Cable modem

Encyclopedia : C : CA : CAB : Cable modem

Cable modem for broadband Internet access

A cable modem is a unique 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.

Contents

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

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 Megabits per second (Mbit/s) up to 15 Mbit/s or more. The upstream bandwidth on residential cable modem service usually ranges from 384 Kilobits per second (kbit/s) to 2 Mbit/s 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 telephone company's nearest central office.

There are two 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, although in most areas, this has been eliminated due to redundant and fiber networks. 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.
Many cable Internet providers are reluctant to offer cable modem access without tying it to a cable television subscription. They do this by charging higher rates, say $40/month for cable modem only access, than if one bundles it with a cable TV plan where it might be $30/month for cable modem service plus $20/month for cable TV service. This has ramifications similar to those of the lack of naked DSL.

CDLP

CDLP is a proprietary standard made by Motorola. CDLP CPE was capable of both PSTN (telephone network) and RF (cable network) return paths. The PSTN return path cable modem service was considered 'one way cable' and had many of the same drawbacks as satellite internet service, and as a result it quickly gave way to two way cable. Cable modems that used the RF cable network for the return path were considered 'two way cable', and were better able to compete with DSL which was bidirectional. The standard is more or less defunct now with new providers using and existing providers having changed over to the DOCSIS standard. [The Motorola CDLP Proprietary CyberSURFR] is an example of a modem that was built to the CDLP standard, capable of a peak 10 Mbit/s downstream and 1.532 Mbit/s. (CDLP supported a maximum downstream bandwidth of 30 Mbit/s which could be reached by using several modems.)

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 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 VoIP through a single piece of customer premise equipment.

Cable modem

Cable Internet Access

CDLP

Cable Modems and VoIP

See also

Cable modem manufacturers

External links

Further reading