ConnectPort LTS 32 issues vs serial based port server

We are looking to replace a serial based Digi XEM Acceleport Portserver with an IP based Digi ConnectPort LTS 32.
We use this to allow our software to communicate with a series of modems over serial connections. We use fairly old V23 modems at 1200 baud. This works fine with the older Digi XEM Acceleport Portserver but does not work with the Digi ConnectPort LTS 32. Other faster modems that we use are fine with both Digi units.

Does anybody have any thoughts about what might be the cause of this difference in behavior at this slower speed? The older Digi is serial based whereas the newer one is IP based and of course this may well be a factor. Are there some tuning parameters on the Digi ConnectPort LTS 32 that would be worth trying out? We are using the RealPort profile as our software just sends and receives bytes over the serial port. I can of course provide more detail of settings if they may be relevant.

I notice a number of framing errors and breaks on the port we use for V23. The others are error free. What might be the cause of these?

What software are you using, that’s interfacing with the modems?

What OS is the computer running?

What is the symptom of the problem? Why do you think these older modems aren’t working, in other words? And are there any error messages (if so, what do they say)?

Are you pretty sure the modems are cabled properly, regarding the serial cabling?

Thanks for coming back. Have been doing some more testing and below is what we have.

We are running on Red Hat Linux v6.8 64-bit
Cable - 10 core RJ45 to DB25 (Digi part number 76000195)
Modem - Telebit Xpresso 8396A using v23
Old serial server - ACCELEPORT XEM HOST ADPT-PCI (16 port)
New serial sever - ConnectPort LTS 32

Using the old server we get no issues and all communication between the server and the modem is fine. If we move to using the new serial server we see DTR set high, RTS low. When we try to make a call, DTR goes low for about 1 seconds and then goes high again, but there are no changes in the RTS or CTS lines.

So everything is consistent apart from the serial port server.

It must be a setting on the ConnectPort LTS, but not sure which one.

  • using the realport profile,
  • 1200 8N1 settings
  • Enable DCD disabled (as we have a 10 core cable)
  • Enable RTS Toggle disabled

Are you using the RealPort driver on the Linux host to provide tty devices?

If so, the only applicable setting on the ConnectPort LTS would be configuring the serial port profile to RealPort. All other settings would be applied from the Linux host (i.e. ditty-rp or stty).

Additionally, with modems, you will want to be sure hardware flow control is configured to ensure data integrity.

If you are not using RealPort, please advise what method is being used to communicate with the attached modem.