Video Conferencing Internals

Necessity is the mother of invention. First there were the telephones and then came the Internet. And we thought it was good enough to be able to send a text message (e-mail) to any one in the world. Then came the ability to make telephone calls over the same infrastructure. But, being able to see a person (or thing) can vastly expand our understanding and knowledge of the person or thing. As they say, a picture speaks a thousand words, so video conferencing can convey much more than a mere telephone call or e-mail. Hence, came video over the existing infrastructure. Standards were developed, technologies improved upon. So let’s see what goes into setting up a video conferencing system. 

What type of video conference 



A video conferencing setup depends upon the number of parties involved. If it’s just between two parties, it’s a one-to-one or point-to-point setup. Note that we said parties, because it’s not just between two people, as more than one person can be at either end. Imagine such a conference to be like a tele-conference call, but with video. Then there’s the one-to-many setup in which a number of people can have a conference with a single party. This setup can be best understood when thought of as being applied in distance education. Here you’ll have one teacher (may be in the US) delivering lectures to many students who are in one room (may be in India). Both parties can see and interact with each other. Finally, there’s the many-to-many setup, which involves multiple participants, all of whom can see/hear each other. These three kinds of setup determine what kind of video conferencing equipment is needed. 

Plus, you should also address issues like whether the participants will use their desktops or a meeting room for conferences, Will video be necessary? Will everybody need to speak, or will one leader present? Will participants need to share files or work on a document or whiteboard?

Here’s the checklist



Once you’ve created a broad outline for your video conferencing setup, you’re ready to decide upon the equipment. This includes hardware to sense the video and audio, codec, control software, H.323 gateway and gatekeeper. You also have to decide upon the kind of bandwidth you need, as that will decide the quality you can expect from the sessions. If you’d like to hold a conference from multiple locations, you will need an MCU (for multi-point video conferencing) and a carrier. 

Base hardware



Basic video conferencing equipment is called an endstation. This could be desktop based or a professional one independent of it. Desktop-based setups could either have a webcam or a video conferencing camera along with mic and speakers. Both of these would come with software to control everything, and the setup would be fairly inexpensive. More sophisticated, and consequently much more expensive, are professional endstations, which let you do much more than desktop-based solutions. They would connect to a composite or S-Video connection, as in a TV. You can break up the screen into multiple quadrants to see yourself in one, the remote party in another, a presentation in the third and a whiteboard in the fourth. Or, if you’re having a conference with multiple people, then you could see the different participants in different quadrants. The video camera in an endstation would also give much better quality, and would be capable of panning, zooming and tilting, amongst other things. Professional endstations usually also come with a remote control that lets you control all functions like control the camera movement, mute the audio, or dial a number. In fact, many endstations have a voice detector to automatically find the person who’s speaking. Their built-in microphones are so strong that you don’t need to face the camera for it to catch your voice. 

If your meeting requires you to use visual aids and presentation material–paper pages, transparencies, drawings, three-dimensional objects like circuit boards–you will need secondary cameras like document cameras. A document camera captures the details of these and communicates them in high resolution. Regarding display, since you usually see video from the other end of the conference on a computer monitor or TV screen, screen size and resolution will influence the clarity of video. Smoother display can come from increasing bandwidth, as it will give you more frames per second. But, remember that since the H323 standard supports fixed resolutions, increasing bandwidth beyond a point will not be worthwhile. 

The audio requirements for desktop based video conferencing are different from the professional endstations used in a conference room. If you use a desktop solution, make sure that you have a full-duplex sound card, which can record and play audio at the same time. Plus, if at one end you’re the only one video conferencing and your system doesn’t have echo cancellation, you should use a headset as a microphone and speakers. This eliminates echo found in desktop systems. If video conferencing from a large room, you should use multiple microphones such that they reach all participants. But, don’t keep them very close to noisy projectors or air-conditioning outlets. Also, if you need to move a microphone during a meeting, first mute it to prevent loud noises being heard at the other end. 

Codec



Perhaps more important than audio and video capture and playback is the Codec (Coder-Decoder) as it largely determines how fast and accurately video and audio are played at each end. A video conference happens in near real time, which means that the video and audio you see and hear actually happen just a little before you see and hear it. At one end of a video conference, the codec compresses picture and sound such that they can be transmitted fast through the Internet, network or ISDN link. At the other end, it decompresses video and audio, which are then played through the display and speakers.

Codecs can be built-into a software or hardware, where the latter are more expensive. In an ordinary webcam, the codec is the built into the cam software. Professional video conferencing systems (for many users) use hardware codecs, which have their own processing power so that they don’t tax your system’s resources for encoding and decoding data. This makes them faster and better in terms of quality. Another significant advantage of a hardware codec is that it allows you to have a completely stand-alone system that doesn’t need a computer for functioning at all. You can plug it into your network and it will work. But this functionality comes at a price higher than that of software

codecs.

Control software



The software for video conferencing is the user interface through which you interact with the system. This includes a GUI dial-pad, status monitors, the video window, and volume controls. The engine behind the software also does the work of generating dial tones, taking care of the quality of service parameters, maintaining a directory (address book) and other miscellaneous functions.

H323 Gateway and Gatekeeper



A H.323 Gateway bridges H.320 and H.323 systems and takes care of the required transcoding between two transport networks–IP and ISDN (Integrated Services Digital Network). H.320 is an ITU standard for video conferencing over ISDN, while the H.323 standard is for video conferencing over regular networks, where there’s no guaranteed bandwidth. The H.323 standard specifies how the audio, video, data and control information will be assembled into an IP packet. It also supports multicasting, making it possible for broadcasts and video-on-demand applications on a LAN. This reduces network load while at the same time allows multiple non-interactive participants. The standard can work on an ordinary 10/100 Mbps network. The clients using H.323 based video conferencing need a static IP address so that they can communicate with each other. IP-based transport is simpler because it uses TCP/IP protocol for communication, which is there on most networks and the Internet.

A gateway device bridges ISDN with the network, and a Gatekeeper is an H.323 network component, which maintains a record of all H.323 devices on a network including their IP addresses and assigned aliases for routing. It can be compared to a DNS, which routes calls according to aliases. It makes the user’s address book, a collection of simple names rather than

IPs.

Transport carriers for video-conferencing data are either ISDN or IP networks. ISDN offers guaranteed, dedicated bandwidth and is a part of PSTN. It’s available in two connection options: BRI (Basic Rate Interface) and PRI (Primary Rate Interface). A BRI gives two 64 kbps B channels, which are aggregated (sharing the same number) to give you 128 kbps for video conferencing. If you can afford, you can buy 3 BRI (through what’s called inverse multiplexing) to get a line speed of 384 kbps. The H.323 gateway generally takes care of this bandwidth aggregation. Generally, for desktop-based video conferencing solutions 1 BRI is reasonably good quality whereas 3 BRI should be used for room-based conferences. Also note that the switch you use for connecting to the line should be configured to transport both voice and data. The H.320 standard specifies the guidelines for data, audio and video over ISDN. 

Video conferencing loses value if the experience is not real-time. Though this obviously depends on the kind of available bandwidth, it is also a function of bandwidth management. This is done by means of QoS (Quality of Service) protocols’ implementation. QoS needs to be implemented at various nodes on the network and allocates a certain part of the network bandwidth to video conferencing data. This ensures that neither critical network data nor the video conferencing data suffers. 

MCU



If your conferencing will be between more than two sites, then you’ll need an MCU (Multipoint Control unit), which is like your computer’s CPU. This has a multi-port interface that does the job of connecting multiple video conferencing calls to each other. It consists of its own processor, memory bank, audio and video conditioning cards, multimedia cards that route audio and video to the processor and even an iMUX to aggregate the bandwidth.

MCUs can be hardware (more expensive than software) or software. Which to choose will depend on your budget (hardware MCUs are more expensive than software ones) and how powerful the host computer is (software MCUs require powerful host computers). Some endstations come with a built-in MCU that can support up to four to eight sites.

Remember that the video transmission in a multi-point conference could be poorer and slower than in point-to-point conference, because the bandwidth gets divided. Therefore, the amount of bandwidth needs to be planned out when implementing a

MCU. 

Ashish Sharma and Juhi Bhambal