Circuit Switched Network Three Phases

Three Phases of circuit switching Network The actual communication in circuit switched network require 3-phases. Setup phase Data transfer phase Teardown phase

Three Phases Setup phase If the two parties want (or multiple) to communicate, a dedicated connection needs to be established. connection setup means creating dedicated channels between the switches.

Setup Phase For example, If station A wants to sends a data ,request to node 4 requesting a connection to station E. Typically, the link from A to 4 is a dedicated line, ,so that part of the connection already exist. Based on routing information and measures of availability ,node 4 selects the link to node 5,allocates a free channel on that link .Node 5 allocates a channel to node 6 and internally ties that channel to the channel from node 4. In completing the connection , a test is made to determine if E is busy or is prepared to accept the connection.

Setup Phase Diagram

Data transfer Phase Data can now be transmitted from A through the network to E. The transmission may be analog or digital , depending on the nature of the network. As the carriers evolve to fully integrated digital networks , the use of digital (binary) transmission for both voice and data is becoming the dominant method.

Data Transfer Phase The path is A-4 link , internal switching through 4,4-5 channel , internal switching through 5,5-6 channel , internal switching through 6,6-E link. Generally , the connection is full duplex.

Teardown Phase After some time of data transfer , connection is terminated , generally by the action of one or two station. Signals must be propagated to nodes 4,5,and 6 to deallocate the dedicated resources. Note that the connection path is established before data transmission begins.

Efficiency Circuit switching networks are no efficient as packet message switched network. The switches know how to find the route to the destination and how to allocate bandwidth (channel) to establish a connection. Once the dedicated path is established between two computers, the path may remains connected even when no data transmission is taking place.

Delay The delay in this type of network is minimal. The total delay is due to the time needed to create a connection, transfer data and disconnect the circuit. The delay caused by the setup is the sum of four parts, the propagation time , request signal transfer time , propagation time of the acknowledgment from the destination computer , signal transfer time of the acknowledgment.

Problem of circuit switching Network designed for only voice services. Resources dedicated to a particular call. For data transmission, much of the time the connection is idle . Data rate is fixed. Both ends must operate at the same rate during the entire period of connection.