Undocumented behaviour with dialplans on MS Teams

In Skype for Business on-prem, there is a global dialplan that applies to users when there isn’t an appropriate site or user-level dialplan. In the Teams documentation, the tenant Global dialplan serves a similar purpose, but there are additional features outside of what can be done on-prem. 

In Teams, Microsoft has published a series of very simple pre-defined dialplans called service country dialplans that apply to nearly every country in the world. You can see these by running Get-CsDialPlan and Get-CsVoiceNormalizationRule. They do the bare minimum, and don’t do any real validation. These dialplans cannot be modified. 

The documentation goes on to say that you can define normalization rules in the tenant global dialplan or any number of tenant user dialplans. If a user tenant dialplan isn’t assigned to a user, they will be assigned an effective dialplan of whatever is in the tenant global dialplan and the default service country dialplan for that user. Similarly, if a user is assigned to a tenant user dialplan, their effective dialplan will consist of the contents of the assigned tenant user dialplan along with the user’s service country dialplan. The tenant dialplans have higher priority than the service country ones. 

The hidden feature is that if you have defined any normalization rules in the tenant global dialplan, those normalization rules will appear at the top of the list of any new tenant user dialplans created afterwards. This can be very useful in large organizations with many sites, but have a common set of extension dial rules. You simply have to define the rules once in the tenant global dialplan, and they will show up in every new tenant user dialplan created from that point forward. This applies to dialplans created in both PowerShell and the Teams Admin Center.

Unfortunately, there isn’t a real link between the tenant global and tenant user dialplans. They are simply copies of the original. If you make a change to the tenant global dialplan, it won’t be reflected in all your other dialplans. As with Skype for Business, you’re still stuck with using PowerShell to manage bulk changes. Overall, it might make deploying new dialplans just a little bit simpler if you choose to take advantage of this undocumented feature.

The Bugs

Unfortunately, there are also a number of annoying bugs/oversights with the new UI. Some are cosmetic, but some will force you to re-create your dialplan if you accidentally encounter one.

Description Discrepancies

What makes this even more odd, is that the UI for the individual normalization rules exhibits NONE of these issues. It renders the linebreaks properly, and doesn’t complain when the description is longer than 255 characters and includes “special” characters.

The External Dialing Prefix Bug

This is a big bug, and am quite surprised it made it through QA. For a bit of background, you can configure Teams so that users can dial an external access prefix (like 9), before dialing an external number. For users coming from a legacy PBX, this is undoubtedly a boon and doesn’t force them to retrain years of muscle memory. It also makes off-hook dialing more reliable. For an extended explanation of this feature, go waaay back to one of my posts from 2011 on the topic. I haven’t tested it myself, but the details should still apply to Teams.

Most customers don’t bother with this feature, and have been happily creating dialplans in Teams/Skype for Business Online for years via PowerShell without defining an external dialing prefix. However, if you create a new dialplan or edit an existing one in the UI, you will not be able to save your changes unless you set an external dialing prefix.

Also, this seems to have found itself into the PowerShell commands themselves, but not completely. You can create a new dialplan with New-CsTenantDialplan without an external dialing prefix, and you can make changes to an existing dialplan with Set-CsTenantDialplan, but if you try to remove an external dialing prefix via PowerShell by setting it to either $NULL or “”, you will be denied.

As long as you don’t set a prefix, you should be fine. Don’t do what I did and set a prefix in the UI to see what happens, and expect to be able to remove it in PowerShell. This forced me to redo my entire dialplan from scratch. Thankfully, UCDialplans.com took care of that in a minute.

Spelling Mistakes

A minor quibble, but one that will force me to keep a close eye on (boo hoo me). The New/Get/Set-CsOnlinePSTNGateway command has options for setting inbound and outbound translation rules:

• InboundPstnNumberTranslationRules
• InboundTeamsNumberTranslationRules
• OutboundPstnNumberTranslationRules
• OutbundTeamsNumberTranslationRules

Do you see the problem?

Someone’s spellcheck didn’t work.

Conclusion

I’m trying to get this in front of the right people at Microsoft to get them to fix. Hopefully, this half of my post will have a limited shelf life. Have any of you experienced any of these issues or come across any others? Let me know in the comments.