[e2e] TCP Local Area Normal behaviour? any references?

[Craig Partridge]

In message <Pine.LNX.4.58.0501211436140.11281 at tesla.psc.edu>, Matt Mathis write
s:

>I think capture effect does not become a problem unless the end-system and
>routers/switches can send true back-to-back packets for a large portion of the
>window.  Just a small amount of idle makes the channel arbitration much more
>fair.  It might be kind of interesting to try to reconstruct the Boggs result
>with modern PC's.....

Sounds like great fun.  Let's see, what would the experiments be (always
fun to do experimental science on the fly)....

Van tested a single TCP connection over cable (in the old days when you
actually tapped into a cable!) with just two hosts.  He used two different
Ethernet adapters (and showed that one couldn't go full line rate, and
the other could).  It seems to me that in today's world you'd do this
experiment four ways:

    * single cable, two hosts (which I think you can do with a crossover
      cable), one TCP connect.

	    This is about as close as we can get to Van's original
	    experiment.  Note that the length of the cable may matter
	    (and should be tested)

    * same experiment but with a switch in between

	    Probably try multiple switches.

    Notes: probably worth doing at various TCP window sizes, to eliminate/
     identify window effects -- e.g., the delay bandwidth product is probably
     small, but worth computing, especially through the switch.

     If one is feeling ambitious, one could also do 802.11 (both direct
       and through a hub).

Boggs and Mogul tested an Ethernet by using 1 to 25 hosts that
concurrently each tried to send 20 seconds of fixed length packets 
as fast as possible.  During the middle 10 seconds it measured a bunch
of stats (which may or may not be accessible from current adapters).
They also experimented with cable length effects.  I think you can't
quite replicate it now, but you can certainly load up a single switch
(probably want an 8-port) and also try networks with more than one
switch.  There's also a question of what the max capacity of the network
is, if the switch is full duplex on all ports (you may end up measuring
the switch backplane if you're not careful).

My gut says the Jacobson experiment is the easier one to replicate and may
reveal a lot on its own.  I don't have time to do this experiment, but happy
to help if someone else wants to take it on.

Craig