Re: Linking LAN's via Public X.25


Mark Crispin (MRC@PANDA.PANDA.COM)
Sat, 4 Jun 88 11:09:46 PDT


Dan -

     I'm responsible for one of the TCP/IP implementations used on a
9600 baud link in Canada. The system is a DEC-2065 running a TOPS-20
with a heavily modified TCP. It has two IP interfaces; a NIA20 to the
local Ethernet and an AN20 to a C/30 PSN using 1822.

     This TCP lacks RFNM counting which is a serious deficiency, but
in the case of this link it doesn't really matter all that much since
(at least the last I read) there is only one place for the 1822-grams
to go to. If you're RFNM blocked to the friendly not-so-local gateway,
you can't do anything anyway.

     What makes the burden worse, this machine is the only path between
the local Ethernet (which talks TCP/IP and DECnet) and the rest of the
world. It has a rudimentary EGP-speaker that babbles updates to Friend
Gateway.

     I've seen no indication of a bottleneck at the DEC-20. Instead,
it seems to be more that the DEC-20 (and the Symbolics Lisp machines
behind it on the Ethernet) are communicating almost exclusively with
the Internet in the US, across two gateways over a long long wire.
There isn't all that much traffic to begin with, so any latency in a
connection can easily stop the line...because there is no other traffic!

-- Mark --
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