Cable modem

From Free net encyclopedia

A cable modem is a special type of modem that is designed to modulate a data signal over cable television infrastructure. Cable modems are primarily used to deliver broadband Internet access, taking advantage of unused bandwidth on a cable television network. There were 22.5 million cable modem users in the United States during Q1 2005, up from 17.4 million in Q1 2004. It is also commonly found in Canada and Europe.

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 utilised the same sort of cable as CATV systems.

1 Cable Internet Access
2 CDLP
3 Cable Modems and VoIP
4 See also
5 Cable modem manufacturers
6 External links

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Cable Internet Access

The term cable Internet access (or simply cable) refers to the delivery of Internet service over this infrastructure. The proliferation of cable modems, along with DSL technology, has ushered in the age of broadband Internet access in developed countries.

Bandwidth of residential cable modem service typically range from 3 mbps up to 15 mbps or more. The upstream bandwidth on residential cable modem service usually ranges from 384kbps to 2 mbps or more. There are few attempts to offer different service tiers beyond the traditional 'home' and 'business' designations.

In comparison, DSL tends to offer less speed and more variance between service packages and prices. Service quality is also far more dependent on your location in relation to the local ISP.

There are three traditional disadvantages to cable internet:

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. 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. This has become much less of an issue in recent years.
Cable networks using a shared line risk a loss of privacy, especially in light of 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.
Many cable Internet providers are reluctant to offer cable modem access without tying it to a cable television subscription. This has ramifications similar to those of the lack of naked DSL.

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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

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.

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Cable Modems and VoIP

With the advent of Voice over IP telephony, cable modems can also be used to provide telephone service. Many people who have cable modems have opted to eliminate their Plain Old Telephone Service (POTS). Because most telephone companies do not offer naked DSL (DSL service without a POTS line), many VoIP users prefer cable modems.

VoIP and other new data services that require broadband Internet access are driving demand for increased bandwidth delivery via cable modems. As of 2005, several national cable systems in the United States have announced plans to upgrade their networks to meet this demand.

An alternative to cable modems is the Embedded Multimedia Terminal Adapter (EMTA or E-MTA). An EMTA allows MSOs to offer both High Speed Internet and IP Voice through a single piece of customer premise equipment. The following is an excerpt from "Touchstone™ – Setting the Standards for E-MTAs", a white paper published by the manufacturer Arris (http://www.arrisi.com). The full text of the white paper is available at http://www.arrisi.com/products_solutions/applications/white_papers/Touchstone_Setting_Standards.pdf:

An Embedded Multimedia Terminal Adapter (E-MTA) is the interface device located at the subscriber’s premise that enables IP telephony and high-speed data access from a Cable Multiple System Operator (MSO). E-MTAs are based on the latest requirements from either CableLabs® (DOCSIS™ 1.1/PacketCable™) or the Euro-DOCSIS Certification Board (ECB) for delivering Voice over Internet Protocol (VoIP). These standards help set a baseline for services and interoperability. There are a number of details above and beyond DOCSIS, though, which really differentiate E-MTAs in the marketplace. These factors can impact voice quality and the ability to deliver all the services subscribers expect at all times. In order to be a significant competitor to the incumbent local exchange carrier (ILEC), an MSO must be able to deliver the carrier grade experience subscribers have come to expect. Following is a review of the additional requirements that ARRIS has found to be essential to deliver telephony worldwide. These are requirements that operators should be demanding of their E-MTA vendors.

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