Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!lll-crg!ames!ucbcad!ucbvax!CCQ.BBN.COM!pogran From: pogran@CCQ.BBN.COM (Ken Pogran) Newsgroups: mod.protocols.tcp-ip Subject: Re: Arpanet outage Message-ID: <8612170038.AA04624@ucbvax.Berkeley.EDU> Date: Tue, 16-Dec-86 09:13:04 EST Article-I.D.: ucbvax.8612170038.AA04624 Posted: Tue Dec 16 09:13:04 1986 Date-Received: Wed, 17-Dec-86 19:41:33 EST Sender: daemon@ucbvax.BERKELEY.EDU Organization: The ARPA Internet Lines: 39 Approved: tcp-ip@sri-nic.arpa Dan, Your question to Andy, "How on earth does it come to happen that 7 'trunks' are 'routed' through one fiber optics cable" is more properly addressed to the common carriers whose circuits the ARPANET uses, rather than to the packet switching folks. Here we are in the world of circuits leased from common carriers, where economies of scale (for the carriers!) imply very high degrees of multiplexing. As the customer of a common carrier, you specify the end points that you'd like for the circuit, and the carrier routes it as he sees fit. This is a personal opinion, and not a BBNCC official position, but I think it's safe to say that without spending a lot of extra money, and citing critical national defense needs, it's going to be hard to get a carrier to promise -- and achieve! -- diverse physical routings for a given set of leased circuits. I would also venture the opinion that there are lots of places in the U. S. where there's only one physical transmission system coming into the area that can provide the 56 Kb/s Digital Data Service that the ARPANET (and MILNET, and ...) uses. An implication of this is that almost any wide-area network (doesn't matter whose, or what the technology is) is going to be somewhat more vulnerable to having nodes isolated than its logical map would suggest. In fairness to the common carriers (are there any in the audience?), the higher the degree of multiplexing, the more well-protected the carrier's facilities are, and the more attention is paid to issues of automatic backup (carriers call this "protection") and longer-term rerouting of circuits when there's an outage (carriers call this "restoration"). So an outage of the type that's been discussed ought to be a very low-prob event. Kind of like wide-spread power failures ... Hope this discussion helps. Ken Pogran