Computer networks have become the critical part of every business in the world

Computer networks have become the critical part of every business in the world. Networks use the communication devices such as hubs, switches and routers to better manage the traffic between nodes. Modern network use different kind of switching technology to benefit the network with more capacity, scalability, performance and speed. A switch is a centralized network communication device that is used to connect all the computers with each other. It uses to reduce the congestions in the networks and to increase the performance and capacity of the networks.

It can connect different types of the networks or the networks of the same type. Advanced switches offer the high speed links which are used to connect the different switches with each other. Switches determine the Ethernet and IP address of the computers and maintain the switching table.

Circuit Switching Technology

In the circuit switching, caller establishes the connection before making the call. All the network resources are fully allocated during the transmission. The path between the source and destination is determined by the circuit.

Virtual Circuit Packet Switching Technology

It is the combination of the circuit switching and datagram switching technology to make advantages of both technologies. It uses the traffic engineering features of the circuit switching and resources usage efficiency of the datagram packet switching technology.

Switching technology has always been evolved and a new generation known as optical switches is in place to provide the optimal performance, speed, scalability and efficiency to the networks.

In circuit switching, resources remain allocated during the full length of a communication, after a circuit is established and until the circuit is terminated and the allocated resources are freed. Resources remain allocated even if no data is flowing on a circuit, hereby wasting link capacity when a circuit does not carry as much traffic as the allocation permits. This is a major issue since frequencies (in FDM) or time slots (in TDM) are available in finite quantity on each link, and establishing a circuit consumes one of these frequencies or slots on each link of the circuit. As a result, establishing circuits for communications that carry less traffic than allocation permits can lead to resource exhaustion and network saturation, preventing further connections from being established. If no circuit can be established between a sender and a receiver because of a lack of resources, the connection is blocked.

A second characteristic of circuit switching is the time cost involved when establishing a connection. In a communication network, circuit-switched or not, nodes need to lookup in a forwarding table to determine on which link to send incoming data, and to actually send data from the input link to the output link. Performing a lookup in a forwarding table and sending the data on an incoming link is called forwarding. Building the forwarding tables is called routing. In circuit switching, routing must be performed for each communication, at circuit establishment time. During circuit establishment, the set of switches and links on the path between the sender and the receiver is determined and messages are exchanged on all the links between the two end hosts of the communication in order to make the resource allocation and build the routing tables. In circuit switching, forwarding tables are hardwired or implemented using fast hardware, making data forwarding at each switch almost instantaneous. Therefore, circuit switching is well suited for long-lasting connections where the initial circuit establishment time cost is balanced by the low forwarding time cost.

The circuit identifier (a range of frequencies in FDM or a time slot position in a TDM frame) is changed by each switch at forwarding time so that switches do not need to have a complete knowledge of all circuits established in the network but rather only local knowledge of available identifiers at a link. Using local identifiers instead of global identifiers for circuits also enables networks to handle a larger number of circuits.

Virtual circuit packet switching (VC-switching) is a packet switching technique which merges datagram packet switching and circuit switching to extract both of their advantages. VC-switching is a variation of datagram packet switching where packets flow on so-called logical circuits for which no physical resources like frequencies or time slots are allocated. Each packet carries a circuit identifier which is local to a link and updated by each switch on the path of the packet from its source to its destination. A virtual circuit is defined by the sequence of the mappings between a link taken by packets and the circuit identifier packets carry on this link. This sequence is set up at connection establishment time and identifiers are reclaimed during the circuit termination.

We have seen the trade-off between connection establishment and forwarding time costs that exists in circuit switching and datagram packet switching. In VC-switching, routing is performed at circuit establishment time to keep packet forwarding fast. Other advantages of VC-switching include the traffic engineering capability of circuit switching, and the resources usage efficiency of datagram packet switching. Nevertheless, a main issue of VC-Switched networks is the behavior on a topology change. As opposed to Datagram Packet Switched networks which automatically recompute routing tables on a topology change like a link failure, in VC-switching all virtual circuits that pass through a failed link are interrupted. Hence, rerouting in VC-switching relies on traffic engineering techniques.

In practice, major implementations of VC-switching are X.25 [70], Asynchronous Transfer Mode (ATM [6]) and Multiprotocol Label Switching (MPLS [50]). The Internet, today's most used computer network, is entirely built around the Internet Protocol (IP), which is responsible for routing packets from one host to another. Because of the central role of IP in the Internet, we now discuss how ATM and MPLS interact with IP.

You can use a network switching technology to provide LAN segmentation features. LAN switches can assist in increasing bandwidth availability for workstations because LAN switches support simultaneous switching of packets between the ports in the switch.