Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site mulga.SUN Path: utzoo!watmath!clyde!floyd!harpo!decvax!mulga!kre From: kre@mulga.SUN (Robert Elz) Newsgroups: net.unix-wizards Subject: Re: UNIX IPC Datagram Reliability under - (nf) Message-ID: <205@mulga.SUN> Date: Mon, 13-Feb-84 00:58:57 EST Article-I.D.: mulga.205 Posted: Mon Feb 13 00:58:57 1984 Date-Received: Fri, 10-Feb-84 00:31:52 EST References: <235@hou3c.UUCP> Organization: Comp Sci, Melbourne Uni, Australia Lines: 26 There's nothing remarkable about datagrams not being reliable under unix. No output is reliable. You're not guaranteed to get an error if the disk that you happen to be writing on developes a coughing fit just at the time you do your write, you're not guaranteed to get an error if the process at the other end of a pipe dies before reading your data (though you will if its already dead when you send it), nor will you get an error if your output to a terminal is mangled by noise on the phone, or simply by some super-user type doing a "wall" at the relevant time. Why should unix datagrams do something different? (As has been mentioned before, they would also cease to be datagrams by the traditional definition.) You will often get an error indication if something is wrong, but you may not. I do agree though that for most programs, datagrams are not an intelligent service to use. As to X.25, that can certainly not be considered to be reliable. DCE's are permitted to RESET a virtual circuit as often as they deem fit, and each RESET may cause data to be lost. Higher level protocols are necessary to guarantee data integrity. Robert Elz, decvax!mulga!kre