0 Preface

With the rapid development of communication technology, the core network is developing towards IP-bearing, broadband, flat structure and open capacity. With the acceleration of LTE, the core network will face the coexistence of multiple wireless access technologies. While solving the problems of 2G / 3G / 4G network access and interoperability, it is also necessary to consider heterogeneous networks (such as Wi-Fi Fi / WiWAX). A large number of new services arising from the rapid development of emerging industries such as the mobile Internet and the Internet of Things have put new demands on the core network. Traditional telecom services are facing the challenge of Internet OTT services. In order to avoid becoming a pipeline, telecom operators are accelerating the process of pipeline intelligence and capacity opening. The core network must also adapt to this change.

This paper discusses the evolution direction of the core network from the aspects of user data fusion, voice service migration, packet network evolution, IMS network introduction, and policy control development, proposes the core network target architecture, and analyzes the challenges and challenges faced by the long-term development of the core network. The future development trend of the core network.

1 Core network evolution

The core network is the core control layer of the communication network, and its technical standards are constantly evolving to meet the needs of new business development. There are several obvious trends in the research of core network standards: network architecture tends to converge, from human-oriented communication to machine-oriented communication, research on traffic optimization is started, and more attention is paid to the opening of capabilities. The existing core network is mainly based on the 3GPP R6 standard. The R7 version introduced the PCC architecture and began to pay attention to the control strategy of the network. Based on the unified authentication of the WLAN and WCDMA version of the R6 version, the R7 version further studies the fusion of WLAN and WCDMA . The R8 version proposes to study a unified EPC core network that integrates 2G / 3G / 4G / WLAN. The PCC began to consider the unified control architecture of BBERF and other non-3GPP. At the same time, the research on the ANDSF technology and machine-type communication (MTC) of WLAN service offloading was launched . The R9 version proposes a user data fusion (UDC) framework and distributed architecture, and further optimizes the MTC problem. The R10 version studies the multiple access of user data, the PCC interface to the service and charging system, and the GTP-based WLAN access problem. The R11 version is studying a series of issues such as the UDC data model, the PCC's unified control architecture for fixed mobility, data service offload, operator capability opening (MOSAP), and MTC performance optimization.

In a certain period, the core network will evolve in the following directions: the circuit domain and the packet domain of the mobile core network will coexist for a long time; the packet domain evolves into a unified and flat architecture; IMS is the target architecture of voice and multimedia services; with the LTE network With the gradual expansion of coverage, some voice services have gradually migrated to packet networks; non-3GPP heterogeneous networks such as WLAN will gradually integrate into the 3GPP network architecture; with the introduction of IMS and LTE networks, user data will gradually transform into a unified user data center.

Figure 1 shows the target architecture of the core network evolution.

1.1 User data fusion A variety of user data in the future network will bring new challenges to data management. There are a variety of user data in the existing network. 2G and 3G users share the HLR. WLAN and broadband user data are deployed in AAA. User value-added service data is stored in VAS. In the future, with the introduction of new network equipment such as IMS, PCC, and LTE, network elements of user data will become complicated, and various types of databases such as HLR, HSS, SPR, and AAA will appear. At the same time, the development of mobile Internet will also There are a variety of application servers that provide rich services. These servers will also store different types of user data. At the same time, the development of the Internet of Things will bring a lot of data to store machine and equipment information. The emergence of various types of user data will bring forward data management new challenge.

From the perspective of technological development, User Data Fusion (UDC) proposed by 3GPP is dedicated to the research of database fusion technology, and data fusion has become an industry-recognized development trend of user data management. From the perspective of user data management technology, with the development of IT technology, telecommunications equipment itself will have higher processing and storage capabilities, and user data management is moving toward a centralized database and distributed architecture. The hierarchical architecture of user data management separates the front-end data query and the back-end data storage architecture, increasing the flexibility and scalability of user data management. 2G / 3G, LTE, IMS, AAA, AS and other data present a convergent management trend The future goal is to establish a unified user data center. Generally speaking, the form of user data organization is gradually changing from network-centric to user-centric, and the overall development is toward the direction of data fusion.

The existing user data management will gradually realize the integration of HLR / HSS user data. Starting from the mobile core network, the unified user data management of 2G / 3G / LTE will be realized. Based on the integrated HLR / HSS, more types of data integration will be considered. To build the operator ’s own unified converged data center. In the long run, we will gradually consider the openness of user data centers, promote business innovation, and enhance users' business experience. The core network will gradually introduce user data equipment with a distributed architecture in the near future; after the introduction of LTE and IMS, priority will be given to gradually achieving the integration of HLR and EPC-HSS, IMS-HSS equipment on the mobile core network; based on HLR / HSS fusion equipment, users As the center, gradually consider consolidating fixed-line user data devices, business platforms and other related user data to build a unified converged data center.

1.2 The evolution of the circuit domain The core network circuit domain mainly carries voice services. Traditional fixed TDM switches and fixed softswitches are being replaced by IMS networks. Mobile TDM switches have been replaced by mobile softswitch equipment. Network circuit domain bearer will gradually withdraw from the stage of history. The mobile core network circuit domain currently generally uses 2G / 3G common core network. Figure 1 The target architecture of the core network evolution 2 This issue focuses on Monthly Focus He Gang, Teng Jiaxin, and Zhu Bin. At the local network level, the softswitch end office has completely replaced the TDM end office, which has achieved the separation of control and bearer. At the long-distance network level, there are also two long-distance networks: TDM and softswitch. At the local network level of the fixed core network, traditional TDM switches and fixed-line soft switching equipment coexist. At the long-distance network level, the TDM long-distance network and soft-switching long-distance network coexist.

Target architecture of core network evolution

At present, IP transformation is the main content of the core network circuit domain upgrade. IP makes the network structure simpler and improves the utilization rate of network resources. After the IP transformation, the implementation of Pool further optimizes the business performance of the core network. The IP transformation of the mobile core network extends from the Nc and Nb core network interfaces to A, Iu-CS and other interfaces at the local network level. The traditional TDM end office at the mobile long-distance network level gradually withdraws from the network, and the long-distance softswitch will gradually transform into a call coordination node (CMN), no longer processing voice bearer services, and only performing call signaling processing. Due to the complicated structure of the fixed network core network, the IP process is also relatively slow. With the acceleration of broadband and the acceleration of the optical copper access process, the fixed network TDM end office gradually withdraws from the network, and its traffic is blocked by the fixed network softswitch end office and IMS absorption, fixed network softswitch and IMS will coexist for a certain period of time. The fixed TDM long-distance network gradually withdraws from the network as the TDM end office exits. The fixed softswitch implements SIP interworking after the IP transformation. Finally, fixed mobile long-distance traffic is cleared through the flat network.

The long-term evolution of the circuit domain of the mobile core network is closely related to the provision of voice and short message services. The circuit domain voice and short message services tend to migrate to packet networks. With the rapid development of the mobile Internet and the maturity of the LTE industry chain, the LTE era is accelerating. There are currently nearly 50 LTE commercial networks worldwide. LTE networks mainly provide high-speed data services. In the early stages of LTE network deployment, voice and SMS services are still provided by the circuit domain. This requires circuit domain upgrades to support CSFB and SMS fallback functions. With the continuous improvement of LTE network coverage, voice and SMS The SMS business is gradually migrating to the LTE network, and the LTE network will gradually adopt the SRVCC solution to solve the voice service problem. The migration of voice services is a long-term process. Voice and SMS services will be provided by the circuit domain for a long time, and the circuit domain will be gradually upgraded to meet the interoperability requirements with LTE / IMS.

With the widespread adoption of the blade architecture of the core network circuit domain equipment and the development of software technology, the core network circuit domain has a trend toward large-capacity centralized deployment and virtualization development. There are many old platforms for circuit domain devices in the current network, and the number of devices is large, and most provinces adopt a decentralized deployment method. With the widespread adoption of the Soft Switch Equipment Blade Architecture (ATCA), equipment capabilities have been greatly improved, making centralized deployment possible.

Centralized deployment can effectively reduce operation and maintenance costs, make softswitches more cost-effective and efficient, and more importantly, the introduction of future virtualization technologies on the basis of platform convergence will allow operators to build multiple vendors on a common hardware platform Coexistence system.

1.3 Packet network supporting multiple access

The mobile core network packet domain mainly provides mobile data services. With the acceleration of mobile broadband, the core network packet domain is also evolving. At present, the core network packet domain generally adopts the 2G / 3G common core network. With the rapid growth of mobile data service traffic, the current network has begun to introduce 3G DT technology to reduce the pressure of SGSN data forwarding and basically achieve the separation of control and bearer. The large-capacity centralized deployment of packet-domain network elements makes the disaster-tolerance problem of the packet-domain equipment more important. The existing network solves the SGSN disaster-tolerance problem by adopting the SGSN Pool technology and realizes the SGSN load capacity balance.

The target architecture of the packet domain evolution is a 2G / 3G / 4G common core network. In the process of evolution to the target, the problem of how to smoothly upgrade the existing network must be solved. In order to provide users with a better service experience, existing packet networks must first be upgraded to support interoperability with LTE networks. In addition, in order to achieve business continuity, 2G / 3G access needs to have the same anchor point as LTE access. This anchor point It is the fusion node of GGSN and PGW, which requires GGSN to support GGSN / PGW fusion function through software upgrade. There are two different options for the evolution of the existing network SGSN to MME, one is to upgrade to a Gn / Gp SGSN and MME fusion node, and the other is to upgrade to a S3 / S4 SGSN and MME fusion node. The existing network SGSN can be upgraded to Gn / Gp SGSN and MME fusion node, and the newly created MME node requires to support both Gn / Gp SGSN and S3 / S4SGSN. The expansion and transformation of the existing network GGSN and SGSN will use a hardware platform that can be smoothly upgraded to EPC, and the integration of SGSN / MME and GGSN / EPC-GW will be achieved through software upgrade.

As a wireless access technology with wide application, low cost, and high bandwidth, Wi-Fi is more and more valued by operators, and has become an important means of offloading data services and optimizing network coverage. The 3GPP system is gradually integrating Wi-Fi technology into a unified packet core network. Since Wi-Fi is a non-3GPP access technology, the integration with the 3GPP system becomes more complicated. The integration of Wi-Fi and mobile networks can be roughly divided into several stages, including unified authentication, unified access, and business continuity between systems. Unified authentication refers to the Wi-Fi reuse 3GPP access authentication mechanism. Compared with the Portal authentication method, unified authentication is more convenient for users to access, and also improves security. Because the terminal and network support is better, each operator The deployment of unified certification has begun. Unified access and continuous service between systems have relatively high requirements on terminals and networks, and need to support Mobile IP protocol and IPSec tunnel. In order to reduce the technical requirements on the network, especially terminals, standards organizations are studying solutions using GTP protocol. This is also the future development direction. In order to more effectively implement Wi-Fi service offload, the packet network begins to introduce the access network discovery and selection function (ANDSF). The network side delivers the inter-system mobility policy information to the terminal. Based on these information, the terminal selects the appropriate connection. Into the network, so as to achieve effective distribution of data services.

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