Interactive TV Video High speed Internet MP3 etc Ethernet Ethernet Ethernet Ethernet ATM, FR switch Edge node Copper Fiber with broad- Network terminal Access node band access server, Broadband High bit rate service provider Figure 13.35 Combined ADSL - Ethernet solution 13.16 CABLE MODEM A cable modem (or cable TV) solution extends from the modem to the head-end. The head-end is a central distribution point for a CATV system. Video signals are received here from satellites and other sources, frequency is converted to the appropriate channels, combined with locally originated signals, and rebroadcast onto the hybrid fibre-coaxial (HFC) plant. The head-end is where the cable modem termination system (CMTS) is normally located. A CMTS is a system of devices located in the cable head-end that allows CATV operators to offer high-speed Internet Older CATV systems were provisioned using only coaxial cable. Modern systems use fibre transport from the head-end to an optical node located in the subscriber neighbour- hood to reduce system noise. Coaxial cable runs from the node to the subscriber. The fibre plant is generally a star configuration with all optical node fibres terminating at a head- end. The coaxial cable part of the system is generally a trunk-and-branch configuration. The solution is called HFC (cable network). The upstream frequency used to transmit data from the cable modem to the CMTS is normally in the 5-42 MHz range for US systems and 5-65 MHz for European systems. The downstream frequency used for transmitting data from the CMTS to the cable modem is normally in the 42/65-850 MHz range depending on the actual cable plant capabilities. Data over cable service interface specification (DOCSIS) is the dominating cable modem standard. It defines technical specifications for both cable modem and CMTS. Access Network 13.17 WLAN The increasingly popular WLAN or wireless LAN is used as a common LAN in office environment but also as a home LAN and as a public access network to the Internet at hot spots, such as