Local Area Network Technology: Part 4 - Topologies

by Jeffrey L. Carrell
Issue v1n4 - August 1997

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.

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.

Linear bus:

Many folks who have been around the networking industry will be familiar with this topology if they have worked with coax based Ethernet. The linear bus has two finite end points, meaning the ends don't connect together (as in the ring topology). Because of its design, in order to connect each node into the network, you have to daisy chain the cable from each node 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. Although this topology was the most prominently deployed, over the years network support personnel discovered that its most major headache was when someone disconnected the cables at the T connector, instead of disconnecting the T from the NIC.

Star wired:

Since the mid to late 1980's, the star wired topology has been the most popular deployed technology. Since the star wired 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 now allowed network designers the capability of forming structured cabling systems, and then deciding which network technology to run over it. Today, almost every network technology that comes out runs over a star wired topology configuration.

Star Wired Ring
Star Wired
Linear Bus
Token Ring
IBM 3270 (mainframe)
IBM 5250 (AS/400)
Gateway Comm G-Net
Corvus Omninet
Novell S-Net
IBM PC Network


10Base2 10Mbs Ethernet running on RG-58 coax at a max distance of 185M per segment

10Base5 10Mbs Ethernet running on thicknet coax at a max distance of 500M per segment

10BaseFL 10Mbs Ethernet running on fiber optic 62.5um cabling at a max distance of 2KM per segment

10BaseT 10Mbs Ethernet running on UTP/STP at a max distance of 100M per segment

100BaseTX 100Mbs Ethernet running on UTP at a max distance of 100M per segment

100BaseF 100Mbs Ethernet running on fiber optic 62.5um cabling at a max distance of 2KM per segment

Ethernet Baseband network specification as defined by the IEEE 802.3 series standards

FDDI Fiber Distributed Data Interface

NIC Network Interface Card

STP Shielded Twisted Pair

Token Ring Token passing LAN technology developed by IBM

UTP Unshielded Twisted Pair

In the next article I'll discuss network protocols.

Copyright © 1997 Jeffrey L. Carrell. All Rights Reserved.

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