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Cable Internet is the type of high speed access to the Internet that makes use of the same infrastructure as cable television. To access this type of broadband Internet, a customer typically connects a cable modem to the same coaxial output as his television, sometimes making use of a splitter. At the other end of the connection is some type of cable modem termination system (CMTS), which can provide connectivity to anywhere between 4,000 and 150,000 subscribers within a 100 mile (160 kilometer) radius. Cable Internet often offers large upstream and downstream bandwidth, though these both can be limited if a great number of users are connected at once.
A large portion of broadband Internet services are provided through existing cable or telephone line infrastructures. Each of these types of broadband comes with inherent benefits and drawbacks, and a number of other options, such as WiMAX™ and broadband over power lines (BPL), have also emerged. Cable Internet is often available in any location that is served by cable television, though some remote areas may lack the necessary CMTS. Though the cable network service provided between CMTS and the cable modem is typically known by the term last mile infrastructure, the actual distance may be 100 miles (160 kilometers) or more, and large networks often feature a number of hubs.
Similar to other broadband services, such as WiMAX™, cable Internet uses a shared bandwidth pool for subscribers in the same local area. Cable Internet systems typically share the bandwidth of the access network, which is the infrastructure that connects the modem to the CMTS. This can result in a degradation of service during peak access times, which may result in slow transfer speeds and a difficulty staying connected to the network.
Cable Internet providers typically take a number of precautions to avoid service issues during peak usage. The bandwidth that each subscriber uses may be monitored so that each user can be provided with a fair percentage of what is available. Bandwidth caps may sometimes be instituted if a particular subscriber is using too much upstream or downstream throughput, or has transferred excessive data in a billing period. Such caps may be instituted only when the network is stressed, or they can be left in place for extended periods of time.
Internet service providers (ISPs) that offer access via cable infrastructures are typically the local cable company. This same company that provides television and voice services will usually also be responsible for operating the cable television termination system and other associated equipment. Subscribing to television services is not usually necessary to get cable Internet, though it is often less expensive. In some cases, resellers ISPs may also buy connections from the cable company and then offer them to the public at a discount.