1.8 Token Ring Network Performance

The question previously asked concerning how fast frames can flow on an Ethernet network is also applicable to Token Ring networks. That is, if you can determine the flow of information on a Token Ring network, you can use this information to estimate the performance of the network as additional stations are added to the network. You can also use this information to determine the filtering and forwarding rates required by bridges, switches, and routers connected to a Token Ring network prior to those devices potentially becoming a bottleneck and congesting the flow of data between networks. Last, but not least, by determining the frame flow on a Token Ring network, you can use this information to develop a model to project network and inter-LAN transmission time. If the inter-LAN network is to be created or was created through the use of a WAN transmission facility, you can easily adjust the model to reflect different WAN operating rates. Then, you can determine an optimum WAN operating rate that will satisfy your organization's communications requirements without having to simply guess upon the selection of a WAN transmission facility or initiate an expensive trial-and-error process.

As might be expected from the previous paragraph, the initial focus of Chapter 8 is on the development of a model to reflect the flow of frames on a Token Ring network. Once this is accomplished, the model will be exercised to determine the frame carrying capacity of a Token Ring network under different operating conditions and network configurations.

The development of a Token Ring traffic model will require consideration of a large number of operating conditions and network configuration data. Some of the parameters that will have a bearing on the flow of frames on a Token Ring network include the number of stations on the network, the length of each lobe and the length of the ring, the average frame size , and the operating rate of the network. To facilitate our computations , we again turn to the BASIC programming language and develop several programs as well as spreadsheet models to facilitate our computations. Both the Token Ring program and spreadsheet model listings and results from executing each program are contained in this chapter. In addition, readers are referred to the use of a set of tables contained in a file at http://www.crcpress.com/e_products/downloads/default.asp that can be used to reduce the Token Ring frame flow projection process to a simple table lookup operation.

Once the Token Ring model is developed and exercised, this information is used as a foundation for determining bridge, switch, and router performance requirements. In doing so, frame flow information is used to project a range of performance that network devices should support, as well as the effect of network changes on the frame flow on a Token Ring network.