Freeze one exact failed attempt
Record timestamp and timezone, handset model, hardware revision and firmware, manager and base models and firmware, regional DECT variant, PBX account, serving location, call direction, dialed identity and the precise symptom. Distinguish failure to register, failure to start a call, one-way or missing audio, a drop while stationary, and a drop or gap only while moving between cells.
Preserve the manager and base inventory, synchronization state, handset status, PBX registration or contact, signaling result and authorized network or radio observations before rebooting or re-registering. A registered handset proves one identity reached a base system and PBX state; it does not prove every radio cell, handover path, codec, media path or call feature.
Separate handset, base, manager and PBX state
Confirm the handset belongs to the intended manager system and exact account. Then identify each W75DM or W90DM manager role, each W75B or W90B radio base, regional hardware and loaded firmware. A base with power and an IP address can still be absent from the managed topology, unsynchronized or outside the handset system.
Compare the PBX view independently: account or endpoint loaded, registration or contact current, source identity expected and route available. Do not delete the handset, factory-reset the base or change PBX credentials while manager membership, synchronization and PBX state remain mixed.
Prove synchronization before blaming coverage
Inspect the configured synchronization method, levels and active relationships from the manager. For W75, preserve the active Level 1 base and any documented backup state. For W90, preserve manager and base roles, synchronization source and any VIM boundary. A neighboring cell can have strong local radio coverage while still failing to participate in a call-preserving handover.
If a base is missing or unsynchronized, trace its power, Ethernet, VLAN, addressing, time, manager reachability and configuration owner before moving it. Do not broaden multicast, disable segmentation or copy another unit configuration blindly. Correct the managed membership or network prerequisite through the supported owner and then confirm the base returns to the expected synchronization state.
Measure the radio boundary and per-cell load
Repeat the stationary call at the last known-good point and at the first failing point, then walk one controlled path with a willing test caller. Record serving cell, signal trend, handover point, audible gap, call continuity and manager event. Published indoor and outdoor ranges are ideal-condition figures, not acceptance distances for walls, lifts, shelving, occupancy or interference.
Check the smallest capacity limit at the affected cell. W75 documentation lists eight narrowband calls per base and a wideband line with eight calls but four active handsets; W90 documents its own per-base boundaries. System totals do not override a busy cell, and switching codec policy to chase capacity changes audio and PBX evidence that must be evaluated separately.
Trace signaling and media after the radio succeeds
If the handset remains associated and the call survives the cell transition, continue through the PBX and media path. Preserve the SIP response, selected route, negotiated codec and both RTP directions for the exact attempt. Registration, DECT handover, SIP dialog continuity and two-way audio are four different results.
If every stationary call fails, stay on account, route, signaling or media evidence instead of redesigning radio cells. If only one movement path fails, keep the comparison on synchronization, overlap, handover timing and per-cell load. The W74H product page lists W70B, W75B, W80B and W90B compatibility, but that does not make their topologies or handover evidence interchangeable.
Apply one correction and replay the same path
Correct only the demonstrated owner: handset assignment, supported firmware pair, manager membership, synchronization, base placement, overlap, PoE or LAN path, cell capacity, PBX account, route, codec or media policy. Preserve a rollback and avoid moving multiple bases, changing firmware and resetting the handset in one step.
Replay stationary inbound and outbound calls, the original movement path, a neighboring path and a representative busy-cell condition. Confirm manager and base state, registration, call setup, continuous audio, transfer and hangup, then remove temporary captures. This workflow is derived from current manufacturer documentation and was not reproduced on a customer or laboratory DECT system.
Sources & applicability
Primary references for the technical details above. Operational examples and planning checklists are VoIP.info editorial guidance.
- Yealink W75 product page ↗
- Yealink W75 datasheet ↗
- Yealink W90 product page ↗
- Yealink W90 datasheet ↗
- Yealink W74H product page ↗
Examples require adaptation to your topology. No live PBX or hardware testing is claimed.