Why internal calls dialed by extensions fail in Cisco Webex Calling

Today I am going to share with you, my dear readers, some experience of working with Cisco cloud telephony - Cisco Webex Calling. One of my customers received his own tenant in Webex Calling and started using it. So, they received access to Webex Control Hub, they configured some users with extensions for testing, etc. The users could normally login to Webex Application with their accounts and see their extensions. 

However, they were surprised to discover that when they try to make an internal call from Webex App to Webex App and dial extensions of each other, the call just fails. They can hear the message from Webex Annunciator like ""We're sorry, but your call can not be competed at this time..." This not what our customer expected from the newest cloud telephony system, right? ))) Let me tell you, how it was solved.

What was strange in their tenant - the users could call to each other via URIs (user@domain). If they dialed URI, everything was pretty fine: the destination App rings, the recipient can normally answer the call an they of course can talk. So, this got me thinking, that there is something wrong at higher, let's even say, organization level settings. After a thorough check, finally we found the origin of this issue.

There is a setting in Webex Control Hub named Locations (you can see it under Calling -> Locations in the Webex Control Hub). Locations allow you to organize users and workspaces based on a physical location. You can configure both calling and workspace management functions into the same location. Locations help organize your organization’s workforce into logical groupings. For example, a multinational enterprise may have multiple offices around the world, each with markedly different Webex collaboration requirements. Then users and workspaces can be assigned to a location. For your organization you have to configure at least one Location. Actually, Locations in Webex Calling are very similar to Device Pools in CUCM. 

You can find multiple settings in your Location - such as Emergency Calling settings, Call Settings, Device Configurations etc. But what is very important - you should mandatory configure Main Number at which the location's main contact can be reached. Typically it is one of the PSTN numbers you created for your tenant at Webex Control Hub. 

If you don't configure it, see what system says to you: 

The system warns you that the calls will not be possible until you add a Main Number!!! And this was what our customer just ignored. Of course, I can understand them, because it is difficult to suggest, that all internal calls will not work, if you don't configure this. It is logical to think that this setting is for external call, right? How could you know that it influences the internal calls in so cruel way?! 

Thus, we offered to configure a Main Number for the Location to our customer. They added one of their PSTN numbers like so:

You can see that the warning immediately disappeared. And then the magic happened - the internal calls now started working as expected. Well, assigning a Main Number changed everything and now the users could call to each other just dialing their extensions.

What I don't still understand - how could the URI calls work then? Well, it is Cisco, and everything is possible )))