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5.1.17 US Robotics (now 3com) Courier/Sportster Fax/Data modems

There are a number of major lines of 3com/US Robotics modems:

Some older USR firmware versions had severe bugs when doing RTS/CTS (that is, hardware) flow control. Occasionally, a byte got lost, and sometimes this confuses the modem enough to abort transmission with the error message

Transmission error: +FHNG:44 (Unrecognized Transparent data command)

Sam Leffler recommends using Xon/Xoff flow control for both fax sending and fax receiving (#define FAX_SEND_FLOW FLOW_SOFT and #define FAX_REC_FLOW FLOW_SOFT in policy.h).

Some day in the future, I’ll make those "quirks" configurable from the config file, but until then, you’ll have to live with recompiling. Sorry. (Upgrade your firmware!).

Fax polling with the USRs is not working, even though the modem claims so. It will work half-way through, but fail miserably later.

When sending faxes with an USR faxmodem, set ignore-carrier yes in sendfax.config. Otherwise it will fail after the first page with a read error and error code -5. (But that is default anyway, if you use mgetty 1.1.16 and up).

For some fax receivers, a problem remains: the USR modems do not want to negotiate 7200 bps transmission speed. If the receiving modem won’t accept 9600 bps, transmission will fail after sending three DCS frames, with the error code +FHS:25. In that case, try setting fax-max-speed 7200 in sendfax.config.

RSPEC errors: some series of USR Sportsters and early Couriers have bugs in the handling of the AT+FCC command. It’s meant to specify the maximum transmission speed, like “14400”, but these modems interpret it as minimum speed, so they fail if sending to a machine that can only do 9600 bps. If you see RSPEC errors in the sendfax log (+FHS:24), try the setting modem-quirks 0x20 in sendfax.config. This will tell sendfax not to set the corresponding AT+FCC parameter.

The USR modems support Caller ID delivery (both the I-Modem series and the analog ones). Switch it on with AT#CID=1 and mgetty should automatically be able to recognize the incoming caller ID. If not, show me a detailed log file...

Firmware upgrades and documentation are available on in the directory /pub/USRobotics/modem/....

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