Direct routing is a feature where you can bring your own telecom carrier for making PSTN call from Teams client. Logically most of the certified SBC follow same logic. But the option & terminology is slightly different. Audiocodes SBC are certified by MS for Direct Routing.
Now we will configure various component of SBC for direct routing.
- Ethernet Devices lets us configure the ethernet devices and corresponding VLAN onto the SBC. The devices will be used to assign the IP address onto the next steps. We will configure VLAN by adding Ethernet devices from Setup menu > IP Network tab > Core Entities folder > Ethernet Devices.
- IP Interfaces lets us assign the actual IP addresses for management and other connectivity such as Media and control. This can be set from setup menu > IP Network tab > Core Entities folder > IP Interfaces
- TLS Contexts to ensure the TLS connectivity from SBC to other devices/component. This will be achieved by creating a certificate request and importing certificate to the SBC. The Microsoft Phone System Direct Routing Interface allows only TLS connections from SBCs for SIP traffic with a certificate signed by one of the Trusted Certification Authorities. Setup menu > IP Network tab > Security folder > TLS Contexts
- Media Realm allow dividing the UDP port ranges for use on different interfaces.
- SIP Interfaces will configured to handle SIP signaling request. Open the SIP Interfaces table from Setup menu > Signaling & Media tab > Core Entities folder > SIP Interfaces. SIP interface is basically set to accept Signaling request To & From remote party.
- DNS settings allow proper name resolution of various FQDN. Setup > IP Network > DNS
- Proxy Sets is basically the addresses where SBC will communicate Or route the traffic e.g. sip.pstnhub.microsoft.com for Teams. As a part of security measure sbc should be receiving calls originating from the endpoints defined in Proxy sets. Configure Proxy sets & proxy set tables from Setup menu > Signaling & Media tab > Core Entities folder Proxy Sets
- Media security under setup > Signaling & Media > Media > Media Security.
- Coder Group configuration with allowed codecs and map it properly to IP-Profile Under setting Extension Coders Group.
- Configure IP Profile for Teams and PSTN.
- Configure the IP Group.
- IP-to-IP Routing to route the call between 2 networks. From PSTN to Teams and another Route from Teams to PSTN network.
- SRTP at SBC level to secure the RTP traffic.
- Below diagram depict a top level flow to configure SBC components. Every block will be used as input onto the next block as per arrow direction.
