Analysing the Latency of World Wide Web Applications

As the Web becomes increasingly used for routine social and economic interactions, the issue of interactive delay, as experienced by end-users, has become an ongoing cause for concern. This paper reports on an approach of identifying and analysing the factors that contribute towards that delay. The evolution of a structured timing model is described, which forms the basis for decomposing delay into its constituent parts. The four high-level components identified are the server, network, protocol and client. Methodologies for determining the contribution of each element are presented and their use is illustrated in a case study of the traffic associated with an operational distributed learning environment (DLE) serving six universities over a period of several months. Quality of service (QoS) is key to the success of DLEs and this includes an understanding of their relationship with the underlying networks and systems upon which they are built and deployed. Delay, as experienced by the end user, is one of the key QoS parameters for a DLE. The importance of developing an understanding of the nature of delay in a DLE is twofold: it informs decisions about where to target effort and resources in order to achieve improvements; and it provides techniques that can be used as the basis for an early-warning and advisory system for QoS aware applications. The latter functionality is illustrated by a novel solution that modifies TCP's congestion avoidance algorithm for the benefit of interactive Web traffic. Copyright (C) 2003 John Wiley Sons, Ltd.