Unlock the Full Potential of Microsoft Teams with Direct Routing: A Complete Guide

Microsoft Teams has become the go-to platform for communication and collaboration, but did you know that you can enhance its functionality even further with Direct Routing? Direct Routing allows you to integrate Teams with your existing telephony system (PABX), giving you access to advanced call and voicemail features, and enabling seamless communication both inside and outside your organization.

In this blog post, we’ll explore what Direct Routing is, why it’s essential for your business, and how you can set it up.

Microsoft Teams Direct Routing IP Addresses

When using your own SIP Trunk (BYOT) in combination with a SBC to setup Direct Routing to Microsoft Teams you will need to make some firewall rules. You can find the up to date IP addresses in belows chapters.

This will only be for Microsoft 365, Office 365, and Office 365 GCC tenants.

Signaling IPs

When configuring Direct Routing you will need to setup 3 FQDNs for signaling.

• sip.pstnhub.microsoft.com
• sip2.pstnhub.microsoft.com
• sip3.pstnhub.microsoft.com

The first one will be located by location and performance metrics. If your location is EMEA, you 2nd location will be US and the 3th ASIA.

Microsoft Teams - Direct Routing Root Certificates Update

On May 12, 2025, the current root certificate “Baltimore CyberTrust Root” expires. This certificate now handles the encryption of Microsoft Teams but also Azure Communication Services and even still the old Skype for Business Online components.

The transition to the new root certificates has started by Microsoft in January 2022 and will be completed this month, October 2022. In case you are using Direct Routing with your Microsoft 365 tenant you probaly have uploaded the Baltimore CyberTrust Root certificate in to your SBC.

Microsoft Teams - Using the SIP Gatway

While native Microsoft Teams phone devices provide the complete Teams user experience, we still met customers with an bunch of legacy SIP devices. In order to help these customers with their migration to Microsoft Teams, Microsoft has launched the Teams SIP Gateway. This is a cloud service that enables core Teams calling functionality on compatible SIP phone models from Cisco, Poly, Yealink and AudioCodes.

I’m going to describe the steps on how to provision SIP phones for Teams calling using this SIP Gateway with a Cisco CP-7841 IP Phone.

Microsoft Teams - Assign Direct Routing phone number in TAC

Microsoft released a new feature within the Teams Admin Center. It’s now possible to assign Direct Routing phone numbers in the GUI.

Setting up tag based routing in Audiocodes Mediant

In this post i want to show the configuration steps of configuring tag based routing.

You can use Dial Plan tags for determining the destination (IP Group) of an IP-to-IP Routing rule. One of the advantages of using Dial Plan tags is that it can reduce the number of IP-to-IP Routing rules that you would normally need to configure.

For example: When you have an SBC with SIP trunk and legacy PBX and you would like to implement Microsoft Teams Direct Routing you can route specific numbers to Teams and the rest goes automatically to the legacy PBX. This way you can migrate your users in steps to Microsoft Teams.

Transcoding issue on the Audiocodes Mediant

I have had a issue with a customer where we have implemented Direct Routing. It’s a HA setup version 7.20A.260.095 running virtual on a VMware cluster.

The alarm says: License Pool Alarm. Some of the license pool allocations exceed maximum capability and will not be applied.

In the syslog i see the followig errors show up:

            20:11:35.145  172.20.1.1  local0.warn    [S=3603724] [SID=815d0e:57:143476]  (N  3305189)!! [ERROR] ResourceCounter: Cannot allocate more Media channel [0/0] [Time:23-11@20:11:36.770]
            20:11:35.145  172.20.1.1  local0.warn    [S=3603725] [SID=815d0e:57:143476]  (N  3305190)!! [ERROR] (#430)RTS::AllocateResource Allocate Resource - cannot allocate DSP. probably lack of resources [Time:23-11@20:11:36.770]

When i look in to my license i have transcoding assigned by the OVOC, but they are not allocated: