Implementation of telecom services under Softswitch

1. Overview
Softswitch is a technical system that separates services from call control, call control, and bearer to provide telecom-level services to users. Through in-depth understanding and analysis of softswitch, we found that the architecture of softswitch has moved from the simulation of traditional telecom networks to an open business system with Internet architecture and multiple users and Multimedia Based on the SIP protocol, the application field of Softswitch is gradually expanding to the core field of telecommunication business-business development capability. At present, the service development capability of softswitch has expanded from simple telephone service and intelligent network service to an application-driven softswitch system with multimedia service capabilities that can be customized as needed.
2. Softswitch Business System Architecture
Softswitch is a business-driven network. By separating services from call control, call control, and bearer, the softswitch system realizes that upper-layer services have nothing to do with underlying heterogeneous networks, make the business truly independent from the network, so as to provide more flexible and effective services, and support different bandwidth, real-time or non-real-time media business use; on the other hand, you can configure and define your own business characteristics without worrying about the network type and terminal type of the business, making the business and application provision more flexible. It can be said that Softswitch truly embodies the business-driven ideas and concepts, achieves a good convergence of multiple networks, and provides an open and flexible business provision system.
I. Open Architecture:

The layered network system achieves the separate evolution of each layer. By setting up network APIs between layers, you can change the current service provision methods in the following aspects:

• Business Portability: currently, the development of various technologies and applications is limited by the specific interface, which increases the development cost of applications, prolongs the time for pushing to the market, and makes maintenance inconvenient. With standard network APIs, you can write your business once and run it anywhere.
  
• Multi-network convergence: the current trend of network convergence is becoming more and more obvious, but it is mainly through gateway interconnection information, network APIs abstract the similar capabilities of different networks, and provide unified control interfaces to external users, to achieve the convergence of business layers between networks.
  
• Supports secure network access: communication applications and services, internal networks running on the carrier's reliable network, or completely outside the network. If the functional entities and intelligence inside the carrier's network can be provided to the controlled external access, it will provide a huge market opportunity for creating new businesses.

Ii. value-added business architecture:
The softswitch architecture introduces an application server, a new entity for value-added services. The application server is responsible for generating and managing logic of various value-added services, and also provides various open APIs to provide a creation platform for third-party business development. The Application Server is an opposite entity that has nothing to do with the control layer's Softswitch, thus realizing the separation of business and call control, which is conducive to the introduction of new businesses. There are currently two mainstream application servers in the industry:
(1) SIP Application Server:
The SIP protocol is an application-layer control signaling protocol proposed and presided over by IETF. It is used to create, modify, and end the session Process attended by one or more participants.
IETF developers for SIP applications provide two types of business development technologies:
The first is for sip cgi and SIP Servlets with high credibility, and the sip cgi and SIP Servlet API specifications are developed. These two technologies have strong functions, but improper use may cause insecure application servers.
The other Language is CPLCall Processing Language (CPLCall Processing Language), which is a scripting Language based on XMLExtensible Markup Language developed by IPTEL Working Group of IETF, it is mainly used to describe and control Personalized Internet telephone services, including call Policy Routing, call screening, call logs, and other services, with weak processing capabilities, this ensures that the CPL business logic compiled by common users will not cause damage to the application server.
(2) Parlay Application Server:
The Parlay Application Server can provide different abstract levels of business development interfaces, so that different capabilities and types of business developers can develop a wide range of businesses. For example, you can provide the Parlay API interface based on CORBA, Java API interface based on jain spa standard, Java API Based on ans, and interface based on XML, CPL, and VoiceXML. The abstract layers of these interfaces gradually increase, but the interface capabilities are also gradually reduced. business developers can select the appropriate development interfaces based on their business needs and capabilities.
3. Softswitch-based No. 1 Communication Service
A Softswitch-based No. 1 service refers to a user's application for a unique personal communication number to transfer future calls to a specified number of terminals using the softswitch network, A call can be initiated on any terminal using a single-digit communication number as the caller ID.
You can set your business through web pages, voice interactions, or the Software Terminal Management Interface (optional.

(1) system composition
The No. 1 Communication System Based on the softswitch network includes:

• No. 1 business application server:
  Provides business logic of No. 1, stores business-related data, and provides business management functions.
  
• Softswitch
  As a core control device, Softswitch is a scalable carrier-level platform. It is located in the control layer of the NGN network and provides call and Connection Control, protocol processing, service provision, network resource management, billing, authentication, and other functions for a variety of services.
  
• Media Resource Server:
  Entities that provide voice interaction functions, such as the radio number.
  
• Relay gateway TGW ):

Provides the ability to communicate with PSTN networks.
(2) Business functions
The Softswitch-based No. 1 Communication Service can easily implement the functions of the traditional No. 1 Communication Service: sequential and simultaneous ringing.

• Ordered ringing
  When a user calls a pass number, the user calls the number sequentially from the first transfer number to the last transfer number according to the pass number table set by the user; if the previous number fails to respond without a response, is busy, or fails to be routed, the next number is automatically continued until the last number is reached. The user's No. 1 pass number is the first transfer number of the forward call code table. You can set multiple call numbers.
  
• Simultaneous ringing

When you call a single phone number, call all phone numbers at the same time according to the same vibration number table set by the user. When a user answers any of these calls, the other terminals automatically stop the ringing. The user's No. 1 pass number is the first transfer number of the same vibrating number table. You can set multiple same-vibration numbers.
Compared with the traditional PSTN, the softswitch network is more convenient to interwork with the Internet. Traditional No. 1 communication services, similar to the setting of zhenshun call numbers, are generally completed through IVR interaction. The No. 1 Communication Service under Softswitch not only supports IVR interaction, you can also use the B/S mode to complete the settings through WEB page settings or C/S mode through the terminal, giving you more options.
(3) Call Control

The SoftSwitch and No. 1 application servers are generally interconnected through the SIP protocol, and the Access Gateway is generally interconnected through the H.248 or Megaco Protocol.
As the SIP proxy server, Softswitch can distinguish between common call and one-stop call based on the call information, and switch the call to the One-Stop Application Server. The Application Server of No. 1 provides the execution and management of No. 1 services.
Common calls follow the existing call procedures and standards.
One-to-one call can be divided into two types: Synchronous call and forward call. When a user calls one-to-one call, the softswitch switches the call to the application server. The application server obtains user data based on the called Number: Same-vibration or forward call, and the transfer number table. The application server will initiate a call to the same vibration number according to the user settings, or call the number table in a certain order and at a certain interval. All subsequent messages of a call are sent to the application server. The application server processes the messages based on the feedback. The application server will also generate corresponding records for calls.
4. signaling process
Figure 4 PSTN user A calls user 1, which is connected to POTS user B and SIP User C under the AG of the softswitch domain. The SoftSwitch and Application Server are connected by the SIP protocol, softswitch and AG, SoftSwitch and TG are connected with H.248 protocol. As you can see, user B and user C are ringing at the same time, user C is picking up and responding, and the Application Server cancels the ringing on user B. When both parties call and the call ends, user C is suspended and the system releases the connection.
Figure 5 PSTN user A calls user 1 and calls POTS user B and SIP User C under the softswitch domain AG. The SoftSwitch and Application Server are connected by the SIP protocol, softswitch and AG, SoftSwitch and TG are connected with H.248 protocol. As you can see, user B first rings the bell. After the specified time is reached, the app server cancels the ring on user B and then calls user C. User C is disconnected and the call ends. User C is suspended and the system releases the call.

Figure 4: Same-vibration signaling Diagram

Figure 5: Call-forward signaling Diagram

5. Conclusion
Since its birth, the communication network has evolved constantly. We have gone through step switches, vertical switches, and programmable switches. Today, with its layered structure, flexible and efficient features, Softswitch has become the main direction for the evolution of the exchange network. As a business-driven network, the softswitch network inherits existing concurrent services to meet users' personalized and evolving needs, it is an important research direction for SoftSwitch. Although the No. 1 service in this article is a traditional service of the PSTN network, the implementation of the No. 1 service through the softswitch service system demonstrates the service implementation of the softswitch network from a specific development, it is more flexible and convenient than traditional networks.