Um protocolo para gerência de handoff em redes pessoais sem fio para aplicações de tempo real.

Abstract

Wireless personal area networks (WPANs), are a mobile short range wireless network, with typical range of 10 meters, where the user is the center. The general usage scenario is where devices within the WPANs range communicate directly to each other or with resources from the external world (outside the WPAN) through access points which offer routing service. WPANs have been gaining attention over the last few years mainly due the emergence and popularization of novel wireless communication technologies that enable this kind of network, notably Bluetooth. In fact, the development of WPANs is closely related to the development of Bluetooth, which has been used as starting point to several studies and prototypes in this field. As the user mobility is the main feature of WPANs, a number of questions arise when developing applications targeted to this new paradigm. One of the most important refers to the handoff management. Handoff is the process through which network connections, routes, and states associated to services in course are seamlessly transferred between access points as the user moves through their coverage areas. Despite its alignment with the WPAN's network model, Bluetooth has no facilities for aiding the management of handoffs besides its standard operations for querying nearby devices and connect to them, inquiry and paging respectively. Moreover, the data traffic of these operations has priority over user applications' data traffic. This property has special impact for a particular kind of application: those that require real-time data transfer, such as streaming applications. When the wireless channel is unavailable for data transfers, with temporary connection loss with access points during handoffs, or interface preemption for the inquiry and paging operations, real-time applications have their performance compromised in consequence of violation of temporal requirements. In this work, a protocol for managing handoffs in Bluetooth-based WPANs is presented. The protocol is focused on the use of applications that demand real-time data transfers. The adequacy of the protocol to this kind of application is analyzed through a case study for an audio streaming application. The protocol is designed focusing on the limitations of potential client devices (small portable devices with limited computational power, memory, bandwidth, battery life, etc). Therefore, all the handoff management operations are transferred to access points. There is no need of signaling or any other kind of coordination or message exchange between access points and mobile devices during handoffs. Due to the use of standardized Bluetooth operations, any programmable device with a standard complaint Bluetooth interface can be used without changes on any underlying software layer, such as the Bluetooth stack. It is also presented a formal modelling and validation of the protocol to ensure it behaves according to its specification. The formal model is important to understand the protocol, unanbiguous documentation, and to easy the validation of changes and extension by automatic simulation and proof of properties.