ISSN: 2250-3005 - ijcer

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International Journal Of Computational Engineering Research (ijceronline.com) Vol. 2 Issue. 8Avoidance of Bottleneck in PCS NetworkSidhi Pandey 1 , Alka 2 , Pratima Singh 31, 2, 3(Computer Science & Engineering, Institute of Technology & Management, India)Abstract:This paper contains the concept of Personal Communication Service (PCS) network and schemes to avoidbottleneck in PCS network. One of the key issues in mobile communication is to find the current location of mobile terminal(MT) to deliver the services, which is called as location management. In this paper we will discuss various schemes forimproving location management in PCS network and focus on surveying the location management mechanis ms in PCSsystem.Keywords: De-registration, hand-off, HLR/VLR, Location Management, Mobile terminal, MSC, PCS.1. Introduction:Cellular communicat ion has been experiencing a rapid growth in recent years. From its introduction in the early1980s, cellular communication has been evolved from a costly service with limited availability toward an affordablealternative to wired telephone service. This wide acceptance of cellular communication has led to the development of a newgeneration of mobile communication network called personal communication services, which can support a large mobilesubscriber population while providing various types of services unavailable to traditional cellular system [1].PersonalCommunication Services networks provide wireless communication services that enable mobile terminals to transfer anyform of information between any locations at any time. To support user mobility, the Personal Communication Servicesnetworks have to store and maintain location information of mobile stations so that an incoming call can be delivered to thetarget Mobile Station. The operations on location information consist of location updates and location queries. An updateoccurs when a Mobile Station changes location. A query occurs when a Mobile Station needs to be located, e.g., to deliver anincoming call to this Mobile Station. The widespread deployment of Personal Communication Services will lead to atremendous increase in the number of updates and queries to the location database. Thus, a key challenge to locationmanagement is to develop efficient database architecture so that the location data can be readily available for signaling suchas call setup and routing [1].2. Location management:In cellular systems a mobile unit is free to move around within the entire area of coverage. Its movement is randomand therefore its geographic allocation is unpredictable. This situation makes it necessary to locate the mobile unit and recordits location to Home Location Register and Visitor Location Register when a call has to be delivered to it. Thus, the entireprocess of the mobility management component of the cellular system is responsible for two tasks:2.1 Location Management:It is identification of the current geographical location or current point of attachment of a mobile un it which isrequired by the Mobile Switching Center to route the call.2.2 Hand-off:It is transferring (handing off) the current (active) communication session to the next base station, which seamlesslyresumes the session using its own set of channels.The entire process of location management is a kind of directory management problem where current locations ofMU are maintained continuously. Location management involves tracking of Mobile Terminal's location, moving from placeto place so as to provide those services timely. Two basic operations in mobility tracking are: location update and paging.Basically, whenever Mobile Terminal moves out of its current LA, its geographical location information is updated to thenearest Base Station. On a call arrival, the network searches the called Mobile Terminal by sending polling signals to thevicinity of last reported location of Mobile Terminal. This searching process is called paging. The total LocationManagement cost is generally calculated by summing up the cost of location update and paging. Normally, the LocationUpdate costs higher than paging. The network can require more frequent Location Updates, in order to reduce paging cost.Inversely, the network may require rare Location Updates, storing less information about user mobility to reducecomputational overhead, but at a higher paging cost. To reduce the total location man agement cost, it is essential to providegood trade-off among paging and Location Update operations One of the main objectives of efficient location managementschemes is to minimize the communication overhead due to updating of Home Location Register. The other related issue isthe distribution of Home Location Register to shorten the access path, which is similar to data distribution problem in||Issn 2250-3005(online)|| ||December||2012|| Page 245
International Journal Of Computational Engineering Research (ijceronline.com) Vol. 2 Issue. 8distributed database systems. Motivated by these issues, recently a number of innovative location management sch emes haveappeared in the research world.The location management approaches can broadly be classified as: Centralized approaches and Distributed approaches.Centralized approach keeps information only on one node in the mobile network. For example, exist ing location managementstandards, IS-41 and Global System for Mobile Communication are centralized approaches. Location lookup and updateoperations are simple in this case but they suffer from severe problems like congestion, central point failure etc. InDistributed approaches user information is distributed among many nodes in the network. This has better stability incomparison to centralized approach but location lookup and update operations are somewhat complex in this case. However,many schemes have come forward to solve this problem [7].3. Conventional HLR/VLR scheme:In this section we will describe the existing standard of location management along with the approaches to overcomeits drawbacks. The two popular standards used are Global System for Mobile Communication and IS-41. They make use oftwo types of registers namely, Home Location Register and Visitor Location Register. These two registers are used to storethe location information of the mobile terminals [3]. Figure 1 shows the basic architecture under this two-level hierarchy.Figure 1: Standard Personal Communication Network architectureThe Home Location Register stores the user profiles of its assigned subscribers. These user profiles containinformation such as the type of services subscribed, the quality-of-service requirements and the current location of the mobileterminals. Each Visitor Location Register stores replications of the user profiles of the subscribers currently residing in itsassociated LA. In order to effectively locate a mobile terminal when a call arrives, each mobile terminal is required to reportits location whenever it enters a new LA. This reporting process is called location update. On receiving a location updatemessage, the Mobile Switching Center updates its associated Visitor Location Register and transmits the new locationinformation to the Home Location Register. We call this register update process as location registration. The Home LocationRegister will acknowledge the Mobile Switching Center for the successful registration and it will also deregister the mobileterminal at the Visitor Location Register of old LA. In order to locate a mobile terminal for call delivery, the Home LocationRegister is queried to determine the serving MSC of the target mobile terminal. The Home Location Register then sends amessage to this Mobile Switching Center which, in turn, will determine the serving base station of the mobile terminal bypaging all cells within its associated LA. This location tracking scheme requires the exchange of signaling messages betweenthe Home Location Register and the new and old Mobile Switching Center's whenever the mobile terminal crosses an LAboundary. This may result in significant traffic load to the network especially when the current location of the mobileterminal is far away from its Home Location Register and the mobile terminal is making frequent movements among LA's.Besides, the Home Location Register may experience excessively high database access traffic as it is involved in everylocation registration and call delivery. This may result in increased connection set up delay during periods of high networkutilization [3].The major steps of the IS-41 location registration scheme are as follows (Fig 2)Step 1: The mobile terminal moves into a new LA and sends a location update message to the nearby base station.Step 2: The base station forwards this message to the new serving Mobile Switching Center.Step 3: The new Mobile Switching Center updates its associated Visitor Location Register, indicating that the mobileterminal is now residing in its services area and sends a location registration message to the Home Location Register.Step 4: The Home Location Register sends a registration acknowledgement message to the new Mobile Switching Center/Visitor Location Register together with a copy of the subscriber’s user profile.Step 5: The Home Location Register sends a registration cancellation message to the old Mobile Switching Center/ VisitorLocation Register.||Issn 2250-3005(online)|| ||December||2012|| Page 246
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