Three main features of NGN with Softswitch technology as the core

The next generation network, NGN, is a product of triple play. It is a comprehensive and open network that provides various services, including voice, data, and multimedia. The architecture of NGN has become the focus of attention at home and abroad. During the evolution to NGN, the network development trend is a Unified IP core network, layered structure and open interfaces. The softswitch system is a highly-respected NGN evolution solution and an overall solution for new-generation multimedia services for network convergence. It not only achieves network convergence by optimizing the network structure, but also achieves business convergence. Softswitch is positioned at the control layer of NGN and is the core technology of NGN.

Evolution from the existing PSTN network to the softswitch-Based NGN network is an inevitable direction for the development of telecom networks. The Unified IP core network, layered structure, and open interfaces are key features of NGN.

Idea of separating gateways

In the traditional IP Phone System, IP Phone gateway can establish a call connection between the circuit switching network SCN) and the IP network. The traditional gateway not only needs to convert the media format, but also to convert the signaling. It implements the H.323 or SIP protocol on the IP network side and the ISDN/PSTN signaling on the SCN side. In addition, the system also needs to control the internal resources of the gateway and establish the internal voice channels of the gateway for each call.

This integrated gateway structure imposes considerable constraints on the large-scale deployment of IP phones. It is mainly manifested in the fact that the gateway integrates multiple functions and is too complex, as a result of poor scalability and no fault assurance mechanism, the industry has proposed the concept of gateway decomposition. Traditional gateways are divided into three parts: Media Gateway MG, which is responsible for media transformation and connections between SCN and IP addresses. Signaling Gateway SG is responsible for signaling conversion, only the underlying conversion of SCN signaling is performed, that is, the TDM circuit is switched to the IP network transmission mode without changing the application layer message. The Softswitch is responsible for controlling the establishment and release of the Media Gateway connection based on the received signaling. Softswitch is used to analyze and process signaling messages and implement intercommunication and transformation at the application layer. Softswitch also controls resources and is responsible for authentication and network security. It is the controller of the entire system. Softswitch is also called a call proxy or media gateway controller.

Gateway separation leads to a new protocol standard. Interfaces A between SoftSwitch and MG use Megaco, also known as H.248) or MGCP. Interfaces B between SoftSwitch and SG use Sigtran. In Softswitch, there are Megaco Protocol stacks and Sigtran protocol stacks; in MG, there are Megaco Protocol stacks; in SG, the IP side is the same as the Sigtran protocol stack in softswitch, And the SCN side is the SS7 protocol stack.

Unified IP core network

NGN adopts a Unified IP core network structure, which consists of the service layer, control layer, media layer, and access layer from top to bottom. The application server is located at the business layer and is responsible for providing value-added services and management functions. At the control layer, Softswitch is responsible for implementing various call control and transmitting corresponding service processing information. It is the core control device of NGN; on the media layer, the gateway converts the information sent by users to the IP Address Transmission Format. wireless networks, telephone networks, and cable television networks exist as access networks.

Traditional wired and mobile phones have their own independent exchange and transmission networks, and the access networks of mobile phones are even more complex. They have different air transmission standards, which not only increases costs, it also brings inconvenience to users and managers. In NGN, the integration of the fixed network and the mobile network will be realized. fixed and mobile communication are only different access methods.

The IP network adopts an open architecture and unified standard protocol. Any access network can communicate with it as long as the IP protocol is used. Access networks can be fixed telephone networks, mobile telephone networks, cable TV networks, ADSL, and LAN access. The Unified IP core network replaces the independent devices of the original systems with a unified set of devices, which can greatly reduce the development and operation costs.

From the existing network to the NGN is a gradual evolution process. To make full use of existing devices, the overlapping network strategy with Softswitch as the core is a feasible transition strategy. Softswitch is the core device of the Next Generation grouping network. It is independent of the access network and mainly implements call control, resource allocation, protocol processing, routing, authentication, billing, and other functions, at the same time, it can provide users with all the services that the existing circuit switches can provide and third-party programmable capabilities. Softswitch is the center of coordination between the SCN and the IP network. By controlling various gateways such as SG and MG, the service layers of different networks are integrated.

Open interfaces

Softswitch is one of the main features of NGN, which has many advantages over traditional circuit switching. Traditional circuit switching is integrated, and communication between different subsystems adopts proprietary protocols. Softswitch is an open and hierarchical architecture with open API interfaces. In this way, changes to a layer will not affect other layers.

Softswitch is also called soft SSP, because its function is equivalent to the SSP in the traditional Intelligent Network. However, the softswitch architecture is open and programmable. On the one hand, SoftSwitch and lower-layer interfaces are protocol APIs that integrate multiple protocols in the IP network. For example, SIP, H.323, Megaco, and ISUP/IP. On the other hand, SoftSwitch and upper-layer interfaces are application APIs, which are programmable for service providers and third-party developers. Softswitch truly separates services from call control and calls control from bearer services. The idea that "business is implemented by User Programming" is not the first in softswitch, but the traditional intelligent network is based on this idea. However, because the intelligent network is built on the circuit switching network, the separation of services and switches is incomplete. At the same time, its access and control functions are not separated, it is not convenient for devices to integrate multiple networks. In addition, the SCE service generation environment of the intelligent network is implemented by SIB components unrelated to services, SIB is closely related to complex INAP intelligent network application protocols. It is not conducive to the large-scale participation of third-party application vendors and cannot generate new services conveniently and quickly.

Softswitch draws on the strengths of IP, ATM, IN Intelligent Network, and TDM to form a layered and fully open system architecture, which not only achieves network convergence, more importantly, it enables business integration. The business is truly independent from the network and can be flexibly and effectively provided.

At present, international research on open APIs mainly includes ParlayAPI, JAIN and OSA. ParlayAPI is an application API. JAINAPI includes the application API and Protocol APISIP, MGCP, H.323, TCAP, ISUP, INAP/AIN, MAP, etc.). OSA is an application API, focuses on mobile terminal services. The latest research trends show that the three are becoming more integrated.