1. Field of the Invention
The present invention relates generally to a service data multicasting system, a method therefor and a security key generating system. More particularly, the invention relates to a service data multicasting system delivering service data, such as video image and so forth to general public mobile stations in a mobile communication system.
2. Description of the Related Art
As a multicast service content in such service data multicasting system, image, such as video image and so forth may be delivered, for example. Such system is premised in that a user in receipt of multicasted service data, is enabled to receive the multicasted data only after subscribing such service.
In the multicast service in the mobile communication system, the multicast service data is multicasted through a common radio channel in a certain radio communication area. The reason is to simplify a process in a control station of a radio base station by transferring data through certain single common radio channel which all users may receive, rather than transferring the same service data to a plurality of users through respective dedicated channels, since it becomes unnecessary to set radio channels corresponding to individual users.
Since a service provider charges per service for the users, only users subscribing the multicasting service can receive the service data. In other words, the service provider is liable to enable all of the subscribing users to receive the service data. However, as feature of the multicasting system, the multicasted service data is transferred through one common channel to be received by all users so that the user not subscribing may receive such service data. Therefore, certain restriction control is required for the users receiving the service data.
As the most effective means for restricting reception for the users, it is possible to enable decoding of the transferred service data only for the subscribing users. In order to realize this, security may be applied for the service data to disable decoding for the not subscribing users.
However, a current security control method in the mobile communication system is a system for generating security key (cipher key) for security per the mobile station. Therefore, the current security control system is not applicable for the foregoing multicasting system. The reason is that since the multicasting system has to enable all of subscribing users to receive the service data as set forth above, if security key corresponding to particular terminal is applied, other terminal may not release security lock even though it receives the service data.