P-Handoff: a protocol for fine grained peer-to-peer vertical handoff

1 Introduction Wireless data technologies promises high benefits to the user, such as ubiquitous and mobile computing, but for those to be realised, both application developers and users need to make sense of it. For now, they are both overwhelmed and puzzled by the complexity and diversity of available implementations. The goal of this paper is to explore the impact of this wireless diversity on users and developers. As part of the CoolTown project [10], we are especially interested in how we can harness this wireless diversity in appliances, how we can manage peer to peer wireless links and how we can make wireless connectivity transparent to applications (especially mobile and ubiquitous applications). Wireless connectivity is no longer a dream : various technologies are available at reasonable price. Most of these technologies are mature and reliable. Most wireless technology in use today fall in one of the following four main categories. 2.1.1 Infrared Infrared, such as IrDA [3], offers a simple, directional, ad-hoc way to communicate to close range devices. It is well suited for short ad-hoc transactions directly between peers as well as to/from a network infrastructure [13]. On the other hand, because of the need to keep line of sight, it is tedious to use infrared to perform data exchanges exceeding one second. 2.1.2 Wide area cellular connectivity Cellular networks [4] are improving their ability to carry data traffic ; the third generation cellular networks (3G) will increase the bandwidth available to those services, improving both throughput and latency. Despite this, cellular will still remain slow and expensive (billing charges) compared to alternate local wireless technologies. However, cellular connectivity has a major advantage : the wide coverage available. Therefore, we can assume that cellular can always provide a connection to the infrastructure. 2.1.3 Wireless LANs Wireless LAN [1] is a technology deployed locally, and offer isolated pockets of connectivity. It may be ad-hoc (single cell) or may be connected to the infrastructure. Wireless LANs, such as 802.11b, offer higher speed, lower price and less power consumption than cellular connectivity, but have much more restricted coverage. PAN [2] is a technology designed to bind together the distributed parts of a logical system, like attaching peripherals to a main unit (Wireless USB). In addition, it is possible to use this technology to also connect to peers and access points (in a similar fashion to Wireless LANs). Most proponents of a …