What is the Circuit switching?

[Brruno]

I am now into the data transmission. Just came to know about the switching operation. It is establishing a temporary connection between two network points. We can make the switching circuit that uses the telephone network (PSTN) and packet switching using the network (IP) internet. Also I am having some ideas about the bandwidth. Bandwidth, analog communications: the difference between the highest frequency and lowest within a given range. For digital, the bandwidth is expressed in bits per second (bps). Is the volume of information that can pass on a computer communication medium (telephone wire, coaxial cable, fiber optics, radio waves, etc..). It is also the frequency range within which the data will be transmitted successfully. Now all I want to know about circuit switching. I am here for the same reason. So please help me regarding that.

[Wannabe]

The voice, even scanned, does not lend itself to division into packets for the digital / analog conversion necessary for the return of the voice signal to the recipient requires strict adherence to time constraints (eg, digitized voice at 64 kbit / s, equivalent to a sample of one byte every 125 ms). This specific need of voice over data characterizes a signal isochronous (Communications where data transmitted according to a precise timing). The digitized voice is sensitive to the time of transfer which should be scrupulously respected, but is insensitive to data errors to a certain threshold. The allocation of a fixed capacity for a fixed term, solves the problem of variable delay

[Brunoz]

This technique, known as circuit switching, if it is well adapted to the information flows such as voice, is not very efficient for data transmission. In circuit switching, all network resources, contributing to this capacity is fixed for the duration of the connection. The principle of circuit switching is to establish, prior to switching, a link interconnecting multiple pathways. Each communication passes through three stages:

• Handshake: active phase switching for detecting the service request, receive and interpret the identity of the called terminal, seek and take a route and interconnect the two terminals (pick up, dial, ring).
• Maintaining liaison throughout the duration of the connection
• Release of connections in order and return to the free state.

[RogerFielden]

In time switching or digital, it is no longer current (generated by the voice) that is transported but the numerical values of the amplitudes of signals at regularly spaced sampling instants. The current can no longer central in one side and emerges on the other: between what is abstract information which, according to the principles of pulse code modulation (PCM, Pulse Code Modulation) describes point by point the curve of the sound. I think that you should also know about the packet switching, because that is also an important topic when Circuit Switching is considered. Technology which involves dividing the data into packets and sent across the network. Each packet has a header indicating the source, destination, sequence number to reassemble the information, a block of data content and code verification errors. The data packets may take different routes to their destination where the original information is reassembled after the arrival of packets. The international standard for packet switching networks is X.25.

[ComPaCt]

The international standard for packet switching networks is X.25.

The X25 specification defines the interaction point to point between the terminal equipment for data processing (DTE) and terminating equipment data circuit (DCE). A DTE is connected to a DCE by a translation unit called assembler / disassembler package (PAD, packet assembler / disassemble). The X25 specification is the work of telephone companies. Communication from end to end between the DTE is via a virtual circuit. Virtual circuits allow communication between separate network elements, by any number of intermediate nodes, without having to spend their portions of the fixed network.

[S_Asnodkar]

Virtual circuits keep the packet order, authorize the exchange in full duplex, use the flow control and allow multiplexing. There are two types of virtual circuits:

• Permanent Virtual Circuit (PVC). Logical way to network between origin and destination. Once the logical channel has been established under normal conditions, all the packets follow. In case of failure, a new path is negotiated. PVCs are used to transfer data more frequently.
  
• Switched Virtual Circuits (SVC). Makes no logical path. Each packet makes its way to the destination, and marked the route most appropriate to the moment of transmission. With this method, the packets follow different routes and can therefore reach their destination in the wrong order. X25 takes this situation into account to ensure an error free transmission. SVCs are used for sporadic data transfers.