Large scale and mobile group communication systems

Sammanfattning: This doctoral thesis examines different attributes of large scale group communication systems such as scalability, security and mobility by studying two different prototype systems - mIR (multicast Interactive Radio) and MES (Mobile E-meeting Services). mIR is a system for large scale real-time music distribution, designed as an interactive radio system for the Internet. MES is a collection of tools for improving the use of e-meeting and video conferencing tools in a mobile environment. The mIR prototype has been used to study scalability and security. Scalability in mIR concerns how to support as many users as possible without degrading the experience. This is achieved using IP multicast together with algorithms that limits the bandwidth usage regardless of the number of users. The work on security have focused on copy prevention through digital watermarking. By adding a unique watermark, i.e. a fingerprint, to each media copy a pirated copy can be traced back to a specific user, which can act as a deterrent. The thesis shows how we can combine the different goals of fingerprinting and IP-multicast while still maintaining the scalability features of multicast. Many issues need to be considered if e-meetings and video conferencing will become widespread and popular. Scalability and security, discussed in the first part of the thesis are two examples, and the second part of the thesis tries to address a third issue: mobility. In particular we are interested in enabling access to an e-meeting in a mobile environment, where we often have difficult conditions such as bad network connections, the user only have access to the Internet through a web browser or the available devices are small and limited. In many cases it is currently impossible to participate in an e-meeting when you're not in the office. The prototype system developed in the second part of the thesis aims to enable participation from any location and device that have some sort of Internet connection. We try to achieve this by allowing a mobile user to access an e-meeting session from a web browser or from a Java enabled mobile phone. Further, the system makes it possible to review missed events in an e-meeting as it is likely that there are many times where no Internet connection at all is available. The general style of work has been prototype driven with a goal of creating usable prototypes - i.e. the prototypes should be easy to deploy and it should be possible to use and test the prototypes daily. Most the prototypes described in this thesis have indeed been deployed and have seen daily use.