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Friday, August 16, 2013

PPT On Switching And Networks


Switching And Networks Presentation Transcript: 
1.Switching & Networks

A switch network consists of a series of interlink nodes called switches.
These are hardware and software devices capable of creating connections between two or more devices link to the switch.

3.Taxonomy of switched networks
Circuit switching
 Packet switching
Packet switching
In packet-based networks,  the message gets broken into small data packets. 
Each packet may go a different route from the others.
Each packet is sent with a ‘header address’.  This tells it where its final destination is, so it knows  where to go. The header address also describes the sequence for reassembly at the destination computer so that the packets are put back into the correct order.
If a packet fails to arrive, the recipient computer sends a message back to the computer  which  originally sent the data, asking for the missing packet to be resent.

4.Circuit switching
Circuit switching creates a direct physical connection between two devices such as computer or phones.
Advantages of circuit switching
 Once the circuit is set up communication is passed and error free.
 It is highly reliable.
Disadvantages of circuit switching
Takes a relatively long time to set up the circuit
 During a crisis or disaster, the network may become unstable or unavailable.
 Inefficient – the equipment may be unused for a lot of the call, if no data is being sent,  the dedicated line still remains open

5.Circuit Switching Communication
 Circuit establishment
 Data transfer
 Circuit disconnect
Circuit  establishment
Before any signals can be transmitted and end to end circuit must be established.
Data  transfer
Information can know be transmitted that can be analog or digital.

6.Circuit  disconnect
After some period of data transfer the connection is terminated.
EXAMPLES: Public telephone network

7.Telecommunication components
A public telecommunication network consists of the
 Subscriber line

 The devices that attach to the network
 Most subscriber devices in public communication networks are telephones.
Subscriber line:
The link between subscriber and network are called subscriber line.
 The switching centers in the network
 A switching center that directly support subscriber is known as end office.
The branches between exchanges
Trunks carry multiple voice frequency circuit using FDM or TDM.

9.Communications Network
The end devices that wish to communicate maybe referred to as stations.
The switching devices, connected to each other in some topology by transmission links are the nodes.
Each station attaches to a node, and the collection of node is referred to as a communications network.

A station is a device that a user interacts with to access a network and it contains the software applications that allows someone to use the network.
It maybe a microcomputer, a workstation, a cell phone or a mainframe.

A node is a device that allows one or more station to access a physical network and is a point to transfer information through the network.

12.Switching Concepts
Digital switch
Most important in modern systems
Function is to provide transparent signal path between any pair of attached devices
Allows full duplex mode

The network-interface element represent the functions and hardware needed to connect digital devices, such as data processing devices and digital telephones, to the network.

14.Control Unit
The control unit has three general tasks
Establish connection on demand
Maintain the connection
Tear down the connection

Multistage switch-The solution to limitation of the crossbar switch is the multistage switch which combines crossbar switches in several(normally three)stages.
In a single crossbar switch, only one row and one column is active for any connection. So we need n*n cross points. If we can allow multiple paths inside the switch ,we can decrease the no of cross points.
 Each cross points in the middle stage can be accessed by multiple cross points in the first or third stage.
 The multistage switch has one drawback-blocking during periods of heavy traffic. The whole idea of multistage switching is to share the cross points in the middle stage crossbars.

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