draft-ietf-mmusic-media-loopback-16.txt   draft-ietf-mmusic-media-loopback-17.txt 
Internet Draft K. Hedayat Internet Draft H. Kaplan (ed.)
Expires: March 6, 2012 EXFO Expires: August 12, 2012 Acme Packet
K. Hedayat
EXFO
N. Venna N. Venna
Saperix Saperix
P. Jones P. Jones
Cisco Systems, Inc. Cisco Systems, Inc.
A. Roychowdhury A. Roychowdhury
Hughes Systique Corp. Hughes Systique Corp.
C. SivaChelvan C. SivaChelvan
Cisco Systems, Inc. Cisco Systems, Inc.
N. Stratton N. Stratton
BlinkMind, Inc. BlinkMind, Inc.
September 6, 2011 March 10, 2012
An Extension to the Session Description Protocol (SDP) for Media An Extension to the Session Description Protocol (SDP) for Media
Loopback Loopback
draft-ietf-mmusic-media-loopback-16 draft-ietf-mmusic-media-loopback-17
Status of this Memo Status of this Memo
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Copyright Notice Copyright Notice
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Copyright (c) 2012 IETF Trust and the persons identified as the
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Abstract Abstract
The wide deployment of Voice over IP (VoIP), Real-time Text and The wide deployment of Voice over IP (VoIP), Text and Video over IP
Video over IP services has introduced new challenges in managing services has introduced new challenges in managing and maintaining
and maintaining voice/real-time Text/video quality, reliability, real-time voice/real-time Text/video quality, reliability, and
and overall performance. In particular, media delivery is an area overall performance. In particular, media delivery is an area that
that needs attention. One method of meeting these challenges is needs attention. One method of meeting these challenges is
monitoring the media delivery performance by looping media back to monitoring the media delivery performance by looping media back to
the transmitter. This is typically referred to as "active the transmitter. This is typically referred to as "active
monitoring" of services. Media loopback is especially popular in monitoring" of services. Media loopback is especially popular in
ensuring the quality of transport to the edge of a given VoIP, ensuring the quality of transport to the edge of a given VoIP,
Real-time Text or Video over IP service. Today in networks that Real-time Text or Video over IP service. Today in networks that
deliver real-time media, short of running 'ping' and 'traceroute' deliver real-time media, short of running 'ping' and 'traceroute'
to the edge, service providers are left without the necessary tools to the edge, service providers are left without the necessary tools
to actively monitor, manage, and diagnose quality issues with their to actively monitor, manage, and diagnose quality issues with their
service. The extension defined herein adds new SDP media service. The extension defined herein adds new SDP media
attributes which enables establishment of media sessions where the attributes which enables 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...................................................5
3. Offering Entity Behavior ...................................... 6 3. Offering Entity Behavior......................................6
4. Answering Entity Behavior ..................................... 6 4. Answering Entity Behavior.....................................6
5. SDP Constructs Syntax ......................................... 6 5. SDP Constructs Syntax..............Error! Bookmark not defined.
5.1 Loopback Type Attribute ................................... 6 5.1 Loopback Type Attribute...................................7
5.2 Loopback Mode Attribute ................................... 7 5.2 Loopback Mode Attribute...................................7
5.3 Generating the Offer for Loopback Session 5.3 Generating the Offer for Loopback Session.................8
5.4 Generating the Answer for Loopback Session ................ 9 5.4 Generating the Answer for Loopback Session................9
5.5 Offerer Processing of the Answer ......................... 11 5.5 Offerer Processing of the Answer.........................11
5.6 Modifying the Session .................................... 11 5.6 Modifying the Session....................................11
5.7 Establishing Sessions Between Entities Behind NAT ........ 11 5.7 Establishing Sessions Between Entities Behind NAT........12
6. RTP Requirements ............................................. 11 6. RTP Requirements.............................................12
7. Payload formats for Packet loopback .......................... 12 7. Payload formats for Packet loopback..........................12
7.1 Encapsulated Payload format .............................. 12 7.1 Encapsulated Payload format..............................13
7.2 Direct loopback RTP payload format ....................... 15 7.2 Direct loopback RTP payload format.......................15
8. RTCP Requirements ............................................ 16 8. RTCP Requirements............................................16
9. Congestion Control ........................................... 16 9. Congestion Control...........................................17
10. Examples .................................................... 17 10. Examples....................................................17
10.1 Offer for specific media loopback type .................. 17 10.1 Offer for specific media loopback type..................17
10.2 Offer for choice of media loopback type ................. 17 10.2 Offer for choice of media loopback type.................18
10.3 Response to INVITE request rejecting loopback media ..... 18 10.3 Response to INVITE request rejecting loopback media.....19
11. Security Considerations ..................................... 19 11. Security Considerations.....................................19
12. Implementation Considerations ............................... 19 12. Implementation Considerations...............................20
13. IANA Considerations ......................................... 20 13. IANA Considerations.........................................20
13.1 SDP Attributes .......................................... 20 13.1 SDP Attributes..........................................20
13.2 MIME Types .............................................. 21 13.2 MIME Types..............................................21
14. Normative References ........................................ 30 14. Normative References........................................30
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 VoIP, Real-time 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
services. services.
The goal of active monitoring is to measure the media quality of a The goal of active monitoring is to measure the media quality of a
VoIP, Real-time Text or Video over IP session. A way to achieve VoIP, Text or Video over IP session. A way to achieve this goal is
to request an endpoint to loop media back to the other endpoint and
endpoint and to provide media statistics (e.g., RTCP and RTCP XR to provide media statistics (e.g., RTCP and RTCP XR information).
information). Another method involves deployment of special Another method involves deployment of special endpoints that always
endpoints that always loop incoming media back for sessions. loop incoming media back for sessions. Although the latter method
Although the latter method has been used and is functional, it does has been used and is functional, it does not scale to support large
not scale to support large networks and introduces new network networks and introduces new network management challenges.
management challenges. Further, it does not offer the granularity Further, it does not offer the granularity of testing a specific
of testing a specific endpoint that may be exhibiting problems. endpoint that may be exhibiting problems.
The extension defined in this memo introduces new SDP media The extension defined in this memo introduces new SDP media
attributes that enable establishment of media sessions where the attributes that enable establishment of media sessions where the
media is looped back to the transmitter. The offer/answer model media is looped back to the transmitter. The offer/answer model
[RFC3264] is used to establish a loopback connection. Furthermore, [RFC3264] is used to establish a loopback connection. Furthermore,
this extension provides guidelines on handling RTP [RFC3550], as this extension provides guidelines on handling RTP [RFC3550], as
well as usage of RTCP [RFC3550] and RTCP XR [RFC3611] for reporting well as usage of RTCP [RFC3550] and RTCP XR [RFC3611] for reporting
media related measurements. 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
skipping to change at page 4, line 24 skipping to change at page 4, line 27
"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. The negotiation also includes details which one acts in which role. The negotiation also includes details
such as the type of loopback to be used. such as the type of loopback to be used.
This specification supports three use cases: "encapsulated packet This specification supports three use cases: "encapsulated packet
loopback", "direct loopback", and "media loopback". These are loopback", "direct loopback", and "media loopback". These are
distinguished by the treatment of incoming RTP packets at the distinguished by the treatment of incoming RTP packets at the
loopback mirror. loopback mirror.
As a supplement to these use cases, this specification also allows
the loopback source to request the loopback mirror to begin sending
a media stream to the loopback source, ending when the mirror
begins to receive packets from the source. This facility is needed
in some circumstances to establish the media path through
middleboxes lying between the peers.
1.1.1 Encapsulated Packet Loopback 1.1.1 Encapsulated Packet Loopback
In the encapsulated packet loopback case, the entire incoming RTP In the encapsulated packet loopback case, the entire incoming RTP
packet is encapsulated as payload within an outer payload type that packet is encapsulated as payload within an outer payload type that
is specific to this use case and specified below (Section 7.1). is specific to this use case and specified below (Section 7.1).
The encapsulated packet is returned to the loopback source. The The encapsulated packet is returned to the loopback source. The
loopback source can generate statistics for one-way path loopback source can generate statistics for one-way path
performance up to the RTP level for each direction of travel by performance up to the RTP level for each direction of travel by
examining sequence numbers and timestamps in the outer header and examining sequence numbers and timestamps in the outer header and
the encapsulated RTP packet payload. The loopback source can also the encapsulated RTP packet payload. The loopback source can also
skipping to change at page 6, line 5 skipping to change at page 5, line 41
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 reencoded according to an outgoing format determined by then reencoded according to an outgoing format determined by
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.
3. Offering Entity Behavior SDP: Session Description Protocol, as defined in [RFC4566]. This
document assumes the SDP offer/answer model is followed, per
[RFC3264], but does not assume any specific protocol for carrying
the SDP.
An offering entity compliant to this memo and attempting to The following terms are borrowed from [RFC3264] definitions: offer,
establish a media session with media loopback MUST include offerer, answer, answerer, and agent.
"loopback" media attributes for each individual media description
in the offer message. The offering entity MUST look for the
"loopback" media attributes in the media description(s) of the
response from the answering entity for confirmation that the
request is accepted.
4. Answering Entity Behavior 3. SDP Offerer Behavior
An answering entity compliant to this specification and receiving An SDP offerer compliant to this memo and attempting to establish a
an offer containing media descriptions with the "loopback" media media session with media loopback MUST include "loopback" media
attributes for each individual media description in the offer
message. The offerer MUST look for the "loopback" media attributes
in the media description(s) of the response from the answer for
confirmation that the request is accepted.
4. SDP Answerer Behavior
An SDP answerer compliant to this specification and receiving an
offer containing media descriptions with the "loopback" media
attributes MUST acknowledge the request by including the received 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
response if it agrees to do the loopback. If the answerer does not asnwer if it agrees to do the loopback. If the answerer does not
want to do loopback or wants to reject the "loopback" request for want to do loopback or wants to reject the "loopback" request for
specific media types, it MAY do so as defined in section 5.4.1 of specific media types, it MAY do so as defined in section Error!
this specification. Reference source not found. of this specification.
An answering entity that is not compliant to this specification and An answerer MAY reject an offered stream (either with loopback-
which receives an offer with the "loopback" media attributes MAY source or loopback-mirror) if the loopback-type is not specified,
ignore the attribute and treat the incoming offer as a normal the specified loopback-type is not supported, or the endpoint
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
in the answer as defined in RFC 3264 [RFC3264], or by rejecting the
entire offer (e.g., by rejecting the session request entirely).
5. SDP Constructs Syntax Note that an answerer that is not compliant to this specification
and which receives an offer with the "loopback" media attributes
would ignore the attribute and treat the incoming offer as a normal
request. If the offerer does not wish to establish a "normal" RTP
session, it would need to terminate the session upon receiving such
an answer.
Two new media attributes are defined: one indicates the type of 5. New SDP Attributes
loopback and the other indicates the mode of the loopback.
5.1 Loopback Type Attribute Three new SDP media-level attributes are defined: one indicates the
type of loopback, and the other two define the mode of the
loopback.
The loopback type is a property media attribute with the following 5.1 Loopback Type Attribute
This specification defines a new 'loopback' attribute, which
indicates the type of loopack that the agent is able to do. The
loopback type is a property media attribute with the following
syntax: 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:"
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
skipping to change at page 7, line 31 skipping to change at page 7, line 47
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. formats that MUST be used for this type of loopback.
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. the sender.
5.2 Loopback Mode Attribute 5.2 Loopback Mode Attribute
The loopback mode is a value media attribute that is used to The loopback mode defines two value media attributes that are used
indicate the mode of the loopback. These attributes are additional to indicate the mode of the loopback. These attributes are
mode attributes like sendonly, recvonly, etc. The syntax of the additional mode attributes like sendonly, recvonly, etc. The
loopback mode media attribute is: syntax of the loopback mode media attributes are based on the
following:
a=<loopback-mode>:<fmt>... a=<loopback-mode>:<fmt>...
The loopback-mode values are loopback-source and loopback-mirror. The loopback-mode values are 'loopback-source' and '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.
loopback-mirror: This attribute specifies that the entity that loopback-mirror: This attribute specifies that the entity that
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.
skipping to change at page 8, line 16 skipping to change at page 8, line 36
SDP is willing to send. When loopback-mode is specified as SDP is willing to send. When loopback-mode is specified as
loopback-mirror, the media format corresponds to the RTP payload loopback-mirror, the media format corresponds to the RTP payload
types the mirror is willing to receive. The "m=" line in the SDP types the mirror is willing to receive. The "m=" line in the SDP
MUST include all the payload types that will be used during the MUST include all the payload types that will be used during the
loopback session including those specified in the loopback-mode loopback session including those specified in the loopback-mode
attribute line. The complete payload space for the call is attribute line. The complete payload space for the call is
specified in the "m=" line and the rtpmap attribute is used to map specified in the "m=" line and the rtpmap attribute is used to map
from the payload type number to an encoding name denoting the from the payload type number to an encoding name denoting the
payload format to be used. payload format to be used.
5.3 Generating the Offer for Loopback Session 5.3 Generating the 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-mode parameters in a valid SDP both the loopback-type and loopback-mode 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:0 8 100 a=loopback-source:0 8 100
a=rtpmap:0 pcmu/8000 a=rtpmap:0 pcmu/8000
a=rtpmap:8 pcma/8000 a=rtpmap:8 pcma/8000
a=rtpmap:100 G7221/16000/1 a=rtpmap:100 G7221/16000/1
Note: A loopback offer in a given media description MUST NOT A loopback offer in a given media description MUST NOT contain the
contain the standard mode attributes sendonly, recvonly, sendrecv, standard mode attributes sendonly, recvonly, sendrecv, or inactive.
or inactive. The loopback-mode attributes (loopback-source and
loopback-mirror) replace the standard attributes. The loopback-mode attributes (loopback-source and loopback-mirror)
replace the standard attributes.
The offerer may offer more than one loopback-type in the SDP offer. The offerer may offer more than one loopback-type in the SDP offer.
The port number and the address in the offer (m= line) indicate The port number and the address in the offer (m/c= lines) indicate
where the offerer would like to send and receive the media stream. where the offerer would like to send and receive the media stream.
The payload type numbers indicate the value of the payload the The payload type numbers indicate the value of the payload the
offerer expects to send and receive. If the offerer is the offerer expects to send and receive. If the offerer is the
loopback-source, the subset of payload types indicated in the loopback-source, the subset of payload types indicated in the
a=loopback-source line are the payload types for the codecs the a=loopback-source line are the payload types for the codecs the
offerer is willing to send. However, the answer might indicate a offerer is willing to send. However, the answer might indicate a
different payload type number for the same codec in the loopback- different payload type number for the same codec in the loopback-
mirror line. In that case, the offerer MUST send the payload type mirror line. In that case, the offerer MUST send the payload type
received in the answer. If the offerer is the loopback-mirror, the received in the answer. If the offerer is the loopback-mirror, the
subset of payload types indicated in the a=loopback-mirror line are subset of payload types indicated in the a=loopback-mirror line are
the payload types for the codecs the offerer is willing to receive. the payload types for the codecs the offerer is willing to receive.
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
payload 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:0 8 a=loopback-source:0 8
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:0 8 a=loopback-source:0 8
a=rtpmap:112 rtploopback/8000 a=rtpmap:112 rtploopback/8000
5.4 Generating the Answer for Loopback Session 5.4 Generating the Answer for Loopback Session
As with the offer, a loopback answer in a given media description As with the offer, an SDP answer for loopback MUST NOT contain the
MUST NOT contain the standard mode attributes sendonly, recvonly, standard mode attributes sendonly, recvonly, sendrecv, or inactive.
sendrecv, or inactive. The loopback-mode attributes (loopbackThe The port number and the address in the answer (m/c= lines) indicate
port number and the address in the answer (m= line) indicate where where the answerer would like to receive the media stream. The
the answerer would like to receive the media stream. The payload payload type numbers indicate the value of the payload types the
type numbers indicate the value of the payload types the answerer answerer expects to send and receive. The loopback-mode attributes
expects to send and receive. If the offerer is the loopback- (a=loopback-source or a=loopback-miror) MUST contain at least one
source, the answerer MUST be a loopback-mirror and the subset of codec the answerer is willing to send or receive depending on
payload types indicated in the a=loopback-mirror line are the whether it is the loopback-source or the loopback-mirror. In
payload types for the codecs the answerer is willing to receive. addition, the "m=" line MUST contain at least one codec that the
Similarly, if the offerere is the loopback-mirror, the answerer answerer is willing to send or receive depending on whether it is
MUST be aloopback-source and the subset of payload types indicated the loopback-mirror or the loopback-source.
in the a=loopback-source line are the payload types for the codecs
the answerer is willing to send. If the offerer is the loopback-source, the answerer MUST be a
loopback-mirror and the subset of payload types indicated in the
a=loopback-mirror line are the payload types for the codecs the
answerer is willing to receive. Similarly, if the offerer is the
loopback-mirror, the answerer MUST be aloopback-source and the
subset of payload types indicated in the a=loopback-source line are
the payload types for the codecs the answerer is willing to send.
If an answerer wishes to accept the loopback request it MUST If an answerer wishes to accept the loopback request it MUST
include both the loopback mode and loopback type attribute in the include both the loopback mode 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 that answerer is capable
of supporting the requested loopback-type. of 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:0 8 a=loopback-source:0 8
skipping to change at page 11, line 5 skipping to change at page 11, line 31
m=audio 41352 RTP/AVP 0 8 112 m=audio 41352 RTP/AVP 0 8 112
a=loopback:rtp-pkt-loopback a=loopback:rtp-pkt-loopback
a=loopback-mirror:0 8 a=loopback-mirror:0 8
a=rtpmap:112 encaprtp/8000 a=rtpmap:112 encaprtp/8000
m=audio 41352 RTP/AVP 0 8 113 m=audio 41352 RTP/AVP 0 8 113
a=loopback:rtp-pkt-loopback a=loopback:rtp-pkt-loopback
a=loopback-mirror:0 8 a=loopback-mirror:0 8
a=rtpmap:113 rtploopback/8000 a=rtpmap:113 rtploopback/8000
5.4.1 Rejecting the Loopback Offer The previous examples used the 'encaprtp' and 'rtploopback'
encoding names, which will be defined in sections 7.1.3 and 7.2.3.
An offered stream (either with loopback-source or loopback-mirror)
MAY be rejected if the loopback-type is not specified, the
specified loopback-type is not supported, or the endpoint cannot
honor the offer for any other reason. The Loopback request may be
rejected by setting the media port number to zero in the answer as
per RFC 3264 [RFC3264].
5.5 Offerer Processing of the Answer
The answer to a loopback-source MUST be loopback-mirror. The 5.5 Offerer Processing of the Answer
answer to a loopback-mirror MUST be loopback-source. The
loopback-mode line MUST contain at least one codec the answerer is
willing to send or receive depending on whether it is the loopback-
source or the loopback-mirror. In addition, the "m=" line MUST
contain at least one codec that the answerer is willing to send or
receive depending on whether it is the loopback-mirror or the
loopback-source.
If the answer does not contain a=loopback-mirror or If the received answer does not contain a=loopback-mirror or
a=loopback-source, it is assumed that the loopback extensions are a=loopback-source, it is assumed that the loopback extensions are
not supported by the target UA. not supported by the remote agent. This is not a protocol failure,
and instead merely completes the SDP offer/answer exchange with
whatever normal rules apply; the offerer MAY decide to end the
established RTP session (if any) through normal means of the upper-
layer signaling protocol (e.g., by sending a SIP BYE).
5.6 Modifying the Session 5.6 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. In case of SIP this is defined in section 8 of RFC 3264 session, as defined in section 8 of RFC 3264 [RFC3264]. This also
[RFC3264]. This also includes transitioning from a normal media includes transitioning from a normal media processing mode to
processing mode to loopback mode, and vice a versa. loopback mode, and vice a versa.
5.7 Establishing Sessions Between Entities Behind NAT 5.7 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. Loopback sessions sessions between entities that are behind NATs. Loopback sessions
that involve one or more end points behind NATs SHOULD use these that involve one or more end points behind NATs SHOULD use these
general solutions wherever possible. general solutions wherever possible.
6. RTP Requirements 6. RTP Requirements
A loopback-mirror that is compliant to this specification and A loopback-mirror that is compliant to this specification and
accepting a media with rtp-pkt-loopback loopback-type MUST loopback accepting a media with rtp-pkt-loopback loopback-type MUST loopback
the incoming RTP packets using either the encapsulated RTP payload the 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.
An answering entity that is compliant to this specification and An answering entity that is compliant to this specification and
accepting a media with the loopback type rtp-media-loopback MUST accepting a media with the loopback type rtp-media-loopback MUST
transmit all received media back to the sender. The incoming media transmit all received media back to the sender, unless congestion
MUST be treated as if it were to be played (e.g. the media stream feedback or other lower-layer constraints prevent it from doing so.
MAY receive treatment from PLC algorithms). The answering entity The incoming media MUST be treated as if it were to be played (e.g.
MUST re-generate all the RTP header fields as it would when the media stream MAY receive treatment from PLC algorithms). The
transmitting media. The answering entity MAY choose to encode the answering entity MUST re-generate all the RTP header fields as it
loopback media according to any of the media descriptions supported would when transmitting media. The answering entity MAY choose to
by the offering entity. Furthermore, in cases where the same media encode the loopback media according to any of the media
type is looped back, the answering entity MAY choose to preserve descriptions supported by the offering entity. Furthermore, in
number of frames/packet and bitrate of the encoded media according cases where the same media type is looped back, the answering
to the received media. entity MAY choose to preserve number of frames/packet and bitrate
of the encoded media according to the received media.
7. Payload formats for Packet loopback 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
skipping to change at page 12, line 48 skipping to change at page 13, line 18
loopback-mirror. As described in RFC 3550 [RFC3550], sequence loopback-mirror. As described in RFC 3550 [RFC3550], sequence
numbers and timestamps in the RTP header are generated with initial numbers and timestamps in the RTP header are generated with initial
random values for security reasons. If this were not mandated and random values for security reasons. If this were not mandated and
the source payload is sequence number aware, the loopback-mirror the source payload is sequence number aware, the loopback-mirror
will be required to understand that payload format to generate will be required to understand that payload format to generate
looped back packets that do not violate RFC 3550 [RFC3550]. looped back packets that do not violate RFC 3550 [RFC3550].
Requiring looped back packets to be in one of the two formats means Requiring looped back packets to be in one of the two formats means
loopback-mirror does not have to look into the actual payload loopback-mirror does not have to look into the actual payload
received before generating the loopback packets. received before generating the loopback packets.
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
MUST be encapsulated in a different packet, the encapsulated packet MUST be encapsulated in a different packet, the encapsulated packet
MUST be fragmented only if required (for example: due to MTU MUST be fragmented only if required (for example: due to MTU
limitations). 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
skipping to change at page 15, line 18 skipping to change at page 15, line 31
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 encapsulated stream, so dynamic payload type assignment for the encapsulated stream, so dynamic payload
type numbers MUST be used. The binding to the name is indicated by type numbers MUST be used. The binding to the name is indicated by
an rtpmap attribute. The name used in this binding is "encaprtp". an rtpmap 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 where the 16 byte overhead of the encapsulated payload format is
significant. This payload format MUST NOT be used in cases where significant. This payload format MUST NOT be used in cases where
the MTU on the loopback path will cause fragmentation of looped the MTU on the loopback path will cause fragmentation of looped
back RTP packets. When using this payload format, the receiver back RTP packets. When using this payload format, the receiver
MUST loop back each received packet in a separate RTP packet. MUST loop back each received packet in a separate RTP packet.
7.2.1 Usage of RTP Header fields 7.2.1 Usage of RTP Header fields
skipping to change at page 16, line 25 skipping to change at page 16, line 41
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. 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 entity that is answering entities. An offering or answering entity 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 client or and RTCP-XR per RFC 3611 [RFC3611]. Furthermore, if the client or
the server choose to support RTCP-XR, they SHOULD support RTCP-XR the server 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 client and the 4.1, 4.2, 4.6, and 4.7 of RFC 3611 [RFC3611]. The client and the
server MAY support other RTCP-XR reporting blocks as defined by RFC server MAY support other RTCP-XR reporting blocks as defined by RFC
3611 [RFC3611]. 3611 [RFC3611].
9. Congestion Control 9. Congestion Control
All the participants in a loopback session SHOULD implement All the participants in a loopback session SHOULD implement
congestion control mechanisms as defined by the RTP profile under congestion control mechanisms as defined by the RTP profile under
which the loopback mechanism is implemented. For audio video which the loopback mechanism is implemented. For audio video
profiles, implementations SHOULD conform to the mechanism defined profiles, implementations SHOULD conform to the mechanism defined
in Section 2 of RFC 3551. in Section 2 of RFC 3551.
10. Examples 10. 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 10.1 Offer for specific media loopback type
A client sends an INVITE request with offer SDP 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=Example s=Example
i=An example session i=An example session
e=alice@example.com e=alice@example.com
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
a=loopback-source:0 a=loopback-source:0
a=rtpmap:0 pcmu/8000 a=rtpmap:0 pcmu/8000
The client is offering to source the media and expects the server The agent is offering to source the media and expects the answering
to mirror the RTP stream per rtp-media-loopback loopback type. agent to mirror the RTP stream per rtp-media-loopback loopback
type.
A server sends a response with answer SDP which looks like: An answering agent sends an SDP answer which looks like:
v=0 v=0
o=bob 2890844526 2890842807 IN IP4 host.biloxi.example.com o=bob 1234567890 1122334455 IN IP4 host.biloxi.example.com
s=Example s=Example
i=An example session i=An example session
e=bob@example.com e=bob@example.com
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:0 a=loopback-mirror:0
a=rtpmap:0 pcmu/8000 a=rtpmap:0 pcmu/8000
The server is accepting to mirror the media from the client at the The answerer is accepting to mirror the media from the offerer at
media level. the media level.
10.2 Offer for choice of media loopback type 10.2 Offer for choice of media loopback type
A client sends an INVITE request with offer SDP 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=Example s=Example
i=An example session i=An example session
e=alice@example.com e=alice@example.com
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
a=loopback-source:0 a=loopback-source:0
a=rtpmap:0 pcmu/8000 a=rtpmap:0 pcmu/8000
a=rtpmap:112 encaprtp/8000 a=rtpmap:112 encaprtp/8000
a=rtpmap:113 rtploopback/8000 a=rtpmap:113 rtploopback/8000
The client is offering to source the media and expects the server The offerer is offering to source the media and expects the
to mirror the RTP stream at either the media or rtp level. answerer to mirror the RTP stream at either the media or rtp level.
A server sends a response with answer SDP which looks like: An answering agent sends an SDP answer which looks like:
v=0 v=0
o=box 2890844526 2890842807 IN IP4 host.biloxi.example.com o=box 1234567890 1122334455 IN IP4 host.biloxi.example.com
s=Example s=Example
i=An example session i=An example session
e=bob@example.com e=bob@example.com
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:0 a=loopback-mirror:0
a=rtpmap:0 pcmu/8000 a=rtpmap:0 pcmu/8000
a=rtpmap:112 encaprtp/8000 a=rtpmap:112 encaprtp/8000
The server is accepting to mirror the media from the client at the The answerer is accepting to mirror the media from the offerer at
packet level using the encapsulated RTP payload format. the packet level using the encapsulated RTP payload format.
10.3 Response to INVITE request rejecting loopback media 10.3 Answerer rejecting loopback media
A client sends an INVITE request with offer SDP 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=Example s=Example
i=An example session i=An example session
e=user@example.com e=user@example.com
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
a=loopback-source:0 a=loopback-source:0
a=rtpmap:0 pcmu/8000 a=rtpmap:0 pcmu/8000
The client is offering to source the media and expects the server The offerer is offering to source the media and expects the
to mirror the RTP stream at the media level. answerer to mirror the RTP stream at the media level.
A server sends a response with answer SDP which looks like: An answering agent sends an SDP answer which looks like:
v=0 v=0
o=bob 2890844526 2890842807 IN IP4 host.biloxi.example.com o=bob 1234567890 1122334455 IN IP4 host.biloxi.example.com
s=Example s=Example
i=An example session i=An example session
e=user@example.com e=user@example.com
c=IN IP4 host.biloxi.example.com c=IN IP4 host.biloxi.example.com
t=0 0 t=0 0
m=audio 0 RTP/AVP 0 m=audio 0 RTP/AVP 0
a=loopback:rtp-media-loopback a=loopback:rtp-media-loopback
a=loopback-mirror:0 a=loopback-mirror:0
a=rtpmap:0 pcmu/8000 a=rtpmap:0 pcmu/8000
NOTE: Loopback request may be rejected by either not including the 11. Security Considerations
loopback mode attribute (for backward compatibility) or setting the
media port number to zero, or both, in the response.
11. Security Considerations
The security considerations of [RFC3261] and [RFC3264] apply. The security considerations of [RFC3264] apply. Furthermore, given
Furthermore, given that media loopback may be automated without the that media loopback may be automated without the end user's
end user's knowledge, the server of the media loopback should be knowledge, the server of the media loopback should be aware of
aware of denial of service attacks. It is recommended that sessions denial of service attacks. It is recommended that sessions with
with media loopback are authenticated and the frequency of such media loopback are authenticated and the frequency of such sessions
sessions is limited by the server. is limited by the server.
12. Implementation Considerations 12. 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 believed that the solution may not be light-weight enough for
the common case. In light of this concern, this section clarifies the common case. In light of this concern, this section clarifies
which features of the loopback proposal MUST be implemented for all which features of the loopback proposal MUST be implemented for all
implementations and which features MAY be deferred if the complete implementations and which features MAY be deferred if the complete
solution is not desired. solution is not desired.
All implementations MUST support the rtp-pkt-loopback option for All implementations MUST support the rtp-pkt-loopback option for
loopback-type attribute. In addition, for the loopback-mode loopback-type attribute. In addition, for the loopback-mode
attribute, all implementations of an offerer MUST at a minimum be attribute, all implementations of an offerer MUST at a minimum be
able to act as a loopback-source. All implementation MUST also at a able to act as a loopback-source. All implementation MUST also at a
minimum support the direct media loopback payload type. The rtp- minimum support the direct media loopback payload type. The rtp-
media-loopback attribute MAY be implemented in complete media-loopback attribute MAY be implemented in complete
implementations of this draft. implementations of this draft.
13. IANA Considerations 13. IANA Considerations
13.1 SDP Attributes 13.1 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
skipping to change at page 21, line 4 skipping to change at page 21, line 15
as a loopback-mirror. as a loopback-mirror.
Allowed attribute values: The parameter to 'loopback-source' is Allowed attribute values: The parameter to 'loopback-source' is
a media format ("<fmt>") description a media format ("<fmt>") description
as defined in RFC 4566 Section 5.14. as defined in RFC 4566 Section 5.14.
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: The parameter to 'loopback-mirror' is Allowed attribute values: The parameter to 'loopback-mirror' is
a media format ("<fmt>") description a media format ("<fmt>") description
as defined in RFC 4566 Section 5.14. as defined in RFC 4566 Section 5.14.
13.2 MIME Types 13.2 MIME Types
The IANA has registered the following MIME types: The IANA has registered the following MIME types:
13.2.1 audio/encaprtp 13.2.1 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
skipping to change at page 30, line 13 skipping to change at page 30, line 23
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. Normative References 14. Normative References
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G.,
Johnston, A., Peterson, J., Sparks, R., Handley, M.
and E. Schooler, "SIP: Session Initiation Protocol",
RFC 3261, June 2002.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer [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.,
Duffield, N., Friedman, T., Hedayat, K., Sarac, K. Duffield, N., Friedman, T., Hedayat, K., Sarac, K.
skipping to change at page 31, line 13 skipping to change at page 31, line 17
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.
Authors' Addresses Authors' Addresses
Hadriel Kaplan
Acme Packet
100 Crosby Drive
Bedford, MA 01730
USA
EMail: hkaplan@acmepacket.com
URI: http://www.acmepacket.com
Kaynam Hedayat Kaynam Hedayat
EXFO EXFO
285 Mill Road 285 Mill Road
Chelmsford, MA 01824 Chelmsford, MA 01824
US US
Phone: +1 978 367 5611 Phone: +1 978 367 5611
EMail: kaynam.hedayat@exfo.com EMail: kaynam.hedayat@exfo.com
URI: http://www.exfo.com/ URI: http://www.exfo.com/
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