The data provided by these counters is collected by different methods, is displayed in different units, and represents the view of different system objects. Some guidelines for interpreting the data follow:
The IIS service counters display the number of bytes transmitted on behalf of each service that server provides. To calculate the total number of bytes sent or received by all IIS services, sum the values for each service. You can determine the proportion of bytes transmitted by each service by computing the ratio of bytes for one service to the sum of bytes for all services, or for the network.
Data collected by the IIS service counters underestimates the total number of bytes actually being transmitted to the network by the IIS services. These values are collected at the Application Layer, so they measure data only. They do not measure protocol headers, control packets, or retransmitted bytes.
In general, the bytes counted by the services represent approximately 60 to 70 percent of the total number of bytes transmitted by the services on the network. If the sum of bytes for all services accounts for two-thirds or more of total network bandwidth, you can assume your network is running at or near the total capacity of its communications link.
Counters on the TCP and IP performance objects display the rate at which data is sent and received on a Transmission Control Protocol/Internet Protocol (TCP/IP) connection at the Transport and Network layers, but they do not count in bytes. Counters on the IP performance object display data in datagrams, and counters on the TCP performance object display data in segments. It is difficult to convert segments to bytes because the bytes per segment can vary from 8K to 64K; the number of bytes per segment depends upon the size of the TCP/IP receive window and the maximum segment size negotiated when each connection is established.
Counters on the Network Interface performance object display the rate at which bytes are transmitted over a TCP/IP connection by monitoring the counters on the network adapter at the Data Link Layer. The values of these Network Interface counters include all prepended frame header bytes and bytes retransmitted. These values provide a relatively accurate estimate of the numbers of bytes transmitted over the network, but they do not relate the bytes transmitted to a specific IIS service.
Despite the difficulty of comparing these counters to each other, they can all be related to other performance measures, such as the total number of connections served at a given bandwidth, or processor use at different throughput rates.