 tele- phone directory and a library card catalog. For a telephone directory, the objects listed are people; the names are arranged alphabetically and the details given about each person typically include an address and telephone number. Books in a bookstore are ordered by author or by title, and infor- mation such as the ISBN number of the book and other publication infor- mation is also contained. In computer terms, a directory is a specialized database (also called a data repository) that stores typed and ordered information about objects. A particular directory might list information about printers (the objects) con- sisting of typed information, such as location, speed in pages per minute (numeric), print data streams supported (for example, PostScript or ASCII), and SO on. Directories enable users or applications to find resources that have the characteristics needed for a particular task. The LDAP is used with the corporate intranet so that the tunneling wireless users can access the various services on the intranet. The words "local," "global," "centralized," and "distributed" are often used to describe a directory or directory service. These words mean different things to different people in different contexts. In this section, these terms are explained as they apply to directories in different contexts. In general, local means something is close by, and global means that something is spread across the universe of interest. The universe of interest might be a company, a country, or the carrier's PLMN. Local and global are two ends of a continuum. That is, something may be more or less global or local than Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hil Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. SGSN-to-GGSN (Gn) and GGSN-to-PDN (Gi) Interface Chapter 10 something else. Like local and global, something can be distributed to a greater or lesser extent. The information stored in