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.     

An analysis of location record checkpointing interval for mobility database in PCS networks

Mobility database that stores the users’ location records is very important to connect calls to mobile users on personal communication networks. If the mobility database fails, calls to mobile users may not be set up in time. This paper studies failure restoration of mobility database. We study per-user location record checkpointing schemes that checkpoint a user’s record into a non-volatile storage from time to time on a per-user basis. When the mobility database fails, the user location records can be restored from the backup storage. Numeric analysis has been used to choose the optimum checkpointing interval so that the overall cost is minimized. The cost function that we consider includes the cost of checkpointing a user’s location record and the cost of paging a user due to an invalid location record. Our results indicate that when user registration intervals are exponentially distributed, the user record should never be checkpointed if checkpointing costs more than paging. Otherwise, if paging costs more, the user record should be always checkpointed when a user registers.     

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.     

Ad hoc mobility management with uniform quorum systems

A distributed mobility management scheme using a class of uniform quorum systems (UQS) is proposed for ad hoc networks. In the proposed scheme, location databases are stored in the network nodes themselves, which form a self-organizing virtual backbone within the flat network structure. The databases are dynamically organized into quorums, every two of which intersect at a constant number of databases. Upon location update or call arrival, a mobile's location information is written to or read from all the databases of a quorum, chosen in a nondeterministic manner. Compared with a conventional scheme [such as the use of home location register (HLR)] with fixed associations, this scheme is more suitable for ad hoc networks, where the connectivity of the nodes with the rest of the network can be intermittent and sporadic and the databases are relatively unstable. We introduce UQS, where the size of the quorum intersection is a design parameter that can be tuned to adapt to the traffic and mobility patterns of the network nodes. We propose the construction of UQS through the balanced incomplete block designs. The average cost, due to call loss and location updates using such systems, is analyzed in the presence of database disconnections. Based on the average cost, we investigate the tradeoff between the system reliability and the cost of location updates in the UQS scheme. The problem of optimizing the quorum size under different network traffic and mobility patterns is treated numerically. A dynamic and distributed HLR scheme, as a limiting case of the UQS, is also analyzed and shown to be suboptimal in general. It is also shown that partitioning of the network is sometimes necessary to reduce the cost of mobility management     

Predictive distance-based mobility management for multidimensional PCS networks

This paper presents a mobile tracking scheme that exploits the predictability of user mobility patterns in wireless PCS networks. In this scheme, a mobile's future location is predicted by the network, based on the information gathered from the mobile's recent report of location and velocity. When a call is made, the network pages the destination mobile around the predicted location. A mobile makes the same location prediction as the network does; it inspects its own location periodically and reports the new location when the distance between the predicted and the actual locations exceeds a threshold. To more realistically represent the various degrees of velocity correlation in time, a Gauss-Markov mobility model is used. For practical systems where the mobility pattern varies over time, we propose a dynamic Gauss-Markov parameter estimator that provides the mobility parameters to the prediction algorithm. Based on the Gauss-Markov model, we describe an analytical framework to evaluate the cost of mobility management for the proposed scheme. We also present an approximation method that reduces the computational complexity of the cost evaluation for multidimensional systems. We then compare the cost of predictive mobility management against that of the regular, nonpredictive distance-based scheme, for both the case with ideal Gauss-Markov mobility pattern and the case with time-varying mobility pattern.     

Impact of mobility on TCP/IP: an integrated performance study

This paper presents a simulation analysis of the impact of mobility on TCP/IP augmented with features to support host mobility in wide area networks. Our results show that the existing version of TCP can yield low throughput in highly mobile environments due to the fact that TCP cannot discriminate packets dropped due to hand-offs with those dropped due to congestion in one or more network resources. As a result, TCP invokes a congestion recovery process when packets are lost during internetwork hand-offs of the mobile host. We investigate a proposal in which the transport layer explicitly receives information from the network layer of any ongoing mobility. We show that by effectively capitalizing this information, TCP can appropriately extend the slow-start phase in the recovery process and achieve higher throughput. Based on the simulation analysis we also show the robustness of this scheme in the presence of both host mobility and network congestion     

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     

PCS中的移动性管理的发展研究

介绍了个人移动通信系统(PCS)中移动性管理的基本概念，从移动性管理的总体框架、位置管理和切换管理两个主要功能流程方面阐述了PCS中移动性管理的体系结构及移动性管理的实现。详细描述了常见的位置管理方法和切换管理方法及这两方面的改进措施，并对几种PCS中的移动性管理机制进行了分析比较，最后给出了结论。     

Optimal Utilization and Effects of Inaccurate Estimation in Mobile Database Failure Restoration

Mobility databases such as home location register and visitor location register are adopted to support mobility management in personal communications services networks. If a visitor location register fails or crashes, the subscribers' services will be seriously degraded due to the loss or corruption of location information. In this paper, we optimize utilization of demand re-registration messages for an adaptive p-persistent backoff database failure restoration scheme. An analytical model is developed and validated with simulations to obtain the optimal utilization using appropriate parameters so that the failed visitor location register is restored with the fastest speed. Some interesting aspects on the performance are studied and their deep insights are observed, such as effects of message sizes on choices of system parameters, effects of the inaccurate estimated number of stations, etc. One observation is that optimizations of utilization and successful transmission probability are two different goals, and a value to achieve the optimal successful transmission probability does not necessarily ensure optimal utilization. Furthermore, we also propose a scheme how to handle the problem with inaccurate (estimated) number of stations.     

Near-zero triangular location through time-slotted mobility prediction

To setup efficient wireless mesh networks, it is fundamental to limit the overhead needed to localize a mobile user. A promising approach is to rely on a rendezvous-based location system where the current location of a mobile node is stored at specific nodes called locators. Nevertheless, such a solution has a drawback, which happens when the locator is far from the source–destination shortest path. This results in a triangular location problem and consequently in increased overhead of signaling messages. One solution to prevent this problem would be to place the locator as close as possible to the mobile node. This requires however to predict the mobile node’s location at all times. To obtain such information, we define a mobility prediction model (an agenda) that, for each node, specifies the mesh router that is likely to be the closest to the mobile node at specific time periods. The location service that we propose formalizes the integration of the agenda with the management of location servers in a coherent and self-organized fashion. To evaluate the performance of our system compared to traditional approaches, we use two real-life mobility datasets of Wi-Fi devices in the Dartmouth campus and Taxicabs in the bay area of San Francisco. We show that our strategy significantly outperforms traditional solutions; we obtain gains ranging from 39 to 72% compared to the centralized scheme and more than 35% compared to a traditional rendezvous-based solution.     

A cluster based mobility prediction scheme for ad hoc networks

The ad hoc networks are completely autonomous wireless networks where all the users are mobile. These networks do not work on any infrastructure and the mobiles communicate either directly or via other nodes of the network by establishing routes. These routes are prone to frequent ruptures because of nodes mobility. If the future movement of the mobile can be predicted in a precise way, the resources reservation can be made before be asked, which enables the network to provide a better QoS. In this aim, we propose a virtual dynamic topology, which on one hand, will organize the network as well as possible and decreases the impact of mobility, and on the other hand, is oriented user mobility prediction. Our prediction scheme uses the evidence theory of Dempster–Shafer in order to predict the future position of the mobile by basing itself on relevant criteria. These ones are related to mobility and network operation optimisation. The proposed scheme is flexible and can be extended to a general framework. To show the relevance of our scheme, we combine it with a routing protocol. Then, we implemented the prediction-oriented topology and the prediction scheme which performs on it. We implemented also a mobility prediction based routing protocol. Simulations are made according to a set of elaborate scenarios.     

Overflow control for cellular mobility database

In a cellular phone system, the service area is partitioned into several location areas (LAs). Every LA is associated with a mobility database called visitor location register (VLR). When a mobile user enters an LA, the user must register to the VLR before receiving any cellular service. If the VLR is full, the registration procedure fails and the system cannot deliver services to the user under the existing cellular technology. To resolve this problem, we propose a VLR overflow control scheme to accommodate the incoming mobile users during VLR overflow. Our scheme only requires minor modifications to the existing cellular mobility management protocols. Particularly, no modification is made to the mobile phones. An analytic model is proposed to investigate the performance of the overflow control scheme. When exercising the scheme, the call setup procedure for an “overflow” user is more expensive than that for a “normal” user. Under the range of input parameters considered in our study, we show that even if the VLR overflow situation is serious, the overhead for exercising the overflow control scheme is very low     

AGP: an anchor-geography based routing protocol with mobility prediction for VANET in city scenarios

Vehicular ad-hoc networks (VANET) routing is a key technology for efficient data forwarding in intelligent transport system (ITS). A novel routing scheme, Anchor-Geography based routing protocol (AGP), designed specifically for VANET communication in city environment is proposed in this paper. The reactive broadcasting is used for both getting destination location and routing discovery. Connectivity status and load balancing is considered in routing decision. In addition, the map information and the kinematics parameters are used for the vehicle trajectory prediction. Such a mobility prediction can provide a solution for the situation in which the destination moves away from the location in the routing discovery procedure. In simulation, VanetMobiSim is used as the traffic generator for more realistic traffic scenarios in VANETs than simple mobility model definition. Simulation results in NS2 show that AGP protocol gains obvious improvement in packet delivery ratio and average hops.     

Induction and deduction for autonomous networks

The key issues in network management are the representation and sharing of management information and the automatic management mechanisms based on the underlying information infrastructure. The authors propose a framework, which operates on the standard management information base (MIB) and common management information protocol (CMIP), for a network management system with learning and inference as its management engines. In addition to the general domain knowledge, patterns related to the managed network are learned to enhance the understanding of the network and refine the knowledge base. Facts in object-oriented databases or queries from management applications trigger the inference process on logical rules which are either prespecified knowledge or learned network patterns. Forward inference drives prediction and control, while backward inference directs diagnosis and supports view abstraction. A case study on ATM network topology tuning is presented     

Global mobility management by replicated databases in personalcommunication networks

This paper explores the use of replicated databases for management of customer data (e.g., mobility data, call routing logic) in global, intelligent, and wireless networks. We propose and analyze two, full and partial, data replication schemes-which are compatible with industry protocol standards-and compare them with the traditional, centralized database scheme. By identifying a set of key teletraffic and mobility parameters, we develop a modeling framework based on queueing models and apply it to assess the relative performance and merits of these schemes. The paper also addresses some implementation issues. Numerical results reveal that the full replication scheme outperforms the centralized one over a wide range of the parameters considered in this study. Furthermore, if some customer data-such as location data for highly mobile customers in wireless networks-change frequently, and if each call launches multiple queries into the databases, the partial replication scheme offers further performance improvement. In general, however, the choice of the database design would depend on the specific characteristics of the service and user behavior under consideration     

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.     

A novel attributes anonymity scheme in continuous query

In location-based service (LBS), the un-trusted LBS server can preserve lots of information about the user. Then the information can be used as background knowledge and initiated the inference attack to get user’s privacy. Among the background knowledge, the profile attribute of users is the especial one. The attribute can be used to correlate the real location in uncertain location set in both of the snapshot and continuous query, and then the location privacy of users will be revealed. In most of the existing scheme, the author usually assumes a trusted third party (TTP) to achieve the profile anonymity. However, as the TTP disposes all anonymous procedure for each user, it will become the center of attacks and the bottleneck of the query service. Furthermore, the TTP may be curious about user’s privacy just because of the commercial consideration. In order to deal with the inference attack and remedy the drawback of TTP scheme, we propose a similar attributes anonymous scheme which based on the CP-ABE, and with the help of center server and collaborative users, our scheme can resist the inference attack as well as the privacy detection of any entity in the service of query. At last, security analysis and experimental results further verify the effectiveness of our scheme in privacy protection as well as efficiency of the algorithm execution.     

一种基于用户行为预测的群移动性管理模型

移动性管理是未来5G移动的重要组成部分,如何均衡寻呼负载和位置更新开销,从而合理利用无线资源是当前的研究重点.提出了一种新的群移动性管理(GMM)方案,可以针对具有相同运动特征的用户进行集中式管理,从而可以减少单个用户移动性管理(SMM)时存在的重复开销.仿真结果表明,GMM比SMM可以获得更佳的运行开销.