MULTIPLEXING: USE OF MIDDLEWARE, TRANSACTION SERVERS, AND MULTI-TIERED ARCHITECTURES Sometimes organizations develop network scenarios that use various forms of hardware and/or software that reduce the number of devices or users that directly access or utilize the software on a particular server, often called multiplexing or pooling hardware or software. For example, say a client PC is using a server application that calls the Microsoft Transaction Server (MTS) component of Microsoft Windows® 2000 Server on one server, which in turn pulls data from a Microsoft SQL Server database on another server. In this case, the only direct connection to Microsoft SQL Server is coming from the server running MTS.

The client PC has a direct connection to the server running MTS, but also has an indirect connection to SQL Server because it is ultimately retrieving and using the SQL Server data through MTS. Use of such multiplexing or pooling hardware and/or software does not reduce the number of CALs required in order to access or utilize SQL Server software. A CAL is required for each distinct device or user to the multiplexing or pooling software or hardware front end. If, in the above example, 50 PCs were connected to the MTS server, 50 SQL Server Device CALs would be required. This is true no matter how many tiers of hardware or software exist between the SQL Server and the client devices that ultimately use its data, services or functionality.