Skype for Business

Skype for Business User Cannot dial to PSTN

Balu llag | May 1st, 2019

Skype for Business User Cannot dial to PSTN

Error message:  Cannot complete the call

Multiple users associated with the target phone number

Error Screen


Recently, I came across issue where multiple users are unable to make outbound call or receive inbound calls using Skype For Business. Users are unable to Dial out or receive any PSTN number and unable to join dial-in conference. For outbound calls, Skype client throws a call error on client that “Multiple users associated with the target phone number” OR “There is more than one contact with your phone number”. When incoming calls comes, the calls end as fast busy or dial tone no user existing with this phone number.

When started checking UCCAPI log shows “Multiple users associated with the target phone number” this happens because one or more users are assigned with same phone number/ Direct inward dialing numbers (DID). Although In an enterprise environment not all the DID’s assigned to the users must be unique, however the extensions assigned to a DID in every instance has to be unique. For example, a user is assigned with +123456789;ext=12345 and another user is assigned with +123456789;ext=12346, then Skype inbound/outbound calls works perfectly fine. However, you cannot assign +123456789 without extension to any other user.

Every user has SIPURI (User address) and LineURI (Phone number) assigned and when a call comes, Skype For Business Front End server tries to do Reverse number Look Up for that DID. FE server Cannot resolve DID into a SIP URI because multiple users are associated with the DID and eventually call fails.

Follow the below steps in order to fix this issue:

First step needs to be checked is if the any other user is assigned similar DID. This can be checked easily running following PowerShell commands in Skype for Business PowerShell.

Get-csuser | Where-Object {$_.lineuri –eq “123456789” -Or $_.Privatelineuri –eq“123456789”} | select displayname, lineuri

If you find any similar entry, you can either change the extension of the user or assign user a unique DID number. However, phone numbers (DID) are not only assigned to user but also assigned to common area phone, Analog device, Response group, UM etc.

If a user is provisioned with a DID and similar DID was assigned to a common area phone, Response group or Analog device, Skype for business PowerShell or control panel will not prompt for an error while creating user account and User will be successfully provisioned with Enterprise voice. However, Incoming and outgoing calls fail under these situations as well.

To check this run the following commands in Skype for Business PowerShell.

Get-csexumcontact | Where-Object {$_.lineuri –like ‘*123456789*’} 

Get-cscommonareaphone | Where-Object {$_.lineuri –like ‘*123456789*’}

Get-csrgsworkflow | Where-Object {$_.lineuri –like ‘*123456789*’} |

Get-csanalogdevice | Where-Object {$_.lineuri –like ‘*123456789*’}|

If you find any similar entry, assign user a with unique DID. In most of the cases, above troubleshooting steps will resolve the issue.

If the issue does not resolve by above troubleshooting steps or if you are unable to identify any common entry, then there is a possibility that Skype For Business 2015 Active Directory attributes of any disabled user with same DID are still stored in Skype for Business 2015 SQL Data Base. The Attributes that we are interested in are msrtcSIP-line which stores LineURI and a non-skype AD attribute Telephonenumber. This can be verified in AD with simple PowerShell command.

Get-aduser -filter {msrtcsip-line -like”*123456789*”} | select samaccountname, msrtcsip-line

Get-aduser -filter {telephonenumber -like”*123456789*”} | select samaccountname, telephonenumber.

If you identify similar attributes, let your Active Directory team know about the issue and either edit or delete the common attributes (msrtcsip-line or telephonenumber) of the disabled user. It is a best practice to clear all the Skype for Business AD attributes as soon as user is disabled.

Once changes are made, user can be successfully able to make and receive calls. Useful command to delete AD attributes.

$thisuser = get-aduser -identity “$displayname” -property msrtcSIP-line

Set-aduser -identity $thisuser -clear msrtcSIP-line

Thank you.

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