Video conferencing is two-way interactive communication delivered using telephone or Internet technologies that allows people at different locations to come together for a meeting. The video conference can be as simple as a conversation between two people in private offices (point-to-point) or involve several sites (multi-point) with more than one person in large rooms at different sites.


A basic video conference setup has a camera and a microphone. Video from the camera and audio from the microphone is converted into a digital format and transmitted to a receiving location using a coding and decoding device, often referred to as a "codec".


At that receiving location is another codec device that decodes the receiving digital stream into a form that can be seen and heard on monitors or televisions. At the same time, video and audio from cameras and microphones at the received location is sent back to the original location. 


Common technologies used at The University of Iowa by different campus users are IP-based systems (Polycom, LifeSize, Tandberg, etc.), collaboration tools (Zoom -- campus standard solution, Adobe Connect, Microsoft Skype for Business, etc.), and free software (Skype, FaceTime, OoVoo, etc.). To see which software or approach is best for your needs, contact the ITS HelpDesk or your local IT support person directly.

There is a wealth of knowledge on campus about how to do video conferencing; you just need to ask!  In addition, many colleges and departments own their own IP-based and web-based video conferencing equipment.  


Collegiate and departmental contacts are excellent to use as a starting point. If your organizational group is not listed or you are not sure who to contact, feel free to contact the ITS Help Desk


  • Solid colors are best. Busy outfits blur when on camera. Simpler patterns aid the video compression.


  • Think "TV studio lighting". Soft white frontal light is preferred. Standard overhead lights can cast shadows. Camera can not focus properly in low light.

Back drop:

  • No hard lines or complicated patterns.
  • Can use a dry erase board, but be aware of glare.
  • Solid darker color is ideal.
  • Avoid red backgrounds they can be hard on the viewing site.
  • Give audience one thing to focus on—YOU.
  • Good idea—use a sign to indicate your location

Audio setup:

  • Keep the microphone away from where the speakers are located. This can cause audio loop back.
  • Test audio levels ahead of time. Make a test call. Use built-in features of the video conferencing system to test.
  • Make sure microphones are away from extraneous noise generators: Air conditioners, laptop/projector fans.
  • May need to add echo canceling hardware. This is less common as conferencing systems are becoming better at handling audio.

Large conference room considerations:

  • Position the camera to see the primary speaker and audience.
  • May want to add additional cameras.
  • Consider investing in good lighting.
  • In especially large rooms, designate locations for Q&A with microphones.
  • Avoid panning the camera too much. Use endpoint “presets."
The quality of a video conference primarily depends on the characteristics of the network connection between the conferencing sites. In the H.323 world, a high-quality conference (excellent audio and video) needs about 768 kbps (kilobits/second) of bandwidth on a switched network. On campus, this is possible since most network connections are 100 Mbps (megabits/second).
When a video conference includes an off-campus site then the type of network connection, the bandwidth between sites, and firewalls must be considered.
General rules for bandwidth: 
Bandwidth Network Quality
768 Kbps Internet2, on campus Excellent
384 Kbps Commodity Internet, ISDN Maximum good connection across the commodity Internet or through an ISDN
256 Kbps Commodity Internet, (use only if 384 Kbps not possible) Audio okay, video barely full motion
128 Kbps Commodity Internet (use only if 256 Kbps not possible)  Audio marginal, choppy video

The H.323 standard specifies the components, protocols, and procedures for the transmission of real-time audio, video, and data communications over IP (packet-based) networks. 


Point to point video conferencing: In its simplest form H.323 video conferencing consists of two H.323 video conferencing systems talking to each other over the Internet. This is called "point to point" conferencing. One station initiates the call, and the other either accepts or rejects it. Once accepted, encoded and compressed audio and video flow between the two stations.


Multipoint video conferencing: The last major piece in the puzzle was to provide a means for multipoint video conferencing, i.e., more than two sites. In the H.320/ISDN world, a Multipoint Control Unit (MCU) was used. This allowed three or more user stations to connect to the MCU. In a "voice switching" mode, the MCU made a decision about which site was currently talking (or talking the loudest). The MCU then transmitted the audio and video stream for the selected terminal back to all other terminals. As users at a different terminal started to talk, that terminal’s audio and video signals were sent to all other terminals.


The H.323 world adopted this same method of providing multipoint operation. H.323 MCU's are far less expensive. They require only a single network connection rather than multiple ISDN lines.


There are four components to H.323:


Terminal/Endpoint/Conferencing System/Codec: A basic video conference system has a camera and a microphone. Video from the camera and audio from the microphone is converted into a digital format and transmitted to a receiving location using a coding and decoding device, often referred to as a "codec".


Multipoint Control Unit (MCUs): Supports conferences between three or more endpoints


Gateway: An optional element, gateways provide translation functions between H.323 conferencing codecs and other conferencing terminals, i.e., H.320.


Gatekeeper: Performs two call control functions - address translation from aliases to IP addresses and bandwidth management. The collection of all terminals, gateways, and MCUs are managed by a single gatekeeper is called an H.323 Zone.

Several standards for video conferencing have been developed. The three most popular standards are:


H.320, used for ISDN (Integrated Switched Digital Networks) or digital telephone lines; developed by the International Telecommunications Union.


H.323, used for IP (Internet Protocol) conferences; allows for video conferences over the Internet; also developed by the International Telecommunications Union.


SIP (Session Initiation Protocol) is a signaling protocol developed by the IETF Multiparty Multimedia Session Control working group. Areas for use of the protocol includes but are not limited to telephony, presence, video, instant messaging, online games and events notification in general.

If you have a choice of having an ISDN versus an IP connection with the off-campus site, you have two issues to consider: quality and cost. 


There will be additional charges (for you or the site you are connecting to) for ISDN. In general, there are no additional charges for IP (based on the current funding model for data connections on campus). You will get consistent quality with an ISDN connection. Over the commodity Internet you do not have guaranteed bandwidth which implies you will not have guaranteed quality. Conferencing over Internet2 implies high quality. 

A video conferencing bridge (also called a Multipoint Control Uni or MCU) is a hardware system that is able to connect multiple videoconferencing systems together into a single conference.


A video conferencing bridge receives digital video and audio signals from codecs in a designated conference, processes and resends digital video and audio signals back to all the codecs. Multiple conferences involving many locations can be conducted simultaneously. Many bridges can provide advanced features such as continuous presence, people plus content or dual streams, transcoding, and transrating.

Continuous Presence is a feature available during video conferences that allows all participants to be visible on the screen at the same time. For instance, if there are 12 participants in the video conference, the screen everyone sees will have 12 windows (which can be of various client defined sizes) with each participant in their own window.

"People plus content" is a standard (ITU H.239) that allows a video conferencing system to process high resolution VGA graphics along with the standard video signal. This means video conferencing system in the conference sends and receives two video streams - video and VGA graphics. Example: In a classroom equipped with two monitors, the students could see both the instructor and the presentation on the two different displays.

Transrating is a function available on the video conferencing bridge that allows conferences among site and locations with different bandwidths. For instance, transrating allows virtual classrooms with Internet2 connections participating at 2 Mbps while another locations with limited bandwidth can participating at a lower 384 Kbps rate.


Transcoding is an option available on video conferencing bridges that allows conferences to be established with participants using different video conferencing formats. For example, systems and locations using ISDN (H.320) can seamlessly communicate with other locations using IP or Internet connections (H.323). 

A firewall protects your network from unwanted Internet traffic. A firewall can be an appliance installed on the network or software running on your computer. When installed, a firewall exists between your computer(s) and the Internet, i.e., a virtual wall. The firewall lets you request web pages, download files, chat, etc. while making sure other people on the Internet can not access services on your computer like file or print sharing.


If a videoconferencing system (any type) is behind a firewall, it cannot receive communications from H.323 gatekeeper, so it cannot complete a registration or use gatekeeper services. (The gatekeeper is not a means of bypassing the restrictions of a firewall.) A videoconferencing system behind a firewall must initiate a videoconference using the IP address of the remote video conferencing system since it cannot make use of the gatekeeper's services. Firewalls makes it difficult to use videoconferencing bridge for multipoint videoconferencing.


There can be a series of firewalls to address:


Does the institution you are at have a campus firewall? Currently, the University of Iowa does not have a campus firewall.


If you are running Windows, is its firewall turned on?


If you have computer protection software installed such as Symantec's Norton Utilities, is its firewall turned on?


If a firewall is required, an external or software firewall with the ability to open specific ports for H.323 "traffic" is recommended.

The following ports must be opened in the firewall and assigned to the videoconferencing endpoint(s):


Port 389 (TCP): For ILS registration


Port 1503 (TCP): Microsoft NetMeeting T.120 data sharing


Port 1718 (UDP): Gatekeeper discovery


Port 1719 (UDP): Gatekeeper RAS (Must be bi-directional)


Port 1720 (TCP) H.323 Call setup (Must be bi-directional)


Port 1731 (TCP): Audio call control (Must be bi-directional)


Ports 3230-3235 (TCP/UDP): Signaling and control for audio, call, video and data/FECC


Port 3603 (TCP): Polycom ViaVideo Web interface (Polycom ViaVideo users only)



Other firewall references:


Packetizer: H.323 Papers and Presentations

To learn more about video conferencing in general and the H.323 standard, here are additional resources:


IMCCA Portal for Conferencing & Collaborative Communications 




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Article number: 
Last updated: 
November 16, 2023