DMRlink3 — Python 3 / asyncio IPSC Network Bridge

PURPOSE: Connect multiple Motorola MOTOTRBO IPSC (IP Site Connect) networks together, bridge talkgroup traffic between them, and provide a live web dashboard for monitoring. DMRlink3 is also useful for understanding and troubleshooting IPSC, or as a starting point for writing custom IPSC applications.

ORIGIN: DMRlink3 is a Python 3 / asyncio port of dmrlink (Python 2 / Twisted), aligned in style with the HBlink3 2026_cleanup branch. Only the core files and the conference-bridge application are carried forward; the retired sample applications are not included.

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Protocol Background

IMPACT: Potential concern from Motorola Solutions, as IPSC is a proprietary protocol.

METHOD: Reverse engineering by pattern matching and process of elimination.

PROPERTY: This work represents the author's interpretation of the Motorola™ MOTOTRBO™ IPSC protocol. It is intended for academic purposes and not for commercial gain. It is not guaranteed to work, or be useful in any way, though it is intended to help IPSC users better understand, and thus maintain and operate, IPSC networks. This work is not affiliated with Motorola Solutions™, Inc. in any way. Motorola, Motorola Solutions, MOTOTRBO, IPSC and other terms in this document are registered trademarks of Motorola Solutions, Inc. Other registered trademark terms may be used. These are owned and held by their respective owners.

PRE-REQUISITE KNOWLEDGE: This document assumes the reader is familiar with the concepts presented in the Motorola Solutions™, Inc. MOTOTRBO™ Systems Planner.

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How IPSC Works

IPSC is a full-mesh peer-to-peer protocol, not a client/server protocol. Every device — including the "master" — is functionally a peer. The master peer differs only in that it coordinates joins from newly registering devices and distributes the authoritative peer list. Once a new peer has registered and received the peer list, it establishes direct UDP connections to every other peer and exchanges keep-alives and traffic with each of them independently.

This means:

• Voice and data packets flow directly between peers, not through the master.
• Every peer tracks keep-alive state for every other peer, not just the master.
• Two DMRlink3 instances connected to each other with no other peers form a full-duplex trunk and can carry as many simultaneous packet streams as they have bandwidth for.

CONVENTIONS: PEER → MASTER denotes communication from the peer to the master. The initiator of each exchange is always shown on the left.

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How to Use This Software

dmrlink.py is the IPSC protocol engine and the prerequisite for everything else. It handles registration, keep-alives, peer-list management, and packet dispatch. On its own it only logs traffic; applications are written by subclassing the IPSC class and overriding the packet-type callbacks.

Always verify that dmrlink.py runs and connects cleanly before working with application files. Set LOG_LEVEL: DEBUG and watch the output.

bridge.py is the conference-bridge router. It subclasses IPSC and bridges voice traffic between IPSC networks according to a rule file (bridge_rules.py).

The dashboard/ directory contains a FastAPI web server (server.py) that connects to dmrlink3's NDJSON reporting feed and serves a live monitoring UI over WebSocket.

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Files

File	Purpose
dmrlink.py	IPSC protocol engine; base class for all applications
bridge.py	Conference-bridge router (the primary application)
const.py	IPSC packet-type constants and bitmasks
config.py	.cfg file parser
log.py	Logging configuration
dmrlink-SAMPLE.cfg	Main configuration template — copy to dmrlink.cfg
bridge_rules_SAMPLE.py	Bridge rule template — copy to bridge_rules.py
dashboard/server.py	Web dashboard backend (FastAPI + WebSocket)
dashboard/static/dashboard.html	Dashboard single-page UI
dashboard/config_sample.py	Dashboard config template — copy to dashboard/config.py
systemd/dmrlink3-bridge.service	systemd unit for bridge.py
systemd/dmrlink3-dash.service	systemd unit for the dashboard

Files whose names contain SAMPLE are templates. Remove _SAMPLE (or _sample) from the name and customize. dmrlink.cfg, bridge_rules.py, and dashboard/config.py are git-ignored so that git pull never overwrites your live configuration.

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bridge.py — Conference Bridge

bridge.py connects multiple IPSC networks together using a rules file (bridge_rules.py). A "bridge" is a named group: any system that is ACTIVE on a bridge will receive all voice traffic arriving on that bridge from any other active system on the same bridge.

Key features:

• Per-bridge per-system timeslot and talkgroup matching
• In-band activation and deactivation via TGID triggers — both fire on key-down (VOICE_HEAD), so the bridge activates for the entire call including its first packet, and deactivates the moment an OFF tgid is keyed without waiting for unkey
• Each system manages its own bridge entry independently; a trigger received on one system activates only that system's entry
• Optional timeouts: TO_TYPE: ON deactivates an entry after TIMEOUT minutes of inactivity (timer resets on each ON-trigger key-down); TO_TYPE: OFF reactivates an entry after TIMEOUT minutes
• Entries that start ACTIVE: True with TO_TYPE: ON begin their timeout countdown on load; use TO_TYPE: NONE for entries that should stay active indefinitely without a timer
• Contention handling: group-hangtime and timeslot-clear-time rules prevent simultaneous overlapping calls from being bridged destructively
• Trunk bypass: systems listed in TRUNKS skip contention handling entirely — useful when two DMRlink3 instances are the only devices on an IPSC and you want full-duplex trunking
• Subscriber ACL: optional sub_acl.py can PERMIT or DENY specific radio IDs

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Reporting and Dashboard

DMRlink3 uses NDJSON over TCP for reporting (one JSON object per line). The pickle/binary-opcode protocol from the original dmrlink is not implemented.

Enable reporting in dmrlink.cfg:

[REPORTS]
REPORT_NETWORKS: NETWORK
REPORT_PORT: 4321
REPORT_CLIENTS: 127.0.0.1

The dashboard connects to this feed and serves a browser UI at the configured WEB_PORT. See dashboard/config_sample.py and INSTALL.md for setup instructions.

Dashboard features:

• Live IPSC system status: peer table with radio IDs, addresses, and connection state
• Per-system TS1/TS2 activity pills showing real-time slot state:
  • RX (green) — receiving a call from a peer, with source radio, peer ID, TGID, and elapsed time
  • TX (orange) — forwarding a bridged call, with originating radio, source peer, TGID, and elapsed time
  • Hang (blue) — slot recently freed but still in group-hangtime; shows TGID and countdown to when the slot is available
  • Idle (gray) — slot is free
• Conference bridge table with per-entry active/inactive state, configured timeout duration, live timer countdown, and trigger TGID lists; bridge state changes push to the dashboard immediately on activation or deactivation rather than waiting for the periodic refresh
• Call log with timestamps, event type, system, timeslot, source radio, and TGID

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Configuration Notes

The configuration file is in .ini format and is self-documented in dmrlink-SAMPLE.cfg. A few important points:

• Do not enable features you do not understand. IPSC exposes options that DMRlink3 does not implement (XNL/XCMP, for example). Enabling them may confuse other devices on your IPSC or produce unpredictable results.
• DMRlink3 cannot brick a repeater or subscriber because it does not implement XNL/XCMP, through which those dangerous operations flow.
• PORT must be unique per IPSC system stanza.
• Leave IP: blank to bind all interfaces; specify it only when DMRlink3 bridges between private/VPN and public networks.
• RCM: True and CON_APP: True are both required if you want Repeater Call Monitor packets forwarded to reporting clients.

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dmr_utils3

DMRlink3 depends on dmr_utils3, the Python 3 port of dmr_utils. Install it from source before installing DMRlink3. See INSTALL.md.

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This Software Is Not a Commercial Product

DMRlink3 is not an out-of-the-box replacement for c-Bridge, SmartPTT, GenWatch, RDAC, or similar commercial products. It does not do everything those products do, and will likely never be something you can "just run" without understanding what is happening under the hood. If you want a commercial-grade IPSC bridge, buy one — they work great. If you want to understand IPSC, write your own application on top of it, or need a capable open-source bridge without commercial overhead, then DMRlink3 might be right for you.

Using DMRlink3 requires a basic understanding of Python 3.

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Copyright (C) 2013-2026 Cortney T. Buffington, N0MJS n0mjs@me.com

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA