A video telephony service enables a user to communicate while viewing images of the other party through a mobile communication terminal to which a camera is attached, and can be classified into a circuit-switched method using a Mobile Switching Center (MSC) and a packet-switched method using an all-Internet Protocol (IP) network.
FIG. 1 is a block diagram showing an example of the construction of a mobile communication network for providing video telephony service.
When a video telephony call is attempted by a calling mobile communication terminal 10, a base station 12 receives the call, and performs video telephony with a called mobile communication terminal 20 through an MSC 26, a Base Station Controller (BSC) 24, and a base station 22 that are connected with the called mobile communication terminal 20 through a BSC 14 and an MSC 16. Video telephony service, as described above, is provided through the MSCs 16 and 26 in the case where the circuit-switched method is employed, and the service is provided through a General Packet Radio Service (GPRS) providing register, that is, a Serving GPRS Support Node (SGSN) 30, and a GPRS gate providing register, that is, a Gateway GPRS Support Register (GGSN), that are connected with the BSCs 14 and 24, in the case where the packet-switched method using an all-IP network is employed.
In order to provide video telephony service, an international standard protocol, for example, H.323 or H.324M, defined by International Telecommunication Union (ITU), must be implemented in a mobile communication system. H.323 is a system protocol that enables the provision of video telephony service in an IP network, that is, a packet data network, H.324 is a system protocol developed on the basis of a public network, and H.324 Mobile (M) is a system protocol that has been improved for mobile communication.
In a video telephony service using H.324M as a system protocol, the compression and encoding of moving images are performed using H.261 and H.263, and the encoding of voice is performed using G.723.1. With regard to this, H.261 is a moving image compression/encoding standard for video telephony and video conferencing, and H.263 and MPEG-4 are video compression/encoding standards that have been improved more than H.261. Furthermore, G.723.1 is a standard for converting voice signals to be less than 8 Kbps. A video standard used in 3GPP is 3G-324M, which was created by modifying H.324M to be suitable for 3GPP. 3G-324M is considerably different from H.324M in that Adaptive Multi-Rate (AMR) is basically used as a voice codec, and G.723.1 is an option.
Furthermore, H.324M uses H.223 to multiplex moving images, voice and data, and uses H.245 to allocate a point-to-point or point-to-multipoint channel by selecting a voice codec and performing a function of logical channel signaling.
FIG. 2 is a flowchart illustrating a general video telephony service method, and shows an example of using a 3G-324M protocol.
As shown in the drawing, when a calling mobile communication terminal attempts a call to use video telephony service, a setup process is performed using H.223 at step S10 and, thereafter, the call is set up at step S20.
After the call setup has been completed, a line connection and allocation process based on negotiation between calling and called mobile communication terminals using H.245 is performed at step S30. After a communication path has been established accordingly, moving images, voice, and data (picture, photograph and the like) are exchanged between the calling and called mobile communication terminals at steps S40 to S60.
FIG. 3 is a flowchart illustrating the line connection and allocation process of FIG. 2 in detail.
The line connection and allocation process is a process of exchanging information about the characteristics of mobile communication terminals and, thereby, making settings so that video telephony is made possible, in the case where voice codecs or video codecs used for the calling and called mobile communication terminals are different from each other.
As shown in the drawing, for line connection and allocation between the calling and called mobile communication terminals, a master/slave decision and response process is performed at step S310, a terminal characteristic information exchange process at S320, a multiplexing information exchange process at step S330, a logical channel generation process for voice transmission at step S340, and a logical channel generation process for video transmission at step S350.
As described above, the current negotiation process for video telephony is complicated, and a lot of time is required, so that a problem occurs in that the communication path is not established immediately after call setup, and communication is not performed, and the delay time occurs in proportion to the time for which the negotiation process is performed.