Network Topology

The study of Computer Network Training brings you first to the study of network topology which is the physical or logical way the networked computers are connected.  You can have a physical Bus topology, physical or logical Ring Topology, physical Star Topology, or even a physical Mesh topology.  The logical topology might be different than the physical topology in the way data packets are switched through the network.

Bus Topology

The Bus topology has a single cable that all the computers and devices are connected to.  It is very simple to implement but not very fast or reliable.  The maximum speed for Bus topology is 10 megabits per second using 10Base2 cabling.  There is also a major draw back to the Bus because you create a single collision domain.  When a computer trys to send packets on the Bus it will listen first to make sure the Bus is clear before sending oackets.  However another computer could send packets at the same time creating a collison and no packets get through.  The computers will time, count down, and then try again.  Also if the cable breaks or a device is removed the signal traveling down the cable will reflect back and could interrupt the packets moving through the cable, which can bring down the entire network.  Because of all the draw backs you will not see the Bus topology used with newer networks.

Ring Topology

The Ring topology was popularized by IBM and worked very well because using a token that traveled around the Ring eliminated collisions.  Each computer would have an opportunity to use the token for sending or receiving data packets.  There were two major problems with the Ring.  First as you added more computers it would take longer to get the token and second the speed did not keep up with Ethernet so it lost popularity and you will rarely see it today.

Star Topology

The Star topology is by far the most popular and widely used for networks today.  Switches are generally used as the central hub and provide individual collision domains between just 2 computers, which has reduced the packet collision problem and greatly increased the bandwidth and speed of the networks.

Mesh Topology

The Mesh topology is primarily used on the Internet.  This allows several alternate paths for data to travel in case a segment or path goes down or becomes congested.  The routers on the Internet are constantly measuring the speed of each segment or path and determining dynamically which is the better path for sending packets.  This keeps the Internet very fast and responsive to changes that occur constantly each day as equipment is taken down for maintenance and repair and new equipment is installed to handle the growth.

Network topology is always a consideration when designing a new network.  The Star topology will be the choice used and implemented for the LAN and possibly a Mesh topology for servers and other critical connecting devices, such as, routers that connect to other networks or the Internet.