Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!cmcl2!phri!roy From: roy@phri.UUCP (Roy Smith) Newsgroups: comp.dcom.modems Subject: Re: An interesting modem problem Message-ID: <2499@phri.UUCP> Date: Thu, 13-Nov-86 14:54:00 EST Article-I.D.: phri.2499 Posted: Thu Nov 13 14:54:00 1986 Date-Received: Fri, 14-Nov-86 02:03:38 EST References: <128@gaia.UUCP> <1660@mulga.OZ> Reply-To: roy@phri.UUCP (Roy Smith) Organization: Public Health Research Inst. (NY, NY) Lines: 21 Summary: Uni-directional noise might be due to frequency division multiplexing In article <1660@mulga.OZ> steven@mulga.OZ (Steven Bird) writes: > I have found that the presence of the garbage characters depends on the > direction of communication. ie. any garbage characters generally end up > on the terminal screen this end rather than in a file or command on the > computer at the other end. I've noticed this too. I have a theory about why it happens, but I'm not sure. A 212A (and, I think, 103J and V22.bis) full duplex modem has two distinct communication channels frequency division multiplexed over one phone line. The originate->answer side uses half the bandwidth of the phone line and the answer->originate side uses the other half (probably with a guard band in-between). If the spectrum of "typical" phone noise lies mostly in one band, you'll only see noise in one direction. Any modem mavens care to comment on this? -- Roy Smith, {allegra,cmcl2,philabs}!phri!roy System Administrator, Public Health Research Institute 455 First Avenue, New York, NY 10016 "you can't spell deoxyribonucleic without unix!"