Also known as: TSBK, trunking signalling block, trunking signaling block

A TSBK (trunking signalling block) is the unit of control-channel signalling in P25.¹ Each TSBK is a short, error-protected message on the control channel carrying one piece of system business — a channel grant, a registration, an affiliation, or a system parameter.

The P25 control channel is a stream of TSBKs; one announces a grant pointing radios to a voice channel.

Overview

Decoding TSBKs is exactly how a scanner follows a P25 system: read the grant TSBKs and retune to the assigned voice channel in step with the radios. P25 Phase 2 uses MAC PDU messages for the same role. DMR’s equivalent is the CSBK.

Sources

1. Project 25 — Wikipedia, on the P25 standard and its control-channel signalling. ↩

See also

• Control channel
• Channel grant
• Project 25 (P25)
• P25 Phase 1
• CSBK

Learn it step by step

• What is trunked radio?

From the blog

• SDR Internals, Part 11: The trunking engine & event bus