Refer to the exhibit. Which out-of-dialog SIP OPTIONS ping response put dial-peer tag 1111 into its current operational state?

SIP 503 Service Unavailable is commonly seen in a VoIP network when a SIP device (such as a SIP server) is knowingly unable to process a call. Typically when this happens the endpoint that originated the Invite will try the next available host it receives in the SIP Contact header.