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VC virtual circuits

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Virtual Circuits (VC):

In computer networking, a virtual circuit (VC) is a logical communication path or connection established between two endpoints in a network. Unlike physical circuits, which involve a dedicated physical connection between nodes, virtual circuits are software-based and operate over shared network resources. Virtual circuits are a fundamental concept used in connection-oriented networking protocols, such as Frame Relay and Asynchronous Transfer Mode (ATM).

Connection-Oriented vs. Connectionless Networking:

There are two primary types of networking approaches:

  1. Connection-Oriented: In connection-oriented networking, a predefined logical connection is established between the communicating nodes before data transmission begins. This connection remains in place for the duration of the communication session, providing a reliable and ordered data delivery. Virtual circuits are used in connection-oriented networking.
  2. Connectionless: In connectionless networking, each data packet is transmitted independently and does not require a pre-established connection. Packets are routed independently based on their destination addresses. UDP (User Datagram Protocol) is an example of a connectionless protocol.

Virtual Circuit Establishment:

The process of establishing a virtual circuit involves several steps:

  1. VC Request: The initiating node sends a request to the receiving node to establish a virtual circuit.
  2. VC Setup: The receiving node acknowledges the request and allocates necessary resources, such as buffer space and bandwidth, for the virtual circuit.
  3. Connection Establishment: Once the resources are allocated, the virtual circuit is established, and both nodes agree to use this virtual path for data communication.

Types of Virtual Circuits:

There are two types of virtual circuits:

  1. Permanent Virtual Circuit (PVC): A PVC is a predefined virtual circuit that is manually configured by the network administrator. Once established, it remains active until it is explicitly torn down. PVCs are commonly used in Frame Relay networks.
  2. Switched Virtual Circuit (SVC): An SVC is established dynamically as needed when data needs to be transmitted between two endpoints. The connection is set up on-demand and released after data transmission is complete. SVCs are used in ATM networks.

Virtual Circuit Switching vs. Packet Switching:

Virtual circuit switching is a form of circuit switching, where a dedicated logical path is established between the communicating nodes before data transmission. This is different from packet switching, where data is divided into packets, and each packet is forwarded independently based on the destination address.

In virtual circuit switching, the network resources are reserved and allocated before data transmission, ensuring a predictable and consistent transmission path. In contrast, packet switching provides more flexibility and efficient use of network resources but does not guarantee a fixed transmission path for each packet.

Advantages of Virtual Circuits:

  1. Reliability: Virtual circuits offer reliable data transmission, as they guarantee ordered delivery and error correction.
  2. Efficiency: The setup of a virtual circuit reduces overhead in subsequent data transmissions, as the circuit has already been established.
  3. Resource Allocation: Virtual circuits allow for more efficient allocation of network resources, as the path is predefined and resources can be reserved in advance.

Disadvantages of Virtual Circuits:

  1. Setup Time: The process of establishing a virtual circuit incurs additional setup time before data transmission can begin.
  2. Overhead: Virtual circuits introduce some overhead in maintaining the connection state, which can be a consideration in high-traffic scenarios.

In conclusion, virtual circuits provide a reliable and ordered communication path between network endpoints in connection-oriented networking protocols. They offer advantages in terms of reliability and resource allocation but may have some overhead due to setup time and connection maintenance. Virtual circuits have been widely used in legacy technologies like Frame Relay and ATM, though modern networking technologies like IP/MPLS have largely moved towards connectionless packet switching.