Dialogic Global Call IP Benutzerhandbuch

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Dialogic Corporation

This chapter provides overview information about the following topics: 

Voice over IP (VoIP) can be described as the ability to make telephone calls and send faxes over IP-
based data networks with a suitable Quality of Service (QoS). The voice information is sent in 
digital form using discrete packets rather than via dedicated connections as in the circuit-switched 
Public Switched Telephone Network (PSTN). 

Currently, there are two major international groups defining standards for VoIP:

International Telecommunications Union, Telecommunications Standardization Sector 
(ITU-T), which has defined the following:

Recommendation H.323, covering Packet-based Multimedia Communications Systems 
(including VoIP)

Internet Engineering Task Force (IETF), which has defined drafts of the several RFC (Request 
for Comment) documents, including the following central document:

RFC 3261, the Session Initiation Protocol (SIP) 

The H.323 recommendation was developed in the mid 1990s and is a mature protocol.

SIP (Session Initiation Protocol) is an emerging protocol for setting up telephony, conferencing, 
multimedia, and other types of communication sessions on the Internet.

The H.323 specification is an umbrella specification for the implementation of packet-based 
multimedia over IP networks that cannot guarantee Quality of Service (QoS). This section 
discusses the following topics about H.323: