IEEE 802.11 based wireless networks have seen rapid growth and deployment in the recent years. Critical to the 802.11 MAC operation, is the handoff function which occurs when a mobile node moves its association from one access point to another. In this paper, we present an empirical study of this handoff process at the link layer, with a detailed breakup of the latency into various components. In particular, we show that a MAC layer function - probe is the primary contributor to the overall handoff latency. In our study, we observe that the latency is significant enough to affect the quality of service for many applications (or network connections). Further we find variations in the latency from one hand-off to another as well as with APs and STAs used from different vendors. Finally, we discuss optimizations on the probe phase which can potentially reduce the probe latency by as much as 98% (and a minimum of 12% in our experiments). Based on the study, we draw some guidelines for future handoff schemes.

/pdf/an-empirical-analysis-of-the-ieee-802-11-mac-layer-handoff-3wml8nz9j4.pdf

An empirical analysis of the IEEE 802.11 MAC layer handoff process

Supporting mobile Internet multimedia applications requires more than just the ability to maintain connectivity across subnet changes. We describe how the Session Initiation Protocol (SIP) can help provide terminal, personal, session and service mobility to applications ranging from Internet telephony to presence and instant messaging. We also briefly discuss application-layer mobility for streaming multimedia applications initiated by RTSP.

/pdf/application-layer-mobility-using-sip-cwuns393fx.pdf

Application-layer mobility using SIP

Next-generation wireless systems are envisioned to have an IP-based infrastructure with the support of heterogeneous access technologies. One of the research challenges for next generation all-IP-based wireless systems is the design of intelligent mobility management techniques that take advantage of IP-based technologies to achieve global roaming among various access technologies. Next-generation wireless systems call for the integration and interoperation of mobility management techniques in heterogeneous networks. In this article the current state of the art for mobility management in next-generation all-IP-based wireless systems is presented. The previously proposed solutions based on different layers are reviewed, and their qualitative comparisons are given. A new wireless network architecture for mobility management is introduced, and related open research issues are discussed in detail.

/pdf/a-survey-of-mobility-management-in-next-generation-all-ip-4pf79tkm43.pdf

A survey of mobility management in next-generation all-IP-based wireless systems

Mobile IP is the current standard for supporting macromobility of mobile hosts. However, in the case of micromobility support, there are several competing proposals. We present the design, implementation and performance evaluation of HAWAII (handoff-aware wireless access Internet infrastructure), a domain-based approach for supporting mobility. HAWAII uses specialized path setup schemes which install host-based forwarding entries in specific routers to support intra-domain micromobility. These path setup schemes deliver excellent performance by reducing mobility related disruption to user applications. Also, mobile hosts retain their network address while moving within the domain, simplifying quality-of-service (QoS) support. Furthermore, reliability is achieved through maintaining soft-state forwarding entries for the mobile hosts and leveraging fault detection mechanisms built in existing intra-domain routing protocols. HAWAII defaults to using Mobile IP for macromobility, thus providing a comprehensive solution for mobility support in wide-area wireless networks.

/pdf/hawaii-a-domain-based-approach-for-supporting-mobility-in-3g42k1k4sk.pdf

HAWAII: a domain-based approach for supporting mobility in wide-area wireless networks

Revolutionary drivers for 4G include a push toward universal wireless access and ubiquitous computing through seamless personal and terminal mobility. One of the major challenges for seamless mobility is the criterion of a vertical handoff protocol: a handoff protocol for users that move between different types of networks. Traditional operations for handoff detection policies, decision metrics, and radio link transfer are not able to adapt to dynamic handoff criteria or react to user inputs and changing network availabilities. Nor are they able to deliver context-aware services or ensure network interoperability. Thus, new techniques are needed to manage user mobility between different types of networks. This article presents a tutorial on the design and performance issues for vertical hand-off in an envisioned multinetwork fourth-generation environment. Various network architectures and technologies for 3G and beyond are described, including wireless LANs, cellular, satellite, and Mobile IP. Then the problem of vertical handoff is defined in the context of such a diverse network environment. Finally, research efforts to resolve the open problems are explored, including new techniques for dynamic handoff decision and detection algorithms and context-aware radio link transfer.

Vertical handoffs in fourth-generation multinetwork environments

Next-generation wireless network standards are currently being defined. The access network architectures have several specialized components tailored for their respective wireless link technologies, even though the services provided by these different wireless networks are fairly similar. We propose a homogeneous IP-based network as a common access network for the different wireless technologies. The IP-based access network uses the Internet standard, Mobile IP, to support macro-mobility of mobile hosts, and HAWAII to support micro-mobility and paging functionality of current wireless networks. We also illustrate how the proposed IP-based solution can interwork with existing infrastructure so that deployment can be incremental.

/pdf/ip-based-access-network-infrastructure-for-next-generation-2g097fqp3l.pdf

IP-based access network infrastructure for next-generation wireless data networks

Supporting mobility in asynchronous transfer mode (ATM)-based broad-band networks with wireless access links poses many technical challenges. One of the most important of these challenges is the need to reroute ongoing connections to/from mobile users as these users move among base stations. Connection rerouting schemes must exhibit low handoff latency, maintain efficient routes, and limit disruption to continuous media traffic while minimizing reroute updates to the network switches. In this paper we propose, describe an implementation for, and experimentally evaluate the performance of five different connection rerouting schemes. We show that one of these schemes, which operates in two phases, executes very fast reroutes (with a measured latency of 6.5 ms) in a real-time phase and, if necessary, reroutes again in a nonreal-time phase to maintain efficient routing. The scheme also results in negligible disruption to both audio (e.g., a 1-in-100 chance of a single packet loss at CD-quality audio rates of 128 kb/s) and low-bit-rate video (e.g., a 2-in-100 chance of a single packet loss for 1-Mb/s video) traffic during connection rerouting. Based on these results, we conclude that simple handoff schemes coupled with a connection management architecture are sufficient for supporting low-bit-rate continuous media applications over ATM-based wireless networks.

Performance evaluation of connection rerouting schemes for ATM-based wireless networks

In wireless networks, mobile hosts must update the network with their current location in order to get packets delivered. Paging facilitates efficient power management at the mobile host by allowing the host to update the networkless frequently at the cost of providing the network with only approximate location information. The network determines the exact location of a mobile host through paging before delivering packets destined to the mobile host. In this paper, we propose the concept of paging as an IP service. IP paging enables a common infrastructure and protocol to support the different wireless interfaces such as CDMA, GPRS, wireless LAN, avoiding the duplication of several application layer paging implementations and the inter-operability issues that exists today. We present the design, implementation, and detailed qualitative and quantitative evaluation, using measurements and simulation, of three IP-based paging protocols for mobile hosts.

/pdf/ip-paging-service-for-mobile-hosts-2nkfrvcdjn.pdf

IP paging service for mobile hosts

Wireless messaging, in the form of two-way paging, is an integral part of universal Personal Communications Services (PCS) Basic wireless messaging services include providing reliable (acknowledged) message delivery, reply capabilities, and message origination from a messaging device Many more advanced services can also be envisioned Wireless networks and end devices impose many limitations on system design To overcome the problems caused by such an environment, we have introduced network based proxies, called user agents, to assist simple end devices, and a novel way to define messages, called flexible messages, so that advanced messaging services may be offered In this paper, we describe how user agents and flexible messages assist in providing messaging services in the Pigeon two-way messaging research prototype at Bell Laboratories

T.F. La Porta

Papers

HAWAII: a domain-based approach for supporting mobility in wide-area wireless networks

IP-based access network infrastructure for next-generation wireless data networks

Performance evaluation of connection rerouting schemes for ATM-based wireless networks

IP paging service for mobile hosts

User agents and flexible messages: a new approach to wireless two-way messaging