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Re: [HSSG] 40G MAC Rate Discussion


Excellent questions. See in-line:

> 1) Application: 40GE vsus 4x10G LAG:
> What application(s) do think will require a 40GE single pipe
> and can  not be addressed by 4x 10GE LAG?

Any application where round-trip latency (rather than bulk throughput)
is of essence. These are request-response type of applications, such
as Oracle. Both 40GE and 4x10GE LAG may be able to handle the same
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.

> Few people mentioned already that 4x LAG was manageable.
> My understanding is high end server are going multi-core/multi-CPI,
> I  would imagine that Network IOs (flows) would fit well within the 4x
> 10GE model.

Correct, but only if you get uniform spreading of the flows. And how do
you guarantee that? That's the "manageable" dilemma that applies for
both carrier and server environments, and is regardless of how many
links you have in the LAG. There is essentially no good way to control
this at the network management level.

For network environments where a link has lots (millions) of flows, you
can rely on statistical multiplexing for getting good spreading of flows.
I would imagine that this would happen more often in carrier links rather
that server links, since they would have a lot more aggregation of users.
Apparently it is a problem for both.

Finally, in the database example that I described earlier (Oracle), 
you get a few dozen flows at best, and the spreading is very poor.

> 2) Relative cost:
> What is the expected relative cost vsus 10GE ports (or 4x 10GE LAG)?
> and in what time frame? Given that the idea is the 40GE  will fill  
> the gap
> between 10G and 100G for servers (say between 2010-2015?). 

I will let the optical vendors speak for themselves, but what I have
heard is that a 40Gb QSFP solution will be 2x of current 10Gb SFP in
2008. By 2010 I would expect it to be similar to SFP.

On the MAC side it should be essentially free, since I expect by 2010
quad 10Gb NICs being the highest volume NICs, and adding 1x40Gb
capability will be trivial.