Modem disconnected



We have 2 GSM modems connected to 2 serial ports of our win 2000 servers.
These modems are working fine for the past 2 yrs. Recently, we would like to add another 2 modems, but since there is no more serial port available, we use serial to usb cable to connect the modem to usb port.
(they become com 3 and com 4)
However, this config is not stable, as one of the new modems will be disconnected after a few hours, sometimes a few days.
The strange thing is only com3 or com 4 will get disconnected, and it’s quite random, sometimes com3 the other time com 4.

Is there any issue with the serial to usb cable converter?


Quite possibly!

Have you tried swapping the two “original” modems from the “real” COM ports onto the USB adaptors, and the “new” modems onto the “real” COM ports?
If the problem moves with the modems, then suspect the modems;
If the problem stays with the USB adaptors, then suspect the adaptors.

Not all USB-to-RS232 adaptors are the same - especially some cheap “consumer” ones can be problematic…


USB-Rs232 are very buggy since theprotocols have diferent speeds, this make a lot of troubles i do not recommend to use, it is always better have a HARDWARE com port, no doubt about it,maybe you can buy a expansion COM ports target.


I very much doubt that this has anything to do with it whatsoever!

I think it is much more likely that dodgy software makes unwarranted assumptions about the COM port which do not hold when a USB adaptor is used…

I use USB-to-RS232 converters all the time without problems!


i used sometimes usb-rs232 converters and the behaviour it was like asantosa describe they fall in a couple of hours.

think about speeds.
what happend with the internal memory buffer of usb-rs232? (it is finite of course and not very large of course)

lets give them 32 KB for example
you for example send to rs232 at 9600
and USB2.0 sent at 480MBPs if you send a chuck of more than 32Kb the data will overflow the usb-rs232 buffer becouse you have more data input that you can send output.

if a port it is a hardware port the excess of data it will be be store in the pc side



A good driver in the OS and a good firmware in the USB converter can handle that.

I find even better and prefer using good USB converter than native COM-ports.



If it allows this to happen, then that is a bug in the converter and/or its driver! :open_mouth:

Only if the driver is correctly written!
If the driver is as bad as you suggest for the USB-to-RS232 converter, then it will have exactly the same problem!