PoC: The highlight of 3G mobile value-added services

JasonYoo

PoC: The highlight of 3G mobile value-added services [Copy link]

PTT is also known as "push to talk". Its characteristics are short call establishment time, occupying the channel only when speaking, and only monitoring the channel when answering. The receiver does not need to pick up the phone to answer the downlink call information at any time. The PTT service based on the public cellular mobile communication network is called PoC service. The mature PoC service in the future is based on the 3G network. It makes full use of the characteristics of the 3G mobile packet network and implements PTT through half-duplex VoIP technology based on the IMS multimedia subsystem. At the same time, PoC also combines service attributes such as instant messaging and Presence to become a personalized service that integrates voice and data.

　　PoC is a two-way, instant, multi-party communication method that allows users to communicate with one or more users. This service is similar to the mobile intercom service - the user presses a button to talk to a certain user or broadcast to the participants of a group. After the receiver hears the voice of the speech, he can do nothing, such as not answering the call, or be notified and must receive the call before hearing the voice of the sender. After the initial voice is completed, other participants can respond to the voice message. PoC communication is half-duplex, and at most one person can speak at a time, and the others can listen.

　　The key technology of PoC service

　　- IMS support for PoC.

　　The realization of PoC service in future 3G network is mainly based on IMS architecture. IMS is called IP multimedia subsystem. IMS mainly realizes the registration and security of PoC service, SIP signaling routing, SIP signaling compression, address resolution, management of logo hiding and billing.

　　In the registration of IMS, the user first establishes PDP context, finds P-CSCF in IMS through GPRS request or DNS resolution process, P-CSCF forwards the registration request to I-CSCF, finds S-CSCF through I-CSCF query HSS, and realizes the registration process in S-CSCF. In this process, PoC user and S-CSCF realize mutual authentication and authorization through AKA algorithm.

　　When the user registration and authentication are successful, the PoC user can initiate a group call request. The SIP message header of the session invitation carries the PoC group session flag. P-CSCF forwards the call invitation to I-CSCF, inquires the address of the S-CSCF to which it belongs, and then forwards the invitation to S-CSCF. S-CSCF forwards the session invitation to the responding PoC server according to the service trigger point through the initial filtering rules downloaded from HSS. The PoC server performs session control and forwards the session invitation to other users in the group through IMS. After media authorization and negotiation, the group call can be established. The billing

　　of PoC services is based on the billing framework of IMS, which can be based on event billing, group session billing, speech billing, etc.

　　——PoC server.

　　PoC server is the core functional entity for the implementation of PoC services. From the perspective of internal implementation technology, there are two implementation methods of PoC server, the integrated service platform method and the soft switch method.

　　In the integrated service platform method, the PoC server is responsible for both call control and media processing, and the internal modules are tightly coupled. This method can be implemented using pure software or developed based on the API of a specific media processing hardware board. The integrated service platform mode is generally suitable for systems with smaller capacity. When the system capacity continues to expand, due to the close coupling between call control and media processing, the upgrade and expansion are not flexible enough, so the cost is high. The

　　soft switch mode adopts the soft switch technology that separates call control and media processing. The PoC server is mainly divided into a call control module and a media processor module, and the standard H. 248 (MEGACO) protocol is used between the two. The call control module is implemented by software, while the media processing module can be implemented by software or hardware. Hardware implementation will greatly improve the performance of media processing. This layered architecture reduces the coupling degree of the system and enhances stability. The soft switch mode is suitable for PoC systems with frequent upgrades or large capacity.

　　Suggestions for the development of PoC services

　　PoC services use the wide coverage of public mobile cellular networks to enable mobile users to realize point-to-multipoint group calls, thereby effectively and timely sharing information among multiple people. PoC services can also bring users IP-based multimedia applications, such as interactive games. PoC services can make users of group calls "always online". This "always online" feature allows members participating in the call to talk as long as they press the PTT key.

　　Although PoC has many advantages, we should also see its shortcomings. The most important one is the low call establishment delay performance and call delay performance. This is mainly because PoC is based on the VoIP technology of the public mobile cellular network. Therefore, PoC cannot be used in emergency linkage and emergency calls like digital trunking communication. At the same time, due to the low reliability and security of PoC, PoC cannot be used in departments with high security requirements. PoC services are more used in companies, hotels and leisure and entertainment venues to enrich people's communication methods and increase people's communication fun.

　　In the future, the development of PoC services should focus more on improving service delay performance, enriching service types and providing more service functions. Try to shorten PTT call delay, develop Push to X (X can be text, voice, pictures and images) services, and add functions such as user priority and disaster handling to make PoC services more complete and truly become a highlight and killer application in future 3G value-added services.