Configuring Citrix MetaFrame for Windows 2000 Terminal Services

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Modem pools require special connections to the RAS server to allow it to provide access via all the modems. Sometimes this is done through software management of the ports involved. Other times there is a serial solution provided. Regardless, the modem pool should not be located too far from the actual RAS server or network latency can develop.

Serial Cards

Obviously, you can only plug so many modem cards into a machine. There has to be some way of providing hundreds, or even thousands, of connections to a single server. In fact, there are several hardware solutions that will fulfill these needs. The first method is to use a dumb serial card solution. Unintelligent (i.e., “dumb”) boards utilize the CPU to handle all processing requirements when sending data through the serial interface. This means that every port on the card will interrupt the CPU every time it has data to send or receive. This can really cut down on the capabilities of your RAS server, but is much more cost effective when the number of users can be small enough to not bog down the server.

The second option is to use an intelligent serial solution. Intelligent boards are capable of performing most of the serial data processing independent of the CPU. Intelligent boards can contain multiple CPUs to support the large number of serial ports they can contain. The system CPU still must be used when data is being transferred from the serial port to the system or when processing that information. Intelligent boards greatly expand the limit of serial ports that can be used by a RAS server. Without an intelligent board solution, a RAS server could easily be pegged at 100 percent usage by as few as 20 users. Unfortunately, without trial and error there is no sure-fire method to determine which serial solution you should use. You could be pegging your processor with 50 users and a dumb board, only to buy a bigger server and still peg the processor. Either use trial and error to determine your load levels, or just invest from the top in an intelligent solution.

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