Path: utzoo!utgpu!watserv1!watmath!att!ucbvax!VM1.ULG.AC.BE!PIRARD From: PIRARD@VM1.ULG.AC.BE (Andr'e PIRARD) Newsgroups: comp.protocols.tcp-ip Subject: Re: Why Fewer Buffers (was Changing TCP port) Message-ID: <9105071910.AA00548@ucbvax.Berkeley.EDU> Date: 7 May 91 10:08:41 GMT References: Sender: daemon@ucbvax.BERKELEY.EDU Distribution: world Organization: University of Liege (Belgium), SEGI (Computing Center) Lines: 32 On Fri 3 May 91 14:08:37-PDT you said: >Avoiding duplicate datagram thrashing (DDT?) is THE major reason for using >smaller queues. This is unfortunately still very prevalent in TCP/IP, even >though the algorithms have been developed to help prevent it. Many other >protocols are much dumber, and don't even have any facility for slowing >down in the presence of congestion. If you believe that ANY queue with >an average size of greater than one represents a congested link, the actual >queue sizes on routers don't have to be very big. Glad to know why you recommend small queues, and the underlying theories. Unhappily, I still don't know how bigger than 1 they should be and I guess no one can tell. Indeed not all TCPs are good. I've seen one transmitting 4 times what's needed when doing FTP alone on a slow link. So, even 0 maybe. Routers can help when this link is not on the culprit's interface itself. > Finally, on grounds of what came in must go, I wonder if the most > drastically effective heuristics wouldn't be to detect and drop duplicate > queued packets, with the excuse of unreliability for rare mistakes. > >Sure, given infinite CPU resources on the routers, one can do anything... I doubt it would spend much CPU on mismatches, especially if the line is slow anyway and this feature used only on them. The larger expense on matches would be pure benefit. But indeed the transport level helping the others a bit would sure help. >Bill Westfield >cisco Systems. Andr'e PIRARD SEGI, Univ. de Li`ege 139.165 IP coordinator B26 - Sart Tilman B-4000 Li`ege 1 (Belgium) +32 (41) 564932 pirard@vm1.ulg.ac.be alias PIRARD%BLIULG11.BITNET@CUNYVM.CUNY.EDU