Have you ever run out of modem lines at your office? With desktop faxing, Internet connections, and direct deposits to banks, practically everyone in a small office needs a modem. Unfortunately, modems cost money, and the cost of having a phone line for each modem can become very high. If you’re running Microsoft’s Small Business Server version 4.5, however, you can get around this problem by sharing a bank of modems directly off of your server. That way, all of your users can dial out as if they had modems connected directly to their PCs. In this Daily Drill Down, I’ll explain how to set up a modem pool. Then, I’ll discuss some common modem-sharing issues.
The techniques that I’m going to discuss only work with Small Business Server; they won’t work with the standard versions of Microsoft BackOffice, Windows NT, or Windows 2000—though several third-party utilities allow for modem pooling. (If anyone knows of a way of enabling modem pooling on other systems—other than Internet connection sharing—please send me an e-mail, and I’ll write about it.) According to the Microsoft Knowledge Base, if you start with Small Business Server and upgrade to Microsoft BackOffice 4.0 or 4.5, the Modem Sharing Services will continue to work normally. The only drawback is that the Modem Sharing Services become non-upgradeable when you upgrade the operating system.
When I attempted to upgrade Small Business Server to BackOffice 4.0, I received a message stating that I had to buy a special version of BackOffice in order to upgrade Small Business Server. Instead, I tried to upgrade to a normal copy of Windows NT Server 4.0. Afterwards, I could still use the Modem Sharing Service; however, the server maintained the license count of Small Business Server rather than switching to my BackOffice Server license count. I couldn’t increase the number of licenses manually, either. This type of problem is something that you’ll want to keep in mind if you manage to acquire a five-user copy of Small Business Server and try to set up a modem pool. And please note that you can’t upgrade Small Business Server to Windows 2000.
Another limitation involves the number and types of modems that you can use. Small Business Server is designed for small businesses with few resources. Therefore, don’t expect to connect huge racks with hundreds of modems to Small Business Server. The limit is four modems, each of which must have its own phone line. Of course, you can share anywhere from one to four modems. If you decide to share multiple modems, all of the modems must be identical. They must be the same brand, model, and speed. I strongly recommend that you use a brand-name modem. Generic modems tend not to work very well with the modem pooling software within Small Business Server.
I also recommend that you use only external modems in your modem pool. If there’s ever a problem with communication, it’s much easier to correct the problem when you’re using external modems. Usually, external modems have a series of lights that indicate what’s going on with the modem. If a modem fails, you can tell which of the modems is having the problem by glancing at the lights. Perhaps a more compelling reason to use external modems is that it’s sometimes necessary to reset a modem if it hangs. If you had four internal modems in your server and one of them were to hang, you’d have to reboot the entire server just to reset one modem. On the other hand, if you use external modems, all you have to do is flip a switch on the modem that’s frozen, and you’re back in business without ever having to take the server offline.
Setting up the modem pool
The ability to create a modem pool depends on the Modem Sharing Service, which is installed automatically during the Small Business Server installation routine. Once Small Business Server has been installed, you can access the Modem Sharing Service’s various configuration options by opening the Control Panel and double-clicking the Modem Sharing icon. Then, you’ll see the Modem Sharing Admin properties sheet, as shown in Figure A. The default tab on this properties sheet is the General tab. It contains buttons that you can use to start and stop the Modem Sharing Service without having to go through the Service Control Manager. From the General tab, you can view the number of active connections, disable new connections, and enable event logging for the Modem Sharing Service.
|The General tab allows you to perform a number of tasks.|
The next tab on the Modem Sharing Admin properties sheet is the Status tab. The status tab, as shown in Figure B, allows you to view which users are using the modem pool at any given moment. You can see which modem they’re using and how long they’ve been using it. If you need to disconnect a user, you may do so by selecting the user and clicking the Disconnect button.
|The Status tab helps you keep up with what your users are doing.|
The final tab on the Modem Sharing Admin properties sheet is the Configuration tab. Here, you can decide which modems will be pooled. As you can see in Figure C, the type of modem that we’re using is listed in the top half of the screen. The bottom half of the screen lets you tell the Modem Sharing Service to which COM port(s) the modems are connected. The Configuration tab allows you to work with a variety of modems; however, you’ll have much better luck if all of your modems are identical.
|The Configuration tab lets you pool modems.|
Setting up the clients
Setting up the clients is the easy part. If you’ll remember, when you loaded Small Business Server, one of the default options was to install something called Client Applications. If you chose not to install this option, you must go back and install it now. The Client Applications option contains the code for allowing your clients to use the modem pool that you’ve established.
Once you’ve installed the Client Applications, log in to your client machine. (For the purposes of this Daily Drill Down, I’ll be using Windows 98; however, the technique is similar for Windows for Workgroups and Windows NT Workstation.) To install the Modem Sharing Service client, open Network Neighborhood and double-click your server. Next, you’ll see a folder called ClientApps. When you locate this folder, navigate to \ClientApps\MS\ModemShr\win95 and run the Setup program.
When the Setup program starts, click Next. The following screen will ask you for the modem pool path. Enter the pool path in this format: \\Server\Pool (as shown in Figure D). If you’re unsure of the name of your modem pool, you can find out by going to the server and double-clicking the Modem Sharing icon in the Control Panel. When you see the Modem Sharing properties sheet, you can locate the modem pool name on the Configuration tab.
|Enter the modem pool path in this format: \\Server\Pool.|
Once you’ve entered this information, click Next. Now, the Setup program will ask you for an installation directory. Unless you have a compelling reason not to do so, accept the defaults and click Next. Windows 98 will copy the necessary files from the server. Click Finish to complete the wizard.
Next, you must set up the modem on the client computer. Open the Control Panel and double-click the Modems icon. When you see the Install New Modems wizard, click Next. The wizard will query all of your local COM ports and the Modem Sharing port. On my computers, Windows set up the modem sharing port as COM 3. (Thus, the Modem Sharing port must be set up as a COM port.) You may run into problems if all of your client’s COM ports are already in use.
Once Windows 98 has detected the modem, complete the wizard just as you would for a normal local modem. Now, you’re free to use the modem pool as if it were a local modem attached to your system. The modem pool is capable of accepting inbound and outbound calls.
Now that I’ve explained how to set up a modem pool and how to configure your clients so that they can use it, you’ve probably got some questions. For example, some of your clients may have difficulty dialing out, but other clients work fine. Or you may have difficulty sharing modems on your server. Since there are so many variables in setting up a modem pool, I’ve provided the following troubleshooting section. It will help you to resolve many of the most common modem sharing problems.
During the Small Business Server Setup process, the Setup program failed to detect my modems (external US Robotics 56K) on each of our test machines. I removed the modems manually during the setup process and used the Have Disk option to load the drivers that came with our modems. After the system rebooted, I still received a warning that Small Business Server was unable to verify my modems. Oddly enough, they worked fine in spite of this warning.
If you decide to add the modem sharing services to a server that has already been set up, Small Business Server may fail to detect your modems properly. Often, this problem is caused by another application or process reserving the COM port or the modem for itself. I’ve heard stories of this situation happening when the RAS services are in use.
Trouble sharing TAPI devices
If you have trouble sharing a TAPI device (such as an ISDN adapter), the device may not be capable of using a serial port. Only TAPI devices that use serial ports may be shared. If you’re trying to share an ISDN adapter that doesn’t use a serial port, you’re not completely out of luck. There are some ISDN adapters that use serial ports. Simply replace your ISDN adapter, and you’re back in business.
Open Port Error 100D Server Not Found
The Open Port Error 100D Server Not Found usually occurs when your client has trouble accessing the shared modem pools. To test the connection, make sure that you’re logged in correctly. Then, check the path to the shared modem port by opening the Control Panel and double-clicking the System icon. When you see the System Properties sheet, select the Device Manager tab. Then, navigate to Ports and select the Modem Sharing Port. Click the Properties button. The port’s properties sheet will appear. Finally, select the Modem Sharing Settings tab and verify that the pool path is set to \\Server\Pool.
Modem is slow
Regardless of the speed of your pooled modems, Windows 98 sets the Modem Sharing port speed to 9600 bps. To change that setting, open the Control Panel and double-click the System icon. When you see the System Properties sheet, select the Device Manager tab. Now, navigate to Ports and select the Modem Sharing Port. Then, click the Properties button. Doing so will display the port’s properties sheet. Now, select the Port Settings tab and adjust the port speed through the Bits Per Second drop-down list.
Modem is inaccessible for a long time
One very common problem that you may experience is when a modem remains inaccessible to clients even though nobody is using it. This problem occurs because of the way in which the Modem Sharing Service works. The Modem Sharing Service shares modems exclusively. That is, if a client uses a modem, nobody else can use that modem until the client releases it. If all clients claim to have released the modems, check to see if someone is running software that’s set to wait for a call. Such software will make a modem inaccessible to all other clients.
Brien M. Posey is an MCSE who works as a freelance technical writer and as a network engineer for the Department of Defense. If you’d like to contact Brien, send him an e-mail. (Because of the large volume of e-mail he receives, it's impossible for him to respond to every message. However, he does read them all.)The authors and editors have taken care in preparation of the content contained herein, but make no expressed or implied warranty of any kind and assume no responsibility for errors or omissions. No liability is assumed for any damages. Always have a verified backup before making any changes.