Internet service providers (ISPs) enable businesses to connect to the Internet. Large-scale ISPs offer private line hookups such as ATM, T-1, T-3, and fractional T-1. Asynchronous transfer mode (ATM) is a high-speed, high-bandwidth, packet switching and transmission system which Internet service providers (ISPs) use to ntegrate voice, video, and data communications. ATM or cell relay uses fixed-sized packets called cells. T-1 lines have 24 voice or data channels and can reach transmission speeds of 1.54 Mbps. T-1 lines are used by small and medium-sized companies with heavy network traffic. T-3 lines provide up to 28 channels and can achieve transmission rates of 44.74 Mbps. These leased line connections are relatively expensive to maintain and suitable for only the largest networks. Some Internet service providers (ISP) offer fractional T-1 lines as an alternative to a full T-1 or T-3 connection. Fractional T-1 is a point-to-point arrangement in which a multiplexer channelizes a carrier’s signals.
Internet service providers (ISPs) use ISDN and DSL to enable small and medium-size businesses to connect to the Web. Integrated services digital network (ISDN) is a set of standards for digital transmissions over copper telephone wires. Subscribers who use an ISDN adapter instead of a standard modem can achieve transmission speeds of up to 128 Kbps. Because ISDN requires the use of an adapter at both ends of the transmission, internet service providers (ISPs) who offer ISDN already have ISDN adapters in place. Like ISDN, digital subscriber line (DSL) technology can be used to bring high-bandwidth signals over copper telephone lines. Internet service providers who offer xDSL provide DSL variations such as ADSL, HDSL, and RADSL. A DSL line can carry both data and voice signals. The data part of a DSL line is connected continuously.
Internet service providers (ISPs) who serve small businesses and residential customers offer dial-up connections. Dial-up access uses a modem to establish and maintain an Internet connection for a limited amount of time. The connection can be established manually or automatically. The modem modulates outgoing digital signals from the computer and demodulates incoming analog signals from the copper telephone line. Most personal computers (PC) include modems cable of 56 Kbps or higher. Modems can be leased from Internet service providers (ISPs) or purchased outright.