Cable telephony

Voice over Cable ( VoC, cable telephony) is a variant of IP telephony ( VoIP), in telephony over broadband cable networks (existing usually cable TV networks ) is provided.

Analog to IP telephony, the voice information is not a permanently established connection (such as the conventional circuit-switched telephone network), but over the cable network broadcast packet-oriented.

For data transmission in cable networks the DOCSIS standard is used that specifies the requirements for the fast transfer of data over the cable network. An integral part of a DOCSIS architecture are a cable modem on the customer side and a cable modem termination system ( CMTS ) at the cable head of the provider.

In the VoC telephony an analog phone via an analog telephone adapter to a cable modem can be connected. The modem digitized and coded speech information and forwards it to the CMTS on.

Since April 2008, there is also the first time "ISDN " with two trunks, via cable.

Since DOCSIS specifies only the two lowest layers in the OSI model, the actual addressing and transmitting the voice data on the Layer 3 eventually happens as in the IP telephony.

Data compression is used here with the use of data reduction may ISDN protocols that rely on a 1-to - 1 transmission - such as fax and data transmission - do not work. Therefore, the ISDN connection is not real and is usually advertised as " ISDN feature ".

Emergency calls are possible without restrictions with Voice over Cable. In addition, the location of the caller and the transmission of the location information to the monitoring station when an emergency call is possible. VoC thus complies with the requirements of the German Telecommunications Act.

Voice over Cable has ' first-line quality ', comparable with the conventional fixed network reliability. The only problem is the power supply of the phones in case of failure or malfunction of the public grid. This is currently not the case in contrast to the fixed line or ISDN network.