As operators are getting closer to full-service operations, Chinese operators have or will have more than two networks to provide homogeneous services. For example, after obtaining 3G licenses, China Telecom and Netcom will provide voice and data services through mobile networks, PHS and fixed networks. Since each network is independent of each other, it is bound to become a competitive relationship. In this case, network convergence has also become a hot topic in current network technology. Telecom experts hope to find a technology to integrate network resources of various access technologies and provide unified services. For example, integrating mobile networks, PHS and fixed network resources to provide voice and data services will change the current competitive relationship between these networks and make them a complementary relationship. To achieve such a network convergence goal, a network control technology is needed. This network control technology is independent of the access network and the upper-layer application.
Currently, various standard organizations agree that IMS has the ability to achieve network convergence.
IMS (IP Multimedia Subsystem) was originally the core technical standard for 3G networks developed by the 3GPP organization. It has now been recognized by ITU-T and ETSI (European Telecommunications Standards Institute), incorporated into the core standard framework of NGN (Next Generation Network), and is considered to be an important technical foundation for realizing future FMC (fixed/mobile network convergence).
IMS is an IP multimedia architecture proposed by 3GPP in the version. So far, there are three versions: R5, R6 and R7. It proposes a full IP network architecture, uses the SIP protocol for control, implements mobility management, multimedia session signaling and bearer service transmission, and realizes end-to-end IP services.
The IMS full-service network is divided into four parts: IMS core control part, application layer, access layer and traditional TDM/R4 network interoperability layer.
The core control part of IMS includes this network unit, including CSCF, HSS, PDF and other components, providing unified authentication of users, call control, policy management, roaming and billing functions. The IMS network selects the SIP protocol as the call control protocol; the authentication mechanism adopts the AKA challenge response authentication mechanism commonly used in mobile networks; the database query adopts the Diameter protocol developed on the basis of the RADIUS protocol; in terms of network security, it adopts IPSec technology and TLS secure transmission protocol. All these protocols are common standard protocols for the Internet. A key difference between IMS and traditional soft switches is the introduction of HSS (Home Subscriber Server) in the core control plane. This inherits the unique network technology of the cellular mobile communication system, uses the concepts of home network and access network, and adopts mobility management technology and a centrally set network database to support user roaming and switching.
Application Level
This layer provides multimedia services for users. It exists independently of the access layer and core control layer of the network to ensure the independence of service development and provision.
At the access layer
, IMS serves as the core control layer. Users can access service networks through GPRS, UMTS, WMN/WLAN, CDMA, DSL, etc. These networks are collectively referred to as IP-CAN.
At the interconnection and interoperability level
, a gateway-based interoperability solution is adopted for interoperability with fixed and mobile phone networks. There are also network elements such as signaling gateway (SGW), media gateway (MGW), and media gateway controller (MGCF). In addition, the H.248 protocol jointly developed by IETF and ITU-T is also used in MGCF and MGW.
Characteristics of IMS technology
IMS is a core control layer. The access network to the IMS network is IP-CAN, that is, the access network can be any IP network: WCDMA network, CDMA2000 network, WLAN or ADSL, Cable can all be connected to the IMS domain. The core control layer provided by IMS is independent of access, so that FMC can be truly realized.
IMS can bind numbers to people. No matter what kind of terminal or access network a user uses to communicate, IMS can use one number to identify the user. And users can register on multiple different types of terminals at the same time to achieve one number.
In the IMS network structure, the application layer is independent of the access network, and the service layer is connected to the IMS control layer through an open interface. This structure allows service developers to develop services independently and then provide them to users in various access environments through IMS, greatly speeding up service development.
The IMS domain has the feature of roaming. No matter where the user accesses the network, he can return to the CSCF in his home area to provide services through IMS roaming or GGSN roaming.
IMS has the ability to control the use of network resources, and users' control over network resources is restricted by IMS.
IMS can effectively and flexibly charge services and provide basic information such as service category, service flow, and service time period of the session, so that operators can formulate different charging strategies.
The role of IMS in network convergence
Although IMS was proposed for mobile communications, driven by the desire to achieve network convergence, IMS has been extended to the field of fixed-line communications.
The NGN architecture currently recommended by the TISPAN working group adopts an IMS-based NGN.
In TISPAN's NGN architecture, the core network of 3GPP's IMS is mainly used as the core control system, and the IMS system is expanded based on the 3GPP specification to support fixed access methods such as xDSL. Since wired and wireless networks differ in network bandwidth, terminal authentication, location information, and resource management, TISPAN will expand these aspects to achieve fixed access.
The convergence of future networks is mainly reflected in the convergence of the control layer. The convergence of the control layer uses IMS technology. Of course, the IMS of 3GPP and R6 is mainly for mobile access networks. After the support of fixed network access is added in R7, IMS can truly become a converged control layer.
The biggest feature of R7 is fixed network access. It can be said that R7 is the basic version for the future IMS as the core network, as a fixed and mobile network or as the core network of NGN. The first step towards fixed network access is VCC (Voice Call Continuity) technology, which is used to achieve seamless switching control between GSM\UMTS\WLAN.
Although IMS is now widely accepted as a network convergence technology, it still has many problems in terms of standards and even product maturity. However, IMS has taken a solid step towards network convergence. Let us wait and see whether IMS can truly take on the responsibility of network convergence.
Nortel IMS Network Convergence System
As early as six years ago, Nortel began to develop multimedia services based on SIP. Nortel's multimedia control and service platform MCS5200 based on SIP protocol is the basis of Nortel's IMS platform. On this basis, Nortel developed CSCF and application server AS5200. At the same time, HSS was developed based on Nortel's HLR.
Nortel has always been in the leading position in the research and development of SIP technology and VoIP technology. So far, we have deployed more than 40 SIP-based networks around the world. These networks are quasi-IMS networks and can be easily upgraded to standard IMS networks.
Nortel is currently the manufacturer with the most extensive VoIP deployment, with 20 million VoIP ports deployed worldwide. These network deployments have laid the foundation for the future large-scale commercial use of IMS.
Nortel's IMS system has good compatibility. Nortel has 6 IMS open laboratories around the world, which are provided to service providers for service integration testing. We have more than 100 partners, covering service platforms and terminal equipment. These systems are interconnected with the IMS core control platform. Therefore, through Nortel's IMS, operators can provide users with a variety of services such as V-CRBT, IP Centrex, Conference, IM, POC, etc.
We have also established an IMS laboratory in Beijing, China, where we have successfully conducted interoperability tests with application servers from nearly 10 application developers, including many Chinese application server suppliers, such as the multimedia ringback tone platform of Eastcom Beiyou. In this laboratory, we have also completed the first phase of IMS testing in China and achieved very good results.
Nortel also has two innovation labs for cooperation with customers, and develops and tests IMS technology and services with operators. Nortel and IBM have also established a joint laboratory, which can greatly simplify the network deployment and service development cycle of operators. Nortel
's VCC (Voice Call Continuity) implementation solution, which is about to be commercialized, can achieve seamless switching between GSM\UMTS\WLAN. Nortel Networks Wireless Mobility Gateway 6000 (WMG 6000) is a key network component of this solution. This device complies with the 3GPP R7 specification and provides core control layer guarantees for the seamless integration of 3G and WLAN. The deployment of this technology can greatly reduce the cost of operators to deploy 3G networks. The implementation of this technology can truly achieve the integration of various wireless access networks, taking a solid step towards FMC.
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