The cable industry has expanded its competitive offerings to include business and residential telephone services delivered over its fiber optic infrastructure. Once upgraded to two-way fiber optics, a cable system can offer telephone service over the same cable line that already carries digital video, high speed Internet and other advanced services to consumers. Cable companies are certified local exchange carriers offering competitive residential voice services across the country.
In addition to the deployment of circuit-switched telephony, many companies are launching Digital Phone (VoIP,Voice over Internet Protocol) service. Through the use of software, Digital Phone provides all of the functionality of the public switched telephone network (PSTN), while making possible new features not available through traditional circuit-switched telephony. Calls are placed over an IP-based data network and voice is transmitted with data "packets." The IP data packets used by services from some of the Internet telephony providers travel over the public Internet. Facilities-based cable offerings, in contrast, transport IP data packets over their private managed IP networks with end-to-end quality of service monitoring (while still interconnecting with the PSTN as necessary).