Application semantics for cost-effective media distribution

Abstract: Public use of the Internet increases as wideband connections become pervasive and applications suitable for media distribution grow popular. Group collaboration applications have attracted interest during recent years. Wireless connectivity and business applications also furthers a need for reliable communication protocols. Multicast is a driving force for new applications involving one-to-many as well as many-to-many user scenarios like lecturing, discussions, and collaborative work. In some applications guaranteed delivery of every packet is not crucial, while in other this is a requirement. Error handling in reliable protocols can present a substantial challenge already in a homogeneous environment. Including a plethora of end-user terminal types with widely varying resources it becomes even more challenging. Protocols and applications must therefore be able to handle receiver and network link heterogeneity. The thesis addresses some of the challenges facing the applications in this field, related to multicast and unicast alike. Although the obstacles each of them must overcome may differ, there are similarities with regards to possible solutions with respect to error handling or resource allocation. Error handling protocols are proactive or reactive. Proactive protocols transmit redundant information along with the original information, enabling the receivers to repair lost packets without feedback to the sender. Reactive protocols rely either on positive or negative feedback from the receivers in order to establish reliability. According to a definition of semantic reliability the reliability concept can be interpreted in terms of application semantics. It is proposed to view reliable multicast as a special case of semantically reliable multicast and to implement a dynamically configurable transport layer with an error-handling rule set that can be configured from the application or even from the sender in- session. It is also proposed to make use of the application's knowledge of specific semantics to improve on the recovery of lost packets, congestion handling, or resource allocation. The thesis also presents a bandwidth-sharing scheme for video in group collaboration using application semantics in the form of user hints. The presence of such events is made available to all senders via message passing between session members. As information relating to a user's interest in another user is conveyed, the sender may increase its use of resources on the expense of other senders. A scheme is proposed and a prototype implementation and experimental results are presented.