draft-ietf-avtext-rtp-duplication-04.txt   draft-ietf-avtext-rtp-duplication-05.txt 
AVTEXT A. Begen AVTEXT A. Begen
Internet-Draft Cisco Internet-Draft Cisco
Intended status: Standards Track C. Perkins Intended status: Standards Track C. Perkins
Expires: April 05, 2014 University of Glasgow Expires: August 11, 2014 University of Glasgow
October 02, 2013 February 7, 2014
Duplicating RTP Streams Duplicating RTP Streams
draft-ietf-avtext-rtp-duplication-04 draft-ietf-avtext-rtp-duplication-05
Abstract Abstract
Packet loss is undesirable for real-time multimedia sessions, but can Packet loss is undesirable for real-time multimedia sessions, but can
occur due to congestion, or other unplanned network outages. This is occur due to congestion, or other unplanned network outages. This is
especially true for IP multicast networks, where packet loss patterns especially true for IP multicast networks, where packet loss patterns
can vary greatly between receivers. One technique that can be used can vary greatly between receivers. One technique that can be used
to recover from packet loss without incurring unbounded delay for all to recover from packet loss without incurring unbounded delay for all
the receivers is to duplicate the packets and send them in separate the receivers is to duplicate the packets and send them in separate
redundant streams. This document explains how Real-time Transport redundant streams. This document explains how Real-time Transport
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
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Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 05, 2014. This Internet-Draft will expire on August 11, 2014.
Copyright Notice Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
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1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology and Requirements Notation . . . . . . . . . . . . 3 2. Terminology and Requirements Notation . . . . . . . . . . . . 3
3. Dual Streaming Use Cases . . . . . . . . . . . . . . . . . . 3 3. Dual Streaming Use Cases . . . . . . . . . . . . . . . . . . 3
3.1. Temporal Redundancy . . . . . . . . . . . . . . . . . . . 3 3.1. Temporal Redundancy . . . . . . . . . . . . . . . . . . . 3
3.2. Spatial Redundancy . . . . . . . . . . . . . . . . . . . 4 3.2. Spatial Redundancy . . . . . . . . . . . . . . . . . . . 4
3.3. Dual Streaming over a Single Path or Multiple Paths . . . 4 3.3. Dual Streaming over a Single Path or Multiple Paths . . . 4
3.4. Requirements . . . . . . . . . . . . . . . . . . . . . . 5 3.4. Requirements . . . . . . . . . . . . . . . . . . . . . . 5
4. Use of RTP and RTCP with Temporal Redundancy . . . . . . . . 6 4. Use of RTP and RTCP with Temporal Redundancy . . . . . . . . 6
4.1. RTCP Considerations . . . . . . . . . . . . . . . . . . . 6 4.1. RTCP Considerations . . . . . . . . . . . . . . . . . . . 6
4.2. Signaling Considerations . . . . . . . . . . . . . . . . 6 4.2. Signaling Considerations . . . . . . . . . . . . . . . . 7
5. Use of RTP and RTCP with Spatial Redundancy . . . . . . . . . 8 5. Use of RTP and RTCP with Spatial Redundancy . . . . . . . . . 7
5.1. RTCP Considerations . . . . . . . . . . . . . . . . . . . 8 5.1. RTCP Considerations . . . . . . . . . . . . . . . . . . . 8
5.2. Signaling Considerations . . . . . . . . . . . . . . . . 8 5.2. Signaling Considerations . . . . . . . . . . . . . . . . 8
6. Use of RTP and RTCP with Temporal and Spatial Redundancy . . 9 6. Use of RTP and RTCP with Temporal and Spatial Redundancy . . 9
7. Congestion Control Considerations . . . . . . . . . . . . . . 9 7. Congestion Control Considerations . . . . . . . . . . . . . . 9
8. Security Considerations . . . . . . . . . . . . . . . . . . . 10 8. Security Considerations . . . . . . . . . . . . . . . . . . . 10
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
11.1. Normative References . . . . . . . . . . . . . . . . . . 11 11.1. Normative References . . . . . . . . . . . . . . . . . . 11
11.2. Informative References . . . . . . . . . . . . . . . . . 11 11.2. Informative References . . . . . . . . . . . . . . . . . 11
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the receiving end, the node responsible for duplicate suppression can the receiving end, the node responsible for duplicate suppression can
look into various RTP header fields, for example SSRC and sequence look into various RTP header fields, for example SSRC and sequence
number, to identify and suppress the duplicate packets. number, to identify and suppress the duplicate packets.
If source-specific multicast (SSM) transport is used to carry such If source-specific multicast (SSM) transport is used to carry such
redundant streams, there will be a separate SSM session for each redundant streams, there will be a separate SSM session for each
redundant stream since the streams are sourced from different redundant stream since the streams are sourced from different
interfaces (i.e., IP addresses). Thus, the receiving host has to interfaces (i.e., IP addresses). Thus, the receiving host has to
join each SSM session separately. join each SSM session separately.
Alternatively, an RTP source might send the redundant streams to Alternatively, destination host could also have multiple IP addresses
separate IP destination addresses. for an RTP source to send the redundant streams to.
3.3. Dual Streaming over a Single Path or Multiple Paths 3.3. Dual Streaming over a Single Path or Multiple Paths
Having described the characteristics of the streams, one can reach Having described the characteristics of the streams, one can reach
the following conclusions: the following conclusions:
1. When two routing-plane identical streams are used, the two 1. When two routing-plane identical streams are used, the two
streams will have identical IP headers. This makes it streams will have identical IP headers. This makes it
impractical to forward the packets onto different paths. In impractical to forward the packets onto different paths. In
order to minimize packet loss, the packets belonging to one order to minimize packet loss, the packets belonging to one
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To summarize, dual streaming allows an application and a network to To summarize, dual streaming allows an application and a network to
work together to provide a near zero-loss transport with a bounded or work together to provide a near zero-loss transport with a bounded or
minimum delay. The additional advantage includes a predictable minimum delay. The additional advantage includes a predictable
bandwidth overhead that is proportional to the minimum bandwidth bandwidth overhead that is proportional to the minimum bandwidth
needed for the multimedia session, but independent of the number of needed for the multimedia session, but independent of the number of
receivers experiencing a packet loss and requesting a retransmission. receivers experiencing a packet loss and requesting a retransmission.
For a survey and comparison of similar approaches, refer to [IC2011]. For a survey and comparison of similar approaches, refer to [IC2011].
3.4. Requirements 3.4. Requirements
One of the following conditions is REQUIRED to hold in applications One of the following conditions is currently REQUIRED to hold in
using this specification: applications using this specification:
o The original and duplicate RTP streams are carried (with their own o The original and duplicate RTP streams are carried (with their own
SSRCs) in the same "m" line (There could be other RTP streams SSRCs) in the same "m" line (There could be other RTP streams
listed in the same "m" line) listed in the same "m" line).
o The original and duplicate RTP streams are carried in separate "m" o The original and duplicate RTP streams are carried in separate "m"
lines and there is no other RTP stream listed in either "m" line. lines and there is no other RTP stream listed in either "m" line.
When the original and duplicate RTP streams are carried in separate When the original and duplicate RTP streams are carried in separate
"m" lines in an SDP description and if the SDP description has one or "m" lines in a Session Description Protocol (SDP) description and if
more other RTP streams listed in either "m" line, duplication the SDP description has one or more other RTP streams listed in
grouping is not trivial and further signaling will be needed, which either "m" line, duplication grouping is not trivial and further
is left for future standardization. signaling will be needed, which is left for future standardization.
4. Use of RTP and RTCP with Temporal Redundancy 4. Use of RTP and RTCP with Temporal Redundancy
To achieve temporal redundancy, the main and duplicate RTP streams To achieve temporal redundancy, the main and duplicate RTP streams
SHOULD be sent using the sample 5-tuple of transport protocol, source SHOULD be sent using the sample 5-tuple of transport protocol, source
and destination IP addresses, and source and destination transport and destination IP addresses, and source and destination transport
ports. Due to the possible presence of network address and port ports. Due to the possible presence of network address and port
translation (NAPT) devices, load balancers, or other middleboxes, use translation (NAPT) devices, load balancers, or other middleboxes, use
of anything other than an identical 5-tuple might also cause spatial of anything other than an identical 5-tuple might also cause spatial
redundancy (which might introduce an additional delay due to the redundancy (which might introduce an additional delay due to the
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between their timelines. However, the RTP timestamps and sequence between their timelines. However, the RTP timestamps and sequence
numbers MUST be identical in the main and duplicate streams, making numbers MUST be identical in the main and duplicate streams, making
the mapping quite trivial. the mapping quite trivial.
Both the main and duplicate RTP streams, and their corresponding RTCP Both the main and duplicate RTP streams, and their corresponding RTCP
reports, will be received. If RTCP is used, receivers MUST generate reports, will be received. If RTCP is used, receivers MUST generate
RTCP reports for both the main and duplicate streams in the usual RTCP reports for both the main and duplicate streams in the usual
way, treating them as entirely separate media streams. way, treating them as entirely separate media streams.
4.2. Signaling Considerations 4.2. Signaling Considerations
Signaling is needed to allow the receiver to determine that an RTP Signaling is needed to allow the receiver to determine that an RTP
stream is a duplicate of another, rather than a separate stream that stream is a duplicate of another, rather than a separate stream that
needs to be rendered in parallel. There are two parts to this: an needs to be rendered in parallel. There are two parts to this: an
SDP extension is needed in the offer/answer exchange to negotiate SDP extension is needed in the offer/answer exchange to negotiate
support for temporal redundancy; and signaling is needed to indicate support for temporal redundancy; and signaling is needed to indicate
which stream is the duplicate (the latter can be done in-band using which stream is the duplicate (the latter can be done in-band using
an RTCP extension, or out-of-band in the SDP description). an RTCP extension, or out-of-band in the SDP description).
We require out-of-band signaling for both features. The required SDP Out-of-band signalling is needed for both features. The SDP
attribute to signal duplication in the SDP offer/answer exchange attribute to signal duplication in the SDP offer/answer exchange
('duplication-delay') is defined in ('duplication-delay') is defined in
[I-D.ietf-mmusic-delayed-duplication]. The required SDP grouping [I-D.ietf-mmusic-delayed-duplication]. The required SDP grouping
semantics are defined in [I-D.ietf-mmusic-duplication-grouping]. semantics are defined in [RFC7104].
In the following SDP example, a video stream is duplicated, and the In the following SDP example, a video stream is duplicated, and the
main and duplicate streams are transmitted in two separate SSRCs main and duplicate streams are transmitted in two separate SSRCs
(1000 and 1010): (1000 and 1010):
v=0 v=0
o=ali 1122334455 1122334466 IN IP4 dup.example.com o=ali 1122334455 1122334466 IN IP4 dup.example.com
s=Delayed Duplication s=Delayed Duplication
t=0 0 t=0 0
m=video 30000 RTP/AVP 100 m=video 30000 RTP/AVP 100
c=IN IP4 233.252.0.1/127 c=IN IP4 233.252.0.1/127
a=source-filter:incl IN IP4 233.252.0.1 198.51.100.1 a=source-filter:incl IN IP4 233.252.0.1 198.51.100.1
a=rtpmap:100 MP2T/90000 a=rtpmap:100 MP2T/90000
a=ssrc:1000 cname:ch1a@example.com a=ssrc:1000 cname:ch1a@example.com
a=ssrc:1010 cname:ch1a@example.com a=ssrc:1010 cname:ch1a@example.com
a=ssrc-group:DUP 1000 1010 a=ssrc-group:DUP 1000 1010
a=duplication-delay:50 a=duplication-delay:50
a=mid:Ch1 a=mid:Ch1
As specified in Section 3.2 of As specified in Section 3.2 of [RFC7104], it is advisable that the
[I-D.ietf-mmusic-duplication-grouping], it is advisable that the SSRC SSRC listed first in the "a=ssrc-group:" line (i.e., SSRC of 1000) is
listed first in the "a=ssrc-group:" line (i.e., SSRC of 1000) is sent sent first, with the other SSRC (i.e., SSRC of 1010) being the time-
first, with the other SSRC (i.e., SSRC of 1010) being the time-
delayed duplicate. This is not critical, however, and a receiving delayed duplicate. This is not critical, however, and a receiving
host should size its playout buffer based on the 'duplication-delay' host should size its playout buffer based on the 'duplication-delay'
attribute, and play the stream that arrives first in preference, with attribute, and play the stream that arrives first in preference, with
the other stream acting as a repair stream, irrespective of the order the other stream acting as a repair stream, irrespective of the order
in which they are signaled. in which they are signaled.
5. Use of RTP and RTCP with Spatial Redundancy 5. Use of RTP and RTCP with Spatial Redundancy
When using spatial redundancy, the duplicate RTP stream is sent using When using spatial redundancy, the duplicate RTP stream is sent using
a different source and/or destination address/port pair. This will a different source and/or destination address/port pair. This will
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numbers MUST be identical in the main and duplicate streams, making numbers MUST be identical in the main and duplicate streams, making
the mapping quite trivial. the mapping quite trivial.
Both the main and duplicate RTP streams, and their corresponding RTCP Both the main and duplicate RTP streams, and their corresponding RTCP
reports, will be received. If RTCP is used, receivers MUST generate reports, will be received. If RTCP is used, receivers MUST generate
RTCP reports for both the main and duplicate streams in the usual RTCP reports for both the main and duplicate streams in the usual
way, treating them as entirely separate media streams. way, treating them as entirely separate media streams.
5.2. Signaling Considerations 5.2. Signaling Considerations
The required SDP grouping semantics have been defined in The required SDP grouping semantics have been defined in [RFC7104].
[I-D.ietf-mmusic-duplication-grouping]. In the following example, In the following example, the redundant streams have different IP
the redundant streams have different IP destination addresses. The destination addresses. The example shows the same UDP port number
example shows the same UDP port number and IP source address for each and IP source address for each stream, but either or both could have
stream, but either or both could have been different for the two been different for the two streams.
streams.
v=0 v=0
o=ali 1122334455 1122334466 IN IP4 dup.example.com o=ali 1122334455 1122334466 IN IP4 dup.example.com
s=DUP Grouping Semantics s=DUP Grouping Semantics
t=0 0 t=0 0
a=group:DUP S1a S1b a=group:DUP S1a S1b
m=video 30000 RTP/AVP 100 m=video 30000 RTP/AVP 100
c=IN IP4 233.252.0.1/127 c=IN IP4 233.252.0.1/127
a=source-filter:incl IN IP4 233.252.0.1 198.51.100.1 a=source-filter:incl IN IP4 233.252.0.1 198.51.100.1
a=rtpmap:100 MP2T/90000 a=rtpmap:100 MP2T/90000
a=mid:S1a a=mid:S1a
m=video 30000 RTP/AVP 101 m=video 30000 RTP/AVP 101
c=IN IP4 233.252.0.2/127 c=IN IP4 233.252.0.2/127
a=source-filter:incl IN IP4 233.252.0.2 198.51.100.1 a=source-filter:incl IN IP4 233.252.0.2 198.51.100.1
a=rtpmap:101 MP2T/90000 a=rtpmap:101 MP2T/90000
a=mid:S1b a=mid:S1b
6. Use of RTP and RTCP with Temporal and Spatial Redundancy 6. Use of RTP and RTCP with Temporal and Spatial Redundancy
This uses the same RTP/RTCP mechanisms from Sections Section 4 and This uses the same RTP/RTCP mechanisms from Sections Section 4 and
Section 5, plus a combination of both sets of signaling. Section 5, plus a combination of both sets of signaling.
7. Congestion Control Considerations 7. Congestion Control Considerations
Duplicating RTP streams has several considerations in the context of Duplicating RTP streams has several considerations in the context of
congestion control. First of all, RTP duplication MUST NOT be used congestion control. First of all, RTP duplication MUST NOT be used
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points. Thus, these end-points will apply any congestion control, if points. Thus, these end-points will apply any congestion control, if
applicable, on the de-duplicated RTP stream. This output stream will applicable, on the de-duplicated RTP stream. This output stream will
have less losses than either of the original and duplicated stream, have less losses than either of the original and duplicated stream,
and the end-point will make congestion control decisions accordingly. and the end-point will make congestion control decisions accordingly.
However, if de-duplication takes place at the ultimate end-point, However, if de-duplication takes place at the ultimate end-point,
this end-point MUST consider the aggregate of the original and this end-point MUST consider the aggregate of the original and
duplicated RTP stream in any congestion control it wants to apply. duplicated RTP stream in any congestion control it wants to apply.
The end-point will observe the losses in each stream separately, and The end-point will observe the losses in each stream separately, and
this information can be used to fine-tune the duplication process. this information can be used to fine-tune the duplication process.
For example, the duplication interval can be adjusted based on the For example, the duplication interval can be adjusted based on the
duration of a common packet loss in both streams. duration of a common packet loss in both streams. In these
scenarios, the RTP Monitoring Framework[RFC6792] can be used to
monitor the duplicated streams in the same way an ordinary RTP would
be monitored.
8. Security Considerations 8. Security Considerations
The security considerations of [RFC3550], The security considerations of [RFC3550],
[I-D.ietf-mmusic-delayed-duplication], [I-D.ietf-mmusic-delayed-duplication], [RFC7104], and any RTP
[I-D.ietf-mmusic-duplication-grouping], and any RTP profiles and profiles and payload formats in use apply.
payload formats in use apply.
Duplication can be performed end-to-end, with the media sender Duplication can be performed end-to-end, with the media sender
generating a duplicate RTP stream, and the receiver(s) performing de- generating a duplicate RTP stream, and the receiver(s) performing de-
duplication. In such cases, if the original media stream is to be duplication. In such cases, if the original media stream is to be
authenticated (e.g., using SRTP [RFC3711]) then the duplicate stream authenticated (e.g., using SRTP [RFC3711]) then the duplicate stream
also needs to be authenticated, and duplicate packets that fail the also needs to be authenticated, and duplicate packets that fail the
authentication check need to be discarded. authentication check need to be discarded.
Stream duplication and de-duplication can also be performed by in- Stream duplication and de-duplication can also be performed by in-
network middleboxes. Such middleboxes will need to rewrite the RTP network middleboxes. Such middleboxes will need to rewrite the RTP
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[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.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[I-D.ietf-mmusic-delayed-duplication] [I-D.ietf-mmusic-delayed-duplication]
Begen, A., Cai, Y., and H. Ou, "Delayed Duplication Begen, A., Cai, Y., and H. Ou, "Delayed Duplication
Attribute in the Session Description Protocol", draft- Attribute in the Session Description Protocol", draft-
ietf-mmusic-delayed-duplication-02 (work in progress), May ietf-mmusic-delayed-duplication-03 (work in progress),
2013. December 2013.
[I-D.ietf-mmusic-duplication-grouping] [RFC7104] Begen, A., Cai, Y., and H. Ou, "Duplication Grouping
Begen, A., Cai, Y., and H. Ou, "Duplication Grouping Semantics in the Session Description Protocol", RFC 7104,
Semantics in the Session Description Protocol", draft- January 2014.
ietf-mmusic-duplication-grouping-03 (work in progress),
July 2013.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)", Norrman, "The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, March 2004. RFC 3711, March 2004.
11.2. Informative References 11.2. Informative References
[RFC2354] Perkins, C. and O. Hodson, "Options for Repair of [RFC2354] Perkins, C. and O. Hodson, "Options for Repair of
Streaming Media", RFC 2354, June 1998. Streaming Media", RFC 2354, June 1998.
[RFC4588] Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R. [RFC4588] Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R.
Hakenberg, "RTP Retransmission Payload Format", RFC 4588, Hakenberg, "RTP Retransmission Payload Format", RFC 4588,
July 2006. July 2006.
[RFC6363] Watson, M., Begen, A., and V. Roca, "Forward Error [RFC6363] Watson, M., Begen, A., and V. Roca, "Forward Error
Correction (FEC) Framework", RFC 6363, October 2011. Correction (FEC) Framework", RFC 6363, October 2011.
[RFC6792] Wu, Q., Hunt, G., and P. Arden, "Guidelines for Use of the
RTP Monitoring Framework", RFC 6792, November 2012.
[IC2011] Evans, J., Begen, A., Greengrass, J., and C. Filsfils, [IC2011] Evans, J., Begen, A., Greengrass, J., and C. Filsfils,
"Toward Lossless Video Transport (to appear in IEEE "Toward Lossless Video Transport (to appear in IEEE
Internet Computing)", November 2011. Internet Computing)", November 2011.
Authors' Addresses Authors' Addresses
Ali Begen Ali Begen
Cisco Cisco
181 Bay Street 181 Bay Street
Toronto, ON M5J 2T3 Toronto, ON M5J 2T3
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