SWITCHING: A NETWORK LAYER FUNCTION

• Switching technologies that are gaining prominence: frame relay and cell relay (ATM).
   
• Point-to-point (e.g. mesh) and multipoint communications (bus) solutions discussed thus far have limitations such as cost and distance.
• An alternative solution to point-to-point and multipoint communications is to use switching.
• A switched network consists of a series of interlinked nodes, called switches .
• A switch is a device connecting multiple communication lines together.
• Switches are hardware and/or software devices capable of creating temporary connections between two or more devices linked to the switch, but not to each other.
• Example : Telephone system. When you place a telephone call, the switching equipment within the telephone system seeks out a physical "copper" path all the way from your telephone to the receiver's telephone, using circuit switching.   
• When a call passes through a switching office (end office, central office, toll office, etc.) a physical connection is (conceptually) established between the line on which the call came in and one of the output lines.
   
• In the early days of telephony, the connection was made via the operator who plugged in a jumper cable into the input and output sockets.
   
• The term switch is a telephony term for the piece of equipment that handles telephone calls.
   
• Three main methods of switching: circuit switching, packet switching, and message switching .