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Choosing video signaling infrastructure

Determining which video signaling infrastructure is best to interconnect your endpoints is a major decision when embarking on video conferencing implementation. Learn about the options, including direct IP dialing, standalone H.323 infrastructure, telephony-based dialing and unified communications.

Determining which video signaling infrastructure is best to interconnect your endpoints is a major decision when embarking on video conferencing implementation. You'll need to consider existing systems in your IT environment and how much video conferencing is intended to interoperate and be used with them.

In order to make a comprehensive decision about signaling, make sure you take the time and trouble to understand your overall video conferencing requirements, choose the type of video conferencing that is most suitable for your company, understand the video conferencing quality you must deliver to users, and locate your MCU where it will most cost-effectively scale to meet your needs.

Choosing the right video signaling infrastructure option depends in large part on the level of integration you need with existing telephone or unified communications solutions. The market currently offers four alternatives:

  • Direct IP dialing
  • Standalone H.323-based dialing
  • Telephony-based (PBX) dialing integrated with voice
  • Unified communications (UC)

Direct IP dialing

Direct IP dialing is, in essence, an infrastructure-free approach to video signaling in which endpoints rely on IP addressing, DNS names, or an address book at each endpoint containing IP addresses associated with endpoint or conference room names. This approach works for a limited deployment of fixed-location systems, such as in a room-based structure.

But IP address dialing is difficult and unfamiliar to users. In addition, maintaining an address book is challenging in any case, and nearly impossible for endpoints that move or for networks that supply dynamic IP addresses (DHCP).

H.323 infrastructure

Traditional video conferencing vendors, such as Polycom, Tandberg (now owned by Cisco), Lifesize, Sony and Radvision, offer standalone H.323 infrastructure. An H.323 gatekeeper manages the dialing. Each endpoint registers to the gatekeeper, which resolves E.164 addresses (phone numbers) or aliases (such as conference room names) to IP addresses. Because each endpoint communicates with the gatekeeper, it always has up-to-date information about available endpoints and their current IP addresses.

Video signaling gatekeepers have become increasingly sophisticated and now provide enhanced controls to determine who can call whom and when, how much bandwidth they can use, how to find a gateway, and what the best route is. And they can even manage bandwidth for the network.

H.323 infrastructure is very useful for large video conferencing environments because it enables the IT team to control how video conferencing is used, and it helps optimize network and gateway resources.

Telephony-based (PBX) dialing

The PBX video signaling option substitutes the voice PBX for the H.323 gatekeeper. Some solutions continue to use the H.323 protocol, while others use Session Initiation Protocol. Call control is managed by the PBX, and dialing relies on conventional E.164 telephone numbers which are very familiar to users.

The downside is that, because PBX vendors are rooted in voice applications, some video conferencing functionality may not be supported. If you have never deployed video, this may not be an issue; but if you are moving from H.323 to PBX infrastructure, be prepared for complaints about lost functionality. Make sure the solution you choose will support all the calling features needed for your video-enabled business processes.

Unified communications (UC)

Unified communications is the latest incarnation of voice communications and another option for video signaling. In this environment, users find each other through buddy lists and other application or context-sensitive mechanisms based on presence. Once you have an active buddy on your presence panel, you can choose to communicate via instant messaging (IM), voice calling, data (desktop) sharing or video.

A number of vendors, including IBM, Cisco, Microsoft and Avaya, offer UC solutions. With the exception of Cisco, which now owns Tandberg, none of these vendors has a strong video conferencing background. That means building an integrated UC environment requires marrying best-in-class video conferencing endpoints with UC infrastructure. While vendors are working to make this integration simple and seamless, as yet not all the software is written and debugged. Following the telephony model, UC environments focus primarily on individual users, so this environment is better suited to desktop video conferencing than video conferencing rooms or telepresence suites.


About the authors:
John R. Bartlett is a principal consultant at NetForecast, where he focuses on network support for voice and video conferencing. NetForecast provides consulting to enterprises and networking equipment vendors on application performance issues and convergence of voice and video conferencing on the IP network. John has 32 years of experience in the semiconductor, computer and telecommunications, and has been consulting since 1996. John can be reached at

Rebecca Wetzel is a principal of NetForecast and a networking industry veteran with unparalleled inside knowledge of the network service and product markets. She works with network product vendors and service providers to develop and implement product strategies. She can be reached at

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