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.
