V.90 and V.92: the analogue modem¶
This page is about D-Modem as the analogue end of a 56k call: the
customer's modem on an ordinary phone line, calling an internet
provider's V.90 or V.92 server (see
the two ends of a 56k call).
D-Modem runs as this end when it drives real modem hardware with
dmodemd -a or dmodemd --usb (see Softmodem hardware).
For the plan, each phase of the start-up, the receiver and the tests, see the technical details.
Status¶
All of it is done and on by default:
| Part | What it gives |
|---|---|
| V.90 | up to 56000 bit/s down, 33600 up |
| Retrains and speed changes during a call | the call adapts as the line changes |
| V.92 with modem-on-hold | the call can wait while you take a call-waiting call |
| V.92 PCM upstream | up to 48000 bit/s up instead of 33600 |
| V.92 quick connect | a faster start-up, about a second sooner on every call |
| Speed changes for PCM upstream | both directions can adapt |
It has been tested against D-Modem's own digital modem on a simulated network, because that is the only digital modem available to test against. It has not yet been tried on a real phone line against a real provider's server.
Settings¶
- Keep the line at 9600 Hz (the default,
-r 9600). At 8000 Hz the modem's clock and the network's drift apart and the 56k signal is lost every few seconds, so V.90 is off there unless you setDSP_V90A=1. DSP_V90A=0turns V.90 off as the analogue modem (V.34 is used instead).DSP_V92A_UP=0turns off only the faster V.92 upload.