Performance and functionality in overlay networks

Overlay networks create virtual topologies on top of the existing networking infrastructure and come as a middle layer between end-user applications and the basic network services. The main reasons of using an intermediate level of communication are the new service functionality and the improved performance offered by application specific protocols that can be deployed in overlay networks. This thesis explores the benefits offered by overlay networks and introduces new mechanisms that improve performance and offer additional functionality to networking applications.; Multicast services are rarely used today, mainly due to scalability and security concerns. An overlay architecture addresses these issues by moving the service management and deployment above the network infrastructure. We present an architecture for transparent overlay multicast and an optimal distributed flow control for reliable multicast in overlay networks that scales with the number of participants and groups.; Even though capacity grows exponentially over time, latency is difficult to improve. We present an overlay approach that can substantially decrease the number of delayed packets in wide area reliable communication and increase the delivery ratio of best effort communication, leading to improved performance in time-sensitive applications such as Voice over IP.