SIP Option Messages

SIP Option Messages can be used to dynamically track the state of a SIP trunk’s destination(s) by periodically sending Option Request Messages. A destination address is considered to be "out of service" if it fails to respond to an OPTIONS Request, if it sends a Service Unavailable (503) response or Request Timeout (408) response, or if using the TCP or TLS protocol, a connection cannot be established. When a destination is “out of service,” it will not be considered in the call routing logic, which can significantly shorten call complete times. 

SIP Option Messages from the Peeredge Orchestrator

When trunk monitoring in enabled on the customer trunk group, the Peeredge Orchestrator determines the availability of the customer’s SBCs/PBXs by periodically (every 60 seconds) sending SIP Option messages to the SBCs/PBXs. The Peeredge Orchestrator will retransmit a Option message two more times if it fails to receive a valid response. If there is no response to all three consecutive SIP Option messages, the Peeredge Orchestrator will consider the SIP Trunk group to be down. The Peeredge Orchestrator will not forward SIP messages (except SIP Option messages) to a SIP Trunk group in a down status. Once the SIP Trunk group is considered down, two consecutive valid responses (i.e. SIP 200OK) to the SIP Option messages must be received to bring the SIP Trunk group back to an operational state. The Peeredge Orchestrator does not validate the source IP address for the responses. For SBCs/PBXs with multiple IP addresses and multiple SIP Trunks, 46 Labs strongly recommends that the SBCs/PBXs be configured to use the same IP address in the response that was sent in the SIP Option message.

SIP Option Messages to the Peeredge Orchestrator

Sending SIP Option messages to the Peeredge Orchestrator can reduce the call setup times for outbound calls in the event of certain partial service disruptions (i.e. a Peeredge Orchestrator has failed, or a routing failure exists within the MPLS or Internet network). The Peeredge Orchestrator will respond to SIP Option messages generated by the SBC/PBX(s). 46 Labs recommends the frequency of SIP Option messages to be set at 60 seconds or greater from each SBC/PBX and recommends the Max-Forwards header in the SIP Option message be set to a value of one. 

Recommendation

46 Labs recommends implementing SIP Option Messages between every customer SBC/PBX to each Peeredge Orchestrator. We also recommend enabling trunk monitoring on all customer trunk groups.