Circuit Switching pot

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 [...]... Switch  Time division    No crosspoints Delay Space division  Many crosspoints  Zero delay Space- and Time-Division Switching Combinations    Advantage of space-division switching is it is instantaneous; however, requires too many crosspoints Advantage of time-division switching is it needs no crosspoints; however, processing connections creates delays Combining them optimizes the number of... all switches are occupied) Does not occur in single-stage switch; a non-blocking path is always available Time-Division Switches     Uses time-division multiplexing to achieve switching Used by most modern switches TD switching involves partitioning low speed bit stream into pieces that share higher speed stream Two methods:   Time-slot interchange (TSI) TDM bus     Based on synchronous time... Trunks between switching offices: coax, microwave, fiber optics All trunks and switches are now digital Major Components  Local loops – twisted-pair cable connecting subscriber phone to nearest end office or local central office   Trunks – transmission media that handles communication between offices   Bandwidth of 4000 Hz (4 KHz) Muxing through optical fibers or satellite links Switching Office... LEC inside a LATA   The LEC that owns the local loops system is called incumbent LEC (ILEC) => provide main services Extra carrier = competitive LEC (CLEC) => extra services: mobile, toll calls, etc Switching Offices in a LATA Calls that go through a tandem office is charged Calls that are completed by using only end offices are toll-free Inter-LATA Services  IXCs: inter-exchange carriers, a k a... is normally digitized How do IXCs interact with LECs? Use POP Point of Presence (POP) Example PSTN Network Belongs to LEC (Local-Exchange Carrier) C.O Phone Phone Local loop Local loop Inter-exchange circuit LATA - A P.O.P LATA - B trunk line P.O.P Belongs to IXC (Inter-eXchange Carrier) GOLDMAN & RAWLES: ADC3e FIG 02-03 C.O Example PSTN Network Class 1: regional centers Class 1: regional centers... customer Residential customer Local Carrier's Dom ain of Influence, Intra-LATA Business customer Making Connections    Subscriber telephones are connected through local loops to end offices Accessing the switching station at the end offices is accomplished via dialing Dialing  Before: use Rotary or pulse dialing    for each number dialed, a digital signal is sent to end office Prone to errors due to . connection for duration of transmission Circuit Switching  Space-division switching  Time-division switching  TDM Bus  Combinations Circuit switching: create a direct physical connection. and Time-Division Switching Combinations  Advantage of space-division switching is it is instantaneous; however, requires too many crosspoints  Advantage of time-division switching is it needs. 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