SWITCHING NODE MODELING OF A PACKET-SWITCHED DATA TRANSMISSION NETWORK

The article considers probabilistic modeling of the information transfer process in a packet-switched data network in datagram mode. In such networks, messages are divided into smaller fragments called packets and sent over the network from one switching node to another independently of each other. So-called smart switches and routers with the appropriate software are considered as switching nodes. Each packet is provided with a header, which specifies the address required to deliver the packet to the destination node. The presence of an address in each packet allows the switch to process the packet independently of other packets in the information flow. In addition to the header, the packet has another additional field, which contains the checksum. The switch checks the checksum, and only if it indicates that the packet data is not distorted, begins to process the packet and determines the destination address in the next switch. Therefore, each packet is sequentially placed bit by bit in the input buffer. Depending on the type of traffic, the packet size may be different. When transmitting voice, the packet size can be 64 bytes, while when transmitting video or text information, the packet size can reach 1500 bytes and higher. Accordingly, the processing and switching time of packets varies widely, which leads to the stochastic nature of the switching nodes' operation, which can be studied using the apparatus of the mass service theory. The paper proposes to use a multi-line mass service system with several input streams and a common buffer as a model of the switching node's operation process. A system of linear equations with respect to the state probabilities is derived for it, the solution to which is obtained in analytical form. The most important characteristic is derived - the probability of packet loss depending on the packet incoming rate and the buffer memory size. It is proven that the buffer size has a lesser effect on the probability of packet loss than the packet incoming rate, which requires the corresponding power from the switching node's processors.