[Tmrg] router buffer sizes

[Roman Chertov]

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Hello,

I am posting this email as per my conversation with Lachlan at INFOCOM.

In our INFOCOM, "A Device Independent Router Model", paper and in our
current work that extends that paper, we used empirical methods to
ascertain the size of queues in various commercial routers.  In the four
commercial routers that we have experimented with, we have observed the
following queue configurations:
  Byte Based
  Slot Based
  Separate buffers for various packet ranges (small, medium, large)

Furthermore, the delay due to queuing ranged from 14 ms to almost 400
ms.  In a variety of TCP papers that I have read, people used either
default queue sizes in ns-2 (50 slots), or they used some arbitrary
queue size.  I think it will be useful for the future version of ns-3 to
provide a variety of router "groups".  Each group would be a collection
of commercial routers which have similar characteristics, and then some
representative for the group can be chosen.  For instance, if an
experimenter creates a routing node with many 1+ Gbps links, then
choosing a queue size of 200 is not very representative of the real
world.  However, for such a scenario, choosing a group "backbone" will
configure routing node to have fairly large queues of 16K+ packet slots,
hence making the test more representative of a real network.

The major problem with the proposed approach is the difficulty of
obtaining the data.  Sometimes the data is available on a company's
website, in other cases, empirical methods are required to get the
needed information.  The major drawback of an empirical approach is the
need for physical hardware.  However, even with the drawbacks, I think
it is worthwhile to do this, as then simulation accuracy should increase.

Our INFOCOM paper is available at:
http://www.cs.purdue.edu/homes/fahmy/papers/infocom08-roman.pdf

Roman Chertov

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