Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!watmath!clyde!rutgers!sri-spam!nike!ucbcad!ucbvax!sdcsvax!noscvax!tetra!embick From: embick@tetra.UUCP (Edward M. Embick) Newsgroups: net.periphs Subject: Re: Line Drivers vs. Short Haul Modems Message-ID: <143@tetra.UUCP> Date: Fri, 24-Oct-86 15:05:47 EDT Article-I.D.: tetra.143 Posted: Fri Oct 24 15:05:47 1986 Date-Received: Sat, 25-Oct-86 07:17:59 EDT References: <41@cogent.UUCP> Reply-To: embick@tetra.UUCP (Edward M. Embick) Followup-To: net.periphs Distribution: net Organization: Naval Ocean Systems Center, San Diego Lines: 40 Keywords: pros and cons Summary: Experience with mx-2 modems Mark, We have had very good experience using bo-sherel mx-2 asynchronous short haul modems. They mux 8 ports over two twisted pair. We are running them between two buildings. I have vt100's, vt220's, h19's, pc's, and several vt100 and h19 compatibles running at 9600 baud to our VAX 11/780 with Emulex dmf type ports (Emulex CC32 subsystem). I chose the mx-2's because I could run eight ports over two twisted pair, rather than having to have four copper wires for each terminal. I've got communications for 40 ports (5 pairs of mx-2's) between the two buildings using only 20 wires (10 pair). Cost wise the mx-2's are just under $500 a piece ($1000/pair). They have been very reliable (no failures in over a year of operation). All eight ports can run full bore without any perceptable degredation in response or character overruns. The only problem I have is that if the transmit line (pin 2) is not properly terminated, the receive line will cross talk. Since my mx-2's at my VAX are always hot, the situation of UNIX sending out the login message and talking to itself, resulting in a getty failure message, can occur. I cured that by making up connectors for the terminal end so when a users terminal is disconnected, I jumper pin 2 to pin 7 (signal ground). This cures the problem and allows me to connect and disconnect terminals at will in the remote building without having to go to the host. We are running our terminals to the mx-2's through three wire cables (transmit-pin 2, receive-pin 3, and signal ground-pin 7). We jumper pins 4-5 and pins 6-8-20 at both ends. All of our terminals are cabled into a central communications room where the mx-2's are located. Some runs are almost 300 ft. I've had no problems with this setup. FYI bo-sherrel co. is at 36133 Niles Blvd., Fremont, CA 94536. Their phone is (415) 792-0354. I have no connection with them except for being a satisfied customer. ------------------------------------------------------------------------------ Ed Embick (the more paths I make, the more paths they break! waaaaaaa....) Computer Sciences Corp. embick@noscvax.UUCP or 4045 Hancock St. {akgua,allegra,decvax,ihnp4,ucbvax}!sdcsvax!noscvax!embick San Diego, CA 92110 MILNET: EMBICK@NOSC (619) 225-8401 x516