The highlight of 3G mobile value-added service

PTT is also known as "one-link", which is characterized by a short call set up time, to occupy the channel when talking, only listening to listen to the channel, the receiver does not need to pick the machine at any time to listen to the downlink call information. The PTT business based on public cellular mobile communication Network is called POC business. The future mature POC business is based on the 3G network, it fully utilizes the characteristics of the 3G Mobile packet Network, based on the IMS multimedia subsystem, through Half-duplex VoIP technology to achieve PTT. At the same time, POC also combines instant messaging, presence and other business attributes to become a personalized business that integrates voice and data.

POC is a two-way, real-time, multi-party communication, allowing users to communicate with one or more users. The business is similar to mobile intercom--The user presses a button to talk to a user or broadcasts to a group of participants. When the receiver hears this voice, it can have no action, such as not answering the call, or being notified and must receive the call before it hears the sender's voice. After the initial speech is complete, the other participants can sound the voice message. POC communication is Half-duplex and can only be spoken by one person at a time, and others are answered.

Key Technologies of POC business

--ims support for the POC.

The implementation of POC service in future 3G Network is based on IMS architecture. IMS is called the IP Multimedia subsystem. IMS mainly realizes the functions of the POC business registration and security, SIP signaling routing, SIP signaling compression, address resolution, the management of logo hiding and billing. (Computer science)

In the IMS registration, first the user establishes the PDP context, through the GPRS request or the DNS parsing process discovers the P-CSCF,P-CSCF in the IMS to send the registration request to the I-CSCF, through I-CSCF inquiry HSS to find S-CSCF, Implement the registration process in S-CSCF. In this process, the POC user and S-CSCF the authentication and verification of both sides through AKA algorithm.

When the user registers and authentication succeeds, the POC user can initiate the group call request. The SIP message header that is invited in the session has a POC group session flag. P-CSCF sends the call invitation to I-CSCF, inquires the S-CSCF address of the attribution, and forwards the invitation to S-CSCF,S-CSCF, by forwarding the session invitation to the POC server for the response, according to the business trigger point, via the initial dump rule downloaded from HSS, The POC server carries out session control and forwards the session invitations through IMS to other users in the group, which can be set up after media authorization and negotiation.

POC Business billing based on the IMS billing framework, can be based on event billing, group session billing, billing and so on.

--poc server.

The POC server is the core function entity of POC business implementation. From the point of view of internal implementation technology, POC server has two kinds of implementation, integrated service platform and soft switching mode.

In the integrated service platform mode, the POC server is responsible for call control and media processing, and the internal modules are tightly coupled. This approach can be implemented using pure software, or it can be used to process the API development of hardware boards based on specific media. Integrated service platform is generally suitable for small capacity system, when the system capacity continues to expand, due to call control and media processing coupled tightly, upgrade and expansion is not flexible enough, so the cost is high.

In SoftSwitch, the soft switching technology of call control and media processing is adopted, and the POC server is mainly divided into the call control module and the Media processor module, and the standard H is adopted between the two. 248 (MEGACO) agreement. The call control module is implemented by software, and the media processing module can be implemented by software or hardware, and the hardware implementation will greatly improve the performance of media processing. This layered architecture reduces the coupling of the system and enhances the stability. Soft switching mode is suitable for POC systems with frequent upgrades or large capacity.

Suggestions on the development of POC business

The POC business utilizes the broad features of the public mobile cellular network to enable mobile users to achieve multicast group calls, thus sharing information effectively and in a timely manner among many people. POC business can also provide users with ip-based multimedia applications, such as interactive games. POC Business can make group call users "always online", this "always online" feature so that members who participate in the call just press the PTT key to call.

Although the POC has many advantages, we should also see the deficiencies of the POC, the most important is the call to establish delay performance and call delay performance is not high, this is mainly because the POC is based on the public mobile cellular network VoIP technology implementation. Therefore, POC can not be used in the case of emergency linkage and emergency call like digital trunking communication. At the same time, because of the low reliability and security of POC, POC can not be applied to departments with high security requirements. POC business is more used in companies, hotels and leisure entertainment, enrich people's communication, add people's communication fun.

The future development of POC business should focus more on improving business time delay performance, enriching business types and providing more business functions. As far as possible to shorten the PTT call delay, the development of Pushtox (x can be text, voice, pictures and images and other forms) business, and increase such as user priority and disaster management functions, so that the POC business more perfect, truly become the future 3G value-added services in the bright spot and killer application