Separate registration from monitored state
A phone can make calls while a busy-lamp field remains stale. Record one monitored extension, the observing phone, its firmware and the action that should change the lamp. Check whether dialing the button still works; a speed-dial action and an event-state indicator are different observations.
Compare two observing phones or two monitored extensions. This helps separate a single button mapping from a shared subscription or PBX-state problem.
Inspect the subscription lifecycle
Find the SUBSCRIBE for the monitored resource and its response, followed by NOTIFY. Check the Event package, resource address and authentication outcome. In the event framework, Subscription-State distinguishes active, pending and terminated; an accepted subscription request does not guarantee a lasting active subscription.
Watch the expiry and refresh boundary. If the indicator works immediately after a reboot and later freezes, capture the refresh cycle rather than repeatedly restarting the phone.
Compare state generation with state delivery
Place a controlled call on the monitored extension. Determine whether the PBX changes its internal extension state, emits a notification and delivers it to the observing phone. Asterisk endpoint controls include whether subscriptions are permitted and which subscription context applies.
If the phone acknowledges notifications but displays the wrong state, compare the body and event package with the exact model’s expected format. If no notification leaves the PBX, inspect the monitored resource or hint mapping before editing the phone’s LED colors.
Test the button through a full cycle
Apply one supported mapping, permission or provisioning correction and confirm that it survives reprovisioning. Test idle, ringing, answered and hangup states, then wait through a refresh. For parking keys, use the actual slot and retrieve a parked call; a lamp alone is not a retrieval test.
Document the account used by the button and the monitored resource. Remove obsolete subscriptions when extensions are reassigned. Avoid publishing full presence traces without redacting staff identities and calling details.
Watch the explanation
Maps an extension’s credentials to a phone account, then adds voicemail access and busy-lamp keys. Changing the default phone administration password is part of the walkthrough.
Read applicability and editorial notes →Watch this video here
FreePBX 15 and Yealink T58A in 2021. Use current firmware documentation for your exact model. Review used the available transcript and primary references; audio and screen readability remain unverified.
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Sources & applicability
Primary references for the technical details above. Operational examples and planning checklists are VoIP.info editorial guidance.
- IETF RFC 6665: event subscription state and refresh ↗
- Asterisk 22: subscription permissions and context ↗
Examples require adaptation to your topology. No live PBX or hardware testing is claimed.