Editing Voice over IP (section)

==Power requirements==
Telephones for traditional residential analog service are usually connected directly to telephone company [[phone line]]s which provide direct current to power most basic analog handsets independently of locally available electrical power. The susceptibility of phone service to power failures is a common problem even with traditional analog service where customers purchase telephone units that operate with wireless handsets to a base station, or that have other modern phone features, such as built-in voicemail or phone book features.

VoIP phones and VoIP telephone adapters connect to [[Network router|routers]] or [[cable modem]]s which typically depend on the availability of [[mains electricity]] or locally generated power.<ref>{{cite web|url=http://www.ictregulationtoolkit.org/en/Section.3083.html|title= 4.4 VOIP&nbsp;– Regulatory Issues&nbsp;– Universal Service |website=ICT Regulation Tool Kit |access-date=September 21, 2017|archive-date=June 4, 2009|archive-url=https://web.archive.org/web/20090604204232/http://www.ictregulationtoolkit.org/en/Section.3083.html|url-status=dead}}</ref> Some VoIP service providers use customer premises equipment (e.g., cable modems) with battery-backed power supplies to assure uninterrupted service for up to several hours in case of local power failures. Such battery-backed devices typically are designed for use with analog handsets. Some VoIP service providers implement services to route calls to other telephone services of the subscriber, such a cellular phone, in the event that the customer's network device is inaccessible to terminate the call.