Videoconferencing 101, Chapter 1

Update:  Chapter 2 has been added. 🙂


I will start new series where I will try to make videoconferencing, collaboration, streaming, and related technologies easy to understand for “Everyone”.

Taking advantage of the Blog format, I will be able to add to this entry as new information appears, and make changes as needed (a living document). Hopefully, in a few months I will be able to provide an entire “course” for people to refer to.

For the following information, here is a diagram showing all the pieces.  I will try to use this diagram as the basis of the discussions and examples in the next chapters.  



Lets get started and see how this works out…let me know!

Basic Terms You Will Need To Know

H.320—is an umbrella standard (meaning it covers video, audio, and signaling standards) developed in the ITU (International Telecommunication Union) that defines how voice and video content is processed and transmitted over an Integrated Services Digital Network (ISDN) telephone call. This standard was developed in the late 1980’s and first used in videoconferencing equipment in the early 1990’s.

H.320 is still in use but is rapidly falling by the wayside with the emergence of high speed Internet Protocol (IP) connectivity. Truthfully, a 384 kbps IP call is better than ISDN and cheaper.

H.323—is an umbrella standard that defines how voice and video content is processed and transmitted over Internet Protocol (IP) networks. This standard was ratified in late 1996, and, now, in 2008 is widely used and reliable. To use H.323, you need an H.323 client and an IP network.

SIP–Session Initiation Protocol is a signaling protocol for the use of video and audio over IP networks. This protocol appeared several years ago and is widely used in Voice Over IP (VoIP) calls but not so much for video. In fact, when I first learned about SIP, it was expected to overtake H.323 very rapidly. That never happened. We will see what the future holds. SIP controls the registration, call establishment, and take down but uses the same protocols for video and audio transfer as H.323 (we will get into these later).

T.120—defines how data collaboration takes place between two or more end users. This standard defines such data collaboration tasks such as: white-boarding, file transfer, application sharing, etc. Many new Internet based application provide much of the functionality of T.120 but are proprietary.

MCU—a multipoint control unit (MCU) allows three or more endpoints to meet at a central location. MCUs exist for audio-conferencing, H.320 videoconferencing, H.323 videoconferencing, and for all three together. An MCU can be hardware based or software based. In H.323, an MCU is optional.

Figure 1: Polycom MCU          

Gatekeeper—this device allows the registration of H.323 devices and controls the call set-up and take-down of H.323 calls. It also provides a way for H.323 units to easily call each other using either an E.164 (a fancy word for a telephone like) number or H.323 alias.The E.164 number can be a simple multi-digit telephone number(like 3456 or 30987) while the H.323 alias can be a persons email address (like, name, or other alphanumeric designation. In H.323, a gatekeeper is optional.

Gatekepers can be: Software on a Windows or Linux / Unix based server (example: Radvision, Open323), software on a router (example: Cisco), or a dedicated Linux box (example: Tandberg). The system you choose depends on a number of factors including expertise in house, cost, and features / capabilities.

Figure 2: Tandberg Gatekeeper          

Gateway—the gateway allows H.323 and H.320 systems to communicate with each other. One side of the gateway is attached to the IP network while the other side of the gateway connects to ISDN. A person using a cell phone can attend a meeting by calling into a gateway. In H.323, a gateway is optional.

Figure 3: Codian / Tandberg Gateway          

See the video below for an example of H.323 videoconferencing. This call was made from our home using a DSL connection to San Diego, CA. We did not use a gatekeeper in this particular call preferring to call using on the Professor’s IP address (a number assigned to his system by his Internet service provider) of his videoconferencing endpoint.



  1. Initially the concept of video conferencing was new to me but due to the change in technologies I felt that work and the performance of business can be effectively be increased positively due to the investment I made in more than one telepresence room. However, many telepresence solutions are now standards based, so they are compatible with other desktop.

  2. I come here from the video on this site that’s on Youtube. I have an H323 Polycom unit and I’m trying to find a way to use it at home. Can you say how you were able to make the call in chapter 1?

    1. I have DSL at home with 5 statics (although that is not entirely needed). I simply set the PVX (what are you using?) with the right gateway, IP address, maybe a few tweaks to select the right LAN card (for some reason I have to manually select the right one) and it works. At AltamontCowork I have Comcast Business and WiFi. Again all I need to do is manually select the wireless card and it works great. NOW…the PVX is pretty old (I’ve been fading from the business a bit) so I’m sure things have changed.

  3. H323 is what I’m using. Were you calling another PVX on that video? Do you know of applications that the endpoint could use and be able to see the PVX video from the call source?

    1. Probably just another H.323 EP. I’ve connected to dozens of diff ones over the years, no problems (well….few problems). I’ve even used the PVX in SIP mode and connected to a new Lifesize Desktop app….very cool.

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