DNS Query using SRV Record

The IMG 2020 supports utilizing an A-Record, SRV or Service Record, or both to specify which sip server to route a call to. The determination of which record to use is configured in the DNS Servers object. DNS Queries on SRV records will be described below. SRV Records are defined in RFC 2782 and identifies the server(s) that will support a particular service. In this case the IMG 2020 will be looking for the best way to route a call to a server which employs the sip service. A Channel Group can be configured so that a query is sent to a DNS server and the DNS response would be an SRV record including all the sip servers that match the initial DNS service request. From the SRV Record the IMG 2020 will handle load balancing from the priority/weight of each server using Random number method. The final result will be that the IMG 2020 will send the outbound INVITE message to the server with highest priority/weight and attempt to connect to that SIP server. If however after a few Re-INVITES the initial SIP Server cannot be reached, an outbound INVITE will be sent to the SIP server with the next highest priority/weight. This will continue until all responses in the DNS query have been exhausted and the call will fail. Up to five DNS responses in each SRV Record are supported.

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