Send incoming calls to more than one PBX or site, with failover

How a load balancer decides where a call goes

A load balancer is a list of places where Cloud SIP can deliver a call. It's kept inside your SIP domain, and it has its own address, such as sip:main-office@example.sip.enfonica.com. Your phone numbers send calls to that address instead of straight to one PBX (private branch exchange, your phone system).

Each place in the list is an endpoint. Two numbers decide the order in which Cloud SIP tries them:

• Priority. Endpoints with the lowest number are tried first. Higher numbers are backups.
• Weight. Among endpoints with the same priority, calls are shared in proportion to their weight. With weights of 20 and 10, the first endpoint is tried first for about two calls in three.

These examples show common setups.

Cloud SIP moves on to the next endpoint when one doesn't respond, or answers with a server error, such as 500 or 503. When a PBX answers that the line is busy, that the call is declined, or that the number isn't found, the answer is final. It goes back to the caller. If every endpoint fails, the call goes to the load balancer's failover URIs, such as a voicemail flow or a mobile.

Create the load balancer

Add one endpoint for each PBX or site. Then add a failover destination for when none of them can take the call.

1. In the Enfonica Console, go to Cloud SIP, and open your SIP domain.
2. Under Load balancers, select Add load balancer.
3. In Alias ID, enter a short name, such as main-office. Use lowercase letters, numbers, and hyphens. The alias becomes the load balancer's address, sip:main-office@example.sip.enfonica.com, and you can't change it later.
4. Optionally, add a Display name that your team will recognize.
5. Under Endpoints, select Add endpoint.
6. In Endpoint URI, after the sip: that's already shown, enter your PBX's address, for example 203.0.113.10 or pbx.example.com. The table after these steps shows each format.
7. Set Priority and Weight. Both start at 10.
8. Leave the Enabled checkbox selected, and then select Add.
9. Repeat steps 5 to 8 for each PBX or site, up to 10 endpoints.
10. Under Failover URIs, select Add, and choose where calls go if every endpoint fails. For the options, see Choose a failover destination.
11. Select Save, and then select Save Changes on the SIP domain page. The load balancer isn't saved until you select Save Changes.

Use the Endpoint URI format that matches your PBX.

Use an IPv4 address or a DNS name. IPv6 isn't supported.

Cloud SIP sends the number that was called in E.164 format, such as +61255501234, so set your PBX's inbound routes to match that format. For more information, see Which number format should my PBX use?

Each site's firewall must accept SIP and call audio from Enfonica's addresses. For the list, see Connect your PBX to Cloud SIP. A backup site that can't receive them won't take calls when you need it.

Choose a failover destination

Failover URIs run inside Enfonica, so they keep working when your office, internet connection, or phone system is offline. They're tried in order. Most people need only one.

• Voicemail or a message. Select Flow, and then select a flow that takes a voicemail, plays a message, or both. To learn how to build one, see Set up voicemail to email in Flow. Our voicemail failover video also walks through it.
• A mobile or another number. Select Phone Number, and enter the number in E.164 format, for example +61491570156.
• Another system. Select SIP, and enter the system's SIP URI.

Point your phone numbers at the load balancer

Each phone number that should use the load balancer needs it as its incoming call handler. One load balancer can serve as many numbers as you like.

1. Go to Phone Numbers > My numbers, and open the number.
2. Under Call settings, in Incoming call handlers, select Add, and then select SIP.
3. Select Load balancer, and then select your load balancer from the list.
4. If the number has another handler from before, delete it.
5. Select Save Changes.

A phone number can use only a load balancer in the same project.

Failover URIs run when calls reach the load balancer in one of these ways:

• From a phone number's handler, as in these steps
• Through a Flow Load Balancer step
• Through VoiceML

A Flow Call step that dials the load balancer's address tries its endpoints, but skips its failover URIs.

Check that it worked

1. Call one of your numbers from a mobile. It rings on the endpoint with the lowest priority number.
2. To test the backup, open the load balancer, and edit that endpoint.
3. Clear the Enabled checkbox, and then select Update.
4. Select Save, and then select Save Changes. Cloud SIP skips disabled endpoints.
5. Call again. The call rings at your next endpoint.
6. To test the failover destination, make each PBX reject a test call with a server error, such as SIP 500. Or take them offline briefly at a quiet time. The call reaches your voicemail, message, or mobile.
7. On every endpoint you turned off, select the Enabled checkbox again, and save.

If a test call doesn't arrive where you expect, open it in Cloud Voice > Calls. Its SIP Insights show the answer your PBX sent. To learn what the common answers mean, see Calls aren't reaching your PBX.

Questions