Introduction:
Super-charger concept is a mobility related concept located in Core Network. The aim of Super-Charger concept is to reduce the mobility management signalling (and costs) associated with inter-VLR and SGSN location updates.
Bacic Concept:
The concept of super-charged networks is very simple. At present in UMTS networks (or GSM networks; This policy can be applied to GSM networks as well), when a UE moves from one MSC/VLR (or SGSN) to another, HLR inserts UE related data in the new MSC/VLR and removes it from old MSC/VLR. In a super-charger network, the main change is that the HLR will not remove the subscriber data from the old MSC/VLR.
This might look like a very small change but it could have significant impacts. The Subscribers typically move around same routes everyday. A typical journey includes going from Home to Office/workplace in the morning and returning back to home in evening. In traditional network this causes the following signalling:
1. Update Location Request (New MSC/VLR --> HLR)
2. Cancel Location (HLR --> Old MSC/VLR)
3. Cancel Location Response (Old MSC/VLR --> HLR)
4. Insert Subscriber Data (HLR --> New MSC/VLR)
5. Insert Subscriber Data Response (new MSC/VLR --> HLR)
6. Update Location Response (HLR --> New MSC/VLR)
If instead Super-charged ntwork is used then the signalling will be as follows:
1. Update Location Request (New MSC/VLR --> HLR)
2. Update Location Response (HLR --> New MSC/VLR)
The above signalling examples are ofcourse ideal scenarios. In case the subscriber information changes between the two updates then some intermediate signalling would be needed. This would stil be much less then the traditional networks ofcourse.
[1] explains the above concept with the help of diagram as shown below: (shamelessly copied from [1])
Problems and Solutions:
The obvious problem associated with Super-Charger concept is that the subscriber data is never deleted and hence the size of database required to store this data would keep growing continuously. The standards propose three schemes to handle this problem. Other schemes can be implemented depending on the operator.
Utilisation of Larger Databases: The database size will have to be increased significantly to handle data of these new UE's. Even though this scheme will help, it will not remove the need for other schemes.
Periodic Audit Scheme: A periodic audit will be performed (say every couple of days) and all the users that have been found to be inactive for a specified period of time can be removed from the database. The period will depend of course on the size of the database and the network activity. This would also mean that a new paramater, 'age' would need to be stored in the database that will contain the time elapsed since the last Iu interface activity.
Dynamic Subscriber Data Deletion: This scheme allows run time removal of information from database. When the database reaches a critical level, the old subscriber data can be removed. It would be based on the oldest cell being removed first.
Advantages:
1. Reduction in volume of signalling traffic associated with Mobility. The Cancel Location Procedure will become redundant.
2. No new network entities are required to implement this.
3. In the CS Domain, super-charger can remove additional signalling between the old and new entities in inter-VLR location updates.
4. The implementation impact is quite low as the majority of Super-Charger concept refers to internal functionality. Some MAP messages would require minor enhancements though.
Disadvantages:
Removal of the PURGE MS means that the HLR is not notified when a subscriber is removed from a particular VLR or SGSN. Consequently, the HLR will continue to route calls and packets to the respective entities where the subscriber information was deleted assuming that that was the last reported location of the subscriber. This will increase mobility related signalling traffic, and cause extra work for the GMSC, HLR, MSC/VLR and SGSN if the subscriber cannot be reached. However, the enhancement of the provide roaming number response message and the optionally the deployment of Super-Charger in conjunction with Pre-Paging will limit the impact of this disadvantage.
References:
[1] 3GPP TR 23.912: Technical Report on Super Charger; Release 4
[2] 3GPP TS 23.116; Super-Charger Technical Realisation; Stage 2; Release 5
[3] 3GPP TR 23.908: Technical Report on Pre-Paging; Release 4