by Jeff Carrell, Electronic Communications Chairman
[reprinted from IEEE - Fort Worth Section Signals
A topology is the representation of the network's layout. There are a few basic types including: star, ring, star wired and linear bus. Of these, the most commonly deployed topology today is the star wired.
In a star topology, there is a central device to which all nodes are connected. The central device polls each connected node and allows that node to communicate its information for the destination node to the central computer which stores that data until it communicates to the destination node and can pass the data on. The most common type of star topology is the mainframe and terminal type systems. These have been deployed all over the world for many years, and there are still many of them in service today.
A ring configuration has all nodes connected to each other in a series; in to an out, and the two end points also connecting each other. Unfortunately, this design makes for a very difficult cabling plant, so it was never really implemented on a large scale. There were a few proprietary systems marketed this way. The better design called for a star wired ring.
A star wired ring affords the same function of the ring communication, while allowing a much better designed and implemented cable plant for the network. The basic function of a ring is that every node, whether PC or server, gets an equal time to communicate on the network. The design of the ring also provides some self-healing properties in the case of the IBM Token Ring system. Token Ring is the most widely deployed star wired ring topology.
Many folks who have worked with coax based Ethernet will be familiar with this topology. The linear bus has two finite end points (meaning the ends don't connect together as in the ring topology). Therefore, in order to connect each node into the network, you have to daisy chain the cable from one to the next. The actual connection is only broken at the NIC, and each cable end is connected to a "T" connector, which then connects to the NIC. This topology was once the most prominently deployed, however, over the years, network support personnel encountered major headaches when the cables were disconnected at the T connector, instead of at the NIC.
Since the mid to late 1980's, the star wired topology has been the most popular deployed technology. Since this topology is configured in a spoke or star of spokes configuration, Ethernet and token ring networks can use the same cable plant. IBM first used the star wired configuration for its token ring network technology during the mid 1980's. In late 1989, 10BaseT (twisted pair Ethernet) was standardized. This provided network designers the capability of forming structured cabling systems, and then deciding which network technology to run over it. Today, almost every new network technology runs over a star wired topology configuration.
|Star||Ring||Star Wired||S. W. Ring||Linear Bus|
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|IBM PC Network||-||-||-||-||X|
Copyright © 1997 Jeffrey L. Carrell All Rights Reserved