Windows networking problems for modem connection

December 15, 2006 4:04 PM

I'm trying to set up an non-internet-connected Windows XP computer to receive incoming connections via modem. Somewhat reproducibly, the "Incoming Connections" icon in the Network Connections dialog goes away after a reboot.

I've seen this on several computers, both XP SP1 and XP SP2. It doesn't always happen but it happens quite often with this latest machine. I've also just discovered that the icon can go away and I can still connect in certain situations. For example, logged in with VNC I can restart the computer and then dial back and connect again a few minutes later. Interestingly in this case, the Server IP changed (auto-assigned in the 169.254.X.X range). Not sure if that means anything...

Now I'm trying to reproduce the problem and can't get it to happen again, whether I restart/shutdown directly or remotely. I'll fill in more clues as I find them. Does anyone have any insight on how this stuff works or things I can try to shed more light on the problem?

posted by jacobsee to computers & internet (6 comments total)

169.x.x.x is an automatically assigned IP when no DHCP serve ris found (IPEIA? or something).

Assign it a static IP address on the interface.
posted by SirStan at 4:26 PM on December 15, 2006

I wonder if it might have to do with the modem device not existing, or not being detected as present/attached, at boot time. What kind of modem is it?
posted by Myself at 6:03 PM on December 15, 2006

intel 56k modem...pretty standard and works just fine except when the "incoming connection" goes away
posted by jacobsee at 8:09 PM on December 15, 2006

It's possible that your "modem" is actually a "Winmodem" and not a "real" modem. A Winmodem specifically works with Windows, and offloads a significant portion of the processing load to the CPU through Windows drivers. Accordingly, these things are fairly low in cost, since there aren't many components on the modem, and sometimes, they're still even offered as motherboard options. But, since they depend on Windows to work at all, they are subject to the frailties of Windows, and as a low level device needing frequent attention, they are the kind of thing that has a pretty low likelihood of working smoothly over a long period of time.

If this function is important to you, get a carrier class "real" modem, such as the USR Courier. Couriers "just work" and have the on board intelligence to manage call setup, connection, data rate negotiation, and link completion, all before bothering your CPU via the serial port. Put 'em on a quality UPS, and when the phone rings, it will be answered, and Windows will be notified. Since servicing a 16550 serial port is a well defined Windows function, I bet most of your problems will immediately disappear.

Personally, I prefer the slightly older Courier model that you can get as refurbished units, because they are made with a balance transformer for the phone line, that makes the modem insensitive to miswired jacks and some kinds of electrical line problems. The newest Couriers are built without this feature. Generally, you should verify that your modem is flashed to current firmware revision level, to get the most stable performance.
posted by paulsc at 10:42 PM on December 15, 2006

wow, that sounds very plausible because I know this modem was about $12

when a modem says it's "controller based" is that what you're talking about (like this one)?
posted by jacobsee at 11:08 PM on December 15, 2006

(just answered my own question...clicked on Modems 101 on my last link and they talk about Control-based and controlerless modems...sounds like just what you're describing)

Also sounds like Myself was onto it...so if Windows doesn't detect it at some point in the boot process, it may dump the setup for the Incoming Connection...
posted by jacobsee at 11:17 PM on December 15, 2006