The proxy server is in service to the following on-premises business cases:
- SBC Routing based on LDAP (AD) in Microsoft Teams
- Updating AD for Extension Dialing for Auto-Attendants in Microsoft Teams
- Hybrid CUCM and Microsoft Teams Dial Plan Management
Read more about the Proxy Server 
Connectivity to Active Directory (AD) and Cisco Unified Communications Manager (CUCM)
Hybrid CUCM and Microsoft Teams Dial Plan Management
Check assigned CUCM numbers for an exact match with a Teams phone number
This feature streamlines the management of your hybrid dial plan throughout Cisco to Teams migration projects. Its primary purpose is to guarantee that numbers are exclusively assigned on one platform, avoiding potential conflicts. In other words, ZPM and ZPC will ensure that your helpdesk never assigns a number that is already assigned in the other system.
Check assigned CUCM numbers for corresponding Teams phone numbers with matching last digits
You can customize the feature to support more complex hybrid dial plans where CUCM users are transitioning from shorthand dial extensions (where the user’s number consists of the last few digits of their DID number) to full E.164 numbers in Microsoft Teams. In this case, select the last matching digits option and specify how many digits should be matched.
Note: The last matching digits function works only for hybrid dial plans where Teams users have full E.164 numbers. It is not supported for Teams users with a shared main number and extension.