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RE: [10GBASE-T] latency


To make a clarification on my request, I was not considering end-to-end
latency as this is not the realm of 802.3.  I was considering
point-to-point latency, not for PAUSE although a latency number will be
required for those that do implement flow control.  The question comes
to my mind, can we afford to (or better yet, can we afford not to) make
trade-offs against latency for better performance.  What are the pros
and cons of these trade-offs?  Do we need to consider latency against
the coding proposals?

BTW, I think it is great to see so much discussion around this.  Maybe
we should discuss line codes, etc. while we're at it?


-----Original Message-----
[] On Behalf Of Stephen
Sent: Friday, February 20, 2004 2:34 PM
Subject: RE: [10GBASE-T] latency

Hi All

My thanks to everyone who has responded to my email. 

The responses I've been getting tend to suggest that PAUSE should not be
(and is not) enabled in most Ethernet systems. If flow control is
required it should be handled higher up the stack. This obviously
increases the latency and if TCP/IP is implemented in software no exact
bound on latency can be given since it will be architecture specific.

However, although latency is not an issue for PAUSE it is a major issue
for certain applications 10G may be targetting. I believe this brings us
back to Brad's original request for some figures on end to end latency
for applications such as cluster computing and RDMA.

Serag mentioned that we should stick to the low latency solutions if the
power remains comparable with that of 10G optical transponder. My
concern is that the balance between digital and analog power will be
totally biased to the analog. This implies power consumption will not
drop as much with technology scaling. In this case we will not see the
same kind of power consumption drop over time that we saw for




Dr. Stephen Bates

Dept. of Electrical and Computer Engineering      Phone: +1 780 492 2691
The University of Alberta                         Fax:   +1 780 492 1811
Canada, T6G 2V4