Networking: switching

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Basic Concepts

Circuit Switching Systems

A circuit switched system is one where a dedicated connection must be set up between two nodes before they may communicate. For the duration of the communication, that connection may only be used by the same two nodes, and when the communication has ceased, the connection must be explicitly cancelled. A good example of this is the early telephone exchange systems, where one caller would ask the operator to connect them to a receiver, where the end result was a physical electrical connection between the subscriber's telephones for the duration of the call. The primary characteristics of a circuit switched network are fixed-bandwidth and low transmission delay once a connection has established. Also it can be quite expensive as when traffic is low on a virtual circuit unused transmission capacity is wasted i.e. during international or long distance calls the charges will add up until the call is ended, even when either party are not speaking. When data is sent it must arrive in sequencing order and at a constant arrival rate.

References: Introduction to Networking, WestNet Learning Technologies

Packet Switching Systems

Packet-Switched networks, this networks divides all messages on the LAN (local area network) into small chunks called packets and attaches information to the front of the packet that identifies the recipient. The packets from all the machines on the local area network are placed on a high-bandwidth cable running through all the machines on the network. As packets move around the network, each machine analyses the header to see if the packet is for it. If not, it is sent further on. While packet switching is a more flexible approach than circuit switching, it does have a few problems. The primary problem is network traffic. As the number of nodes on the network increases, the network traffic increases too, sometimes reaching the network limit. Another problem with packet switching is that there is no guarantee of packets getting from source to destination, which is one of the strong points of circuit switching.

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References: Introduction to Networking, WestNet Learning Technologies

http://www.privateline.com/Switching/packet.html

Cell Switching Systems (ATM)

ATM (asynchronous transfer mode) is an international standard for a high-speed connection oriented, cell-switching technology.  Cell switching closely resembles packet switching in that it breaks a data stream into packets which are then placed on lines that are shared by several streams. One major difference is that cells have a fixed size, each being 53 bytes while packets can have different sizes.

 

References: telecom.tbi.net/switching.htm

General Routing and Congestion Control Algorithms

Routing is the act of moving information across an internetwork from a source to a destination. Along ...

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