CircuitSwitching

Circuit Switching by Dr. Nguyen Minh Hoang hoang.dhbk@gmail.com March 2007 References  Reference books:  Data Communications and Networking, 4/e, by Behrouz A. Forouzan, DeAnza College (http://highered.mcgraw- hill.com/sites/0072967757/information_center_view0/)  Data & Computer Communications by William Stallings ( http://williamstallings.com/DCC/DCC7e.html) Introduction  How can we connect multiple devices?  Point-to-point vs.  Multipoint  Better solution  switching  Switches: hardware and/or software devices allowing temporary connections between two or more devices  Three methods: circuit, packet, and message Example of a Switched Network Circuit Switching  Creates a direct physical connection between two devices  Originally developed for voice traffic  Does not use point-to-point connections between every device to every other device  Instead, devices link to a switch which may in turn link to other switches  Allows for a dedicated connection for duration of transmission Circuit Switching  Space-division switching  Time-division switching  TDM Bus  Combinations Circuit switching: create a direct physical connection between 2 devices such as phones or computers Circuit Switch vs. Folded Switch n inputs, m outputs n lines in full duplex Folded Switch: An n -by -n folded switch allows every device to connect to every other device in full-duplex mode Space-Division Switch  The paths in the circuit are separated from each other spatially  Originally for analog networks, but now for both analog and digital  Crossbar switch  Multistage switch Crossbar Switch Inputs and outputs connected in a grid using electronic microswitches (transistors) at crosspoints Disadvantage??? Too many crosspoints, only a few used at any given time Inefficient; fewer than 25% of switches are in used at a given time Multistage Switches  Combine crossbar switches in several stages  Devices are linked to switches that are linked to a hierarchy of other switches  Middle stages usually have fewer switches than first and last stages  Fewer crosspoints but still allowing multiple paths through the network  increased reliability