Also known as: failsoft, fail-soft, fallback mode
Failsoft is the fallback mode a trunked system enters when its controller or control channel fails: rather than going silent, the site abandons dynamic channel assignment and reverts to fixed, conventional operation so that communication survives in a degraded form.1 Each talkgroup is mapped to a specific repeater channel, and radios fall back to that channel — losing the efficiency of trunking but keeping basic conventional contact.
How it works
Normal trunking depends on a controller assigning channels on demand through the control channel. If the controller fails, or the control channel is lost, that coordination disappears. In failsoft the site’s repeaters revert to a pre-programmed conventional plan: each talkgroup is pinned to one repeater, and radios programmed for that system automatically switch to the failsoft channel for their selected talkgroup. Multiple talkgroups may share a channel, so the tidy separation trunking provides is gone — several groups may end up hearing each other — but the site keeps carrying voice.
Radios usually signal failsoft to the user (a distinctive tone or a display indication) so operators know they have lost trunked features such as private calls, patches, and dynamic channel access. When the controller recovers and the control channel returns, the site resumes normal trunked operation and radios re-affiliate.
In practice
Failsoft is deliberately simple because it must work when the smart part of the system is broken. The mapping of talkgroups to channels is fixed in advance, and the repeaters often transmit a low-speed failsoft identifier so radios (and monitors) can recognize the degraded state. It is distinct from a site trunking fallback, where a multi-site system loses its network link but each site still trunks locally — failsoft is the deeper fallback where even local trunking is unavailable and the system is effectively conventional.
It is worth placing failsoft on the ladder of degraded modes a wide-area system can occupy. At the top is full wide-area trunking, where all sites are networked and a call reaches every site that has affiliated members. If the network backhaul fails, sites drop to site trunking: each site still trunks normally on its own, assigning channels through its own control channel, but calls no longer cross between sites. Only when a site’s own controller or control channel fails does it fall all the way to failsoft, abandoning dynamic assignment entirely. Each rung sacrifices more capability for more robustness, and failsoft is the floor — the mode designed to keep working when almost everything smart has stopped. Radios and monitors can often tell which rung a system is on from what the control channel is (or is not) doing and from the identifiers the site transmits.
Failsoft is intentionally the least-loved but most-tested part of a system’s design. It has to work with no controller intelligence behind it, so its rules are static and its channel plan is fixed in the radios and repeaters ahead of time. That simplicity is the point: when the smart infrastructure is gone, a mode that depends on more of that same infrastructure would be worthless. The cost is everything trunking normally buys — efficient channel sharing, private calls, patches, wide-area reach — all of which vanish until the controller returns. Well-run agencies rehearse operating in failsoft precisely because it is the mode they will be in on the worst day, and recognizing it quickly, both for users and for anyone monitoring, is what keeps that day manageable.
Relevance to SDR
Failsoft matters to a monitor because a system in failsoft no longer behaves like a trunked system at all — there is no control channel to follow, and a trunk-tracking scanner that keeps hunting for one will hear nothing. Recognizing the failsoft identifier (or simply the disappearance of the control channel and the appearance of fixed talkgroup-to-channel traffic) tells GopherTrunk to treat the site as a set of conventional channels rather than as a trunk. In that mode a monitor reverts to scanning the known voice channels directly, since the metadata-rich control-channel grants it normally relies on are gone.
Real systems with a defined failsoft mode include P25, Motorola Type II/SmartNet, and EDACS. GopherTrunk’s job in failsoft is diagnostic and adaptive: detect that the trunking site has degraded, and fall back to conventional monitoring so the user still hears whatever traffic the site is carrying.
Sources
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Trunked radio system — Wikipedia, on failsoft and degraded-mode fallback in trunked systems. ↩