Re: ISO8473 vs. IP


Paul Tsuchiya (tsuchiya@gateway.mitre.org)
Tue, 8 Sep 87 14:38:21 EDT


> From: "Marty Schoffstall" <schoff@nic.nyser.net>
> Status: R
>
>
> - 'congestion experienced'. Set by a router, when a router
> experiences congestion.
>
> The infamous "DEC Bit", which reports to the recipient of the packet
> that there is congestion. This bit has debatable merit, would the
> two camps like to expound?
>
> Marty

Ok, I'll bite.

The DEC bit is used, at least in DECNET (phase 4 or 5, I don't know)
to control the transport window such that the network doesn't get
congested. It is a "congestion avoidance" mechanism. As far as I
know, the algorithm assumes it knows the round trip time. I don't
know if DEC measures this or assumes a value. (I understand the
problems associated with trying to measure it.) The algorithm
seems to be a good one, and works as long as all of the parts are
there and everyone participates. (Please, someone from DEC correct
me if I have this screwed up).

DEC has released there algorithm for doing this (until recently, it
was proprietary). In their IS-IS routing proposal, they have said
when to set the bit. I am not sure how or if they intend to standardize
the part that tells the transport machine what to do. I suppose this
could be done right in ISO, or in one of the profile organizations like
COS.

Tsuchiya

PS. We may be in two camps, but lets face it: if it rains, all of
our campfires are going to go out.



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