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Basic concepts of switched networks

Switched Network
Circuit-Switched Network
Datagram Networks
Virtual-Circuit Network

In large networks we need some means to allow one-to-one communication between any two nodes.
In LANs this is achieved using one of three methods:
Direct point-to-point connection (mesh)
Via central controller (star)
Connection to common bus in a multipoint configuration (bus/hub)
None of the previous works in larger networks with large physical separation or consisting of a large number of computers.
The solution is a switching network
Consists of a series of interlinked nodes called switches.
Switches are capable to create temporary connections between two or more devices
Circuit switched network:
A circuit-switched network consists of a set of switches connected by physical links.
A connection between two stations is a dedicated path made of one or more links
Each connection uses only one dedicated channel on each link
Each link is normally divided into n channels.
The link can be permanent (leased line) or temporary (telephone)

Switching take place at physical layer
Such as channels (bandwidth in FDM and time slot in TDM)
Switch buffer
Switch processing time
Switch I/O ports
Data transferred are not packetized, continuous flow
No addressing involved during data transfer
Transmission phase:
Data transfer phase
After the establishment of dedicated circuit, two parties can transfer data
Teardown phase
Signal is sent to each switch to release resources, when one of the parties needs to disconnect

Delay is minimal, no waiting time
Total delay is due to time needed to create the connection, transfer data, and disconnect the connection.
The delay caused by set up is the sum of four things:
Propagation time of the source computer request,
Request signal transfer time,
Propagation time of acknowledgement from the destination and
Signal transfer time of the acknowledgement
The delay due to data transfer is sum of two:
Propagation time and
Data transfer time

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