RAF@CU.NIH.GOV ("Roger Fajman") (10/27/90)
I got no response to this on Telecom Digest, so I thought I would try Info-Modems Digest. Some people here would like to use a laptop PC and modem with a celluar telephone for the purpose of giving demonstrations in various locations where a modular jack may not be available. Can anyone recommend cellular telephones and adapters for this purpose? We don't have a particular cellular telephone yet -- it would be purchased specifically for this. The phone would be stationary, of course, while the demonstration is going on, but would be inside various buildings. A related question is how well various modem technologies work over cellular telephones. We are mainly interested in v.22bis (2400 bps) and V.32 (9600 bps) so that so special modem would be needed at the other end. Is it important to have MNP or V.42 error correction?
cpcahil@virtech.uucp (Conor P. Cahill) (10/27/90)
In article <9010262354.AA04244@alw.nih.gov> RAF@CU.NIH.GOV ("Roger Fajman") writes: >Some people here would like to use a laptop PC and modem with a celluar >telephone for the purpose of giving demonstrations in various locations >where a modular jack may not be available. Can anyone recommend >cellular telephones and adapters for this purpose? We don't have a >particular cellular telephone yet -- it would be purchased specifically >for this. The phone would be stationary, of course, while the >demonstration is going on, but would be inside various buildings. Just make sure that you get a telephone that transmits at the maximum wattage (I think this is something like 3 watts). Most hand-helds will only transmit at .3 watts and this will have a hard time getting out of interior rooms of buildings. The other thing you might want to get is a good antenna that can be plugged into the phone. >A related question is how well various modem technologies work over >cellular telephones. We are mainly interested in v.22bis (2400 bps) >and V.32 (9600 bps) so that so special modem would be needed at the >other end. Is it important to have MNP or V.42 error correction? To work with cellular systems you have to have an extremely good error correction algorithm that is hardened for very bad lines. Telebit PEP modems would probably do OK. V.32 modems would probably die and drop the line very often (this often happen on standard phone lines). V.22bis would probably do OK. For the error correction protocol, MNP-10 sounds like the one you need, but this is only available on Microcom modems at this time. I don't know how well v.42 performs on bad lines, but MNP-7 and below do not handle it very well. -- Conor P. Cahill (703)430-9247 Virtual Technologies, Inc., uunet!virtech!cpcahil 46030 Manekin Plaza, Suite 160 Sterling, VA 22170
alan@mq.com (Alan H. Mintz) (10/28/90)
In article <9010262354.AA04244@alw.nih.gov>, RAF@CU.NIH.GOV ("Roger Fajman") writes: > Some people here would like to use a laptop PC and modem with a celluar > telephone for the purpose of giving demonstrations in various locations > where a modular jack may not be available. Can anyone recommend > cellular telephones and adapters for this purpose? We don't have a > particular cellular telephone yet -- it would be purchased specifically > for this. The phone would be stationary, of course, while the > demonstration is going on, but would be inside various buildings. Telebit makes a modem called the Cellblazer, specifically designed for cellular. I believe it operates at a peak rate of 10000 bps (no, not 9600, 10K). Unfortunately, it's high-speed protocol is not compatible with any other Telebit product (yet), so you'll have to use 2 Cellblazers. Telebit claims that they will be offering a firmware upgrade to their rack-mount modems to support the Cellblazer protocol. They are also planning a new product (T2500LL?) that, in addition to the T2500 features, will support leased-line connections and the Cellblazer. Unfortunately, they don't seem to have plans for firmware upgrade to the Trailblazers (even T2500!!). There are a number of telephones specifically made with RS232 connections. I know that Motorola produces such a phone (but I don't have the model number - it's not here yet). -- < Alan H. Mintz | Voice +1 714 980 1034 > < Micro-Quick Systems, Inc. | FAX +1 714 944 3995 > < 10384 Hillside Road | uucp: ...!uunet!mq!alan > < Alta Loma, CA 91701 USA | Internet: alan@MQ.COM >
lindsay@dscatl.UUCP (Lindsay Cleveland) (10/29/90)
In article <9010262354.AA04244@alw.nih.gov> RAF@CU.NIH.GOV ("Roger Fajman") writes: >Some people here would like to use a laptop PC and modem with a celluar >telephone for the purpose of giving demonstrations in various locations >where a modular jack may not be available. Can anyone recommend >cellular telephones and adapters for this purpose? We don't have a >particular cellular telephone yet -- it would be purchased specifically >for this. The phone would be stationary, of course, while the >demonstration is going on, but would be inside various buildings. I have actually seen what you describe. At a demo here in Atlanta of the Telebit "Cellblazer", a digital still-camera was used to take a person's picture. It was then read into a lap-top which then used a standard package to "crop" the photo and include it into a "employee id" form, and then transmit the entire file from the laptop's internal "Cellblazer" modem via a cellular telephone there in the demo room, up to Chicago. (Since I could see the number on the handset's read-out, I know it really was Chicago (-: ) Next, he went over to another cellular phone which was connected to a external "Cellblazer" modem hooked up to a regular PC. He dialed the Chicago computer, went through the proper login sequence, and then down-loaded the same form and picture (in color!) to the PC. I seem to recall the actual thru-put speed as being around 14KB. >A related question is how well various modem technologies work over >cellular telephones. We are mainly interested in v.22bis (2400 bps) >and V.32 (9600 bps) so that so special modem would be needed at the >other end. Is it important to have MNP or V.42 error correction? At the demo, they mentioned that they had to put some very special "smarts" into their program contained in the modem, and it handles the problems of fading and reflections of the signal. The protocol they use is (I assume) a variant of the Telebit PEP protocol. Anyway...I was impressed! Cheers, Lindsay Lindsay Cleveland Digital Systems Co. Atlanta, Ga gatech!dscatl!lindsay (404) 497-1902 (U.S. Mail: PO Box 1149, Duluth, GA 30136)
mrapple@quack.sac.ca.us (Nick Sayer) (10/29/90)
RAF@CU.NIH.GOV ("Roger Fajman") writes: >I got no response to this on Telecom Digest, so I thought I would try >Info-Modems Digest. >Some people here would like to use a laptop PC and modem with a celluar >telephone for the purpose of giving demonstrations in various locations >where a modular jack may not be available. Can anyone recommend >cellular telephones and adapters for this purpose? If you don't mind doing a little "dirty work," there is a product called "Celjack" that aparently works by hooking some wires to the speaker, mic and keypad on your cell phone. It is a circuit board with a standard RJ11 jack, two wires bearing 12VDC, a switch (presumably power), some LEDs, and what looks like a DB-15 or something to hook up the wires from the cell phone. It aparently waits for the RJ11 jack to go "off hook," provides a phony dial tone, translates DTMF or pulse into keypad closures, closes "send" momentarily a couple seconds after the last DTMF, and finally, pushes "end" on hang-up. The only thing I don't think it can do is handle ringing. Apart from that, the only way you can tell it apart from a real phone line is that it takes longer for your dialed number to ring (about 7 seconds or so), and of course, if you're moving, it may suffer the normal cellular fading and switching sort of stuff. The product is reviewed/described in this November's "73" magazine, and is intended for Amateur Radio autopatch (remote phone patch) equipment running on far away hilltops. Telular, Inc. 1215 Washington Ave. Wilmette, IL, 60091-2566 (708) 256-8000 Suggested list price $480 Disclaimer: I don't have anything to do with these people, I just read the review. -- Nick Sayer | Disclaimer: "Don't try this at home, | RIP: Mel Blanc mrapple@quack.sac.ca.us | kids. This should only be done by | 1908-1989 N6QQQ [44.2.1.17] | trained, professional idiots." | May he never 209-952-5347 (Telebit) | --Plucky Duck | be silenced.
lan@cup.portal.com (Los Altos Networks) (11/01/90)
Roger,
I did a lot of work with the TELEBIT CellBlazer for
TELEBIT while I was with them. Let me give you the full
scoop so you will know what you are getting your self into.
So far, the responses I have seen are fairly accurate
as to the CellBlazers performance. Realistically, I have seen
8,000 bits per second going cellular-to-cellular and 12,000 bps
going cellular-to-land line. This is using TELEBIT PEP and special
register settings in the modem which affect the PEP packetization
and use special algorithms to handle station-to-station hand-off
at the cell. There is a bit of a write-up on this available from
TELEBIT tech support or sales support called: TELEBIT PEP MODEM
CONSIDERATIONS FOR ADVERSE COMMUNICATIONS LINKS. Please request
this from them. If you have any trouble, let me know and I'll
send you a copy.
Now here's the hard part. The CellBlazer standalone requires
an external 120V AC power source. Just like a regular standalone
TELEBIT modem. This means you need a 12VDC-to-120VAC converter and
a hefty car battery. The CellBlazer PC-AT card will draw power from
your laptop, but chances are it will draw so much power as to drain
your laptop battery twice as fast as usual. Power to the CellBlazer
is non-trivial.
Next. The cellular phone interface. Here's the real bitch.
There is no standard for RJ-11 interfaces to cellular phones. This
means that there is a different interface adaptor for EVERY cellular
phone made, a different price for the interface, and some phones
with no such interface available. These interfaces are usually
referred to as FAX interfaces. Tellular and their CellJack product
are the most commonly used interface by TELEBIT in their demos. Also,
you should get an active (amplified/filtered) interface if possible.
The Passive interfaces tend to lower the signal strength of the
modem to the cellular phone. There may be an additional power require-
ment for the interface, as well :-(. Ther interfaces tend to run
from $500 and up.
The cellular phone should be set to its maximum VOICE output
volume level. This will assure maximum signal strength. The
Modem is also adjusted for boosted signal strength via its registers.
Experimentation is conducted to find the best settings for the
modem and phone. This might have to be done everytime that you
are at a new remote site or are mobile. Cellular carriers may also
present a problem due to their carrier specs. Some companded channels
or digitally encoded channels may present a barrier to the PEP
modulation which will either lower throughput or kill transmission
altogether.
With these issues in mind, I wish you good luck! If you
are interested in more info or acquiring a CellBlazer, give me a
call.
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Network Consultant || //__\\ || \\ || Los Altos
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