draft-ietf-mmusic-media-loopback-23.txt   draft-ietf-mmusic-media-loopback-24.txt 
MMUSIC Working Group H. Kaplan (ed.) MMUSIC Working Group H. Kaplan (ed.)
Internet-Draft Acme Packet Internet-Draft Acme Packet
Intended status: Proposed Standard K. Hedayat Intended status: Proposed Standard K. Hedayat
Expires: March 9, 2013 EXFO Expires: May 6, 2013 EXFO
N. Venna N. Venna
Saperix Saperix
P. Jones P. Jones
Cisco Systems, Inc. Cisco Systems, Inc.
N. Stratton N. Stratton
BlinkMind, Inc. BlinkMind, Inc.
September 9, 2012 November 6, 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-23 draft-ietf-mmusic-media-loopback-24
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.
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This Internet-Draft will expire on March 9, 2013. This Internet-Draft will expire on May 6, 2013.
Copyright Notice Copyright Notice
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Abstract Abstract
The wide deployment of Voice over IP (VoIP), Text and Video over IP The wide deployment of Voice over IP (VoIP), Text and Video over IP
services has introduced new challenges in managing and maintaining services has introduced new challenges in managing and maintaining
real-time voice/text/video quality, reliability, and overall real-time voice/text/video quality, reliability, and overall
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
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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 types and The extension defined herein adds new SDP media types and
attributes, which enable establishment of media sessions where the attributes, which enable establishment of media sessions where the
media is looped back to the transmitter. Such media sessions will media is looped back to the transmitter. Such media sessions will
serve as monitoring and troubleshooting tools by providing the serve as monitoring and troubleshooting tools by providing the
means for measurement of more advanced VoIP, Real-time Text and means for measurement of more advanced VoIP, Real-time Text and
Video over IP 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.....................................7 3.2 SDP Answerer Behavior.....................................7
4. New SDP Attributes............................................7 4. New SDP Attributes............................................7
4.1 Loopback Type Attribute...................................7 4.1 Loopback Type Attribute...................................7
4.2 Loopback Role Attributes: loopback-source and loopback- 4.2 Loopback Role Attributes: loopback-source and loopback-
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7.1 Encapsulated Payload format..............................14 7.1 Encapsulated Payload format..............................14
7.2 Direct loopback RTP payload format.......................16 7.2 Direct loopback RTP payload format.......................16
8. SRTP Behavior................................................17 8. SRTP Behavior................................................17
9. RTCP Requirements............................................18 9. RTCP Requirements............................................18
10. Congestion Control..........................................18 10. Congestion Control..........................................18
11. Examples....................................................18 11. Examples....................................................18
11.1 Offer for specific media loopback type..................18 11.1 Offer for specific media loopback type..................18
11.2 Offer for choice of media loopback type.................19 11.2 Offer for choice of media loopback type.................19
11.3 Answerer rejecting loopback media.......................20 11.3 Answerer rejecting loopback media.......................20
12. Security Considerations.....................................21 12. Security Considerations.....................................21
13. Implementation Considerations...............................21 13. Implementation Considerations...............................22
14. IANA Considerations.........................................22 14. IANA Considerations.........................................22
[Note to RFC Editor: Please replace "XXXX" with the appropriate RFC
number on publication]..........................................22
14.1 SDP Attributes..........................................22 14.1 SDP Attributes..........................................22
14.2 Media Types.............................................23 14.2 Media Types.............................................23
15. Acknowledgements............................................31 15. Acknowledgements............................................31
16. Normative References........................................31 16. Normative References........................................31
17. Informative References......................................32 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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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 specification and attempting to An SDP offerer compliant to this specification and attempting to
establish a media session with media loopback MUST include establish a media session with media loopback MUST include
"loopback" media attributes for each individual media description "loopback" media attributes for each individual media description
in the offer message. The offerer MUST look for the "loopback" in the offer message. The offerer will look for the "loopback"
media attributes in the media description(s) of the response from media attributes in the media description(s) of the response from
the answer for confirmation that the request is accepted. the answer for 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 If an SDP answerer compliant to this specification receives 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 and it wants to accept such for the purposes of media-
loopback, 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
answer if it agrees to do the loopback. If the answerer does not answer. If the answerer does not want to do loopback or wants to
want to do loopback or wants to reject the "loopback" request for reject the "loopback" request for specific media descriptions, it
specific media descriptions, it MUST do so as defined in this MUST do so as defined in this section.
section.
An answerer MAY reject an offered stream (either with loopback- An answerer can 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 is rejected by setting the stream's media port number to zero in
in the answer as defined in RFC 3264 [RFC3264], or by rejecting the 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
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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
receive direction to a point after the encoder/decoder function in receive direction to a point after the encoder/decoder function in
the send direction. This effectively re-encapsulates the RTP the send direction. This effectively re-encapsulates the RTP
payload with the RTP/UDP/IP headers appropriate for sending it in payload with the RTP/UDP/IP headers appropriate for sending it in
the reverse direction. Any type of encoding related functions, the reverse direction. Any type of encoding related functions,
such as packet loss concealment, MUST NOT be part of this type of such as packet loss concealment, MUST NOT be part of this type of
loopback path. In this mode the RTP packets are looped back with a loopback path. In this mode the RTP packets are looped back with a
new payload type and format. Section 7 describes the payload new payload type and format. Section 7 describes the payload
formats that MUST be used for this type of loopback. This type of formats that are to be used for this type of loopback. This type
loopback applies to the encapsulated and direct loopback use-cases of loopback applies to the encapsulated and direct loopback use-
described in Section 1.1. cases 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 property media attributes [RFC4566] The loopback role defines two property media attributes [RFC4566]
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send packets from the 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 loopback 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 loops back 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; for incoming media is treated as if it were to be played; for example,
example, the media stream MAY receive treatment from Packet Loss the media stream may receive treatment from Packet Loss Concealment
Concealment (PLC) algorithms. The mirroring entity MUST re- (PLC) algorithms. The mirroring entity re-generates all the RTP
generate all the RTP header fields as it would when transmitting header fields as it would when transmitting media. The mirroring
media. The mirroring entity MAY choose to encode the loopback media entity MAY choose to encode the loopback media according to any of
according to any of the media descriptions supported by the the media descriptions supported by the offering entity.
offering entity. Furthermore, in cases where the same media type is Furthermore, in cases where the same media type is looped back, the
looped back, the mirroring entity MAY choose to preserve number of mirroring entity can choose to preserve number of frames/packet and
frames/packet and bitrate of the encoded media according to the bitrate of the encoded media according to the received media.
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 requirements prevent the use of should be used when bandwidth requirements prevent the use of
encapsulated RTP payload format. encapsulated RTP payload format.
7.1 Encapsulated Payload format 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 is
MUST be encapsulated in a separate encapsulating RTP packet; the encapsulated in a separate encapsulating RTP packet; the
encapsulated packet MUST be fragmented only if required (for encapsulated packet would be fragmented only if required (for
example: due to MTU limitations). example: due to MTU limitations).
7.1.1 Usage 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).
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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].
7.1.2 RTP Payload Structure 7.1.2 RTP Payload Structure
The outer RTP header of the encapsulating packet MUST be followed
by the payload header defined in this section, after any header The outer RTP header of the encapsulating packet is followed by the
payload header defined in this section, after any header
extension(s). If the received RTP packet has to be looped back in extension(s). If the received RTP packet has to be looped back in
multiple encapsulating packets due to fragmentation, the multiple encapsulating packets due to fragmentation, the
encapsulating RTP header in each packet MUST be followed by the encapsulating RTP header in each packet is followed by the payload
payload header defined in this section. The header is devised so header defined in this section. The header is devised so that the
that the loopback-source can decode looped back packets in the loopback-source can decode looped back packets in the presence of
presence of moderate packet loss [RFC3550]. The RTP payload of the moderate packet loss [RFC3550]. The RTP payload of the
encapsulating RTP packet starts with the payload header defined in encapsulating RTP packet starts with the payload header defined in
this section. 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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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 loops back each received RTP packet payload
payload (not header) in a separate RTP packet. (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-back 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.
7.2.1 Usage 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
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operates at a lower logical layer than RTP, and thus if both sides operates at a lower logical layer than RTP, and thus if both sides
negotiate to use SRTP, each side uses its own key, performs negotiate to use SRTP, each side uses its own key, performs
encryption/decryption, authentication, etc. Therefore the loopback encryption/decryption, authentication, etc. Therefore the loopback
function on the mirror occurs after the SRTP packet has been function on the mirror occurs after the SRTP packet has been
decrypted and authenticated, as a normal cleartext RTP packet decrypted and authenticated, as a normal cleartext RTP packet
without an MKI or authentication tag; once the 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- or payload is mirrored - either at the media-layer, direct packet-
layer, or encapsulated packet-layer - it is encrypted by the mirror layer, or encapsulated packet-layer - it is encrypted by the mirror
using its own key. using its own key.
In order to provide the same level of protection to both forward
and reverse media flows (media to and from the mirror), if SRTP is
used it MUST be used in both directions with the same properties.
9. RTCP Requirements 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 Run Length Encoding (RLE) report block, Duplicate RLE report Loss Run Length Encoding (RLE) report block, Duplicate RLE report
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implemented for all implementations and which features MAY be implemented for all implementations and which features MAY be
deferred if the complete 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.
14. IANA Considerations 14. IANA Considerations
[Note to RFC Editor: Please replace "XXXX" with the appropriate RFC [Note to RFC Editor: Please replace "XXXX" with the appropriate RFC
number on publication] number on publication]
14.1 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
Email address: kaynam.hedayat@exfo.com Email address: kaynam.hedayat@exfo.com
Telephone number: +1-978-367-5611 Telephone number: +1-978-367-5611
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