Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!decvax!ucbvax!BRL.ARPA!mike From: mike@BRL.ARPA.UUCP Newsgroups: mod.protocols.tcp-ip Subject: Re: Arpanet outage Message-ID: <8612190012.aa08695@SEM.BRL.ARPA> Date: Fri, 19-Dec-86 00:12:38 EST Article-I.D.: SEM.8612190012.aa08695 Posted: Fri Dec 19 00:12:38 1986 Date-Received: Fri, 19-Dec-86 23:46:32 EST Sender: daemon@ucbvax.BERKELEY.EDU Organization: The ARPA Internet Lines: 40 Approved: tcp-ip@sri-nic.arpa Since nobody from DCA has spoken up yet, I'll add a few comments. As the MILNET is being rebuilt using the "new" IMP packaging (with link encryption capability), some (most?) of the data circuits are being moved to DCTN (?Defense Computer Telecomunications Network?), which is an ISDN-oriented base of somewhat switchable circuit capabilities. I believe DCTN has a phased implementation plan, probably with automatic switching happening much later. My general impression is that DCA and Army Signal Corps (now the "Information Systems Command") both tend to do a good to excellent job implementing systems designed around traditional concepts such as point-to-point circuits, so DCTN is likely to be a big win. In addition, I suspect that routing of DCTN circuits is likely to be carefully controlled to prevent excessive bundling onto single transmission links, precisely for survivability. (Blind faith here). What we have seen of DCTN so far is a T1 line terminating in our Post's Central Office at a D4 channel-bank, with a bunch (7?) of 56k DDS links from there to the location of the MILNET IMP. This gives much better signal quality than previous arrangements where the DDS lines traveled over 5 miles of wire to the town CO. It does not provide any additional reliability, as everything still travels over the big black cable from our CO to the town CO. This cable is especially attractive to heavy earthmoving equipment, and is neutralized several times each year. Presumably when the T1 gets to the town CO, it terminates in something resembling a circuit switch or patch pannel or something (behind another D4 channel bank, of course), so that some alternate routing capability exists at that point. Of course, it might be that the T1 gets zipped through a bunch of repeaters to some regional circuit switch, extending our line of vulnerability a good long way. Personally, I find the concept of layering a packet switching network on top of a switchable circuit network rather amusing, but quite realistic and practical. More grist for the Rumor Mill, may it grind long and fine... Best, -MIKE