The MoSaKa QoS system : Architecture and evaluation
The provision of Quality-of-Service (QoS) in packet-switched transmissions over highly mobile satellite terminals presents challenges not solved by existing schemes like Integrated Services and Differentiated Services. Such schemes rely on stable link conditions, a requirement that cannot be guaranteed in a mobile environment. To support robust audio and video conferencing, an end-to-end reservation-based approach is inevitable. This led to the development of the MoSaKa QoS System, which combines a reservation-based QoS scheme with the ability to deal with changing link conditions. The main idea was to enable applications to degrade gracefully if an unstable link deteriorates. Each router implements a crosslayer QoS agent, which tracks the network-layer-based QoS and takes the current status of the lower layers into account. Certain flows can be suspended without canceling them if the capacity of a link deteriorates. To select which flow has to be suspended, an optimizer was implemented which examines the flows for their priority and respective QoS requirements. To depict how this optimizer works and how the system performs, a testbed with an emulated satellite link was set up. The obtained results show, that the presented system is able to provide appropriate QoS over unstable links.