draft-ietf-avt-rapid-rtp-sync-06.txt | draft-ietf-avt-rapid-rtp-sync-07.txt | |||
---|---|---|---|---|
Network Working Group C. Perkins | Network Working Group C. Perkins | |||
Internet-Draft University of Glasgow | Internet-Draft University of Glasgow | |||
Updates: RFC3550 T. Schierl | Updates: RFC3550 T. Schierl | |||
(if approved) Fraunhofer HHI | (if approved) Fraunhofer HHI | |||
Intended status: Standards Track October 26, 2009 | Intended status: Standards Track November 9, 2009 | |||
Expires: April 29, 2010 | Expires: May 13, 2010 | |||
Rapid Synchronisation of RTP Flows | Rapid Synchronisation of RTP Flows | |||
draft-ietf-avt-rapid-rtp-sync-06.txt | draft-ietf-avt-rapid-rtp-sync-07.txt | |||
Status of this Memo | Status of this Memo | |||
This Internet-Draft is submitted to IETF in full conformance with the | This Internet-Draft is submitted to IETF in full conformance with the | |||
provisions of BCP 78 and BCP 79. | provisions of BCP 78 and BCP 79. | |||
Internet-Drafts are working documents of the Internet Engineering | Internet-Drafts are working documents of the Internet Engineering | |||
Task Force (IETF), its areas, and its working groups. Note that | Task Force (IETF), its areas, and its working groups. Note that | |||
other groups may also distribute working documents as Internet- | other groups may also distribute working documents as Internet- | |||
Drafts. | Drafts. | |||
skipping to change at page 1, line 34 ¶ | skipping to change at page 1, line 34 ¶ | |||
and may be updated, replaced, or obsoleted by other documents at any | and may be updated, replaced, or obsoleted by other documents at any | |||
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." | |||
The list of current Internet-Drafts can be accessed at | The list of current Internet-Drafts can be accessed at | |||
http://www.ietf.org/ietf/1id-abstracts.txt. | http://www.ietf.org/ietf/1id-abstracts.txt. | |||
The list of Internet-Draft Shadow Directories can be accessed at | The list of Internet-Draft Shadow Directories can be accessed at | |||
http://www.ietf.org/shadow.html. | http://www.ietf.org/shadow.html. | |||
This Internet-Draft will expire on April 29, 2010. | This Internet-Draft will expire on May 13, 2010. | |||
Copyright Notice | Copyright Notice | |||
Copyright (c) 2009 IETF Trust and the persons identified as the | Copyright (c) 2009 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 in effect on the date of | Provisions Relating to IETF Documents in effect on the date of | |||
publication of this document (http://trustee.ietf.org/license-info). | publication of this document (http://trustee.ietf.org/license-info). | |||
Please review these documents carefully, as they describe your rights | Please review these documents carefully, as they describe your rights | |||
skipping to change at page 7, line 40 ¶ | skipping to change at page 7, line 40 ¶ | |||
16 kbps| 2.50 2.50 2.73 2.73 2.73 2.73 2.73 2.73 | 16 kbps| 2.50 2.50 2.73 2.73 2.73 2.73 2.73 2.73 | |||
32 kbps| 2.50 2.50 2.50 2.50 2.50 2.50 2.50 2.50 | 32 kbps| 2.50 2.50 2.50 2.50 2.50 2.50 2.50 2.50 | |||
64 kbps| 2.50 2.50 2.50 2.50 2.50 2.50 2.50 2.50 | 64 kbps| 2.50 2.50 2.50 2.50 2.50 2.50 2.50 2.50 | |||
128 kbps| 1.41 1.41 1.41 1.41 1.41 1.41 1.41 1.41 | 128 kbps| 1.41 1.41 1.41 1.41 1.41 1.41 1.41 1.41 | |||
256 kbps| 0.70 0.70 0.70 0.70 0.70 0.70 0.70 0.70 | 256 kbps| 0.70 0.70 0.70 0.70 0.70 0.70 0.70 0.70 | |||
512 kbps| 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35 | 512 kbps| 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35 | |||
1 Mbps| 0.18 0.18 0.18 0.18 0.18 0.18 0.18 0.18 | 1 Mbps| 0.18 0.18 0.18 0.18 0.18 0.18 0.18 0.18 | |||
2 Mbps| 0.09 0.09 0.09 0.09 0.09 0.09 0.09 0.09 | 2 Mbps| 0.09 0.09 0.09 0.09 0.09 0.09 0.09 0.09 | |||
4 Mbps| 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 | 4 Mbps| 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 | |||
Figure 1: Average RTCP reporting interval in seconds for an RTP | Figure 1: Average initial synchronisation delay in seconds for an RTP | |||
Session with 1 sender. | Session with 1 sender. | |||
These numbers assume a source specific multicast channel with a | These numbers assume a source specific multicast channel with a | |||
single active sender, assuming an average RTCP packet size of 70 | single active sender, assuming an average RTCP packet size of 70 | |||
octets. These intervals are sufficient for lip-synchronisation | octets. These intervals are sufficient for lip-synchronisation | |||
without excessive delay, but might be viewed as having too much | without excessive delay, but might be viewed as having too much | |||
latency for synchronising parts of a layered video stream. | latency for synchronising parts of a layered video stream. | |||
The RTCP interval is randomised in the usual manner, so the minimum | The RTCP interval is randomised in the usual manner, so the minimum | |||
synchronisation delay will be half these intervals, and the maximum | synchronisation delay will be half these intervals, and the maximum | |||
skipping to change at page 8, line 43 ¶ | skipping to change at page 8, line 43 ¶ | |||
16 kbps| 2.50 2.50 2.73 3.42 5.47 5.47 5.47 5.47 | 16 kbps| 2.50 2.50 2.73 3.42 5.47 5.47 5.47 5.47 | |||
32 kbps| 2.50 2.50 2.50 2.50 2.73 2.73 2.73 2.73 | 32 kbps| 2.50 2.50 2.50 2.50 2.73 2.73 2.73 2.73 | |||
64 kbps| 2.50 2.50 2.50 2.50 2.50 2.50 2.50 2.50 | 64 kbps| 2.50 2.50 2.50 2.50 2.50 2.50 2.50 2.50 | |||
128 kbps| 1.41 1.41 1.41 1.41 1.41 1.41 1.41 1.41 | 128 kbps| 1.41 1.41 1.41 1.41 1.41 1.41 1.41 1.41 | |||
256 kbps| 0.70 0.70 0.70 0.70 0.70 0.70 0.70 0.70 | 256 kbps| 0.70 0.70 0.70 0.70 0.70 0.70 0.70 0.70 | |||
512 kbps| 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35 | 512 kbps| 0.35 0.35 0.35 0.35 0.35 0.35 0.35 0.35 | |||
1 Mbps| 0.18 0.18 0.18 0.18 0.18 0.18 0.18 0.18 | 1 Mbps| 0.18 0.18 0.18 0.18 0.18 0.18 0.18 0.18 | |||
2 Mbps| 0.09 0.09 0.09 0.09 0.09 0.09 0.09 0.09 | 2 Mbps| 0.09 0.09 0.09 0.09 0.09 0.09 0.09 0.09 | |||
4 Mbps| 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 | 4 Mbps| 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 | |||
Figure 2: Average RTCP reporting interval in seconds for an RTP | Figure 2: Average initial synchronisation delay in seconds for an RTP | |||
Session with 2 senders. | Session with 2 senders. | |||
Session| Number of receivers: | Session| Number of receivers: | |||
Bandwidth| 2 3 4 5 10 100 1000 10000 | Bandwidth| 2 3 4 5 10 100 1000 10000 | |||
--+------------------------------------------------ | --+------------------------------------------------ | |||
8 kbps| 2.73 4.10 5.47 6.84 13.67 54.69 54.69 54.69 | 8 kbps| 2.73 4.10 5.47 6.84 13.67 54.69 54.69 54.69 | |||
16 kbps| 2.50 2.50 2.73 3.42 6.84 27.34 27.34 27.34 | 16 kbps| 2.50 2.50 2.73 3.42 6.84 27.34 27.34 27.34 | |||
32 kbps| 2.50 2.50 2.50 2.50 3.42 13.67 13.67 13.67 | 32 kbps| 2.50 2.50 2.50 2.50 3.42 13.67 13.67 13.67 | |||
64 kbps| 2.50 2.50 2.50 2.50 2.50 6.84 6.84 6.84 | 64 kbps| 2.50 2.50 2.50 2.50 2.50 6.84 6.84 6.84 | |||
128 kbps| 1.41 1.41 1.41 1.41 1.41 3.42 3.42 3.42 | 128 kbps| 1.41 1.41 1.41 1.41 1.41 3.42 3.42 3.42 | |||
256 kbps| 0.70 0.70 0.70 0.70 0.70 1.71 1.71 1.71 | 256 kbps| 0.70 0.70 0.70 0.70 0.70 1.71 1.71 1.71 | |||
512 kbps| 0.35 0.35 0.35 0.35 0.35 0.85 0.85 0.85 | 512 kbps| 0.35 0.35 0.35 0.35 0.35 0.85 0.85 0.85 | |||
1 Mbps| 0.18 0.18 0.18 0.18 0.18 0.43 0.43 0.43 | 1 Mbps| 0.18 0.18 0.18 0.18 0.18 0.43 0.43 0.43 | |||
2 Mbps| 0.09 0.09 0.09 0.09 0.09 0.21 0.21 0.21 | 2 Mbps| 0.09 0.09 0.09 0.09 0.09 0.21 0.21 0.21 | |||
4 Mbps| 0.04 0.04 0.04 0.04 0.04 0.11 0.11 0.11 | 4 Mbps| 0.04 0.04 0.04 0.04 0.04 0.11 0.11 0.11 | |||
Figure 3: Average RTCP reporting interval in seconds for an RTP | Figure 3: Average initial synchronisation delay in seconds for an RTP | |||
Session with 10 senders. | Session with 10 senders. | |||
2.1.4. Discussion | 2.1.4. Discussion | |||
For unicast sessions, the existing RTCP SR-based mechanism allows for | For unicast sessions, the existing RTCP SR-based mechanism allows for | |||
immediate synchronisation, provided the initial RTCP packet is not | immediate synchronisation, provided the initial RTCP packet is not | |||
lost. | lost. | |||
For SSM sessions, the initial synchronisation delay is sufficient for | For SSM sessions, the initial synchronisation delay is sufficient for | |||
lip-synchronisation, but may be larger than desired for some layered | lip-synchronisation, but may be larger than desired for some layered | |||
skipping to change at page 9, line 52 ¶ | skipping to change at page 9, line 52 ¶ | |||
In this case, the receiver will not be able to synchronise the media | In this case, the receiver will not be able to synchronise the media | |||
until the reporting interval has passed, and the next RTCP SR packet | until the reporting interval has passed, and the next RTCP SR packet | |||
is sent. This is undesirable. Section 3.2 defines a new RTP/AVPF | is sent. This is undesirable. Section 3.2 defines a new RTP/AVPF | |||
transport layer feedback message to request an RTCP SR be generated, | transport layer feedback message to request an RTCP SR be generated, | |||
allowing rapid resynchronisation in the case of packet loss. | allowing rapid resynchronisation in the case of packet loss. | |||
2.2. Synchronisation for Late Joiners | 2.2. Synchronisation for Late Joiners | |||
Synchronisation between RTP sessions is potentially slower for late | Synchronisation between RTP sessions is potentially slower for late | |||
joiners than for participants present at the start of the session. | joiners than for participants present at the start of the session. | |||
The reasons for this are two-fold: | The reasons for this are three-fold: | |||
1. Many of the optimisations that allow rapid transmission of RTCP | 1. Many of the optimisations that allow rapid transmission of RTCP | |||
SR packets apply only at the start of a session. This implies | SR packets apply only at the start of a session. This implies | |||
that a new participant may have to wait a complete RTCP reporting | that a new participant may have to wait a complete RTCP reporting | |||
interval for each session before receiving the necessary data to | interval for each session before receiving the necessary data to | |||
synchronise media streams. This might potentially take several | synchronise media streams. This might potentially take several | |||
seconds, depending on the configured session bandwidth and the | seconds, depending on the configured session bandwidth and the | |||
number of participants. | number of participants. | |||
2. Additional synchronisation delay comes from the nature of the | 2. Additional synchronisation delay comes from the nature of the | |||
End of changes. 7 change blocks. | ||||
8 lines changed or deleted | 8 lines changed or added | |||
This html diff was produced by rfcdiff 1.46. The latest version is available from http://tools.ietf.org/tools/rfcdiff/ |