A GSM-R mobile communication network consists of several functional entities.The collection of functions realized by each functional entity is the basic service and supplementary service provided by GSM-R network to users.Gsm-r mobile communication network structure is based on GSM mobile communication network, mainly composed of base station subsystem (BSS), network subsystem (NSS) and operation and maintenance subsystem (OSS).
 

BSS is mainly composed of base station controller (BSC) and base station transceiver station (BTS).It is connected to mobile station (MS) through wireless interface (Um), and interface A is connected to NSS.BTS is the communication relay between the fixed part of the network and the wireless part. MS is connected to BTS through the air interface. It is the wireless access part of the mobile communication network and the part where the end users most directly experience the network quality.One or more BTS are connected to a BSC, which provides radio resource management and mobility management functions within its coverage area, as well as radio network operation and maintenance functions.BSS may also have a coding rate adaptor unit (TRAU) to achieve coding rate conversion.NSS is generally composed of six functional entities, namely, mobile switching Center (MSC), Home location Register (HLR), Visiting location register (VLR), Identification center (AUC), Device Identification register (EIR), and group call Register (GCR).The NSS is responsible for end-to-end calling, user data management, mobility management, and fixed network connectivity.MSC is the core of NSS, which is used to establish business channel and exchange signaling messages between MSCS and other networks.Connected to the MSC is the VLR, which manages a dynamic database of mobile user information roaming within a MSC area.HLR stores static information about mobile users who are permanently registered in the network, such as user information, hosted and customized user information, etc.AUC completes the authentication of the user and encrypts the wireless communication between the mobile station and the network.EIR is used to store IMEI (International Mobile Equipment Identifier) [2].As a unique component of the GSM-R network, GCR is used to store mobile user group ids, cell information referenced by mobile station initiated voice group call (VGCS) and voice broadcast (VBS), and instructions on whether the MSC initiating the call is responsible for handling the call.