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Re: [HSSG] 40G MAC Rate Discussion

On Thu, 5 Apr 2007, Shimon Muller wrote:

> number of transactions, however from a single user's perspective, the
> 40GE network will respond 4 times faster. This has direct correlation to
> the application's performance.

Isn't that an overly simplification to state that a network with 4 times 
the speed has 1/4 the end-to-end latency? (In case I now interpreted your 
statement correctly that you by "reponse" mean that latency of all kinds 
are that important.

If my calculations about serialisation are correct, then it takes:

0.3 microseconds to serialise a 1500 byte packet on 40GE and 1.2 
microseconds to serialise it on 10GE. A 64 byte packet takes 0.0128 
microseconds on 40GE and .0512 microseconds on 10GE.

At 10GE 64 byte packet (512 bits) is 10 meters "long" in the fiber 
(200.000km/s speed of light in fiber) and 2.5 meters long at 40GE.

This means that you'd have to start to worry about patch cable length in 
case you want to keep the response time down as per your example, because 
if you had a 10 meter patch cable instead of a 2.5 meter one, you'd wasted 
the serialisation advantage of 40GE (in case you had 10GE with 2.5 meter 
patch cable and 10 meter cable with 40GE).

To me it sounds like serialisation delay is a very small issue at these 

PS. Please tell me if I mad a major error in calculation and assumption in 
the above...

Mikael Abrahamsson    email: