SWITCHING TECHNIQUES

Introduction:

Data is often transmitted from source to destination through a network of intermediate nodes.

Switching Techniques deal with the methods of establishing communication links between the sender and receiver in a communication network.

A basic model of a Switched communication is shown in below Figure

The end devices that wish to communicate with each other are called stations.

The switching devices are called nodes. Some nodes connect to other nodes and some are too connected to some stations.

 

Features:

§  Network Topology is not regular.

§  There exist multiple paths between a source-destination pair for better network reliability.

§  The switching nodes are not concerned with the contents of data.

§  Their purpose is to provide a switching facility that will move data from node to node until they reach the destination.

 

Types of Switching Techniques:

  • Circuit Switching
  • Message Switching
  • Packet Switching

Circuit Switching:

§  Circuit switching is a technique that directly connects the sender and the receiver in an unbroken path.

§  Circuit Switching implies that there is a dedicated communication path between the two stations

§  The path is a connected through a sequence of links between network nodes.

§  With this type of switching technique, once a connection is established, a dedicated path exists between both ends until the connection is terminated.

§  Telephone switching equipment, for example, establishes a path that connects the caller’s telephone to the receiver’s telephone by making a physical connection.

§  It transfers the data from the source to the destination. The data may be analog or digital.

§  The connection is generally full-duplex.

Advantages:

§  The communication channel is dedicated when it is established.

 

Disadvantages:

§  Possible long wait to establish a connection in which no data can be transmitted at that time.

§  A dedicated path is required for each connection. Therefore, This technique is more expensive than other techniques.

Message Switching:

§  With Message Switching there is no need to establish a dedicated path between two stations.

§  When a station sends a message, the destination address is appended to the message.

§  The message is then transmitted through the network, in its entirety, from node to node.

§  Each node receives the entire message, stores it in its entirety on disk, and then transmits the message to the next node.

§  This type of network is called a store-and-forward network.

Advantages:

§  Traffic congestion can be reduced, because messages may be temporarily stored in route.

§  Message priorities can be established to manage traffic due to store-and-forward technique.

§  Data channels are shared among communication devices, improving the use of bandwidth.

§  Messages can be stored temporarily when network congestion becomes a problem.

Disadvantages:

§  Message switching is not compatible with interactive applications.

§  Store-and-forward devices have large disks to hold temporarily long messages. So it can be expensive.

Packet Switching:

§  Packet Switching can be seen as a solution that tries to combine the advantages of message and circuit switching and to minimize the disadvantages of both.

§  In both Packet Switching Methods, a message is broken into small parts, called packets.

§  These packets are of varying lengths, and reach packet is assigned an address.

§  These packets can travel at same route or different routes.

§  At the end station, the packets are received and the receiver has to check all packets are received or not.

§  If not then the signal can send to the sender for the specific package is not received.

§  And then sender can send the particular packet to the receiver.

§  There are two methods of Packet Switching: Datagram and Virtual Circuit.

Advantages:

§  Packet switching is cost effective.

§  Packet can be rerouted if there is any problem, such as, busy or disabled links.

§  Many network users can share the same channel at the same time.

Disadvantages:

§  Protocols for packet switching are typically more complex.

§  If packet is lost, sender needs to retransmit the data.

§  Protocols for packet switching are complex.

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