draft-ietf-mmusic-media-loopback-18.txt   draft-ietf-mmusic-media-loopback-19.txt 
Internet Draft H. Kaplan (ed.) Internet Draft H. Kaplan (ed.)
Expires: August 12, 2012 Acme Packet Expires: December 12, 2012 Acme Packet
K. Hedayat K. Hedayat
EXFO EXFO
N. Venna N. Venna
Saperix Saperix
P. Jones P. Jones
Cisco Systems, Inc. Cisco Systems, Inc.
A. Roychowdhury
Hughes Systique Corp.
C. SivaChelvan
Cisco Systems, Inc.
N. Stratton N. Stratton
BlinkMind, Inc. BlinkMind, Inc.
March 26, 2012 July 12, 2012
An Extension to the Session Description Protocol (SDP) An Extension to the Session Description Protocol (SDP)
and Real-time Transport Protocol (RTP) for Media Loopback and Real-time Transport Protocol (RTP) for Media Loopback
draft-ietf-mmusic-media-loopback-18 draft-ietf-mmusic-media-loopback-19
Status of this Memo Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with This Internet-Draft is submitted to IETF in full conformance with
the provisions of BCP 78 and BCP 79. the provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet- other groups may also distribute working documents as Internet-
Drafts. Drafts.
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documents at any time. It is inappropriate to use Internet-Drafts documents at any time. It is inappropriate to use Internet-Drafts
as reference material or to cite them other than as "work in as reference material or to cite them other than as "work in
progress." progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
This Internet-Draft will expire on August 12, 2012. This Internet-Draft will expire on December 12, 2012.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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performance. In particular, media delivery is an area that needs performance. In particular, media delivery is an area that needs
attention. One method of meeting these challenges is monitoring attention. One method of meeting these challenges is monitoring
the media delivery performance by looping media back to the the media delivery performance by looping media back to the
transmitter. This is typically referred to as "active monitoring" transmitter. This is typically referred to as "active monitoring"
of services. Media loopback is especially popular in ensuring the of services. Media loopback is especially popular in ensuring the
quality of transport to the edge of a given VoIP, Real-time Text or 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 Video over IP service. Today in networks that deliver real-time
media, short of running 'ping' and 'traceroute' to the edge, media, short of running 'ping' and 'traceroute' to the edge,
administrators are left without the necessary tools to actively administrators are left without the necessary tools to actively
monitor, manage, and diagnose quality issues with their service. monitor, manage, and diagnose quality issues with their service.
The extension defined herein adds new SDP media attributes, which The extension defined herein adds new SDP media types and
enable establishment of media sessions where the media is looped attributes, which enable establishment of media sessions where the
back to the transmitter. Such media sessions will serve as media is looped back to the transmitter. Such media sessions will
monitoring and troubleshooting tools by providing the means for serve as monitoring and troubleshooting tools by providing the
measurement of more advanced VoIP, Real-time Text and Video over IP means for measurement of more advanced VoIP, Real-time Text and
performance metrics. Video over IP performance metrics.
Table of Contents Table of Contents
1. Introduction..................................................3 1. Introduction..................................................3
1.1 Use Cases Supported.......................................4 1.1 Use Cases Supported.......................................4
2. Terminology...................................................6 2. Terminology...................................................6
3. Overview of Operation.........................................6 3. Overview of Operation.........................................6
3.1 SDP Offerer Behavior......................................6 3.1 SDP Offerer Behavior......................................6
3.2 SDP Answerer Behavior.....................................6 3.2 SDP Answerer Behavior.....................................6
4. New SDP Attributes............................................7 4. New SDP Attributes............................................7
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5. Rules for Generating the SDP offer/answer.....................9 5. Rules for Generating the SDP offer/answer.....................9
5.1 Generating the SDP Offer for Loopback Session.............9 5.1 Generating the SDP Offer for Loopback Session.............9
5.2 Generating the SDP Answer for Loopback Session...........10 5.2 Generating the SDP Answer for Loopback Session...........10
5.3 Offerer Processing of the SDP Answer.....................11 5.3 Offerer Processing of the SDP Answer.....................11
5.4 Modifying the Session....................................12 5.4 Modifying the Session....................................12
5.5 Establishing Sessions Between Entities Behind NAT........12 5.5 Establishing Sessions Between Entities Behind NAT........12
6. RTP Requirements.............................................12 6. RTP Requirements.............................................12
7. Payload formats for Packet loopback..........................13 7. Payload formats for Packet loopback..........................13
7.1 Encapsulated Payload format..............................13 7.1 Encapsulated Payload format..............................13
7.2 Direct loopback RTP payload format.......................16 7.2 Direct loopback RTP payload format.......................16
8. RTCP Requirements............................................17 8. SRTP Behavior................................................17
9. Congestion Control...........................................17 9. RTCP Requirements............................................17
10. Examples....................................................18 10. Congestion Control..........................................18
10.1 Offer for specific media loopback type..................18 11. Examples....................................................18
10.2 Offer for choice of media loopback type.................18 11.1 Offer for specific media loopback type..................18
10.3 Answerer rejecting loopback media.......................19 11.2 Offer for choice of media loopback type.................19
11. Security Considerations.....................................20 11.3 Answerer rejecting loopback media.......................20
12. Implementation Considerations...............................21 12. Security Considerations.....................................20
13. IANA Considerations.........................................21 13. Implementation Considerations...............................21
13.1 SDP Attributes..........................................21 14. IANA Considerations.........................................22
13.2 MIME Types..............................................22 14.1 SDP Attributes..........................................22
14. Acknowledgements............................................31 14.2 Media Types.............................................22
15. Normative References........................................31 15. Acknowledgements............................................31
16. Informative References......................................32 16. Normative References........................................31
17. Informative References......................................32
1. Introduction 1. Introduction
The overall quality, reliability, and performance of VoIP, The overall quality, reliability, and performance of VoIP,
Real-time Text and Video over IP services rely on the performance 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 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 delivered media there is a need to monitor the performance of
the media transport. One method of monitoring and managing the the media transport. One method of monitoring and managing the
overall quality of real-time VoIP, Text and Video over IP Services overall quality of real-time VoIP, Text and Video over IP Services
is through monitoring the quality of the media in an active is through monitoring the quality of the media in an active
session. This type of "active monitoring" of services is a method session. This type of "active monitoring" of services is a method
of proactively managing the performance and quality of VoIP based of proactively managing the performance and quality of VoIP based
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to request an endpoint to loop media back to the other endpoint and to request an endpoint to loop media back to the other endpoint and
to provide media statistics (e.g., RTCP and RTCP XR information). to provide media statistics (e.g., RTCP and RTCP XR information).
Another method involves deployment of special endpoints that always Another method involves deployment of special endpoints that always
loop incoming media back for sessions. Although the latter method loop incoming media back for sessions. Although the latter method
has been used and is functional, it does not scale to support large has been used and is functional, it does not scale to support large
networks and introduces new network management challenges. networks and introduces new network management challenges.
Further, it does not offer the granularity of testing a specific Further, it does not offer the granularity of testing a specific
endpoint that may be exhibiting problems. endpoint that may be exhibiting problems.
The extension defined in this document introduces new SDP media The extension defined in this document introduces new SDP media
attributes that enable establishment of media sessions where the types and attributes that enable establishment of media sessions
media is looped back to the transmitter. The SDP offer/answer where the media is looped back to the transmitter. The SDP
model [RFC3264] is used to establish a loopback connection. offer/answer model [RFC3264] is used to establish a loopback
Furthermore, this extension provides guidelines on handling RTP connection. Furthermore, this extension provides guidelines on
[RFC3550], as well as usage of RTCP [RFC3550] and RTCP XR [RFC3611] handling RTP [RFC3550], as well as usage of RTCP [RFC3550] and RTCP
for reporting media related measurements. XR [RFC3611] for reporting media related measurements.
1.1 Use Cases Supported 1.1 Use Cases Supported
As a matter of terminology in this document, packets flow from one 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 peer acting as a "loopback source", to the other peer acting as a
"loopback mirror", which in turn returns packets to the loopback "loopback mirror", which in turn returns packets to the loopback
source. In advance of the session, the peers negotiate to determine source. In advance of the session, the peers negotiate to determine
which one acts in which role, using the SDP offer/answer exchange. which one acts in which role, using the SDP offer/answer exchange.
The negotiation also includes details such as the type of loopback The negotiation also includes details such as the type of loopback
to be used. to be used.
This specification supports three use cases: "encapsulated packet This specification supports three use cases: "encapsulated packet
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type. The packet is taken as close as possible to the analog level, type. The packet is taken as close as possible to the analog level,
then re-encoded according to an outgoing format determined by SDP then re-encoded according to an outgoing format determined by SDP
negotiation. The reencoded content is returned to the loopback negotiation. The reencoded content is returned to the loopback
source as an RTP packet with payload type corresponding to the source as an RTP packet with payload type corresponding to the
reencoding format. reencoding format.
This usage allows trouble-shooting at the codec level. The This usage allows trouble-shooting at the codec level. The
capability for path statistics is limited to what is available from capability for path statistics is limited to what is available from
RTCP reports. RTCP reports.
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in RFC 2119. this document are to be interpreted as described in RFC 2119.
SDP: Session Description Protocol, as defined in [RFC4566]. This SDP: Session Description Protocol, as defined in [RFC4566]. This
document assumes the SDP offer/answer model is followed, per document assumes the SDP offer/answer model is followed, per
[RFC3264], but does not assume any specific signaling protocol for [RFC3264], but does not assume any specific signaling protocol for
carrying the SDP. carrying the SDP.
The following terms are borrowed from [RFC3264] definitions: offer, The following terms are borrowed from [RFC3264] definitions: offer,
offerer, answer, answerer, and agent. offerer, answer, answerer, and agent.
3. Overview of Operation 3. Overview of Operation
This document defines two loopback 'types', two 'roles', and two This document defines two loopback 'types', two 'roles', and two
encoding formats for loopback. For any given SDP offerer or encoding formats for loopback. For any given SDP offerer or
answerer pair, one side is the source of RTP packets, while the answerer pair, one side is the source of RTP packets, while the
other is the mirror looping packets/media back. Those define the other is the mirror looping packets/media back. Those define the
two loopback roles. As the mirror, two 'types' of loopback can be two loopback roles. As the mirror, two 'types' of loopback can be
performed: packet-level or media-level. When media-level is used, performed: packet-level or media-level. When media-level is used,
there is no further choice of encoding format - there is only one there is no further choice of encoding format - there is only one
format: whatever is indicated for normal media, since the "looping" format: whatever is indicated for normal media, since the "looping"
is performed at the codec level. When packet-level looping is is performed at the codec level. When packet-level looping is
performed, however, the mirror can either send back RTP in an performed, however, the mirror can either send back RTP in an
encapsulated format or direct-loopback format. The rest of this encapsulated format or direct-loopback format. The rest of this
document describes these loopback types, roles, and encoding document describes these loopback types, roles, and encoding
formats, and the SDP offer/answer rules for indicating them. formats, and the SDP offer/answer rules for indicating them.
3.1 SDP Offerer Behavior 3.1 SDP Offerer Behavior
An SDP offerer compliant to this memo and attempting to establish a An SDP offerer compliant to this memo and attempting to establish a
media session with media loopback MUST include "loopback" media media session with media loopback MUST include "loopback" media
attributes for each individual media description in the offer attributes for each individual media description in the offer
message. The offerer MUST look for the "loopback" media attributes message. The offerer MUST look for the "loopback" media attributes
in the media description(s) of the response from the answer for in the media description(s) of the response from the answer for
confirmation that the request is accepted. confirmation that the request is accepted.
3.2 SDP Answerer Behavior 3.2 SDP Answerer Behavior
An SDP answerer compliant to this specification and receiving an An SDP answerer compliant to this specification and receiving an
offer containing media descriptions with the "loopback" media offer containing media descriptions with the "loopback" media
attributes MUST acknowledge the request by including the received attributes MUST acknowledge the request by including the received
"loopback" media attributes for each media description in its "loopback" media attributes for each media description in its
asnwer if it agrees to do the loopback. If the answerer does not answer if it agrees to do the loopback. If the answerer does not
want to do loopback or wants to reject the "loopback" request for want to do loopback or wants to reject the "loopback" request for
specific media types, it MAY do so as defined in this section. specific media descriptions, it MUST do so as defined in this
section.
An answerer MAY reject an offered stream (either with loopback- An answerer MAY reject an offered stream (either with loopback-
source or loopback-mirror) if the loopback-type is not specified, source or loopback-mirror) if the loopback-type is not specified,
the specified loopback-type is not supported, or the endpoint the specified loopback-type is not supported, or the endpoint
cannot honor the offer for any other reason. The loopback request cannot honor the offer for any other reason. The loopback request
MUST be rejected by setting the stream's media port number to zero 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 in the answer as defined in RFC 3264 [RFC3264], or by rejecting the
entire offer (i.e., by rejecting the session request entirely). entire offer (i.e., by rejecting the session request entirely).
Note that an answerer that is not compliant to this specification Note that an answerer that is not compliant to this specification
and which receives an offer with the "loopback" media attributes and which receives an offer with the "loopback" media attributes
would ignore the attributes and treat the incoming offer as a would ignore the attributes and treat the incoming offer as a
normal request. If the offerer does not wish to establish a normal request. If the offerer does not wish to establish a
"normal" RTP session, it would need to terminate the session upon "normal" RTP session, it would need to terminate the session upon
receiving such an answer. receiving such an answer.
4. New SDP Attributes 4. New SDP Attributes
Three new SDP media-level attributes are defined: one indicates the Three new SDP media-level attributes are defined: one indicates the
type of loopback, and the other two define the role of the agent. type of loopback, and the other two define the role of the agent.
4.1 Loopback Type Attribute 4.1 Loopback Type Attribute
This specification defines a new 'loopback' attribute, which This specification defines a new 'loopback' attribute, which
indicates that the agent wishes to perform loopback, and the type indicates that the agent wishes to perform loopback, and the type
of loopack that the agent is able to do. The loopback-type is a of loopack that the agent is able to do. The loopback-type is a
property media attribute with the following syntax: value media attribute [RFC4566] with the following syntax:
a=loopback:<loopback-type> a=loopback:<loopback-type>
Following is the Augmented BNF [RFC5234] for loopback-type: Following is the Augmented BNF [RFC5234] for loopback-type:
Loopback-attr = "a=loopback:" SP loopback-type loopback-attr = "a=loopback:" SP loopback-type
loopback-type = loopback-choice [1*SP loopback-choice] loopback-type = loopback-choice [1*SP loopback-choice]
loopback-choice = loopback-type-pkt / loopback-type-media loopback-choice = loopback-type-pkt / loopback-type-media
loopback-type-pkt = "rtp-pkt-loopback" loopback-type-pkt = "rtp-pkt-loopback"
loopback-type-media = "rtp-media-loopback" loopback-type-media = "rtp-media-loopback"
The loopback-type is used to indicate the type of loopback. The The loopback-type is used to indicate the type of loopback. The
loopback-type values are rtp-pkt-loopback, and rtp-media-loopback. loopback-type values are rtp-pkt-loopback, and rtp-media-loopback.
rtp-pkt-loopback: In this mode, the RTP packets are looped back to 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 the sender at a point before the encoder/decoder function in the
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formats that MUST be used for this type of loopback. This type of formats that MUST be used for this type of loopback. This type of
loopback applies to the encapsulated and direct loopback use-cases loopback applies to the encapsulated and direct loopback use-cases
described in Section 1.1. described in Section 1.1.
rtp-media-loopback: This loopback is activated as close as possible rtp-media-loopback: This loopback is activated as close as possible
to the analog interface and after the decoder so that the RTP to the analog interface and after the decoder so that the RTP
packets are subsequently re-encoded prior to transmission back to packets are subsequently re-encoded prior to transmission back to
the sender. This type of loopback applies to the media loopback the sender. This type of loopback applies to the media loopback
use-case described in Section 1.1.3. use-case described in Section 1.1.3.
4.2 Loopback Role Attributes: loopback-source and loopback-mirror 4.2 Loopback Role Attributes: loopback-source and loopback-mirror
The loopback role defines two value media attributes that are used The loopback role defines two property media attributes [RFC4566]
to indicate the role of the agent generating the SDP offer or that are used to indicate the role of the agent generating the SDP
answer. The syntax of the two loopback role media attributes are as offer or answer. The syntax of the two loopback role media
follows: attributes are as follows:
a=loopback-source a=loopback-source
and and
a=loopback-mirror a=loopback-mirror
loopback-source: This attribute specifies that the entity that loopback-source: This attribute specifies that the entity that
generated the SDP is the media source and expects the receiver of generated the SDP is the media source and expects the receiver of
the SDP message to act as a loopback-mirror. the SDP message to act as a loopback-mirror.
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generated the SDP will mirror (echo) all received media back to the generated the SDP will mirror (echo) all received media back to the
sender of the RTP stream. No media is generated locally by the sender of the RTP stream. No media is generated locally by the
looping back entity for transmission in the mirrored stream. looping back entity for transmission in the mirrored stream.
The "m=" line in the SDP MUST include all the payload types that The "m=" line in the SDP MUST include all the payload types that
will be used during the loopback session. The complete payload will be used during the loopback session. The complete payload
space for the session is specified in the "m=" line and the rtpmap space for the session is specified in the "m=" line and the rtpmap
attribute is used to map from the payload type number to an attribute is used to map from the payload type number to an
encoding name denoting the payload format to be used. encoding name denoting the payload format to be used.
5. Rules for Generating the SDP offer/answer 5. Rules for Generating the SDP offer/answer
5.1 Generating the SDP Offer for Loopback Session 5.1 Generating the SDP Offer for Loopback Session
If an offerer wishes to make a loopback request, it MUST include If an offerer wishes to make a loopback request, it MUST include
both the loopback-type and loopback-role attributes in a valid SDP both the loopback-type and loopback-role attributes in a valid SDP
offer: offer:
Example: m=audio 41352 RTP/AVP 0 8 100 Example: m=audio 41352 RTP/AVP 0 8 100
a=loopback:rtp-media-loopback a=loopback:rtp-media-loopback
a=loopback-source a=loopback-source
a=rtpmap:0 pcmu/8000 a=rtpmap:0 pcmu/8000
a=rtpmap:8 pcma/8000 a=rtpmap:8 pcma/8000
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since it is implied by default. If either the loopback source or since it is implied by default. If either the loopback source or
mirror wish to disable loopback use during a session, the direction mirror wish to disable loopback use during a session, the direction
mode attribute "inactive" MUST be used as per [RFC3264]. The mode attribute "inactive" MUST be used as per [RFC3264]. The
direction mode attributes "recvonly" and "sendonly" are direction mode attributes "recvonly" and "sendonly" are
incompatible with the loopback mechanism and MUST NOT be indicated incompatible with the loopback mechanism and MUST NOT be indicated
when generating an SDP Offer or Answer. When receiving an SDP when generating an SDP Offer or Answer. When receiving an SDP
Offer or Answer, if "recvonly" or "sendonly" is indicated for Offer or Answer, if "recvonly" or "sendonly" is indicated for
loopback, the SDP-receiving agent SHOULD treat it as a protocol loopback, the SDP-receiving agent SHOULD treat it as a protocol
failure of the loopback negotiation and terminate the session failure of the loopback negotiation and terminate the session
through its normal means (e.g., by sending a SIP BYE if SIP is through its normal means (e.g., by sending a SIP BYE if SIP is
used). used), or reject the offending media stream.
The offerer may offer more than one loopback-type in the SDP offer. 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 The port number and the address in the offer (m/c= lines) indicate
where the offerer would like to receive the media stream(s). The where the offerer would like to receive the media stream(s). The
payload type numbers indicate the value of the payload the offerer payload type numbers indicate the value of the payload the offerer
expects to receive. However, the answer might indicate a subset of expects to receive. However, the answer might indicate a subset of
payload type numbers from those given in the offer. In that case, payload type numbers from those given in the offer. In that case,
the offerer MUST only send the payload types received in the the offerer MUST only send the payload types received in the
answer, per normal SDP offer/answer rules. answer, per normal SDP offer/answer rules.
If the offer indicates rtp-pkt-loopback support, the offer MUST If the offer indicates rtp-pkt-loopback support, the offer MUST
also contain either an encapsulated or direct loopback encoding also contain either an encapsulated or direct loopback encoding
format encoding names, or both, as defined in later sections of format encoding name, or both, as defined in later sections of this
this document. If the offer only indicates rtp-media-loopback document. If the offer only indicates rtp-media-loopback support,
support, then neither encapsulated nor direct loopback encoding then neither encapsulated nor direct loopback encoding formats
formats apply and they MUST NOT be in the offer. apply and they MUST NOT be in the offer.
If loopback-type is rtp-pkt-loopback, the loopback-mirror MUST send If loopback-type is rtp-pkt-loopback, the loopback-mirror MUST send
and the loopback-source MUST receive the looped back packets and the loopback-source MUST receive the looped back packets
encoded in one of the two payload formats (encapsulated RTP or encoded in one of the two payload formats (encapsulated RTP or
direct loopback) as defined in section 7. direct loopback) as defined in section 7.
Example: m=audio 41352 RTP/AVP 0 8 112 Example: m=audio 41352 RTP/AVP 0 8 112
a=loopback:rtp-pkt-loopback a=loopback:rtp-pkt-loopback
a=loopback-source a=loopback-source
a=rtpmap:112 encaprtp/8000 a=rtpmap:112 encaprtp/8000
Example: m=audio 41352 RTP/AVP 0 8 112 Example: m=audio 41352 RTP/AVP 0 8 112
a=loopback:rtp-pkt-loopback a=loopback:rtp-pkt-loopback
a=loopback-source a=loopback-source
a=rtpmap:112 rtploopback/8000 a=rtpmap:112 rtploopback/8000
5.2 Generating the SDP Answer for Loopback Session 5.2 Generating the SDP Answer for Loopback Session
As with the offer, an SDP answer for loopback MUST follow SDP As with the offer, an SDP answer for loopback MUST follow SDP
offer/answer rules for the direction attribute, but directions of offer/answer rules for the direction attribute, but directions of
"sendonly" or "recvonly" do not apply for loopback operation. \ "sendonly" or "recvonly" do not apply for loopback operation and
hence MUST NOT be used.
The port number and the address in the answer (m/c= lines) indicate The port number and the address in the answer (m/c= lines) indicate
where the answerer would like to receive the media stream. The where the answerer would like to receive the media stream. The
payload type numbers indicate the value of the payload types the payload type numbers indicate the value of the payload types the
answerer expects to send and receive. answerer expects to send and receive.
If an answerer wishes to accept the loopback request it MUST If an answerer wishes to accept the loopback request it MUST
include both the loopback role and loopback type attributes in the include both the loopback role and loopback type attributes in the
answer. When a stream is offered with the loopback-source answer. When a stream is offered with the loopback-source
attribute, the corresponding stream in the response MUST be attribute, the corresponding stream in the response MUST be
loopback-mirror and vice versa, provided that answerer is capable loopback-mirror and vice versa, provided the answerer is capable of
of supporting the requested loopback-type. supporting the requested loopback-type.
For example, if the offer contains the loopback-source attribute: For example, if the offer contains the loopback-source attribute:
m=audio 41352 RTP/AVP 0 8 m=audio 41352 RTP/AVP 0 8
a=loopback:rtp-media-loopback a=loopback:rtp-media-loopback
a=loopback-source a=loopback-source
The answer that is capable of supporting the offer MUST contain the The answer that is capable of supporting the offer must contain the
loopback-mirror attribute: loopback-mirror attribute:
m=audio 12345 RTP/AVP 0 8 m=audio 12345 RTP/AVP 0 8
a=loopback:rtp-media-loopback a=loopback:rtp-media-loopback
a=loopback-mirror a=loopback-mirror
If a stream is offered with multiple loopback type attributes, the If a stream is offered with multiple loopback type attributes, the
answer MUST include only one of the loopback types that are answer MUST include only one of the loopback types that are
accepted by the answerer. The answerer SHOULD give preference to accepted by the answerer. The answerer SHOULD give preference to
the first loopback-type in the SDP offer. the first loopback-type in the SDP offer.
For example, if the offer contains: For example, if the offer contains:
m=audio 41352 RTP/AVP 0 8 112 m=audio 41352 RTP/AVP 0 8 112
a=loopback:rtp-media-loopback rtp-pkt-loopback a=loopback:rtp-media-loopback rtp-pkt-loopback
a=loopback-source a=loopback-source
a=rtpmap:112 encaprtp/8000 a=rtpmap:112 encaprtp/8000
The answer that is capable of supporting the offer and chooses to The answer that is capable of supporting the offer and chooses to
loopback the media using the rtp-media-loopback type MUST contain: loopback the media using the rtp-media-loopback type must contain:
m=audio 12345 RTP/AVP 0 8 m=audio 12345 RTP/AVP 0 8
a=loopback:rtp-media-loopback a=loopback:rtp-media-loopback
a=loopback-mirror a=loopback-mirror
As specified in section 7, if the loopback-type is As specified in section 7, if the loopback-type is
rtp-pkt-loopback, either the encapsulated RTP payload format or rtp-pkt-loopback, either the encapsulated RTP payload format or
direct loopback RTP payload format MUST be used for looped back direct loopback RTP payload format MUST be used for looped back
packets. packets.
skipping to change at page 11, line 48 skipping to change at page 11, line 50
a=rtpmap:112 encaprtp/8000 a=rtpmap:112 encaprtp/8000
m=audio 12345 RTP/AVP 0 8 113 m=audio 12345 RTP/AVP 0 8 113
a=loopback:rtp-pkt-loopback a=loopback:rtp-pkt-loopback
a=loopback-mirror a=loopback-mirror
a=rtpmap:113 rtploopback/8000 a=rtpmap:113 rtploopback/8000
The previous examples used the 'encaprtp' and 'rtploopback' The previous examples used the 'encaprtp' and 'rtploopback'
encoding names, which will be defined in sections 7.1.3 and 7.2.3. encoding names, which will be defined in sections 7.1.3 and 7.2.3.
5.3 Offerer Processing of the SDP Answer 5.3 Offerer Processing of the SDP Answer
If the received SDP answer does not contain an a=loopback-mirror or If the received SDP answer does not contain an a=loopback-mirror or
a=loopback-source attribute, it is assumed that the loopback a=loopback-source attribute, it is assumed that the loopback
extensions are not supported by the remote agent. This is not a extensions are not supported by the remote agent. This is not a
protocol failure, and instead merely completes the SDP offer/answer protocol failure, and instead merely completes the SDP offer/answer
exchange with whatever normal rules apply; the offerer MAY decide exchange with whatever normal rules apply; the offerer MAY decide
to end the established RTP session (if any) through normal means of to end the established RTP session (if any) through normal means of
the upper-layer signaling protocol (e.g., by sending a SIP BYE). the upper-layer signaling protocol (e.g., by sending a SIP BYE).
5.4 Modifying the Session 5.4 Modifying the Session
At any point during the loopback session, either participant MAY At any point during the loopback session, either participant MAY
issue a new offer to modify the characteristics of the previous issue a new offer to modify the characteristics of the previous
session, as defined in section 8 of RFC 3264 [RFC3264]. This also session, as defined in section 8 of RFC 3264 [RFC3264]. This also
includes transitioning from a normal media processing mode to includes transitioning from a normal media processing mode to
loopback mode, and vice a versa. loopback mode, and vice versa.
5.5 Establishing Sessions Between Entities Behind NAT 5.5 Establishing Sessions Between Entities Behind NAT
ICE/STUN/TURN provide a general solution to establishing media ICE/STUN/TURN provide a general solution to establishing media
sessions between entities that are behind NATs, as defined in sessions between entities that are behind NATs, as defined in
[RFC5245]. Loopback sessions that involve one or more end points [RFC5245]. Loopback sessions that involve one or more endpoints
behind NATs SHOULD use these general solutions wherever possible. behind NATs SHOULD use these general solutions wherever possible.
Furthermore, if the mirroring entity is behind a NAT, it MUST send Furthermore, if the mirroring entity is behind a NAT, it MUST send
some packets to the identified address/port(s) of the peer, in some packets to the identified address/port(s) of the peer, in
order to open the NAT pinhole. Using ICE this would be order to open the NAT pinhole. Using ICE this would be
accomplished with the STUN connectivity check process, or through a accomplished with the STUN connectivity check process, or through a
TURN server connection. If ICE is not supported, either [RFC6263] TURN server connection. If ICE is not supported, either [RFC6263]
or Section 10 of ICE [RFC5245] SHOULD be followed to open the or Section 10 of ICE [RFC5245] SHOULD be followed to open the
pinhole and keep the NAT binding alive/refreshed. pinhole and keep the NAT binding alive/refreshed.
Note that for any form of NAT traversal to function, symmetric Note that for any form of NAT traversal to function, symmetric
RTP/RTCP MUST be used. In other words both agents MUST send RTP/RTCP [RFC4961] MUST be used. In other words both agents MUST
packets from the same source address and port they receive packets send packets from the source address and port they receive packets
on. on.
6. RTP Requirements 6. RTP Requirements
A looback source MUST NOT send multiple source streams on the same A loopback source MUST NOT send multiple source streams on the same
5-tuple, since there is no means for the mirror to indicate which 5-tuple, since there is no means for the mirror to indicate which
is which in its mirrored RTP packets. is which in its mirrored RTP packets.
A loopback mirror that is compliant to this specification and A loopback mirror that is compliant to this specification and
accepts media with rtp-pkt-loopback loopback-type MUST loopback the accepts media with rtp-pkt-loopback loopback type MUST loopback the
incoming RTP packets using either the encapsulated RTP payload incoming RTP packets using either the encapsulated RTP payload
format or the direct loopback RTP payload format as defined in format or the direct loopback RTP payload format as defined in
section 7 of this specification. section 7 of this specification.
A device that is compliant to this specification and performing the A device that is compliant to this specification and performing the
mirroring using the loopback type rtp-media-loopback MUST transmit mirroring using the loopback type rtp-media-loopback MUST transmit
all received media back to the sender, unless congestion feedback all received media back to the sender, unless congestion feedback
or other lower-layer constraints prevent it from doing so. The 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 incoming media MUST be treated as if it were to be played (e.g. the
media stream MAY receive treatment from PLC algorithms). The media stream MAY receive treatment from PLC algorithms). The
mirroring entity MUST re-generate all the RTP header fields as it mirroring entity MUST re-generate all the RTP header fields as it
would when transmitting media. The mirroring entity MAY choose to would when transmitting media. The mirroring entity MAY choose to
encode the loopback media according to any of the media encode the loopback media according to any of the media
descriptions supported by the offering entity. Furthermore, in descriptions supported by the offering entity. Furthermore, in
cases where the same media type is looped back, the mirroring cases where the same media type is looped back, the mirroring
entity MAY choose to preserve number of frames/packet and bitrate entity MAY choose to preserve number of frames/packet and bitrate
of the encoded media according to the received media. of the encoded media according to the received media.
7. Payload formats for Packet loopback 7. Payload formats for Packet loopback
The payload formats described in this section MUST be used by a The payload formats described in this section MUST be used by a
loopback-mirror when 'rtp-pkt-loopback' is the specified loopback-mirror when 'rtp-pkt-loopback' is the specified
loopback-type. Two different formats are specified here - an loopback-type. Two different formats are specified here - an
encapsulated RTP payload format and a direct loopback RTP payload encapsulated RTP payload format and a direct loopback RTP payload
format. The encapsulated RTP payload format should be used when format. The encapsulated RTP payload format should be used when
the incoming RTP header information needs to be preserved during the incoming RTP header information needs to be preserved during
the loopback operation. This is useful in cases where loopback the loopback operation. This is useful in cases where loopback
source needs to measure performance metrics in both directions. source needs to measure performance metrics in both directions.
However, this comes at the expense of increased packet size as However, this comes at the expense of increased packet size as
described in section 7.1. The direct loopback RTP payload format described in section 7.1. The direct loopback RTP payload format
should be used when bandwidth requirement prevents the use of should be used when bandwidth requirements prevent the use of
encapsulated RTP payload format. encapsulated RTP payload format.
To keep the implementation of loopback-mirrors simple it is 7.1 Encapsulated Payload format
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 A received RTP packet is encapsulated in the payload section of the
RTP packet generated by a loopback-mirror. Each received packet RTP packet generated by a loopback-mirror. Each received packet
MUST be encapsulated in a separate encapsulating RTP packet; the MUST be encapsulated in a separate encapsulating RTP packet; the
encapsulated packet MUST be fragmented only if required (for encapsulated packet MUST be fragmented only if required (for
example: due to MTU limitations). example: due to MTU limitations).
7.1.1Usage of RTP Header fields 7.1.1 Usage of RTP Header fields
Payload Type (PT): The assignment of an RTP payload type for this Payload Type (PT): The assignment of an RTP payload type for this
packet format is outside the scope of this document; it is either packet format is outside the scope of this document; it is either
specified by the RTP profile under which this payload format is specified by the RTP profile under which this payload format is
used or more likely signaled dynamically out-of-band (e.g., using used or more likely signaled dynamically out-of-band (e.g., using
SDP; section 7.1.3 defines the name binding). SDP; section 7.1.3 defines the name binding).
Marker (M) bit: If the received RTP packet is looped back in 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 multiple encapsulating RTP packets, the M bit is set to 1 in every
fragment except the last packet, otherwise it is set to 0. fragment except the last packet, otherwise it is set to 0.
skipping to change at page 14, line 36 skipping to change at page 14, line 28
the loopback-mirror is transmitting this packet to the loopback- the loopback-mirror is transmitting this packet to the loopback-
source. The RTP timestamp MUST use the same clock rate as that of source. The RTP timestamp MUST use the same clock rate as that of
the encapsulated packet. The initial value of the timestamp SHOULD the encapsulated packet. The initial value of the timestamp SHOULD
be random for security reasons (see Section 5.1 of RFC 3550 be random for security reasons (see Section 5.1 of RFC 3550
[RFC3550]). [RFC3550]).
SSRC: set as described in RFC 3550 [RFC3550]. SSRC: set as described in RFC 3550 [RFC3550].
CC and CSRC fields are used as described in RFC 3550 [RFC3550]. CC and CSRC fields are used as described in RFC 3550 [RFC3550].
7.1.2RTP Payload Structure 7.1.2 RTP Payload Structure
The outer RTP header of the encapsulating packet MUST be followed The outer RTP header of the encapsulating packet MUST be followed
by the payload header defined in this section. If the received RTP by the payload header defined in this section, after any header
packet has to be looped back in multiple encapsulating packets due extension(s). If the received RTP packet has to be looped back in
to fragmentation, the encapsulating RTP header in each packet MUST multiple encapsulating packets due to fragmentation, the
be followed by the payload header defined in this section. The encapsulating RTP header in each packet MUST be followed by the
header is devised so that the loopback-source can decode looped payload header defined in this section. The header is devised so
back packets in the presence of moderate packet loss [RFC3550]. that the loopback-source can decode looped back packets in the
presence of moderate packet loss [RFC3550]. The RTP payload of the
encapsulating RTP packet starts with the payload header defined in
this section.
0 1 2 3 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 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 | | receive timestamp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| F | R | CC |M| PT | sequence number | | F | R | CC |M| PT | sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| transmit timestamp | | transmit timestamp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 15, line 33 skipping to change at page 15, line 33
encapsulated by creating a new outer RTP header followed by 4 new encapsulated by creating a new outer RTP header followed by 4 new
bytes of a receive timestamp, followed by the original received RTP bytes of a receive timestamp, followed by the original received RTP
header and payload, except that the first two bits of the received header and payload, except that the first two bits of the received
RTP header are overwritten as defined here. RTP header are overwritten as defined here.
Receive Timestamp: 32 bits Receive Timestamp: 32 bits
The Receive timestamp denotes the sampling instant for when the The Receive timestamp denotes the sampling instant for when the
last octet of the received media packet that is being encapsulated last octet of the received media packet that is being encapsulated
by the loopback-mirror is received from the loopback-source. The by the loopback-mirror is received from the loopback-source. The
Receive timestamp MUST be based on the same clock used by the same clock rate MUST used by the loopback-source. The initial
loopback-source. The initial value of the timestamp SHOULD be value of the timestamp SHOULD be random for security reasons (see
random for security reasons (see Section 5.1 of RFC 3550 Section 5.1 of RFC 3550 [RFC3550]).
[RFC3550]).
Fragmentation (F): 2 bits Fragmentation (F): 2 bits
First Fragment (00) /Last Fragment (01) /No Fragmentation(10)/ First Fragment (00) /Last Fragment (01) /No Fragmentation(10)/
Intermediate Fragment (11). This field identifies how much of the Intermediate Fragment (11). This field identifies how much of the
received packet is encapsulated in this packet by the loopback- received packet is encapsulated in this packet by the loopback-
mirror. If the received packet is not fragmented, this field is mirror. If the received packet is not fragmented, this field is
set to 10; otherwise the packet that contains the first fragments 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 00, the packet that contains the last fragment
sets this field to 01, all other packets set this field to 11. sets this field to 01, all other packets set this field to 11.
7.1.3Usage of SDP 7.1.3 Usage of SDP
The payload type number for the encapsulated stream can be The payload type number for the encapsulated stream can be
negotiated using SDP. There is no static payload type assignment negotiated using SDP. There is no static payload type assignment
for the encapsulating stream, so dynamic payload type numbers MUST for the encapsulating stream, so dynamic payload type numbers MUST
be used. The binding to the name is indicated by an rtpmap be used. The binding to the name is indicated by an rtpmap
attribute. The name used in this binding is "encaprtp". attribute. The name used in this binding is "encaprtp".
The following is an example SDP fragment for encapsulated RTP. The following is an example SDP fragment for encapsulated RTP.
m=audio 41352 RTP/AVP 112 m=audio 41352 RTP/AVP 112
a=rtpmap:112 encaprtp/8000 a=rtpmap:112 encaprtp/8000
7.2 Direct loopback RTP payload format 7.2 Direct loopback RTP payload format
The direct loopback RTP payload format can be used in scenarios The direct loopback RTP payload format can be used in scenarios
where the 16 byte overhead of the encapsulated payload format is of where the 16 byte overhead of the encapsulated payload format is of
concern, or simply due to local policy. When using this payload concern, or simply due to local policy. When using this payload
format, the receiver MUST loop back each received RTP packet format, the receiver MUST loop back each received RTP packet
payload (not header) in a separate RTP packet. payload (not header) in a separate RTP packet.
Because a direct loopback format does not retain the original RTP Because a direct loopback format does not retain the original RTP
headers, there will be no indication of the original payload-type headers, there will be no indication of the original payload-type
sent to the mirror, in looped returning packets. Therefore, the sent to the mirror, in looped-back packets. Therefore, the
loopback source SHOULD only send one payload type per loopback RTP loopback source SHOULD only send one payload type per loopback RTP
session, if direct mode is used. session, if direct mode is used.
7.2.1Usage of RTP Header fields 7.2.1 Usage of RTP Header fields
Payload Type (PT): The assignment of an RTP payload type for the Payload Type (PT): The assignment of an RTP payload type for the
encapsulating packet format is outside the scope of this document; encapsulating packet format is outside the scope of this document;
it is either specified by the RTP profile under which this payload it is either specified by the RTP profile under which this payload
format is used or more likely signaled dynamically out-of-band format is used or more likely signaled dynamically out-of-band
(e.g., using SDP; section 7.2.3 defines the name binding). (e.g., using SDP; section 7.2.3 defines the name binding).
Marker (M) bit: Set to the value in the received packet. Marker (M) bit: Set to the value in the received packet.
Extension (X) bit: Defined by the RTP Profile used. Extension (X) bit: Defined by the RTP Profile used.
Sequence Number: The RTP sequence number SHOULD be generated by the Sequence Number: The RTP sequence number SHOULD be generated by the
loopback-mirror in the usual manner with a constant random offset. loopback-mirror in the usual manner with a constant random offset,
as per [RFC3550].
Timestamp: The RTP timestamp denotes the sampling instant for when Timestamp: The RTP timestamp denotes the sampling instant for when
the loopback-mirror is transmitting this packet to the the loopback-mirror is transmitting this packet to the
loopback-source. The RTP timestamp MUST be based on the same clock loopback-source. The same clock rate MUST be used as that of the
as that of the received RTP packet. The initial value of the received RTP packet. The initial value of the timestamp SHOULD be
timestamp SHOULD be random for security reasons (see Section 5.1 of random for security reasons (see Section 5.1 of RFC 3550
RFC 3550 [RFC3550]). [RFC3550]).
SSRC: set as described in RFC 3550 [RFC3550]. SSRC: set as described in RFC 3550 [RFC3550].
CC and CSRC fields are used as described in RFC 3550 [RFC3550]. CC and CSRC fields are used as described in RFC 3550 [RFC3550].
7.2.2RTP Payload Structure 7.2.2 RTP Payload Structure
This payload format does not define any payload specific headers. This payload format does not define any payload specific headers.
The loopback-mirror simply copies the RTP payload data from the The loopback-mirror simply copies the RTP payload data from the
payload portion of the RTP packet received from the loopback- payload portion of the RTP packet received from the loopback-
source. source.
7.2.3Usage of SDP 7.2.3 Usage of SDP
The payload type number for the payload loopback stream can be The payload type number for the payload loopback stream can be
negotiated using a mechanism like SDP. There is no static payload negotiated using a mechanism like SDP. There is no static payload
type assignment for the stream, so dynamic payload type numbers type assignment for the stream, so dynamic payload type numbers
MUST be used. The binding to the name is indicated by an rtpmap MUST be used. The binding to the name is indicated by an rtpmap
attribute. The name used in this binding is "rtploopback". attribute. The name used in this binding is "rtploopback".
The following is an example SDP fragment for direct loopback RTP The following is an example SDP fragment for direct loopback RTP
format. format.
m=audio 41352 RTP/AVP 112 m=audio 41352 RTP/AVP 112
a=rtpmap:112 rtploopback/8000 a=rtpmap:112 rtploopback/8000
8. RTCP Requirements 8. SRTP Behavior
Secure RTP [RFC3711] MAY be used for loopback sessions. SRTP
operates at a lower logical layer than RTP, and thus if both sides
negotiate to use SRTP, each side uses its own key, performs
encryption/decryption, authentication, etc. Therefore the loopback
function on the mirror occurs after the SRTP packet has been
decrypted and authenticated, as a normal cleartext RTP packet
without an MKI or authentication tag; once the cleartext RTP packet
or payload is mirrored - either at the media-layer, direct packet-
layer, or encapsulated packet-layer - it is encrypted by the mirror
using its own key.
9. RTCP Requirements
The use of the loopback attribute is intended for monitoring of The use of the loopback attribute is intended for monitoring of
media quality of the session. Consequently the media performance media quality of the session. Consequently the media performance
information should be exchanged between the offering and the information should be exchanged between the offering and the
answering entities. An offering or answering agent that is answering entities. An offering or answering agent that is
compliant to this specification SHOULD support RTCP per [RFC3550] compliant to this specification SHOULD support RTCP per [RFC3550]
and RTCP-XR per RFC 3611 [RFC3611]. Furthermore, if the offerer or and RTCP-XR per RFC 3611 [RFC3611]. Furthermore, if the offerer or
answerer choose to support RTCP-XR, they SHOULD support RTCP-XR answerer choose to support RTCP-XR, they SHOULD support RTCP-XR
Loss RLE report block, Duplicate RLE report block, Statistics Loss RLE report block, Duplicate RLE report block, Statistics
Summary report block, and VoIP Metric Reports Block per sections Summary report block, and VoIP Metric Reports Block per sections
4.1, 4.2, 4.6, and 4.7 of RFC 3611 [RFC3611]. The offerer and the 4.1, 4.2, 4.6, and 4.7 of RFC 3611 [RFC3611]. The offerer and the
answerer MAY support other RTCP-XR reporting blocks as defined by answerer MAY support other RTCP-XR reporting blocks as defined by
RFC 3611 [RFC3611]. RFC 3611 [RFC3611].
9. Congestion Control 10. Congestion Control
All the participants in a loopback session SHOULD implement All the participants in a media-level loopback session SHOULD
congestion control mechanisms as defined by the RTP profile under implement congestion control mechanisms as defined by the RTP
which the loopback mechanism is implemented. For audio video profile under which the loopback mechanism is implemented. For
profiles, implementations SHOULD conform to the mechanism defined audio video profiles, implementations SHOULD conform to the
in Section 2 of RFC 3551. mechanism defined in Section 2 of RFC 3551.
10. Examples For packet-level loopback types, the loopback source SHOULD
implement congestion control. The mirror will simply reflect back
the RTP packets it receives (either in encapsulated or direct
modes), therefore the source needs to control the congestion of
both forward and reverse paths by reducing its sending rate to the
mirror. This keeps the loopback mirror implementation simpler, and
provides more flexibility for the source performing a loopback
test.
11. Examples
This section provides examples for media descriptions using SDP for This section provides examples for media descriptions using SDP for
different scenarios. The examples are given for SIP-based different scenarios. The examples are given for SIP-based
transactions and are abbreviated and do not show the complete transactions and are abbreviated and do not show the complete
signaling for convenience. signaling for convenience.
10.1 Offer for specific media loopback type 11.1 Offer for specific media loopback type
An agent sends an SDP offer which looks like: An agent sends an SDP offer which looks like:
v=0 v=0
o=alice 2890844526 2890842807 IN IP4 host.atlanta.example.com o=alice 2890844526 2890842807 IN IP4 host.atlanta.example.com
s=- s=-
c=IN IP4 host.atlanta.example.com c=IN IP4 host.atlanta.example.com
t=0 0 t=0 0
m=audio 49170 RTP/AVP 0 m=audio 49170 RTP/AVP 0
a=loopback:rtp-media-loopback a=loopback:rtp-media-loopback
skipping to change at page 18, line 45 skipping to change at page 19, line 20
c=IN IP4 host.biloxi.example.com c=IN IP4 host.biloxi.example.com
t=0 0 t=0 0
m=audio 49270 RTP/AVP 0 m=audio 49270 RTP/AVP 0
a=loopback:rtp-media-loopback a=loopback:rtp-media-loopback
a=loopback-mirror a=loopback-mirror
a=rtpmap:0 pcmu/8000 a=rtpmap:0 pcmu/8000
The answerer is accepting to mirror the media from the offerer at The answerer is accepting to mirror the media from the offerer at
the media level. the media level.
10.2 Offer for choice of media loopback type 11.2 Offer for choice of media loopback type
An agent sends an SDP offer which looks like: An agent sends an SDP offer which looks like:
v=0 v=0
o=alice 2890844526 2890842807 IN IP4 host.atlanta.example.com o=alice 2890844526 2890842807 IN IP4 host.atlanta.example.com
s=- s=-
c=IN IP4 host.atlanta.example.com c=IN IP4 host.atlanta.example.com
t=0 0 t=0 0
m=audio 49170 RTP/AVP 0 112 113 m=audio 49170 RTP/AVP 0 112 113
a=loopback:rtp-media-loopback rtp-pkt-loopback a=loopback:rtp-media-loopback rtp-pkt-loopback
skipping to change at page 19, line 30 skipping to change at page 20, line 4
v=0 v=0
o=box 1234567890 1122334455 IN IP4 host.biloxi.example.com o=box 1234567890 1122334455 IN IP4 host.biloxi.example.com
s=- s=-
c=IN IP4 host.biloxi.example.com c=IN IP4 host.biloxi.example.com
t=0 0 t=0 0
m=audio 49270 RTP/AVP 0 112 m=audio 49270 RTP/AVP 0 112
a=loopback:rtp-pkt-loopback a=loopback:rtp-pkt-loopback
a=loopback-mirror a=loopback-mirror
a=rtpmap:0 pcmu/8000 a=rtpmap:0 pcmu/8000
a=rtpmap:112 encaprtp/8000 a=rtpmap:112 encaprtp/8000
The answerer is accepting to mirror the media from the offerer at The answerer is accepting to mirror the media from the offerer at
the packet level using the encapsulated RTP payload format. the packet level using the encapsulated RTP payload format.
10.3 Answerer rejecting loopback media 11.3 Answerer rejecting loopback media
An agent sends an SDP offer which looks like: An agent sends an SDP offer which looks like:
v=0 v=0
o=alice 2890844526 2890842807 IN IP4 host.atlanta.example.com o=alice 2890844526 2890842807 IN IP4 host.atlanta.example.com
s=- s=-
c=IN IP4 host.atlanta.example.com c=IN IP4 host.atlanta.example.com
t=0 0 t=0 0
m=audio 49170 RTP/AVP 0 m=audio 49170 RTP/AVP 0
a=loopback:rtp-media-loopback a=loopback:rtp-media-loopback
skipping to change at page 20, line 24 skipping to change at page 20, line 43
Note in this case the answerer did not indicate loopback support, Note in this case the answerer did not indicate loopback support,
although it could have and still used a port number of 0 to although it could have and still used a port number of 0 to
indicate it does not wish to accept that media session. indicate it does not wish to accept that media session.
Alternatively, the answering agent could have simply rejected the Alternatively, the answering agent could have simply rejected the
entire SDP offer through some higher-layer signaling protocol means entire SDP offer through some higher-layer signaling protocol means
(e.g., by rejecting the SIP INVITE request if the SDP offer was in (e.g., by rejecting the SIP INVITE request if the SDP offer was in
the INVITE). the INVITE).
11. Security Considerations 12. Security Considerations
The security considerations of [RFC3264] and [RFC3550] apply. The security considerations of [RFC3264] and [RFC3550] apply.
Given that media loopback may be automated without the end user's Given that media loopback may be automated without the end user's
knowledge, the answerer of the media loopback should be aware of knowledge, the answerer of the media loopback should be aware of
denial of service attacks. It is recommended that session requests denial of service attacks. It is RECOMMENDED that session requests
for media loopback be authenticated and the frequency of such for media loopback be authenticated and the frequency of such
sessions limited by the answerer. sessions limited by the answerer.
If the higher-layer signaling protocol were not authenticated, a If the higher-layer signaling protocol were not authenticated, a
malicious attacker could create a session between two parties the malicious attacker could create a session between two parties the
attacker wishes to target, with each party acting as the loopback- attacker wishes to target, with each party acting as the loopback-
mirror to the other, of rtp-pkt-loopback type. A few RTP packets 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 sent to either party would then infinitely loop among the two, as
fast as they could process them, consuming their resources and fast as they could process them, consuming their resources and
network bandwidth. network bandwidth.
skipping to change at page 21, line 4 skipping to change at page 21, line 27
loopback-source, and uses the mirror to reflect the attacker's loopback-source, and uses the mirror to reflect the attacker's
packets against a target - perhaps a target the attacker could not packets against a target - perhaps a target the attacker could not
reach directly, such as one behind a firewall for example. Or the reach directly, such as one behind a firewall for example. Or the
attacker could initiate the session as the loopback-mirror, in the attacker could initiate the session as the loopback-mirror, in the
hopes of making the peer generate media against another target. hopes of making the peer generate media against another target.
If end-user devices such as mobile phones answer loopback requests If end-user devices such as mobile phones answer loopback requests
without authentication and without notifying the end-user, then an without authentication and without notifying the end-user, then an
attacker could cause the battery to drain, and possibly deny the attacker could cause the battery to drain, and possibly deny the
end-user normal phone service or cause network data usage fees. end-user normal phone service or cause network data usage fees.
This could even occur naturally if a legitimate loopback session This could even occur naturally if a legitimate loopback session
does not terminate properly and the end device does not have a does not terminate properly and the end device does not have a
timeout mechanism for such. timeout mechanism for such.
For the reasons noted above, end user devices SHOULD provide a For the reasons noted above, end user devices SHOULD provide a
means of indicating to the human user that the device is in a means of indicating to the human user that the device is in a
loopback session, even if it is an authenticated session. Devices loopback session, even if it is an authenticated session. Devices
which answer or generate loopback sessions SHOULD either perform that answer or generate loopback sessions SHOULD either perform
keepalive/refresh tests of the session state through some means, or keepalive/refresh tests of the session state through some means, or
time out the session automatically. time out the session automatically.
12. Implementation Considerations 13. Implementation Considerations
The media loopback approach described in this document is a The media loopback approach described in this document is a
complete solution that would work under all scenarios. However, it complete solution that would work under all scenarios. However, it
is believed that the solution may not be light-weight enough for is possible that the solution may not be light-weight enough for
the common case. In light of this concern, this section clarifies some implementations. In light of this concern, this section
which features of the loopback proposal MUST be implemented for all clarifies which features of the loopback proposal MUST be
implementations and which features MAY be deferred if the complete implemented for all implementations and which features MAY be
solution is not desired. deferred if the complete solution is not desired.
All implementations MUST at least support the rtp-pkt-loopback mode All implementations MUST at least support the rtp-pkt-loopback mode
for loopback-type, with direct media loopback payload encoding. In for loopback-type, with direct media loopback payload encoding. In
addition, for the loopback role, all implementations of an SDP addition, for the loopback role, all implementations of an SDP
offerer MUST at least be able to act as a loopback-source. offerer MUST at least be able to act as a loopback-source.
13. IANA Considerations 14. IANA Considerations
13.1 SDP Attributes 14.1 SDP Attributes
This document defines three new media-level SDP attributes. IANA This document defines three new media-level SDP attributes. IANA
has registered the following attributes: has registered the following attributes:
Contact name: Kaynam Hedayat Contact name: Kaynam Hedayat
<kaynam.hedayat@exfo.com>. <kaynam.hedayat@exfo.com>.
Attribute name: "loopback". Attribute name: loopback
Type of attribute: Media level. Type of attribute: Media level.
Subject to charset: No. Subject to charset: No.
Purpose of attribute: The 'loopback' attribute is used to Purpose of attribute: The 'loopback' attribute is used to
indicate the type of media loopback. indicate the type of media loopback.
Allowed attribute values: The parameters to 'loopback' may be Allowed attribute values: The parameters to 'loopback' may be
one or more of "rtp-pkt-loopback" and one or more of "rtp-pkt-loopback" and
"rtp-media-loopback". See section 5 "rtp-media-loopback". See section 5
of this document for syntax. of this document for syntax.
Contact name: Kaynam Hedayat Contact name: Kaynam Hedayat
<kaynam.hedayat@exfo.com>. <kaynam.hedayat@exfo.com>.
Attribute name: "loopback-source". Attribute name: loopback-source
Type of attribute: Media level. Type of attribute: Media level.
Subject to charset: No. Subject to charset: No.
Purpose of attribute: The 'loopback-source' attribute Purpose of attribute: The 'loopback-source' attribute
specifies that the sender is the media specifies that the sender is the media
source and expects the receiver to act source and expects the receiver to act
as a loopback-mirror. as a loopback-mirror.
Allowed attribute values: None. Allowed attribute values: None.
Contact name: Kaynam Hedayat Contact name: Kaynam Hedayat
<kaynam.hedayat@exfo.com>. <kaynam.hedayat@exfo.com>.
Attribute name: "loopback-mirror". Attribute name: loopback-mirror
Type of attribute: Media level. Type of attribute: Media level.
Subject to charset: No. Subject to charset: No.
Purpose of attribute: The 'loopback-mirror' attribute Purpose of attribute: The 'loopback-mirror' attribute
specifies that the receiver will specifies that the receiver will
mirror (echo) all received media back mirror (echo) all received media back
to the sender of the RTP stream. to the sender of the RTP stream.
Allowed attribute values: None. Allowed attribute values: None.
13.2 MIME Types 14.2 Media Types
The IANA has registered the following MIME types: The IANA has registered the following media types:
13.2.1 audio/encaprtp 14.2.1 audio/encaprtp
To: ietf-types@iana.org To: ietf-types@iana.org
Subject: Registration of media type audio/encaprtp Subject: Registration of media type audio/encaprtp
Type name: audio Type name: audio
Subtype name: encaprtp Subtype name: encaprtp
Required parameters: Required parameters:
rate:RTP timestamp clock rate, which is equal to the rate: RTP timestamp clock rate, which is equal to the
sampling rate. The typical rate is 8000; other rates sampling rate. The typical rate is 8000; other rates
may be specified. may be specified. This is specified by the loop back
source, and reflected by the mirror.
Optional parameters: none Optional parameters: none
Encoding considerations: This media type is framed Encoding considerations: This media type is framed.
binary data.
Security considerations: See Section 12 of this document. Security considerations: See Section 12 of this document.
Interoperability considerations: none Interoperability considerations: none
Published specification: This MIME type is described fully Published specification: This document.
within this document.
Applications which use this media type: Applications wishing Applications which use this media type: Applications wishing
to monitor and ensure the quality of transport to the to monitor and ensure the quality of transport to the
edge of a given VoIP, Real-Time Text or Video Over IP edge of a given VoIP Service.
Service.
Additional information: none Additional information: none
Person & email address to contact for further information: Contact: the authors of this document.
Kaynam Hedayat
EMail: kaynam.hedayat@exfo.com
Intended usage: COMMON Intended usage: LIMITED USE
Restrictions on usage: This media type depends on RTP Restrictions on usage: This media type depends on RTP
framing, and hence is only defined for transfer via framing, and hence is only defined for transfer via
RTP. Transfer within other framing protocols is not RTP. Transfer within other framing protocols is not
defined at this time. defined at this time.
Author: Author:
Kaynam Hedayat. Kaynam Hedayat.
Change controller: IETF Audio/Video Transport working Change controller: IETF Audio/Video Transport working
group delegated from the IESG. group delegated from the IESG.
13.2.2 video/encaprtp 14.2.2 video/encaprtp
To: ietf-types@iana.org To: ietf-types@iana.org
Subject: Registration of media type video/encaprtp Subject: Registration of media type video/encaprtp
Type name: video Type name: video
Subtype name: encaprtp Subtype name: encaprtp
Required parameters: Required parameters:
rate:RTP timestamp clock rate, which is equal to the rate: RTP timestamp clock rate, which is equal to the
sampling rate. The typical rate is 8000; other rates sampling rate. This is specified by the loop back
may be specified. source, and reflected by the mirror.
Optional parameters: none Optional parameters: none
Encoding considerations: This media type is framed Encoding considerations: This media type is framed.
binary data.
Security considerations: See Section 12 of this document. Security considerations: See Section 12 of this document.
Interoperability considerations: none Interoperability considerations: none
Published specification: This MIME type is described fully Published specification: This document.
within this document.
Applications which use this media type: Applications wishing Applications which use this media type: Applications wishing
to monitor and ensure the quality of transport to the to monitor and ensure the quality of transport to the
edge of a given VoIP, Real-Time Text or Video Over IP edge of a given Video Over IP Service.
Service.
Additional information: none Additional information: none
Person & email address to contact for further information: Contact: the authors of this document.
Kaynam Hedayat
EMail: kaynam.hedayat@exfo.com
Intended usage: COMMON Intended usage: LIMITED USE
Restrictions on usage: This media type depends on RTP Restrictions on usage: This media type depends on RTP
framing, and hence is only defined for transfer via framing, and hence is only defined for transfer via
RTP. Transfer within other framing protocols is not RTP. Transfer within other framing protocols is not
defined at this time. defined at this time.
Author: Author:
Kaynam Hedayat. Kaynam Hedayat.
Change controller: IETF Audio/Video Transport working Change controller: IETF Audio/Video Transport working
group delegated from the IESG. group delegated from the IESG.
13.2.3 text/encaprtp 14.2.3 text/encaprtp
To: ietf-types@iana.org To: ietf-types@iana.org
Subject: Registration of media type text/encaprtp Subject: Registration of media type text/encaprtp
Type name: text Type name: text
Subtype name: encaprtp Subtype name: encaprtp
Required parameters: Required parameters:
rate:RTP timestamp clock rate, which is equal to the rate: RTP timestamp clock rate, which is equal to the
sampling rate. The typical rate is 8000; other rates sampling rate. This is specified by the loop back
may be specified. source, and reflected by the mirror.
Optional parameters: none Optional parameters: none
Encoding considerations: This media type is framed Encoding considerations: This media type is framed.
binary data.
Security considerations: See Section 12 of this document. Security considerations: See Section 12 of this document.
Interoperability considerations: none Interoperability considerations: none
Published specification: This MIME type is described fully Published specification: This document.
within this document.
Applications which use this media type: Applications wishing Applications which use this media type: Applications wishing
to monitor and ensure the quality of transport to the to monitor and ensure the quality of transport to the
edge of a given VoIP, Real-Time Text or Video Over IP edge of a given Real-Time Text Service.
Service.
Additional information: none Additional information: none
Person & email address to contact for further information: Contact: the authors of this document.
Kaynam Hedayat
EMail: kaynam.hedayat@exfo.com
Intended usage: COMMON Intended usage: LIMITED USE
Restrictions on usage: This media type depends on RTP Restrictions on usage: This media type depends on RTP
framing, and hence is only defined for transfer via framing, and hence is only defined for transfer via
RTP. Transfer within other framing protocols is not RTP. Transfer within other framing protocols is not
defined at this time. defined at this time.
Author: Author:
Kaynam Hedayat. Kaynam Hedayat.
Change controller: IETF Audio/Video Transport working Change controller: IETF Audio/Video Transport working
group delegated from the IESG. group delegated from the IESG.
13.2.4 application/encaprtp 14.2.4 application/encaprtp
To: ietf-types@iana.org To: ietf-types@iana.org
Subject: Registration of media type Subject: Registration of media type
application/encaprtp application/encaprtp
Type name: application Type name: application
Subtype name: encaprtp Subtype name: encaprtp
Required parameters: Required parameters:
rate:RTP timestamp clock rate, which is equal to the rate: RTP timestamp clock rate, which is equal to the
sampling rate. The typical rate is 8000; other rates sampling rate. This is specified by the loop back
may be specified. source, and reflected by the mirror.
Optional parameters: none Optional parameters: none
Encoding considerations: This media type is framed Encoding considerations: This media type is framed.
binary data.
Security considerations: See Section 12 of this document. Security considerations: See Section 12 of this document.
Interoperability considerations: none Interoperability considerations: none
Published specification: This MIME type is described fully Published specification: This document.
within this document.
Applications which use this media type: Applications wishing Applications which use this media type: Applications wishing
to monitor and ensure the quality of transport to the to monitor and ensure the quality of transport to the
edge of a given VoIP, Real-Time Text or Video Over IP edge of a given Real-Time Application Service.
Service.
Additional information: none Additional information: none
Person & email address to contact for further information: Contact: the authors of this document.
Kaynam Hedayat
EMail: kaynam.hedayat@exfo.com
Intended usage: COMMON Intended usage: LIMITED USE
Restrictions on usage: This media type depends on RTP Restrictions on usage: This media type depends on RTP
framing, and hence is only defined for transfer via framing, and hence is only defined for transfer via
RTP. Transfer within other framing protocols is not RTP. Transfer within other framing protocols is not
defined at this time. defined at this time.
Author: Author:
Kaynam Hedayat. Kaynam Hedayat.
Change controller: IETF Audio/Video Transport working Change controller: IETF Audio/Video Transport working
group delegated from the IESG. group delegated from the IESG.
13.2.5 audio/rtploopback 14.2.5 audio/rtploopback
To: ietf-types@iana.org To: ietf-types@iana.org
Subject: Registration of media type audio/rtploopback Subject: Registration of media type audio/rtploopback
Type name: audio Type name: audio
Subtype name: rtploopback Subtype name: rtploopback
Required parameters: Required parameters:
rate:RTP timestamp clock rate, which is equal to the rate:RTP timestamp clock rate, which is equal to the
sampling rate. The typical rate is 8000; other rates sampling rate. The typical rate is 8000; other rates
may be specified. may be specified. This is specified by the loop back
source, and reflected by the mirror.
Optional parameters: none Optional parameters: none
Encoding considerations: This media type is framed Encoding considerations: This media type is framed.
binary data.
Security considerations: See Section 12 of this document. Security considerations: See Section 12 of this document.
Interoperability considerations: none Interoperability considerations: none
Published specification: This MIME type is described fully Published specification: This document.
within this document.
Applications which use this media type: Applications wishing Applications which use this media type: Applications wishing
to monitor and ensure the quality of transport to the to monitor and ensure the quality of transport to the
edge of a given VoIP, Real-Time Text or Video Over IP edge of a given VoIP Service.
Service.
Additional information: none Additional information: none
Person & email address to contact for further information: Contact: the authors of this document.
Kaynam Hedayat
EMail: kaynam.hedayat@exfo.com
Intended usage: COMMON Intended usage: LIMITED USE
Restrictions on usage: This media type depends on RTP Restrictions on usage: This media type depends on RTP
framing, and hence is only defined for transfer via framing, and hence is only defined for transfer via
RTP. Transfer within other framing protocols is not RTP. Transfer within other framing protocols is not
defined at this time. defined at this time.
Author: Author:
Kaynam Hedayat. Kaynam Hedayat.
Change controller: IETF Audio/Video Transport working Change controller: IETF Audio/Video Transport working
group delegated from the IESG. group delegated from the IESG.
13.2.6 video/rtploopback 14.2.6 video/rtploopback
To: ietf-types@iana.org To: ietf-types@iana.org
Subject: Registration of media type video/rtploopback Subject: Registration of media type video/rtploopback
Type name: video Type name: video
Subtype name: rtploopback Subtype name: rtploopback
Required parameters: Required parameters:
rate:RTP timestamp clock rate, which is equal to the rate:RTP timestamp clock rate, which is equal to the
sampling rate. The typical rate is 8000; other rates sampling rate. This is specified by the loop back
may be specified. source, and reflected by the mirror.
Optional parameters: none Optional parameters: none
Encoding considerations: This media type is framed Encoding considerations: This media type is framed.
binary data.
Security considerations: See Section 12 of this document. Security considerations: See Section 12 of this document.
Interoperability considerations: none Interoperability considerations: none
Published specification: This MIME type is described fully Published specification: This document.
within this document.
Applications which use this media type: Applications wishing Applications which use this media type: Applications wishing
to monitor and ensure the quality of transport to the to monitor and ensure the quality of transport to the
edge of a given VoIP, Real-Time Text or Video Over IP edge of a given Video Over IP Service.
Service.
Additional information: none Additional information: none
Person & email address to contact for further information: Contact: the authors of this document.
Kaynam Hedayat
EMail: kaynam.hedayat@exfo.com
Intended usage: COMMON Intended usage: LIMITED USE
Restrictions on usage: This media type depends on RTP Restrictions on usage: This media type depends on RTP
framing, and hence is only defined for transfer via framing, and hence is only defined for transfer via
RTP. Transfer within other framing protocols is not RTP. Transfer within other framing protocols is not
defined at this time. defined at this time.
Author: Author:
Kaynam Hedayat. Kaynam Hedayat.
Change controller: IETF Audio/Video Transport working Change controller: IETF Audio/Video Transport working
group delegated from the IESG. group delegated from the IESG.
13.2.7 text/rtploopback 14.2.7 text/rtploopback
To: ietf-types@iana.org To: ietf-types@iana.org
Subject: Registration of media type text/rtploopback Subject: Registration of media type text/rtploopback
Type name: text Type name: text
Subtype name: rtploopback Subtype name: rtploopback
Required parameters: Required parameters:
rate:RTP timestamp clock rate, which is equal to the rate:RTP timestamp clock rate, which is equal to the
sampling rate. The typical rate is 8000; other rates sampling rate. This is specified by the loop back
may be specified. source, and reflected by the mirror.
Optional parameters: none Optional parameters: none
Encoding considerations: This media type is framed Encoding considerations: This media type is framed.
binary data.
Security considerations: See Section 12 of this document. Security considerations: See Section 12 of this document.
Interoperability considerations: none Interoperability considerations: none
Published specification: This MIME type is described fully Published specification: This document.
within this document.
Applications which use this media type: Applications wishing Applications which use this media type: Applications wishing
to monitor and ensure the quality of transport to the to monitor and ensure the quality of transport to the
edge of a given VoIP, Real-Time Text or Video Over IP edge of a given Real-Time Text Service.
Service.
Additional information: none Additional information: none
Person & email address to contact for further information: Contact: the authors of this document.
Kaynam Hedayat
EMail: kaynam.hedayat@exfo.com
Intended usage: COMMON Intended usage: LIMITED USE
Restrictions on usage: This media type depends on RTP Restrictions on usage: This media type depends on RTP
framing, and hence is only defined for transfer via framing, and hence is only defined for transfer via
RTP. Transfer within other framing protocols is not RTP. Transfer within other framing protocols is not
defined at this time. defined at this time.
Author: Author:
Kaynam Hedayat. Kaynam Hedayat.
Change controller: IETF Audio/Video Transport working Change controller: IETF Audio/Video Transport working
group delegated from the IESG. group delegated from the IESG.
13.2.8 application/rtploopback 14.2.8 application/rtploopback
To: ietf-types@iana.org To: ietf-types@iana.org
Subject: Registration of media type Subject: Registration of media type
application/rtploopback application/rtploopback
Type name: application Type name: application
Subtype name: rtploopback Subtype name: rtploopback
Required parameters: Required parameters:
rate:RTP timestamp clock rate, which is equal to the rate:RTP timestamp clock rate, which is equal to the
sampling rate. The typical rate is 8000; other rates sampling rate. This is specified by the loop back
may be specified. source, and reflected by the mirror.
Optional parameters: none Optional parameters: none
Encoding considerations: This media type is framed Encoding considerations: This media type is framed.
binary data.
Security considerations: See Section 12 of this document. Security considerations: See Section 12 of this document.
Interoperability considerations: none Interoperability considerations: none
Published specification: This MIME type is described fully Published specification: This document.
within this document.
Applications which use this media type: Applications wishing Applications which use this media type: Applications wishing
to monitor and ensure the quality of transport to the to monitor and ensure the quality of transport to the
edge of a given VoIP, Real-Time Text or Video Over IP edge of a given Real-Time Application Service.
Service.
Additional information: none Additional information: none
Person & email address to contact for further information: Contact: the authors of this document.
Kaynam Hedayat
EMail: kaynam.hedayat@exfo.com
Intended usage: COMMON Intended usage: LIMITED USE
Restrictions on usage: This media type depends on RTP Restrictions on usage: This media type depends on RTP
framing, and hence is only defined for transfer via framing, and hence is only defined for transfer via
RTP. Transfer within other framing protocols is not RTP. Transfer within other framing protocols is not
defined at this time. defined at this time.
Author: Author:
Kaynam Hedayat. Kaynam Hedayat.
Change controller: IETF Audio/Video Transport working Change controller: IETF Audio/Video Transport working
group delegated from the IESG. group delegated from the IESG.
14. Acknowledgements 15. Acknowledgements
This document's editor would like to thank the original authors of This document's editor would like to thank the original authors of
the document: Kaynam Hedayat, et al. The editor has made fairly the document: Kaynam Hedayat, Nagarjuna Venna, Paul E. Jones, Arjun
insignificant changes in the end. Also, we'd like to thank Magnus Roychowdhury, Chelliah SivaChelvan, and Nathan Stratton. The
Westerlund, Miguel Garcia, Flemming Andreason, Gunnar Hellstrom, editor has made fairly insignificant changes in the end. Also,
Emil Ivov and Dan Wing for their feedback, comments and we'd like to thank Magnus Westerlund, Miguel Garcia, Flemming
suggestions. Andreasen, Gunnar Hellstrom, Emil Ivov and Dan Wing for their
feedback, comments and suggestions.
15. Normative References 16. Normative References
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer
Model with the Session Description Protocol (SDP)", Model with the Session Description Protocol (SDP)",
RFC 3264, June 2002. RFC 3264, June 2002.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R. and V. [RFC3550] Schulzrinne, H., Casner, S., Frederick, R. and V.
Jacobson, "RTP: A Transport Protocol for Real-Time Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003. Applications", STD 64, RFC 3550, July 2003.
[RFC3611] Almeroth, K., Caceres, R., Clark, A., Cole, R., [RFC3611] Almeroth, K., Caceres, R., Clark, A., Cole, R.,
skipping to change at page 32, line 25 skipping to change at page 32, line 8
[RFC3551] Schulzrinne, H., Casner, S., "RTP Profile for Audio [RFC3551] Schulzrinne, H., Casner, S., "RTP Profile for Audio
and Video Conferences with Minimial Control", STD 65, and Video Conferences with Minimial Control", STD 65,
RFC 3551, July 2003. RFC 3551, July 2003.
[RFC4566] Handley, M., Jacobson, V., Perkins, C., "SDP: Session [RFC4566] Handley, M., Jacobson, V., Perkins, C., "SDP: Session
Description Protocol", RFC 4566, July 2006. Description Protocol", RFC 4566, July 2006.
[RFC4855] Casner, S., "Media Type Registration of RTP Payload [RFC4855] Casner, S., "Media Type Registration of RTP Payload
Formats", RFC 4855, February 2007. Formats", RFC 4855, February 2007.
16. Informative References 17. Informative References
[RFC5245] Rosenberg, J., "Interactive Connectivity [RFC5245] Rosenberg, J., "Interactive Connectivity
Establishment (ICE): A Protocol for Network Address Establishment (ICE): A Protocol for Network Address
Translator (NAT) Traversal for Offer/Answer Translator (NAT) Traversal for Offer/Answer
Protocols", RFC 5245, April 2010. Protocols", RFC 5245, April 2010.
[RFC6263] Marjou, X., Sollaud, A., "Application Mechanism for [RFC6263] Marjou, X., Sollaud, A., "Application Mechanism for
Keeping Alive the NAT Mappings Associated with RTP / Keeping Alive the NAT Mappings Associated with RTP /
RTP Control Protocol (RTCP) Flows", RFC 6263, June RTP Control Protocol (RTCP) Flows", RFC 6263, June
2011. 2011.
skipping to change at page 33, line 21 skipping to change at page 33, line 4
URI: http://www.exfo.com/ URI: http://www.exfo.com/
Nagarjuna Venna Nagarjuna Venna
Saperix Saperix
738 Main Street, #398 738 Main Street, #398
Waltham, MA 02451 Waltham, MA 02451
US US
EMail: vnagarjuna@saperix.com EMail: vnagarjuna@saperix.com
URI: http://www.saperix.com/ URI: http://www.saperix.com/
Paul E. Jones Paul E. Jones
Cisco Systems, Inc. Cisco Systems, Inc.
7025 Kit Creek Rd. 7025 Kit Creek Rd.
Research Triangle Park, NC 27709 Research Triangle Park, NC 27709
US US
EMail: paulej@packetizer.com EMail: paulej@packetizer.com
URI: http://www.cisco.com/ URI: http://www.cisco.com/
Arjun Roychowdhury
Hughes Systique Corp.
15245 Shady Grove Rd, Ste 330
Rockville MD 20850
US
EMail: arjun@hsc.com
URI: http://www. hsc.com/
Chelliah SivaChelvan
Cisco Systems, Inc.
2200 East President George Bush Turnpike
Richardson, TX 75082
US
EMail: chelliah@cisco.com
URI: http://www.cisco.com/
Nathan Stratton Nathan Stratton
BlinkMind, Inc. BlinkMind, Inc.
2027 Briarchester Dr. 2027 Briarchester Dr.
Katy, TX 77450 Katy, TX 77450
EMail: nathan@robotics.net EMail: nathan@robotics.net
URI: http://www.robotics.net/ URI: http://www.robotics.net/
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