Maximum # of DN's

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Marcos Hernandez Wed, 02/11/2009 - 12:00
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There is no way to increase the absolute count of ephone DN's, but I am sure we can find ways to accommodate your setup with what we have. Octo lines, voice hunt groups and secondary numbers, are all examples of tools that can be used to better administer your resources.

Please describe the desired call flow and DN distribution that you have, so we can make suggestions.



The office currently has 12 phones. We have setup groups for Sales, OP's, Q&A, and Purchasing. Each user has a DID and a FAX to e-mail DID. The first 4 EPHONE-DN's have to do with paging. I am not sure what you need as far as call flow but here is a summary that might help. There is a PRI into the system and a block of DID's, Except for the specific DID that are assigned to users all other calls that come in ring on all phones for live answering. The groups are only used after hours in the auto attendant menu tree to make the company appear larger than it really is.  "For Sales dial 300, for Purchasing dial 400, etc" There is really only one person in each of these groups. My first thought was to add more licenses.and thus more DN's - but since that is not an option we have to live within the 88 then perhaps we need to strip down the number of groups to free up some DN's.

Let m eknow what more I can add to help you help me.



Marcos Hernandez Wed, 02/11/2009 - 12:56
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This is very good information and for the benefit of the broader community, I would like to keep the discussion going in the forum (unless we need to talk about something confidential to your business).

Let's talk old math first:

1 x DN for MOH +

2 x DN's for MWI +

4 x DN's for SCCP FXS ports +

4 x DN's for Paging +

12 x DN's for DID's +

12 x DN's fro DID Fax +

12 x DN's for Overlay (shared Line)


47 x DN's

Notice that I assumed overlays for the shared line that rings everybody. Please correct me if that is not the case. So, where are the other 41 DN's? I may be missing one feature DN here and there, but you should have plenty left...

However, you don't, so now let's talk new math:

1) If you are not using the FXS ports, you can reuse their DN number. That gives you 4 DN's back,

2) Your "ring all" shared line could be using a single octal DN. You can assign it to 12 phones, but notice that only 8 simultaneous calls will be possible. This should be OK from an statistical point of view (66% shared access capacity is a lot). Please note that octo DN's cannot be overlaid and that you will need IOS 12.4(20)T and above.

3) Alternatively, you could use a call blast hunt group ("voice hunt-group XX parallel") and include all primary extension's. This uses zero additional DN's. You also need the IOS rev mentioned above.

Some level of CLI will be required, but this beats a platform upgrade :-)

Let me know,


What you are saying makes perfect sense and I feel the config was not done very effeciently. I am limited in my knowledge of CME and CLI but can get around in it.

I don't see where the DID faxes are using DN's. Here  is a fax to email section of the config. If there are DN's for faxing I dont know where they would be. this persons DID fax ends in 5155.

dial-peer voice 306 mmoip
service fax_on_vfc_onramp_app out-bound
destination-pattern 5155
information-type fax
session target mailto:[email protected]

I know we are taking advantage of overlays and here is a sample of one of the EPHONES as an example (this is for a 7975).

ephone  6
device-security-mode none
mac-address 001F.CEA9.D123
username "owner" password 1234
fastdial 1 99545551212 name Home
speed-dial 1 99545551213 label "Bill"
speed-dial 2 99545551214 label "John"
paging-dn 4
type 7975
button  1o11,51 2o79,28 3o29,38 4o39,40
button  5o41,43 6:31

Here are some of the DN's you did not mention in your formula and I am not sure what they are used for (the list goes on and on).

ephone-dn  67
number 5803
call-forward all 600
!ephone-dn  68
number 5804
call-forward all 600

ephone-dn  69
number 5805
call-forward all 600

ephone-dn  70
number 5100
call-forward all 600

ephone-dn  71
number 5101
call-forward all 600

I can send a copy of the show run if that will help.

Thanks again - Craig

Marcos Hernandez Wed, 02/11/2009 - 14:19
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In the spirit of posting something that may help others in the future, I would ask you to go ahead and post your config, but it may contain stuff that you want to keep confidential. Go ahead and email it to me, [email protected]

I will review it, suggest changes and get back to you. Then, I will update this thread with what we did. I should be able to get back to you within 24 hrs.



Marcos - Thank you so much for your time and expertise to explain so details of our config and finding ways to free up DN's that were redundant. I feel the biggest help was to see that there are many DN's that come configured out of the box with the UC500.  In our case the we wanted to use extension numbers in the 100 range to match the extensions we were used to on our old system. By default Cisco programs extensions in the 200 range. Because we didn't need those extensions all the DN's associated with them could be deleted and freed up for other uses.

Another key point was something you told me is in the latest build 12.4(20)Tx called OCTO DN's. So now we can expand the utilization of some of the DUAL use DN's to OCTO's allowing us to free up even more DN's.

I appreciate your help in answering my questions.


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