Problem with Conferencing

Unanswered Question
Apr 3rd, 2009


I am unable for some reason to setup a 3 way conference call on my UC.

Here is my procedure:

  1. Call person A
  2. Put person A on hold
  3. Call person B
  4. Hit Conference softkey

When I hit the softkey, The phone displays the following error message: "Cannot complete conference.".

I have recently configured MeetMe conferencing. Not sure if that might be conflicting.



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Marcos Hernandez Fri, 04/03/2009 - 07:36

When yo configure hardware conferencing, all conferencing methods on the system will be hardware based, including ad-hoc sessions (like the one you are trying to establish). Make sure you have your Ad-hoc DN's configured. For example:

ephone-dn 31 dual-line
description ad-hoc conference extension
number A000
conference ad-hoc
no huntstop
ephone-dn 32 dual-line
description ad-hoc
number A000
conference ad-hoc
preference 1
no huntstop

Please ensure you keep honoring teh CCA out of band rules.


Marcos Hernandez
Technical Marketing Engineer
Cisco Systems, Inc.

jaydien1358 Fri, 04/03/2009 - 07:49

Ok great.

Couple questions.

  1. Is there an CCA out-of-band reference document?
  2. Depending on how many conference DN's you make, that dictates how many simultanious conference calls you can make?

Thanks for the help.


Steven Smith Fri, 04/03/2009 - 07:56

Yes, there are CCA out of band reference documents.

Here is the one for CCA 1.9.

The amount of conferencing is dependent on channels from ephone-dn's, and from the amount of DSPs setup for conferencing.  For conferencing, you might also consider using octo-line DN's.  More channels, less ephone-dn's used.

jaydien1358 Fri, 04/03/2009 - 08:01

Ah.... Octo-DN. That makes sence.

An octo DN can have up to 8 voice channels, or 8 people on a call, where the Dual-line can have a max of 3 people on a conference call, correct?

As far as DSP's, that depends on how many users the UC has been licensed for when you purchased it correct? So an 8 user UC would have how many DSP's?


If you upgrade the licensing on your UC, to lets say a 24 user, you are going to be limited by the DSP's that your motherboard has been configured with from the factory though correct?


Marcos Hernandez Fri, 04/03/2009 - 08:11

We are in the process of creating a *much needed* DSP calculator for UC500. It will be a static document to begin with and I will make it available shortly.


jaydien1358 Fri, 04/03/2009 - 09:39

From reading the documentation that you posted, I assume we can add more DSP modules if we would like? Up to a max of 64.

Are DSP's only used for conference calls or does each phone call, internal or external, use up a DSP channel?



Marcos Hernandez Fri, 04/03/2009 - 09:51

Onboard DSP's on the UC500 cannot be upraded or replaced (NRU). The table is just a general reference. The DSP flowchart that I am about to post will hopefully clear this confusion.



jaydien1358 Mon, 04/06/2009 - 05:09


Can you please update this thread when you post that flowchart? Thanks.


jaydien1358 Mon, 04/06/2009 - 09:04

This helps out a great deal. Thanks for your assistance on this.

In your chart, for a 8/16 user UC520 with a 4fxo card installed, there are a total of 64 voice channels that can be used. 8 sessions with 8 users on each sessions. Can you do 1 Meet-Me session with 64 users?

Lastly, does DSP capacity at all relate to the capacity for the UC520 to handle basic internal and external phone call, without any conferencing involved. In other words, can I assume that the UC is capable of 64 individual voice call as well? Or is there a different module that handles that.

Thanks again for answering all my questions.


Marcos Hernandez Mon, 04/06/2009 - 09:16


The capabilities for conferencing and regular voice calls are different. Refer to the "DSP Facts" section of that document. I have modified slightly to make it more understandable.

You cannot do 1x64. Only what's on the table.




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