[plug] Modems that provide line quality metrics

[Leon Brooks]

On Fri, 27 Jun 2003 14:35, Harry McNally wrote:
> Can anyone suggest V90 et al modems that have this sort of capabilty?

Almost all to some degree.

> Naturally, I'd also be interested in ways to fetch and manipulate
> the data under Linux :-)

As I understand it, you have to interrupt your PPP session, pause for 1 
second (adjustable via ATS2=# (ASCII escape char), ATS12=# (max delay 
in 200ths of a sec between escape chars, default 1/4s) and I'm sure 
there's another one fopr the lead-in delay), +++, brief pause (10ms? or 
wait for "OK"), ATblahdeblah^M, interpret the results, ATO^M (or 
ATO0^M). Probably the easiest way to do this is by matching pppd or 
adding a module, either way earning yet another piece of immortality 
and world-wide fame. (-:

The manual for an external modem I happen to have sitting on my desk 
(http://www.aopen.com/tech/manual/modem/modem_box/fm56-ea.pdf - 
warning, this is *huge*, took a few minutes to pull down at 512k, might 
try your patience on an analog modem) suggests that the following may 
be a useful sub for blahdeblah:

    S91?    (transmission power level, in - dBm)
    V90?    (mode, 0=disabled, 1=auto, 2=28k...21=53k)

AT\V1 (default) adds protocol result codes to CONNECT string (as does W1 
or W2, W1 reports DTE, W2 reports DCE speeds on CONNECT). Adding a 
semicolon (;) to the dial string goes to command mode after dialling 
but stays connected. ATO1 does a retrain, ATO3 renegotiates the data 
rate.

The queries you do are supposed to end with OK. What happens to multiple 
queries in one AT command introducer string is undefined, most modems 
return one OK at the end, some return an OK for each command, so the 
best policy is probably one query per AT.

Cheers; Leon