On service level agreements for IP networks

Many corporate WAN architects are considering migrating from costly leased line circuits to ´private IP´ services. In order to do so IP service providers must provide service level agreements (SLA) that offer robust assurances that cover service availability and performance. The industry direction is to model IP SLA after those offered by frame relay networks. The reality however is that the SLA surrounding today´s private IP services only loosely mirror frame relay SLA. In this paper, we examine the intent and limitations of current IP SLA. We explore the feasibility of two significant enhancements. First we study the feasibility of reducing the time scales associated with the performance assessment to something that is meaningful to the corporate end user. Second we explore the potential benefits of extending current performance assessment methods with application level performance metrics. We present preliminary results suggesting that it is possible to offer performance assurances based on carefully chosen latency objectives as long as the average utilization of the access link is less than 50% over time scales identical to those used by the performance metrics. We introduce a Web-oriented performance metric (the Web Response Time metric) and show promising benefits over traditional ping based metrics. However, for either ping or Web-based performance metrics, due to the inherent nature of a best-effort IP service, IP performance assurances are only practical when applied over long time scales.