Snom M400 dual-cell DECT base

Choose one or two cells before applying capacity figures

Snom publishes M400 as a single- or dual-cell system. One base is limited to the single-cell totals; two bases form the dual-cell topology. Record the exact base count, regional part numbers, placement, power source, firmware versions, handset set, repeaters, PBX or service and provisioning owner before accepting any headline total.

The datasheet separates up to twenty handsets from up to ten narrowband or five wideband calls in one cell and twenty narrowband or ten wideband calls in dual cell. Handset enrollment, active calls, ringing branches, local conferencing and external trunk capacity remain different limits. A second base does not turn M400 into an unrestricted M900 multicell deployment.

Survey radio coverage, synchronization and handover

The published 50 m indoor and 300 m outdoor range values are ideal-condition inputs, not a building design radius. The administration guide says M400 is for indoor installation and warns that metal, current lines, water pipes and unsuitable environmental conditions can affect placement. Survey the occupied site with doors, lifts, shelving, walls, crowds and normal interference represented.

For dual cell, preserve each base identity, synchronization relationship, RSSI and one controlled handover path. Snom attributes dropped connections and failed handovers in multicell systems to weak synchronization-source RSSI and identifies -75 dBm as its troubleshooting floor. That vendor diagnostic is not proof of a compliant survey or of performance in an untested building.

Keep handset movement and SIP registration as separate events

Snom documents a roaming case in which a handset moving between bases can cause the new base to register the same SIP account. Its multiple-registration support control changes whether the first base sends a de-REGISTER before the next REGISTER. Record the selected value, the PBX or platform policy, both base identities, Contact values and the actual transition before changing it.

A successful DECT handover does not prove the SIP service accepted the new registration, and a stable registration does not prove audio stayed on the correct radio path. Test registration state, ringing, answer, handover, both media directions and hangup separately. Do not broaden PBX contact limits or disable registration controls merely to hide one failed transition.

Validate power, provisioning and protection independently

Confirm the actual switch port, LLDP or VLAN policy, PoE class, cable path and recovery after the base loses power. The optional adapter is a separate supply path and does not prove backup runtime. Inventory web-interface ownership, provisioning URL, certificate, downloaded configuration, firmware source and rollback before change.

Snom lists SIPS over TLS, SRTP and TLS 1.2, while DECT base-to-handset authentication and encryption are another layer. Confirm server name, certificate chain, SIP transport, SDP result, negotiated media and radio security independently. No M400, handset, repeater, radio, PBX, credential, PoE source, provisioning server, protection control, availability, compatibility, price, emergency route, audio path or live call was inspected or tested for this reference.

Diagnose a dual-cell drop without collapsing radio and SIP state

When a moving call drops or the account becomes unreachable after changing bases, use the M400 dual-cell roaming diagnostic. It separates synchronization RSSI, serving-base transition, SIP registration ownership, PBX contact policy and media.