These applications later came out with voice conversation features in which users utilize computer headsets or IP telephone handsets in communicating with one another. Services like call forwarding, conference calling, voicemail, contact management and directory assistance were later added and paved the way for the creation of a new revolutionary technology - Voice over Internet Protocol or VoIP. This development has captured the attention of telecom regulators and operators who have now started to embrace the technology as one of their mainstream services. The two most popular protocols, H.323 and SIP will be discussed in this report.
H.323 is a standard for the transmission of real-time audio, video, and data information over IP-based networks. The standard contains specifications on the components, protocols, and procedures required in providing multimedia communication over local-area networks (LANs), metropolitan-area networks (MANs), wide-area networks (WANs) and even enterprise networks (ENs). Applications of H.323 may include IP telephony (audio only), videotelephony (audio and video), audio+ data and audio+video+data. H.323 can also be used for point-to-point or point-to-multipoint-multimedia communications like videoconferencing. Based on these applications, it can be seen that the standard can be utilized in a wide market segment - from consumer to enterprise to telco services.
The H.323 standard is specified by the ITU-T Study Group 16. Version 1 was formulated in 1996 and refers to visual telephone systems and equipment for LANs that provide a nonguaranteed quality of service (QoS). It is geared more for consumer applications via LANs and the Internet.
Version 2 of the standard was formulated in 1998 to accommodate the introduction of new voice-over-IP (VoIP) applications and IP telephony. The absence of a governing standard for these applications resulted to incompatibility of PC-based equipment and PBX or PSTN-based peripherals, so the new H.323 version was defined.
At present, there are moves to add new specifications to the standard for new applications like fax-over-IP networks, gatekeeper-to-gatekeeper communications, and fast-connection mechanisms. This will pave the way for Version 3 of the standard.
The H.323 standard specifies four kinds of components:
1. Terminals. An H.323 terminal can either be a personal computer (PC) or a stand-alone device, running the multimedia applications. It primarily supports audio communications but can optionally support video or data communications. The primary goal of H.323 is to interface standard-defined equipment with other multimedia terminals.
2. Gateways. A gateway refers to the equipment used to provide connectivity between an H.323 network and a non-H.323 network. The H.323 network can consist of PCs and PC-based peripherals while a non-H.323 network can refer to a PBX or PSTN network. In order to achieve connectivity between these two dissimilar networks, translating protocols were developed for traditional telephony features like call setup and release. It should be noted that a gateway is not required for communication between two H.323 terminals within an H.323 network.
3. Gatekeepers. A gatekeeper is necessary if an H.323 network will be implemented with services such as billing, addressing, call-routing, bandwidth management and authorization and