VoIP or Voice over IP enables telephones, fax and other communications devices to initiate and receive calls over a VoIP network using VoIP protocols. VoIP works with Internet and mobile services to send/receive voice calls as digital signals over the Internet using voice over IP technology.

Voice over IP
An example of a VoIP network with different end points, including telephones, fax machines and mobile VoIP terminals

There is a variety of software/hardware solutions and applications that can adapt mobile or landline phones and other devices to access VoIP services. The figure shows an example of a hybrid network depicting different ways of accessing an IP network for the purpose of using voice services.

There are two major protocols that support VoIP.

Both protocols differ in flexibility, format, scalability and other aspects. H.323 is a vertically integrated suite of protocols for voice, video, fax and data communication over packet-based networks while SIP provides a more flexible standard for initiating multimedia sessions between endpoints, including video, chat, interactive games, and virtual reality.

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