Media problems occur when there are too many devices on the same segment. Having numerous devices on a single LAN segment causes excessive collisions in Ethernet networks and long delays in token passing networks. Media contention problems are recognized by users as slow response times and an inability to reach network services.

The first step toward identifying and eventually solving media problems is a thorough analysis of network traffic. After using a network-monitoring tool to gather information about the network, it is time to analyze the data. Here are a couple of items that would indicate a media problem with the network:

  • Network utilization is consistently above 40% in an Ethernet network
  • Network utilization is consistently above 70% in a token ring or FDDI network

So with this knowledge in hand, how do you solve media problems?

Making the switch
Essentially, media problems are caused by having too many devices sharing the same bandwidth domain. (A bandwidth domain, known as a collision domain in Ethernet networks, is a group of devices all sharing the same bandwidth.) For example, a group of devices connected to an Ethernet hub would be a collision domain. Dividing these devices into segments can solve media problems. How do you segment the network and provide high-speed data exchange? Segment the network with a switch.

LAN switching is a good strategy for network segmentation. A few of the benefits provided by switching include:

  • High-speed data exchange
  • Full-duplex communication
  • Low latency
  • Dedicated communication between devices

LAN switches forward frames based on the frame’s layer 2, or MAC, address. This allows the frames to be switched through the network very quickly with less latency than a routed network. Additionally, because of the dedicated, collision-free communication between devices, network throughput and user response times are greatly improved.

On the downside, switches also forward broadcasts throughout the network. This can become a scalability issue. Table A shows scalability constraints of a switched network.

Table A
Protocol Maximum Number of Workstations
IP 500
IPX 300
Mixed 200

When switched networks grow in size, the number of broadcast frames increases. When broadcasts become more than 20% of the traffic on a LAN, network performance is degraded. This type of network degradation is classified as a protocol problem.

Join me next week for a detailed look at how to identify and resolve protocol problems.

Warren Heaton, CCDA, CCNA, MCSE+I is the Cisco Program Manager for A Technological Advantage in Louisville, KY.

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