The simplest measure of the effective bandwidth of a server is the rate at which the server sends and receives data. Performance Monitor displays counts of data transmissions that are collected by many components of the server computer. The components that collect data each reside in different Open Systems Interconnectivity (OSI) layers:
Counters on the HTTP Service, FTP Server, and Gopher Service performance objects measure data transmitted at the OSI Application Layer. (HTTP stands for hypertext transfer protocol; FTP stands for File Transfer Protocol.)
Counters on the TCP object measure data transmitted at the Transport Layer.
Counters on the IP object measure data at the Network Layer. (IP stands for Internet Protocol.)
Counters on the Network Interface object measure data at the Data Link Layer.
As a result of their different positions in the OSI stack, the counters display different data. For example, the counters at the Application Layer count the bytes sent before the data is divided into packets and prefixed with protocol headers and control packets. Counters at the Application Layer measure data in this way because the data is in this form when the application sends it. Counts at the Application Layer also do not include retransmitted data.
In addition, the counters display the data in units native to the component measured. For example, the HTTP Service object displays data in bytes, and the TCP object displays data in segments.
The next section lists and describes the Performance Monitor counters you can use to measure data sent and received by your server. The following section also offers help in interpreting the data you collect.