GridNet2 Trip Report: 68th IETF Meeting
Dr. Colin Perkins
University of Glasgow
25 April 2007
I attended the 68th IETF meeting in Prague from 18–23 March 2007, funded by a GridNet2 award. This brief report
summarises the outcomes of my trip, in accordance with GridNet2 requirements. The GridNet2 project is funding
my continued activities as co-chair of the Audio/Video Transport (AVT) and Multiparty Multimedia Session Control
(MMUSIC) working groups in the IETF, and my work to develop protocols for collaborative work and other realtime applications. This report will focus on activities in those working groups, and my related activities in the IETF,
of interest to the UK e-science community. Opinions expressed herein are those of the author, and do not necessarily
represent those of the IETF or its working groups.
The AVT working group develops standards for real-time audio/visual data transfer on IP networks. Those standards
underpin modern voice over IP, 3G mobile telephony, and video conferencing systems, including the AccessGrid,
VRVS, and similar tools used by the e-science community. I co-chaired the AVT working group session at the 68th
IETF meeting. The main areas of discussion are as follows: Generalisation of the RTCP framework to allow noncompound packets and to report more detailed performance metrics for IPTV systems; Extensions to RTP to support
and signal layered codecs, in particular the SVC extension to H.264; Codec control messages, to better support
centralised small group video conferencing systems; and Congestion control for real-time streaming sessions. This
work is primarily aimed at improving the quality of small group video conferencing systems, although the latter
item is also applicable to data streaming (e.g. the e-VLBI work discussed later).
The work I presented at the previous IETF meeting on multiplexing RTP and RTCP on a single port, to ease NAT
traversal, went to working group last call at the meeting, and should be published as a Proposed Standard in the
coming months. My work on RTP and the Datagram Congestion Control Protocol (complementing the RTP congestion control work) was discussed in the DCCP working group. Issues with keep-alives, to ensure NAT pinholes
remain open, were discussed. The draft is expected to go to working group last call shortly, once the RTP and RTCP
multiplexing work, on which it depends, is completed.
The MMUSIC working group develops protocol standards for initiation and control of real-time sessions. The
main work items are the Interactive Connectivity Establishment (ICE) methodology for NAT traversal, and the
Session Description Protocol (SDP) media capability negotiation framework. I co-chaired the MMUSIC session at
the 68th IETF meeting, managing discussion of these, and related, issues. I also participated in the design team
developing the media capability negotiation framework, with a particular emphesis on deployability and backwards
compatibility of the resulting protocols, and ensuring they fit with the SDP architecture (I’m one of the authors of
the SDP specification).
In addition to my work chairing and contributing to these working groups, I continued discussions with Marshall
Eubanks (representing part of the eVLBI community) on how developemnt effective network transport protocols
for eVLBI data, utilising work done in the Audio/Video Transport working group as a basis. This followed on from
previous discussions at the 67th IETF meeting.
Funding from GridNet2 continues to be essential for this work, and I believe the outcomes of this work will be of
interest to the e-Science community, and will underpin future developments in Grid toolkits and collaborative work
environments.