The Latency Budget: How to Save and What to Buy

Abstract

Novel applications have driven innovation in the Internet over decades. Electronic mail and file sharing drove research for communication and congestion control protocols. Hypertext documents then created the web and put the web browser at the center. Online advertisement commercialized the web and accelerated development in web technologies such as JavaScript along with content delivery and caching. Video streaming then demanded higher bandwidth both in the data center and the home network. The web is now headed towards increased interactivity and immersion. With high bandwidth available to many subscribers, end-to-end network latency is likely to be the bottleneck for interactive applications in the future. While some applications have very stringent latency requirements, many have a "good enough" latency floor, beyond which further speed-up is imperceptible to humans. In the latter case, time saved from reduced network latency can be used to improve other aspects of user experience. For example, most private information retrieval protocols require more computation or multiple roundtrips, and reduced network latency can allow clients to use such protocols to protect user privacy while also delivering good quality of experience. The latency budget is then set by the "good enough" latency floor (which may vary over applications). We can save by reducing network latency, and then spend to improve various aspects of the web ecosystem. This thesis (a) addresses a widespread pitfall in measuring latency on the web, and highlights that (b) there is ample potential to reduce infrastructural, long-distance latency, and (c) the saved latency enables improvements in the web ranging from increased publisher revenues for online ads to improved user privacy for DNS queries.