Network Topologies Overview

Network Topologies

Network topology is a schematic layout or map of the arrangement of nodes over a network. This layout also determines the manner in which information is exchanged within the network.
However, topologies can be implemented physically or logically.


Bus Topology
In the bus topology, nodes or stations of the network connect to a central communication link. Each node has a unique address along the bus that differentiates it from other users on the network. Information can be placed on the bus by any node. The information must contain network address information about the node or
nodes. Other nodes along the bus ignore the information.

Bus Topology

Ring Topology
In a ring network configuration, the communication bus is formed into a closed loop. Each node inspects the information on the LAN as it passes by. A repeater, built into each ring LAN card, regenerates every message not directed to it and sends the message to the next appointed node. The originating node eventually receives the message back and removes it from the ring.

Ring topologies tend to offer very high data transfer rates but require additional management overhead. The additional management is required for dependability. If a node in a ring network fails, the entire network fails.

Primary Ring Topology

 To overcome this, ring designers have developed rings with primary and secondary data paths as shown in the following figure. If a break occurs in a primary link, the network controller can reroute the data onto the secondary link to avoid the break.

Primary&Secondary Ring Topology

Star Topology
In a star topology, the logical layout of the network resembles the branches of a tree. All nodes are connected in branches that eventually lead back to a central unit. Nodes communicate with each other through the central unit. The central station coordinates the network’s activity by polling nodes, one by one, to determine whether they have any information to transfer. If so, the central station gives that node a predetermined slice of time to transmit. If the message is longer than the time allotted, transmissions are divided into small packets of information that are transmitted over several polling cycles.

Star Topology

Mesh Design
The mesh design offers the most basic network connection scheme. In this design, each node has a direct physical connection to all other nodes in the network. While the overhead for connecting a mesh network topology together in a LAN environment is very high, this topology is employed in two very large network environments, the public telephone system and the Internet.

Mesh Topology

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