pogran@CCQ.BBN.COM (Ken Pogran) (11/10/87)
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 growth. 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