Earlier to enable enterprise voice with calling plan on skype for business online we would need to install cloud connector locally on a virtual machines as a separate appliance which requires complex configuration for integrating with the certified session border controllers.

Now Microsoft have made it easier to configure them with direct routing where we do not need to deploy the cloud connector agent locally in the on-premise systems.

When paired with Microsoft Calling plans or direct routing with local ISP calling plan, they provide a full enterprise experience for office 365 users in Teams on a global scale. With Direct Routing we can Connect Existing Telephony Infrastructure to MS teams with the help of  local session border controllers. A SIP connection is created between the cloud call controllers and our local session border controllers.

In this article we will look at the options , readiness and steps  to Enable users for Direct Routing from the Microsoft office 365 perspective.

Readiness for Direct Routing:

Decide on Session Border Controller (Self or hosted SBC):

Session border controller connects Teams call to PSTN next hop or to the configured sip trunk with the local ISP. Here we have two options either to have own session border controllers on premise or to have this functionality hosted to a managed service provider who will host the session border controller for your organization to perform the SIP proxy and the PSTN routing for Microsoft Teams.

Make sure to select the supported session border controllers by Microsoft to configure direct routing in Microsoft Teams.

Figure out licenses based on deployment: Decide on media bypass Configuration

We need to figure out licenses on Microsoft office 365 to utilize the full enterprise functionality of Microsoft Teams.

Option1: Full Microsoft License

In this case no direct routing is required unless there is coexistence required with existing telephony system because we will be having the full calling plan with Microsoft and will utilize the Microsoft call controller, PSTN, Media controllers and Media processor.

• 

Option 2 : Full Teams feature plus Local Telcom Calling plan

This option requires to perform direct routing with Microsoft Teams SIP proxy  services to create the SIP trunk between Microsoft Teams in the cloud and local session border controllers to utilize the calling plan from local PSTN provider.

Below Licenses are required:

SBC readiness:

Decide on SBC Host Name:

Microsoft communicates to session border controllers only via FQDN. We need to decide on a hostname for Session border controller which will be public available to configure direct routing. In our case we will be having voicegw.ezcloudinfo.com

Configure the certificate:

The SBC must be configured with a certificate from public certificate authority with the decided host name. We could also use wild card and SAN certs but the CSR needs to be generated from the certified SBC.

Firewall:

Below source and destination ports needs to be opened for communication between Microsoft PSTN hub FQDNs and the session border controllers.

Above Necessary source and destination ports needs to be opened in Firewall for the SIP Signaling, SIP Proxy ,Media Processing and Media Bypass to happen for the STUN, TURN , ICE connectivity and for successful Teams audio/video call .

Direct Routing configuration in Microsoft Teams:

1. Flow differs for external and internal media bypass.
2. Internal media bypass – Flows within the network teams and SBC and traffic is routed to local PSTN provider.
3. External Media bypass – Flows users will try to connect via certified SBC if now will take the SIP Proxy Route.
4. Office 365 network is enhanced for teams traffic.
5. Call Queues and Auto attendant configuration needs to be verified and configured according to the current setup.

Thanks & Regards

Sathish Veerapandian