VMWare ESX Server - Using Analog Modem Through Serial Port

Posted on 2008-10-16
Last Modified: 2013-12-27
We are using a banking package called Barclays Businessmaster on a virtual machine, which needs to use an analog modem for connections. Before now we used VMWare Server: the virtual machine used the serial port on the host server to see the modem, and after a little config this worked fine. We are now using ESX Server 3, and again have connected the physical serial port on the host to the relevant virtual machine. However, whilst the application can see the modem, and indeed can dialout, the line soon drops out (perhaps because of noise or some other comms failure). So for now we've returned this virtual machine to a VMWare Server running on a different physical host server (but with -exactly- the same hardware as the ESX Server). It works fine. So we know it's something to do with ESX Server rather than the host server hardware or the service we are trying to reach. I have tried lowering the port speed within the virtual machine itself, and have also called the support desk for Barclays BusinessMaster to ensure we have all the correct settings. Neither helped.

As a point of interest: for USB devices (not serial modems) we use DIGI AnywhereUSB, which works fine with things like smartcards and the like. However when I tried an analog USB modem (US Robotics) through this method it failed miserably - mostly it couldn't finish handshaking with the modem, and when it did the line would soon drop with comms failures. I have also tried using the Connexant serial modem over the network using a Keyspan Serial Port over Ethernet device, which was also stop-starty and didn't really work with the modem.

Technical details:
Host Server: Dell PE 2900 III + 2 x Quad Core Xeon E5410 (2.33GHz, 2x6MB, 1333MHz FSB) running ESX Server 3
Host Access: VI3 on Windows Server 2003 Standard
Modem: Connexant 56k Fax Modem (Serial)

Are there any known issues (+workarounds / configs) with regard to ESX Server and the serial port and/or dialup analog modems?
Are there any setups of serial or USB modems that are known to work with ESX Server virtual machines? Either using the serial port on the host server directly, or using serial / USB over ethernet solutions? (what is the exact modem and/or devices I would need to buy?).

Just one other point: The Barclays BusinessMaster application talks directly with the modem using (e.g.) ATDT commands, rather than Windows TAPI etc.

This is my first question, so apologies if it's badly formed or has been answered previously.
Question by:JonFisher99
LVL 18

Expert Comment

ID: 22739013
I would not recommend you to use modems attached locally to the server. It prevents VMotion and similar functionality from working.

What you have tried by using a serial over ip-box is the way to go and there are several success stories@VMTN, but it might require some tweaking. Please have a look at the following thread:


Accepted Solution

JonFisher99 earned 0 total points
ID: 22785672
Larstr, many thanks for taking the time to help. Unfortunately the link you gave does not have any success stories. Some have advised to use Avocent ESP, but that seems to create more problems than it helps. Someone also asked if anyone had tried "DIGI Connect SP ". I have tried the 'Digi Realport' device, but could never get it to work. It seemed more focused on covering every possible RS standard (rather than just basic DB9 PC serial port), was awful to configure (DIP switches, too many different operating modes and settings, strange cable types), and simply didn't work. Also Digi have a UK company doing sales and post-sales support, and they are absolutely rude and unhelpful. Love their AnywhereUSB product regardless! :)

HOWEVER, I now have a working solution!!!! I stumbled accross the following product whilst looking at something completely different: " RS-232 Serial Ethernet IP Adapter". I took a chance and ordered it, and it works a treat!!! It's easy to configure, and once connected it truly acts just like an attached serial port to any virtual machine. The analog modem performs exactly as it should. I've tried it with VMWare Server and also ESX Server, both work perfectly well and were configured in minutes. And our Barclays BusinessMaster application loves it. So a happy ending, and hopefully helpful to anyone who doesn't want to spend the months of hell I've had trying to get a stable working solution. Cheers!

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