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Stacking up trouble?
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20/05/2005
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In the early 1990s, as Ethernet began to develop as the dominant local area network (LAN) technology, all networks were based on physical designs, structures and layouts. That is, the network mimed the physical construction of a building and the predetermined ‘office’ layout. Each floor or area would have its own connecting device with physical links separating the various business elements of the network. Whilst a LAN could be physically extended using bridges and hubs, they had to be connected by a router. This type of network is similar to rail networks, where physical connections bind stations together for the benefit of many users. To leave a defined branch, however, requires going through a major rail hub to access a new branch line. The physical carrier (the train) cannot shed carriages to go to their individual destinations.
The mid 1990s saw the development of switches that considerably reduced the cost of having a router separating each LAN. However, the router was there for more than a physical purpose. A large amount of traffic on any network is broadcast traffic. This is in effect the engineering and management information being distributed around the network. The bigger the LAN, the more broadcast traffic is generated, so a router was used to physically separate these broadcast domains. Switching devices allowed the combining LANs together to form a single management domain. This created problems that each manufacturer sought to solve by introducing their own virtual separation techniques. Eventually, in 1996/7 the IEEE formalised a standard for Virtual LANs in 802.1q, allowing interconnectivity of different vendor’s equipment.
What this really meant was that a single physical LAN entity could now support multiple Virtual LANs, each with their own memberships and management constraints. This type of network compares more to a postal network. In effect every business, family or friendship runs its own virtual LAN across the national postal system.
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Author
Murray Coleman
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