A Shining Light Through the H.323 Mire
by Kyle Nisenson

Confused by H.323? Gateways. Gatekeepers. Bandwidth. Latency. Intranets. So many terms, and not enough definitions. Let's spend just a few minutes this month identifying what some of this stuff means, and what it means to your business.

Gateways vs. Gatekeepers

No, this isn't something out of Ghostbusters. Both are key pieces to getting H.323 off the ground. A Gateway is used for connecting H.323 video clients on your IP network to the legacy H.320 / ISDN systems you have been using for years. If you are running H.323 clients today and want to be able to connect to an H.320 system, you must have a gateway somewhere on your network. Some of the vendors who currently sell gateway technology include PictureTel, Madge, Rad-Vision, and Cisco.

A Gatekeeper is something completely different. Gatekeepers are utilities that help manage your video network. Gatekeepers enable aliases, which allow you to call Joe in his office instead of trying to remember his IP address. Gatekeepers also attempt to maintain certain levels of video quality by managing bandwidth and limiting the number of simultaneous calls within the parameters of the network. Gatekeepers are often software solutions and they should be part of any H.323 installation.

Latency Labors

Newton's Telecom Dictionary defines Latency as a fancy term for waiting time, or time delay. Networks that are congested suffer from latency because it takes time for packets to be routed through the network. Consider how one day it takes mere seconds to send an e-mail, then later in the day it may take a minute or two. This is latency, and is a big enemy of real-time communications. If it takes too long for an audio or video packet to arrive, it will be discarded. Packet delays greater than 200 milliseconds is generally where latency becomes a factor in real-time communications. Such delays can cause frozen video, broken audio, artifacts on the screen, and other common problems. Network administrators should be able to pinpoint latency counts during peak hours for your network. Latency can be reduced through a number of different solutions, the simplest of which is to add more bandwidth.

The Bandwidth Specter

The big benefit to using H.323 technologies is that you can run video over existing IP infrastructure, i.e. the network that you currently use for e-mail, web access, etc. The upside is eliminating expensive ISDN access and network charges. The downside is constricting the bandwidth on the existing IP pipes makes other applications run slower. The equation that must be considered is at what point does usage justify adding more bandwidth? Any Local Area Network can be upgraded to support video traffic through better segmentation (separating video users out from the rest of the traffic), switching (using dedicated instead of shared connections to endpoints), and actually making the pipes bigger (gigabit Ethernet, 1Billion bits per second, is now becoming reasonably affordable). Expanding the wide area network for video is a bigger challenge.

Making the Intranet Video Enabled

The term Intranet usually refers to sites connected to your private network that are outside of the main building or campus. Connections to these sites usually have access to considerably less bandwidth than sites on the Local Area Network, which can cause greater latency. Right now, the cost of dedicated IP over long distances is very high, but this will change over the next few years. Every long distance provider is aware of the rapidly increasing demand, and soon bandwidth will become much more affordable. You can expect much pushback from your organization for using the Wide Area Network for real-time communications. There are several solutions to try and levy the problem, such as separate connections for real-time and passive traffic, priority routing to give real-time packets an easier time getting though the network, or even sanctioning off bandwidth specifically for audio and video.

Frontier Solutions

Frontier understands that all of this is a lot to consider, and we stand ready to help you with any questions you may have on IP video and audio. Our lab has been looking at video over IP for over a year now, and has modeled several real-life scenarios. Feel free to contact us with any questions or guidance as you proceed down the path of IP conferencing.

About Kyle Nisenson

back to top

© 2000 Global Crossing Conferencing. All Rights Reserved.