[?] Would like to decode and display V22bis data (2400baud)

[David Chapman]

Hi,
I have some high-quality DAT recordings of a V22bis (2400 baud)
data exchange between a modem and a computer, which were made by
recording across the telephone line via a suitable interface.

I'd like to be able to decode, display and analyse the data in these
recordings, preferably using hardware circuitry to drive a suitable
serial interface program (such as Tera Term or similar). I realise that
my recordings are of a two-way data exchange, so any decoded information
will need some 'untangling' to separate the go and return paths,
however, since I'm only interested in observing and understanding the
actual handshaking procedures, I'd be happy to accept results that are
not entirely perfect.

Can anyone recommend a simple and effective way to do this? I was
wondering if any of the dedicated data modem ICs that were all the rage
when modem speeds were much slower than today, are still available. If
so, can anyone recommend one that could translate the actual V22bis
tones into suitable logic levels?

I'm sure that the experts in this NG will have already realised that
data is NOT my speciality subject so, if I'm asking for something silly
or unreasonable, please feel free to tell me (but gently) the error of
my ways. ;-)

TIA - Dave

 

[Steve Hayes]

Hi,
I have some high-quality DAT recordings of a V22bis (2400 baud)
data exchange between a modem and a computer, which were made by
recording across the telephone line via a suitable interface.

I'd like to be able to decode, display and analyse the data in these
recordings, preferably using hardware circuitry to drive a suitable
serial interface program (such as Tera Term or similar). I realise that
my recordings are of a two-way data exchange, so any decoded information
will need some 'untangling' to separate the go and return paths,
however, since I'm only interested in observing and understanding the
actual handshaking procedures, I'd be happy to accept results that are
not entirely perfect.

Can anyone recommend a simple and effective way to do this? I was
wondering if any of the dedicated data modem ICs that were all the rage
when modem speeds were much slower than today, are still available. If
so, can anyone recommend one that could translate the actual V22bis
tones into suitable logic levels?

I'm sure that the experts in this NG will have already realised that
data is NOT my speciality subject so, if I'm asking for something silly
or unreasonable, please feel free to tell me (but gently) the error of
my ways. ;-)

TIA - Dave

V22bis (like other low-speed protocols) uses separate frequency ranges
for each direction so disentangling the data shouldn't be a problem. In
principle, you could feed the signal back into a commercial modem and get
it to demodulate it and spill the data to the controlling PC where you
could capture it (e.g. with HyperTerminal).

The trick would be to get the modem to think it was connected which might
require a lot of trial and error with initialisation settings, etc. It'll
be easier if you can establish the connection via a real phone line (e.g.
a PBX extension) as the modem may not cooperate if the line voltage and
current aren't right. The older (and dumber) the modem, the more likely
it is to work.

 

[Sjouke Burry]

Hi,
I have some high-quality DAT recordings of a V22bis (2400 baud)
data exchange between a modem and a computer, which were made by
recording across the telephone line via a suitable interface.

I'd like to be able to decode, display and analyse the data in these
recordings, preferably using hardware circuitry to drive a suitable
serial interface program (such as Tera Term or similar). I realise that
my recordings are of a two-way data exchange, so any decoded information
will need some 'untangling' to separate the go and return paths,
however, since I'm only interested in observing and understanding the
actual handshaking procedures, I'd be happy to accept results that are
not entirely perfect.

Can anyone recommend a simple and effective way to do this? I was
wondering if any of the dedicated data modem ICs that were all the rage
when modem speeds were much slower than today, are still available. If
so, can anyone recommend one that could translate the actual V22bis
tones into suitable logic levels?

I'm sure that the experts in this NG will have already realised that
data is NOT my speciality subject so, if I'm asking for something silly
or unreasonable, please feel free to tell me (but gently) the error of
my ways. ;-)

TIA - Dave

Are you trying to get yourself or us int jail??
If so, no thank you...

 

[Cydrome Leader]

Hi,
I have some high-quality DAT recordings of a V22bis (2400 baud)
data exchange between a modem and a computer, which were made by
recording across the telephone line via a suitable interface.

I'd like to be able to decode, display and analyse the data in these
recordings, preferably using hardware circuitry to drive a suitable
serial interface program (such as Tera Term or similar). I realise that
my recordings are of a two-way data exchange, so any decoded information
will need some 'untangling' to separate the go and return paths,
however, since I'm only interested in observing and understanding the
actual handshaking procedures, I'd be happy to accept results that are
not entirely perfect.

Can anyone recommend a simple and effective way to do this? I was

first stop is to get a nice old modem that you can locate the AT command
set for.

You can force old modems into believing there is a connect with the
correct commands. This will all depend on the modem. This assumes you want
the data itself. I fail to believe you're after handshake data, as that's
so easy to replicate with two modems.

I'd grab my external MultiTech or Microcom 2400 baud modems for a task
like this.

 

[JosephKK]

V22bis (like other low-speed protocols) uses separate frequency ranges
for each direction so disentangling the data shouldn't be a problem. In
principle, you could feed the signal back into a commercial modem and get
it to demodulate it and spill the data to the controlling PC where you
could capture it (e.g. with HyperTerminal).

The trick would be to get the modem to think it was connected which might
require a lot of trial and error with initialisation settings, etc. It'll
be easier if you can establish the connection via a real phone line (e.g.
a PBX extension) as the modem may not cooperate if the line voltage and
current aren't right. The older (and dumber) the modem, the more likely
it is to work.

That is more of a maybe. Though two modems (to two ports) may do it
well. V.22bis is QAM not FSK. Higher speeds can get really ugly for
using recordings.

 

[David Chapman]

I

That is more of a maybe. Though two modems (to two ports) may do it
well. V.22bis is QAM not FSK. Higher speeds can get really ugly for
using recordings.

I've recently been told about this product which seems to be ideally
suited to the job:-

http://www.3amsystems.com/products/linescope.htm

Many thanks to all those in this NG who offered other interesting
suggestions.

- Dave