2. Why Is It All?  A Network is a set of connected devices. Whenever we have multiple devices, we have the problem of how to connect them to make one-to-one communication possible.  One solution is to make a point-to-point connection b/w each pair of devices(mesh topology) OR B/w a central device & every other device(star topology)  When applied to very large N/W, these methods are impractical & wasteful.  Other topologies employing multipoint connections, such as a bus,all ruled out because distance b/w devices & the total no. of devices increases beyond the capacities of the media & equipment.  To overcome this, networking introduced Switching

3. Contents:  Introduction to Switching.  Concepts Of Switching. 1.Circuit Switching.  Advantages & Disadvantages of Circuit Switching. 2.Packet Switching.  Advantages & Disadvantages of Packet Switching.  Categorized into 1. Datagram Packet Switching. 2. Virtual Circuit Packet Switching. 3. Message Switching  Advantages & Disadvantages of Message Switching.  Differences B/W Circuit Switching And Packet Switching.

4. Introduction Switches: A switch is a device that channels incoming data from any of multiple input ports to the specific output port that will take the data toward its intended destination. Switching: Switching are the base packet or data delivering methods in network and each device like router, switch, hub, firewall, proxy, cash server, modem are using one of these methods.

5. Concepts Of Switching: SWITCHING CIRCUIT SWITCHING PACKET SWITCHING MESSAGE SWITCHING Datagram Packet Switching Virtual Circuit Packet Switching

6. CIRCUIT SWITCHING: Circuit switching is a mechanism of assigning a predefined path from source node to destination node during the entire period of connection. A circuit-switched network is excellent for data that needs a constant link from end-to-end. For example real-time video. old telephone system (POTS) is a well known example of analogue circuit switching. Packet Switching:  In this network type, no specific path is used for data transfer. Instead, the data is broken down into small pieces called packets and sent over the network.  The packets can be routed, combined or fragmented, as required to get them to their eventual destination.  On the receiving end, the process is reversed—the data is read from the packets and re-assembled into the form of the original data.

7. Advantages And Disadvantages Advantages of Circuit Switching: Once the circuit has been set up, communication is fast and without error. It is highly reliable Disadvantages of Circuit Switching: Inefficient – the equipment may be unused for a lot of the call, if no data is being sent, the dedicated line still remains open. Waists a lot of bandwidth, especial in speech where by a user is sometimes listening, and not talking. Channel set up may take longer.

8.  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.  One packet also contains details of how many packets should be arriving so that the recipient computer knows if one packet has failed to turn up.  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.

9. Two major packet switching  Connectionless/Datagram packet switching: In this case each packet includes complete addressing or routing information. The packets are routed individually, sometimes resulting in different paths and out-of-order delivery. Ex:-Ethernet, IP,UDP  connection-oriented/ virtual circuit packet switching: In this case a connection is defined and reallocated in each involved node during a connection phase before any packet is transferred. The packets include a connection identifier rather than address information, and are delivered in order.

10. Advantages & Disadvantages Of Packet Switching Advantages of Packet Switching It makes very efficient use of the network - no tied-up lines. It can easily get around broken bits of the network. As customers increase, the network only has to expand slowly compared to circuit switching. Disadvantages of Packet Switching The time it takes to put back the data package changes each time, which can be a problem for time-critical information such as an emergency signal. The fancy name is for this is 'latency'. Not very good for small data packages - for example if the data package itself is only 600 bytes long, then two packets of 512 bytes need to be used, plus the address information.

11. Message switching: Message switching systems are nowadays mostly implemented over packet-switched or circuit-switched data networks. Each message is treated as a separate entity. Each message contains addressing information, and at each switch this information is read and the transfer path to the next switch is decided. Depending on network conditions, a conversation of several messages may not be transferred over the same path. Each message is stored (usually on hard drive due to RAM limitations) before being transmitted to the next switch. Because of this it is also known as a 'store-and-forward' network. Email is a common application for Message Switching.

12. Advantages & Disadvantages Of Message Switching Advantages Data channels are shared among communication devices improving the use of bandwidth. Messages can be stored temporarily at message switches, when network congestion becomes a problem. Priorities may be used to manage network traffic. Disadvantages The only real disadvantage to Message Switching is it's not suitable for real time applications such as data communication, video or audio.

13. Packet Vs Circuit Switching Circuit Switching Packet Switching In circuit switching, there are various nodes used in the network through which the signals are passed from one system to another. In this a number of nodes are available between two devices and hence multiple paths are available to pass a signal. This concept is mainly used in telephony systems. This is best used for transmission of audio signals and not suitable for data transmission. This type of switching is connection oriented and may be connectionless also. Due to its old version, this technique is less popular and more expensive. In packet switching, the data is sent over the network in the form of packets i.e. a large unit of data items wrapped into a single bigger unit. In these, the packets follows the same path that is defined for them before passing into the network. It can be used for telephony, DSL services and other data transmission services. It is best used for sending data over the network and audio and video signals can also be sent over the network in the form of packets. It is usually a connection less service. It is a new technology and economic than the circuit switching approach.

14. Bibliography:- http://en.wikipedia.org/wiki/Network_switch/ http://en.wikipedia.org/wiki/Network_switch http:// www.tcpipguide.com/free/t_CircuitSwitchingand/www.tcpipguide.com/free/t_CircuitSwitchingand http:// www.ustudy.in/node/3759www.ustudy.in/node/3759 http://www.indiastudychannel.com/ www.voipnsms.com/ tag/circuit-switching Data Communications & Networking - Forouzan (4th Edition)