[14975] in North American Network Operators' Group
Re: backbone routers' priority settings for ICMP & UDP
daemon@ATHENA.MIT.EDU (Dave Siegel)
Wed Feb 4 14:40:47 1998
From: Dave Siegel <dave@rtd.net>
In-Reply-To: <Pine.WNT.3.96.980203144705.-249235B-100000@swhyte-pc.cisco.com> from Scott Whyte at "Feb 3, 98 02:55:13 pm"
To: swhyte@cisco.com (Scott Whyte)
Date: Wed, 4 Feb 1998 12:15:13 -0700 (MST)
Cc: marcs@znep.com, nanog@merit.edu
> Marc, I'd have to agree, ICMP is more for flow control than congestion
> control. A source quench is to slow a fast machine from overrunning a slow
> machine, not preventing all flows from going through one link.
>
> One (weak) metaphor is that traffic lights at an intersection are for flow
> control, while the traffic lights to get onto the freeway (common here in
> California) are for congestion control...
Extremely weak metaphore, since a source quench indicates there weren't
enough buffers available to send your packets.
Now, if the freeway was full, and cars started dropping out of the space/time
continuum, that'd be more like a source quench. ;-) The freeway would call
your wife at home and say "sorry, but your husband didn't make it to work
because the freeways were too full." If wife runs correct a correct
TCP implementation, she would know to initiate "slow start" and would
send out her husbands at a slower rate until she gets a feel for how
bad the traffic is.
> One then
> wonders how well Win95 implements source quench, if at all.
Which side of the implementation do you mean? as a client, or as a gateway?
I suppose it doesn't really matter. Since source quenches are not supposed
to be used on routers anymore, the expectation of receiving a source
quench on a large network (like the Internet) is a bad one, so the TCP
implementations have to implement congestion controls through other means
anyhow.
TCP/IP Illus. Vol. I by W. Richard Stevens has a pretty good explanation
of what source quenches are.
Dave
--
Dave Siegel dave@rtd.net
Network Engineer dave@pager.rtd.com (alpha pager)
(520)579-0450 (home office)
http://www.rtd.com/~dsiegel/
