hes@ecsvax.UUCP (03/08/84)
<> I received a brochure from Chung Telecommunications (4046 Ben Lomond Dr., Palo Alto, CA 94036 (415)858-2456) about a box which squeezes 2400 bps through a 212A modem. It will either multiplex two 1200 bps devices or send one 2400 bps. The price is $695 for a one-channel version, and it also provides automatic error detection and retransmit. (Remember, you need on at each end of the line.) The modem required is "Modem type: Bell-212A, with synchronous option. Operating mode: full-duplex on 2-wire dial-up line." The gadget is called a turboMUX(tm). Has anybody actually seen/touched/used this critter? --henry schaffer ncsu genetics
daemon@decwrl.UUCP (03/08/84)
From: tonto::belasco (Steven G. Belasco UHO DTN 264-4920) I have been following the exchanges about modems with some interest since I was once involved that facet of the industry for some time. Perhaps this may help to clear up some of the confusion which appears to exist on the subject at the present time. There are currently three US manufacturers who are delivering wide ranging compatibility product in the 2400 bps, full-duplex (FDX) (transmit and receive simultaneously), 2-wire dial line market: Codex Corporation (subsidary of Motorola), Mansfield, MA Codex 224; Codex V.22bis Concord Data Systems, Waltham, MA CDS 224 Racal-Vadic Corporation, Sunnyvale, CA Vadic Quad Modem (VA4400) There are also several manufacturers (i.e. NEC America) who have announced similar products, but at present, I am unaware of any large quantity of them in the field at this time. All of these units are 2400 bps, 2-wire, FDX operating over the public switched (dial telephone) network, compatible with the soon to be announced AT&T "Bell 224" mode as well as the soon to be approved (at the Nov.'84 session in Geneva) CCITT Recommendation V.22bis. They also operate in fallback mode at 1200 bps in a compatible mode with Bell 212A or CCITT V.22 equipment. Under the terms of these "standards", the modems transmit a specific signal pattern which is in fact 2400 bps at 600 baud. In other words, every 1/600 of a second (one baud time), four bits of data are transmitted. At 1200 bps, only two bits are transmitted each baud time. Since both the CDS and Codex 224 units are compatible with the standards in V.22bis or V.22 mode, these modems can "talk" over international dial circuits to other CCITT compatible modems supplied by local national Postal Telephone Telegraph administrations (the equivalent to AT&T, Bell, the FCC and the PUC all rolled into one) throughout the rest of the world. Both the Concord and Codex units are mechanically designed so that you unplug your telephone's RJ-11 plastic line cord plug from the wall socket, plug the modem into the wall, and then connect the telephone to the RJ-11 jack on the rear panel of the modem. This makes it possible to place calls manually through the modem, or with the appropriate switch settings in the modem, answer the telephone as though the modem did not exist. Although I haven't seen them yet, I'm told both manufacturers either currently offer or have announced and will soon deliver automatic dial versions of these products. While price isn't everything when you should look at when you buy a unit like this, the last time I checked, Concord offered the lowest price at $995. Although the Codex units cost $1195 each, they can be ordered at discounted rates through Codex's direct sales staff in many major cities around the country, or directly from their factory at full price with shipment in 72 hours through their catalog sales department by calling 800-446-6336. The Vadic unit offers added capability (at around $1800+) in that their QUAD modem will also run Bell 103 mode (300 bps, 2-wire, FDX) and Vadic's proprietary VA3400 mode (1200 bps, 2-wire, FDX) as well. From bench tests I saw run, all the units tested performed quite well in 224 and 212 mode with the most noteworthy difference being that the Codex unit provided between 2 db and 4 db better signal to noise ratio performance over the competing products under similar degraded communications line conditions.