RE: [10GBASE-T] latency
Stephen,
A little off topic, but the congestion control in TCP is a very different mechanism from the flow control in 802.3. It doesn't attempt to keep frames from being dropped so it isn't latency sensitive and it definately doesn't require a strict upper bound on latency. It was devised to work over internet delays so any 10GBASE-T delay would be pretty insignificant to it.
Regards,
Pat
-----Original Message-----
From: Stephen Bates [mailto:stephen.bates@ece.ualberta.ca]
Sent: Friday, February 20, 2004 12:34 PM
To: THALER,PAT (A-Roseville,ex1)
Cc: stds-802-3-10gbt@ieee.org
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
1000BASE-T.
Regards
Stephen
--------------------------------------------------------------------------
Dr. Stephen Bates
Dept. of Electrical and Computer Engineering Phone: +1 780 492 2691
The University of Alberta Fax: +1 780 492 1811
Edmonton www.ece.ualberta.ca/~sbates
Canada, T6G 2V4 stephen.bates@ece.ualberta.ca
--------------------------------------------------------------------------