Location tracking with distributed HLR's and pointer forwarding

Location tracking operations in a personal communications service (PCS) network are expensive. A location tracking algorithm called pointer forwarding has been proposed to reduce the location update cost. The key observation behind forwarding is that if users change PCS registration areas (RAs) frequently, but receive calls relatively infrequently, it should be possible to avoid registrations at the home-location register (HLR) database by simply setting up a forwarding pointer from the previous visitor-location register (VLR). Calls to a given user will first query the user's HLR to determine the first VLR, which the user was registered at, and then follow a chain of forwarding pointers to the user's current VLR. To reduce the “find” cost in call delivery, the PCS provider may distribute HLR databases in the network. This paper integrates the concept of distributed HLRs with pointer forwarding, and the new scheme is referred to as the pointer forwarding with distributed HLR (PFDHLR). Since no registration to the HLR is performed in the pointer forwarding scheme when a user moves to the new locations, the cost of updating multiple HLRs is eliminated in PFDHLR. Our study indicates that PFDHLR may significantly reduce the mobility management cost compared with the single HLR approach     

A caching strategy to reduce network impacts of PCS

We propose an auxiliary strategy, called per-user caching, for locating users who move from place to place while using Personal Communications Services (PCS). The caching strategy augments the basic location strategy proposed in existing standards such as GSM and IS-41, with the objective of reducing network signaling and database loads in exchange for increased CPU processing and memory costs. Since technology trends are driving the latter costs down, the auxiliary strategy will become increasingly attractive. The idea behind caching is to reuse the information about a called user's location for subsequent calls to that user, and is useful for those users who receive calls frequently relative to the rate at which they change registration areas. This idea attempts to exploit the spatial and temporal locality in calls received by users, similar to the idea of exploiting locality of file access in computer systems. We use a reference PCS architecture and the notion of a user's local call-to-mobility ratio (LCMR) to quantify the costs and benefits of using caching and classes of users for whom it would be beneficial. We also present two simple algorithms for estimating users' LCMR and the situation in which each is preferable. We show that under a variety of assumptions caching is likely to yield significant net benefits in terms of reduced signaling network traffic and database loads     

Double Delegation-Based Authentication and Key Agreement Protocol for PCSs

Many protocols have been proposed for solving the user authentication in portable communication system. One of the schemes is based on the delegation concept. Home Location Register (HLR) delegates Mobile Station (MS) to be authenticated by Visitor Location Register (VLR). The main drawback of the scheme is that the HLR is required during the online authentication phase between VLR and MS. In this paper, a double delegation-based authentication and key agreement protocol is proposed. The main advantage of our protocol is that this scheme requires only MS and VLR online. This protocol will thoroughly utilize the proxy signature features to facilitate the operation of this protocol while only requires two members (MS, VLR) to be online at the same time.     

Enhanced privacy and authentication for the global system for mobile communications

The Global System for Mobile Communications (GSM) is widely recognized as the modern digital mobile network architecture. Increasing market demands point toward the relevancy of securityrelated issues in communications. The security requirements of mobile communications for the mobile users include: (1) the authentication of the mobile user and Visitor Location Register/Home Location Register; (2) the data confidentiality between mobile station and Visitor Location Register, and the data confidentiality between Visitor Location Register and Visitor Location Register/Home Location Register (VLR/HLR); (3) the location privacy of mobile user. However, GSM does not provide enough security functions to meet these requirements. We propose three improved methods to enhance the security, to reduce the storage space, to eliminate the sensitive information stored in VLR, and consequently to improve the performance of the system. Proposed methods include an improved authentication protocol for the mobile station, a data confidentiality protocol, and a location privacy protocol. The merit of the proposed methods is to improve but not to alter the existing architecture of the system. Furthermore, this study also performs computational and capacity analyses to evaluate the original GSM system and proposed approaches on a comparative basis.     

带门槛的环形搜索移动性管理策略中移动台所 越过的位置区环数

位置管理或移动性管理是移动计算研究领域的一个具有挑战性的问题.我国及其他国家目前正在使用的个人通信网络如GSM、IS-41中,用两层数据库HLR/VLR支持位置管理.在这些网络中,每当移动台从一个位置区LA(Location area)移动到另一个位置区,其基本的位置管理策略(简称"基本策略")不管是否必要均立即进行位置更新操作,因而造成系统资源的极大浪费,降低了系统的性能.本文给出一种带门槛的环形搜索策略(简称"门槛环形策略")——将位置区分成环,设定一个门槛(整数),当移动台越过的位置区的环数没有达到门槛时,系统不进行位置更新操作,以减少位置管理的费用.在假定移动台的呼入是一个泊松过程,移动台在各个位置区的逗留时间是符合一般概率分布的随机变量的条件下,推导出在两次呼入之间移动台处于各位置区环的概率及移动台所越过的位置区环数公式,给出了"门槛环形策略"的位置管理费用小于"基本策略"的条件.     

Location Management in PCS Networks by Caching Two-Level Forwarding-Pointers

One of the challenging tasks in Personal Communication Services (PCS) is to efficiently maintain the location of PCS subscribers who move from one region to another (hereafter called mobile users). When a mobile user receives a call, the network has to quickly determine its current location. The existing location management scheme suffers from high signaling traffic in locating the mobile users. Two-level forwarding pointer scheme has been proposed from per-user forwarding pointer scheme to reduce the cost of signaling traffic. In this paper, we enhance the two-level forwarding pointer scheme. When a mobile user moves from its current Registered Area (RA), which is served by Mobile Switching Center (MSC), to another RA the local switch that acts as a parent of those two MSCs maintains this movement in its memory (hereafter called cache entry). A cache entry is used to locate rapidly the mobile user instead of querying the Home Location Register (HLR) and waiting for its reply. HLR is centralized in the network and far away from the mobile users so that the signaling traffic crossing it is expensive. Sometimes the cache entry may be failed to reach the mobile user then a two-level forwarding pointers will be created from the corresponding Visitor Location Register (VLR), attached to its MSC, through a correct path to locate the mobile user. Thus, there is a saving in cost of querying the underlying HLR. The analytical results indicate that such proposal efficiently reduces the signaling traffic cost for all values of Call to Mobility Ratio (CMR), this is especially considerable when CMR ≥1, without any increase in the call setup delay. Salah M. Ramadan (samohra@yahoo.com) received the BS and MS degrees from Computers Engineering Department, Al-Azhar University, Cairo, Egypt, in 1995 and 2002, respectively. From 2002, he was a Ph.D. student in Computers Engineering Department at Al-Azhar University and is currently pursuing the Ph.D. degree, where he is a research assistant in the Wireless Networks Branch. His research interests include traffic management in ATM networks, routing protocols, mobility management in PCS networks, and mobile computing. He is currently an instructor in Cisco Academy, Egypt. Ahmed M. El-Sherbini (Sherbini@mcit.gov.eg) received the Ph.D. in Electrical and Communication Engineering, Case Western University, U.S.A. March 1983 and M.Sc. in Communication Engineering, Cairo University, Giza, Egypt, June 1980. (M. Sc. Research Studies at the Ecole Nationale Superieure des Telecommunications (ENST), Paris, France). He is the Director, National Telecommunication Institute – Ministry of Communications and Information Technology, Egypt and Professor of Electrical and Communication Engineering Dept. Faculty of Engineering, Cairo University, Egypt. M. I. Marie received his B.Sc., M.Sc. and Ph.D. in electronic and communication engineering from Cairo University on 1972, 1981, 1985, respectively. Now he is a professor of communications at Computer and System Engineering department Al-Azhar University, Cairo, Egypt. His fields of interest includes digital communication, computer networks and protocols development. M. Zaki (azhar@mailer.scu.eun.eg) is the professor of software engineering, Computer and System Engineering Department, Faculty of Engineering, Al-Azhar University at Cairo. He received his B.Sc. and M.Sc. degrees in electrical engineering from Cairo University in 1968 and 1973 respectively. He received his Ph.D. degrees in computer engineering from Warsaw Technical University, Poland in 1977. His fields of interest include artificial intelligence, soft computing, and distributed system.     

基于阈值的两级指针推进的移动性管理策略

提出了基于阈值的两级指针推进策略(TPFT,two-level pointer forwarding with thresholds)将一部分VLR(visitor location register)中的移动用户选为移动代理(MA,mobile agent),在MA之间建立第一级指针链;在MA与VLR之间建立第二级指针链,两级指针链均设定长度阈值。将该策略与“基本位置管理策略”及“通行用户指针推进策略”和“带门槛的指针推进策略”的开销进行比较得出:选择适当的两级阈值,TPFT策略的开销优于上述策略。同时,TPFT策略是将系统中对HLR(home location register)的修改与查询的信号量分布到各个MA中,提高了系统效率。     

一种改进的基于HLR/VLR体系结构的终身号码方案

在PCS系统中，终身号码允许用户在改变运营商时保留其原有电话号码，本文提出的基于HLR/VLR体系结构Cache改进算法，能保证用户在多次改变运营商时，使用户实现真正的号码携带。在当前无线网络运营中，基于HLR/NLR体系结构位置管理的无线网络取得了极大成功，使得研究基于HLR/NLR体系结构的终身号码方案具有非常重要的现实意义。与原基于HLR／VLR位置管理Cache算法相比，本文算法的实现只需要软件升级和存储器扩容。随着软硬件技术的发展，使本文提出的方案具有较强的可行性。     

3G移动网络中逆向GLR故障恢复算法及分析

在3G网络中,当漫游用户在网关位置寄存器(GLR)中的位置信息不正确时,其位置查询将失败,此时将严重恶化系统性能,而传统的位置恢复算法需占用大量长途电路资源。为减少GLR位置恢复过程中对长途电路资源的占有及缩短GLR故障恢复时延,本文提出了一种新的算法逆向GLR故障恢复算法。该算法充分利用用户在访问位置寄存器(VLR)中的用户信息,从而避免在恢复过程中GLR和归属位置寄存器(HLR)的长途信令开销。通过对算法的性能作分析,证明所提出的算法是可行的。     

Improving the fault tolerance of GSM networks

A PCS network constantly tracks the locations of the mobile stations so that incoming calls can be delivered to the target mobile stations. In general, a two-level database system is used to store location information of the mobile stations. When the location databases fail, incoming calls may be lost. This article describes the standard GSM database failure restoration procedure which reduces the number of lost calls. Then we propose an efficient visitor location register (VLR) identification algorithm for the home location register (HLR) failure recovery procedure, which utilizes mobile station movement information to speed up the recovery procedure     

个人通信系统中的用户登记认证

个人通信系统(PCS)的智能网络层上每个结点的数据库采用全分布式结构。根据PCS的智能层数据库结构特点以及X.509目录认证架构,提出了一种移动用户登记认证方案。此方案克服了X.509所具有的“静态”特性,使其能够满足PCS用户移动性及终端移动性的要求。在进行用户登记认证的同时,用户与本地的访问网络之间还建立起一个秘密数据。基于这一秘密数据,用户与网络之间可以在呼叫建立阶段进行相互认证。这就避免了现有的移动通信系统(如GSM,IS-41等)呼叫建立阶段的认证受归属网位置登记数据库(HLR)控制的缺陷。因此,用于位置修订和查询的信令负荷大大减小;同时,有关骨干网络(如PSPDN或共路信令网)安全的假定也可以被取消。     

Research on HLR mobility database failure recovery and performance analysis for CDMA2000 systems

In this paper, a novel Home Location Register(HLR) mobility database recovery scheme is proposed. With database backing-up and signal sending as its key processes, the presented scheme is designed for the purpose of both decreasing system costs and reducing number of lost calls. In our scheme, an algorithm is developed for an HLR to identify such VLRs that there are new MSs roaming into them since the latest HLR database backing up. The identification of those VLRs is used by the HLR to send Unreliable Roaming Data Directive messages to each of them to get the correct location information of those new MSs.Additionally, two kinds of relationships, one between the number of lost calls and the database backing-up period and the other between the backing-up cost and the period, are well analyzed. Both analytical and numerical results indicate that there will be an optimal HLR database backing-up period if certain system parameters are given and the total cost can be consequently minimized.     

一种3G中基于三层数据库的呼叫建立机制研究

基于3G网络三层数据库结构中GLR (Gateway Location Register)服务区远大于VLR (Visitor Location Register)服务区的情况,考虑被呼业务本地化(即本地移动用户呼叫本地移动用户的比例占总呼叫数的比例大),通过在GLR中设置缓存的方法,给出了一种新的呼叫建立机制。建立分析模型得到新机制的总代价函数和总时间延迟函数,并同基本呼叫建立机制以及2G网络基于VLR缓存的呼叫建立机制进行了对比分析,验证了新呼叫建立机制的优越性。     

More efficient location tracking in PCS systems using a noveldistributed database system

In personal communication services (PCS), the complete location information and subscribers' profiles are kept in a database called the home location register (HLR). Another database, the visitor location register (VLR), is used to store partial location information. When a mobile user is called, the system queries the HLR to determine the location of the called party. Distributed databases have been introduced to improve the efficiency of querying the HLR. This paper presents an alternative means of constructing a distributed database. The proposed database design employs fixed pointers to link distributed data. Each database contains a portion of the system's information as well as several pointers. The pointers identify the location of real data, enabling the system to obtain the required information efficiently. The database of the proposed design is markedly smaller than the fully distributed databases since each database of the proposed design stores only partial information. Subscriber information is stored only in one database, thus allowing a single database, rather than multiple databases, to be updated. The single update presented herein notably reduces the signal traffic load. If the caller is in the registration area of some HLR, which holds the called party's information, the response time is significantly decreased since the transactions are served only by the local database. This phenomenon is referred to as the calling locality. The proposed method effectively shares the database and the network loading that originates from several databases' tracking mobile users in a PCS system. According to the results presented, this method is highly effective for systems with a heavy load and high calling locality. The single update feature of the proposed design reduces the traffic in the signaling link and the processing load of a database. However, the proposed method includes no fault tolerance and therein differs from the fully distributed design     

3G 蜂窝网络中GLR 故障恢复分析

在3G蜂窝网络中,归属位置寄存器(HLR)、网关位置寄存器(GLR)、访问位置寄存器(VLR)组成三级数据库结构。当漫游移动用户在GLR中的位置信息错误或过时时,对该用户的入呼将失败。由于三层结构设计中,GLR与HLR的通信一般涉及国际长途信令,使得GLR的故障恢复设计非常重要。为尽可能减少对长途资源的占有,对GLR故障恢复提出了一种新的算法并对其性能作了相应的分析。     

HLR Replication Protocols for Global Mobility Management in PCS Networks

The new trend for PCS networks is to provide mobile users with large-scalemobile capability across many service areas. In this scenario, global databasemanagement for PCS networks has become an increasingly important researchissue.In this paper, we examined two replicated database strategies,single-replica (SR) and multiple-replica (MR), for large-scalemobility of per-user data management in personal communicationnetworks. The SR strategy uses a single replica approach of HLR.The MR strategy replicates the per-user data of HLR in manyregions. The two strategies are based a partial replicationscheme, and a primary copy method is used to maintain replicas'consistency. Our numerical results show that the MR strategyoutperforms the SR strategy in most situations; however, it may beworse when the probability of a mobile user visiting a foreignregion is high and the query rates from other foreign regions arelow. Additionally, the number of replicas should be compact in theMR strategy in order to achieve a reasonable query response time.Therefore, we propose an adaptive multiple replication protocol tochoose a suitable replication strategy and to decide the optimizednumber of replicas.     

One-step pointer forwarding strategy for location tracking indistributed HLR environment

One of the main challenges in personal communication service (PCS) is to locate many mobiles that may move frequently from place to place. Such a system operation is called location tracking. Many network signals flow, and database queries are required to achieve such a task. In addition to the two-level hierarchical strategy in IS-41 and GSM, several strategies have been proposed to improve the efficiency of location tracking. Pointer forwarding was used to reduce the expensive home location register (HLR) accesses. Previously, the distributed HLR scheme was proposed to prevent the HLR from becoming a bottleneck in the signaling network. However, the length of a forwarding pointer chain may be lengthened in a distributed HLR environment. We propose a more efficient strategy to overcome this potential problem. This strategy attempts to migrate the locating chains in a distributed HLR system when a mobile issues a registration operation. As a consequence, the length of any forwarding pointer chain does not exceed one in our strategy. Simulation results indicate that our strategy significantly decreases the locating cost. In fact, this strategy provides an upper bound of location tracking time owing to the fact that the length of any locating path does not exceed one. Furthermore, obsolete entries in local databases visitor location registers can be reclaimed in this strategy     

低空空域VHF动态接入移动性管理

低空空域超短波( VHF)动态接入移动性管理技术是保障低空飞行不间断、跨区域通信的关键。根据低空空管通信网络框架,设计了低空空管二级移动性管理模型;借鉴GSM经典移动性管理模型,引入访问/归属位置寄存器机制,解决了地面通信网有效管理低空飞行器位置信息的问题。详细阐述了登记注册、入网/退网、站内移动性管理和站间移动性管理等流程。最后,分析了移动性管理时延,并给出了系统演示和仿真,为进一步研究打下了基础。     

Demand re‐registration for PCS database restoration

In a Personal Communications Services (PCS) network, mobility databases such as Home Location Register (HLR) and Visitor Location Register (VLR) are utilized to support mobility management for Mobile Stations (MSs). If the location databases fail, the location information loss or corruption will seriously degrade the service offered to the subscribers. In this paper, we propose a new VLR failure recovery scheme called demand reregistration. In this scheme, the VLR broadcasts a reregistration request to all MSs after the VLR failure. When an MS receives the reregistration request, it sends a registration message to the VLR to recover the location record. Since all MSs will reregister after receiving the broadcasting request, traffic jam (and thus collisions) may occur. If a collision occurs, then the involved MSs must resend the registration messages. This paper studies the performance of demand reregistration by investigating how effectively the reregistration can recover the location record for an MS before the first MS call termination occurs. Our results indicate that demand reregistration can effectively recover VLR failure.