SoftSwitch Technology thesis: On the interworking of 3G and WLAN based on SoftSwitch

In recent years, SoftSwitch technology has become the focus of public attention, it will become the core technology of the next Generation network, the information industry after a turn to put forward to the next generation of IP Fusion network SoftSwitch technology, is currently active in 3G core network technology research, the ultimate goal is to have the integration of multimedia business capabilities of the full IP network.

In this regard, 3GPP has played a significant role, this paper puts forward the IP multimedia Subsystem (IMS) structure based on SoftSwitch technology, in addition, the rapid development of WLAN technology and the sharp decrease of price, make the supplementary wiring way of the original enterprise and the family gradually develop into the more and more important public wireless interconnection way. The interconnection of 3G and WLAN fully embodies the advantages of SoftSwitch technology in the next generation networking technology, and this paper discusses it based on this viewpoint.

1. Soft Switch Network structure

Figure 1 shows a general hierarchical structure for softswitch networks. Among them, the access layer supports various types of terminals, the equivalent of SoftSwitch network user-network interface function, Transport layer is responsible for communication media information End-to-end transmission, corresponding to the next 3 layers of network functions. The control layer is responsible for call control, corresponding to the session layer function of the network. The main equipment of this layer is SoftSwitch system (SSW), its position is equivalent to the switch in traditional communication network is the core equipment of network, the business layer is based on the ability of lower network to provide value-added service, corresponding network application layer function.



2, 3G network structure

3G Network is the future development direction of wireless communication, it is an important goal is to provide voice services and diversified multimedia services, and realize 3G core-hosted network and IP network integration and unification. The integration of 3G network and IP network can not only improve the utilization of network resources, but also the mobile terminals can access and enjoy the information and services on the Internet conveniently through the unified IP network. (Computer science)

3G mobile network as a part of NGN, the development of its architecture is also influenced by SoftSwitch technology because its core network is carried by the whole IP mode, so that the 3G all IP core network can realize effective fusion and interworking with the NGN core network, according to the model of soft switching network function layering, 3G network can also be divided into 4 levels, namely, access layer, transport layer, control layer and business layer.

The following is an example of an IP-based mobile network structure UMTS Release5 in 3GPP, and the location of the main functional entities in the circuit domain and the IP multimedia subdomain in the hierarchical model is shown in Figure 2.



Because the grouping domain in the UMTS RELEASE5 Reference model is not constructed according to the idea of SoftSwitch, the main functional entities in the group domain are not listed in the hierarchical model of Figure 2. From the layered model can be seen MGCF (Media Gateway control function), CSCF (call State control function), MSC Server (mobile Switching center server) is located in the control layer of the logic function entity, mainly completes the call control function, namely the establishment and release of call connection, and to achieve with a variety of networks (such as GSM, CDMA, PSTN, other operators UMTS network, IP Multimedia network, etc.) of the exchange of signaling. The bearer channel of MGW (Media Gateway and CDMA network) is transformed into a function suitable for transmission on IP network.

It should be pointed out that the IP multimedia subdomain and the circuit domain all exist MGW function entities, from the realization of the function, the MGW in the IP multimedia subdomain and the MGW in the circuit domain are the same equipment. For the clarity of the network structure, the MGW of the circuit domain can be expressed as IM-MGW,SGW in the CS-MGW,IP multimedia subdomain, and the translation and conversion of the IP network side signaling and the circuit Exchange Network side Signaling Protocol (7th number signaling) are mainly completed. MRFP (multimedia resource processor) and MRFC (multimedia resource Controller) are the logical function entities that realize multiparty call and multimedia service supply and control in 3G core network. In the core network layered model, MRFP is the logical function entity in the access layer, which mainly realizes the provision and load of multimedia resources. MRFC is a logical function entity in the control layer, which mainly realizes the control of multimedia resources in MRFP.

At this point, from the core network of layered model, we can see that the 3G core network to achieve control, load, business separation of the three. Therefore, we can say that the UMTS RELEASE5 network is actually the next generation mobile network constructed based on SoftSwitch technology.
3, Wireless LAN

In the current WLAN market, 802.11b with its mature technology, the compatibility of different manufacturers and compatible with 802.11g and other characteristics, occupy a major position, 802.11B standard public WLAN network basic extension structure has peer-to-peer interconnection, AP structure, wireless bridge structure. The following is a brief description of the structure with an access point.

A typical WLAN topology has an access point structure that is suitable for wireless access services in which access points are used to perform synchronization and coordination, forward packets, and connect to the upper network. The number of users the access point can service is related to the product supplied by the manufacturer. Although it is theoretically possible to support more users, only 15-50 users are usually supported in practical applications. This is because an AP can only access one end user at a time, and when the channel is idle, the other terminals contend for it. If an AP supports too many users, the network access rate will be reduced.

4, 3G and WLAN integration scheme

In the area of WLAN system devices and networks, combined with mobile technology with high speed mobility and greater coverage, in the public access area through WLAN to provide users with low-cost and higher bandwidth of the so-called "nomadic" wireless data services, in other locations through the 2-generation, 3-generation mobile communications technology to provide real "roaming" -Type wireless data services are booming, at present, the major mobile communications equipment manufacturers to provide a different degree of integration programs.

According to the close degree of fusion with mobile communication, this kind of solution can be divided into two kinds: loose coupling and tight coupling. The following is a brief introduction to the tight coupling solution. As shown in Figure 3.



The standardized interface in the mobile communication is used in the tight coupling scheme. To emphasize the overall integration at the mobility, business and application level, fully embodies the ultimate goal of integration of 3G and WLAN-the integration of business and applications, and users in the current 2.5g/3g and WLAN loosely coupled solutions, can only get two models, They are unified billing and user management, based on 3GPP system WLAN access control and billing, of course, user experience convenience and consistency is the most important prerequisite for integration success. Therefore, the 3G and WLAN tight coupling solution has been able to support seamless packet-domain business switching integration, and is currently in the forefront of the industry.

The solution in Figure 3 uses centralized signaling and billing management, the distributed traffic forwarding mode is a distributed SGSN function for WLAN access network, which is connected with the standard GR interface and the Attribution position Register (HLR) to support the authentication process and user management, 2G, 3G, HLR without any special requirements. On the client side, the SIM card can be placed inside the WLAN network card that supports the SIM, or it can be read by a standard USB card reader.

Billing is another important part of user experience, and it is also the most concerned problem for operators. Billing by flow and content is the mode that operators and users want. The above plan not only achieves the merger of the bill, but also is more important is to integrate WLAN billing into the 2.5g/3g billing system, directly provide the CDR conforming to the 3GPP standard, so that the billing system of both is truly unified on a platform.

In addition to supporting the time and flow rate of the mobile communication standard CDR, the above scheme also supports tariff switching. It also constructs a distributed SGSN function that obtains the 2.5G/3G standard mobile data service via standard GN interface and GGSN connection, such as wireless VPN application, security and value-added billing, etc.

5, summary

SoftSwitch technology becomes the core technology of 3G, it makes 3G to have the integration Multimedia Service ability the whole IP packet network direction development, causes the WLAN and the 3G tight coupling to become possible, it not only makes the WLAN to be able to enjoy the Internet resources conveniently through the 3G network, but also may make the WLAN and the 3G network other WLAN as 3G in the enterprise complement, promote the development of mobile business users, through better mobility and security, the WLAN enterprise users to the 3G network.