With the development of the telecom market and the gradual evolution to the next generation network (NGN), softswitch technology is playing a key role and is increasingly becoming the technology link for circuit switching and packet switching networks. Therefore, the application of softswitch technology in telecommunication networks has increasingly attracted the attention of the telecommunications industry . The International Softswitch Association (ISC) defines softswitch as "softswitch is a software entity that provides call control functionality." The definition of softswitch technology by the Institute of Telecommunications Transmission of the Ministry of Information Industry of China is "softswitch is one of the core devices of network evolution and next-generation packet network. It is independent of the transport network and mainly completes call control, resource allocation, protocol processing, and routing. Key functions such as authentication, billing, etc., can provide users with all the services that the existing circuit switches can provide, and provide programmability to third parties." Softswitch has ten functions:
First, the media gateway access function
The media gateway function is an endpoint/network relay or a collection of several endpoints that access the IP network. It is an interface device between the packet network and the external network, providing media stream mapping or transcoding. For example, PSTN/ISDNIP relay media gateway, ATM media gateway, user media gateway and integrated access gateway support MGCP protocol and H.1248/MEGACO protocol for resource control, media processing control, signal and event processing, and connection management. Many complex functions such as maintenance management, transmission and security.
Second, call control and processing functions
Call control and processing functions are one of the important functions of softswitch, which can be said to be the soul of the entire network. It provides control functions for the establishment, maintenance, and release of basic service/multimedia service calls, including call processing, connection control, intelligent call trigger detection, and resource control. Support basic two-party call control function and multi-party call control function, including multi-party call special logic relationship, call member join/exit/isolation/side listening.
Third, the business provides functions
In the evolution of the network from circuit switching to packet switching, the softswitch technology must be able to implement all the services provided by the PSTN/ISDN switch, including basic services and supplementary services. It should also cooperate with the existing intelligent network to provide intelligent network services. It can also work with third parties to provide a variety of value-added services and intelligent services.
Fourth, interconnection and interoperability
The next-generation network is not an isolated network. Especially in the evolution of the existing network to the next-generation network, it is inevitable to achieve interoperability, interconnection and smooth evolution with the existing network. For example, the signaling gateway can be used to implement interworking between the packet network and the existing signaling network No. 7; the signaling gateway can communicate with the existing intelligent network to provide multiple intelligent services for users; and the H.323 protocol can be implemented and implemented. Interworking with IP telephony networks with H.323 system; SIP protocol can be used to communicate with future SIP network systems; SIP or BICC protocol can be used to interconnect with other softswitch technologies; H.248 terminals and SIPs in IP networks can also be provided. Interworking between the terminal and the MGCP terminal.
Fifth, the protocol function
Softswitch is an open, multi-protocol entity. Therefore, various standard protocols must be used to communicate with various media gateways, application servers, terminals, and networks to maximize user protection and maximize the role of existing communication networks. These protocols include H.323, SIP, H.248, MGCP, SIGTRAN, RTP, INAP, and others.
Sixth, resource management functions
The softswitch should provide resource management functions to centrally manage various resources in the system, such as resource allocation, release, configuration and control, resource status detection, resource usage statistics, and resource usage thresholds.
Seven, billing function
The softswitch should have the function of collecting detailed bills and multiple counting functions, and can transmit the bills to the corresponding billing centers according to the needs of the operators.
Eight, certification and authorization functions
The softswitch should support the local authentication function, which can authenticate and authorize users and media gateways in the jurisdiction to prevent unauthorized users/devices from accessing. At the same time, it should be able to connect with the authentication center, and send the user and media gateway information in the jurisdiction to the authentication center for access authentication and authorization to prevent illegal users and devices from accessing.
Nine, address resolution function
The softswitch device should be able to complete the conversion function from E.164 address to IP address, alias address to IP address, and also complete the redirection function. For the number analysis and storage function, the softswitch technology is required to support storing the calling number 20 bits, the called number 24 bits, and the ability to analyze the 10-digit number and then select the route, and have the ability to add and delete numbers at any position.
Ten, voice processing function
The softswitch device should be able to control whether the media gateway uses voice signal compression and provide a voice compression algorithm that can be selected. The algorithm should include at least G.729, G.723.1 algorithm, and optional G.726 algorithm. At the same time, it can control whether the media gateway adopts echo cancellation technology, and can set the size of the voice packet buffer area to reduce the impact of the jitter voice quality.
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