A switched network consists of a series of intermediate nodes called switches. Switches are H/W and/or S/W devices capable of creating temporary connections between two or more devices linked to the switch not to each other.

Circuit switching creates direct physical connection between two devices.—is a device with n inputs and m outputs that creates temporary connection between an input link and an output link—no of inputs does not have to match no of outputs An n by n folded switch can connect n lines in full duplex mode.

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Synchronous optical network (SONET) is ANSI standard whereas Synchronous digital hierarchy (SDH) is ITU-T standard. SONET/SDH is a synchronous network. Single clock is used to handle the timing of transmission and equipment across the entire network so it adds a level of predictability to the system.—improved speed and reducing cost. SONET/SDH contains recommendations for the standardization of fiber optic transmission equipment (FOTS). SONET/SDH physical specification and frame design include mechanism that allow it to carry signals from incompatible tributary systems (e.g. asynchronous services –DS-0 and DS-1) SONET is a multiplexed transport mechanism and can be a carrier for broadband services e.g. ATM and B-ISDN. SONET defines a hierarchy of signaling levels called synchronous transport signals (STSs). The physical links defined o carry each level of STS is called Optical Carriers (OCs). OC describe the conceptual and physical specification of the links required to support each level of signaling.

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ISDN consists of following

Bearer Services: provide the means to transfer information between users without the network manipulating the contents of that
information. Belongs to first three layers.
Teleservices: the network may change or process the contents of the data. Correspond to 4-7 layers.
Supplementary services: provide additional functionality to the bearer services and teleservices.

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ATM: Asynchronous Transfer Mode

The most important technical innovation to come out of the standardization work on broadband ISDN is asynchrounous transfer mode (ATM), is a cell relay uses fixed size cell transmission technique. It has less overhead than frame relay and designed to operate at significantly  higher data rates than frame relay.

view / download: ATM(Asynchronous Transfer Mode) (size 600KB )