Path: utzoo!telecom-request Date: 13 Apr 91 13:19 +0200 From: Morten Reistad Newsgroups: comp.dcom.telecom Subject: Re: Is a Data Conference Using Three-Way Calling Possible? Message-ID: Organization: TELECOM Digest Sender: Telecom@eecs.nwu.edu Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 11, Issue 291, Message 4 of 10 Lines: 32 Leryo Malbito asks: > Would anyone know how one could set up a data conference using > three-way calling? This seems like an idea that would be not too [...] Yes, you can. You would have to have the vintage line discipline for half-duplex modems in place, ie. have explicit control over the carrier, and you would have some kind of line discipline to decide which one will have a go at the carrier. Most access control schemes can be used, CSMA, Token-passing, time-slots have all been used in similar setups. The setup is called multidrop in telco lingo (even in Norwegian it is spelled multidrop ;-) and is mostly used with leased, voice grade lines on low speeds. The V.23 standard (1200 bps, one channel only) is mostly used for this. I have one such fully functional vintage 1980 NOKIA modem as a bookstopper. The advanced modems used for dialup lines are ill-suited for such use, mostly because they are automated and "user-friendly", and because they need to analyze (train) for several hundred milliseconds before they have a useful connection. This training is needed because more advanced (faster) modulation techniques are used. Many IBM sites use this kind of setup (multidrop, on leased, el-cheapo voice grade lines) for their infrequent users. My local travel agency had that kind of setup until January this year. Morten Reistad