Switching Techniques

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Communication networks carry information signals among entities, which are geographically far apart. An entity may be a computer or human being. A printer, a data terminal and so on. The entities are involved in the process of information transfer which may be in the form of a telephone conversation or a file transfer between two computers or message transfer between two terminal etc. so in this presentation we will be looking at how messages are forwarded through the network. Specifically, how and when buffers and switch ports of individual routers are allocated and released and thereby the timing which messages or message components can be forwarded to the next router on the destination path.

In computer networking and communications, switching communication network is a communication network which uses switching for connection of two non-adjacent nodes. Switching Communication Networks are divided into circuit switching networks, message switching networks, and packet switching networks. Communication is the most popular use of the Internet, with email topping the list of all the technologies used. Some of the types of communication technologies used also include email discussion groups, and chat groups. These are unique to networked computer environments and have come into wide popularity because of the Internet. Other technologies, including video and audio conferencing and Internet telephony, are also available on the Internet. They require more multimedia capabilities of computer systems and are more taxing of network resources than the others. They also are adaptations of other technologies to the Internet. In large networks there might be multiple paths linking sender and receiver. Information may be switched as it travels through various communication channels. There are three typical switching techniques available for digital traffic.

* Circuit Switching
* Message Switching
* Packet Switching
Circuit switching is a technique that directly connects the sender and the receiver in an unbroken path. Telephone switching equipment, for example, establishes a path that connects the caller's telephone to the receiver's telephone by making a physical connection. With this type of switching technique, once a connection is established, a dedicated path exists between both ends until the connection is terminated. Routing decisions must be made when the circuit is first established, but there are no decisions made after that time. Circuit switching in a network operates almost the same way as the telephone system works. A complete end-to-end path must exist before communication can take place. The computer initiating the data transfer must ask for a connection to the destination. Once the connection has been initiated and completed to the destination device, the destination device must acknowledge that it is ready and willing to carry on a transfer.

1. The communication channel (once established) is dedicated.

1 Possible long wait to establish a connection, (10 seconds, 2 More on long- distance or international calls.) During which no data can be transmitted. 3 More expensive than any other switching techniques, because a dedicated path is required for each connection. 4 Inefficient use of the communication channel, because the channel is not used when the connected systems are not using it.

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.

A message-switching node is typically a general-purpose computer. The device...
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