Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!decvax!ucbvax!CCV.BBN.COM!haverty From: haverty@CCV.BBN.COM.UUCP Newsgroups: mod.protocols.tcp-ip Subject: Re: Arpanet outage Message-ID: <8612161942.AA29740@ucbvax.Berkeley.EDU> Date: Tue, 16-Dec-86 08:09:50 EST Article-I.D.: ucbvax.8612161942.AA29740 Posted: Tue Dec 16 08:09:50 1986 Date-Received: Wed, 17-Dec-86 18:38:51 EST Sender: daemon@ucbvax.BERKELEY.EDU Organization: The ARPA Internet Lines: 32 Approved: tcp-ip@sri-nic.arpa Dan, It's misleading to think that you are ordering a "trunk" from a communications supplier. What you are buying is a plug at one site through which you can pass bits, which appear by some magic at the plug you have bought at the other site. Assuming that there is a physical wire between the two with any particular characteristics other than what is specified in the service offering (e.g., BER, speed, conditioning) is a dangerous practice. The nice network maps we all draw are topological, not physical. We've often deduced physical characteristics from observed behavior, and seen this kind of thing in many networks. I remember one in particular that had a microwave "sweeper" on a tower, which swept a beam in a circle to hit N other microwave stations around the horizon; the observed effect of this was a propagation delay of about 100 msec., which is far too short for any normal satellite trunk, and far too long for any normal terrestrial circuit. I also remember a backhoe in a farmer's field in Illinois which dug up N of our carefully redundantized trunks with a single flip of the scoop. I think in most cases even if you figure out something about the physical implementation, there is no guarantee that it will be the same next week. Vendors do offer some options that you can specify, usually at extra cost, like a guaranteed terrestrial routing to control delay; I think you can also specify separate physical routes for different circuits in some cases. Jack