The bandwidth of commonly available broadband connections is growing less quickly than the capacity of commonly available storage devices. UK broadband speeds for the home are commonly 512kbps for downloading and 256kbps for uploading, while the Apple iPod can hold 40 GB of data and the home PC often has a 120 GB hard drive. Downloading a 1GB file to a domestic PC may take a day. In contrast, short–range wireless networking technologies are improving dramatically. In the last year or so we have seen 802.11 speeds increase from 11mbits/s to 54mbits/s, and access points are appearing that can transfer at 108mbit/s. Transferring a 1GB file over wireless takes as little as 3 minutes in such conditions. These figures point towards a near future in which high bandwidth peer–to–peer short–range wireless connections are just as commonly used as the Internet. In addition, P2P ad hoc networks may alleviate some of the real world deployment issues of communications systems. The publicity about ‘wi–fi hotspots’ tends to distract attention from the large and cold expanses between such hotspots, i.e. the large areas with little network coverage. Even less is said of the way that the cost of commercial 802.11 access is a significant constraint on the use of hotspots. Since many everyday applications are built on the assumption of constant network access, they tend to perform poorly, or not at all, on mobile devices that are actually mobile. Ad hoc networks present difficulties in terms of transience and security, but they do support many interesting research avenues in the areas of mobile systems and ubiquitous computing. Applications that have no reliance on central servers, or only intermittent or indirect reliance on such servers, are capable of running at any location without requiring an active Internet connection, a connection to a particular access point or having a specific, static IP address.
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