The Research And Implementation Of The Control Plane's Protocol Stack Of The 4G's Core Network

With the prevalence of 3G, people pay more and more attention on mobile Internet, but 3G has its own disadvantage, for instance,3G does not have a unified standard which makes it difficult for users to roam around the world seamlessly.4G has a different network structure from 3G. which is based on IP-connectivity. Under 4G, core network is separated from access network.which makes all kinds of access technology if compatible with 4G, in the meantime, user data is also separated from control data.This kind of flat net structure makes 4G has great data transfer speed.The core network consists of MME (Mobility Management Entity), S-GW (Serving Gate Way), HSS (Home Subscriber Server) and so on. In the CN (core network). MME is the most important part, which is responsible for user's access, authentication, bear-allocation and so on. This thesis focus on S1AP (S1 application protocol) which is used between MME and eNodeB. We first give the reason why 4G will replace 3G to be new standard, and then introduce CN's structure including the function of each element especially the MME. The functions of the CN are all implemented through according procedure. We take Attach procedure as an example to explain how we manipulate them; Secondly, we introduce the principle and the advantage of the SCTP(Stream Control Transport Protocol); Thirdly, this thesis introduce the protocol stack of the S1AP and it communicating format with a procedure as an example.When it comes to the implementation of the protocol, this thesis first shows the structure of MME, and introduces the function of the module we focus on, and then presents the sketch map of message processing to explain how our system processes the incoming message. When introducing specific design, we first explain the principle of memory manager including fixed memory manager and hierarchical memory manager. The hierarchical memory manager fits the condition that we don't know how much we need before allocation, but its time complexity is higher, the fixed-size memory manager can fit the condition that we know the size ahead of time and time complexity is low. These two algorithms make it more efficient when allocating or freeing a block of memory. The use of memory manager can reduce the time complexity of memory allocation; reduce the probability of memory leak. Secondly we give the principle of timer, the timer use time-wheel algorithm which makes the complexity of adding, deleting and adjusting timer all O (1), the timer manager can improve the performance of the program; reduce the cost of timer management. S1AP uses SCTP as its transport-protocol; we introduce the package of the SCTP including the establishment, deleting and restore of the connection. The management of the connection mainly focuses on the management of the state of the connection, we explain this specifically through state-transfer diagram. The capsulation of the long connection make communication between different node become transparent, avoid multiple development, it can also reduce the net traffic, improve communication speed. Thirdly, we introduce the implementation of serializing tool which uses key-value pattern to reduce the communicating traffic and improve communication speed. Finally, we use some examples to explain how to process specific message of the S1AP and the structure that the procedure concerns.