Elsevier

Computer Communications

Volume 29, Issue 9, 31 May 2006, Pages 1363-1385
Computer Communications

Mobility management across hybrid wireless networks: Trends and challenges

https://doi.org/10.1016/j.comcom.2005.09.003Get rights and content

Abstract

Future 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 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 continuity 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 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 challenges that still need to be addressed to achieve portable and scalable handoff solutions for continuous connectivity across wireless access networks.

Introduction

Mobile wireless technology has gained tremendous popularity due to its ability to provide ubiquitous information access to users on the move. However, presently, there is no single wireless network technology that is capable of simultaneously providing a low latency, high bandwidth, and wide area data service to a large number of mobile users. Wireless Overlay Networks [1]—a hierarchical structure of room-size, building-size, and wide area data networks solve the problem of providing network connectivity to a large number of moving consumers in an efficient and scalable way. In an overlay network, lower levels are comprised of high bandwidth wireless cells that provide a small coverage area. Higher levels in the hierarchy provide a lower bandwidth but a much wider access network. A mobile device with multiple wireless network interfaces can access these networks as it moves between different network environments. Next generation wireless systems typically constitute different types of access technologies [15]. The heterogeneity that will characterize future wireless systems instigates the development of intelligent and efficient handoff management mechanisms that can provide seamless roaming capability to end-users moving between several different access networks.

Section snippets

Wireless overlay networks

Fig. 1 shows a typical structure [2] of wireless overlay networks. First, the networks' service areas are overlapped. For example, the General Packet Radio Service (GPRS) network acts as an umbrella network to the Wireless Local Area Network (WLAN) network. Even the different cells of the same network overlap. This overlapping can be utilized to reduce service disruption, by simultaneously connecting to different subnets of the same access technology during transition from one network to

Handoffs in wireless overlay networks

Handoff is the process by which a mobile terminal keeps its connection active when it migrates from the coverage of one network access point to another. Different types of handoffs can occur in wireless overlay networks.

Vertical handoff process

The vertical handoff process may be divided into three phases [5]:

  • 1.

    Network Discovery

  • 2.

    Handoff Decision

  • 3.

    Handoff Implementation

Terminal requirements for future heterogeneous wireless networks

As future wireless systems are expected to support several heterogeneous access networks, we need to develop terminals that that have the capability to access these diverse technologies. In this context, terminals and devices capable of supporting different types of access technologies are being designed. Current multimode devices are of two different types:

  • The first type includes those devices capable of supporting multiple access systems by incorporating several network interface cards and

Recent vertical handoff management techniques proposed for heterogeneous wireless networks

Several techniques have been proposed for performing handoffs while roaming across heterogeneous wireless access networks. These approaches operate at different layers of the network protocol stack. Most of these approaches are based on a modification to the Mobile IP protocol and are implemented at the network layer [7], [9], [11], [23], [28]. Other handoff strategies include SIP-based handoff (operating at the application layer) [29], and SCTP-based handoff (operating at the transport layer)

Research challenges for mobility management in future heterogeneous wireless networks

Several issues [3], [14] still need to be resolved in order to build a complete solution for seamless roaming across various radio access systems. First, it is imperative that the user application session persists without timing out during mobility. However, current handoff management techniques do not provide such persistence and may time out before the handoff to a new subnet is achieved. This requires the user to have to restart the application at the new point of attachment. Since in a

Conclusion

In this article, we have presented a detailed discussion of various components of handoff management as well as recent handoff techniques for mobility across heterogeneous wireless access networks. We have also discussed about various features of multimodal mobile terminals that will enable the deployment of efficient mobility solutions. We have presented several handoff implementation issues and challenges that still need to be addressed to allow seamless mobility in future radio access

Acknowledgements

This work was supported by grants from Microsoft (Seattle), Sun Microsystems (Palo Alto) and Ixia Corporation (Calabasas). We express our gratitude to the anonymous reviewers and the editor for their remarks and suggestions which helped to improve the paper.

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