AVP 0
    a=loopback:rtp-media-loopback
    a=loopback-mirror:0

    NOTE: Loopback request may be rejected by either not including the
    loopback mode attribute (for backward compatibility) or setting the
    media port number to zero, or both, in the response.

 12.      Security Considerations

    The security considerations of [RFC3261] apply. Furthermore, given
    that media loopback may be automated without the end user's
    knowledge, the server of the media loopback should be aware of
    denial of service attacks. It is recommended that sessions with
    media loopback are authenticated and the frequency of such sessions
    is limited by the server.

 13.      Implementation Considerations

    The media loopback approach described in this document is a
    complete solution that would work under all scenarios. However, it
    is believed that the solution may not be light-weight enough for
    the common case. In light of this concern, this section clarifies
    which features of the loopback proposal MUST be implemented for all
    implementations and which features MAY be deferred if the complete
    solution is not desired.

    All implementations MUST support the rtp-pkt-loopback option for
    loopback-type attribute. In addition, for the loopback-mode
    attribute, all implementations of an offerer MUST at a minimum be
    able to act as a loopback-source. All implementation MUST also at a
    minimum support the direct media loopback payload type. The rtp-
    media-loopback attribute MAY be implemented in complete
    implementations of this draft.

 14.      IANA Considerations

 14.1       SDP Attributes

    This document defines three new media-level SDP attributes.  IANA
    has registered the following attributes:

       Contact name:             Kaynam Hedayat
    <kaynam.hedayat@exfo.com>.
       Attribute name:           "loopback".
       Type of attribute:        Media level.
       Subject to charset:       No.
       Purpose of attribute:     The 'loopback' attribute is used to
                                 indicate the type of media loopback.
       Allowed attribute values: The parameters to 'loopback' may be
                                 one or more of "rtp-pkt-loopback" and
                                 "rtp-media-loopback". See section 5
                                 of this document for syntax.

       Contact name:             Kaynam Hedayat
    <kaynam.hedayat@exfo.com>.
       Attribute name:           "loopback-source".
       Type of attribute:        Media level.
       Subject to charset:       No.
       Purpose of attribute:     The 'loopback-source' attribute
                                 specifies that the sender is the media
                                 source and expects the receiver to act
                                 as a loopback-mirror.
       Allowed attribute values: The parameter to 'loopback-source' is
                                 a media format ("<fmt>") description
                                 as defined in RFC 4566 Section 5.14.

       Contact name:             Kaynam Hedayat
    <kaynam.hedayat@exfo.com>.
       Attribute name:           "loopback-mirror".
       Type of attribute:        Media level.
       Subject to charset:       No.
       Purpose of attribute:     The 'loopback-mirror' attribute
                                 specifies that the receiver will
                                 mirror (echo) all received media back
                                 to the sender of the RTP stream.

       Allowed attribute values: The parameter to 'loopback-mirror' is
                                 a media format ("<fmt>") description
                                 as defined in RFC 4566 Section 5.14.

 14.2       MIME Types

    The IANA has registered the following MIME types:

 14.2.1    audio/encaprtp

           To: ietf-types@iana.org

           Subject: Registration of media type audio/encaprtp

           Type name: audio

           Subtype name: encaprtp

           Required parameters:

                rate:RTP timestamp clock rate, which is equal to the
                sampling rate. The typical rate is 8000; other rates
                may be specified.

           Optional parameters: none

           Encoding considerations: This media type is framed
                binary data.

           Security considerations: See Section 12 of this document.

           Interoperability considerations: none

           Published specification: This MIME type is described fully
                within this document.

           Applications which use this media type: Applications wishing
                to monitor and ensure the quality of transport to the
                edge of a given VoIP, Real-Time Text or Video Over IP
                Service.

           Additional information: none

           Person & email address to contact for further information:

                Kaynam Hedayat
                EMail: kaynam.hedayat@exfo.com

           Intended usage: COMMON

           Restrictions on usage: This media type depends on RTP
                framing, and hence is only defined for transfer via
                RTP. Transfer within other framing protocols is not
                defined at this time.

           Author:
                Kaynam Hedayat.

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

 14.2.2    video/encaprtp

           To: ietf-types@iana.org

           Subject: Registration of media type video/encaprtp

           Type name: video

           Subtype name: encaprtp

           Required parameters:

                rate:RTP timestamp clock rate, which is equal to the
                sampling rate. The typical rate is 8000; other rates
                may be specified.

           Optional parameters: none

           Encoding considerations: This media type is framed
                binary data.

           Security considerations: See Section 12 of this document.

           Interoperability considerations: none

           Published specification: This MIME type is described fully
                within this document.

           Applications which use this media type: Applications wishing
                to monitor and ensure the quality of transport to the
                edge of a given VoIP, Real-Time Text or Video Over IP
                Service.

           Additional information: none

           Person & email address to contact for further information:

                Kaynam Hedayat
                EMail: kaynam.hedayat@exfo.com

           Intended usage: COMMON

           Restrictions on usage: This media type depends on RTP
                framing, and hence is only defined for transfer via
                RTP. Transfer within other framing protocols is not
                defined at this time.

           Author:
                Kaynam Hedayat.

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

 14.2.3    text/encaprtp

           To: ietf-types@iana.org

           Subject: Registration of media type text/encaprtp

           Type name: text

           Subtype name: encaprtp

           Required parameters:

                rate:RTP timestamp clock rate, which is equal to the
                sampling rate. The typical rate is 8000; other rates
                may be specified.

           Optional parameters: none

           Encoding considerations: This media type is framed
                binary data.

           Security considerations: See Section 12 of this document.

           Interoperability considerations: none

           Published specification: This MIME type is described fully
                within this document.

           Applications which use this media type: Applications wishing
                to monitor and ensure the quality of transport to the
                edge of a given VoIP, Real-Time Text or Video Over IP
                Service.

           Additional information: none

           Person & email address to contact for further information:

                Kaynam Hedayat
                EMail: kaynam.hedayat@exfo.com

           Intended usage: COMMON

           Restrictions on usage: This media type depends on RTP
                framing, and hence is only defined for transfer via
                RTP. Transfer within other framing protocols is not
                defined at this time.

           Author:
                Kaynam Hedayat.

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

 14.2.4    application/encaprtp

           To: ietf-types@iana.org

           Subject: Registration of media type
                application/encaprtp

           Type name: application

           Subtype name: encaprtp

           Required parameters:

                rate:RTP timestamp clock rate, which is equal to the
                sampling rate. The typical rate is 8000; other rates
                may be specified.

           Optional parameters: none

           Encoding considerations: This media type is framed
                binary data.

           Security considerations: See Section 12 of this document.

           Interoperability considerations: none

           Published specification: This MIME type is described fully
                within this document.

           Applications which use this media type: Applications wishing
                to monitor and ensure the quality of transport to the
                edge of a given VoIP, Real-Time Text or Video Over IP
                Service.

           Additional information: none

           Person & email address to contact for further information:

                Kaynam Hedayat
                EMail: kaynam.hedayat@exfo.com

           Intended usage: COMMON

           Restrictions on usage: This media type depends on RTP
                framing, and hence is only defined for transfer via
                RTP. Transfer within other framing protocols is not
                defined at this time.

           Author:
                Kaynam Hedayat.

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

 14.2.5    audio/rtploopback

           To: ietf-types@iana.org

           Subject: Registration of media type audio/rtploopback

           Type name: audio

           Subtype name: rtploopback

           Required parameters:

                rate:RTP timestamp clock rate, which is equal to the
                sampling rate. The typical rate is 8000; other rates
                may be specified.

           Optional parameters: none
           Encoding considerations: This media type is framed
                binary data.

           Security considerations: See Section 12 of this document.

           Interoperability considerations: none

           Published specification: This MIME type is described fully
                within this document.

           Applications which use this media type: Applications wishing
                to monitor and ensure the quality of transport to the
                edge of a given VoIP, Real-Time Text or Video Over IP
                Service.

           Additional information: none

           Person & email address to contact for further information:

                Kaynam Hedayat
                EMail: kaynam.hedayat@exfo.com

           Intended usage: COMMON

           Restrictions on usage: This media type depends on RTP
                framing, and hence is only defined for transfer via
                RTP. Transfer within other framing protocols is not
                defined at this time.

           Author:
                Kaynam Hedayat.

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

 14.2.6    video/rtploopback

           To: ietf-types@iana.org

           Subject: Registration of media type video/rtploopback

           Type name: video

           Subtype name: rtploopback

           Required parameters:

                rate:RTP timestamp clock rate, which is equal to the
                sampling rate. The typical rate is 8000; other rates
                may be specified.

           Optional parameters: none

           Encoding considerations: This media type is framed
                binary data.

           Security considerations: See Section 12 of this document.

           Interoperability considerations: none

           Published specification: This MIME type is described fully
                within this document.

           Applications which use this media type: Applications wishing
                to monitor and ensure the quality of transport to the
                edge of a given VoIP, Real-Time Text or Video Over IP
                Service.

           Additional information: none

           Person & email address to contact for further information:

                Kaynam Hedayat
                EMail: kaynam.hedayat@exfo.com

           Intended usage: COMMON

           Restrictions on usage: This media type depends on RTP
                framing, and hence is only defined for transfer via
                RTP. Transfer within other framing protocols is not
                defined at this time.

           Author:
                Kaynam Hedayat.

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

 14.2.7    text/rtploopback

           To: ietf-types@iana.org

           Subject: Registration of media type text/rtploopback

           Type name: text
           Subtype name: rtploopback

           Required parameters:

                rate:RTP timestamp clock rate, which is equal to the
                sampling rate. The typical rate is 8000; other rates
                may be specified.

           Optional parameters: none

           Encoding considerations: This media type is framed
                binary data.

           Security considerations: See Section 12 of this document.

           Interoperability considerations: none

           Published specification: This MIME type is described fully
                within this document.

           Applications which use this media type: Applications wishing
                to monitor and ensure the quality of transport to the
                edge of a given VoIP, Real-Time Text or Video Over IP
                Service.

           Additional information: none

           Person & email address to contact for further information:

                Kaynam Hedayat
                EMail: kaynam.hedayat@exfo.com

           Intended usage: COMMON

           Restrictions on usage: This media type depends on RTP
                framing, and hence is only defined for transfer via
                RTP. Transfer within other framing protocols is not
                defined at this time.

           Author:
                Kaynam Hedayat.

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

 14.2.8    application/rtploopback
           To: ietf-types@iana.org

           Subject: Registration of media type
                application/rtploopback

           Type name: application

           Subtype name: rtploopback

           Required parameters:

                rate:RTP timestamp clock rate, which is equal to the
                sampling rate. The typical rate is 8000; other rates
                may be specified.

           Optional parameters: none

           Encoding considerations: This media type is framed
                binary data.

           Security considerations: See Section 12 of this document.

           Interoperability considerations: none

           Published specification: This MIME type is described fully
                within this document.

           Applications which use this media type: Applications wishing
                to monitor and ensure the quality of transport to the
                edge of a given VoIP, Real-Time Text or Video Over IP
                Service.

           Additional information: none

           Person & email address to contact for further information:

                Kaynam Hedayat
                EMail: kaynam.hedayat@exfo.com

           Intended usage: COMMON

           Restrictions on usage: This media type depends on RTP
                framing, and hence is only defined for transfer via
                RTP. Transfer within other framing protocols is not
                defined at this time.

           Author:
                Kaynam Hedayat.

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

 14.2.9    audio/loopbkprimer

           To: ietf-types@iana.org

           Subject: Registration of media type audio/loopbkprimer

           Type name: audio

           Subtype name: loopbkprimer

           Required parameters:

                rate:RTP timestamp clock rate, which is equal to the
                sampling rate. The typical rate is 8000; other rates
                may be specified.

           Optional parameters: none

           Encoding considerations: This media type is framed
                binary data.

           Security considerations: See Section 12 of this document.

           Interoperability considerations: none

           Published specification: This MIME type is described fully
                within this document.

           Applications which use this media type: Applications wishing
                to monitor and ensure the quality of transport to the
                edge of a given VoIP, Real-Time Text or Video Over IP
                Service.

           Additional information: none

           Person & email address to contact for further information:

                Kaynam Hedayat
                EMail: kaynam.hedayat@exfo.com

           Intended usage: COMMON

           Restrictions on usage: This media type depends on RTP
                framing, and hence is only defined for transfer via
                RTP. Transfer within other framing protocols is not
                defined at this time.

           Author:
                Kaynam Hedayat.

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

 14.2.10   video/loopbkprimer

           To: ietf-types@iana.org

           Subject: Registration of media type video/loopbkprimer

           Type name: video

           Subtype name: loopbkprimer

           Required parameters:

                rate:RTP timestamp clock rate, which is equal to the
                sampling rate. The typical rate is 8000; other rates
                may be specified.

           Optional parameters: none

           Encoding considerations: This media type is framed
                binary data.

           Security considerations: See Section 12 of this document.

           Interoperability considerations: none

           Published specification: This MIME type is described fully
                within this document.

           Applications which use this media type: Applications wishing
                to monitor and ensure the quality of transport to the
                edge of a given VoIP, Real-Time Text or Video Over IP
                Service.

           Additional information: none

           Person & email address to contact for further information:

                Kaynam Hedayat
                EMail: kaynam.hedayat@exfo.com

           Intended usage: COMMON

           Restrictions on usage: This media type depends on RTP
                framing, and hence is only defined for transfer via
                RTP. Transfer within other framing protocols is not
                defined at this time.

           Author:
                Kaynam Hedayat.

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

 14.2.11   text/loopbkprimer

           To: ietf-types@iana.org

           Subject: Registration of media type text/loopbkprimer

           Type name: text

           Subtype name: encaprtp

           Required parameters:

                rate:RTP timestamp clock rate, which is equal to the
                sampling rate. The typical rate is 8000; other rates
                may be specified.

           Optional parameters: none

           Encoding considerations: This media type is framed
                binary data.

           Security considerations: See Section 12 of this document.

           Interoperability considerations: none

           Published specification: This MIME type is described fully
                within this document.

           Applications which use this media type: Applications wishing
                to monitor and ensure the quality of transport to the
                edge of a given VoIP, Real-Time Text or Video Over IP
                Service.

           Additional information: none
           Person & email address to contact for further information:

                Kaynam Hedayat
                EMail: kaynam.hedayat@exfo.com

           Intended usage: COMMON

           Restrictions on usage: This media type depends on RTP
                framing, and hence is only defined for transfer via
                RTP. Transfer within other framing protocols is not
                defined at this time.

           Author:
                Kaynam Hedayat.

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

 14.2.12   application/loopbkprimer

           To: ietf-types@iana.org

           Subject: Registration of media type
                application/loopbkprimer

           Type name: application

           Subtype name: loopbkprimer

           Required parameters:

                rate:RTP timestamp clock rate, which is equal to the
                sampling rate. The typical rate is 8000; other rates
                may be specified.

           Optional parameters: none

           Encoding considerations: This media type is framed
                binary data.

           Security considerations: See Section 12 of this document.

           Interoperability considerations: none

           Published specification: This MIME type is described fully
                within this document.

           Applications which use this media type: Applications wishing
                to monitor and ensure the quality of transport to the
                edge of a given VoIP, Real-Time Text or Video Over IP
                Service.

           Additional information: none

           Person & email address to contact for further information:

                Kaynam Hedayat
                EMail: kaynam.hedayat@exfo.com

           Intended usage: COMMON

           Restrictions on usage: This media type depends on RTP
                framing, and hence is only defined for transfer via
                RTP. Transfer within other framing protocols is not
                defined at this time.

           Author:
                Kaynam Hedayat.

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

 15.      Acknowledgements

    The authors wish to thank Nagarjuna Venna, Muthu ArulMozhi Perumal,
    Flemming Andreasen, Jeff Bernstein, Paul Kyzivat, and Dave Oran for
    their comments and suggestions.

 16.      Normative References

       [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G.,
                  Johnston, A., Peterson, J., Sparks, R., Handley, M.
                  and E. Schooler, "SIP: Session Initiation Protocol",
                  RFC 3261, June 2002.

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

       [RFC3550] Schulzrinne, H., Casner, S., Frederick, R. and V.
                  Jacobson, "RTP: A Transport Protocol for Real-Time
                  Applications", STD 64, RFC 3550, July 2003.

       [RFC3611] Almeroth, K., Caceres, R., Clark, A., Cole, R.,
                  Duffield, N., Friedman, T., Hedayat, K., Sarac, K.
                  and M. Westerlund, "RTP Control Protocol Extended
                  Reports (RTCP XR)", RFC 3611, November 2003.

       [RFC5234] Crocker, P. Overell, "Augmented ABNF for Syntax
                  Specification: ABNF", RFC 5234, October 2005.

       [RFC2119] Bradner, S.,"Key words for use in RFCs to Indicate
                  Requirement Levels", BCP 14, RFC 2119, March 1997.

       [RFC2736] Handley, M., Perkins, C., "Guidelines for Writers of
                  RTP Payload Format Specifications", RFC 2736, BCP
                  0036, December 1999.

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

       [RFC4566] Handley, M., Jacobson, V., Perkins, C., "SDP: Session
                  Description Protocol", RFC 4566, July 2006.

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

 Authors' Addresses

       Kaynam Hedayat
       EXFO
       285 Mill Road
       Chelmsford, MA  01824
       US

       Phone: +1 978 367 5611
       EMail: kaynam.hedayat@exfo.com
       URI:   http://www.exfo.com/
       Nagarjuna Venna
       EXFO
       285 Mill Road
       Chelmsford, MA  01824
       US

       Phone: +1 978 367 5703
       EMail: nagarjuna.venna@exfo.com
       URI:   http://www.exfo.com/

       Paul E. Jones
       Cisco Systems, Inc.
       7025 Kit Creek Rd.
       Research Triangle Park, NC  27709
       US

       Phone: +1 919 392 6948
       EMail: paulej@packetizer.com
       URI:   http://www.cisco.com/

       Arjun Roychowdhury
       Hughes Systique Corp.
       15245 Shady Grove Rd, Ste 330
       Rockville MD 20850
       US

       Phone: +1 301 527 1629
       EMail: arjun@hsc.com
       URI:   http://www. hsc.com/

       Chelliah SivaChelvan
       Cisco Systems, Inc.
       2200 East President George Bush Turnpike
       Richardson, TX  75082
       US

       Phone: +1 972 813 5224
       EMail: chelliah@cisco.com
       URI:   http://www.cisco.com/

       Nathan Stratton
       BlinkMind, Inc.
       2027 Briarchester Dr.
       Katy, TX 77450
       Phone: +1 832 330 3810
       EMail: nathan@robotics.net
       URI:   http://www.robotics.net/