[Qemu-devel] Qemu phone modem emulation

[Eric Koldeweij]

Hello all,

I am currently working on a serial telephone modem emulation 
implementation for Qemu. My question is if it would be a good idea to 
offer it for inclusion in the qemu main trunk when it's ready. These are 
the requirements I am working with:

- The modem device is accessible through a new option for a serial 
device. A new -serial option has been added (so far, might change in the 
future):
    -serial modem:[<listenIP>]:<listenPort>

- The modem device will emulate a generic serial modem using a 
Rockwell/Conexant RC144xxx chipset. The reasons I have chosen this 
chipset are:
    - It was extremely common in its time and you could argue it was 
the de facto modem standard.
    - It is supported by most if not all serial communications programs.
    - It was the chipset of the first cheap and easily available modems 
with Facsimile/Fax support.
    - I have quite some documentation on this chipset as well as the 
working hardware to compare it against.
    - Since speed is not an issue (there is no bandwidth limiter) there 
is no need to support higher speeds and standards, it's just more 
programming work.

- The modem will be able to receive "calls" on a telnet or telnet-like 
interface. The modem will generate the appropriate "RING" messages to 
the serial port. Serial data and Fax transmission/reception are going to 
be supported.

- The modem will be able to "dial out" to a telnet-like interface 
service. This includes of course a qemu modem device.
    - This is the biggest problem I am encountering so far: it is 
extremely difficult to embed an IP adress and port number into a legal 
"telephone number". Suggestions on how to solve this are more than welcome.
For instance: "ATDT127.0.0.1:14400" works fine now but the dot and colon 
are not allowed in the dial string. Also there is a line limit of 39 
characters for each modem command which makes IPv6 addresses a bit 
difficult to encode. Of course I can make it any way I like but a lot of 
software won't allow it entered as a telephone number either.

- If two qemu instances are "dialing" each other, a speed negotiation 
will take place using unused telnet IAC options in which speed 
capabilities, error-correcting and compression abilities are exchanged. 
This is purely cosmetic however and it is going to be disable-able :) If 
no options are exchanged the emulation will assume a 
can-do-anything-modem at the other side and connect with the highest 
speed as allowed by the settings.

- The emulated modem will not be able to talk to a real modem. Just in 
case it wasn't obvious.

- I am open for feature requests.

I am looking forward to comments. Thanks for your time.

Regards,
Eric Koldeweij.