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The standards for VoIP via cable

While Voice over IP is already available for private networks and has been shown to be a viable if not always reliable form of telephony over the public internet, except for a few trials and demonstrations it has not been available to the cable modem consumer and even though everyone agrees that it is the future of telephony there are a few reasons why it has not made inroads into the consumer space. Standards for one.

Until recently cable modems suffered from a lack of standards for high speed data transfer as well as limitations on bi-directional communications, such as the need for a telephone connection for upstream data traffic. Even high performance modems could not provide the reliable "Quality of Service" (QoS) that most telephone companies do because there was no guarantee that packets of data would arrive on time.

Facing numerous proprietary solutions and the need to compete with the telephone companies in the newly de-regulated telecommunications market, the cable companies began work on a set of standards  to define hardware and software specifications that would enable interoperability among cable modem systems and provide protocols to open cable systems up to voice, data, and networking services.

This effort was spearheaded by Cable Television Laboratories (CableLabs), an organization made up of cable providers from the U.S., Canada, Mexico and South America whose goal is to provide technological support and foster interoperability standards within the cable industry.

CableLabs currently two has specifications available for cable modem  hardware and software supporting high speed data transfer over cable networks. 

On the hardware side new cable modems are required to be CableLabs certified to the Data Over Cable Service Interface Specification (DOCSIS) providing cable modem vendors with a market recognized seal of approval for modems capable of high speed bi-directional data transfer.

For software the PacketCable 1.1 specification defines a standard for packet based communications over cable modems using the Internet Protocol as well as providing the Quality of Service (QoS) capabilities needed for implementing IP telephony.

These two standards together provide a foundation for the development of telephony, data and multimedia applications software.

While there are additional standards for the delivery of voice, or other real-time data over network hardware this document will focus on the CableLabs efforts as it is assumed that with the cable industry support it's standards will be the dominant reference for high speed data over cable modems especially considering the list of CableLabs members.

The next section will detail the current standards available for developing VoIP Cable Modem hardware and software.