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SIP 481 received on BYE Message due to DNS query for RECORD-ROUTE

Štěrba David 1 Reputation point
2021-12-09T16:43:36.05+00:00

Hi, we have configured our SBC for Microsoft Teams Direct Routing, according to the following link https://learn.microsoft.com/en-us/azure/communication-services/concepts/telephony/direct-routing-infrastructure. The SBC makes the DNS query for the primary sip.pstnhub.microsoft.com which is resolved to CNAME sip-du-a-euwe.westeurope.cloudapp.azure.com (52.114.75.24) or CNAME sip-du-a-euno.northeurope.cloudapp.azure.com (52.114.76.76) with TTL value 10. In the 18x or 200 OK response there is RECORD-ROUTE: <sip:sip-du-a-eu.pstnhub.microsoft.com:5061;transport=tls;lr> and it tells to where route the sequential request (e.g. BYE). And this FQDN is resolved to the same IP, but with TTL value 10, so in some cases the BYE is send to the same destination IP like for the INVITE message, but in some cases it's send to the other destination IP and then the SIP/2.0 481 Call Leg/Transaction Does Not Exist is received.

Do you have any solution to ensure the sequential requests routing to the appropriate SIP PROXY?

Thanks David

Azure Communication Services
Azure Communication Services
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