Voice Routing backup

Hi all,
in this (quite long) article I’ll explain how to configure Lync and Skype for Business to manage an SBA/SBS or an SBC outage in a Branch Office.

In this article we have a Lync/Skype for Business Enterprise Voice deployment with a Main Site (HQ) and a Branch Office Site, both with a local Sonus SBC Voice GW (1000/2000/SWe Lite), like the image below

Topology settings on HQ

Topology settings on Branch Office

Assuming you have a Voice Routing configuration like this one, with one or more Voice Policy, PSTN Usage Record and Route for every sites.

How to manage SBA/SBS failure

If you do not configure anything else, this is what happens to Branch Office’s calls when SBA/SBS fail:

  1. SBA/SBS fail
  2. Branch Office users and IP-Phone registration fail
  3. Branch Office Users fail-over on Main Site Front-End
  4. Registration on FE is OK
  5. Branch Office User do not find any suitable Voice Route

So let’s fix the issue!

Step 1: create a new Trunk between Branch Office Voice Gateway and Main Site Front-End.
This step will allow Front-End to use remote Voice GW

Open Topology Builder and create a new Trunk between remote voice gateway (bovoicegw01 in this example) and Main Site Front-End (sfbfe01 in this example).
At the end publish new topology.

In SfB Control Panel -> Voice Routing -> Trunk Configuration create a new Pool Trunk

Select the trunk you have just created

Set the parameter to reflect the configuration of the Branch Office Voice GW, take care of number of channels, encryption, Refer Support, Media Bypass and leave enabled the Outbound routing failover timer

Step 2: setup the Voice Gateway
This step will allow remote Voice Gateway to accept connection from Front-End server and use it as a secondary mediation server in case of failure of Branch Office SBA/SBS

On Sonus Settings tab, open Signaling Group associated to SBA/SBS (UC in this example).
Scroll dows to “Federated IP/FQDN” and add the Front-End FQDN.

This will allow incoming connection from Front-End to this Signaling GroupVRB_2_03

In the same Signaling Group change the Load Balancing method to Priority.
This will instruct the SG to use the local SBA/SBS Mediation first (Priority 1) and the Main Site Front-End Mediation Server in case of SBA/SBS fault (Priority 2)VRB_2_04

In SIP -> SIP Server Table open the name of the SfB Mediation Server.
Normally you will find one line of the SBA/SBS Server (sfbsbs01.uclab.local in this example).
We have to add the Front-End Server, so click on Create SIP Server -Z IP/FQDN and add server data as the example below, take care to set the Priority to 2VRB_2_05

SBA/SBS Settings (Priority 1) VRB_2_06

Frond-End settings (Priority 2)VRB_2_07

Step 3: setup the Voice Routing for SBA/SBS outage backup
Step 1 and 2 allow SBA/SBS, SBC and Front-End to speak each other.
In case of SBA/SBS fault, incoming calls are routed to Front-End (step 2 and Load Balancing Priority method), but without changes in Voice Routing no one could take advantage of these new settings for outgoing calls.

On Voice Routing -> Route panel create a new routeVRB_3_01

Call it as you like, respecting your name convention.
In this example I call it IT-Branch-Backup
Add Number Pattern that you want to allow during SBA/SBS outage (outbound calls). In this example we’ll allow European Emergency Numbers, Italy Landline Numbers and Italy Mobile Numbers.

As associated trunk you have to choose the backup trunk, in this case “bovoicegw01-sfbfe01”VRB_3_02

Place the new route as last of the corresponding branch’s rules, then Committ AllVRB_3_04

Now we have to add the new route “IT-Branch-Backup” to PSTN Usage Policies used in Branch’s Voice Policies.
In this example I add “IT-Branch-Backup” route to PTN Usage into Branch Office Pool Voice Policy and to IT-Branch-All Voice Policy.
IT-Branch-Restricted do not gain this setting so users with this policy will not be able to make calls during SBA/SBS outage.

At this point, with these settings, we’ve achieved the goal to make and receive calls during a SBA/SBS fault.VRB_3_10

How to manage SBC failure

Step 4: setup the Voice Routing for SBC outage backup

Last but not least, we need to manage a fault on Branch Office SBC also (on SBA/SBS only is too easy!) 🙂
Our objective is described in this image: if the SBC on Branch Office goes down, Branch Office’s Users cannot place calls (point #5), so in this step we’ll setup a new route to intercept this situation and place calls on HQ’s Voice Gatway (point #6)VRB_4_1

On Voice Routing -> Route panel create a new route, call it as your conventions, in this case I use IT-HQ-Backup.
Enter the Number Pattern you want to allow on this “emergency line” and chose the HW Voice GW (voicegw01.uclab.local) as Associated trunk.VRB_4_2

Place this Route at the very bottom of the Route list, the system should use it as a last resourceVRB_4_3

In Voice Routing -> Voice Policy open a Branch Office policy and create a new PSTN Usage Record (I suggest to use a different PSTN Usage, or you can add the Route to the same PSTN Usage used in steps above).
Call it as you want, I call it as the Route I will add, IT-HQ-BackupVRB_4_4

The newly created PSTN Usage need to be the last one, like the image below.
Add this PSTN Usage to every Voice Policies you want to give ability to call via HQ Voice GW in case of Branch Office SBC fault.
Commit All at the end.VRB_4_5

Response Group Service fallback solution

If you route one or more Branch Office’s incoming calls to a Response Group on the Main Site Front-End, you need to read this article and use one of the two solutions presented.

As always, I hope this quite long article could help one of you.


6 thoughts on “Voice Routing backup

Add yours

  1. The sign of a true engineer (and consultant): clear, consistent, and logical naming standards. Topology Trunk names. PSTN Usage names. Route names. I could go on and on.

    Your naming scheme is almost 100% what I use. I almost cried with joy when I saw it. Thank you for displaying that level of excellence to the world. Too many consultants lack that skill and it leaves those that follow them (other consultants or internal IT folks) dumbfounded due to the lack of foresight.


    Liked by 1 person

  2. thanks Luca for this great article! 2 questions:
    1. in the first case you are using voice routes order instead of using pstn usage records order as recommended by MS, just curious why?
    2. in the second case, what if i have 2 different telcos in the HQ and branch… for egress calls, how HQ carrier will handle the DIDs issued by branch carrier? Do i need to setup translation rules on a trunk level?

    Liked by 1 person

    1. Hi Andrew,
      thank you for your kind words.
      1. I suppose it’s my way to configure the voice routing, you can choose the best option fits your “way” 🙂
      2. Yes, you have to hide the DID of Branch Carrier to the HQ Carrier, if not the calls will fail. You can do that via Route (Suppress Caller ID) or via SBC, your choice. The important thing is: choose one and follow it, do not merge them.


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