Chapter 2 THE IDMAPS MEASUREMENT INFRASTRUCTURE 2.1. Design Goals of IDMaps A network distance service, such as SONAR [Moore et aI., 1996] or HOPS [Francis, 1998], could be called upon to support a wide range of applications, from a client's accessing a single Web page once, to Network Time Proto- col (NTP) servers establishing long-term peering relationships with each other. Internet Distance MapS (IDMaps) [IDMaps Project, 1999] is an underlying measurement service that can support some of these network distance services. Since network applications are likely to be interested in different network dis- tances, there will be a large spectrum of network distances or even distance services that are useful in the Internet. However, a measurement infrastruc- ture like IDMaps cannot satisfy all conceivable requirements for all network distance services. For instance, due to technology constraints and the need for global scalability of the service, we cannot hope for a general IDMaps service to provide near-instantaneous information about current delays and bandwidth seen between two Internet hosts, even though such information could be useful to many applications. Rather, we take the opposite approach. We determine roughly the best service that we are able to provide, given technology con- straints and the need for global scalability of the service, and then consider whether there are applications for which this level of service would be useful. The following paragraphs discuss the goals of IDMaps in detail. Separation of Functions: We envision IDMaps as an underlying measure- ment infrastructure to support a distance information query/reply service such as SONAR. The full separation ofIDMaps and the query/reply service is neces- sary because the different functionalities place different constraints on the two systems. The requirements for IDMaps call for reasonably accurate distance measurements with low measurement overhead, while the requirements for the C. Jin et al. (eds.), Building Scalable Network Services: Theory and Practice © Springer Science+Business Media New York 2004