H.323 , SIP Standards, Gatekeeper

H.323

H.323 is a standard approved by the International Telecommunication Union (ITU) in 1996 to promote compatibility in videoconference transmissions over IP networks. H.323 was originally promoted as a way to provide consistency in audio, video and data packet transmissions in the event that a local area network (LAN) did not provide guaranteed service quality (QoS). Although it was doubtful at first whether manufacturers would adopt H.323, it is now considered to be the standard for interoperability in audio, video and data transmissions as well as Internet phone and voice-over-IP (VoIP) because it addresses call control and management for both point-to-point and multipoint conferences as well as gateway administration of media traffic, bandwidth and user participation.

H.323, which describes how multimedia communications occur between terminals, network equipment and services, is part of a larger group of ITU recommendations for multi-media interoperability called H.3x. The latest of these recommendations, H.248, is a recommendation to provide a single standard for the control of gateway devices in multi-media packet transmissions to allow calls to connect from a LAN to a Public Switched Telephone Network (PSTN), as well as to other standards-based terminals. This recommendation was announced in August 2000, by the ITU-TU Study Group 16 and the Megaco Working Group of the Internet Engineering Task Force (IETF).

Gatekeeper

A gatekeeper is a management tool for H.323 multimedia networks. A single gatekeeper controls interactions for each zone, which comprises the terminals, multipoint control units (MCUs), and gateways within a particular domain. Although the gatekeeper is an optional component, when it is included, it becomes the central administrative entity.

Depending on the demands of the specific network, the gatekeeper oversees authentication, authorization, telephone directory and PBX (private branch exchange) services, as well as call control and routing. Other functions may include monitoring the network for load balancing and real-time network management applications, intrusion detection and prevention, and providing interfaces to legacy systems. Gatekeepers are available as either hardware devices or software applications, and are offered as proprietary products from a number of vendors, including Cisco and Symantec, or as freeware.

SIP

SIP (Session Initiation Protocol) is a signaling protocol used to create, manage and terminate sessions in an IP based network. A session could be a simple two-way telephone call or it could be a collaborative multi-media conference session. This makes possible to implement services like voice-enriched e-commerce, web page click-to-dial or Instant Messaging with buddy lists in an IP based environment. 

SIP has been the choice for services related to Voice over IP (VoIP) in the recent past. It is a standard (RFC 3261) put forward by Internet Engineering Task Force (IETF). SIP is still growing and being modified to take into account all relevant features as the technology expands and evolves. But it should be noted that the job of SIP is limited to only the setup and control of sessions. The details of the data exchange within a session e.g. the encoding or codec related to an audio/video media is not controlled by SIP and is taken care of by other protocols.