Overview of interoperability of Azure Communications Gateway with Operator Connect and Teams Phone Mobile

Azure Communications Gateway can manipulate signaling and media to meet the requirements of your networks and the Operator Connect and Teams Phone Mobile programs. This article provides an overview of the interoperability features that Azure Communications Gateway offers for Operator Connect and Teams Phone Mobile.

Role and position in the network

Azure Communications Gateway sits at the edge of your fixed line and mobile networks. It connects these networks to the Microsoft Phone System, allowing you to support Operator Connect (for fixed line networks) and Teams Phone Mobile (for mobile networks). The following diagram shows where Azure Communications Gateway sits in your network.

Calls flow from Microsoft Teams clients through the Microsoft Phone System and Azure Communications Gateway into your network.

Compliance with Certified SBC specifications

Azure Communications Gateway supports the Microsoft specifications for Certified SBCs for Operator Connect and Teams Phone Mobile. For more information about certification and these specifications, see Session Border Controllers certified for Direct Routing and the Operator Connect or Teams Phone Mobile documentation provided by your Microsoft representative.

Call control integration for Teams Phone Mobile

Teams Phone Mobile allows you to offer Microsoft Teams call services for calls made from the native dialer on mobile handsets, for example presence and call history. These features require anchoring the calls in Microsoft's Intelligent Conversation and Communications Cloud (IC3), part of the Microsoft Phone System.

The Microsoft Phone System relies on information in SIP signaling to determine whether a call is:

• To a Teams Phone Mobile subscriber.
• From a Teams Phone Mobile subscriber or between two Teams Phone Mobile subscribers.

Your core mobile network must supply this information to Azure Communications Gateway, by using unique trunks or by correctly populating an X-MS-FMC header as defined by the Teams Phone Mobile SIP specifications. If you don't have access to these specifications, contact your Microsoft representative or your onboarding team.

Your core mobile network must also be able to anchor and divert calls into the Microsoft Phone System. You can choose from the following options.

• Using Mobile Control Point (MCP) in Azure Communications Gateway. MCP is an IMS Application Server that queries the Teams Phone Mobile Consultation API to determine whether the call involves a Teams Phone Mobile Subscriber. MCP then adds X-MS-FMC headers and updates the signaling to divert the call into the Microsoft Phone System through Azure Communications Gateway. For more information, see Mobile Control Point in Azure Communications Gateway for Teams Phone Mobile.
• Deploying an on-premises version of Mobile Control Point (MCP) from Metaswitch. For more information, see the Metaswitch description of Mobile Control Point. This version of MCP isn't included in Azure Communications Gateway.
• Using other routing capabilities in your core network to detect Teams Phone Mobile subscribers and route INVITEs to or from these subscribers into the Microsoft Phone System through Azure Communications Gateway.

SIP signaling

Azure Communications Gateway automatically interworks calls to support the following requirements from Operator Connect and Teams Phone Mobile:

• SIP over TLS
• X-MS-SBC header (describing the SBC function)
• Strict rules on a= attribute lines in SDP bodies
• Strict rules on call transfer handling

You can arrange more interworking function as part of your initial network design or at any time by raising a support request for Azure Communications Gateway. For example, you might need extra interworking configuration for:

• Advanced SIP header or SDP message manipulation
• Support for reliable provisional messages (100rel)
• Interworking between early and late media
• Interworking away from inband DTMF tones
• Placing the unique tenant ID elsewhere in SIP messages to make it easier for your network to consume, for example in tgrp parameters

The Microsoft Phone System requires calling (A-) and called (B-) telephone numbers to be in E.164 format. This requirement applies to both SIP and TEL numbers. We recommend that you configure your network to use the E.164 format for all numbers. If your network can't convert numbers to the E.164 format, contact your onboarding team or raise a support request to discuss your requirements for number conversion.

SIP trunks between your network and Azure Communications Gateway are multitenant, meaning that traffic from all your customers shares the same trunk. By default, traffic for Operator Connect or Teams Phone Mobile contains an X-MS-TenantID header. This header identifies the enterprise that is sending the traffic and can be used by your billing systems.

RTP and SRTP media

The Microsoft Phone System typically requires SRTP for media. Azure Communications Gateway supports both RTP and SRTP, and can interwork between them. Azure Communications Gateway offers further media manipulation features to allow your networks to interoperate with the Microsoft Phone System.

Media handling for calls

You must select the codecs that you want to support when you deploy Azure Communications Gateway.

Operator Connect and Teams Phone Mobile require core networks to support ringback tones (ringing tones) during call transfer. Core networks must also support comfort noise. If your core networks can't meet these requirements, Azure Communications Gateway can inject media into calls.

Media interworking options

Azure Communications Gateway offers multiple media interworking options. For example, you might need to:

• Change handling of RTCP
• Control bandwidth allocation
• Prioritize specific media traffic for Quality of Service

For full details of the media interworking features available in Azure Communications Gateway, raise a support request.

Provisioning and Operator Connect APIs

Operator Connect and Teams Phone Mobile require API integration between your IT systems and Microsoft Teams for flow-through provisioning and automation. After your deployment is certified and launched, you must not use a portal for provisioning. Azure Communications Gateway offers an alternative method for provisioning subscribers with its Provisioning API (preview) that allows flow-through provisioning from your BSS clients to Azure Communications Gateway and the Operator Connect environments. Azure Communications Gateway also provides a Number Management Portal (preview), integrated into the Azure portal, for browser-based provisioning that can be used to get you started while you complete API integration.

For more information, see:

• Provisioning Azure Communications Gateway and Integrate with Azure Communications Gateway's Provisioning API.
• Manage an enterprise with Azure Communications Gateway's Number Management Portal (preview) for Operator Connect and Teams Phone Mobile.

Providing call duration data to Microsoft Teams

Azure Communications Gateway can use the Operator Connect APIs to upload information about the duration of individual calls (CallDuration information) into the Microsoft Teams environment. This information allows Microsoft Teams clients to display the call duration recorded by your network, instead of the call duration recorded by Microsoft Teams. Providing this information to Microsoft Teams is a requirement of the Operator Connect program that Azure Communications Gateway performs on your behalf.

Compatibility with monitoring requirements

The Azure Communications Gateway service includes continuous monitoring for potential faults in your deployment. The metrics we monitor cover all metrics that operators must monitor as part of the Operator Connect program and include:

• Call quality
• Call errors and unusual behavior (for example, call setup failures, short calls, or unusual disconnections)
• Other errors in Azure Communications Gateway

We'll investigate the potential fault, and determine whether the fault relates to Azure Communications Gateway or the Microsoft Phone System. We might require you to carry out some troubleshooting steps in your networks to help isolate the fault.

Next steps

• Learn about monitoring Azure Communications Gateway.
• Learn about requesting changes to Azure Communications Gateway.