Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!mailrus!accuvax.nwu.edu!nucsrl!telecom-request From: Michael.Fryd@g.gp.cs.cmu.edu Newsgroups: comp.dcom.telecom Subject: Re: Data Over Voice Message-ID: <2107@accuvax.nwu.edu> Date: 13 Dec 89 01:26:17 GMT Sender: news@accuvax.nwu.edu Organization: TELECOM Digest Lines: 66 Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 9, Issue 570, message 2 of 8 Around here, DOV means "Data Over Voice" and refers to the Gandlaf DOV 640 modems that provide 64kb synchronous communications over a standard voice pair, without interfering with normal voice service. In Pittsburgh, this service is known as Metropolitan Campus Network (MCN) and is provided by some combination of Carnegie-Mellon University (CMU) and Bell of PA. My house was a beta-test site for this service a few years ago, and in the many technician visits I picked up a few things. I have since moved, so some of the details may have changed. Two DOV modems are actually used for each house served. One is placed at the Bell of PA Central office(CO), between the switch and the cable pair to your house. The second DOV is installed in your house, electrically between the Network Interface Jack and your existing household phone wires. +---------+ | Central | voice +--------+ data and voice +---------+ voice +---------+ | Office |-------| CO DOV | ----------------| user DOV|-------|telephone| | switch | +--------+ +---------+ +---------+ +---------+ | | |data |data Port Selector in CO--- + +-------Home terminal or PC The modems communicate using frequencies above the voice band. The DOVs completely ignore all of the normal telephone signals, allowing uninterrupted data communications regardless of whether the phone line is in-use, ringing, or idle. The DOV operates as 64Kb synchronous. In order for the DOVs to work you must be within a pre-set distance (I think on the order of a few miles) from the CO. The real problem with this setup, is that it only allows you to communicate with the CO. Bell of PA installed port selectors in three of the COs near CMU. These were connected by fiber to CMU. At my house, I just plugged my terminal into the DOV, and hit return. This got the attention of Bell's port selector. There were few destinations at CMU that I could select (Most of which were additional port selectors or terminal concentrators). When I left the program, only 9600 and 19.2 kBd async was supported, with plans for 64Kb, possibly using Serial Line IP. The most amazing thing was that the system worked very well. Voice and data operated independently on the same copper pair. Incoming and outgoing calls did not affect data at all. I have no idea what the applicable tariffs were. Payments were made to CMU, but installations and service was provided by Bell of PA. I was always amazed that the Bell service operators (just dial 611) were able to cope with MCN trouble reports. The biggest problem during the testing phase was noise on the phone line. The DOVs went through quite a few revisions before there was no audible interference with the standard voice usage. If I've left anything out, let me know and I'll be happy to give the answer if I know it. Michael Fryd President Voice: (412) 751-5557 MEFCO, Inc. Fax: (412) 751-8403 2401 Coulter Road Email: Michael.Fryd@CS.CMU.EDU McKeesport, PA 15131-4251