Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.3 alpha 4/15/85; site ucbvax.ARPA Path: utzoo!watmath!clyde!burl!ulysses!ucbvax!tcp-ip From: tcp-ip@ucbvax.ARPA Newsgroups: fa.tcp-ip Subject: Retransmission policies Message-ID: <8124@ucbvax.ARPA> Date: Thu, 13-Jun-85 11:54:20 EDT Article-I.D.: ucbvax.8124 Posted: Thu Jun 13 11:54:20 1985 Date-Received: Fri, 14-Jun-85 04:40:03 EDT Sender: daemon@ucbvax.ARPA Organization: University of California at Berkeley Lines: 45 From: MILLS@USC-ISID.ARPA Mail-From: MILLS created at 13-Jun-85 10:22:22 Date: Thu 13 Jun 85 10:22:22-EDT From: The Mailer Daemon To: MILLS@USC-ISID.ARPA Subject: Message of 13-Jun-85 10:21:51 Message failed for the following: shasta!tcp-ip@SRI-NIC.ARPA: 550 No such local mailbox as "shasta!tcp-ip", recipient rejected ------------ Date: 13 Jun 1985 10:21:51 EDT From: MILLS@USC-ISID.ARPA Subject: Re: TCP Timer To: imagen!geof@SU-SHASTA.ARPA, shasta!tcp-ip@SRI-NIC.ARPA cc: MILLS@USC-ISID.ARPA In response to the message sent Wednesday, 12 Jun 1985 16:19-PDT from imagen!geof@shasta Geoff, Having as much experience as anybody with noisy TCP paths, I can certainly confirm that the best strategy is to retransmit just the head end of the retransmission queue. However, I gather from the tone of your note that you are considering only the first packet on that queue, which is what the TOPS-20s do. We have found much better performance allowing several combined up to MSS in total length when a retransmission is necessary. This greatly reduces the gateway loading when TELNET traffic is involved and also helps to control damage when the retransmission is due to congestive losses in the net. Another thing we have done is to carefully count outstanding packets and block further transmission if the total is greater than a magic number (currently eight). The magic number is reduced if an ICMP Source Quench arrives and returns to its original value in a controlled way. The bookeeping to accomplish this is fairly complicated, since segments can be combined, retransmitted, etc. The fuzzballs used to use this mechanism exclusively to control packet fluxes, but recently switched to the send/ack policy I described recently to this list. However, that send/ack policy leads to severly suboptimal performance in many cases. We are planning to integrate both the old and new policies to see if performance can be maintained even in these cases. Dave ------- ------- -------