With rapid growth of mobile subscribers and incessant development of communication techniques, the unit capacity of single HLR in mobile communication system has reached tens of thousands or even more. Since HLRs have stored subscription information of mobile subscribers, mobile services for all the subscribers will cease when the HLRs fail for a long period of time due to unforeseeable causes such as power failure, fire, earthquake or lightning strike, etc. Therefore, it is urgent to provide remote redundancy for the HLRs.
The redundancy for HLRs includes two aspects, one aspect is data redundancy simply for backup subscribers' data, the other is service redundancy which is based on the former aspect, i.e., when a master HLR breaks down, a redundant HLR is able to take over the services by means of signaling switchover according to the backup subscribers' data, so as to prevent the calling services from being interrupted at a maximum level.
The topology structures of data redundancy for HLRs are classified into two types. One is 1+1 redundancy solution, and the other is N+1 redundancy solution.
The so-called 1+1 redundancy solution is to provide a redundant HLR for each master HLR in the existing network so as to achieve real-time backup for external services. Though the 1+1 redundancy solution is able to take over the services seamlessly by adopting the redundant HLR when the master HLR fails, apart from some extremely important places, the application field of this solution is relatively limited in consequence of its high investment and low rate of utilization.
The N+1 redundancy solution is to set up a special redundant center HLR for providing redundancy for N master HLRs. In the N+1 redundancy solution, the redundancy can be further divided into compatible redundancy and non-compatible redundancy according to the result whether the master HLRs and the redundant center HLR belong to the same manufacturer. Because there are many HLR equipment providers, and different HLRs have different data saving formats and data processing methods, the compatible solution is more widely used. Since the N+1 compatible redundancy solution is unable to back up subscribers' dynamic data in real time, it will lead to the situation that the subscribers cannot act as the called party in a period of time after a failure has appeared and the services have been taken over. However, as one redundant center is able to back up data for a plurality of master HLRs made by different manufacturers, the return rate on investment of the N+1 compatible redundancy solution is relatively better, thus this solution is broadly adapted in the network.
At present, the N+1 compatible redundancy solution mainly has two types, one is a baseline synchronization solution, and the other is a BOSS (Business Operation Support System) increased command synchronization solution.
What is called the baseline synchronization solution is to output the data files containing all subscribers' subscription information, i.e., the service data baseline of subscriber, by the master HLRs periodically, then convert the format of these files automatically by the redundant center into the format recognizable by the redundant center HLR, and load the files into the redundant center HLR. Thereby, it will realize the synchronization of subscribers' data between the master HLRs and the redundant center HLR. As the baseline synchronization solution requires the master HLRs to output the service data baseline of all subscribers periodically, performance of the host machine of the redundant center HLR is affected greatly, and it takes quite a long time to perform conversion and synchronization for the subscribers' data, it is seldom used in practical engineering.
The BOSS increased command synchronization solution is to convert the successfully executed business operation commands which were formerly sent to the master HLRs for modifying the subscribers' subscription data according to the interface format of the redundant center HLR, and load the commands into the host machine in real time via the business operation interface of the host machine of the redundant center HLR. Thus, as long as the master HLRs and the redundant center HLR implement baseline synchronization for one time in initial state, the conformity of the subscribers' data between the master HLRs and the redundant center HLR will be guaranteed by means of this way to achieve the synchronization of the subsequent increased command or data.
Since the BOSS solution does not have any special requirements on the performance and function of the host machine of the redundant center HLR, and only needs to add converting function for operation commands of different manufacturers' formats in the BOSS, this solution is simple and is low cost because of low engineering work required. Therefore, the solution is widely used in the network and has gradually turned into a mainstream of N+1 redundancy solution.
However, only operation commands processed by the business hall can be synchronized automatically by the BOSS solution, a large number of other operation commands processed out of the business hall, such as the operation commands for setting a batch of subscriber services in a Local Maintenance Terminal (LMT) of HLR, and setting parameters of HLR in the system level, can merely be synchronized manually by the administrator in terms of the procedure. Therefore, the maintenance workload of this solution is heavy.