for the travelers among us (real space types)

[David Farber <farber () central cis upenn edu>]

From: oppedahl () panix com (Carl Oppedahl)
Subject: Modem Traveling FAQ (was Re: European Modem Standards)
Date: 26 Sep 1993 23:39:35 -0400
Organization: PANIX Public Access Internet and Unix, NYC




In <telecom13.663.2 () eecs nwu edu> jwhite () panix com (Jonathan White) writes:


> Please excuse me if this is talked over a lot, I don't get a chance to
> read this group much anymore. A friend has asked me to send her a
> modem to Rome but I'm not sure what standards are neccessary and what
> they are and what manufactuers support them. Is v.22 1200 baud and
> v.22bis 1200 baud 2400bps etc.? I'd appreciate replies by e-mail. If
> there is interest I can sumerize and post.


Here is an FAQ on the subject.


I request that readers send me proposed additions and changes to this
FAQ.


Dialing -  If you use rotary dial, be aware that many countries use
make/break ratios differing from those used in the US.  If you have
trouble reliably rotary-dialing, study your modem manaul and try
setting the make/break ratio to the other ratio.


Some countries do rotary dialing differently than in the US.  Sweden,
for example, relates one click with "0", two clicks with "1", and so
on up to ten clicks meaning "9" on the dial.  This differs from most
countries where one click means "1" and so on.  New Zealand, I have
been told, uses a reversed correspondence, so that ten clicks means
"1", nine clicks means "2", and so on up to one click meaning "0".  In
such countries you would need to translate the phone number to be
dialed, before giving the dialing string to the modem.


  US:      1 2 3 4 5 6 7 8 9 0
  NZ:      0 9 8 7 6 5 4 3 2 1
  Sweden:  0 1 2 3 4 5 6 7 8 9
 
If you use tone dialing you should have no trouble dialing.  The
dual-tone-multifrequency (DTMF) tones used are standard worldwide.


Dial tone detection - Some modems (most of them, nowadays) actively
listen for dial tone, and will not commence dialing until they hear a
dial tone.  If they are picky and listen only for a precision US dial
tone (a mix of two defined sine waves) they might not work well in
some other country where the dial tone is different.  So you might
have to program the modem to "blind dial", namely, to dial without
having actually recognized a dial tone.  My Practical Peripherals
14400FX PKT (which is a good choice for traveling) can be programmed
to blind dial by putting X0 in the dialing string.  You would have to
study your manual to see how your modem can be told to do this.


Call progress detection - Some modems will attempt to detect and
report such things as busy signals and ringing sounds.  They may not
be able to recognize the sounds emitted by non-US exchanges.  You may
have to disable these features in the modem, or in your communications
software.


Distinctive ringing - Some equipment (e.g. fax switcher boxes) will
watch for patterns of sound and silence in an incoming ring.  The
patterns are different from country to country and the equipment could
get confused.  You might have to turn off this feature if you are
receiving calls.


The plugs and jacks - To complete your hookup you will typically need
an adaptor.  One way to do this is to find an adaptor that will
receive the US-style modular plug and that will in turn plug into the
wall.  Another way is to buy a replacement cord that has the domestic
plug at one end (to plug into the wall) and a modular plug on the
other end (to plug into your CPE (customer provided equipment).
Sometimes I will get luck when traveling and the place I am visiting
will already have US-style modular plugs in place.  Some hotels do
this, for example, outside of the US.


Ground start - Some exchanges use "ground start", in which CPE
requests a dial tone by grounding one of the wires of the telephone
line.  US CPE is loop start, which requests a dial tone by connecting
the two wires of the line to each other (through a 600 ohm impedence).
To use US-style equipment you need to order a loop start line from
your telco.


The data signaling protocols - Most modems nowadays are 2400 bps or
faster, following the V.22bis, V.32 and V.32bis protocol standards.
If the number you are calling is also V.22bis, V.32 or V.32bis, you
should have no trouble.


But if the modem you are calling is slower than 2400 bps, you need to
check further.  The standards for 300 and 1200 bps data communications
are different in the US and elsewhere.  Study the documentation for
your modem to be sure it can be programmed to follow the protocol for
the modem you are calling, if it is slower than 2400 bps.


Modems in Germany - I have been told that to be PTT-approved in
Germany, a modem must be programmed so that it will never retry a busy
number more than a preset number of times.


Fax sending - If you have a Group III fax machine and are sending to
Group III fax machines, then you will have no fax compatibility
problems anywhere in the world.


The law - Finally, you must keep in mind that some countries are
rather strict about what you can and cannot plug into their telephone
jacks.  It is possible to imagine any of several motives for this,
from the concern that defective CPE might electrocute a telephone
worker to the concern that CPE obtained from a source other than the
PTT would reduce the PTT's revenues on overpriced CPE.


If the CPE you propose to use has a US FCC Part 68 registration
number, it is unlikely it would pose any safety risk anywhere in the
world.  Most PTT's, in certifying equipment for use in their systems,
use the same standards the FCC does under Part 68.


Nonetheless, you would be wise to find out what is legal and what is
not in your country before connecting CPE to your lines.


However, even though it may not pose a safety risk, the equipment may
not *work* if it expects U.S. signalling levels.  However, modem
manufacturers don't like to change their product for export, and most
modems are designed to work even at the lower signalling levels
present in some other countries.


Thanks to:  


H. Peter Anvin N9ITP (hpa () nwu ed)




Carl Oppedahl AA2KW  (patent lawyer)
1992 Commerce Street #309
Yorktown Heights, NY  10598-4412
voice 212-777-1330