Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site ttidcb.UUCP Path: utzoo!watmath!clyde!burl!ulysses!allegra!mit-eddie!genrad!panda!talcott!harvard!seismo!cmcl2!philabs!ttidca!ttidcb!jackson From: jackson@ttidcb.UUCP (Dick Jackson) Newsgroups: net.dcom Subject: More on High Speed Modems over Dialled Circuits Message-ID: <276@ttidcb.UUCP> Date: Mon, 11-Feb-85 14:55:03 EST Article-I.D.: ttidcb.276 Posted: Mon Feb 11 14:55:03 1985 Date-Received: Thu, 14-Feb-85 01:44:31 EST Organization: TTI, Santa Monica, CA. Lines: 30 OK. So now we have a debate on what factors make a good versus bad dial-up data circuit. Does anyone know? I would guess that if your call is digitized at the serving CO and stayed digital until it got to the SCO at the destination, then you should have a good circuit provided all the intermediate hops were decently within spec. But maybe there are sources of impairment that I am not aware of (e.g. the synchronization slip outage we have been hearing about re. 212 errors). But cross country I believe that calls go analog microwave. In this case there is repeated amplification, which is presumably why you hear thermal noise on most long distance (voice) calls. If on a multi-stage path there are continual conversions between digital and analog there would seem good reason to expect trouble. On what kind of routes would you expect this? When we make voice calls from Santa Monica (Los Angeles) to Huntington, Long Island, you know you're talking long distance; amplitude is down and there's a lot of thermal type noise evident. As I reported in a previous posting, regular 9600 bd modems work well over such lines. Are there circuit impairments (e.g. phase effects) that affect modems but are not detectable by ear? If so, what type of paths are most likely to produce them? One more anecdote: we have done a lot of calling on 224 modems between Santa Monica and Sioux Falls, SD. I don't know whether that qualifies as a rural end point but we have had no trouble at all.