In recent years, softswitch technology has increasingly become the focus of public attention. It will become the core technology of the next-generation network. The information industry has put forward a softswitch technology for the next-generation IP converged network after a double effort, and is currently actively carrying out 3G core The ultimate goal of network technology research is also an all-IP network with the ability to integrate multimedia services.
In this regard, 3GPP has played a great role, proposing an IP multimedia subsystem (IMS) structure based on softswitch technology. In addition, the rapid development of wireless LAN technology and the sharp drop in price have caused the original enterprises and families The internal supplementary wiring method has gradually developed into an increasingly important public wireless interconnection method. The interconnection between 3G and wireless LAN fully reflects the advantages of softswitch technology in the next generation networking technology. This article will discuss based on this point of view.
1. Softswitch network structure
Figure 1 shows the general layered structure of a softswitch network. Among them, the access layer supports various types of terminals, which is equivalent to the user-software network interface function of the softswitch network, and the transport layer is responsible for the end-to-end transmission of communication media information, corresponding to the lower three layers of the network. The control layer is responsible for call control and corresponds to the session layer functions of the network. The main equipment of this layer is the Soft Switching System (SSW), which is equivalent to the switch in the traditional communication network is the core equipment of the network. The business layer provides value-added services based on the capabilities of the lower layer network, corresponding to the application layer functions of the network.
2. 3G network structure
3G network is the future development direction of wireless communication. An important goal of it is to provide voice services and diversified multimedia services in VoIP mode, and realize the integration and integration of 3G core bearer network and IP network. The integration of the 3G network and the IP network not only enables the operation to improve the utilization of network resources, but also mobile terminals can easily access and enjoy information and services on the Internet through the unified IP network.
As a part of NGN, 3G mobile network's development and evolution of its architecture is also less affected by the softswitch technology. Because its core network is carried by all-IP, it ensures that 3G's all-IP core network can effectively achieve the NGN core network. Convergence and interworking, according to the layered model of softswitch network function, 3G network can also be divided into 4 layers, namely access layer, transport layer, control layer and business layer.
The following uses the all-IP-based mobile network structure UMTS Release5 developed by 3GPP as an example for analysis. The position of each main functional entity in the circuit domain and IP multimedia subdomain in its core network in the layered model is shown in Figure 2.
Since the packet domain in the UMTS Release5 reference model is not constructed according to the idea of ​​softswitching, the main functional entities in the packet domain are not listed in the layered model in Figure 2. It can be seen from the layered model that MGCF (Media Gateway Control Function), CSCF (Call Status Control Function), and MSC Server (Mobile Switching Center Server) are logical functional entities located at the control layer, which mainly complete the call control function, that is, call connection The establishment and release of the system, as well as the signaling interworking with various networks (such as GSM, CDMA, PSTN, UMTS networks of other operators, IP multimedia networks, etc.). The bearer channel of MGW (Media Gateway and CDMA Network) is transformed into a function suitable for transmission on the IP network.
It should be pointed out that there are MGW functional entities in both the IP multimedia sub-domain and the circuit domain. In terms of function implementation, the MGW in the IP multimedia sub-domain and the MGW in the circuit domain are the same device. For the clarity of the network structure, the MGW in the circuit domain can be expressed as CS-MGW, the MGW in the IP multimedia subdomain is expressed as IM-MGW, and the SGW mainly completes the IP network side signaling and circuit switched network side signaling protocol (7 Signalling) translation and conversion. MRFP (Multimedia Resource Processor) and MRFC (Multimedia Resource Controller) are logical functional entities that provide multi-party calling and multimedia service provision and control in the 3G core network. In the layered model of the core network, MRFP is a logical functional entity at the access layer, which mainly provides the provision and bearing of multimedia resources. MRFC is a logical functional entity at the control layer, which mainly realizes the control of multimedia resources in MRFP.
So far, from the layered model of the core network, we can see that the 3G core network has achieved the separation of control, bearer and service. Therefore, we can say that the UMTS Release5 network is actually a next-generation mobile network based on softswitch technology.
3. Wireless LAN
In the current WLAN market, 802.11b occupies a major position due to its mature technology, good compatibility of equipment from different manufacturers and compatibility with 802.11g. The basic extension structure of the 802.11b standard public WLAN network is equivalent Interconnection, AP structure, wireless bridge structure. The following briefly describes the structure with an access point.
The typical topology of WLAN has the structure of an access point, which is suitable for developing wireless access services. In this structure, the access point is used to perform synchronization and coordination work, forward data packets, and connect to upper-layer networks. The number of users that the access point can serve is related to the products provided by the manufacturer. Although it can theoretically support more users, in practice it can usually only support 15-50 users. This is because an AP can only access one terminal user at a time, and when the channel is idle, other terminals contend. If an AP supports too many users, the network access rate will be reduced.
4. Integration of 3G and WLAN
In terms of WLAN system equipment and network, it is combined with mobile technology with high-speed mobile performance and greater coverage to provide users with inexpensive and higher-bandwidth so-called "nomad" wireless data services through WLAN in public access areas. In other locations, the use of 2nd and 3rd generation mobile communication technologies to provide truly "roaming" wireless data services is booming. At present, major mobile communication equipment manufacturers provide different levels of integration solutions.
According to the degree of integration with mobile communications, this type of solution can be divided into two categories: loosely coupled and tightly coupled. The following describes the tight coupling solution. As shown in Figure 3.
Tightly coupled solutions mostly use standardized interfaces in mobile communications to emphasize the full integration of mobility, services and applications, fully reflecting the ultimate goal of 3G and WLAN integration-the integration of services and applications. In the 2.5G / 3G loosely coupled WLAN solution, there are only two modes available, which are unified charging and user management, WLAN access control and charging based on the 3GPP system. Of course, the convenience of user experience and Consistency is the most important prerequisite for successful integration. Therefore, the tightly coupled 3G and WLAN solution can support the seamless integration of packet-domain service switching, and is currently in a leading position in the industry.
The solution in Figure 3 uses centralized signaling and billing management. The distributed traffic forwarding method builds a distributed SGSN function for the WLAN access network. The network element is connected to the home location register (HLR) through a standard Gr interface. It supports the above authentication process and user management, and has no special requirements for 2G, 3G and HLR. On the user side, the SIM card can be built into a WLAN network card that supports SIM, or can be read by a standard USB card reader.
Billing is another important part of the user experience and the most concern of operators. Billing by traffic and content is the model that operators and users want. The above solution not only achieves the consolidation of bills, but more importantly, it incorporates WLAN charging into the 2.5G / 3G charging system, directly provides CDRs that comply with the 3GPP standard, and makes the two charging systems truly unified on one platform .
In addition to supporting the length of the mobile communication standard CDR and flow rate charging, the above scheme also supports rate switching. It also builds a distributed SGSN function, and connects to the GGSN through the standard Gn interface to obtain 2.5G / 3G standard mobile data services, such as wireless VPN applications, security, and value-added charging.
5. Summary
Softswitch technology has become the core technology of 3G. It has enabled 3G to develop into an all-IP packet network with integrated multimedia service capabilities. It has made it possible for WLAN and 3G to be tightly coupled. It can enable WLAN to communicate with other terminals on the 3G network. As a supplement to 3G in the enterprise, WLAN promotes the development of mobile business users and attracts WLAN enterprise users to 3G networks through better mobility and security.
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