ADN-DMR-Peer-Server/docs/en/server/user-guide/bridges-and-talkgroups.md

Bridges and talkgroups

BRIDGES model

The bridge table maps talkgroup keys (strings, e.g. "26811", "#reflector") to rows. Each row describes:

• SYSTEM — which configured system originates or receives this leg.
• TS — timeslot (1 or 2). OpenBridge sources are normalised to TS1 in routing (bridge_match_slot).
• TGID — destination ID bytes for LC rewrite toward that leg.
• ACTIVE — whether this leg participates.
• TIMEOUT, TO_TYPE, ON/OFF/RESET — activation semantics (user-activated bridges, reflectors, etc.).

The router scans BRIDGES for an ACTIVE row matching the current source system, slot, and destination TG before forwarding (dmrd_received → to_target).

Dynamic vs static

• User-activated bridges are created when a user keys a TG without a pre-built row (subject to DEFAULT_UA_TIMER and options).
• Static TGs and STAT bridges are created from OPTIONS / make_static_tg / GEN_STAT_BRIDGES flows.

Source-row guard and safe iteration

Forwarding is allowed only when the current system has a matching ACTIVE source row for that TG/slot context. This prevents accidental forwarding from rows that are present but not currently eligible as source legs.

BRIDGES scans and updates are also protected against concurrent row mutations during runtime loops, so timer/debug passes do not corrupt active iteration state.

OpenBridge and TG display

For OpenBridge, the DMR destination in the packet may differ from the TGID in a bridge row (remap). Monitoring may show RX TG (as received) vs TX TG (as rewritten for a destination); correlate by stream_id, not TG alone.

Contention

Group voice uses hang time, STREAM_TO, and slot TX_* / RX_* state to avoid colliding transmissions on the same resources.

See also: Special numbers, OpenBridge protocol.