Subject: reliability and congestion control

From: Yoshihiro Ohba <[email-masked]>
Date: Wed, 9 Jan 2002 12:26:25 -0500

I have a basic question on ICMP-based schemes (SNARD and EAPoverICMP).

There is a statement in the charter:

"The PANA protocol needs reliability and congestion ontrol, taking
into account that the PANA protocol needs to be able to operate over
multiple router hops.  The congestion control principles are
documented in RFC 2914."

When a PAA is more than one-hop away from a device, is it easy for
ICMP to provide reliability and congestion control?  (I don't think
so.)

Yoshihiro Ohba

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From: Erik Nordmark <[email-masked]>
Date: Mon, 14 Jan 2002 10:02:19 +0100 (CET)

> The charter is quite detailed (and sometimes suggesting requirements
> as well) in order to ensure that everyone is quite clear of the
> protocol work being undertaken in this WG. If however you do believe
> that some of the *suggested* requirements (in the charter) are
> non-essential to PANA in your requirements I-D, please do feel free to
> capture them as such. Congestion control for a protocol that is
> limited to the host and the access network seems like an overkill.

If the packets traverse a single L2 (i.e. a single IP hop) and the L2 itself
can never be subject to congestion that might be the case.

But I think even Ethernet switches need to drop packets when congested.
And spread-spectrum radio behaves similarely - as more stations are
transmitting the S/N drops for everybody causing a loss probability that
increases. Of course the latter isn't "traditional" congestion but it can be
handled by having congestion control in the upper protocols.

Note that for a pure stop-wand-wait protocol (send request, wait form response,
repeat a few times until done) each host can have only one outstanding packet
at any time. This might be good enough from the congestion control perspective
when coupled with TCP-like retransmission timer management.

  Erik