Path: utzoo!utgpu!watserv1!watmath!att!linac!uwm.edu!rpi!clarkson!grape.ecs.clarkson.edu!nelson From: nelson@sun.soe.clarkson.edu (Russ Nelson) Newsgroups: comp.protocols.tcp-ip Subject: Re: Monitoring TCP/IP sockets Message-ID: Date: 31 Jan 91 07:04:54 GMT References: <9101291553.AA06606@litwin.jpl.nasa.gov.> <12657895596.14.BILLW@mathom.cisco.com> Sender: @grape.ecs.clarkson.edu Reply-To: nelson@clutx.clarkson.edu (aka NELSON@CLUTX.BITNET) Organization: Clarkson University, Potsdam NY Lines: 34 In-Reply-To: BILLW@MATHOM.CISCO.COM's message of 30 Jan 91 00:57:12 GMT In article <12657895596.14.BILLW@mathom.cisco.com> BILLW@MATHOM.CISCO.COM (William "Chops" Westfield) writes: I have a program that uses TCP/IP sockets and needs to know quickly, within a second or so, if the physical connection between the two systems is broken. Foo. tcp/ip is designed for reliability over many media. You have no guarantee that your packet will even get to its destination within a second, even if the network is working perfectly. If you really need to know that quickly whether the network has gone away, tcp/ip is not a suitable protocol to be using. You didn't foo him very well, Bill. Yes, he shouldn't be using TCP/IP. But he *can* use IP. It's just a matter of protocol design. If you *really* want to know if your network has gone away in a second, you obviously have to have a network whose packets can make a round trip in less than a second. Moreover, we need to communicate in *much* less than a second, because we have to be able to retry several times. We also need to be able to limit traffic on the network, so that we can guarantee a certain probability that no return packet *really* means dead machines. And if the protocol is designed well, it could constantly update a probability measure of connection downness. So, he can't do it on an arbitrary LAN (or LANs), nor guarantee a 100% correct answer, but he *can* do it over IP. -- --russ (nelson@clutx [.bitnet | .clarkson.edu]) FAX 315-268-7600 It's better to get mugged than to live a life of fear -- Freeman Dyson I joined the League for Programming Freedom, and I hope you'll join too.