Gateways to the Internet Connecting all the users and individual networks together are Internet Service Providers (ISPs). ISPs are companies that provide the technical gateway to the Internet. What's the Address? These companies own blocks of registered access addresses that they assign to their customers, to give them an identity on the network. These addresses are called the Internet protocol addresses, or IP addresses. Having a registered IP address makes each site a valid member of the Internet. This is how individual users are identified to receive file transfers, e-mail, and file requests. IP Addresses IP addresses exist in the numeric format of XXX.YYY.ZZZ.AAA. Each address consists of four 8-bit fields separated by dots. This format of specifying addresses is referred to as dotted decimal notation. The decimal numbers are derived from the binary address that the hardware understands. For example, the following network address: 10000111.10001011.01001001.00110110 (binary) corresponds to 135.139.073.054 (decimal). ISDN Links Other users, who require quicker data transfers, contract with the telephone company to use special, high-speed Integrated Service Digital Network (ISDN) lines. These types of links require a digital modem to conduct data transfers. Because the modem is digital, no analog conversion is required. T1 and T3 Dedicated Connections Users who require very high volumes will lease dedicated T1 and T3 lines from the telephone company. These applications generally serve businesses who put several of their computers or networks online Metropolitan Area Networks In some areas, high-speed intermediate-sized networks, referred to as Metropolitan Area Networks (MANs), are popping up. These networks typically cover areas up to 50 kilometers in diameter and are operated to provide access to regional resources. They are similar to LANs in speed and operation but use special high-speed connections and protocols to increase the geographical span of the network — more similar to WANs TCP/IP The language of the Internet is Transmission Control Protocol/Internet Protocol, or TCP/IP for short. No matter what type of computer platform or software is being used, the information must move across the Internet in this format. TCP/IP is now supported on virtually every brand of computing equipment. The TCP/IP Packet TCP/IP calls for data to be grouped together in bundles called network packets. The TCP/IP packet is designed primarily to allow for message fragmentation and reassembly. Packet information is conveyed through two header fields: the IP header, and the TCP header, followed by the data field, as shown. Domain Name System The IP addresses of all the computers connected to the Internet are tracked using a listing system called the domain name system (DNS). This system evolved as a method of organizing the members of the Internet into a hierarchical management structure. The DNS structure consists of various levels of computer groups called domains. Each computer on the Internet is assigned a domain name, such as email@example.com. Each domain name corresponds to an additional domain level. Names and Addresses In addition to its domain name tracking function, the DNS system links the individual domain names to their current IP address listings Site Identifiers In the example firstname.lastname@example.org, the .com notation at the end of the address is a major domain code that identifies the user as a commercial site. The following list identifies the Internet's major domain codes: .com = Commercial businesses .edu = Educational institutions .gov = Government agencies .int = International organizations .mil = Military establishments .net = Networking organizations .org = Nonprofit organizations Subdomain Names The .owt identifies the organization that is a domain listed under the major domain heading. Likewise, the .oneworld entry is a subdomain of the .owt domain. It is very likely one of multiple networks supported by .owt. The Marcarft entry is the address location of the end user. If the end user location is an e-mail address, it is usually denoted by an ampersand (@) between its name and the name of its host domain (that is, email@example.com).