A Distributed Database Architecture for Global Roaming in Next-Generation Mobile Networks

ABSTRACT

The next-generation mobile network will support terminal mobility, personal mobility, and service provider portability,making global roaming seamless. A location-independent personal telecommunication number (PTN) scheme is conducive to implementing such a global mobile system. However, the non geographic PTNs coupled with the anticipated large number of mobile users in future mobile networks may introduce very large centralized databases. This necessitates research into the design and performance of high-throughput database technologies used in mobile systems to ensure that future systems will be able to carry efficiently the anticipated loads. This project proposes a scalable, robust,efficient location database architecture based on the location-independent PTNs. The proposed multi tree database architecture consists of a number of database subsystems, each of which is a three-level tree structure and is connected to the others only through its root. By exploiting the localized nature of calling and mobility patterns, the proposed architecture effectively reduces the database loads as well as the signaling traffic incurred by the location registration and call delivery procedures. In addition, two memory-resident database indices, memory-resident direct file and T-tree, are proposed for the location databases to further improve their throughput. Analysis model and numerical results are presented to evaluate the efficiency of the proposed database architecture.Results have revealed that the proposed database architecture for location management can effectively support the anticipated high user density in the future mobile networks. A Distributed Database Architecture for Global Roaming in Next-Generation Mobile Networks

EXISTING SYSTEM:

The existing method uses current two-level database architecture. Two main categories of strategies have been proposed: auxiliary strategies based on the two-level database architecture and distributed strategies employing the hierarchical database architecture.The auxiliary strategies try to exploit the spatial and temporal locality in each user’s calling and mobility patterns to reduce the signaling traffic and database loads. Examples include the forwarding strategy, the anchoring strategy, the caching strategy,and the replication strategy. In the forwarding strategy ,a forwarding pointer is set up in the old VLR pointing to the new VLR of an MT to avoid a location update at the HLR as theMT changes its RA. When a call for the MT arrives, the HLR isqueried first to determine the first VLR which the MT was registered at, and a forwarding pointer chain is followed to locate the MT in its current VLR. The forwarding strategy reduces location update signaling but increases the call setup delay. Thus,the length of the forwarding point chain needs to be limited. Itis shown that this scheme may not always result in a cost savings as compared to the standard IS-41 scheme. The forwarding scheme is effective only when the call arrival rate is low relative to the mobility rate for an MT. With the anchoring strategy,location updates are performed at a nearby VLR (i.e, localanchor) for an MT to reduce signaling traffic between the HLRand the VLRs. The HLR maintains a pointer to the MT’s local anchor. As an incoming call occurs, the HLR forward the call to the local anchor, which in turn queries the serving VLR of the MT for a TLDN. The call delivery time is increased due to one extra database query to the local anchor. Similar to the forwarding scheme, the local anchoring scheme is efficient only when an MT’s call arrival rate is low relative to its mobility rate.With the caching strategy , an MT’s location obtained from previous call is cached and re-used for subsequent calls to that MT. After a cache entry of the MT’s location information is created at a signal transfer point (STP), if another call for the MTis received by the STP, the STP will forward the call to the VLRas specified by the cache. If the MT is still in the same VLR,a hit occurs and the call is successfully delivered. However, if the MT has moved to another VLR, a miss occurs and the IS-41call delivery process has to be followed to find the MT, thus incurring a much longer setup delay. When an MT changes its location more often than receiving calls, the caching scheme may become inefficient in reducing cost. In the replication strategy, an MT’s location is replicated at selected local databases,so that calls to the MT originating from the service area of these replicated databases can be routed without querying the HLR.When the MT changes its location, all replicated databases need to be updated for the MT, thus incurring a high database update load and signaling traffic, especially for highly mobile users.In summary, each auxiliary strategy outperforms the IS-41 only under certain calling and mobility parameters. As the cell sizes become smaller to support an increasing user density and the number of mobile subscribers increases, even these augmentation swill not be sufficient to meet the future demands of mobile networks.It becomes obvious that reducing the access rate to the centralizer is a critical step to support an increasing number of mobile subscribers. The hierarchical database architecture can reduce the access load on an upper-level database by distributing query load into the lower-level databases, thus it has been studied extensively in previous research.An extra level of databases called directory registers(DRs), was added between the HLR and the VLRs of current cellular systems. The DR periodically computes the location information distribution strategy for each associated MT in order to achieve a reduced access rate to the HLR. The performance of this scheme depends on the availability and accuracy of the user’s calling and mobility parameters. It is usually computationally intensive to obtain these parameters. Given the large number of MTs, the burden on the DRs would be very heavy.

PROPOSED SYSTEM:

The proposed database architecture for location tracking isa multi tree structure, where each subsystem is a three-level architecture(Fig. 1), referred to as a database subsystem (DS) inthis project. Various DSs may represent networks operated possibly by different service providers. All these DSs are interconnected together via a fixed network, such as PSTN or ATM network,and communicate with each other only through their root databases. This architecture can support a multi operator environment which is expected in future mobile networks. In eachDS, databases DB0 and DB2 may correspond to the HLR and the VLR in the two-level database system, respectively. EachDB2 may control an RA where a user can roam freely without triggering registrations. Each DB2 is colocated with an MSC,which performs call processing on origination or termination calls. A number of DB2s are grouped into one DB1 and severalDB1s are connected to a single DB0. Each DB1 and DB0 also needs a switch, called the STP, that provides routing functionality for message exchange between various location databases.The DB0 maintains the service profile for each user currently residing in its service area, and maintains an entry for each user inthe global mobile system. The entry contains either a pointer to another DB0 where the user is residing or a pointer to the user record that contains a pointer to the DB1 with which the user is currently associated. Each DB1 has an entry for every currently residing user, storing a pointer to the DB2 the user is currently visiting. Every DB2 has a copy of the service profiles of the users currently roaming within its area. With this architecture,the frequency of queries to the higher level databases is greatly reduced due to the locality of calling and mobility patterns.However, when a call or a location update is not local,more databases—including the large centralized databaseDB0—need to be visited. This increases the end-to-end delay sin call setup and location registration. In addition, as the number of mobile subscribers increases, the access time of each database is increased, which also increases the end-to-end delays. To meet the delay demands in call setup and location registration, the number of database levels in a DS has to be limited. Moreover, to support a larger amount of mobile subscribers while keeping the end-to-end delays low, it is critical to reduce the access times to the databases. Thus, investigation into efficient database access indices for the location databases is as important as research into the overall location database architecture.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Related Post