This paper presents Virgil, an automatic access point discovery and selection system. Unlike existing systems that select access points based entirely on received signal strength, Virgil scans for all available APs at a location, quickly associates to each, and runs a battery of tests to estimate the quality of each AP's connection to the Internet. Virgil also probes for blocked or redirected ports, to guide AP selection in favor of preserving application services that are currently in use. Results of our evaluation across five neighborhoods in three cities show Virgil finds a usable connection from 22% to 100% more often than selecting based on signal strength alone. By caching AP test results, Virgil both improves performance and success rate. Our overhead is acceptable and is shown to be faster than manually selecting an AP with Windows XP.

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Improved access point selection

This article surveys research in service advertising, discovery, and selection for mobile ad hoc networks and related issues. We include a categorization of service discovery architectures for MANETs and their modes of operation, presenting their merits and drawbacks. We pay particular attention to cross-layer service discovery - a special class of efficient service discovery approaches for MANETs. We also present security issues and discuss service description options, service selection mechanisms, and service-state maintenance techniques. We conclude with a summary, an outlook, and directions for future research in this area.

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Service discovery for mobile Ad Hoc networks: a survey of issues and techniques

Discovery of services between devices is provided prior to establishing a connection between devices, including wireless-enabled devices or devices that are communicatively coupled to wireless access points. Discovering services prior to establishing a connection may facilitate finding a desired service. The services that may be discovered may be, for example, print services, camera services, PDA services or any other suitable services. Services may be discovered using 802.11, UWB or any other suitable wireless technology. As one example, particular services may be requested. As another example, services that are provided by a device may be advertised.

Proximity service discovery in wireless networks

Discovery of services between devices is provided prior to establishing a connection between devices, including wireless-enabled devices or devices that are communicatively coupled to wireless access points or other wireless communication devices. Discovering services prior to establishing a connection may facilitate finding a desired service. The services that may be discovered may be, for example, print services, camera services, PDA services or any other suitable services. Services may be discovered using 802.11, Bluetooth, UWB or any other suitable wireless technology. An information element is used to wirelessly convey information related to a service and/or information related to service discovery.

Mechanism to convey discovery information in a wireless network

Mobile devices face a diverse and dynamic set of networking options. Using those options to the fullest requires knowledge of application intent. This paper describes Intentional Networking, a simple but powerful mechanism for handling network diversity. Applications supply a declarative label for network transmissions, and the system matches transmissions to the most appropriate network. The system may also defer and re-order opportunistic transmissions subject to application-supplied mutual exclusion and ordering constraints. We have modified three applications to use Intentional Networking: BlueFS, a distributed file system for pervasive computing, Mozilla's Thunderbird e-mail client, and a vehicular participatory sensing application. We evaluated the performance of these applications using measurements obtained by driving a vehicle through WiFi and cellular 3G network coverage. Compared to an idealized solution that makes optimal use of all aggregated available networks but that lacks knowledge of application intent, Intentional Networking improves the latency of interactive messages from 48% to 13x, while adding no more than 7% throughput overhead.

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Intentional networking: opportunistic exploitation of mobile network diversity

In this paper, we contend that ubiquitous computing environments will be highly heterogeneous, service rich domains. Moreover, future applications will consequently be required to interact with multiple, specialised service location and interaction protocols simultaneously. We argue that existing service discovery techniques do not provide sufficient support to address the challenges of building applications targeted to these emerging environments.

This paper makes a number of contributions. Firstly, using a set of short ubiquitous computing scenarios we identify several key limitations of existing service discovery approaches that reduce their ability to support ubiquitous computing applications. Secondly, we present a detailed analysis of requirements for providing effective support in this domain. Thirdly, we provide the design of a simple extensible meta-service discovery architecture that uses database techniques to unify service discovery protocols and addresses several of our key requirements. Lastly, we examine the lessons learnt through the development of a prototype implementation of our architecture.

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Nat Wallbank

Papers

Supporting service discovery, querying and interaction in ubiquitous computing environments