To understand the main Local Area Network technologies.

On completing this section you should be familiar with the three main types of Local Area Network technologies and their key features.

In order to put the choice issues between Ethernet and its rivals into context, it is necessary to have some kind of theoretical understanding of the protocol issues underlying the various systems. This is quite hard stuff and not of immediate apparent relevance to network selection and design. That is, not until your Ethernet gets clogged up all day with streaming audio or Internet videoconferencing - then it becomes very relevant.

The key thing to remember is that CSMA/CD may seem too simple to be useful, but it works and it is quite hard to improve on it.

We have not set any activities in this subsection.

The most popular Local Area Network technology is Ethernet. It has spread all over the world, pushed out most of its rivals and been enhanced to 10 and 100 times its original speed, with a further enhancements under consideration. (Compare that with ISDN, a technology of a similar age but not similar success.)

Yet the ideas on which Ethernet is based are very simple - almost too simple, purists would say. In addition, there are well-known (or at least frequently-alleged) restrictions on Ethernet, such as its "inability" to transport multimedia traffic. So how is it that it has occupied its position in the world? One has to delve into the history and the theory to find out.

The main alternative to Ethernet that remains in the marketplace is Token Ring, still very popular on sites with IBM equipment.

Another early rival to Ethernet was Token Bus. It never became very popular despite having an elegant architecture.

To finish this section, you should read about comparing the various types of LAN, and some extensions of the LAN concept.

By "fast networks" we mean networks that operate considerably faster than the 10 Mbit/s of Ethernet. Examples include:

• Fast Ethernet (100 Mbit/s)
• a rival to Fast Ethernet called 100VG-AnyLAN
• FDDI - Fibre Distributed Data Interface
• various other fibre-based networks
• ATM.

In this subsection we deal with all of these except the last.

To many commentators it now seems inexorable that Fast Ethernet will win the day; but the other network types have their devotees and in particular FDDI has a substantial installed base.

The components that one needs for a Local Area Network comprise:

L1 The cabling

L2 The network cards - for PCs, servers, workstations and mainframes

L3 hubs and switches (needed for certain types of LAN such as Switched Ethernet)

L4 repeaters, bridges, and routers, to link each LAN to others.

Although cabling can consume a considerable amount of money, and planning time to ensure that it is done right, few network managers get excited or strategic about choice of cabling supplier.

As network technologies such as Ethernet grow in popularity, network cards move from being high-priced items from a few advanced suppliers, to being commoditised items from anonymous suppliers anywhere in the world. Thus increasingly, manufacturers cannot differentiate themselves in the minds of end-users by their approach to development and marketing of network cards.

The competition between network vendors is increasingly focused on areas L3 and L4. These areas are not in fact separate but blur into each other.

Some main 'LAN' vendors include:

• Cisco Systems Inc - http://www.cisco.com
• Bay Networks - http://www.baynetworks.com
• 3Com - http://www.3com.com