Telephony Redundancy

[prakashrajasekaran2807]

HI folks,

 we have cisco  ISR4331-V/K9 as a Voice router and We have currently terminated a PRI line in this router. The service Provider allotted 400 DID numbers to this circuit.  currently, we have a requirement for making this a redundant connection.

 we are using a centralized CUCM for managing the route pattern and route rules. My desk phones are cisco 8851.

How can we achieve redundancy?

1. SInce the telephone numbers are unique like IP ? how can we form redundancy with two providers.

2. Do I need to buy a New router for this redundancy setup

3. is there any we can use CUCM to work on this.

4. I am ok with Active and standby setup but do I need to do manual failover in case of link down

if the solution won't work what will be the best way to do this. do I need to move for SIP.

Can someone from the IP Telephony system advise me for this setup?   

[Nithin Eluvathingal]

Each ISP has different number plan, so you cannot have same DID range from two different ISP. 

For a scenario where you need to have both incoming call and outgoing calls working for the whole 400 DID when a PRI line fails you can try the below. 

Bring another gateway. Subscribe for another PRI line(no DID required) from same service porvider . Ask ISP to hunt the whole 400 DID on both these PRI  lines. in this case if one PRI line fails all the inbound and outbound calls will be go  through the other PRI line. 

[prakashrajasekaran2807]

Hi Nithin,

Thanks for the replay, We are looking for redundancy because we should not depend on a single provider. As the Location is near an upcoming metro station and lots of cable cuts are happening here and there, it takes more time to restore. The plan is to have a backup as we are planning to set up a call center in the office. what's your suggestion?  

If only incoming is the choice will it work out..  How about changing these links to SIP will that give any difference. 

Sorry for the silly questions, I am from a Data Network background and don't have that much knowledge over telephony. 

[Roger Kallberg]

As @Nithin Eluvathingal wrote you can not use two service providers to route calls inbound for the same range of DIDs. Using SIP would not change anything.

[Nithin Eluvathingal]

Each  IPS is allocated with different numbering Plan. Same numbering plan will not be available  even if you choose SIP. 

You can take another connection(sip/PRI/analogue) From  a different ISP and ask your first ISP to forward the call to the new during the outage.Even in this case, your first ISP won't be Able to do call forwarding for each 400 DID. Either they DID  it for the pilot or for all the DID to a single number.  Regarding the outgoing calls, its work from the new lines but  will show the new line number. 

For internet , we take two connection for redundancy. that doesn't work in Telephony. 

[prakashrajasekaran2807]

Many Thanks to Nithin and Roger,

   In case of an outage in the primary provider, for forwarding the call . Can this be done through our CUCM or we need to call the provider every time to do this?

[Nithin Eluvathingal · Accepted solution]

We can only control the outgoing, incoming is controller by ISP. 

For example, You have line 1 from ISP 1 with DID 24588600 and line 2 from ISP 2 with DID 34654000. Assume that line 1 failed. Now You need to forward the calls coming for  line 1 to 34654000, this can be only be done by ISP.

For outgoing calls we configure CUCM in such a way that if PRI 1 is done use PRI 2.