PSTN Gateways

A PSTN gateway (Online PSTN Gateway) in Microsoft Teams Direct Routing is a configuration entity that acts as a pointer to an SBC device. It interfaces Microsoft Teams to a telephone carrier SIP trunk or IP-PBX, allowing external PSTN calling functionality. Key functions include mediating call signaling and enabling voice routing policies.

For the Live Platform hosting model (Microsoft Super Trunk), only the carriers need to set up and manage a single trunk (carrier trunk in the carrier domain). For the customer tenant, the carrier needs to only add the derived trunk FQDN to the voice routing policies of the users. There is no need to create a new PSTN gateway for a customer trunk.

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To add a PSTN gateway:

Click the PSTN Gateways tab and then click Add New PSTN Gateway.

Configure parameters according to the table below and then click Save PSTN Gateway.

Parameter

Description

Identity

The name of the entity.

SIP Signaling Port

The communication port used for signaling.

Failover Response Codes

The response codes used in the event of communication failure.

Gateway Site Id

The logical identifier used to group or associate a gateway with a specific SIP Connection.

FQDN

The FQDN of the SBC device used for call routing.

Max Concurrent Sessions

The maximum number of concurrent call sessions available for the SBC device configured as the Online PSTN gateway.

Failover Time

Defines the time (seconds) that the Direct Routing service waits before routing calls to an alternate SBC when the primary SBC becomes unavailable.

Enabled

■

When enabled, the gateway is active and receives new incoming/outgoing PSTN call traffic.

■

When disabled, existing calls continue uninterrupted and no new calls are routed to this SBC.

Forward Call History

Determines whether Microsoft Teams includes call history information when forwarding calls from Teams to the SBC.

Forward PAI

Determines whether Microsoft Teams includes a P‑Asserted‑Identity (PAI) header when forwarding calls to the SBC (your PSTN gateway).

Send SIP Options

Determines whether the SBC sends SIP OPTIONS messages to Microsoft Teams for keep‑alive and health‑checking purposes.

Media Bypass

Determines whether media (RTP audio) flows directly between the Teams client and the SBC, instead of being proxied through Microsoft’s cloud media relays.

Gateway Site Lbr Enabled

Determines whether Location‑Based Routing (LBR) is enforced at the network site level for calls passing through that specific gateway.

An example of a configured PSTN gateway is shown in the figure below.