Packet Switching Technology Definition
Packet switching technology emerged when computer technology had developed to a certain level, and in addition to direct voice communication by telephone, packet switching adds a packet header to each packet to indicate the destination address to which the packet is sent, and the switch then forwards each packet to its destination based on the address flag of each packet. This process is called packet switching.
A communication network that performs packet switching is called a packet-switched network. From the perspective of the development history of switching technology, data switching has gone through the development process of circuit switching, message switching, packet switching, and integrated service digital switching. Packet switching is essentially developed on the basis of "store-and-forward." It combines the advantages of both circuit switching and message switching. Packet switching uses dynamic multiplexing technology on the line to transmit data—packets—that are divided into many small segments according to a certain length. After each packet is identified, multiple data packets are transmitted simultaneously on one physical line using dynamic multiplexing technology. The data from the calling user's end is temporarily stored in the switch's memory and then forwarded within the network. Upon reaching the receiving end, the packet headers are removed, and the data fields are reassembled in sequence into a complete message. Packet switching offers higher circuit utilization than circuit switching and lower transmission delay and better interactivity than message switching.
A packet-switched network is a new type of switching network that follows circuit-switched networks and message-switched networks. It is mainly used for data communications. Packet switching is a store-and-forward switching method that divides the user's message into packets of a certain length and performs store-and-forward on a packet basis. Therefore, it has higher utilization than circuit switching, lower delay than message switching, and the capability of real-time communication. Packet switching utilizes the principle of statistical time-division multiplexing to multiplex one data link into multiple logical channels, ultimately forming an information transmission path between the calling and called users, which is called a virtual circuit (V.C), to achieve packet transmission of data.
A packet-switched network has the following characteristics:
(1) Packet switching has the capability of multiple logical channels, so the circuit utilization of trunk lines is high;
(2) It enables interworking between terminals with different code formats, rates, and protocols on the packet-switched network;
(3) Because packet switching has error detection and correction capabilities, the bit error rate of circuit transmission is extremely low;
(4) Packet switching has strong network management functions.
The basic services of packet switching include switched virtual circuit (SVC) and permanent virtual circuit (PVC). A switched virtual circuit is like a telephone circuit: when two data terminals need to communicate, they first establish a circuit (i.e., a virtual circuit) using a call setup procedure, then transmit data, and after communication is completed, the virtual circuit is released using a disconnect procedure. A permanent virtual circuit is like a dedicated line: it provides a permanent logical connection between two terminals within the packet network during the contract period, without the need for call setup and disconnect procedures. During the data transmission phase, it is the same as a switched virtual circuit.
A packet-switched data network is composed of packet switches, a network management center, remote concentrators, packet assembly/disassembly equipment, and transmission equipment.