[Tmrg] Towards a Common TCP Evaluation Suite

[Sally Floyd]

Lachlan -

>
> - For the 3-hop topology in which each flow gets 60ms delay, we  
> currently
>  specify having seven delay elements.  It is possible to achieve this
>  with only two delay elements (one of the "access" links, and one of
>  the bottleneck links).
>
>  Are these equivalent?  They both result in the same RTTs; most TCP
>  throughput models only care what the RTTs, not which links it  
> occurs on.
>  We can't do the same with shifting buffers around, but I think we can
>  shift propagation delays around freely, can't we?
>
>  If they're not equivalent, could we standardize on the one with
>  two delays instead of seven?  It would mean we only need 4 dummynets
>  instead of 7.


I think it makes more sense to specify the topology as it is specified  
now
in Section G ("a “parking-lot” topology with three (horizontal)  
bottleneck
links and four (vertical) access links"), and then to add that in a  
testbed,
this can be *implemented* with only N delay elements.  Because we want
the scenarios to be useful for simulators as well as testbeds, and some
simulators don't use delay elements.  And it makes it more clear the
real-world topology that corresponds to our simulation or experiment.

- Sally
http://www.icir.org/floyd/