Multiplexing is the use of hardware and/or software to reduce the number of devices that directly access or use the software on a particular server. An example of multiplexing is 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 SQL Server database on another server. The client computer has a direct connection to the server running MTS, but it 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, pooling, or related hardware and/or software does not reduce the number of CALs required for SQL Server. Regardless of how many tiers of hardware or software exist between the SQL Server and the client devices that ultimately use its data, services, or functionality, a CAL is required for each distinct input to the multiplexing, pooling, or related software or the hardware front end. Processor licensing will likely be the appropriate licensing option in these situations, due to its simplicity and affordability.

For more information about multiplexing and SQL Server licensing, see the SQL Server Processor Licensing Clarification page.