Switching and Types of Switching
Switching is used for local exchange and long distance carrier. switching method in which a communication way in physical form between two ways within a network is established.
Switching play a greater role in the network paradigm. There are various types of switching and these are hardware based as well as their latency is different. Switching technology is provided by local exchange and long distance carrier.
Switching techniques :
In the main frame and minicomputer environment, each user is connected to the main system through a dump terminal that is unable to perform any of its own processing tasks. In this computing environments , processing and memory are centralized. This type of computerization has its merits but the major disadvantages is that the system can easily get overloaded as the number of users and consequently terminals increase. Secondly , most of the informer is centralized to one group of people rather than the end users. This type of centralized processing system differs from the distributed processing system used by LANs. In distributed processing system, most of the processing is done in the memory of the individual PCs or workstations besides sharing expensive computer resources like software, disk files printers and plotters etc.There is always a limit to how many hosts can be attached. It also raises the question why any number of PCs cannot be connected together in point-to-point manner. The point-to-point scheme provides separate communication channels for each pair of computers.
When more than two computers need to communicate with one another, the number of connections grows very quickly as number of computers increases.
Circuit Switching :
Circuit switching is a switching method in which a communication way in physical form between two ways within a network is established, maintained and for each communication. It has three establishment, data transfer and circuit disconnect. Once the connection is created, the data transfer is transparent. The main feature of such a connection is that provides a fixed data rate channel, and both subscribers must operate at this rate. It is considered inefficient as compared to packet switching because channel capacity is completely for the duration of connection. If there is no data at any amount of time, channel capacity goes wasted. Moreover, setting up of connection takes time. These differences may be more evident when we learn the packet switching.
Circuit switching has two types of transmission. These are datagram transmissions and data-stream transmissions. Data gram transmissions have individually addressed frames. Data-stream transmissions have a stream of data for which address checking occurs only once. The routing in switching may have either static routing. Incase of static routing, this methodology uses the same approach all the time white dynamic routing allows alternate routing depending on traffic.
Packet Switching :
In packet switching data networks, all user data to be transmitted is first divided into one or more units, called packets, by the source DTE. These packets are of varying lengths, and reach packet is assigned an address and the necessary control information. In each switching node, packets are received, stored briefly, and passed on to the text node. Packets includes both the source and the destination DTE network addresses. On receipt of each packet, the switching node inspects the destination address contained in the packet. Each switching nodes contains a routing director specifying the outgoing links to be used for each network address . On the receipt of each packet, the switching node forwards the packet on the appropriate link at the maximum available bit rate, which is not possible in case of circuit switching.
To prevent unpredictably long delays and ensure that the network has a fast transit time, a maximum length is allowed for each packet. Therefore, a message submitted to the transport layer within the DTE is divided by the transport protocol entity into a number of small packet units before transmission. These packets are handled in the following two ways :
Virtual Circuit and Permanent Virtual Circuit
A datagram is a self-contained, independent packet of data carry sufficient information to be routed from a source to the destination DTE without relying on earlier exchange between this source and destination DTE and the network. Here, each packet is treated independently that can take any practical rout to reach the destination in any arbitrary order. There may also be some packet missing at destination. It is the responsibility of DTE to reassemble the out of order packet in sequence and request for missing packets.
Virtual Circuit and Permanent Virtual Circuit :
Packet switching was developed to mitigate the drawbacks offered by circuit-switched telephone network. It is now clear that a virtual circuit is created between users in a packet switched network to make use of transmission resource is the most efficient way during the actual transfer of information. The virtual connection show created may either be connection-oriented for connection-less.
A short description about the different components of Switching Yard
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N K Ravishankara
Vijay Kumar Vishwakarma
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