Communication Switching Techniques For more notes and topics

Communication Switching Techniques For more notes and topics visit: www. e. ITnotes. com

Switched Network §A Switched Network consists interlinked nodes called Switches. of §Switches are hardware and software that are capable of creating temporary connections between two or more devices linked to the switch. §In a Switched network, some of nodes are connected to the end system or communication devices like computer or telephone. e. ITnotes. com

Switched Network A, B, C, D, E and so on are end systems or communication devices. Switches are labeled as I, III, IV, V and soe. ITnotes. com on.

Types of Switching Techniques Switching Circuit Switching Packet Switching Virtual Circuit Switching Message Switching Datagram Switching e. ITnotes. com

Circuit Switching §Dedicated physical connection or path is established between the sending and receiving device. §Dedicated path made of one or more links. §Routing is made when the path or link is set up across the network. After the has been set between the sender and receiver, the information is forwarded continuously over the link. e. ITnotes. com

§Data transferred between the two stations are not in the form of packets. The data are continuous flow sent by the source station and received station. §No addressing involved in data transfer. §Communication takes place in three phases: -Circuit establishment -Data transfer phase -Circuit disconnect e. ITnotes. com

§ Path is release only when data transmission between sender and receiver is over. § In circuit switching, the resources need to be reserved during the setup phase, the resources remain dedicated for the entire duration of data transfer until the teardown phase. e. ITnotes. com

§The four switches are connected these computers thus provide dedicated links by reducing the line cost. I, III and IV are circuit switches. Switch I, III, IV are connected to computers while II is only routing node. e. ITnotes. com

Advantages of Circuit Switching v. Dedicated path establish guaranteed data rate. provides a v. Data is transmitted without any delay, as there is no waiting time at each switch. v. Suitable for long continuous transmission. e. ITnotes. com

Disadvantages of Circuit Switching v. It cannot be used to transmit any other data even if the channel is free. v. Inefficient resources. in terms of utilization of v. Long time is required to establish a physical link. e. ITnotes. com

Packet Switching §Message is broken up into packets of fixed and variable size. Each packet includes header that contains source address , destination address and other control information. § §Size of packets depend upon type of network and protocol used. §Resources are allocated on demand on a first come first basis. e. ITnotes. com

§Packet are sent over network node to node. §At each node, packet is stored briefly and then routed according to information in its header. These types of networks are called store and forward networks. §Individual packets may follow different routes to reach destination. §Two types of Packet Switching: -Datagram Packet Switching -Virtual Packet Switching e. ITnotes. com

Datagram Packet Switching §Each packet is separately addressed that is contains destination address in its header and is treated independently. §Packets datagram. §Datagram layer. in this approach are called Switching is done at network e. ITnotes. com

Datagram Packet Switching e. ITnotes. com

Datagram approach is used to deliver four packets from station A to X. All the four packets belong to same message but they travel via different paths to reach the destination. § §It can cause the datagram to arrive out of order at their destination with different delays between the packets. §Packets may also be lost because of lack of resources. e. ITnotes. com

Virtual Packet Switching §Circuit connection called virtual circuit is set up between sender and receive before any data transfer takes place. §Virtual circuit approach has a set up, data transfer and tear down phase. §Resources can be allocated during set up phase or on demand. e. ITnotes. com

§All the packets of a message follow the same path establish during the connection. §It is implemented in the data link layer. e. ITnotes. com

Advantages of Packet Switching v. Switching node can route the packet as and when required. v. Routing is done on packet basis, the intermediate nodes do not have to wait for entire message, hence transmission is very. v. It increases the bandwidth of network by allowing many devices to communicate through the same network channel. e. ITnotes. com

Disadvantages of Packet Switching v. Packets may be lost on their route, so sequence numbers are required to identify the missing packets. v. Large amount RAM is required to handle the large quantities of packets. e. ITnotes. com

Message Switching §Message is a logical unit of information and can be of any length. §If a station wishes to send a message to another station, it first adds destination address to the message. §No direct link is sender and receiver. established e. ITnotes. com between

§Each unit. message is treated as an independent §Each complete message is then transmitted from device to device through internetwork i. e. message is transmitted from source node to intermediate node. §Intermediate node stores complete message temporarily, inspect it for errors and transmits message to next node based on available channel and its routing information. It is called Store and Forward network. e. ITnotes. com

§When message reaches a node, the channel on which it came is released for use by another message. §Message M 1 is transmitted from A to D and M 2 is transmitted from C to B. Message M 1 follows route A->I->II->D and M 2 follows route C->IV->II->B depending upon availability of free path at that particular moment. e. ITnotes. com

Message Switching e. ITnotes. com

Advantages of Message Switching v. No physical connection is required between source and destination. v. Reduces traffic congestion on network because of store and forward facility. v. Support message length of unlimited size. e. ITnotes. com

Disadvantages of Message Switching v. As message length is unlimited, each switching node must have sufficient storage to buffer message. v. Storing and forwarding facility introduces delay thus unsuitable for real time applications like voice and video. e. ITnotes. com

Comparison between Switching Techniques Parameter Circuit Switching Packet Switching Message Switching Path or Route Path is created between two points by setting switches. Virtual circuit is created between two points. No need to create a link or path. Dedicated or sharing Links that make a path are dedicated and cannot be used other connections. In virtual circuit , links that make a route can be shared by other connections. Message reaches a node the channel on which it came is released by another message. Store and forward transmission No use Each node may store incoming packet temporarily & forward them later. Store and forward transmission is used. e. ITnotes. com

Parameter Circuit Switching Packet Switching Message Switching Path followed by packets It is always same. May or may not be different May or may not be same. Call setup It is required. Not required. Application Real time transfer of voice signal. Internet for datagram and reliable stream service between computers. Telegraph network for transmission of telegrams. Layer used for implementation It is implemented at physical layer. Virtual circuit network is implemented at data link layer and datagram network at network layer. e. ITnotes. com

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