Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.

GPS is the now well-known network of satellites that offers global positioning and timing data for land and sea navigation. The system consists of 24 Navstar satellites that orbit at an altitude of 11,000 miles. It was originally put in place by the U.S. Department of Defense, but its services are now available free to anyone. GPS location devices are now sold in stores and included in automobiles as a way to track their position for driver navigation and servicing.

GPS works by triangulating a radio signal from the satellites. The signals are located at 1575.42 MHz. Receivers detect these signals and automatically calculate their position on the global grid.

A number of Internet applications can take advantage of GPS. RFC 2009 (GPS-Based Addressing and Routing, November 1996) proposes a family of protocols and addressing methods to integrate GPS into the Internet Protocol to enable the creation of location dependent services such as:

• Multicasting selectively only to specific geographical regions defined by latitude and longitude. For example, sending an emergency message to everyone who is currently in a specific area, such as a building or train station.
• Providing contiguous information services for mobile users when information depends on the user's location. In particular providing location-dependent bookmarks, which provides the user with any important information that happens to be local (within a certain range), possibly including other mobile servers.
• Providing a given service only to clients who are within a certain geographic range from the server (which may be mobile itself), say within 2 miles.
• Advertising a given service in a range-restricted way, say, within 2 miles of the server.

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