Microsoft Teams Direct Routing Local Media Optimization, unlocks new SBC topology options

Microsoft has announced the general availability of Local Media Optimization for Direct Routing.

Media Bypass

Direct Routing already supported Media bypass, released mid-2019. Meaning that media would “bypass” routing to the Microsoft cloud Media Transport Relays and stay direct between the Teams client and the SBC. This is optimal if the user is on a local/internal network with an SBC and there is no need to route the traffic out to Microsoft, only to route it back to the SBC.

For media bypass, the Teams client must have access to the public IP address of the SBC even from an internal network.

Local Media Optimization for Direct Routing now opens up 2 new abilities:

• Media Bypass to the Internal IP of a local SBC for more optimal media routing
• Organisations putting an SBC on a local site, for example, a branch office with ISDN connection, where there is no local internet/Public IP/connectivity to Microsoft Phone System

Media Bypass to the SBC Internal IP Address

If the client is in the internal network, Local Media Optimization detects the location of the client and provides the internal IP of the SBC. If the client is outside of the corporate network, the technology also detects this, and provide the external or public IP of the SBC. Previous to Local Media Optimization they had to route to the Public IP of the SBC, often through a suboptimal route and/or firewall.

If a user is connected to the local subnet of a corporate network (that is, the user is internal), media flows between the internal IP of the central SBC and the user’s Teams client.

If a user is outside the boundaries of the corporate network–for example, if the user is using a public Internet connection–then the user is considered to be external. In this case, the media flows between the external IP of the SBC and the Teams client.

In this diagram, the German user can route media directly to the internal IP address of the Amsterdam SBC

SBC on a local branch site where there is no Public IP/Internet/connection to Microsoft Phone System.

An organisation wants an SBC on a site where there is no Public IP/Internet/connection to Microsoft Phone System. For example, they are replacing a local PBX with local ISDN but that site has no direct internet connectivity and not enough bandwidth to send all calls back to a centralised SBC or want to keep using the local ISDN PSTN connectivity.

In addition, some countries impose regulatory requirements that cannot be fulfilled without having local PSTN network connectivity.

The branch-site SBC on the private internal IP can be paired virtually to another central SBC with Microsoft/Internet connectivity. Branch site SBCs are communicating through internal IPs and are not directly visible to Microsoft Phone System.

Media always stays local when possible. External users have media flowing between the Teams client and the public IP of the central proxy SBC.

Media route when the user is in the branch

In this diagram, the user in Vietnam Teams client communicates with Phone System directly through the REST API, but media generated during the call flows to local SBC’s internal IP address and local ISDN/PSTN connection.

Media route when the user is external

When the Vietnam user is external to the corporate network.

• The user’s Teams client communicates with Phone System directly through the REST API, but the media generated during the call flows first to the external IP address of the proxy SBC in Singapore.
• Based on configuration and voice policies (see Configure Local Media Optimization for details), the proxy SBC redirects the flow to the downstream SBC in Vietnam.
• The downstream SBC in Vietnam redirects the flow to the connected local PSTN network.

Local Media Optimization modes

Local Media Optimization supports two modes:

• Mode 1: Always bypass. In this case, if the user is internal, the media will flow through the local downstream SBC’s internal IP address regardless of the actual location of the internal user; for example, within the same branch office where the downstream SBC is located or in some other branch office. If you have good connectivity between branch offices, the recommended mode is Always bypass.
• Mode 2: Only for local users. In this mode, media will flow directly to the local downstream SBC’s internal IP address only when generated by the internal user located in the same branch office as the downstream SBC. If there are bad connections between local branch offices but good connections between each local branch office and regional office, then this is recommended

Which SBCs support Direct Routing Local Media Optimization

The list of SBC that support the technology with instructions is on this page https://docs.microsoft.com/en-us/MicrosoftTeams/direct-routing-media-optimization-configure#configure-sbcs-for-local-media-optimization-according-to-the-sbc-vendor-specification

More details

Principal Product Manager Lead Nikolay Muravlyannikov’s  blog here Local Media Optimization for Direct Routing now available

Local Media Optimization for Direct Routing

Configure Local Media Optimization for Direct Routing