Overview of the five development directions of the NGN System

1. Fixed architecture and mobile evolution to nomadic Network

At present, telecom operators, equipment manufacturers, and standards-making organizations at home and abroad are stepping up research on NGN technology. International standardization organizations have put the standardization of NGN technology on the agenda, there are four main camps: ITU-T, ETSI, 3GPP and IETF. ITU-T has made a clear definition of NGN, and has introduced a number of related draft standards. There are mainly two kinds of system architecture, the NGN system architecture proposed by the ITU-T and the NGN system architecture proposed by the TISPAN, The ITU-TSG13 has developed the NGN modular system architecture, according to the IMS architecture of 3GPP, the system structure and logic function structure of NGN are proposed. However, the standard progress of ITU-T is slow, and the speed of TISPAN is faster, and the standard progress of ITU-T has been influenced, therefore, ITU-T may directly reference the TISPAN standard in the future.

NGN should be a network that supports both fixed businesses, nomadic businesses and mobile businesses. The NGN architecture proposed by TISPAN can be connected to both mobile users and fixed users. However, the evolution of the existing fixed network and mobile network to the NGN network will be a gradual process and will follow two completely different paths: the fixed network first evolves to a softswitch network that supports both the fixed and nomadic nature, and then to a NGN network that supports both the mobility; based on the evolution steps developed by 3GPP and PP2, the mobile network gradually evolves to support fixed and nomadic networks.

China has formulated a series of standards related to Softswitch, including a series of equipment technical specifications, test specifications and business specifications. China's telecom operators are also actively carrying out tests and trial commercialization of NGN, however, these tests and technical research in China are mainly aimed at providing fixed Softswitch for fixed businesses and nomadic businesses.

2. Softswitch hierarchical networking and interconnection protocols　

TISPAN divides the control plane into four subsystems: other multimedia subsystems, streaming media subsystems, IP Multimedia subsystems, and PSTN/ISDN simulation subsystems. At present, it mainly researches and develops the STN/ISDN simulation subsystems and IP Multimedia subsystems, it is also stipulated that two logical functional entities provide related functions and services. You can put these two functional entities in one physical entity or separately set them in the network according to your needs. China's Softswitch equipment standards also stipulate the provision of PSTN/ISDN simulation services and IP multimedia services, the Softswitch devices produced by domestic manufacturers can provide two business control systems in one physical entity, the Softswitch devices produced by foreign manufacturers basically provide PSTN/ISDN simulation by MGC, And the SIP server provides multimedia services.

At present, domestic operators, especially fixed network operators, have invested a lot of enthusiasm in softswitch, especially after China Telecom's North-South split, China Telecom is eager to seize the local market in the north, china Netcom is eager to seize the local market in the south. China tietong also hopes to use Softswitch as an opportunity to enhance its competitiveness. In particular, the implementation of softswitch can directly use users' existing broadband access methods, rapid deployment of softswitch services can be said that the large-scale commercialization of softswitch will soon come. However, to establish a large-scale Softswitch Network involves the way of softswitch layered networking, the intercommunication protocol between Softswitch standardization and other issues, so it is necessary to accelerate the standardization process of softswitch, while tracking the standardization process of ITU-T and TISPAN, improve China's NGN system architecture and guide China's Softswitch to seamless integration with the future NGN system architecture.

3 IPv6 expecting data network router Transformation

The NGN is based on a group network, and the Group network can be based on an ATM network or an IP network. Although the NGN definition does not specify the network to be based on, however, from the current development trend, the bearer network should be an IP-based network, and the practical and feasible solution is to establish an NGN bearer network through VPN isolation on the existing data network. IP addresses are bound to be used as the bearer networks of NGN. IP addresses can be in two formats: IPv4 and IPv6, which are incompatible with each other. IPv6 is suitable for the evolving needs of IP networks. replacing IPv4 with IPv6 is an inevitable trend in the development of IP networks. At present, several carriers in China are conducting experiments on NGI (Next Generation Internet, in addition, operators have basically developed a plan for network transformation of data network routers.

However, the transition from IPv4 to IPv6 is not easy, because the upgrade from IPv4 to IPv6 involves many technical and commercial issues, and even political issues. Of course, the most obvious thing is the technology change strategy and infrastructure upgrade and construction. The reliability and common application of IPv4 are the main factors in the development of IPv6. The existing IP networks mainly adopt IPv4 addresses. IPv6 is only in its infancy, and most devices on the Internet do not support IPv6. Therefore, relying on the existing data network and Using VPN technology to isolate the establishment of the softswitch bearer network solution, IPv6 support will be accompanied by the transformation of the carrier's data network router, faced with the fact that the softswitch network has already begun commercial operation in some regions, it is too early to consider the IPv6 solution for the IP address of the softswitch bearer network before the development of IPv6.

4. Access mature Video Conferencing Systems　

Currently, the technologies and standards of relay gateways and access gateways are relatively mature. For other types of terminal devices, the industry is clamoring for the use of fully-SIP methods. First, the access to the H.323 terminal is not considered in NGN. At the same time, the existing IAD using H.248 or MGCP protocol is replaced with the IAD using the SIP protocol to achieve full SIP of the core network. However, IAD users mainly provide PSTN/ISDN simulation services. It is difficult to use the SIP Protocol to implement all basic and supplementary services of the PSTN, and there is no such standard at all, therefore, this solution is still under discussion.

In addition, various terminal devices basically have no major problems when supporting basic voice calls. However, when supporting video services, different terminals provide different video encoding/decoding codes, in addition, the support of the SIP protocol for video, especially for video conferencing, is not yet mature. It can be said that although the SIP protocol is flexible, it also leads to difficulties in Intercommunication when using the SIP protocol, at the same time, it also affected the use of SIP terminals. Now CCSA (China Communications Standardization Association) is starting the formulation of the technical specifications of SIP terminals. According to the overall technological development trend, the NGN network should be based on the SIP network, but the maturity of terminal devices using the SIP Protocol depends on the maturity of the SIP protocol.

From the implementation of the softswitch network in the near future, the main starting point of the operator is to quickly deploy the softswitch to compete for customer resources and to provide voice services, therefore, IAD devices that use the H.248 or MGCP protocol are used.

5. Access control devices can control users at the edge of the core network.

The concept of separation of bearer and control is put forward in NGN. However, in a complete sense, the separation of bearer and control makes it difficult to guarantee the controllability, reliability, and security of the NGN network, therefore, the NGN network puts forward an entity between the access level and the control level/bearer level to implement the access control function, so as to achieve user control at the edge of the softswitch core network.

Currently, there are two methods. One is that both the signaling stream and the media stream pass through the access control device, and then the access control device sends the signaling stream to the control plane, forward the media through the bearer network to the peer. The access control device determines whether to enable or disable the media port based on the signaling information; another method is to direct the signaling stream from the access plane to the control plane. Then, the control plane controls the access control device based on the signaling interaction process to open or close the corresponding media port.

At present, manufacturers are developing devices that have completed the access control function. This device can ensure the reliable operation of the NGN network and is essential for network construction.

1. Several Opinions on the Development Trend of NGN network technology
2. Next Generation Network (NGN): Research Progress of Softswitch Technology
3. NGN development strategy based on Softswitch