Video Conferencing

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Most video conferencing uses the H.323 protocol. You can join a videocall (between two persons) or videoconference (between more then two parties) using hardware (Polycom and Tandberg are well known vendors) or using software on your own computer.

SIP is a less-often used alternative to initiate VoIP or video calls.

There are plenty of proprietory alternatives, including Skype and Microsoft Office Live Meeting, which are incapable of interworking with any other product.


It is possible to contact someone using the IP address of their system, but more often GDS (Global Dialing System) numbers are used to contact someone. A GDS number looks like a regular phone number (e.g. 0031800101001). A Gatekeeper is used to translate this to the IP address of the remote videoservice.

If more than two persons are involved in a call, it is necessary to use a MCU (Multipoint Control Units) which combines the videostreams of the different parties together. The MCU is usually a stand-along server, since it requires fast hardware, but some Polycom or Tandbert video conference room systems include a lightweight MCU.

A h.323 system can include four components:

The camera and monitor at the end user.
System to translate a GDS number to an IP adres, and to register your own GDS number so you can be reached by others.
System that allows people to use a regulare (PSTN) telephone to dial into a H.323 videoconference.
System that combines the video feeds of all partipants into a single feed.


Clients (Terminals)

End users can install any of the following software:

  • NetMeeting from Microsoft is no longer supported, but recommended (It's successor, Microsoft Office Live Meeting, does not support H.323 anymore). NetMeeting works up to Windows Vista.
  • Ekiga (formerly GnomeMeeting) for Linux and Windows.
  • Xmeeting for Mac OS X. Not longer supported, but still works petty well.
  • Polycom PVX commercial product.
  • EVO from Caltech, a Java webbased client. Love it or hate it.
  • YateClient for Windows, Linux and Mac OS X is a new project. Seems promising, but I have not got it to work yet.
  • The H323plus library (successor of OpenH323) list some more software for Windows and Linux, including MyPhone.

AArnet compared man videoconferencing solutions in 2010

Firewall Settings

Most H.323 clients requires incoming connections to TCP ports 30000-30010 and UDP ports 5000-5009. This is configurable in most software.

Gatekeeper and MCU

GnuGK Gatekeeper is the recommended open source gatekeeper.

OpenMCU is open source MCU, but is not very mature. A hardware MCU has much better performance. Polycom or Tandberg are happy to separate you from your money.


SURFnet maintains the Dutch National Gatekeeper, offers free gatekeeper accounts to Dutch academia, and offers a paid MCU service.

An account at the Dutch National Gatekeeper can be requested by webform.

The SURFnet MCU service is branded as SURFcontact. Usage is possible for Dutch academia and costs €200 to €2000 each month, depending on the expected usage.