Computer Networks: Network Topology

 What is a topology of a network?

The manner in which computers in a network are geometrically arranged and connected is known as the topology of the network.

 What is a host?

A computer connected to the WAN is called host or end system.

 What is a subnet?

 A computer connected to the WAN is called host or end system. The hosts are connected by a communication subnet or subnet for short. The job of the subnet is to carry messages from host to host.

 what is a router?

 In most WANs, the subnet consists of two distinct components: transmissions lines (also called circuits, channels or trunks) and routers (also called nodes or switching elements).

The transmissions lines move packets between computers. The routers connect two or more transmission lines. Routers are specialized computers.

What is a point-to-point subnet? 

 If two routers that are not directly connected wish to communicate, they must do this via other intermediate router. In this case, the packet is received at each intermediate router in it’s entirely, stored there until the required output line is free then forwarded. A subnet using this principal is called point-to-point (also called store-and-forwarded or packet switching) subnet.

 Describe kind of topologies used in LANs.

Ans: Broadcast networks are commonly used in LANs. The figure shows three commonly used topologies for LANs.

 

Bus topology: In a bus topology, all the computers are connected to a common transmission medium. As a result of this, only a pair of computers on the network can communicate at the same time. Each computer has a unique address which is used when information is transmitted.

When a data packet is sent out, it propagates through the medium and is received by all computers. To receive messages, each computer continuously monitors the medium and copies those messages that are addressed to itself as the data packets go by. Since the transmission medium in a bus is generally time-shared, there must be some type of control mechanism to prevent several stations from transmitting simultaneously.

Ring topology: In a ring topology, consecutive computes are connected by point-to-point links which are arranged to form a single closed path. Data are transmitted from node to node around the ring. The interface at each computer has the ability to recognize packets destined to it.

Star topology:  In a star topology, all computers are joined at a single point called hub.

Describe kind of topologies used in point-to-point subnet of a WAN.

A computer connected to the WAN is called host or end system. The hosts are connected by a communication subnet or subnet for short. The job of the subnet is to carry messages from host to host.

In most WANs, the subnet consists of two distinct components: transmissions lines (also called circuits, channels or trunks) and routers (also called nodes or switching elements).

The transmissions lines move packets between computers. The routers connect two or more transmission lines. Routers are specialized computers.

The collection of transmission lines and routers from the subnet as shown in the figure:

If two routers that are not directly connected wish to communicate, they must do this via other intermediate router. In this case, the packet is received at each intermediate router in it’s entirely, stored there until the required output line is free then forwarded. A subnet using this principal is called point-to-point (also called store-and-forwarded or packet switching) subnet.

Figure (below) shows six possible topologies used in point-to-point subnet: