vgetty: USR AT+VRA and AT+VRN command

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Richard wrote:

> I was playing around with the US_Robotics.c file in vgetty, and I
> noticed
> that you had added the AT+VRA and AT+VRN commands to set the
> ringback settings.  Those two commands fail on my USR Voice 33.6.
> I have to change them to AT#VRA and AT#VRN and then they work
> fine.  I am curious, is there a reason for having the + instead of #?

This is a bug.  The ZyXEL modem uses AT+VRA and I must have copied
the code verbatim.  Other places in US_Robotics.c use AT#VRA.  I will
fix and test this.
 
> Also, have you noticed that those ringback command work at random?
> They don't seem to work right on my modem.  the default settings of
> 70 and 100, cause the modem to wait 12 seconds before VCON-ing
> after the phone has bee picked up.  Setting VRA to 40 makes it wait
> around 4 secs.  Setting VRN to 0 turns ringback detection of, and it
> returns immediately.

It has been a long time since I looked at this, but I remember
similar results with my US Robotics 56K Voice Faxmodem Pro.  The VRA and
VRN settings had an effect, but they were not very precise.  My guess
is that it depends on where in the ring cycle the phone is picked
up, and possibly on the amount of noise on the line that may confuse
the detection of the ringback.

-- Al