Re: tlug: RJ-11 in the UK?

[jwb@example.com (Jim Breen)]

On Oct 16,  9:47am, Jim Tittsler wrote:
} Subject: Re: tlug: RJ-11 in the UK?
>> On Thu, Oct 15, 1998 at 06:12:44PM +0900, Jonathan Byrne - 3Web wrote:
>> > >Another thing to watch for is the "guard tone" setting.  I think
>> > What's a guard tone?
>> 
>> Guard tones were used by the answering V.22/V.22bis modems during the
>> handshake sequence in the UK (1800Hz) and some other European countries (uh,
>> I forget, 500Hz?).  I think their main purpose in life was to give a solid
>> carrier that could be used to control the echo cancellation on the phone
>> network.

Practically the first thing in the V.22 & V.22bis standards is the
statement on the 1800Hz guard tones. Then it adds that there are two
"national options":

- disble the guard tone
- use 550Hz instead of 1800Hz

Those older modem standards were riddled with national options. They are
still around, but (a) the national carriers don't try & control modems as
much, and (b) these days modems are smart enough to try various options
until they can agree.

Jim

-- 
Jim Breen        School of Computer Science & Software Engineering
Email: j.breen@example.com                Monash University
http://www.csse.monash.edu.au/~jwb/     Clayton VIC 3168 Australia
P: +61 3 9905 3298 F: 9905 3574 $B%8%`!&%V%j!<%s(J@$B%b%J%7%eBg3X(J
---------------------------------------------------------------
Next Nomikai: 20 November, 19:30 Tengu TokyoEkiMae 03-3275-3691
Next Meeting: 12 December, 12:30 Tokyo Station Yaesu central gate
---------------------------------------------------------------
Sponsor: PHT, makers of TurboLinux http://www.pht.co.jp