The method for improving the performance of BNs is similar to that for improving LAN performance. First, find the bottleneck, then solve it (or, more accurately, move the bottleneck somewhere else). You can improve the performance of the network by improving the performance of the computers and other devices in the network, by upgrading the circuits between computers, and by changing the demand placed on the network (Figure 8.16).
Improving Computer and Device Performance
The primary functions of computers and devices in BNs are routing and protocol translations. If the devices and computers are the bottleneck, routing can be improved with faster devices or a faster routing protocol. Static routing is accomplished faster than dynamic routing but obviously can impair circuit performance in high-traffic situations. Dynamic routing is usually used in WANs and MANs because there are many possible routes through the network. BNs often have only a few routes through the network, so dynamic routing may not be too helpful since it will delay processing and increase the network traffic because of the status reports sent through the network. Static routing will often simplify processing and improve performance.
Performance Checklist Increase Computer and Device Performance
• Change to a more appropriate routing protocol (either static or dynamic)
• Buy devices and software from one vendor
• Increase the devices’ memory
Increase Circuit Capacity
• Upgrade to a faster circuit
• Add circuits
Reduce Network Demand
• Change user behavior
• Reduce broadcast messages
Figure 8.16 Improving backbone network performance
Most backbone devices are store-and-forward devices. One simple way to improve performance is to ensure that they have sufficient memory. If they don’t, the devices will lose packets, requiring them to be retransmitted.
Improving Circuit Capacity
If network circuits are the bottlenecks, there are several options. One is to increase overall circuit capacity (e.g., by going from 100Base-T Ethernet to gigabit Ethernet). Another option is to add additional circuits alongside heavily used ones so that there are several circuits between some devices.
In many cases, the bottleneck on the circuit is only in one place—the circuit to the server. A switched network that provides 100 Mbps to the client computers but a faster circuit to the server (e.g., 1000Base-T) can improve performance at very little cost.
Reducing Network Demand
One way to reduce network demand is to restrict applications that use a lot of network capacity, such as desktop videoconferencing, medical imaging, or multimedia. In practice, it is often difficult to restrict users. Nonetheless, finding one application that places a large demand on the network and moving it can have a significant impact.
Much network demand is caused by broadcast messages, such as those used to find data link layer.Some application software packages and NOS modules written for use on LANs also use broadcast messages to send status information to all computers on the LAN. For example, broadcast messages inform users when printers are out of paper, or when the server is running low on disk space. When used in a LAN, such messages place little extra demand on the network because every computer on the LAN gets every message.
This is not the case for routed backbones because messages do not normally flow to all computers, but broadcast messages can consume a fair amount of network capacity in switched backbones. In many cases, broadcast messages have little value outside their individual LAN. Therefore, some switches and routers can be set to filter broadcast messages so that they do not go to other networks. This reduces network traffic and improves performance.
