[e2e] Is a non-TCP solution dead?

Hans Kruse kruse at ohio.edu
Tue Apr 15 08:07:58 PDT 2003


There is a fundamental disconnect/problem in this discussion, as I see it:

TCP is either very good or a nuisance, DEPENDING ON the assumptions you can 
make about the underlying network.  Contrary to repeated statements, most 
of the current network infrastructure does not do congestion control at 
intermediate nodes.  An application that is deployed without being able to 
make assumptions about the underlying network, and that requires reliable 
delivery (i.e. re-transmits), needs to make rate-limit its transmission in 
the absence of back-pressure from the network.

IF you can make more specific assumptions about the network with regard to 
congestion control, then TCP's action are superfluous and/or a nuisance. 
For example, if stations always established an ATM VC before sending the 
TCP SYN, TCP would not require slow-start nor congestion control.  But that 
is a very different network from the one we call the Internet now.

On a side note, TCP's share of the overall network traffic is not a 
relevant measure.  TCP's share of reliable transports flows is;  I would 
venture that the vast majority of non-TCP traffic is real-time unreliable 
flow, which does not create congestion problems due to retransmissions.

--On Wednesday, April 09, 2003 09:01 -0700 Cannara <cannara at attglobal.net> 
wrote:

> Love that touch Lloyd -- it's required on some other lists, believe it or
> not.  By the way, you know we can assess how any alternate transport might
> improve over TCP by noting what's been removed -- if slow-start isn't
> there, then it's relatively easy to estimate; if delayed-ack is gone,
> ditto; same for other changes to backoff.  In fact, someone could simply
> recompile NS with items commented out, unless it's too spaghetti like.  :]
>
> I'll see what I can make of an XCP/FAST comparison, as an exercise for
> students.  Might be good.



Hans Kruse, Associate Professor
J. Warren McClure School of Communication Systems Management
Adjunct Associate Professor of Electrical Engineering and Computer Science
Ohio University, Athens, OH, 45701
740-593-4891 voice, 740-593-4889 fax




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