 the dot delimiter to define the user's actual IP address. The DNS servers are spread around the country and are using a fully distributed computing architecture to maintain addressing information of all registered domains. The databases can be updated on a 30-minute timer, or other time limit as set by the ISP. Normal operation requires at least two DNS connections for redundancy purposes. Regional ISPs provide local DNS servers updated from the master database maintained by Network Solutions, Inc. of Virginia. The InterNic (the name assigned to Network Solutions as the custodian of the numbering plan) assigns names and addresses, then promulgates the changes on a regular basis, keeping all the databases as current as possible. Separate DNS systems are used for the extensions of the addresses. Six major extensions are available: .com For commercial organizations .gov For government bodies .edu For educational institutions .mil For military organizations .org For organizations that do not fit the .com role, usually nonprofit organizations .net For systems performing network services A domain is also assigned for each country such as Canada (.ca). An orga- nization may fit into more than one category and can choose whichever naming domain it prefers. Now newer roots in the Internet are being cre- ated like .store and SO on. We could use the IP address instead of the domain name in some cases. For example, the URL 192.168.10.2 will take you to the tcic.com front page, and e-mail sent to bud@[192.168.10.2] will reach bud@tcic.com. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Function of GPRS Elements Function of GPRS Elements (The brackets in the e-mail address are necessary when using IP addresses.) Mapping between domain names and IP addresses using DNS makes things much easier to understand though. They also help with porta- bility; you d