Phone Network Design Query


I am going to soon be doing a major phone network redesign for one my clients that has 8 locations. The main office has a UCM6510 and each remote office has a UCM6204. They are all interconnected via VPNs and have ext to ext calling and LDAP sync working fine.

The current design has each phone connected to their local UCM.

The redesign will see each phone connected to the main office 6510. There are good reasons for this to take place.

In a fail-over situation the plan is to have each phone connect back to their local UCM. Inbound call fail-over at the ITSP level will route inbound calls to the correct UCM depending on the main site’s status.Each local UCM can also make outbound calls, etc.

Each extension will maintain their current extension number.

Now my question relates as to how best to handle the phone fail-over.

My current thinking is to handle fail over by:

  • Creating the same extension number, authID and SIP password for phone on both the main and local UCMs

  • In AccountX -> General Settings set the SIP server to the main office’s UCM IP and the Secondary SIP Server to the local office’s UCM IP

My thinking is that when the main office UCM is up, the phones will connect to the UCM defined as the SIP Server. When the main office UCM is not reachable, the phones will connect to the UCM defined as the Secondary SIP Server. When the main office UCM becomes reachable again, the phone will switch back. Since the credentials are the same, the phone should be able to log into each UCM without issue.

So my questions are:

  • Will this work?

  • What have I missed or not considered?

Thanks for your support.


I don’t have an answer but, if be more than happy to chat this out with you some time.


Yes it will work as you write.

Secondary SIP server is best idea to do it. In case of fail contact 6510 phone will sent call to local UCM.
I would add interconnect to between local UCM so “local” interconnect still work.

Also Phone will be registered to both servers all time. There is no need re register them :slight_smile: in terms of how it work. Register is needed with Backup Sip Server, Secondary greatly make redundancy all better as call will always connect. Phone receive call from both servers all time.


It should work. You will need to set prefer primary SIP server in the phones. Otherwise, when the primary returns and the phones are registered to the secondary, they may not switch back as the secondary is still fine. If you do as Marcin suggests (good idea), a call will be handled regardless of which UCM the phone is connected to.

However, its a two-way street in that when you consolidate the phones to one PBX, all functionality is available to all phones connected to same. However, when they end up being connected to the remote PBXs, they can handle in and out calling, but the park, feature codes such as forwarding, system speed dials, operator, DND, blacklists and others are only resident in the PBX to which the phone was connected at the time when the function was invoked. This could cause problems whenever the phones move from primary to secondary and back.


Yes, I agree. This is already in place - extension to extension calling from each UCM - and I didn’t plan on removing it.

In fail-over, only the main site phones should be unreachable.


Thanks. I didn’t know that. I thought it connected to the main when active and then only connected to the secondary when needed.

Good to know.


Can you advise where to find this setting? I have not been able to find it on the phone’s web GUi.



Absolutely. The client is aware that they will lose functionality in fail-over mode, but they accept that given that is would only come into play in limited circumstances. The main feature they will lose is their cross-company Queues.

It should be noted that each UCM will have the same configs with respect to system settings, including all voicemail being voicemail-to-email, delete when sent.

Other than the Queues, I think the biggest impact will be if they try to park a call in their branch and try to get someone in another branch to pick up that parked call.

Time will tell of course as theory is one thing, the real world another.

Overall, I think this will be a good fail-over option to maintain customer contact in the event the main site goes down.