Question

In a    network topology, all network devices are connected to a common backbone that serves as a shared communications medium.

Answer 1

Network topology is used to describe the arrangement of various telecommunication networks.A wide variety of physical topologies have been used in LANs, including ring,bus,mesh and star etc. All the nodes in these topologies have to share a common communication medium, So there has to be a robust way of making this communication happen without raising any ambiguity.In telecommunication, a Shared medium is a channel of information transfer that serves more than one user at a time.To ensure that each user gets a fair chance to access that communication medium we do :

1.Circuit switching: It is a method in which two nodes establish a dedicated communication channel through network before the nodes may communicate.For example :an early analog telephone network , where a call is made from telephone to another, switches within the telephone exchanges create a continuous wired circuit between the two telephones, for as long as the call lasts.In this each user gets typically a fixed share of the channel capacity.A multiplexing scheme like time-division multiplexing and frequency-division multiplexing are used divides upto the capacity of medium .Channel access methods for circuit switching includes time-division multiple access and frequency-division multiple access etc.

2.Packet switching:The routing and transferring the data by means of addressed packets so that a channel is occupied during the transmission of the packet only, and upon the completion of the transmission the channel is made available for the transfer of other traffic.Packet switching may be classified into connectionless and connection oriented packet switching.ex of connectionless systems are Ethernet,IP,UDP. TCP, Frame Relay,MPLS ,X.25 etc are the example of connection oriented systems. In Connectionless mode each packet is labelled with a destination and a source address which eliminates the need for a pre-established path to help the packet finds its way to destination whereas Connection oriented transmission requires a setup phase to establish the parameters of communication before any packet is transferred.The sharing is more dynamic - each user takes up little or non of the capacity when idle, and can be utilized the entire capacity if transmitting while all other users arre idle.