Which two responses from a SIP device, which is the only remote destination on a Cisco Unified Communications Manager SIP trunk with OPTIONS ping enabled, cause the trunk to be marked as "Out of Service"? (Choose two.)
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A. B. C. D. E. F.AB.
The remote peer may be marked as Out of Service if it fails to respond to OPTIONS, if it sends 503 or 408 responses, or if the Transport Control Protocol (TCP) connection cannot be established.
If at least one IP address is available, the trunk is In Service; if all IP addresses are unavailable, the trunk is Out of Service.
References: http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/8_5_1/ccmcfg/bccm-851-cm/b06siprf.html.
Sure, I'd be happy to provide you with a detailed explanation of the answer to this question from the CCIE Collaboration exam.
When a Cisco Unified Communications Manager (CUCM) SIP trunk has OPTIONS ping enabled, it sends periodic OPTIONS requests to the remote SIP device to check if it's still available. If the SIP device responds with certain SIP response codes, the trunk may be marked as "Out of Service," indicating that the remote destination is no longer reachable.
The two SIP response codes that can cause the trunk to be marked as "Out of Service" are:
503 Service Unavailable: This response code indicates that the SIP device is temporarily unavailable, either because it's busy handling other requests or because it's undergoing maintenance. CUCM interprets this response as a failure to reach the remote destination and marks the trunk as "Out of Service."
408 Request Timeout: This response code indicates that the SIP device did not respond to the OPTIONS request within a certain time period. CUCM considers this to be a failure to reach the remote destination and marks the trunk as "Out of Service."
The other SIP response codes listed in the question (505, 504, 484, and 404) do not cause the trunk to be marked as "Out of Service" in this scenario.
505 Version Not Supported: This response code indicates that the SIP device does not support the SIP protocol version specified in the OPTIONS request. While this may indicate a problem with the remote device's compatibility with CUCM, it does not necessarily mean that the remote destination is unreachable.
504 Server Timeout: This response code is similar to the 408 Request Timeout, but it indicates that an intermediary SIP server (such as a proxy) timed out while trying to forward the OPTIONS request to the remote device. This response does not necessarily mean that the remote destination is unreachable.
484 Address Incomplete: This response code indicates that the remote device could not process the OPTIONS request because the SIP address in the request was incomplete. While this may indicate a problem with the remote device's configuration, it does not necessarily mean that the remote destination is unreachable.
404 Not Found: This response code indicates that the remote device could not find the resource (such as a user or device) specified in the OPTIONS request. While this may indicate a problem with the remote device's configuration, it does not necessarily mean that the remote destination is unreachable.
In summary, the two SIP response codes that can cause a CUCM SIP trunk to be marked as "Out of Service" when OPTIONS ping is enabled are 503 Service Unavailable and 408 Request Timeout.