H.323 Benefits

IP-PBX system designers gain several important benefits by using the H.323 recommendations for support of IP telephony. One of the most important is an open system design because H.323 is not proprietary to any hardware equipment or operating system. There is a multitude of products that support H.323 standards and provide IP-PBX system designers with a flexible choice of system components and solutions. Major system hardware elements, such as servers and clients (telephones, PCs), are available from dozens of sources. Proprietary hardware is associated with circuit switched PBXs and is something IP-PBX system designers hope to avoid. Standards for voice and video codecs and for the compression and decompression of digital bit streams are also established under H.323, ensuring communications and networking between systems from different manufacturers. H.323 also establishes methods for receiving clients to communicate their capabilities to sending clients to establish common call set-up and control protocols, because it is important for clients in different corporate networks to communicate with each other.

The fact that H.323 is designed to operate on top of common network architectures is another important factor in the IP-PBX system open design concept. Network technology is constantly evolving, as are bandwidth management and applications services over the network. Systems based on H.323 standards can evolve as networks evolve. Dependency on one type of network or the currently installed network would limit the functional growth of an IP-PBX system. Many users may want to conference LAN clients to a station user at a remote site. H.323 establishes a means of linking LAN-based desktop systems with ISDN-based group systems. H.323 uses common codec technology from different audio- and videoconferencing standards to minimize transcoding delays and provide optimum performance.

An important PBX feature is multiparty conferencing. H.323 supports conferences of three or more endpoints without requiring a specialized MCU, but the H.323 MCU element can support a more powerful and flexible architecture for hosting multipoint conferences. The MCU element can be embedded in a variety of H.323 system components. H.323 also can support multicast transport in multipoint conferences. Multicast sends a single packet to a subset of destinations on the network without replication. Multicast transmission uses bandwidth more efficiently than unicast or broadcast methods of transmission because all stations in the multicast group read a single data stream. An H.323 conference also can include endpoints with different communication media capabilities. For example, a telephone with audio-only capabilities can participate in a conference with workstations that have audio, video, and data capabilities. Further, an H.323 multimedia terminal can share the data portion of a video conference with a T.120 data-only terminal while sharing voice, video, and data with other H.323 terminals

H.323 also addresses bandwidth management in support of bandwidth-intensive audio and video traffic. The network manager can control the number of simultaneous H.323 connections within a network or the amount of bandwidth available to H.323 applications. Limiting connections (conversations) across the network ensures that critical traffic will not be degraded. The QoS issue is one of the most important facing IP-PBX growth because many customers have problems addressing increased traffic load on their networks. Voice communications is very sensitive to delays, packet loss, and other network problems that do not affect data traffic to the same degree. Assuming that a significant amount of voice traffic will be transmitted on LAN networks based on a mix of old and new equipment originally configured for non–real-time communications, achieving acceptable QoS levels is one of the greatest barriers facing IP-PBX market penetration. Security of voice communications over LANs and WANs is another customer concern addressed by H.323. The H.323 recommendation provides authentication, integrity, privacy, and nonrepudiation support.