| A cable modem is a special type of modem that is designed to modulate a data
signal over cable television infrastructure.
The term cable Internet access (or simply cable) refers to the delivery of Internet service over this infrastucture.
Cable modems should not be confused with older LAN systems
such as 10base2 or 10base5 that used
coaxial cables -- and especially not with 10broad36, which actually utilized the same sort
of cable as CATV systems.
Cable modems are primarily used to deliver broadband Internet access, taking
advantage of unused bandwidth on a cable television network.
Along with digital subscriber line technology,
cable modems ushered in the age of broadband Internet access in developed
countries. Prior to the availability of such systems, Internet access involved slow dial-up access over a public switched telephone network.
Users in a neighborhood share the available bandwidth provided by a single coaxial cable line. Therefore, connection speed can vary depending on how many people are using the service
at the same time.
Often the idea of a shared line is seen as a weak point of cable Internet access. From a technical point of view, all
networks, including DSL services, are sharing a fixed amount of bandwidth between a multitude of users -- but because cable
networks tend to be spread over larger areas than DSL services, more care must be taken to ensure good network performance.
A more significant weakness of cable networks using a shared line is the risk of loss of privacy, especially considering the
availability of hacking tools for cable modems. This issue is addressed by encryption and other privacy features specified in the
DOCSIS (Data Over Cable Service Interface Specification) standard used by most cable
modems.
DOCSIS Specifications
The cable in is a RG-6 tri-shield, with a F connector.
CDLP
CDLP is a proprietary standard made by Motorola. CDLP CPE was capable of both RF (Cable Network) and PSTN return paths. The standard is
more or less defunct now with new providers using DOCSIS and existing providers
changing. Sample Motorola CDLP
Modem (http://broadband.motorola.com/catalog/productdetail.asp?image=large&productID=221)
The Australian ISP BigPond
employed this system when it started Cable Modem trials in 1996. For a number of years cable Internet access was only available
to Sydney, Melbourne and Brisbane via CDLP. This network ran parallel to the newer DOCSIS system for a number of years, in 2004 the CDLP network was switched off
and now is exclusively DOCSIS.
Cable modem manufacturers
External links
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