Date: Thu, 24 Aug 1995 12:27:26 -0500 (CDT) From: Joe Greco <jgreco@brasil.moneng.mei.com> To: rashid@haven.ios.com (Rashid Karimov.) Cc: hackers@freebsd.org Subject: Re: GOOD and W/O extras ISDN modem - advice needed. Message-ID: <199508241727.MAA19891@brasil.moneng.mei.com> In-Reply-To: <199508241652.MAA04899@haven.ios.com> from "Rashid Karimov." at Aug 24, 95 12:52:27 pm
next in thread | previous in thread | raw e-mail | index | archive | help
> just ISDN modem. No fax/V34/TA stuff. Just the serial > port and RJ11 to plug the ISDN line in ( the ability > to go with 128K is a must). > Any suggestions ? Phones ? Hello, We have a terminology problem. And you DON'T want to have a terminology problem when buying things, because you'll end up getting something you don't want. Especially if you tell someone you want an "ISDN modem". An "ISDN modem" is generally a saynothing. ISDN is a *digital* service, and hence modulation and demodulation (mo/dem) has no meaning. Some people will take "ISDN modem" to mean an ISDN device with a built-in V.34 modem. This type of device allows you to use your ISDN line to connect to a conventional V.34 modem on a POTS line (Plain Old Telephone Service, etc). The V.34 "modem" could potentially be all digital, but apparently the typical method is to literally stuff a V.34 modem in along with analog phone line interface circuitry that translates analog to digital. An "ISDN TA" (Terminal Adapter) is a device that takes a serial line (sync V.35 or async RS232) and uses a protocol to transmit that data over the ISDN circuit. Since the protocol does not really introduce any overhead, you are essentially able to run at ISDN speeds (57.6K async or 64K sync). Newer products allow you to connect two channels simultaneously and use both together as a virtual faster link. This is sometimes called "BONDING" (which actually refers to sync links to which this is done). If you want to be able to do 115.2K you need to make sure that the units are able to do this in some fashion. You cannot do 128K on an async link because 128K isn't a standard RS232 speed. Your next choice would probably be 230.4K, but I haven't seen any terminal adaptors that support this speed, and you need a special serial port to handle it. Anyways, in conclusion: An ISDN TA does not deal with analog information in any way. The latest products are generally hybrids - they are terminal adapters that also have an analog circuit so that you can plug in a V.34 or regular telephone. Given your description of what it is you want, you ARE absolutely positively looking for an ISDN TA. Motorola makes several products. The one I've used is the UTA-220. This is a fairly decent and flexible terminal adapter. The Bitsurfer and Bitsurfer Pro are reportedly able to do the things you are asking, as well, and are hybrids of some sort. Ironically I believe that you may find the Bitsurfer and other hybrids for a *lower* price than many of the plain terminal adapters. At least based on the last pricings I've seen... Good luck, ... Joe ------------------------------------------------------------------------------- Joe Greco - Systems Administrator jgreco@ns.sol.net Solaria Public Access UNIX - Milwaukee, WI 414/342-4847
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?199508241727.MAA19891>