Internet Draft                                        H. Kaplan (ed.)
  Expires: August 12, 2012                                  Acme Packet
                                                             K. Hedayat
                                                                   EXFO
                                                               N. Venna
                                                                Saperix
                                                               P. Jones
                                                    Cisco Systems, Inc.
                                                        A. Roychowdhury
                                                  Hughes Systique Corp.
                                                         C. SivaChelvan
                                                    Cisco Systems, Inc.
                                                            N. Stratton
                                                        BlinkMind, Inc.
                                                         March 10, 26, 2012

         An Extension to the Session Description Protocol (SDP)
        and Real-time Transport Protocol (RTP) for Media Loopback
                   draft-ietf-mmusic-media-loopback-17
                   draft-ietf-mmusic-media-loopback-18

 Status of this Memo

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    This Internet-Draft will expire on August 12, 2012.

 Copyright Notice

    Copyright (c) 2012 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), Text and Video over IP
    services has introduced new challenges in managing and maintaining
    real-time voice/real-time Text/video voice/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
    administrators 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 attributes, which enables
    enable 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
       1.1 Use Cases Supported.......................................4
    2. Terminology...................................................5 Terminology...................................................6
    3. Offering Entity Overview of Operation.........................................6
       3.1 SDP Offerer Behavior......................................6
    4. Answering Entity
       3.2 SDP Answerer Behavior.....................................6
    5.
    4. New SDP Constructs Syntax..............Error! Bookmark not defined.
       5.1 Attributes............................................7
       4.1 Loopback Type Attribute...................................7
       5.2
       4.2 Loopback Mode Attribute...................................7
       5.3 Role Attributes: loopback-source and loopback-
       mirror........................................................8
    5. Rules for Generating the SDP offer/answer.....................9
       5.1 Generating the SDP Offer for Loopback Session.................8
       5.4 Session.............9
       5.2 Generating the SDP Answer for Loopback Session................9
       5.5 Session...........10
       5.3 Offerer Processing of the Answer.........................11
       5.6 SDP Answer.....................11
       5.4 Modifying the Session....................................11
       5.7 Session....................................12
       5.5 Establishing Sessions Between Entities Behind NAT........12
    6. RTP Requirements.............................................12
    7. Payload formats for Packet loopback..........................12 loopback..........................13
       7.1 Encapsulated Payload format..............................13
       7.2 Direct loopback RTP payload format.......................15 format.......................16
    8. RTCP Requirements............................................16 Requirements............................................17
    9. Congestion Control...........................................17
    10. Examples....................................................17 Examples....................................................18
       10.1 Offer for specific media loopback type..................17 type..................18
       10.2 Offer for choice of media loopback type.................18
       10.3 Response to INVITE request Answerer rejecting loopback media.....19 media.......................19
    11. Security Considerations.....................................19 Considerations.....................................20
    12. Implementation Considerations...............................20 Considerations...............................21
    13. IANA Considerations.........................................20 Considerations.........................................21
       13.1 SDP Attributes..........................................20 Attributes..........................................21
       13.2 MIME Types..............................................21 Types..............................................22
    14. Acknowledgements............................................31
    15. Normative References........................................30 References........................................31
    16. Informative References......................................32

 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 real-time VoIP, 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, 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 document introduces new SDP media
    attributes that enable establishment of media sessions where the
    media is looped back to the transmitter.  The SDP 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.

 1.1 Use Cases Supported

    As a matter of terminology in this document, packets flow from one
    peer acting as a "loopback source", to the other peer acting as a
    "loopback mirror", which in turn returns packets to the loopback
    source. In advance of the session, the peers negotiate to determine
    which one acts in which role. role, using the SDP offer/answer exchange.
    The negotiation also includes details such as the type of loopback
    to be used.

    This specification supports three use cases: "encapsulated packet
    loopback", "direct loopback", and "media loopback". These are
    distinguished by the treatment of incoming RTP packets at the
    loopback mirror.

 1.1.1 Encapsulated Packet Loopback

    In the encapsulated packet loopback case, the entire incoming RTP
    packet is encapsulated as payload within an outer payload type RTP packet that
    is specific to this use case and specified below (Section 7.1). in Section 7.1.  The
    encapsulated packet is returned to the loopback source.  The
    loopback source can generate statistics for one-way path
    performance up to the RTP level for each direction of travel by
    examining sequence numbers and timestamps in the encapsulating
    outer RTP header and the encapsulated RTP packet payload. The
    loopback source can also play back the returned media content for
    evaluation.

    Because the encapsulating payload RTP packet header extends the packet
    size, it could encounter difficulties in an environment where the
    original RTP packet size is close to the path MTU size.  The
    encapsulating payload type format therefore offers the possibility of
    RTP-level fragmentation of the returned packets.  The use of this
    facility could affect statistics derived for the return path.  In
    addition, the increased bit rate required in the return direction
    may affect these statistics more directly in a restricted-bandwidth
    situation.

 1.1.2 Direct Loopback

    In the direct loopback case, the loopback mirror copies the payload
    of the incoming RTP packet into a new RTP packet, the using a payload type of
    which is again
    format specific to this use case and specified below
    (Section 7.2). in Section 7.2.  The
    loopback mirror returns the new packet to the packet source.  There
    is no provision in this case for RTP-level fragmentation.

    This use case has the advantage of keeping the packet size the same
    in both directions.  The packet source can compute only two-way
    path statistics from the direct loopback packet header, but can
    play back the returned media content.

    It has been suggested that the loopback source, knowing that the
    incoming packet will never be passed to a decoder, can store a
    timestamp and sequence number inside the payload of the packet it
    sends to the mirror, then extract that information from the
    returned direct loopback packet and compute one-way path statistics
    as in the previous case. Obviously, playout of returned content is
    no longer possible if this is done.

 1.1.3 Media Loopback

    In the media loopback case, the loopback mirror submits the
    incoming packet to a decoder appropriate to the incoming payload
    type. The packet is taken as close as possible to the analog level,
    then reencoded re-encoded according to an outgoing format determined by SDP
    negotiation. The reencoded content is returned to the loopback
    source as an RTP packet with payload type corresponding to the
    reencoding format.

    This usage allows trouble-shooting at the codec level. The
    capability for path statistics is limited to what is available from
    RTCP reports.

 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.

    SDP: Session Description Protocol, as defined in [RFC4566].  This
    document assumes the SDP offer/answer model is followed, per
    [RFC3264], but does not assume any specific signaling protocol for
    carrying the SDP.

    The following terms are borrowed from [RFC3264] definitions: offer,
    offerer, answer, answerer, and agent.

 3. Overview of Operation

    This document defines two loopback 'types', two 'roles', and two
    encoding formats for loopback.  For any given SDP offerer or
    answerer pair, one side is the source of RTP packets, while the
    other is the mirror looping packets/media back.  Those define the
    two loopback roles.  As the mirror, two 'types' of loopback can be
    performed: packet-level or media-level.  When media-level is used,
    there is no further choice of encoding format - there is only one
    format: whatever is indicated for normal media, since the "looping"
    is performed at the codec level.  When packet-level looping is
    performed, however, the mirror can either send back RTP in an
    encapsulated format or direct-loopback format.  The rest of this
    document describes these loopback types, roles, and encoding
    formats, and the SDP offer/answer rules for indicating them.

 3.1 SDP Offerer Behavior

    An SDP offerer 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 offerer MUST look for the "loopback" media attributes
    in the media description(s) of the response from the answer for
    confirmation that the request is accepted.

 4.

 3.2 SDP Answerer Behavior

    An SDP answerer 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
    asnwer if it agrees to do the loopback. If the answerer does not
    want to do loopback or wants to reject the "loopback" request for
    specific media types, it MAY do so as defined in section Error!
    Reference source not found. of this specification. section.

    An answerer MAY reject an offered stream (either with loopback-
    source or loopback-mirror) 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
    MUST be rejected by setting the stream's media port number to zero
    in the answer as defined in RFC 3264 [RFC3264], or by rejecting the
    entire offer (e.g., (i.e., by rejecting the session request entirely).

    Note that an answerer that is not compliant to this specification
    and which receives an offer with the "loopback" media attributes
    would ignore the attribute attributes and treat the incoming offer as a
    normal request.  If the offerer does not wish to establish a
    "normal" RTP session, it would need to terminate the session upon
    receiving such an answer.

 5.

 4. New SDP Attributes

    Three new SDP media-level attributes are defined: one indicates the
    type of loopback, and the other two define the mode role of the
    loopback.

 5.1 agent.

 4.1 Loopback Type Attribute

    This specification defines a new 'loopback' attribute, which
    indicates that the agent wishes to perform loopback, and the type
    of loopack that the agent is able to do.  The
    loopback type 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-attr          = "a=loopback:" SP 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 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 headers 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.  This type of
    loopback applies to the encapsulated and direct loopback use-cases
    described in Section 1.1.

    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  This type of loopback applies to the media loopback
    use-case described in Section 1.1.3.

 4.2 Loopback Mode Attribute Role Attributes: loopback-source and loopback-mirror

    The loopback mode role defines two value media attributes that are used
    to indicate the mode role of the loopback.  These attributes are
    additional mode attributes like sendonly, recvonly, etc. agent generating the SDP offer or
    answer. The syntax of the two loopback mode role media attributes are based on the
    following:

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

    The loopback-mode values are 'loopback-source' as
    follows:

       a=loopback-source

    and 'loopback-
    mirror'.

       a=loopback-mirror

    loopback-source: This attribute specifies that the entity that
    generated the SDP is the media source and expects the receiver of
    the SDP message to act as a loopback-mirror.

    loopback-mirror: This attribute specifies that the entity that
    generated the SDP will mirror (echo) all received media back to the
    sender of the RTP stream.  No media is generated locally by the
    looping back entity for transmission in the mirrored stream.

    <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 entity that generated the
    SDP 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 "m=" line in the SDP MUST include all the payload types that
    will be used during the loopback session including those specified in the loopback-mode
    attribute line. session. The complete payload
    space for the call session is specified in the "m=" line and the rtpmap
    attribute is used to map from the payload type number to an
    encoding name denoting the payload format to be used.

 5.3

 5. Rules for Generating the SDP offer/answer

 5.1  Generating the SDP Offer for Loopback Session

    If an offerer wishes to make a loopback request, it MUST include
    both the loopback-type and loopback-mode loopback-role attributes 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=loopback-source
               a=rtpmap:0 pcmu/8000
               a=rtpmap:8 pcma/8000
               a=rtpmap:100 G7221/16000/1

    A

    Since media loopback offer requires bidirectional RTP, its normal
    direction mode is "sendrecv"; the "sendrecv" direction attribute
    MAY be encoded in SDP or not, as per section 5.1 of [RFC3264],
    since it is implied by default.  If either the loopback source or
    mirror wish to disable loopback use during a given media description MUST NOT contain session, the
    standard direction
    mode attributes sendonly, recvonly, sendrecv, or inactive. attribute "inactive" MUST be used as per [RFC3264].  The loopback-mode
    direction mode attributes (loopback-source "recvonly" and loopback-mirror)
    replace "sendonly" are
    incompatible with the standard attributes. loopback mechanism and MUST NOT be indicated
    when generating an SDP Offer or Answer.  When receiving an SDP
    Offer or Answer, if "recvonly" or "sendonly" is indicated for
    loopback, the SDP-receiving agent SHOULD treat it as a protocol
    failure of the loopback negotiation and terminate the session
    through its normal means (e.g., by sending a SIP BYE if SIP is
    used).

    The offerer may offer more than one loopback-type in the SDP offer.
    The port number and the address in the offer (m/c= lines) indicate
    where the offerer would like to send and receive the media stream. stream(s).  The
    payload type numbers indicate the value of the payload the offerer
    expects to send and receive.  If the offerer is the
    loopback-source, the subset of 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 subset of
    payload type number for the same codec numbers from those given in the loopback-
    mirror line. offer.  In that case,
    the offerer MUST only send the payload type types received in the answer.
    answer, per normal SDP offer/answer rules.

    If the offerer is the loopback-mirror, offer indicates rtp-pkt-loopback support, the
    subset of payload types indicated offer MUST
    also contain either an encapsulated or direct loopback encoding
    format encoding names, or both, as defined in later sections of
    this document.  If the a=loopback-mirror line are
    the payload types for the codecs the offerer is willing to receive. offer only indicates rtp-media-loopback
    support, then neither encapsulated nor direct loopback encoding
    formats apply and they MUST NOT be in the offer.

    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
    direct loopback) as defined in section 7.

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

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

 5.4

 5.2  Generating the SDP Answer for Loopback Session

    As with the offer, an SDP answer for loopback MUST NOT contain follow SDP
    offer/answer rules for the
    standard mode attributes sendonly, recvonly, sendrecv, direction attribute, but directions of
    "sendonly" or inactive. "recvonly" do not apply for loopback operation.  \

    The port number and the address in the answer (m/c= lines) indicate
    where the answerer would like to receive the media stream.  The
    payload type numbers indicate the value of the payload types the
    answerer expects to send and receive.  The loopback-mode attributes
    (a=loopback-source or a=loopback-miror) 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 offerer is the loopback-source, the answerer MUST be a
    loopback-mirror and the subset of payload types indicated in the
    a=loopback-mirror line are the payload types for the codecs the
    answerer is willing to receive. Similarly, if the offerer is the
    loopback-mirror, the answerer MUST be aloopback-source and the
    subset of payload types indicated in the a=loopback-source line are
    the payload types for the codecs the answerer is willing to send.

    If an answerer wishes to accept the loopback request it MUST
    include both the loopback mode role and loopback type attributes 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
       a=loopback-source

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

       m=audio 41352 12345 RTP/AVP 0 8
       a=loopback:rtp-media-loopback
       a=loopback-mirror:0 8
       a=loopback-mirror

    If a stream is offered with multiple loopback type attributes, 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 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=loopback-source
       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 12345 RTP/AVP 0 8
       a=loopback:rtp-media-loopback
       a=loopback-mirror:0 8
       a=loopback-mirror

    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 0 8 112 113
       a=loopback:rtp-pkt-loopback
       a=loopback-source:0 8
       a=loopback-source
       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 12345 RTP/AVP 0 8 112
       a=loopback:rtp-pkt-loopback
       a=loopback-mirror:0 8
       a=loopback-mirror
       a=rtpmap:112 encaprtp/8000

       m=audio 41352 12345 RTP/AVP 0 8 113
       a=loopback:rtp-pkt-loopback
       a=loopback-mirror:0 8
       a=loopback-mirror
       a=rtpmap:113 rtploopback/8000

    The previous examples used the 'encaprtp' and 'rtploopback'
    encoding names, which will be defined in sections 7.1.3 and 7.2.3.

 5.5

 5.3  Offerer Processing of the SDP Answer

    If the received SDP answer does not contain an a=loopback-mirror or
    a=loopback-source,
    a=loopback-source attribute, it is assumed that the loopback
    extensions are not supported by the remote agent.  This is not a
    protocol failure, and instead merely completes the SDP offer/answer
    exchange with whatever normal rules apply; the offerer MAY decide
    to end the established RTP session (if any) through normal means of
    the upper-
    layer upper-layer signaling protocol (e.g., by sending a SIP BYE).

 5.6

 5.4  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, as 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

 5.5  Establishing Sessions Between Entities Behind NAT

    ICE/STUN/TURN provide a general solution to establishing media
    sessions between entities that are behind NATs. NATs, as defined in
    [RFC5245]. Loopback sessions that involve one or more end points
    behind NATs SHOULD use these general solutions wherever possible.

    Furthermore, if the mirroring entity is behind a NAT, it MUST send
    some packets to the identified address/port(s) of the peer, in
    order to open the NAT pinhole.  Using ICE this would be
    accomplished with the STUN connectivity check process, or through a
    TURN server connection.  If ICE is not supported, either [RFC6263]
    or Section 10 of ICE [RFC5245] SHOULD be followed to open the
    pinhole and keep the NAT binding alive/refreshed.

    Note that for any form of NAT traversal to function, symmetric
    RTP/RTCP MUST be used.  In other words both agents MUST send
    packets from the same source address and port they receive packets
    on.

 6. RTP Requirements Requirements

    A looback source MUST NOT send multiple source streams on the same
    5-tuple, since there is no means for the mirror to indicate which
    is which in its mirrored RTP packets.

    A loopback-mirror loopback mirror that is compliant to this specification and
    accepting a
    accepts 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

    A device that is compliant to this specification and
    accepting a media with performing the
    mirroring using the loopback type rtp-media-loopback MUST transmit
    all received media back to the sender, unless congestion feedback
    or other lower-layer constraints prevent it from doing so.  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
    mirroring entity MUST re-generate all the RTP header fields as it
    would when transmitting media. The answering mirroring 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 mirroring
    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 '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 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, separate encapsulating RTP packet; the
    encapsulated packet MUST be fragmented only if required (for
    example: due to MTU limitations).

 7.1.1 Usage

 7.1.1Usage 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 encapsulating RTP packets, the M bit is set to 1 in every
    fragment except 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 as that of
    the
    loopback-source. encapsulated packet. 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

 7.1.2RTP Payload Structure

    The outer RTP header in of the encapsulated encapsulating packet MUST be followed
    by the payload header defined in this section.  If the received RTP
    packet has to be looped back in multiple encapsulating packets due
    to fragmentation, the encapsulating 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
    encapsulated RTP header in of the received packet except for the first 4
    2 bits of the first octet.  In effect, the received RTP packet is
    encapsulated by creating a new outer RTP header followed by 4 new
    bytes of a receive timestamp, followed by the original received RTP
    header and payload, except that the first two bits of the received
    RTP header are overwritten as defined here.

    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

 7.1.3Usage 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 encapsulating 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.
    concern, or simply due to local policy. When using this payload
    format, the receiver MUST loop back each received RTP packet
    payload (not header) in a separate RTP packet.

 7.2.1 Usage

    Because a direct loopback format does not retain the original RTP
    headers, there will be no indication of the original payload-type
    sent to the mirror, in looped returning packets.  Therefore, the
    loopback source SHOULD only send one payload type per loopback RTP
    session, if direct mode is used.

 7.2.1Usage of RTP Header fields

    Payload Type (PT): The assignment of an RTP payload type for this the
    encapsulating 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
    as that of the loopback-source. received RTP packet.  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

 7.2.2RTP Payload Structure

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

 7.2.3 Usage loopback-
    source.

 7.2.3Usage 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. 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 agent that is
    compliant to this specification SHOULD support RTCP per [RFC3550]
    and RTCP-XR per RFC 3611 [RFC3611].  Furthermore, if the client offerer or
    the server
    answerer 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 offerer and the
    server
    answerer MAY support other RTCP-XR reporting blocks as defined by
    RFC 3611 [RFC3611].

 9. 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.

 10. 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.

 10.1  Offer for specific media loopback type

    An agent sends an SDP offer which looks like:

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

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

    An answering agent sends an SDP answer which looks like:

    v=0
    o=bob 1234567890 1122334455 IN IP4 host.biloxi.example.com
    s=Example
    i=An example session
    e=bob@example.com
    s=-
    c=IN IP4 host.biloxi.example.com
    t=0 0
    m=audio 49270 RTP/AVP 0
    a=loopback:rtp-media-loopback
    a=loopback-mirror:0
    a=loopback-mirror
    a=rtpmap:0 pcmu/8000

    The answerer is accepting to mirror the media from the offerer at
    the media level.

 10.2  Offer for choice of media loopback type

    An agent sends an SDP offer which looks like:

    v=0
    o=alice 2890844526 2890842807 IN IP4 host.atlanta.example.com
    s=Example
    i=An example session
    e=alice@example.com
    s=-
    c=IN IP4 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=loopback-source
    a=rtpmap:0 pcmu/8000
    a=rtpmap:112 encaprtp/8000
    a=rtpmap:113 rtploopback/8000

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

    An answering agent sends an SDP answer which looks like:

    v=0
    o=box 1234567890 1122334455 IN IP4 host.biloxi.example.com
    s=Example
    i=An example session
    e=bob@example.com
    s=-
    c=IN IP4 host.biloxi.example.com
    t=0 0
    m=audio 49270 RTP/AVP 0 112
    a=loopback:rtp-pkt-loopback
    a=loopback-mirror:0
    a=loopback-mirror
    a=rtpmap:0 pcmu/8000
    a=rtpmap:112 encaprtp/8000

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

 10.3  Answerer rejecting loopback media

    An agent sends an SDP offer which looks like:

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

    The offerer is offering to source the media and expects the
    answerer to mirror the RTP stream at RTP stream at the media level.

    An answering agent sends an SDP answer which looks like:

    v=0
    o=bob 1234567890 1122334455 IN IP4 host.biloxi.example.com
    s=-
    c=IN IP4 host.biloxi.example.com
    t=0 0
    m=audio 0 RTP/AVP 0
    a=rtpmap:0 pcmu/8000

    Note in this case the answerer did not indicate loopback support,
    although it could have and still used a port number of 0 to
    indicate it does not wish to accept that media session.

    Alternatively, the answering agent could have simply rejected the
    entire SDP offer through some higher-layer signaling protocol means
    (e.g., by rejecting the SIP INVITE request if the SDP offer was in
    the INVITE).

 11. Security Considerations

    The security considerations of [RFC3264] and [RFC3550] apply.

    Given that media loopback may be automated without the end user's
    knowledge, the answerer of the media loopback should be aware of
    denial of service attacks.  It is recommended that session requests
    for media loopback be authenticated and the frequency of such
    sessions limited by the answerer.

    If the higher-layer signaling protocol were not authenticated, a
    malicious attacker could create a session between two parties the
    attacker wishes to target, with each party acting as the loopback-
    mirror to the other, of rtp-pkt-loopback type.  A few RTP packets
    sent to either party would then infinitely loop among the two, as
    fast as they could process them, consuming their resources and
    network bandwidth.

    Furthermore, media-loopback provides a means of attack indirection,
    whereby a malicious attacker creates a loopback session as the
    loopback-source, and uses the mirror to reflect the attacker's
    packets against a target - perhaps a target the attacker could not
    reach directly, such as one behind a firewall for example.  Or the
    attacker could initiate the session as the loopback-mirror, in the
    hopes of making the peer generate media level.

    An answering agent sends an SDP against another target.

    If end-user devices such as mobile phones answer which looks like:

    v=0
    o=bob 1234567890 1122334455 IN IP4 host.biloxi.example.com
    s=Example
    i=An example session
    e=user@example.com
    c=IN IP4 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

 11.      Security Considerations

    The security considerations of [RFC3264] apply. Furthermore, given
    that media loopback may be automated requests
    without authentication and without notifying the end user's
    knowledge, end-user, then an
    attacker could cause the server of battery to drain, and possibly deny the media loopback should be aware of
    denial of
    end-user normal phone service attacks. It is recommended that sessions with
    media or cause network data usage fees.

    This could even occur naturally if a legitimate loopback are authenticated session
    does not terminate properly and the frequency end device does not have a
    timeout mechanism for such.

    For the reasons noted above, end user devices SHOULD provide a
    means of such sessions indicating to the human user that the device is limited by in a
    loopback session, even if it is an authenticated session.  Devices
    which answer or generate loopback sessions SHOULD either perform
    keepalive/refresh tests of the server. session state through some means, or
    time out the session automatically.

 12. 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 at least support the rtp-pkt-loopback option mode
    for
    loopback-type attribute. loopback-type, with direct media loopback payload encoding.  In
    addition, for the loopback-mode
    attribute, loopback role, all implementations of an SDP
    offerer MUST at a minimum least 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.

 13. IANA Considerations

 13.1  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. None.

       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. None.

 13.2  MIME Types

    The IANA has registered the following MIME types:

 13.2.1    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.

 13.2.2    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.

 13.2.3    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.

 13.2.4    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.

 13.2.5    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.

 13.2.6    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.

 13.2.7    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.

 13.2.8    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. Acknowledgements

    This document's editor would like to thank the original authors of
    the document: Kaynam Hedayat, et al.  The editor has made fairly
    insignificant changes in the end.  Also, we'd like to thank Magnus
    Westerlund, Miguel Garcia, Flemming Andreason, Gunnar Hellstrom,
    Emil Ivov and Dan Wing for their feedback, comments and
    suggestions.

 15. Normative References

       [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.

 16. Informative References

       [RFC5245] Rosenberg, J., "Interactive Connectivity
                  Establishment (ICE): A Protocol for Network Address
                  Translator (NAT) Traversal for Offer/Answer
                  Protocols", RFC 5245, April 2010.

       [RFC6263] Marjou, X., Sollaud, A., "Application Mechanism for
                  Keeping Alive the NAT Mappings Associated with RTP /
                  RTP Control Protocol (RTCP) Flows", RFC 6263, June
                  2011.

 Authors' Addresses

       Hadriel Kaplan
       Acme Packet
       100 Crosby Drive
       Bedford, MA  01730
       USA

       EMail: hkaplan@acmepacket.com
       URI:   http://www.acmepacket.com
       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
       Saperix
       738 Main Street, #398
       Waltham, MA 02451
       US

       Phone: +1 978 367 5703

       EMail: vnagarjuna@saperix.com
       URI:   http://www.saperix.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/