Super Charger Network Concept in UMTS Networks
By Zahid Ghadialy
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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.
Basic 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 network
is used then the signaling will be as follows:
1. Update Location Request (New MSC/VLR --> HLR)
2. Update Location Response (HLR --> New MSC/VLR)
The above signaling examples are of
course ideal scenarios. In case the subscriber information changes between
the two updates then some intermediate signaling would be needed. This would
still be much less then the traditional networks of course.
[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.
Utilization 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 parameter, '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.
1. Reduction in volume of signaling
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 signaling 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.
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 signaling 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.
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