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I've got a brand-new external USRobotics 56k fax modem attached via serial cable to COM1 on an HP DL380 running vSphere 4.1.

The guest operating system in question in Server 2003 Std, SP2.

Serial passthrough is configured properly, and incoming faxes through the Windows fax server are OK. Outgoing faxes, however, have problems. Dialing and connection seem to happen normally, but the status hangs on 'sending page 1' for about 2 minutes before complaining that the other fax didn't answer in time. The printed output on the receiving end has a lot of bad lines- graphics, especially, come out blurry or with random pixels where the graphics should be. This behavior is not exclusive to images, though.

I've lowered the port speed to 9600 with no positive results; reinstalled modem drivers; purchased a new modem; rebooted the host server, and guest OS. The only obvious thing I haven't tried yet is a new serial cable, but since I'll have to go onsite to install it I was hoping to get more suggestions I can act on while I'm out there.

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Since the cable uses different pins for transmitting and receiving, I'd say that would be the next logical item to test and troubleshoot. – joeqwerty Oct 17 '11 at 21:11
Unlikely - it would have shown up in other ways as well since the modem - computer communication is bidirectional even when receiving a fax. What kind of modem is used? Does it have hardware support for fax transmission or is it done in software? Is there a VoIP connection somewhere in your transmission path? – the-wabbit Oct 18 '11 at 8:41
It's a USRobotics USR5686G 56K Serial Controller Fax. It doesn't feel like a cheap softmodem, but it's been a while since I could eyeball the difference. No VoIP anywhere, just the faxmodem connected directly to a POTS line from the local ilec. I did connect a real fax machine to the line, and things are fine there so I can rule out line issues. – ndespres Oct 18 '11 at 13:05
Replacing the cable with a new one did not help. I feel defeated. – ndespres Nov 1 '11 at 15:14

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