Spec ensures smooth voice/data integration

Voice and data applications are beginning to converge in applications from Internet telephony to Web call center processing. These and the many other voice- and video-over-data applications promised for the future share a single common standard: H.323. The H.323 standard does everything from specifying call signaling procedures to describing the services available in desktops, servers, gateways and other devices that form the new converged infrastructure.

Just as voice, video and data signals must be combined to create converged applications, so must a range of functions be supported within the equipment that will process converged applications.

The International Telecommunication Union knew this support was needed when in 1996 it approved H.323 as the videoconferencing-over-packets member of the H.32X standards family. For that reason, the ITU designated H.323 an umbrella standard rather than a baseline standard. As an umbrella standard, H.323 incorporates - and in some cases, extends - existing standards.

For instance, H.323 makes room for as many as five specifications that govern audio coder/decoder devices; two video-codec standards; one data-multiplexing standard; three control-signaling standards; and a version of Real-Time Transport Protocol for voice and video packet sequencing.

In compliance

To be H.323-compliant, however, convergence products will not have to fully support each standard. Instead, the products will support defined subsets, depending on the roles they play in the H.323 universe. The four product subsets are terminals, gateways, gatekeepers and multipoint control units (see graphic).

For enterprises, H.323 will pay off with the merger of formerly disparate network infrastructures. Once companies have a single voice-capable data network, they will see substantial benefits in reduced complexity and lowered cost of ownership. For users, the H.323 standard will pay off by serving as a catalyst to a growing range of convergence applications, such as workflow collaboration and unified messaging, in which a single mailbox accepts e-mail and voice messages.

Two H.323 applications now emerging in business environments are toll bypass and LAN telephony. In toll bypass, an H.323-equipped gateway takes outgoing calls from the company's voice network, packetizes the voice data, then sends the packets over an IP-enabled WAN link to a second location.

At the second location, the H.323 gateway converts the packets back into analog signals for delivery to the building's voice network and for distribution to the called parties.

LAN telephony takes the concept a step further by enabling the LAN to provide PBX-like voice services, activated through switch-embedded or Windows NT-based voice servers. For intra-LAN calls, the voice servers create, manage and tear down voice connections between user desktops, all without leaving the packet domain. Calls to users outside the LAN will be delivered through appropriate H.323 gateways.

Both applications can bring reductions in phone costs and can be easily extended to handle videoconferencing. More important, these applications represent the tip of the iceberg. They bring the promise of newer productivity-enhancing applications as the H.323-compliant infrastructure becomes more widely adopted.

Many industry observers now see H.323 as a crucial piece of the convergence puzzle, and H.323-related standards bodies are accelerating their approval processes to move the specification to users as quickly as possible.

An important next step in the IP telephony formula will likely involve enhancing H.323, which works at the upper Open Systems Interconnection layers, with class-of-service (CoS) and quality-of-service (QoS) capabilities at the data link and network layers (Layers 2 and 3).

These CoS/QoS definitions will come from a number of initiatives, such as the IEEE's 802.1p and the IETF's Diff-Serv working groups, and from the efforts of the European Telecommunications Standards Institute, which included H.323 products in the scope of its Telecommunications and Internet Protocol Harmonization Over Networks project.

Deschamps is marketing manager and Ostergaard is business development manager for voice, video and data for the Enterprise Business Unit of 3Com. They can be reached at Jean_Paul_Deschamps@3com.com and Paul_Ostergaard@3com.com.