Large Downloads

A user may start several simultaneous downloads, or download large files such as 650MB ISO images. In this way, a single user can use up most of the bandwidth. The solutions to this kind of problem lie in training, offline downloading, and monitoring (including real-time monitoring, as outlined in chapter six). Offline downloading can be implemented in at least two ways:

• At the University of Moratuwa, a system was implemented using URL redirection. Users accessing ftp:// URLs are served a directory listing in which each file has two links: one for normal downloading, and the other for offline downloading. If the offline link is selected, the specified file is queued for later download and the user notified by email when the download is complete. The system keeps a cache of recently downloaded files, and retrieves such files immediately when requested again. The download queue is sorted by file size. Therefore, small files are downloaded first. As some bandwidth is allocated to this system even during peak hours, users requesting small files may receive them within minutes, sometimes even faster than an online download.

• Another approach would be to create a web interface where users enter the URL of the file they want to download. This is then downloaded overnight using a cron job or scheduled task. This system would only work for users who are not impatient, and are familiar with what file sizes would be problematic for download during the working day.