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.     

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     

Performance analysis of cache strategy for signaling traffic management in a wireless ATM network

In a wireless ATM network for mobile multimedia services, conventional signaling protocols generate heavy traffic because the signaling load must be handled in a HLR (Home Location Register). This centralized structure of the wireless ATM network causes critical connection setup delays. Thus, distributed processing based on a reduction of the connection setup delays is needed in wireless ATM networks. A cache strategy for call delivery with cache updates of registration based on ATM multicasting is introduced with a comparison of the cost of cache scheme with the cost of a conventional scheme. Results show that the cache scheme has better performance than conventional methods when portable mobility is low with large traffic density. This revised version was published online in July 2006 with corrections to the Cover Date.     

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     

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.     

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     

Reducing location update cost in a PCS network

Location tracking operations in a personal communications services (PCSs) network are expensive. Several strategies have been proposed to reduce the location update cost. This paper studies a special case of a location tracking algorithm called the alternative location algorithm. This special case is referred to as the two location algorithm (TLA). An analytical model is proposed to compare the performance of the TLA and the IS-41 protocol. Our study indicates that the performance of the TLA is significantly affected by the user moving patterns and the call traffic. If the user mobility is higher than the call frequency or the user tends to move back to the previously visited registration areas, then the TLA may significantly outperform IS-41. We also observe that the variance of the portable residence times in registration areas has an impact on the performance of the TLA (i.e., better performance is expected for larger variance)     

A Mobility Model and Performance Analysis in Wireless Cellular Network with General Distribution and Multi-Cell Model

Multi-cell mobility model and performance analysis for wireless cellular networks are presented. The mobility model plays an important role in characterizing different mobility-related parameters such as handoff call arrival rate, blocking or dropping probability, and channel holding time. We present a novel tractable multi-cell mobility model for wireless cellular networks under the general assumptions that the cell dwell times induced by mobiles’ mobility and call holding times are modeled by using a general distribution instead of exponential distribution. We propose a novel generalized closed-form matrix formula to support the multi-cell mobility model and call holding time with general distributions. This allows us to develop a fixed point algorithm to compute loss probabilities, and handoff call arrival rate under the given assumptions. In order to reduce computational complexity of the fixed point algorithm, the channel holding time of each cell is down-modeled into an exponentially distributed one for purposes of simplification, since the service time is insensitive in computing loss probabilities of each cell due to Erlang insensitivity. The accuracy of the multi-cell analytic mobility model is supported by the comparison of the simulation results and the analytic ones.     

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     

Analysis of cost and quality of service of time-based dynamic mobility management in wireless networks

A key observation of a time-based location management scheme (TBLMS) is that the simple paging method (i.e., the fastest paging method) does not guarantee to find a mobile terminal, no matter how small the location update cycle is and how big the radius of a paging area (PA) is. Therefore, in addition to cost analysis and optimization, there is one extra issue to deal with in a TBLMS, i.e., the quality of service (QoS), which is the probability that a mobile terminal can be found in the current PA. The main contributions of the paper are as follows. First, based on our previous results on random walks among rings of cell structures, we analyze the location distribution of a mobile terminal in a PA and the reachability of a mobile terminal in a PA when a phone call arrives, where the inter-call time and the cell residence time can have an arbitrary probability distribution. Second, using results from renewal processes, we analyze the cost of dynamic mobility management in a TBLMS, where the inter-call time and the cell residence time can have an arbitrary probability distribution. Third, we develop a method to find a TBLMS which has the best combination of the location update cycle and the radius of a PA with the minimum cost of mobility management, while still satisfying the required QoS.     

On Integrated Location and Service Management for Minimizing Network Cost in Personal Communication Systems

We investigate the notion of per-user integrated location and service management in personal communication service (PCS) networks by which a per-user service proxy is created to serve as a gateway between the mobile user and all client-server applications engaged by the mobile user. The service proxy is always colocated with the mobile user's location database such that whenever the MU's location database moves during a location handoff, a service handoff also ensues to colocate the service proxy with the location database. This allows the proxy to know the location of the mobile user all the time to reduce the network communication cost for service delivery. We investigate four integrated location and service management schemes. Our results show that the centralized scheme performs the best when the mobile user's SMR (service to mobility ratio) is low and CMR (call to mobility ratio) is high, while the fully distributed scheme performs the best when both SMR and CMR are high. In all other conditions, the dynamic anchor scheme is the best except when the service context transfer cost is high, under which the static anchor scheme performs the best. Through analytical and simulation results, we demonstrate that different users with vastly different mobility and service patterns should adopt different integrated location and service management methods to optimize system performance. Further, the best integrated scheme always performs better than the best decoupled scheme that considers location and service managements separately and management schemes that do not use any service proxy.     

GroCoca: group-based peer-to-peer cooperative caching in mobile environment

In a mobile cooperative caching environment, we observe the need for cooperating peers to cache useful data items together, so as to improve cache hit from peers. This could be achieved by capturing the data requirement of individual peers in conjunction with their mobility pattern, for which we realized via a GROup-based COoperative CAching scheme (GroCoca). In GroCoca, we define a tightly-coupled group (TCG) as a collection of peers that possess similar mobility pattern and display similar data affinity. A family of algorithms is proposed to discover and maintain all TCGs dynamically. Furthermore, two cooperative cache management protocols, namely, cooperative cache admission control and replacement, are designed to control data replicas and improve data accessibility in TCGs. A cache signature scheme is also adopted in GroCoca in order to provide information for the mobile clients to determine whether their TCG members are likely caching their desired data items and to perform cooperative cache replacement Experimental results show that GroCoca outperforms the conventional caching scheme and standard COoperative CAching scheme (COCA) in terms of access latency and global cache hit ratio. However, GroCoca generally incurs higher power consumption     

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     

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.     

Call admission control for an adaptive heterogeneous multimedia mobile network

A novel call admission control (CAC) scheme for an adaptive heterogeneous multimedia mobile network with multiple classes of calls is investigated here. Different classes of calls may have different bandwidth requirement, different request call holding time and different cell residence time. At any time, each cell of the network has the capability to provide service to at least a given number of calls for each class of calls. Upon the arrival (or completion or hand off) of a call, a bandwidth degrade (or upgrade) algorithm is applied. An arriving call to a cell, finding insufficient bandwidth available in this cell, may either be disconnected from the network or push another call out of the cell toward a neighboring cell with enough bandwidth. We first prove that the stationary distribution of the number of calls in the network has a product form and then show how to apply this result in deriving explicit expressions of handoff rates for each class of calls, in obtaining the disconnecting probabilities for each class of new and handoff calls, and in finding the grade of service of this mobile network     

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.     

命名数据网络中基于内容请求相关性的协作缓存算法

针对命名数据网络(Named Data Networking, NDN)存储空间的有效利用和应答内容的高效缓存问题,该文采用差异化缓存的方式,提出一种依据内容请求序列相关性的协作缓存算法。在内容请求中,预先发送对于后续相关数据单元的并行预测请求,增大内容请求的就近响应概率;缓存决策时,提出联合空间存储位置与缓存驻留时间的2维差异化缓存策略。根据内容活跃度的变化趋势,空间维度上逐跳推进内容存储位置,时间维度上动态调整内容缓存时间,以渐进式的方式将真正流行的请求内容推送至网络边缘存储。该算法减小了内容请求时延和缓存冗余,提高了缓存命中率,仿真结果验证了其有效性。     

Mobile user location update and paging under delay constraints

Wireless personal communication networks (PCNs) consist of a fixed wireline network and a large number of mobile terminals. These terminals are free to travel within the PCN coverage area without service interruption. Each terminal periodically reports its location to the network by a process calledlocation update. When a call for a specific terminal arrives, the network will determine the exact location of the destination terminal by a process calledterminal paging. This paper introduces a mobile user location management mechanism that incorporates a distance based location update scheme and a selective paging mechanism that satisfies predefined delay requirements. An analytical model is developed which captures the mobility and call arrival pattern of a terminal. Given the respective costs for location update and terminal paging, the average total location update and terminal paging cost is determined. An iterative algorithm is then used to determine the optimal location update threshold distance that results in the minimum cost. Analytical results are also obtained to demonstrate the relative cost incurred by the proposed mechanism under various delay requirements.     

Dynamic mobile user location update for wireless PCS networks

The basic architecture of a personal communication network consists of a wireline network and mobile terminals. Each mobile terminal communicates with the wireline network through a nearby base station. In order to route incoming calls to a destination mobile terminal, the network must keep track of the location of each mobile terminal from time to time. This is achieved bylocation update such that each mobile terminal reports its current location to the network at specific time points. When an incoming call arrives, the network will page the mobile terminal starting from the last updated location. A trade-off, therefore, exists between the frequency of location update and the number of locations paged in order to track down the mobile terminal. This paper introduces a location update policy which minimizes the cost of mobile terminal location tracking. A mobile terminal dynamically determines when to update after moving to a new cell based on its mobility pattern and the incoming call arrival probability. The performance of this scheme is close to that of the optimal policy reported earlier. However, the processing time requirement of this scheme is very low. The minimal computation required by this scheme enables its usage in mobile terminals which has limited energy supply and computational power.     

面向物联网数据特征的信息中心网络缓存方案

将信息中心网络(ICN)应用到物联网(IoT)架构(ICN-IoT),可以有效地解决数据分发问题,提高数据的传输效率。但在ICN-IoT中,现有的缓存研究主要是在内容流行度或新鲜度等单一维度上实现缓存配置,无法适应海量和多态的物联网数据特征,导致缓存效率低。针对上述问题,该文首先分析了物联网数据特征,将数据分为周期性数据和事件触发性数据。然后,综合考虑物联网的这两种数据特征,提出一种具有不同缓存决策的ICN-IoT缓存方案(CS-DCI),路由器根据到达数据的特征类型执行相应的缓存决策。最后详细介绍两种数据类型的缓存策略,对于周期性数据,考虑内容流行度和时间请求概率缓存用户请求最多的数据;对于事件触发性数据,考虑内容流行度和事件触发频率缓存有意义的数据。仿真表明,该方案能够提高内容差异率,增加缓存内容的多样性,从而满足ICN-IoT不同应用的请求,获得较优的缓存命中率以及减少内容获取跳数。