In telecommunications cable internet refers to a form of broadband internet access which differs from other forms of access by using the cable television infrastructure. This article provides an overview of the concepts; for a more detailed approach to the technology, see the article on cable modems.
Cable internet is similar to digital subscriber lines and fiber optic networks in that it bridges the last kilometre or mile from the internet provider to the subscriber premises. It is layered on top of the existing network infrastructure used for cable television similar to how DSL uses the existing telephone network. Cable networks remain, along with the telephone network, one of the two predominant means of residential internet access. Recently, both have seen increased competition from dedicated fibre deployments and wireless and mobile networks.
Hardware and bit rates
Downstream (towards the user) bir rates can be as much 50 megabit per second for business connections, but consumers are generally offered between two and ten megabits, depending on country. Upstream (from the user) rates range from 384 kilobits per second to more than 20Mbps.
Broadband cable internet access requires a cable modem (CM) at the customer premises and a CMTS (Cable Modem Termination System) at a cable operator facility (typically a headend or hub location). The two are connected via coaxial cable or, more commonly, a Hybrid Fiber Coaxial plant. While access networks are sometimes referred to as "last-mile" (or "first-mile") technologies, cable internet systems can typically operate where the distance between the CM and CMTS is up to 100 miles (160 km).
Most Data Over Cable Service Interface Specification (DOCSIS) cable modems restrict upload and download rates, with customisable limits. These limits are set in configuration files which uploaded to the modem using the Trivial File Transfer Protocol when the modem first establishes a connection to the provider's equipment.
Criticism
Like all residential broadband network technologies (e.g. DSL, FTTX, Satellite internet, WiMAX), a fixed channel capacity is shared by a population of users (in the case of cable internet, users in a neighborhood share the available capacity provided by a single coaxial cable line). Therefore, service speed can vary depending on how many people are using the service at the same time. This arrangement allows the network operator to take advantage of statistical multiplexing in order to provide an adequate level of service at an acceptable price. However, the operator has to monitor usage patterns, and scale the network appropriately, to ensure that customers receive adequate service even during peak usage times. Some operators also use a bandwidth cap.
Many cable Internet providers offer Internet access without tying it to a cable television subscription. This is achieved by charging higher rates than if one bundles it with a cable television subscription. The extra cost is to cover the cable line access, much like phone companies charge a small line access fee for having DSL Internet service without a phone subscription (naked DSL). The cable line tap outside the residence is adjusted to prevent analog cable television channels from being transmitted through. The customer does not receive any cable television channels, including the basic channels. Internet Service Providers who resell high-speed Internet access from or through cable companies, such as Earthlink and AOL, are generally not subject to these higher rates. They can as well provide you Internet service without a cable television subscription. However, it is likely that the bill will be sent by the cable company on behalf of the Internet Service Provider.
One downstream channel can handle hundreds of cable modems. As the system grows, the CMTS can be upgraded with more downstream and upstream ports. If the HFC network is vast, the CMTS can be grouped into hubs for efficient management. Some users have attempted to override the bandwidth cap and gain access to the full bandwidth of the system (often as much as 30 Mbit/s), by uploading their own configuration file to the cable modem - a process called uncapping. Uncapping is almost always a violation of the Terms of Service agreement