sichermn@beach.csulb.edu (Jeff Sicherman) (01/12/91)
Protocols and other software issues aside, is it possible or practical to have a conference call with modems ? No real need or application but interested in the electronic and telephony issues. Jeff Sicherman
tnixon@hayes.uucp (01/14/91)
In article <1991Jan12.055735.18719@beach.csulb.edu>, sichermn@beach.csulb.edu (Jeff Sicherman) writes: > Protocols and other software issues aside, is it possible or practical > to have a conference call with modems ? No real need or application but > interested in the electronic and telephony issues. It's not possible to have a conference call with the modems that are typically used with PCs. They all use modulation schemes that transmit a continuous carrier, and these could conflict with each other. The way to do a "conference call" with modems is the way it is done on CompuServe and many multi-line BBSes -- the modems don't share a phone line, but the host software takes anything typed on one line and duplicates it out to the users on the other lines. -- Toby Nixon, Principal Engineer | Voice +1-404-449-8791 Telex 151243420 Hayes Microcomputer Products Inc. | Fax +1-404-447-0178 CIS 70271,404 P.O. Box 105203 | UUCP uunet!hayes!tnixon AT&T !tnixon Atlanta, Georgia 30348 USA | Internet hayes!tnixon@uunet.uu.net
ch@dce.ie (Charles Bryant) (01/17/91)
In article <1991Jan12.055735.18719@beach.csulb.edu> sichermn@beach.csulb.edu (Jeff Sicherman) writes: > > Protocols and other software issues aside, is it possible or practical >to have a conference call with modems ? No real need or application but >interested in the electronic and telephony issues. There have been networks that work like that. I believe that bank's ATMs use such a system. Their system is multidrop. This is leased-line based, but with conference-calling it should work over dialup. The modems must work in half-duplex mode (typically V.23 for 1200, V.26 for 2400 etc). The protocol determines who talks at any given time (e.g. a 'master' may poll each station in turn). You could set up a dialup broadcast network (like an ultra low speed Ethernet!) with conference calling. Of course modems such as V.32 which can't operate in half-duplex mode wouldn't work, and many cheap PC modems don't work in half-duplex either. The applications would be very limited. If you want to connect A, B, and C, a conference-call based network would only be worthwhile if it was cheaper than two links A-B and B-C, and the traffic between the three was related (otherwise its easier to make two seperate calls). e.g. some application sends requests from A to B, which triggers a request from B to C, which replies to A. -- Charles Bryant (ch@dce.ie) -- /usr/ch/.signature: Block device required