Andy Malis (malis@CC5.BBN.COM)
Tue, 21 Jul 87 16:51:12 -0400
I would like to respond to a couple of points in your message.
On the need for "clever engineering", and defending the ARPANET:
for all of its sophistication, the PSN's dynamic routing
algorithm was originally designed for, and worked very well in,
an environment where the offered load did not come close to
congesting the network's resources. This is no longer the case,
with network subnet congestion as the predictable result. The
recent changes in routing are actually slight modifications to
one part of the algorithm, to try to prevent routing oscillations
as a result of congested paths and to make the cross-country
satellite link more attractive when the land lines start
As Steve Cohn said in a previous message, a more detailed
description of the change, and its effects, will be forthcoming.
Congestion control will further help the network in these days of
plentiful load and scarce resources.
I really don't see what we are doing as defending ourselves from
network-hostile hosts; rather, we are trying to allocate scarce
resources as fairly and evenly as possible, and trying to keep
the network from going past the point where additional load would
cause the network's total throughput to start degrading. Of
course, that doesn't mean that there aren't "hostile" hosts out
On 40 octets of header per packets: I was referring to the
internals of the ARPANET and MILNET subnets when I was discussing
packet headers and such. However, they are only two networks on
an internet of over 100 networks now. I am not a TCP/IP
implementer so I won't get into whether any of the 40 octets can
be squeezed out; you just have to realize that the environment
TCP/IP runs in is nothing like that of commercial and PTT
networks. X.25 does internetting (X.75) using fixed routes
though transit networks and X.75 gateways without an end-to-end
transport layer like TCP, and is nowhere as reliable and
survivable as the TCP/IP internet. But you have to pay for this
by using large datagram headers and end-to-end retransmissions.
I do agree that some of the assumptions that were made during the
TCP/IP design days (such as a richly configured backbone network)
may no longer be valid. It may be time to revisit TCP/IP's
design, especially in light of the OSI protocol suite, just as
long as we keep in mind the overall requirements of the internet.
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