They transport media streams using special media delivery protocols that encode audio and video with audio codecs, and video codecs.

Some popular codecs include μ-law and a-law versions of G.711, G.722, an open source voice codec known as i LBC, a codec that only uses 8 kbit/s each way called G.729, and many others.

Early providers of voice-over-IP services offered business models and technical solutions that mirrored the architecture of the legacy telephone network.

Third-generation providers, such as Google Talk, adopted the concept of federated Vo IP—which is a departure from the architecture of the legacy networks.

These solutions typically allow dynamic interconnection between users on any two domains on the Internet when a user wishes to place a call.

Second-generation providers, such as Skype, built closed networks for private user bases, offering the benefit of free calls and convenience while potentially charging for access to other communication networks, such as the PSTN.

This limited the freedom of users to mix-and-match third-party hardware and software.Rather than closed architectures, these devices rely on standard interfaces.Vo IP devices have simple, intuitive user interfaces, so users can often make simple system configuration changes.Voice, and all other data, travels in packets over IP networks with fixed maximum capacity.This system may be more prone to congestion than traditional circuit switched systems; a circuit switched system of insufficient capacity will refuse new connections while carrying the remainder without impairment, while the quality of real-time data such as telephone conversations on packet-switched networks degrades dramatically.These protocols can be used by a Vo IP phone, special-purpose software, a mobile application or integrated into a web page.