ARPANET/Internet performance investigation

Ken Pogran (
Mon, 9 Nov 87 17:57:34 EST

BBN has been investigating recent ARPANET and Internet
performance problems. Here's a brief report.

The biggest single problem has been the performance of key LSI-11
gateways, especially the three "EGP Server" Gateways on the
ARPANET located at BBN, Purdue, and ISI. These gateways are
LSI-11/23s, and they are flat out of cycles. As the Internet has
grown, they have been spending more and more of their time
preparing EGP routing updates, at the expense of other
activities, such as servicing their I/O queues. One result of
this has been the buildup of long queues of messages for these
gateways in the PSNs to which they are attached. Frequently,
messages have remained on the queues for more than 30 seconds --
which causes the PSN to declare the gateway "tardy" and reset its
interface to that gateway, thereby flushing the queue (returning
"Incomplete Transmission" messages to the originators) and
starting the process over again.

The short-term fix for this problem is to replace the processors
in these gateways with the faster LSI-11/73s. This was done at
BBN last Friday, with excellent results. BRL and U-Maryland have
generously offered the loan of 11/73 processors which will be
installed in the ARPANET EGP servers at Purdue and ISI. With
these faster processors installed, the Internet should be back to
"normal" -- for another 2-6 months, given the current rate of

The long-term fix is the installation of Butterfly Gateways to
replace the LSI-11s that are the DDN Mailbridge Gateways. This
will enable us to retire the LSI-11 EGP servers. The Butterfly
Mailbridges will provide significantly better performance.
Deployment of the Butterfly Mailbridges in the DDN is expected in
the April timeframe.

Ken Pogran
BBN Communications

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