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- Path: sparky!uunet!ferkel.ucsb.edu!ucsbcsl!spectrum.CMC.COM!lars
- From: lars@spectrum.CMC.COM (Lars Poulsen)
- Newsgroups: comp.dcom.modems
- Subject: Re: Looking for ..[info,cellular,comments]REFRESH
- Message-ID: <1992Nov11.190917.23759@spectrum.CMC.COM>
- Date: 11 Nov 92 19:09:17 GMT
- References: <1992Nov4.172928.49833@ccvax.ucd.ie>
- Organization: CMC Network Systems (Rockwell DCD), Santa Barbara, CA, USA
- Lines: 54
-
- In article <1992Nov4.172928.49833@ccvax.ucd.ie> ctoomey@ccvax.ucd.ie writes:
- >1) I bought an El Cheapo V32.bis/V42.bis 8-bit internal card faxmodem
- > based on the (in)famous Rockwell chipset. It is produced by
- > `Lightning Communications' in California, and is called something like
- > a `LiteFax 14F' [don't have the box in front of me..] It has a 16550a
- > UART. I bought it for the equivalent of $450 which is the VERY
-
- I have a couple of Lightcom 96F's which I picked up when another
- supplier was running behind schedule on 144's. They were inexpensive,
- generic Rockwell modems. The 16550A was a requirement for my project
- which severely limited the selection of vendors. I don't use the fax
- side, but what I do use, I've had no problems with the Lightnings.
-
- > Anyhow, some testing with said Lightning (Zzzzaaap!) modem has shown
- > it to be a bit tempermental;
-
- What problems have you had ?
-
- >2) Does anyone know if there is such thing as a modem that could be used
- > with a laptop (Compaq LTE/20s) that plugs into the DIN socket of a
- > cellular phone, and handles communications through handoff etc.
- > (presumably with V42 or MNP4), allowing someone [although maybe not
- > physically on the move] to dial into a port on an office machine,
- > at some reasonable speed (above 1200bps).
-
- The TELEBIT CellBlazer is specially tuned for this application. I think
- it is the only one of its kind.
-
- The cellular connection differs from a regular telephone connection, in
- that phase distortion is changing as the vehicle moves, even without
- handoffs. "Normal" V.32 modems train themselves carefully to the signal
- characteristics of the line, and then try to use all of the available
- bandwidth, while assuming that the link characteristics don't change
- under them. Cellular links change every few seconds, so you need to
- maintain a MUCH larger margin, and be prepared to retrain more often,
- but on the other hand the retrain can/must be done faster.
-
- >3) Why don't modem manufacturers place flash erasable EPROMs into the
- > new generation of modems, as PC manufacturers are starting to do,
- > making all the business of shipping ROMs etc. to users defunct.
-
- Flash ROMs are not the panacea users seem to think. 1 megabyte of flash
- memory costs almost as much as a floppy drive. Even if you put the
- microcode in flash memory, you still need an EPROM to hold the flash
- programming code. (The very newest flash chips allow you to lock a "boot
- sector" as you wipe the rest of the flash memory; this will help some.)
-
- Finally, it becomes a lot harder to support customers if you have to
- worry about customers bungling the code update end ending up with a dead
- modem.
- --
- / Lars Poulsen, SMTS Software Engineer Internet E-mail: lars@CMC.COM
- CMC Network Products / Rockwell Int'l Telephone: +1-805-968-4262
- Santa Barbara, CA 93117-3083 TeleFAX: +1-805-968-8256
-