I gave brief presentations about our proposed RTCP packet format for
congestion control feedback to the
RMCAT
and
AVTCORE
working groups at IETF 101 in London, March 2018.
Our work to define a circuit breaker algorithm for unicast RTP
sessions has finally been published by the IETF as
RFC 8083.
This RFC defines a minimal set of RTP circuit breakers: conditions
under which an RTP sender needs to stop transmitting media data, in
order to protect the network from excessive congestion. It does not
propose a congestion control algorithm, leaving that for other
specifications, such as those under development in the IETF's
RTP Media
Congestion Avoidance Techniques working group.
How should the
RTP circuit breaker react to persistent excessive congestion
signalled via ECN? Indeed, should the circuit breaker
react to such a congestion signal?
Simon Jouet presented his work on
OTCP: SDN-Managed Congestion Control for Data Centre Networks at
the IEEE/IFIP Network Operations and Management Symposium workshop in
Istanbul, Turkey, in April 2016. OTCP is an OpenFlow-based approach
to tuning TCP congestion control parameters to better match network
characteristics that can improve flow completion times in data centre
networks.
I submitted a draft on the
use of RTCP Feedback for Unicast Multimedia Congestion Control.
Congestion control requires a feedback loop, to report on reception
quality, and in the case of RTP-based multimedia, this is has typically
been provided by RTCP feedback. There have been some suggestions in the
working group that RTCP feedback is too slow for effective congestion
control. This draft provides a rough sketch of how quickly feedback can
be provided by RTCP. It seems clear that per-packet feedback cannot be
provided using RTCP, but per-frame feedback is very possible. If RTCP
is to be used in it's current form for congestion feedback, then the
algorithms should be designed to work with feedback per-frame or
per-RTT, rather than per packet.
I gave an invited talk on
“Can
Congestion-controlled Interactive Multimedia Traffic Co-exist with
TCP?” in the
Capacity Sharing Workshop at
ACM CoNEXT 2012
in Nice, France, yesterday. The abstract for my talk was: “The
WebRTC activity in the Internet Engineering Task Force (IETF) and
World-Wide Web Consortium (W3C) is adding standards-based interactive
multimedia conferencing features to web browsers. WebRTC systems are
expected to see extremely wide deployment, starting in the next year.
This deployment poses a challenge, since congestion control algorithms
for interactive multimedia have not been standardized. The nature of
interactive multimedia traffic complicates congestion control, and the
interactions between WebRTC traffic, TCP flows, and the modern network
worsen the problem. The region where congestion-controlled interactive
multimedia traffic can feasibly co-exist with TCP is outlined, and
areas where additional development seems necessary are
highlighted.”
A birds-of-a-feather (BoF) session on RTP Media Congestion Avoidance
Techniques was held at the
84th IETF meeting in Vancouver on 2 August 2012. I co-chaired this
BoF with Michael Welzl
from the University of Oslo.
This internet-draft describes Content- and Cache-Aware TCP (CATCP).
This is an extension to TCP that allows caching of TCP segments, so
they can be re-used between different flows transmitting same data.
When large amounts of redundant data are being simultaneously sent to
multiple receivers, this can lead to significant load reductions and
performance improvements.
A typical use-case might be to improve the efficiency of HTTP-based
streaming video services, through ubiquitous in-network caching.
Congratulations to Alvaro Saurin, who has completed his MSc thesis
on Congestion Control for Video-conferencing Applications, looking
into how well TCP-Friendly Rate Control (TFRC) works on real-world
networks.
Welcome to Alvaro Saurin, who will be working on integration of TCP
Friendly Rate Control (TFRC) with high performance interactive video,
as part of the UltraGrid project.
Provision of congestion control is a significant open issue for
interactive real-time networked multimedia systems. Numerous
congestion control algorithms have been proposed, but they frequently
conflict with the demands of interactive multimedia applications. My
paper “Building
Adaptive Applications: On The Need For Congestion Control”
(an invited paper presented at the 17th SPIE/IS&T International
Symposium on Electronic Imaging, San Jose, CA, USA, January 2005)
outlines some of the issues.