The Research And Implementation Of LTE Core Network's EMM Protocol Stack

At the end of 2013, the ministry officially issued 4G liscences. This also means that the industry formally entered the long-awaited LTE commercial stage. LTE, relating to 3G, has more technical advantages and better user experience. However, the foreign and domestic communication equipment companies mainly produce large equipments. Therefore, there is a blank in small LTE private network equipment. So the research and implementation of small LTE private network equipment has important significance.This paper implements a LTE private network system which can be applied to complex and dangerous environments such as coal and oil field.This paper mainly studies and implements the EMM protocol stack of LTE core network control protocol stack. The EMM protocol stack is responsible for EMM signaling interaction and transmission of LTE core network's non access stratum and is related to the LTE system's rationnlity. It consists of 7 parts. They are attach procedure, detach procedure, tracking area update procedure, service request procedure, authentication procedure, security command procedure and identity procedure. EMM protocol stack is important to LTE core network equipment.The research and implementation of EMM protocol stack definitely has very important significance.This paper firstly introduces the concept and characteristic of LTE core network,including the LTE core network's overall architecture, interface, network elements and identification such as IMSI, GUTI. The paper talks about the protocol stack of control plane and user plane of LTE core network as follow. Then the paper implements the design of the LTE core network architecture and basic modules relating to EMM. The system architecture uses the event-driven task scheduling model. Once the LTE core network system is started,the system will keep receiving events which is message. The system will decode the message and reply messages to UE to ensure the function of the whole core network LTE system.Several basic modules implemented the following functions: the state machine module is a two-dimensional array of function pointers. Laterally is enumerated state values and longitudinal is enumerated action values. The system can be based on the current status and the received message to judge the next action; UE context management module is a hash table data structure. The module is to ensure the MME to communicate with the specific UE and save its relating information; Message encoding and decoding module is responsible for NAS and S1AP encode and decode to ensure the validity of the signal; The time module controls system time.The signaling procedures of LTE core network system consists of 7 parts. They are attach procedure, detach procedure, tracking area update procedure, service request procedure,authentication procedure, security command procedure and identity procedure. According to the 3 GPP protocol, the seven procedures can be divided into two parts, respectively are specific procedures and common procedures. The specific procedures include attach procedure, detach procedure, tracking area update procedure and service request procedure.Because the specific procedures will invoke the common ones, such kind of procedure is designed as the combination of pretreatment and postreatment. Common procedures include authentication procedure, security mode command procedure and identity procedure. The design only include sending and receiving functions which make the signal procedures more simple and clear.Finally, this design uses python scripts analoging UE and EnodeB and takes Wireshark as the network packet analysis tool. The test results show that this system can cope with all kinds of EMM signaling interaction situations of LTE core network. It can fulfill the technical indicators of LTE core network.