T8 · T8-R01
One hypothesis, one change
Learn it in 5 minutes
- Say what you think is broken, in one sentence.
- Change one thing.
- Capture before and after.
- If the symptom does not move, revert.
- A bundle of changes is not a lesson.
Visual
What is going on
Voice tickets get worse when five settings change before the first ladder is saved. The evidence pack is the hypothesis, the time, the calling and called numbers, the SIP ladder or the CUCM trace, and the result. Store it next to the change.
Worked example
Hypothesis: the trunk CSS cannot see the PSTN partition. Change: add that partition. Result: the same call now leaves CUCM and fails further downstream. You learned something. You did not also restart the cluster.
Quiz
1. Changing the CSS, the codec, and the gateway in one window is a clean test.
False.
Ecosystem
Sister pieces sit on the ecosystem page: the glossary, the mind map, the integration map, and the sibling labs.
- Hypothesis — The single fault you are testing.
- Evidence pack — The traces and notes that show the test.
Config. Paste the relevant lines, not a 40-page trace, into the note.
Troubleshooting. If you cannot revert, you did not have a change. You had an accident.
Bridge. The same habit works on CUBE dial peers and on Calling locations.
Mind map, sister technologies, and future hooks live on the ecosystem page.
Sources
Product screens move. Confirm the guide for your release before you change a live system.
Sources and go deeper
Opened 2026-10. A row marked confirm has no link, because that page was not verified.
- Cisco. System Configuration Guide for CUCM, Release 15 last checked 2026-10
- RFC. RFC 3261, SIP last checked 2026-10
- Community. Cisco Community, Collaboration knowledge base last checked 2026-10
- Wikipedia. Session Initiation Protocol (Wikipedia) last checked 2026-10
- Protocol and ports. CUCM 15 TCP and UDP port usage last checked 2026-10