Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!utgpu!water!watnot!watmath!clyde!cbatt!ucbvax!DECWRL.DEC.COM!kent From: kent@DECWRL.DEC.COM.UUCP Newsgroups: mod.protocols.tcp-ip Subject: Re: ICMP messages Message-ID: <8702231733.AA28625@saturn.dec.com> Date: Mon, 23-Feb-87 12:45:17 EST Article-I.D.: saturn.8702231733.AA28625 Posted: Mon Feb 23 12:45:17 1987 Date-Received: Thu, 26-Feb-87 19:31:33 EST References: <8702220538.AA13788@flash.bellcore.com> Sender: daemon@ucbvax.BERKELEY.EDU Reply-To: "Christopher A. Kent" Organization: The ARPA Internet Lines: 29 Approved: tcp-ip@sri-nic.arpa Gee, this sounds very reminiscent of the (once popular, now extinct?) Delta-T protocol, a "timer-based connectionless protocol" originally proposed by Dick Watson at LLNL. It (and the whole class) are wholly timer based, with a window mechanism for flow control, but no 3-way handshakes on open/close. The key parameter is the "maximum roundtrip packet lifetime", or Delta-T. By knowing the maximum amount of time any packet will live, you can start sending data in the first packet because you know all stragglers will have been discarded. Delta-T essentially assumes everyone is talking to everyone else all the time, but there are gaps in conversations. If the gaps are longer than Delta-T, there is no need to keep state information about. Thus, the protocol state information is essentially a cache of recent interchanges. Of course, this all depends on accurate estimates of Delta-T, but then, so does TCP. Watson proposed a "link timing protocol" which slips in between an IP-type protocol and a transport-type protocol to provide the necessary timing information. I'm not clear on how a Delta-T style protocol fits into a large internet with many gateways on hops, but it's an interesting class of protocols to think aboiut, now that it seems that TCP performance and robustness are turning out to be heavily reliant on accurate timer estimates. Cheers, chris ----------