IP telephony (short for Internet Protocol telephony and Internet telephony) or Voice over IP (short VoIP; from "voice over internet protocol" ), is telephony over computer networks which are set up according to Internet standards. Typical information for telephony, i.e. voice and control information for establishing a connection, is transmitted via a data network. For call participants, computers, telephone terminals specialised in IP telephony or classic telephones connected via special adapters can establish the connection.

IP telephony is a technology that makes it possible to implement the telephone service on IP infrastructure so that it can replace the conventional telephone technology including ISDN and all components.
To gain a general understanding of how Voice over IP works, we will give you some basic knowledge about components, architectures, codecs and protocols.
Since this is an IP network based technology, but there is also a completely independent level of its own that originates from the SIP protocol, we have subdivided this collection of knowledge into:

• Network Essentials
• SIP Essentials