backbone routers' priority settings for ICMP & UDP
Scott Whyte
swhyte at cisco.com
Wed Feb 4 20:24:03 UTC 1998
On Wed, 4 Feb 1998, Dave Siegel wrote:
> 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.
ROFL, nice extension. But this is not true because, as you say below,
gateways don't source quench anyore.
>
> > 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.
As a client, of course, since end-to-end source quench is the only
alternative available. And consider the near future scenario where a user
with a cable-modem connected via Ethernet to their nice new NC (with
cheapest bus design possible to contain costs) has requested a URL from a
<insert whomping fast server here> connected via OC-3 to the Internet. It
seems likely a source quench will come in handy to provide flow control.
>
> TCP/IP Illus. Vol. I by W. Richard Stevens has a pretty good explanation
> of what source quenches are.
Don't have Mr. Stevens handy, but from RFC777 (1981!), when both types of
source quench were defined:
...A destination host may also send a source quench message if datagrams
arrive too fast to be processed. The source quench message is a request
to the host to cut back the rate at which it is sending traffic to the
internet destination.
This is what I was getting at. Flow control versus congestion control.
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Scott Whyte 408.527.5713 |Any opinions expressed herein are
Network Supported Accounts (NSA) |mine and not cisco's...
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