draft-ietf-avtcore-clksrc-07.txt   draft-ietf-avtcore-clksrc-08.txt 
Audio/Video Transport Core Maintenance A. Williams Audio/Video Transport Core Maintenance A. Williams
Internet-Draft Audinate Internet-Draft Audinate
Intended status: Standards Track K. Gross Intended status: Standards Track K. Gross
Expires: April 05, 2014 AVA Networks Expires: May 31, 2014 AVA Networks
R. van Brandenburg R. van Brandenburg
H. Stokking H. Stokking
TNO TNO
October 02, 2013 Novemeber 27, 2013
RTP Clock Source Signalling RTP Clock Source Signalling
draft-ietf-avtcore-clksrc-07 draft-ietf-avtcore-clksrc-08
Abstract Abstract
NTP format timestamps are used by several RTP protocols for NTP format timestamps are used by several RTP protocols for
synchronisation and statistical measurements. This memo specifies synchronisation and statistical measurements. This memo specifies
SDP signalling identifying timestamp reference clock sources and SDP SDP signalling identifying timestamp reference clock sources and SDP
signalling identifying the media clock sources in a multimedia signalling identifying the media clock sources in a multimedia
session. session.
Requirements Language Requirements Language
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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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 May 31, 2014.
Copyright Notice Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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6.1.1. Indicating Support for Clock Source Signalling . . . 19 6.1.1. Indicating Support for Clock Source Signalling . . . 19
6.1.2. Timestamp Reference Clock . . . . . . . . . . . . . . 19 6.1.2. Timestamp Reference Clock . . . . . . . . . . . . . . 19
6.1.3. Media Clock . . . . . . . . . . . . . . . . . . . . . 19 6.1.3. Media Clock . . . . . . . . . . . . . . . . . . . . . 19
6.2. Usage Outside of Offer/Answer . . . . . . . . . . . . . . 20 6.2. Usage Outside of Offer/Answer . . . . . . . . . . . . . . 20
7. Security Considerations . . . . . . . . . . . . . . . . . . . 20 7. Security Considerations . . . . . . . . . . . . . . . . . . . 20
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
8.1. Reference Clock SDP Parameter . . . . . . . . . . . . . . 21 8.1. Reference Clock SDP Parameter . . . . . . . . . . . . . . 21
8.2. Media Clock SDP Parameter . . . . . . . . . . . . . . . . 21 8.2. Media Clock SDP Parameter . . . . . . . . . . . . . . . . 21
8.3. Timestamp Reference Clock Source Parameters Registry . . 22 8.3. Timestamp Reference Clock Source Parameters Registry . . 22
8.4. Media Clock Source Parameters Registry . . . . . . . . . 23 8.4. Media Clock Source Parameters Registry . . . . . . . . . 23
8.5. Source-level Attributes . . . . . . . . . . . . . . . . . 24 8.5. Source-level Attributes . . . . . . . . . . . . . . . . . 23
8.5.1. Source-level Timestamp Reference Clock Attribute . . 24 8.5.1. Source-level Timestamp Reference Clock Attribute . . 24
8.5.2. Source-level Media Clock Attribute . . . . . . . . . 24 8.5.2. Source-level Media Clock Attribute . . . . . . . . . 24
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 24 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 24
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 24 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 24
10.1. Normative References . . . . . . . . . . . . . . . . . . 24 10.1. Normative References . . . . . . . . . . . . . . . . . . 24
10.2. Informative References . . . . . . . . . . . . . . . . . 26 10.2. Informative References . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27
1. Introduction 1. Introduction
RTP protocols use NTP format timestamps to facilitate multimedia RTP protocols use NTP format timestamps to facilitate multimedia
session synchronisation and for providing estimates of round trip session synchronisation and for providing estimates of round trip
time (RTT) and other statistical parameters. time (RTT) and other statistical parameters.
Information about media clock timing exchanged in NTP format Information about media clock timing exchanged in NTP format
timestamps may come from a clock which is synchronised to a global timestamps may come from a clock which is synchronised to a global
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Networked Audio : Networked loudspeakers, amplifiers and analogue I/ Networked Audio : Networked loudspeakers, amplifiers and analogue I/
O devices transmitting or receiving audio signals via RTP can be O devices transmitting or receiving audio signals via RTP can be
connected to various parts of a building or campus network. Such connected to various parts of a building or campus network. Such
situations can for example be found in large conference rooms, situations can for example be found in large conference rooms,
legislative chambers, classrooms (especially those supporting legislative chambers, classrooms (especially those supporting
distance learning) and other large-scale environments such as distance learning) and other large-scale environments such as
stadiums. Since humans are more susceptible to differences in stadiums. Since humans are more susceptible to differences in
audio delay, this use case needs even more accuracy than the video audio delay, this use case needs even more accuracy than the video
wall use case. Depending on the exact application, the need for wall use case. Depending on the exact application, the need for
accuracy can then be in the range of microseconds [1]. accuracy can then be in the range of microseconds [Olsen].
Sensor Arrays : Sensor arrays contain many synchronised measurement Sensor Arrays : Sensor arrays contain many synchronised measurement
elements producing signals which are then combined to form an elements producing signals which are then combined to form an
overall measurement. Accurate capture of the phase relationships overall measurement. Accurate capture of the phase relationships
between the various signals arriving at each element of the array between the various signals arriving at each element of the array
is critically important for proper operation. Examples include is critically important for proper operation. Examples include
towed or fixed sonar arrays, seismic arrays and phased arrays used towed or fixed sonar arrays, seismic arrays and phased arrays used
in radar applications, for instance. in radar applications, for instance.
3. Definitions 3. Definitions
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Note that slaving of a device media clock to a master device does not Note that slaving of a device media clock to a master device does not
affect the usual RTP lip sync / time alignment algorithms. Time affect the usual RTP lip sync / time alignment algorithms. Time
aligned playout of two or more RTP sources still relies upon NTP aligned playout of two or more RTP sources still relies upon NTP
timestamps supplied via RTCP SRs or by the RFC6051 timestamp header timestamps supplied via RTCP SRs or by the RFC6051 timestamp header
extension. extension.
In a given system, master clock identifiers must uniquely identify a In a given system, master clock identifiers must uniquely identify a
single media clock source. Such identifiers MAY be manually single media clock source. Such identifiers MAY be manually
configured, however identifiers SHOULD be generated according to the configured, however identifiers SHOULD be generated according to the
"short-term persistent RTCP CNAME" algorithm as described in RFC6222 "short-term persistent RTCP CNAME" algorithm as described in RFC7022
[RFC6222] or RFC6222bis [I-D.ietf-avtcore-6222bis]. Master clock [RFC7022]. Master clock identifiers not already in base64 format
identifiers not already in base64 format MUST be encoded as a base64 MUST be encoded as a base64 strings when used in SDP. Although the
strings when used in SDP. Although the RTCP CNAME algorithm is used RTCP CNAME algorithm is used to generate the master clock identifier,
to generate the master clock identifier, it is used to tag RTP it is used to tag RTP sources in SDP descriptions and does not appear
sources in SDP descriptions and does not appear in RTCP as a CNAME. in RTCP as a CNAME.
A reference stream can be an RTP stream or AVB stream based on the A reference stream can be an RTP stream or AVB stream based on the
IEEE 1722 [IEEE1722] standard. IEEE 1722 [IEEE1722] standard.
An RTP clock master stream SHOULD be identified at the source level An RTP clock master stream SHOULD be identified at the source level
by an SSRC [RFC5576] and master clock identifier. An RTP stream that by an SSRC [RFC5576] and master clock identifier. An RTP stream that
provides media clock timing directly from a reference media clock provides media clock timing directly from a reference media clock
(e.g. internal crystal, audio word clock or video blackburst signal) (e.g. internal crystal, audio word clock or video blackburst signal)
SHOULD tag the stream as a master clock source using the "src:" SHOULD tag the stream as a master clock source using the "src:"
prefix. If master clock identifiers are declared at the media or prefix. If master clock identifiers are declared at the media or
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9. Acknowledgements 9. Acknowledgements
The authors would like to thank Magnus Westerlund and Paul Kyzivat The authors would like to thank Magnus Westerlund and Paul Kyzivat
for valuable comments which resulted in important improvements to for valuable comments which resulted in important improvements to
this document. this document.
10. References 10. References
10.1. Normative References 10.1. Normative References
[I-D.ietf-avtcore-6222bis]
Begen, A., Perkins, C., Wing, D., and E. Rescorla,
"Guidelines for Choosing RTP Control Protocol (RTCP)
Canonical Names (CNAMEs)", draft-ietf-avtcore-6222bis-06
(work in progress), July 2013.
[IEEE1588-2002] [IEEE1588-2002]
Institute of Electrical and Electronics Engineers, Institute of Electrical and Electronics Engineers,
"1588-2002 - IEEE Standard for a Precision Clock "1588-2002 - IEEE Standard for a Precision Clock
Synchronization Protocol for Networked Measurement and Synchronization Protocol for Networked Measurement and
Control Systems", IEEE Std 1588-2002, 2002, <http:// Control Systems", IEEE Std 1588-2002, 2002, <http://
standards.ieee.org/findstds/standard/1588-2002.html>. standards.ieee.org/findstds/standard/1588-2002.html>.
[IEEE1588-2008] [IEEE1588-2008]
Institute of Electrical and Electronics Engineers, Institute of Electrical and Electronics Engineers,
"1588-2008 - IEEE Standard for a Precision Clock "1588-2008 - IEEE Standard for a Precision Clock
Synchronization Protocol for Networked Measurement and Synchronization Protocol for Networked Measurement and
Control Systems", IEEE Std 1588-2008, 2008, <http:// Control Systems", IEEE Std 1588-2008, 2008, <http://
standards.ieee.org/findstds/standard/1588-2008.html>. standards.ieee.org/findstds/standard/1588-2008.html>.
[IEEE1722] [IEEE1722]
Institute of Electrical and Electronics Engineers, "IEEE Institute of Electrical and Electronics Engineers, "IEEE
Standard for Layer 2 Transport Protocol for Time Sensitive Standard for Layer 2 Transport Protocol for Time Sensitive
Applications in a Bridged Local Area Network", , <http:// Applications in a Bridged Local Area Network", <http://
standards.ieee.org/findstds/standard/1722-2011.html>. standards.ieee.org/findstds/standard/1722-2011.html>.
[IEEE802.1AS-2011] [IEEE802.1AS-2011]
Institute of Electrical and Electronics Engineers, "Timing Institute of Electrical and Electronics Engineers, "Timing
and Synchronization for Time-Sensitive Applications in and Synchronization for Time-Sensitive Applications in
Bridged Local Area Networks", , <http://standards.ieee.org Bridged Local Area Networks", <http://standards.ieee.org/
/findstds/standard/802.1AS-2011.html>. findstds/standard/802.1AS-2011.html>.
[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.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264, June with Session Description Protocol (SDP)", RFC 3264, June
2002. 2002.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006. Description Protocol", RFC 4566, July 2006.
skipping to change at page 25, line 43 skipping to change at page 25, line 35
Media Attributes in the Session Description Protocol Media Attributes in the Session Description Protocol
(SDP)", RFC 5576, June 2009. (SDP)", RFC 5576, June 2009.
[RFC5905] Mills, D., Martin, J., Burbank, J., and W. Kasch, "Network [RFC5905] Mills, D., Martin, J., Burbank, J., and W. Kasch, "Network
Time Protocol Version 4: Protocol and Algorithms Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, June 2010. Specification", RFC 5905, June 2010.
[RFC6051] Perkins, C. and T. Schierl, "Rapid Synchronisation of RTP [RFC6051] Perkins, C. and T. Schierl, "Rapid Synchronisation of RTP
Flows", RFC 6051, November 2010. Flows", RFC 6051, November 2010.
[RFC6222] Begen, A., Perkins, C., and D. Wing, "Guidelines for [RFC7022] Begen, A., Perkins, C., Wing, D., and E. Rescorla,
Choosing RTP Control Protocol (RTCP) Canonical Names "Guidelines for Choosing RTP Control Protocol (RTCP)
(CNAMEs)", RFC 6222, April 2011. Canonical Names (CNAMEs)", RFC 7022, September 2013.
10.2. Informative References 10.2. Informative References
[AES11-2009] [AES11-2009]
Audio Engineering Society, "AES11-2009: AES recommended Audio Engineering Society, "AES11-2009: AES recommended
practice for digital audio engineering - Synchronization practice for digital audio engineering - Synchronization
of digital audio equipment in studio operations", , of digital audio equipment in studio operations",
<http://www.aes.org/standards/>. <http://www.aes.org/standards/>.
[I-D.ietf-avtcore-idms] [I-D.ietf-avtcore-idms]
Brandenburg, R., Stokking, H., Deventer, O., Boronat, F., Brandenburg, R., Stokking, H., Deventer, O., Boronat, F.,
Montagud, M., and K. Gross, "Inter-destination Media Montagud, M., and K. Gross, "Inter-destination Media
Synchronization using the RTP Control Protocol (RTCP)", Synchronization using the RTP Control Protocol (RTCP)",
draft-ietf-avtcore-idms-13 (work in progress), August draft-ietf-avtcore-idms-13 (work in progress), August
2013. 2013.
[I-D.ietf-avtcore-leap-second] [I-D.ietf-avtcore-leap-second]
Gross, K. and R. Brandenburg, "RTP and Leap Seconds", Gross, K. and R. Brandenburg, "RTP and Leap Seconds",
draft-ietf-avtcore-leap-second-05 (work in progress), draft-ietf-avtcore-leap-second-06 (work in progress),
October 2013. November 2013.
[IEEE802.1BA-2011] [IEEE802.1BA-2011]
Institute of Electrical and Electronics Engineers, "Audio Institute of Electrical and Electronics Engineers, "Audio
Video Bridging (AVB) Systems", , <http:// Video Bridging (AVB) Systems", <http://standards.ieee.org/
standards.ieee.org/findstds/standard/802.1BA-2011.html>. findstds/standard/802.1BA-2011.html>.
[IS-GPS-200F] [IS-GPS-200F]
Global Positioning Systems Directorate, "Navstar GPS Space Global Positioning Systems Directorate, "Navstar GPS Space
Segment/Navigation User Segment Interfaces", September Segment/Navigation User Segment Interfaces", September
2011. 2011.
[Olsen] Olsen, D., "Time Accuracy Requirements in Audio Networks",
April 2007, <http://www.ieee802.org/1/files/public/
docs2007/as-dolsen-time-accuracy-0407.pdf>.
[RFC0868] Postel, J. and K. Harrenstien, "Time Protocol", STD 26, [RFC0868] Postel, J. and K. Harrenstien, "Time Protocol", STD 26,
RFC 868, May 1983. RFC 868, May 1983.
[RFC2326] Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time [RFC2326] Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time
Streaming Protocol (RTSP)", RFC 2326, April 1998. Streaming Protocol (RTSP)", RFC 2326, April 1998.
[RFC2974] Handley, M., Perkins, C., and E. Whelan, "Session [RFC2974] Handley, M., Perkins, C., and E. Whelan, "Session
Announcement Protocol", RFC 2974, October 2000. Announcement Protocol", RFC 2974, October 2000.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
skipping to change at page 27, line 7 skipping to change at page 26, line 50
Schooler, "SIP: Session Initiation Protocol", RFC 3261, Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002. June 2002.
[RFC5939] Andreasen, F., "Session Description Protocol (SDP) [RFC5939] Andreasen, F., "Session Description Protocol (SDP)
Capability Negotiation", RFC 5939, September 2010. Capability Negotiation", RFC 5939, September 2010.
[SMPTE-318-1999] [SMPTE-318-1999]
Society of Motion Picture & Television Engineers, Society of Motion Picture & Television Engineers,
"Television and Audio - Synchronization of 59.94- or 50-Hz "Television and Audio - Synchronization of 59.94- or 50-Hz
Related Video and Audio Systems in Analog and Digital Related Video and Audio Systems in Analog and Digital
Areas - Reference Signals", , Areas - Reference Signals", <http://standards.smpte.org/>.
<http://standards.smpte.org/>.
Authors' Addresses Authors' Addresses
Aidan Williams Aidan Williams
Audinate Audinate
Level 1, 458 Wattle St Level 1, 458 Wattle St
Ultimo, NSW 2007 Ultimo, NSW 2007
Australia Australia
Phone: +61 2 8090 1000 Phone: +61 2 8090 1000
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