Switching A Network Layer Function Switched network with interlinked nodes called switches Traditional Switching Methods: Circuit, Packet, and Message switching New Switching Strategies: Asynchronous transfer Mode (ATM) Frame Relaying 11/14/2018 Lin - Swicthing

Circuit Switching Designed for voice communication Circuit switch device: A device with n inputs and m outputs Temporary connector for input and output links Full-duplex mode n x n folded switches n phones 11/14/2018 Lin - Swicthing

A Four Switch Example Hosts or computers: H1 through H7 H1 --| |-- S3 (1-to-2) --| -- H4 H2 --|--- S-1 (4-to-1) -- S2 (1-to-2) --| | -- H5 H3 --| |-- S4 (1-to-2) --| -- H6 H4 --| | | -- H7 Hosts or computers: H1 through H7 Switches: S-1 through S4 11/14/2018 Lin - Swicthing

Circuit Switching (continue) Switching technology: Space-division switches (SDS) Instantaneous connection, require crosspoints Time-division switches (TDS) Time delay, no crosspoints Combination of SDS and TDS 11/14/2018 Lin - Swicthing

Space-Division Switches Analog + digital networks Crossbar switches (n x m) Multistage switches Multipaths connections Blocking – during period of heavy traffic 11/14/2018 Lin - Swicthing

Time-division switches Time-division multiplexer and Time-slot interchange (TSI) A TDS Example H1 --| |-- H4 H2 --|--- TDM -- TSI -- TDM --- |-- H5 H3 --| |-- H6 H4 --| |-- H7 11/14/2018 Lin - Swicthing

Disadvantages of Circuit Switching More idle time: low utilization rate One data rate: can’t interconnect a variety of digital devices Inflexible: fixed circuit connection Cannot setup priority Less well suited for data communication 11/14/2018 Lin - Swicthing

Packet Switching Packets Variable length of data blocks Header Data Priority Control info Destination address Source address Data 11/14/2018 Lin - Swicthing

Packet Switching (continue) Two methods Datagram Virtual Circuit 11/14/2018 Lin - Swicthing

Datagram Approach Datagram is also known as packet Each packet is treated independently Packets may arrive at the destination in any order Packets can be carried simultaneously by either TDM or FDM May use multiple channels 11/14/2018 Lin - Swicthing

Virtual Circuit Approach A single route between sender and receiver is chosen for the session All packets travel on the same route Can have multiplexing at the switches Two formats Switched virtual circuit (SVC) Permanent virtual circuit (PVC) 11/14/2018 Lin - Swicthing