ISDN stands for Integrated Services Digital Network and is an international standard for transmitting high-speed digital data over regular phone lines [source: Michigan Technological University]. With ISDN video conferencing, all of the data from the video conference travels back and forth over the public switched telephone network, not the Internet. For this to work, each of the participants in an ISDN video conference must have the right equipment to prepare video, audio and data for transmission over the telephone network.
Most of the heavy lifting during a video conference is done by a special gateway called an inverse multiplexor or IMUX. The IMUX initiates video conference calls and manages the flow of data between the video-conferencing equipment (called the CODEC) and the telephone network [source: Security for Videoconferencing]. The main job of the IMUX is to make sure that there are enough ISDN channels open to provide sufficient bandwidth to handle the video-conference call. A business-quality video conference requires 384 kbps of bandwidth or six 64-kbps ISDN channels [source: Michigan Technological University].
The video conferencing CODEC communicates with the IMUX over two separate interfaces: an RS-366 line dedicated to dialing information and an RS-449/530 line that carries all of the video, audio and other data associated with the video conference itself.
A video-conference setup is considered unsecure if there's nothing encrypting the data between the "red" or classified CODEC and the "black" or unclassified IMUX. If only one of the interfaces between the camera and the IMUX is encrypted, then it's called a partially secure video-conferencing setup [source: Security for Videoconferencing].
For example, if an encryption box is installed on the video/audio/data line, then the video conference stream will be secure. But that still leaves the dialing line vulnerable. Since dialing lines are typically made of copper, it could leak data radiation that could be picked up by hackers [source: Security for Videoconferencing].
Now let's look at two simple ways to work around or repair a partially secure video-conferencing setup.