TELECOM Digest OnLine - Sorted: Modem/Fax Keeps Timing Out

Modem/Fax Keeps Timing Out
21 Sep 2006 06:54:05 -0700

We are experiencing problems with a fax server that we wrote in
.NET/C#. The server sends and receive faxes, either through multiple
modems or one single modem that is used for both outgoing and

The server works perfectly well with all of our clients -- except one.
This one client receives a "Time out during send/receive" error for
25% of all incoming faxes; outgoing faxes work fine.

The client uses one modem for both incoming and outgoing faxes. The
line they use is a DSL line and has a filter that splits the line to
the fax-modem and the DSL modem.

So far, we have tried the follwing:

1. replaced the modem 5 times. Currently we are down to U.S Robotics
56k ext fax-modem.
2. checked the local phone company for line noises -- the line is fine.
3. replaced the DSL filters with brand new ones.
4. changed INIT strings on the modem several times. We are now using
the same init string which is used by another client
with the same modem -- and this other client receives errors only 5%
of the time.
5. Replaced the computer that the modem was on.
6. Installed WinFax on the same machine and tried sending faxes to
it -- the same problem happened. I must emphasized that we only
tried this once, with one specific caller who kept failing to send
faxes to this client.

... but alas, the problem still persists.

One strange characteristic of this problem, is that the errors come
from specific senders: once someone gets an error sending a fax to
this client, they can keep trying all they want, but the error will
keep happening.

Does anyone know of a specific problem with mixing Fax/DSL lines? does
anyone know of problems sending faxes from regular fax machines to
computerized systems, perhaps specifically under DSL lines? If so, is
this something we could resolve with different init strings?

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