1、Mobility management across hybrid wireless networks: Trends and challenges Computer CommunicationsFuture generation wireless networks are envisioned to be a combination of diverse but complementary access technologies. Internetworking these types of networks will provide mobile users with ubiquitous
2、 connectivity across a wide range of networking environments. The integration of existing and emerging heterogeneous wireless networks requires the design of intelligent handoff and location management schemes to enable mobile users to switch network access and experience uninterrupted service conti
3、nuity anywhere, anytime. Real deployment of such mobility strategies remains a significant challenge. In this article, we focus on handoff management. We discuss in detail handoff decision and implementation procedures and present recent handoff techniques that aim at providing mobility over a wide
4、range of access technologies. We also discuss some of the capabilities of mobile terminals that are necessary to implement seamless mobility over hybrid wireless networks. Furthermore, we also present and discuss limitations of recent handoff design architectures and protocols as well as outstanding
5、 challenges that still need to be addressed to achieve portable and scalable handoff solutions for continuous connectivity across wireless access networks.Article Outline1. Introduction2. Wireless overlay networks3. Handoffs in wireless overlay networks 3.1. Horizontal vs. vertical handoff3.2. Upwar
6、d-vertical handoff vs. downward vertical handoff3.3. Anticipated vs. unanticipated handoff3.4. Hard vs. soft handoff3.5. Mobile-controlled handoff vs. network-controlled handoff vs. mobile-assisted handoff4. Vertical handoff process 4.1. Network discovery4.2. Handoff decision: traditional vs. next g
7、eneration handoff strategies4.3. Handoff metrics in heterogeneous networks 4.3.1. Cost4.3.2. Network conditions4.3.3. Battery power4.3.4. Application types4.3.5. Mobile node conditions4.3.6. User preferences4.4. Handoff implementation 4.4.1. Context transfer for seamless handoffs in heterogeneous wi
8、reless networks4.4.2. Candidate access router discovery and context transfer protocol4.4.3. CARD protocol4.4.4. Context transfer protocol5. Terminal requirements for future heterogeneous wireless networks 5.1. Multimode wireless terminals 5.1.1. Requirements for multimode terminal operation5.1.2. De
9、ployment issues for multimode terminals 5.1.2.1. Network detection5.1.2.2. Network information5.2. Software-defined radios 5.2.1. Motivation for SDR development5.2.2. Key features of SDR technology 5.2.2.1. Reconfigurability5.2.2.2. Multimode operation5.2.2.3. Ubiquitous connectivity5.2.2.4. Interop
10、erability6. Recent vertical handoff management techniques proposed for heterogeneous wireless networks 6.1. Mobile IP6.2. Mobile IPv66.3. Network layer handoff approaches 6.3.1. HOPOVER 6.3.1.1. Handoff Preparation6.3.1.2. Handoff6.3.1.3. Updating mobile IP information6.3.1.4. Limitations of HOPOVER
11、6.3.2. Hierarchical approach 6.3.2.1. Limitations of the hierarchical approach6.3.3. OmniCon 6.3.3.1. Limitations of the Omnicon Approach6.4. Transport layer handoff approaches 6.4.1. SCTP-based vertical handoff 6.4.1.1. Limitations of SCTP-based handoff scheme6.5. Application layer handoff approach
12、 6.5.1. Limitations of SIP6.6. Energy-efficient Handoff Approaches 6.6.1. Adaptive vertical handoff6.6.2. WISE6.7. TCP-based handoff strategies7. Research challenges for mobility management in future heterogeneous wireless networks 7.1. Multimodality7.2. Efficient and seamless roaming 7.2.1. Detecti
13、on of network coverage7.2.2. Selection of the most appropriate access network7.2.3. Handoffs7.3. Quality of service (QoS) 7.3.1. QoS requirements7.3.2. Security7.4. Billing and pricing7.5. Transfer of contextual information 7.5.1. Context transfer7.5.2. Security of context transfer7.6. Inter-service
14、 provider compliance8. ConclusionWireless mesh networks: a survey Computer NetworksWireless mesh networks (WMNs) consist of mesh routers and mesh clients, where mesh routers have minimal mobility and form the backbone of WMNs. They provide network access for both mesh and conventional clients. The i
15、ntegration of WMNs with other networks such as the Internet, cellular, IEEE 802.11, IEEE 802.15, IEEE 802.16, sensor networks, etc., can be accomplished through the gateway and bridging functions in the mesh routers. Mesh clients can be either stationary or mobile, and can form a client mesh network
16、 among themselves and with mesh routers. WMNs are anticipated to resolve the limitations and to significantly improve the performance of ad hoc networks, wireless local area networks (WLANs), wireless personal area networks (WPANs), and wireless metropolitan area networks (WMANs). They are undergoin
17、g rapid progress and inspiring numerous deployments. WMNs will deliver wireless services for a large variety of applications in personal, local, campus, and metropolitan areas. Despite recent advances in wireless mesh networking, many research challenges remain in all protocol layers. This paper pre
18、sents a detailed study on recent advances and open research issues in WMNs. System architectures and applications of WMNs are described, followed by discussing the critical factors influencing protocol design. Theoretical network capacity and the state-of-the-art protocols for WMNs are explored with
19、 an objective to point out a number of open research issues. Finally, testbeds, industrial practice, and current standard activities related to WMNs are highlighted.Article Outline1. Introduction2. Network architecture3. Characteristics4. Application scenarios5. Critical factors influencing network
20、performance6. Capacity of WMNs 6.1. Capacity analysis6.2. Open research issues7. Physical layer 7.1. Advanced physical layer techniques7.2. Open research issues8. MAC layer 8.1. Single-channel MAC8.2. Multi-channel MAC8.3. Open research issues9. Network layer 9.1. Routing protocols with various perf
21、ormance metrics9.2. Multi-radio routing9.3. Multi-path routing for load balancing and fault tolerance9.4. Hierarchical routing9.5. Geographic routing9.6. Open research issues10. Transport layer 10.1. Protocols for reliable data transport 10.1.1. TCP variants10.1.2. Entirely new transport protocols10
22、.2. Protocols for real-time delivery10.3. Open research issues11. Application layer 11.1. Applications supported by WMNs11.2. Open research issues12. Protocols for network management 12.1. Mobility management12.2. Power management12.3. Network monitoring13. Security14. Timing synchronization15. Cros
23、s-layer design16. Testbeds and implementations 16.1. Academic research testbeds16.2. Industrial practice17. Standard activities 17.1. IEEE 802.11 mesh networks17.2. IEEE 802.15 mesh networks17.3. IEEE 802.16 mesh networks18. ConclusionAcknowledgementsReferencesEfficiently reconfigurable backbones fo
24、r wireless sensor networks We present the definition and performance evaluation of a protocol for building and maintaining a connected backbone among the nodes of a wireless sensor networks (WSN). Building backbones first, and then coping with network dynamics is typical of protocols for backbone fo
25、rmation. Rules for building the backbone, however, do not take into account the following network dynamics explicitly. This makes maintaining a connected backbone quite costly, especially in terms of reorganization time, overhead and energy consumption. Our protocol includes in the backbone forming
26、operations a fail-safe mechanism for dealing with the addition and the removal of nodes, which are typical events in a WSN. More specifically, the network is kept partitioned into clusters that are cliques, i.e., nodes in each cluster are directly connected to each others. Therefore, removing a node
27、 does not disrupt a cluster, and adding one requires simple operations for checking node admission to the cluster. The protocol, termed CC (“double C”, for clique clustering), comprises three phases, each designed to render the operations of the others swift and efficient. The first phase partitions
28、 the network into clusters that are cliques. Clusters are then joined to form a backbone that is provably connected. Finally, the third, more on-line phase, maintains the backbone connected in face of node additions and removals. We compare the performance of CC with that of DMAC, a protocol that ha
29、s been previously proposed for building and maintaining clusters and backbones in presence of network dynamics. Our comparison concerns metrics that are central to WSN research, such as time for clustering and backbone reorganization, corresponding overhead, extent of the reorganization (i.e., numbe
30、r of nodes involved in it), and properties of the resulting backbone, such as its size, backbone route length, number of gateways and nodes per cluster. Our ns2-based simulation results show that the design criteria chosen for CC are effective in producing backbones that can be reconfigured quickly
31、and with remarkably lower overhead.Article Outline1. Introduction2. Related work3. Clique clustering (CC) 3.1. Cluster formation phase 3.1.1. Cluster formation correctness3.2. Cluster interconnection3.3. Backbone reorganization 3.3.1. Removing nodes3.3.2. Backbone reorganization correctness: Nodes r
32、emoval3.3.3. Adding new nodes3.3.4. Backbone reorganization correctness: Addition of nodes4. DMAC5. Experimental results 5.1. Simulation scenarios, metrics and experiments5.2. Backbone formation: Setting the network up5.3. Maintaining the backbone: Dealing with node removals5.4. Maintaining the back
33、bone: Addition of a node6. ConclusionsOptimization models and methods for planning wireless mesh networks In this paper novel optimization models are proposed for planning Wireless Mesh Networks (WMNs), where the objective is to minimize the network installation cost while providing full coverage to
34、 wireless mesh clients. Our mixed integer linear programming models allow to select the number and positions of mesh routers and access points, while accurately taking into account traffic routing, interference, rate adaptation, and channel assignment. We provide the optimal solutions of three probl
35、em formulations for a set of realistic-size instances (with up to 60 mesh devices) and discuss the effect of different parameters on the characteristics of the planned networks. Moreover, we propose and evaluate a relaxation-based heuristic for large-sized network instances which jointly solves the
36、topology/coverage planning and channel assignment problems. Finally, the quality of the planned networks is evaluated under different traffic conditions through detailed system level simulations.Article Outline1. Introduction2. Related work and contributions3. Basic model 3.1. Numerical results4. In
37、terference aware model 4.1. Relaxation-based heuristic5. Multiple channel model 5.1. Two-phase heuristic6. Network performance evaluation via simulation7. ConclusionReferencesObstacles constrained group mobility models in event-driven wireless networks with movable base stations Ad Hoc NetworksIn th
38、is paper, we propose a protocol for dynamic reconfiguration of ad-hoc wireless networks with movable base stations in presence of obstacles. Hosts are assigned to base stations according to a probabilistic throughput function based on both the quality of the signal and the base station load. In orde
39、r to optimize space coverage, base stations cluster hosts using a distributed clustering algorithm. Obstacles may interfere with transmission and obstruct base stations and hosts movement. To overcome this problem, we perform base stations repositioning making use of a motion planning algorithm on t
40、he visibility graph based on an extension of the bottleneck matching technique. We implemented the protocol on top of the NS2 simulator as an extension of the AODV. We tested it using both Random Way Point and Reference Point Group mobility models properly adapted to deal with obstacles. Experimenta
41、l analysis shows that the protocol ensures the total space coverage together with a good throughput on the realistic model (Reference Point Group) outperforming both the standard AODV and DSR.Article Outline1. Introduction2. Related work 2.1. Topology maintenance in wireless networks2.2. Mobility mo
42、dels3. Space coverage optimization 3.1. The Antipole Clustering in mobile wireless network with starred backbone3.2. Distributed Antipole Clustering and base stations repositioning in absence of obstacles3.3. Clustering and base stations repositioning in presence of obstacles4. Throughput optimizati
43、on and network maintenance5. Implementation in NS2 and experimental analysis6. Conclusions and future workAcknowledgementsReferencesMedium Access Control protocols for ad hoc wireless networks: A survey Studies of ad hoc wireless networks are a relatively new field gaining more popularity for variou
44、s new applications. In these networks, the Medium Access Control (MAC) protocols are responsible for coordinating the access from active nodes. These protocols are of significant importance since the wireless communication channel is inherently prone to errors and unique problems such as the hidden-
45、terminal problem, the exposed-terminal problem, and signal fading effects. Although a lot of research has been conducted on MAC protocols, the various issues involved have mostly been presented in isolation of each other. We therefore make an attempt to present a comprehensive survey of major scheme
46、s, integrating various related issues and challenges with a view to providing a big-picture outlook to this vast area. We present a classification of MAC protocols and their brief description, based on their operating principles and underlying features. In conclusion, we present a brief summary of k
47、ey ideas and a general direction for future work.Article Outline1. Introduction 1.1. Applications1.2. Important issues1.3. Need for special MAC protocols2. Classification3. Review of non-QoS MAC protocols 3.1. General MAC protocols 3.1.1. Multiple access collision avoidance (MACA)3.1.2. IEEE 802.11
48、MAC scheme3.1.3. Multiple access collision avoidance-by invitation (MACA-BI)3.1.4. Group allocation multiple access with packet sensing (GAMA-PS)3.2. Power aware MAC protocols 3.2.1. Power aware medium access control with signaling (PAMAS)3.2.2. Dynamic power saving mechanism (DPSM)3.2.3. Power cont
49、rol medium access control (PCM)3.2.4. Power controlled multiple access (PCMA)3.3. Multiple channel protocols 3.3.1. Dual busy tone multiple access (DBTMA)3.3.2. Multi channel CSMA MAC protocol3.3.3. Hop-reservation multiple access (HRMA)3.3.4. Multi-channel medium access control (MMAC)3.3.5. Dynamic
50、 channel assignment with power control (DCA-PC)3.4. Protocols using directional antennas3.5. Unidirectional MAC protocols4. QoS-aware MAC protocols 4.1. Issues affecting QoS4.2. Review of selected QoS-aware MAC protocols 4.2.1. Real-time MAC (RT-MAC)4.2.2. DCF with priority classes4.2.3. Enhanced DC
