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CATV aka "Cable Modems"

Strictly speaking, calling Cable TV (CATV) a "cable modem" is not entirely accurate. Unlike ISDN however, CATV does modulate and demodulate, but it also acts as a bridge, an encrytor and SNMP agent and a hub (these terms will be explained in this document). Where available CATV is usually less expensive than ISDN. Cable modems come in three main forms; (i) an external cable modem box that requires an Ethernet Network Information Card (NIC), (ii) an internal cable modem with a 56kbps modem built in or (iii) an internal cable modem for use with a separate 56kbps modem. A CATV connects to the network by using the same coaxial cable connection as the cable TV service. acting as a bridge between the hybrid fibre/coax (HFC) in the individual home to the network that connects all cable modems in the local area. Ensure that the CATV system is two way (upload/download) as some systems have been built on the slower and obsolete one way CATV coax cable. Only the two-way cable will allow network connection independently of the telephone system.

Originally, cable modems were leased to CATV users using a particularly proprietary standard. Now, DOC-SIS (Data Over Cable Service Interface Specification) compliant cable modems are more common and purchasers should ensure that they receive a DOC-SIS compliant modem rather than a proprietary standard. Cable TV uses a broadband network, meaning that bandwidth is split to carry many signals at the same time. A typical network will carry approximately 750MHz of bandwidth, with each channel requiring 6MHz. Upstream and downstream traffic will require different channels and usually doesn't match. Thus, CATV is quite impractical for hosting webservers. However downstream traffic will usually be around 512kbps, about 10 times faster than a modem and about 4 times faster than ISDN.

Whilst security on CATV is an issue (as each individual personal computer is the network in an area with bidectional traffic), proper configuration and encryption can protect a user's PC. In general however, CATV is undoubtedly the best value for money, providing 24-hour access and exceptional download speeds at a reasonable price. It's greatest drawback is that it is not widely available.