Workshop on Adaptive Video Streaming over IP Networks
28 October 2010
/ adaptive-iptv
I attended the Workshop on Adaptive Video Streaming over IP Networks
held at Cisco Systems in Boxborough, MA, USA, on 12-13 October 2010,
to present an update on our adaptive IPTV work.
As usual for these
workshops, the presentations were an interesting mix of academic
research and industry pragmatism. The first day starting with a talk
from Sameer Akshabi and Constantine Dovrolis (Georgia Tech) on some
experimental evaluation of commercial HTTP streaming video systems, to
understand their rate adaptation behaviour. The chunk-based HTTP pull
model seems widely accepted, but there is enormous variation in the
rate at which chunks are fetched, the size of the playout buffer
built-up, and the way in which the applications adapt to changes in the
available bandwidth. Some of the systems tested seem to work reasonably
well, although they're slow to make use of increases in available
bandwidth (possibly intentionally, since variable quality gives a poor
user experience); others show various signs of instability. It's clear
that this is a rapidly evolving area, with much still to learn.
Zhi Li and Bernd Girod from Stanford outlined some ideas on how to make
a more realistic HTTP adaptive streaming simulator using ns-2. Following
on from the previous presentation, they clearly described how the two
control loops—TCP congestion control operating on the RTT
timeframe and application-level adaptation operating over several
seconds—interact, highlighting the cause of the stability problems.
They also noted an interaction between TCP and client request patterns,
which can cause a client that pauses for more than the TCP RTO between
chunk request to go into TCP slow start, negating the advantage of
keeping the connection open.
The morning concluded with a keynote from David D. Clark (MIT) on
“After the triple play: a ten year plan” exploring the
economics of the ISP market in the US. Interesting, but it's clear
that the ISP marketplace in the US is very different from that in many
other parts of the world.
In the afternoon, Ashish Khisti from the University of Toronto presented
some theoretical models for adaptive streaming over multihop wireless
networks. Then, Dina Katabi (MIT) described their
SoftCast system
for joint source-channel coding of wireless video for error resilience.
This is a very interesting system, leveraging the best ideas from analogue
video transmission and modulation to enhance digital video transmission.
The end of the first day, and the morning of the second were filled
with discussion sessions and an Overview of Cisco's Video Streaming
and CDN Products, and a review of Current Developments in Adaptive
Streaming Standards (focussing on IETF, MPEG, and 3GPP work for HTTP
streaming).
In the afternoon, we presented our measurements of UDP streaming
performance of various DSL and cable access links in the UK and in
Finland, including wide area distribution networks to show that loss
patterns include bit error-induced losses as well as losses due to
congestion and (early) data rate caps. Using a trace-driven simulation
of RTP/SSM with feedback and different FEC mechanisms we then showed
that, for the observed links and media transmission rates, simple
parity FEC mechanisms are capable of reducing the loss rate to
acceptable proportions. We concluded with some early thoughts on the
applicability of our measurements to TCP-based streaming.
The final presentation, from Mostafa Ammar of Georgia Tech, focussed on
hybrid CDN/P2P adaptive live streaming. All-in-all, it was an extremely
interesting workshop, covering a lot of ground. Thanks to Dave Oran and
Ali Begen for organising!