Precautions for applying Softswitch networks

We all know that in a softswitch network, each soft switch in its control layer is not classified, which is troublesome for network operators and affects users' usage. Human Communication includes voice, data, video and audio multimedia. For a long time, the above three types of communication services are carried and dredged by different communication networks. The telephone network carries and dredge voice services, data networks carry and clear data services, and multimedia networks carry and clear multimedia services.

With the further deepening of social informatization, communication has become an indispensable tool for people's life and work, people's requirements for communication are no longer just basic voice communication services and simple WWW browsing and sending and receiving E-mail. What people need is the ability to obtain the required information anytime, anywhere and flexibly. Therefore, telecom operators are required to provide users with a wide range of telecommunication services flexibly, however, the operation modes based on different communication networks that provide different services are difficult to meet users' demands for "flexible access to required information, only by building a "full business network-that is, a network that can simultaneously carry and clear voice, data, and multimedia services" can we meet the increasing needs of users for communication services.

The telephone network has a long history. Its core is a telephone switch. The telephone switch has undergone 5 stages of development, namely, magnetic stone, shared battery, step-by-step, horizontal and horizontal, and process control, the difference is that the implementation of vswitches has changed. The emergence of the telephone switch is a historic change. It adopts an advanced architecture. Its functions can be divided into three parts: call service access, route selection (switch), and call service control, the switching and call business control functions are mainly implemented through program software. However, it adopts an exclusive circuit switching mode, and the peer-to-peer bidirectional 64 kbit/s fixed bandwidth channel provided for both parties of the communication is not suitable for data services with large bursts of data and large differences in upstream and downstream data traffic.

The wide area network (WAN) protocol can be divided into DDN, X.25, frame relay, and IP network, since the IP network has simple protocols, low terminal device prices, and the development of WWW services based on the IP protocol, the IP-based Internet has exploded and became synonymous with the data network. The IP network requires the user terminal to encapsulate all user data in the IP package. The core device of the IP network-the router is only a simple task of "best effort" for IP packet forwarding, it uses the packet exchange mode of resource sharing and dynamically occupies the upstream and downstream transmission channels according to the business volume needs. Therefore, the IP network is actually only a data transmission network, and it does not provide any high-level service control function, if the voice service is enabled on the IP network, additional phone service control devices must be added. It is worth mentioning that the IP packet transmitted in the IP network can carry any user data information, which creates conditions for the transmission of voice, data, multimedia streams, and other information in one bearer network. It can be seen that both the telephone network and the data network have some inherent defects and cannot be simply transformed into a "full-service network". Therefore, to enable Simultaneous Delivery of voice, data, and multimedia services on the same network, that is, the convergence of communication services, softswitch technology is introduced.

Introduction to Softswitch Technology

1. General Structure of the softswitch network

The Softswitch technology adopts the advanced architecture of telephone switches and uses IP packets in the IP network to carry various information such as voice, data, and multimedia streams. A Programmable telephone switch can be divided into three functional modules: business access, route selection (switch), and business control. Each function module is connected to a whole through the switch's internal switching network. The Softswitch technology is to separate the above three functional modules, which are implemented by different physical entities. At the same time, some functional extensions are carried out, and various physical entities are connected through a Unified IP network, constitute a Softswitch Network.

The business access function module of the telephone switch corresponds to the edge access layer of the softswitch network; the routing selection (switching) function module corresponds to the control layer of the softswitch network; the business control module corresponds to the business application layer of the softswitch network, and the IP network forms the core transfer layer of the softswitch network.

2. Edge access layer

The Softswitch technology makes the service access module of the telephone switch an independent physical entity called the media gateway (MG). The MG function is to connect various users and services to the softswitch network by various means, MG completes data format and protocol conversion, and converts all media information flows connected to IP-based data packets for transmission in the softswitch network. MG can be subdivided into the following categories based on different users and businesses connected to MG.

Relay Media Gateway (TG): Used to complete relay connection with the PSTN/PLMN telephone switch and convert the 64 kbit/s voice signal in the PCM relay of the telephone switch to an IP packet. Signaling Gateway (SG): used for completing the Signaling connection with the PSTN/PLMN telephone switch, and converting the signaling information of the telephone switch based on the TDM circuit to the IP package. TG and SG jointly complete the connection between the softswitch network and the PSTN/PLMN telephone network switched using the TDMA circuit, and connect the common telephone users and their services in the PSTN/PLMN network to the softswitch network. Access Gateway (AG): provides analog user line interfaces for directly connecting normal telephone users to the softswitch network. It can provide all services provided by the PSTN, such as telephone services and dial-up Internet services, it directly encapsulates user data and user line signaling in the IP package.

Integrated Access Device (IAD): A class of IAD provides both analog user line and Ethernet interfaces for accessing general telephones and computer devices, it is applicable to users who use telephone services and computers to use data services separately. The other type of IAD Only provides Ethernet interfaces for accessing computer devices, it is applicable to users who use telephone services and data services on computers at the same time. In this case, a dedicated "softphone software" needs to be installed on users' computer devices ". Multimedia Service Gateway (malong): used to complete the information of various multimedia data sources and adapt the Multimedia Streams mixed with video and audio to an IP package. H.323 Gateway: used to connect an IP address Telephone Network Gateway using the H.323 protocol. Wireless Access Media Gateway (WAG, WirelessAccessGateway): used to connect wireless access users to the softswitch network.

It can be seen that AG, TG, and SG have jointly completed the functions of the telephone switch service access function module, and achieved the access of voice services of ordinary PSTN/PLMN telephone users, and adapt the voice information to an IP packet suitable for transmitting in the softswitch network. At the same time, the Softswitch technology also expands the service access function, which is embodied in several types of media gateways, such as IAD, mstrap, H.323GW, and WAG. Through various MG and Softswitch networks, PSTN/PLMN users, H.323IP telephone network users, common wired telephone users, and wireless access users' voice, data, and multimedia services are integrated.

3. Control Layer

The Softswitch technology independently converts the switch module of a telephone switch into a physical entity called a soft switch (SS ), the main function of SS is to control the business of all media gateways in the edge access layer and the communication between media gateways. The specific functions are as follows.

(1) determine the user's business use permissions based on the user attributes registered on the relevant servers of the business application layer to determine whether to accept the business requests initiated by the user.

(2) control the resources of various media gateways at the edge access layer, control the use of resources of each media gateway, and master the resource usage of each media gateway, to determine whether there are sufficient network communication resources to meet the business requirements applied by the user.

(3) Complete the routing selection function of the call, and determine which media gateways should establish communication connections based on the information related to the user's business request, the media gateway is notified to establish communication connections and communicate with each other, as well as the information compression and encoding methods used during the communication process, and whether ECHO suppression is enabled.

(4) monitors and controls the communication connection status between media gateways, and instructs the corresponding media gateways to disconnect after the user completes business use.

(5) billing. Because the soft switch only controls the connection of services, and the data streams between users do not pass through the soft switch, the soft switch can only be charged by the connection duration, but cannot be charged by the amount of information. If a soft switch is required to be charged by the amount of information, the media gateway is required to collect statistics on the amount of information used by each user each time, and send the statistical results to the soft switch.

(6) interworking with the H.323 Network for Mutual routing and other messages, so as to achieve interworking between the softswitch network and the H.323IP telephone network.

4. Business Application Layer

The Softswitch technology makes the business control module of the telephone switch independent into a physical entity called the Application Server (AS). The main function of AS is to implement the business. The specific functions are AS follows.

(1) store the user's contract information and determine the user's permission to use the service. Generally, this is achieved using a dedicated user database server + AAA Server or intelligent network SCP.

(2) Use dedicated application servers and intelligent network SCP (requires the soft switch to have the SSP function) to achieve the basic telephone business defined in YDN065-1997 "Ministry of Posts and Telecommunications telephone exchange equipment technical specifications" and its supplementary service functions, as well as intelligent network services such as telephone card, called payment.

(3) Use a dedicated single application server or multiple application servers to achieve integrated voice, data, and multimedia services, and flexibly provide users with a variety of value-added services and special services.

(4) soft switches in the control layer of the softswitch network are not classified. When a soft switch is added to the network, the corresponding local data must be added to all other soft switches; this is extremely troublesome for network operations. The solution is to set a policy server in the business application layer to provide route information for the soft switch. Of course, the Policy Server setting scheme will directly affect the security and reliability of the softswitch network.

5. Core transfer layer

The core transport layer is actually the Bearer Network of the softswitch network, its function is to connect various softswitch network elements, such as various media gateways in the edge access layer, soft switches in the control layer, and various server platforms in the business application layer.

In view of the fact that the IP network can carry multiple types of media information such as voice, data, and video at the same time, it also has the advantages of simple protocols, good protocol support for terminal devices, and low price, therefore, the softswitch network selects the IP network as the bearer network. In the softswitch network, various network elements encapsulate various control information and business data information in IP data packets and communicate with each other through the IP network at the core transport layer.

6. protocols and standards in Softswitch networks

In a softswitch network, network elements of the same layer communicate with each other through standard protocols defined by the Softswitch technology. International organizations engaged in the establishment of softswitch standards mainly include IETF and ITU-T. They contributed to the softswitch network protocol from the standpoint of the computer and telecom respectively.