Quality of Service in Network Systems and Protocols


The definition of QoS, originally quite narrowly given in terms of message delay and jitter in telecom applications, has been recently given the wider meaning of the set of qualitative and quantitative characteristics of a distributed system which are necessary for obtaining the required functionality of an application. Therefore the term QoS encompasses many aspects such as reliability, availability, fault tolerance and even properties such as atomicity or reliability of broadcast/multicast. Current activities go into two directions: QoS evaluation of Protocols and QoS evaluation of network systems.

Following a modeling approach, protocols behavior is analysed and quantitatively evaluated under both typical performance indicators and the coverage of the assumptions the correctness of the protocols is based on. This is a novel evaluation method for protocols, typically evaluated through classical performance measures only, like throughput and execution time. Experience has been gained on analysis of wireless group communication protocols and consensus protocols. Currently, communication protocols to coordinate activities among vital subsystems in the railway field are under study.

On the network systems side, an accurate estimation of the availability of the General Packet Radio Service (GPRS) has been the subject of a recent study. In particular, the impact of outage periods on the service degradation as perceived by users has been analyzed. The framework of the CAUTION++ project, going to start on November 1st offers the opportunity to refine and extend analysis of wireless technologies under critical system conditions.


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Update Time 25 Oct 2005 at 13:10:41
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Dependable Computing Research Lab
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