Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!hplabs!hpda!hpcupt1!hpindwa!kumar
From: kumar@hpindwa.HP.COM (Krishna Kumar)
Newsgroups: comp.protocols.tcp-ip
Subject: Source Quench & Jacobson's Alg.
Message-ID: <36540001@hpindwa.HP.COM>
Date: 20 Mar 89 21:38:07 GMT
Organization: Hewlett-Packard, Cupertino CA
Lines: 40

Hello,

With more and more implementations adopting Van Jacobson's source-based
congestion avoidance and control mechanisms, is it likely that in the near
future gateways will stop sending ICMP source quench messages when they
discard packets? 

There seem to be conflicting documentation on sending ICMP source quench
messages in the first place.

RFC 792 [Postel: Internet Control Message Protocol, Sep '81] states: "If a 
gateway discards a datagram, it *may* send a source quench message to the
internet source host of the datagram."

RFC 896 [Nagle: Congestion Control in TCP/IP Internetworks, Jan '84] states:
"The present ICMP standard specifies that an ICMP Source Quench message
*should* be sent whenever a packet is dropped, and additionally may be sent
when a gateway finds itself becoming short of resources. There is some
ambiguity here but clearly it is a violation of the standard to drop a
packet without sending an ICMP message."

RFC 1016 [Prue and Postel: The Source Quench Introduced Delay (SQUID),
July '87] states: If a gateway discards a datagram, it *may* send a source 
quench message to the Internet source host of the datagram." (referring
to RFC 792). It goes on to suggest, "We propose gateway IP nodes start
SQing before the node is flooded at a level we call SQ Keep but forward
the datagram.... Once the gateway starts sending SQs it *should* continue
to do so until the queue level goes below a low water mark level..."

Can anyone shed some light on these issues? Any comments or suggestions?

Thanks,

Krishna Kumar,
Business Networks Division, HP.
(kumar@hpindwa.HP.COM)

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(Disclaimer: All opinions are my own and not my employer's.)