CME Redundancy

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Sep 5th, 2007
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CME Redundancy

I have a site which has a 3825 with 100 users, it is connected to the pstn via an E1 line, I require some sort of redundancy at the site in the event the 3825 goes down.

From this doc - >

Under the section - Redundant Cisco unified CME router

It states the following :

"The physical setup for redundant Cisco Unified CME routers is as follows. The FXO line from the PSTN is split using a splitter. From the splitter, one line goes to the primary Cisco Unified CME router and the other goes to the secondary Cisco Unified CME router. When a call comes in on the FXO line, it is presented to both the primary and secondary Cisco Unified CME routers. The primary router is configured by default to answer the call immediately. The secondary Cisco Unified CME router is configured to answer the call after three rings using the voice-port ring number 3 command. If the primary router is operational, it answers the call immediately and changes the call state so that the secondary router does not try to answer it. If the primary router is unavailable and does not answer the call, the secondary router sees the new call coming in and answers after three rings"

My question :

Can an E1 be split like this ? or would you have to manually switchover the cable from the E1 on the primary system over to the E1 on the secondary system ?

if it can be split how do I configure the secondary router to only answer calls if the primary is down ?

Also a different question on redundancy...

Can you use a lower end spec cme router with a 24 user feature license as a backup to a bigger system with 100 users, the idea is that only certain phones (ie directors, managers) will register with the secondary router by configuring "no auto-reg-ephone" under telephony services and configuring specific ephone configurations for those phones you wish to register with the system ?

Thanks in advance

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Overall Rating: 5 (2 ratings)
paolo bevilacqua Wed, 09/05/2007 - 03:46
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1. E1 circuits cannot be split like analog pots. So you have to manually switch the cable. You could also use an Y cable but be aware you must always keep shutdown one interface.

2. Yes, you can do that. Note that a nominal 24 ephones platform will actually allow 30 ephones.

In any case, the hardware availability of ISR routers is very high. I still have to see one to fail.

Hope this helps, please rate post if it does!

mark_gardner Wed, 09/05/2007 - 05:51
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Hi paolo

Thanks for that, thought as much.

I wonder why it allows you to configure more ephones than the system is licensed for.



paolo bevilacqua Wed, 09/05/2007 - 13:19
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It gives you slack. Think when you are hiring new people but the bigger router that you've ordered is in backorder :)

Someone at cisco anticipated this evidently :)


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