Chapter 8: Estimating Token Ring Network Performance

Overview

Chapter 7 focused on Ethernet network performance and developed a mathematical model to determine the frame rate based on different frame lengths. The results of that model were then used to determine the information transfer capability of a 10-Mbps Ethernet network based on different frame sizes. As you might intuitively expect, the use of larger frames provided a higher information transfer capability because each Ethernet frame is separated from preceding and succeeding frames by a uniform time gap. Thus, longer frames were expected to be more efficient and this was determined to be true.

In this chapter, our attention will turn to Token Ring network performance in a similar manner to our method of examining Ethernet performance. That is, we will first develop a model that is representative of the flow of data on a Token Ring network. Then we will exercise the model both manually as well as through the use of a BASIC language program to determine the frame rate as a function of the number of stations on the network and the ring length as well as several other variables . In doing so, we will note that the performance models for CSMA/CD and Token Ring networks considerably differ due to the basic differences between each network access protocol.

In a CSMA/CD network, the transmission of a frame is read by all stations without one station's reading activity delaying another station's reading activity. In a Token Ring network, the opposite is true, because station n must process a token or frame prior to passing it onto station n+1 on the network. Thus, the Token Ring model developed in this chapter will considerably differ from the previously developed Ethernet model presented in Chapter 7. A second area of difference concerns the cabling structure of Ethernet and Token Ring networks. Most Ethernet bus-based networks use a fraction of the cabling used in the star-bus topology of a Token Ring network. Thus, propagation delay time plays a much more meaningful role in determining network performance and results in our inclusion of the speed at which tokens and frames traverse the cable in the Token Ring model we develop in this chapter.