Permanent virtual circuit refers to the connection of two computers through connection oriented network. PVC can withstand computer bootstrap or power fluctuation, in this sense, it is permanent. The permanent virtual circuit is shown in Figure 1.
PVC (Permanent Virtual Circuit) permanent virtual circuit: two computers are connected through network oriented connection. PVC can withstand computer bootstrap or power fluctuation, in this sense, it is permanent; PVC is virtual because it places the path in the routing table instead of establishing a physical connection.
Virtual circuit is Packet switched network One of the services provided (the other is datagram service), in brief, is to establish a virtual logical connection between user hosts through the internal control mechanism of the network, and ensure the correctness and sequencing of the packets transmitted on it. Virtual circuits must be established and removed before and after communication. The permanent virtual circuit is a virtual circuit established during network initialization, and the virtual circuit is always maintained. 10. Both the 25 network and B-ISDN provide permanent virtual circuit services. Virtual circuit communication is similar to circuit switching. Both are connection oriented, that is, data is sent in the correct order, and additional overhead is required in the connection establishment phase. However, circuit switching provides a stable Bit rate And delay time, while Virtual circuit service The bit rate and delay time of depends on the following factors: 1. The length of the packet queue on the network node.
2. Bit rate of data generated by the application.
3. Usage statistics Multiplexing technology The load of other users sharing the same network resource. 4. Many virtual circuit protocols retransmit data, including error detection error correction And Automatic Repeat Request (ARQ) to provide reliable communication services. A virtual circuit is a link between two or more endpoint sites on a packet switched hash network. It provides temporary or dedicated connection oriented sessions between two endpoints. Its inherent feature is that there is a predetermined path through the multi-path network. Defining a path in advance can improve performance and eliminate the need for headers in frames and packets, thus increasing Throughput rate 。 Technically Packet switched network The physical path of the two end systems should be changed to avoid congestion and failure lines, but the two end systems should maintain a connection and change the path description as needed. 
