Chapter 7. Analog, Cable TV and Digital Modems and Set-Top Boxes

In this chapter...

• Transferring Data from Computers to Telephone Lines

• DCE—Connections to Telephone Lines

• Modems—Analog Telephone Lines for Transmitting Data from Digital Devices

• NT1S—Connecting Devices to an ISDN Line

• CSU/DSUs—Connecting Devices to a Digital Line

• Cable Modems—Using Cable TV Facilities for Data Communications

• Set-Top Boxes

• Appendix: Modem Standards

Cable TV providers are upgrading their networks to offer high-speed Internet access, Voice over IP (VoIP), two-way video, better reliability and improved reception. Some of them are also beginning to sell Internet access service to small- and medium-sized businesses. Their research organization in the United States, CableLabs, is working on standards so that customers can purchase cable modems and set-top boxes from a variety of manufacturers. Cable providers want to take advantage of technology improvements to offer more sophisticated services such as entertainment guides and set-top boxes with email and instant messaging capability. Standards will let them mix and match set-top boxes from a variety of sources. They hope these additional services will increase their revenues.

This chapter takes the mystery out of connecting computers to telephone lines. Anyone sending data, video or images over a telephone line needs a device between the telephone line and the equipment communicating. The vast majority of Internet subscribers worldwide use analog dialup service. Modems convert their computer's digital signals to analog in such a way that the signals are compatible with analog telephone lines. All devices connected to public and private networks need devices for functions such as error correction and timing between computers, multiplexers or local area networks (LANs) and service providers' facilities. Some business and residential subscribers, particularly those in Europe and Japan, access the Internet with basic rate interface (BRI) ISDN service. Because integrated services digital network (ISDN) is digital, modems are not required. However, ISDN requires terminal adapters and network termination type 1 (NT1) devices. Channel services unit/data service units (CSU/DSUs) are used on T-1 and E-1 type digital circuits.