One-way-delay measurements with CM toolset

Abstract

Internet Quality of Service (QoS) is an actual research topic. The need for more or less guaranteed transmission rates (e.g. for bulk-data transfer applications), upper bounds for transmission delay and jitter (e.g. for real time applications like IP telephony, video-conferencing) stimulated the development of QoS transmission technologies like ATM, IP-RSVP and the actual discussion about Diff-Serv mechanisms. This paper describes the implementation and the first measurement trials with the One-Way-Delay measurement components of CM-Toolset. The overall tool architecture consists of a distributed system of load generators and receivers (agents) and a measurement server, which stores the measurement results in a data-base. To measure the exact One-Way-Delay (OWD) the synchronised GPS clock system was integrated. The measurements were realised in a 4 hop heterogeneous IP and ATM network. The clock drift during the loop measurements was about 10 ms, linear and deterministic. So the drift could be eliminated by statistical computations. The measurements were made for UDP flows under different load situations( 1 UDP....5 UDP, TSDU size, interarrival time), and for n*UDP+1 TCP. The measurements show very clearly the interaction and dependencies between the number of flows, their load parameters and the QoS parameters like packet loss and one way delay. The measurements of UDP+TCP multiplexed flows explains, why the concept of flow separation is important for QoS guarantees. CM Toolset can be used by protocol engineers for the development of new QoS-based network technologies by collecting measurement data for modelling the network behaviour. Network managers can tune the operational network to improve the quality e.g. of IP-Telephon.