What are the layers of GSM wireless UM air interface communication protocol?

Um interface is the air interface of GSM (interface between base station and mobile station).

There are five communication protocols on the Um interface, which are physical layer, MAC (media access control) layer, LLC (logical link control) layer, SNDC layer and network layer from bottom to top. The physical layer of Um interface is RF interface, while the physical link layer is responsible for providing various logical channels of air interface. The carrier frequency bandwidth of GSM air interface is 200KHZ, and one carrier frequency is divided into eight physical channels.

If all eight physical channels are allocated to transmit GPRS data, the original data rate can reach 200Kbps. Considering the overhead of forward error correction code, the final data rate can reach about 164kbps; MAC is the media access control layer. The main function of MAC is to define and allocate logical channels of GPRS air interface so that these channels can be shared by different mobile terminals. The LLG layer is the logical link control layer.

It is a wireless link protocol based on high-speed data link protocol HDLG. SNDC is called subnet-dependent binding layer. Its main function is to complete the grouping and encapsulation of transmission data and determine TCP/IP address and encryption mode; At present, the network layer protocols are mainly TCP/IP and L25 protocols provided by Phasel. TCP/IP and X.25 protocols are transparent to traditional GSM network devices (such as BSS and NSS).