From: Lillie Kittredge (kittredl@u.washington.edu)
Date: Tue Oct 19 2004 - 23:37:38 PDT
Congestion Control Xtreem!
This paper discusses the current state of, and proposes a new generation
of, congestion control.
The driving force for this paper is the increase in both high-bandwidth
and high-delay network technologies. This represents a change in the
environment since the earlier congestion control papers we've been
reading. This again shows how congestion control has evolved with the
available technologies; now a given packet traversing a network may
encounter any number of different media, which may differ drastically in
bandwidth and delay. One of the clever ideas of the authors for
addressing this is a system of feedback information in packet headers
which is updated by the routers along the packet's path; this ends up
recording the information from the bottleneck, so the source (once the
packet is returned to it) knows what it's really dealing with. This is a
much more powerful meme than the source merely getting one of its packets
dropped when the network is congested: now it knows not only that there is
congestion, but exactly what it needs to do to avoid contributing to it.
The main insight of the paper, which I rather like, is that fairness
control should be separated from efficiency control. As such they create
both a fairness and an efficiency manager for their protocol. The
congestion manager uses the cool trick with the traffic feedback in the
header; the fairness manager shuffles the available bandwidth among the
flows.
I like this paper and think it's got good ideas for how we can deal with
the continued evolution of the Internet. I find it ironic that network
technologies have not only gotten much wider - bandwidth, but have in some
cases gotten slower (or at least with larger delays), like wifi. That
seems an interesting and unexpected situation; it makes me wonder what
other unexpected changes in network behavior are in our future.
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