Question

While discussing how to process AT commands with a colleague,
we discovered that contrary to our belief the command
AT&W (store user profile) is not specified in V.250
(it only specifies ATZ and AT&F, which are related),
leaving us wondering – where is it specified then?

Update: Yes, we expected the command to have its origin in the
Hayes command set, virtually all the basic syntax commands does.
However, most of the Hayes command have been imported into formal
standards like V.250 by ITU or 27.007 by 3GPP.
Since V.250 did not import this command we were wondering
that it might be because it was specified in some other standard.

And in any case other standards have defined various commands.
Here is an extract from a comment I put in the source code
when I were working with the AT+VTS command last year
(which has by the way the most non-standard
parameter syntax I have ever seen!).

The AT+VTS command originally
originates from the standard
TIA/EIA/IS-101, “Facsimile Digital
Interfaces – Voice Control Interim
Standard for Asynchronous DCE” from
1993 by Telecommunications Industry
Association. This specification is now
withdrawn and the AT+VTS command is
now specified in ITU-T V.252
“Procedure for control of V.70 and
H.324 terminals by a DTE”.

Does anyone have a reference to a formal standard/documentation
(like above) that defines AT&W ? We are not just looking for
manufacturer documentation of some random modem (unless for the original Hayes modems).

Answer 1

After some searching I think I have found answers to what I was looking for, however please add additional answers if you happen to have a reference to a standard containing AT&W.

Hayes documentation

While I have not found any manual for the Smartmodem 1200 or Smartmodem 2400 modems,
I found a paper called Technical Reference for Hayes Modem Users
which says the following about AT&W:

&W - Write Active Profile to Memory

The &W command stores certain command options and S-register values into 
one of the modem's two nonvolatile stored profile memory locations. The 
command options and register values stored depend on the particular 
modem. These are indicated in the user documentation for your modem. 
In addition, the AT speed and parity are stored, according to the values 
used at the time the command is issued.

------------------------------------------------------------------------
&W0     Store the Active Profile into Stored Profile 0
&W1     Store the Active Profile into Stored Profile 1
------------------------------------------------------------------------

I assume this covers more or less all modems made by Hayes, so I think this probably is the most official reference I get.

Other standards

An (older) alternative specification to V.25ter/V.250 is TIA/EIA-602 with title “Data Transmission Systems and Equipment – Serial Asynchronous Automatic Dialing and Control”. According to Information On Hayes command set:

TIA/EIA-602 is almost identical to the
data-specific commands found in the
Smartmodems 1200 and Smartmodem 2400

but the specification is not including everything,
TIA/EIA-602 is also referred to as the “Minimal AT Command Set”.
According to Frank Durda’s AT Ampersand-Prefixed Command Set Reference

The EIA/TIA-602 standard only
specifies three AT commands with
ampersand prefixes: &C, &D and &F. All
other AT commands with ampersand
prefixes derive either from the Hayes
Smartmodem 2400, Hayes Ultra 14,400 or
are proprietary features of other
makers.

Which I then interpret to mean that either Hayes Smartmodem defines AT&W but EIA/TIA-602 does not import it (most likely) or that it was introduced after the creation of EIA/TIA-602 at some point (no so likely).

Anyone that has access to an original Hayes Smartmodem manual?