H.323 Version 3 - Overview

H.323 version 3 was approved on September 30, 1999. H.323 version 3 makes modest improvements to the H.323 version 2 Recommendation, introducing only a few new powerful features to the base document. However, H.323 has progressed substantially, mostly in the form of new Annexes to H.323 and H.225.0 that add considerable value to the overall H.323 system architecture.

Maintaining and Reusing Connections

In order to provide better performance and preserve system resources, version 3 introduces the ability for an endpoint to specify whether it has the ability to "reuse" a call signaling connection and whether it can support using the same call signaling channel for multiple calls. This is particularly important for gateways that may have thousands of calls running simultaneously. By utilizing these two features, a gateway may maintain a single TCP connection between itself and the gatekeeper in order to perform all call signaling.

Conference out of Consultation

Suppose you place a call to someone and a receptionist answers the phone. Typically, he will put your call on hold while he calls the person you are trying to reach. The receptionist may then connect you to the other party, leaving only you and the person you were calling in a call together. This feature, called "conference out of consultation", is introduced in version 3.

Caller ID

H.323 now supports the feature of "Caller ID" that one finds in the traditional telephone network, including the ability of the caller to request that name and address information be withheld from the callee and the ability of the network equipment (e.g., the gatekeeper) to screen caller information.

Language Preference

With version 3, a caller has the ability to specify a language preference. This information may be utilized by call centers to help route calls to operator who can speak the caller's language. It may also be utilized by interactive voice response (IVR) systems and announcement servers so that they can provide audio streams to the caller in the caller's preferred language.

Usage of Annex E/H.323

Gatekeepers have the ability to mandate the usage of Annex E for call signaling to endpoints that support it. (See the discussion of Annex E below).

Remote Device Control

H.323 now has this ability, through the use of H.282, to perform remote device control. This feature will allow a user to control such devices as cameras from remote.

Generic Capabilities

In the past, each time a new audio or video codec was adopted, the ASN.1 found in H.245 had to be amended to accommodate the new codec. This involves time and money, not to mention debate over the details in adding support for new codecs. With the "generic capabilities" mechanism added to H.245 (1999), codecs may now be fully defined, including various capabilities that may be negotiated when the call is established, in a generic manner which does not require additional code points to be added to the H.245 ASN.1.

Annex G/H.225.0 - Communication between Administrative Domains

This new annex provides H.323 gatekeepers with the ability to perform address resolution and pricing exchange in a scalable manner that will allow large, international H.323 communication networks to be constructed. Service providers may utilize Annex G in order to determine least-cost delivery of calls with a certain level of QoS. It is also possible to use a third party, called a clearinghouse, to help resolve addresses and settle billing between service providers who do not have prearranged service agreements.

Annex E/H.323 - Protocol for Multiplexed Call Signaling Transport

In an IP-based network, H.323 equipment normally uses TCP to establish calls. This works well on a smaller scale, but when a single endpoint wishes to handle tens of thousands of calls, TCP is often insufficient. TCP introduces higher call setup times and consumes system resources. Annex E is a new Annex which specifies a UDP-based signaling mechanism that may be utilized to both improve performance and increase potential call volume.

Annex F/H.323 - Simple Endpoint Type

One of the concerns of equipment manufacturers is that H.323 is "too big" for small hardware devices. To address this concern, Annex F introduces the concept of a "Simple Endpoint Type", or "SET". A SET device utilizes only a small portion of the full H.323 specification, yet still provides users with the ability to establish audio calls with other H.323 endpoints.

H.341 - H.323 Series MIB

This document describes a Management Information Base (MIB) for SNMP-based management of H.323 equipment.

Supplementary Services

Several new supplementary service documents have been added to the H.323 series, including call hold, call park and pickup, message waiting indication, and call waiting.