Failure restoration of mobility databases for personal communication networks

This paper studies failure restoration of mobility databases for personal communication networks (specifically, VLRs and HLRs). We model the VLR restoration with and without checkpointing. The optimal VLR checkpointing interval is derived to balance the checkpointing cost against the paging cost. We also model GSM periodic location updating (location confirmation) to quantify the relationship between the location confirmation frequency and the number of lost calls. The HLR failure restoration procedures for IS-41 and GSM are described. We show the number of lost calls in a HLR failure. Both the procedures in IS-41 and GSM cannot identify the VLRs that need to be accessed by the HLR after a failure. An algorithm is proposed to identify the VLRs, which can be used to aggressively restore a HLR after its failure.     

移动网络前向指针策略的鉴权管理研究

鉴权管理是移动通信移动管理中非常重要的技术,其策略的选择将直接影响网络中各网元的信令负荷。本文主要讨论移动通信系统前向指针位置管理策略中的鉴权管理。当用户在远离其HLR的不同VLR对应覆盖区域移动时,系统通过向其原VLR索取剩余鉴权数据或向其HLR申请新鉴权数据来实现用户的鉴权管理。通过鉴权开销及被呼处理时延等指标的分析,本文提出的鉴权管理算法较适合于CMR较小的MS鉴权管理;当MS的CMR增大时,本文提出的鉴权管理算法与二层管理策略如GSM或IS-41移动系统的开销及时延等指标逐渐接近。     

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.     

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     

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     

Local anchor scheme for reducing signaling costs in personalcommunications networks

A personal communications network (PCN) location tracking scheme called local anchoring is introduced which reduces the signalling cost as compared to the location management strategy proposed in the IS-41 standard. Local anchoring reduces the number of location registration messages between the home location register (HLR) and the visitor location registers (VLRs) in a way that location change is reported to a nearby VLR called the local anchor (LA) instead of to the HLR. This method successfully reduces the cost for location tracking when the call arrival rate is low relative to the mobility rate and the cost for location registration is high. A dynamic local anchoring mechanism is then introduced which dynamically selects the LA such that the expected cost for location registration and call delivery can be further reduced. It is demonstrated that the cost of dynamic local anchoring is always lower than or equal to that of the IS-41 scheme     

A batch‐update strategy for the distributed HLRs architecture in PCS networks

Owing to the increasing population of mobile subscribers, the rapidly expanding signaling traffic has become a challenge to the mobility management in PCS networks. Multiple database schemes to reduce signal traffic and to solve the bottleneck problem of the single home location register (HLR) architecture have been proposed by many researchers. However, in most of the multiple location databases or HLR systems, extra signaling is required for the multiple database updates. We propose a batch‐update strategy, instead of the immediate update method, for the location‐tracking schemes with replication to reduce the signaling overhead. In this paper, we first introduce a distributed HLRs architecture in which each HLR is associated with a localized set of VLRs and the location registrations and queries are processed locally. Then we propose our batch‐update strategy and present two pointing schemes for inter‐HLR call deliveries. The numerical result shows that our approach can effectively decrease the signaling cost of location registration and call delivery compared with the IS‐41 standard. Copyright © 2002 John Wiley & Sons, Ltd.     

An efficient location cache scheme for three‐level database architecture in PCS networks

Recently, hierarchical architecture for location databases has been proposed in order to accommodate the growing number of personal communication systems users. With the three‐level hierarchical database architecture, which is compatible with the current cellular mobile systems, newly developed additional databases, including the regional location database (RLR), are positioned between the HLR and the VLRs. We propose an efficient cache scheme, the double T‐thresholds location cache scheme, which could reduce the network and database costs to lookup a portable using the three‐level architecture. This scheme extends the existing T‐threshold location cache scheme, which is effective only under the two‐level architecture of location databases currently adopted by IS‐41 and GSM. The idea behind our proposed scheme is to use two pieces of cache information, VLR and RLR, which serve the called portables. These two pieces are required in order to exploit not only the locality of a registration area (RA), but also the locality of a regional registration area (RRA), a wide area covered by the RLR. We also use two threshold values in order to determine whether the two pieces are obsolete. In order to model the RRA residence time, the branching Erlang‐∞ distribution is introduced. The cost analysis presented in this paper shows that the double T‐thresholds location cache scheme significantly reduces the network and database costs for most patterns of portables. Copyright © 2001 John Wiley & Sons, Ltd.     

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。     

Dynamic hierarchical database architecture for location managementin PCS networks

This paper introduces a dynamic hierarchical database architecture for location management in personal communications service (PCS) networks. The proposed scheme allows the dynamic adjustments of user location information distribution based on the mobility and calling patterns of the mobile terminals (MTs). A unique distribution strategy is determined for each MT, and location pointers are set up at selected remote locations which indicate the current location of the MTs. This method effectively reduces the signaling and database access overhead for location registration and call delivery. Besides, the required processing is handled by a distributed network of directory registers and centralized coordination is not necessary. The functions of the other network elements, such as the home location register (HLR) and the visitor location registers (VLRs), remain primarily unchanged. This greatly facilitates the deployment of this scheme in current PCS networks     

Phone number portability for PCS systems with ATM backbones usingdistributed dynamic hashing

Current cellular subscribers have a geographic phone number (e.g., in AMPS and US digital cellular systems) or a number which contains the network provider's identity (e.g., in GSM), and whenever subscribers register or receive (and possibly, originate) a call, a home location register (HLR) database has to be queried. The wired infrastructure supports a function called global title translation (GTT) that converts the subscriber's number to an HLR database address. A special feature of next generation wireless access service will be to support personal communication services (PCS) and wireless subscribers with portable personal numbers, or nongeographic phone numbers (NGPNs), that do not indicate the service provider or HLR database serving the user. In addition, the GTT function may not be available when the wired backbone is an ATM network. Thus a key function required in future wireless access systems with wired ATM backbones will be the ability to translate an NGPN to the identity of the HLR which serves the subscriber, a process we call NGPN translation. We discuss the requirements of NGPN translation and some alternative schemes. We propose two schemes for fast, efficient, scalable and flexible NGPN translation which use ideas of dynamic hashing, caching, and indirection. The schemes use a hash function in the visiting location registers (VLRs) (or serving SCP) and a set of distributed translation servers which store the NGPN-to-HLR mapping. We discuss how the operations required to maintain the translation information can be performed. Finally, we perform a simplified analysis of the scalability of the alternative schemes as well as the hash-based schemes we propose     

Two-level pointer forwarding strategy for location management in PCS networks

For a IPCS network to effectively deliver services to its mobile users, it must have an efficient way to keep track of the mobile users. The location management fulfills this task through location registration and paging. To reduce the signaling traffic, many schemes such as a local anchor (LA) scheme, per-user caching scheme and pointer forwarding scheme have been proposed in the past. In this paper, we present a new location management scheme which intends to mitigate the signaling traffic as well as reduce the tracking delay in the PCS systems. In this strategy, we choose a set of visitor location registers (VLRs) traversed by users as the mobility agents (MA), which form another level of management in order to make some registration signaling traffic localized. The idea is as follows: instead of always updating to the home location register (HLR), which would become the bottleneck otherwise, many location updates are carried out in the mobility agents. Thus, the two-level pointer forwarding scheme is designed to reduce the signaling traffic: pointers can be set up between VLRs as the traditional pointer forwarding scheme and can also be set up between MAs. The numerical results show that this strategy can significantly reduce the network signaling traffic for users with low CMR without increasing much of the call setup delay.     

Hybrid Scheme with Adaptive Replication and Mobility Anchoring Point (MAP) in Wireless Networks

Replication strategy is mostly useful for replicating the mobile user’s profile at selected locations from which some callers have higher calling rate. Location management scheme also include replication strategy to reduce the location lookup cost of called mobile user. It plays important role in personal communication services in order to reduce call setup cost, call setup time, and increases the QoS (quality of service). In prior replication schemes, called user’s location profile is placed at some fixed and limited number of visitor location registers (VLRs) based on call history of the caller. In prior hybrid schemes location update and replication strategies are combined together. These prior hybrid schemes apply pointer forwarding strategy and replication. But these schemes have limitations like holding “loose” form of location profile and higher location update cost. We have proposed a new hybrid scheme which includes adaptive replication of updated user’s location profile and mobility anchoring point (MAP) for location update. The main objective of the proposed scheme is to reduce call setup cost and call setup time. In order to achieve the objective, adaptive replication is applied at certain visitor location registers (VLRs) according to movement of caller. The replica is kept updated at MAP and replicated to neighbor VLRs as per movement of the caller. We have presented fluid-flow based analytical modeling which shows that proposed scheme outperforms the prior hybrid scheme.     

Per-user checkpointing for mobility database failure restoration

This paper studies the failure restoration of mobility database for Universal Mobile Telecommunications System (UMTS). We consider a per-user checkpointing approach for the home location register (HLR) database. In this approach, individual HLR records are saved into a backup database from time to time. When a failure occurs, the backup record is restored back to the mobility database. We first describe a commonly used basic checkpoint algorithm. Then, we propose a new checkpoint algorithm. An analytic model is developed to compare these two algorithms in terms of the checkpoint cost and the probability that an HLR backup record is obsolete. This analytic model is validated against simulation experiments. Numerical examples indicate that our new algorithm may significantly outperform the basic algorithm in terms of both performance measures.     

Development of the Home Location Register/Authentication Center in the CDMA Mobile System

In this paper, a home location register (HLR) for CDMA mobile communication system (CMS) is introduced. It stores the mobile station (MS) subscribers’ locations and supplementary service information. Call processing procedures for HLR are developed to receive and store subscriber's location coming from mobile exchange (MX) during the location registration, and to transfer subscriber's location and supplementary service information to the MX during the mobile-terminated call setup. For fast call processing by increasing database access speed, a memory-resident database management system is devised. For easy and secure HLR operation, administration and maintenance functions and overload control mechanisms are implemented. Designed HLR hardware platform is expandable and flexible enough to reallocate software blocks to any subsystems within the platform. It is configurable according to the size of subscribers. An authentication center (AC) is developed on the same platform. It screens the qualified MS from the unqualified. The calls to and from the unqualified MS are rejected in CMS. To authenticate the MS, the AC generates a new authentication parameter called “AUTHR“ using shared secret data (SSD) and compares it with the other AUTHR received from the MS. The AC also generates and stores seed keys called “A-keys” which are used to generate SSDs. The HLR requirements, the AC requirements, software architecture, hardware platform, and test results are discussed.     

大容量GPRS-HLR系统中内存数据库的数据结构组织模式

在移动通信系统中,为了满足HLR系统移动应用部分（MAP）对事务处理的实时需求,需要采用内存数据库供协议处理。同时为了提高HLR系统的容量以及数据的安全与完备性,需要采用高性能商用数据库管理系统。在设计中我们将内存数据库视作商用数据库的缓存以满足HLR系统大容量、高实时性以及高可靠性要求。文中给出了用于大容量HLR系统的内存数据库的数据结构组织模式与设计方案。     

HLP系统HA结构下数据一致的设计与实现

在高性能商用数据库的管理下,以双服务器外挂同一盘 ＨＡ系统模式的结构的ＨＬＲ数据库系统,有良好的数据安全与完备性,但无法满足ＨＬＲ系统的实时性要求。为此引入内存缓存以提高系统处理的实时性,但需解决内外存及主备端内存的数据一致。本文分析了ＨＡ结构下ＨＬＲ数据库系统的结构与数据组织,定义了修改图样,提出了实现数据一致的方法。     

Bandwidth-reservation scheme based on road information for next-generation cellular networks

Channel-reservation techniques have been widely studied in cellular networks in order to meet the desired quality-of-service requirements. In this paper, a distributed predictive channel-reservation scheme, called the road-map-based channel-reservation scheme (RMCR), and a call-admission-control algorithm are proposed. The goal is to reduce the handoff-dropping probability and to improve the bandwidth utilization. In the RMCR scheme, we assume that base stations (BSs) are equipped with road-map information and that mobile stations (MSs) are equipped with global positioning systems (GPS) devices. MSs periodically report their GPS location information to their BSs. Based on the location information of the MSs at two consecutive epochs, the BSs estimate the speed and moving direction of the MSs. Furthermore, the BSs estimate the probability that the MSs will enter the neighboring cells based on their velocity and the road-map information stored in the BSs. The BSs then compute the amount of bandwidth to be reserved, based on such estimation. With the road-map information, the BSs can make a more-accurate prediction on the user's mobility and, hence, reduce unnecessary bandwidth reservation. Simulation results show that RMCR is capable of keeping the handoff-dropping probability low and allocating bandwidth to new/handoff calls efficiently. We also show that RMCR is robust with respect to system parameters such as user's speed, the density of roads, the accuracy of mobility measurement, and so on.     

Determination of the Registration Point for Location Update by Dynamic Programming in PCS

Location management is important to effectively keep track of mobile terminals with reduced signal flows and database queries. Even though dynamic location management strategies are known to show good performance, we in this paper consider the static location management strategy which is easy to implement. A system with single home location register and pointer forwarding is assumed. A mobile terminal is assumed to have memory to store the IDs of visitor location registers (VLRs) each of which has the forwarding pointer to identify its current location. To obtain the registration point which minimizes the database access and signaling cost from the current time to the time of power-off probabilistic dynamic programming formulation is presented. A Selective Pointer Forwarding scheme is proposed which is based on one-step dynamic programming. The proposed location update scheme determines the least cost temporary VLR which point forwards the latest location of the mobile. The computational results show that the proposed scheme outperforms IS-41, pure Pointer Forwarding, and One-step Pointer Forwarding at the expense of small storage and a few computations at the mobile terminals.