Slaves and Masters: Bridging Multipoint Videoconferences

One of the fun challenges of running multipoint events in K12 videoconferencing is cascading bridges together. This happens to me with events such as our Lest We Forget sessions (3 schools in each session), and the MysteryQuests: USA, HistoryQuest5, HistoryQuest8 (all of which have 4-6 classes in them) and other multipoint events.

Ideally, classes would dial in directly so that only one bridge is in the mix. However, there are many education service agencies who prefer to bridge their schools’s calls; or even are set up so that their schools can ONLY connect through their bridge. This means that a call with 6 classes in it could potentially have 6 bridges in the mix!

What does Master/Slave mean for VC?

Each MCU has some type of setting related to cascading bridges (i.e. two or more bridges in a call). As you know, I have the Tandberg MPS MCU, and settings related to Master/Slave are under Conference Mode. The choices are Auto, Master or Slave.

The issue with master/slave is basically who is running the show of the conference? Which bridge has control over that?

The problems arise when the person running the conference (me!) doesn’t have the power necessary (i.e. to force video to certain participants).

The Problem

In the last two weeks, I’ve had troubles with Codian bridges dialing in and taking over the conference. When this happens, video is forced to the endpoint on the Codian bridge, voice switching doesn’t work, and I can’t force the video to any of the other participating sites. Putting a multipoint endpoint (Polycom VSX 7000 in this case) in between the two bridges was the initial fix under distress and hurry.

Official Word: Dial Direction Determines Master/Slave

Last fall in some training, I learned that the official word (?) from vendors recommends this procedure:

  • Whoever dials out is the master
  • Whoever receives is the slave

I have also heard that the call ought to be set up in a certain order: bridges connect first; then the endpoints join.

The Reality

However, with all the multiple bridge calls I have done, this recommend practice has never been possible. Bridges are scheduled for different times. I can emphasize dialing in early, but rarely actually happens. In addition, with my Codian problem, we found the Codian took over the conference no matter which direction the call was established.

The Fix

What I learned in experimentation yesterday, is that Tandberg Management Suite, our scheduling software, was scheduling conferences set to AUTO instead of Master. When my conferences are set to Master and I connect to a Codian bridge, I still lose the ability to force video to the Codian site; but everything else works properly. Voice activation works right. I can force video to the other sites individually if I want to.


All the Codian bridge operators I’ve talked to don’t know where the Master/Slave settings are on their bridges. Do any of you know? Please comment if you know that, or if you have any other comments on this situation…

0 replies on “Slaves and Masters: Bridging Multipoint Videoconferences”

  1. That feature does not appear to be directly setable on the MCU. Instead, after reading through the documentation, it appears that using the gateway calling makes the Codian not assume it is the conference master of that connection. I could not find anything that says that outright, though. The ‘Codian Conference Director’ software does make mention of the Master/Slave cascading setting, though.

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