NPS: a non-interfering deployable web perfectching system

We present NPS, a novel non-intrusive web prefetching system that (1) utilizes only spare resources to avoid interference between prefetch and demand requests at the server as well as in the network , and (2) is deployable without any modifications to servers, browsers, network or the HTTP protocol. NPS's self-tuning architecture eliminates the need for traditional "thresholds" or magic numbers typically used to limit interference caused by prefetching, thereby allowing applications to improve benefits and reduce the risk of aggressive prefetching. NPS avoids interference with demand requests by monitoring the responsiveness of the server and accordingly throttling the prefetch aggressiveness, and by using TCP-Nice, a congestion control protocol suitable for low priority transfers. NPS avoids the need to modify existing infrastructure by modifying HTML pages to include Javascript TM code that issues prefetch requests and by wrapping the server infrastructure with several simple external modules that require no knowledge of or no modifications to the internals of existing servers. Our measurements of the prototype under a web trace indicate that NPS is both non-interfering and efficient under different network load and server load conditions. For example, in our experiments with a loaded server with little spare capacity, we observe that a threshold-based prefetching scheme causes response times to increase by a factor of 2 due to interference, whereas prefetching using NPS decreases response times by 25%.