S91 - PSTN Transmit Attenuation Level

[Franc Zabkar]

The Rockwell documentation suggests that one can control a modem's
transmit level via S-register S91. I tested this by directly
connecting two Rockwell modems and monitoring the "receive level"
using the AT&V1 command. I noticed that the receive level remained at
around 12-13 dBm (and line quality at 8-9) irrespective of the S91
setting. I made sure that S91 was set to the same value for both
modems before each connection attempt. I varied these settings from
the minimum of -15dBm to the maximum of -8dBm (values in the range 0-7
were not allowed - the modem reverted to 8).

Is it possible that the V34 protocol uses the initial transmit levels
as a baseline prior to renegotiating more appropriate signal levels
during the connection process? If not, then what is the purpose of
S91?

BTW, the two modems connected at 33600bps with LAP-M and V.42BIS.

=====================================================================
S91 - PSTN Transmit Attenuation Level
-------------------------------------

S91 sets the transmit attenuation level from 0 to 15 dBm for the PSTN
mode, resulting in a transmit level from 0 to -15 dBm, In some
countries, the transmit level may not be changed and there are checks
to prevent transmit attenuation level change using ConfigurACE.

Range: 0 to 15 dBm (Corresponding to 0 to -15 dBm transmit level.)

Default: 10 (-10 dBm transmit level.)
=====================================================================

%L - Report Line Signal Level
-----------------------------

Returns a value which indicates the received signal level. The value
returned is a direct indication (DAA dependent) of the receive level
at the MDP [= modem data pump?], not at the telephone line connector.
For example, 009 = -9 dBm, 043 = -43 dBm, and so on.
=====================================================================

-- Franc Zabkar

Please remove one 'e' from my address when replying by email.

[Rick Collins]

Sometimes the answer may be more obvious....", In some

countries, the transmit level may not be changed and there are checks
to prevent transmit attenuation level change using ConfigurACE."

"Franc Zabkar" <franc...@ozeemail.com.au> wrote in message
news:399e3fb...@news.ozemail.com.au...

[Franc Zabkar]

The obvious had occurred to me. That's why I stated that I was unable
to set S91 to any value less than 8. Obviously ConfigureACE was
limiting my choices to the range 8-15, rather than the unrestricted
0-15.

I recall that an Australian telecoms engineer, Alan Fowler, once
stated in comp.dcom.modems that he made use of S91 in establishing
dial-up connections. At that time I queried whether this was
necessary. I believed that the V34 protocol would renegotiate optimal
signal levels at both ends during the initial line probe. My recent
testing appears to support this.

On Sat, 19 Aug 2000 17:59:26 -0400, "Rick Collins"
<ab...@debbs.ndhq.dnd.ca> put finger to keyboard and composed: