Cable Telephony

Telephone service can be implemented over two-way cable networks in two ways: via circuit switching and packet switching. In circuit switching, digitized voice signals are delivered in the traditional time-division mode of circuit switching over 6MHz radio frequency channels that are provisioned over hybrid fiber/coax networks. Anywhere from a handful to a maximum of 500 to 2,000 households share access to the service stream in any one coaxially connected service area. The trouble with circuit-switched voice-over cable is that the platforms are proprietary.

Another way to implement telephone service over cable is via packet switching. Similar to the circuit-switched version of cable telephony, IP uses shared 6 MHz channels. While IP over cable offers the advantage of standardization, the migration path to IP is so long that it often justifies the incremental cost of starting with a proprietary system. Vendors of proprietary circuit-switched solutions (i.e., Tellabs, ADC Telecommunications, and others) plan to support migration by producing gateways that connect the local cablephone host digital terminal at the head end with IP backbones. This setup would enable long-haul traffic to be transferred via IP while still retaining the circuit-switched mode for local connections within and outside the cable network.