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, with a portable protocol stack that may be used 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 . Only the core files and the conference-bridge application are carried forward; the retired sample applications are not included.

---

Protocol Background

IMPACT: IPSC is a proprietary protocol ownned by Motorola Solutions, impemented here based on wire captures of traffic between IPSC systems.

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, Linux CLI and basic ability to work with Python.

---

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. IPSC mimics the functions of IP multicast networking in a unicast environment.

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.
• As a consequence, IPSC endpoints can lose partial connectivity with each other and the the remaining endpoints that can communicate with each other continue to. This must be understood and is a common point of confusion during operation.

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

---

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 first. 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.

---

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.

---

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 connected to each other as it can pass an arbitrary number of traffic flows, without any "slot"-based locking. or contention handling.
• Subscriber ACL: optional sub_acl.py can PERMIT or DENY specific radio IDs

---

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_TRANSPORT: tcp          ; 'tcp' (default) or 'unix'
REPORT_PORT: 4321              ; used when REPORT_TRANSPORT = tcp
REPORT_SOCKET: /tmp/dmrlink3-report.sock   ; used when REPORT_TRANSPORT = unix
REPORT_CLIENTS: 127.0.0.1      ; TCP only

When the dashboard runs on the same host, set REPORT_TRANSPORT: unix (and a REPORT_SOCKET path) so the feed rides a local Unix-domain socket instead of TCP — a same-box socket can't be broken by a NIC flap or connection-tracking eviction. Set the dashboard's matching DMRLINK_TRANSPORT/DMRLINK_SOCKET to the same. Use tcp (the default) for a remote dashboard.

The dashboard connects to this feed and serves a browser UI at the configured WEB_PORT. It also shows a per-repeater ping-loss figure (golds a row whose keepalive-loss share crosses PING_LOSS_WARN), controlled by PING_LOSS_WINDOW / PING_LOSS_WARN in [GLOBAL]. See dashboard/config_sample.py and INSTALL.md for setup instructions.

Demo mode — append ?demo to the dashboard URL (e.g. http://localhost:8080/?demo) to load a static pre-populated scenario showing all visual elements: MASTER and PEER systems with connected repeaters, a TRUNK endpoint with active streams, active calls bridged coherently across systems, a slot in group-hangtime, and a populated call log. No dmrlink3 connection is required. This is useful for understanding what the dashboard looks like under normal operating conditions before any traffic has been seen.

Dashboard features:

• Last Heard — most-recent unique callers (user, call type, source peer, timeslot, talkgroup, and when), derived live from the call log; collapsible, with its open/closed state remembered per-browser (LAST_HEARD / LAST_HEARD_COUNT)
• Live IPSC system status: peer table with radio IDs, addresses, and connection state. Each system's peer list is collapsible with the Show/Hide Peers button — the system header and TS1/TS2 activity pills stay visible, so live traffic is always in view even when collapsed. Default state is set by SYSTEM_PEERS ('open'/'closed') and per-system choices are remembered per-browser
• 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

---

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. They remain included as hooks for future handling.
• DMRlink3 cannot brick a repeater or subscriber radio 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. This is another feature that only works with additinoal softaware or hblink.py-based applications.

---

dmr_utils3

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

---

This Software Is Not a Commercial Product

DMRlink3 is not an out-of-the-box replacement for similar commercial products. If you want a commercial-grade IPSC bridge, buy one — they work great. using DMRlink3 requires a little bit of work, though significant effort has gone into simplifying installation and operation in this re-write.

Using DMRlink3 requires a basic understanding of Python 3, Linux CLI and basic systems administration.

No Support Is Provided

This is not commercial software. It is provided free of charge. The author(s) received no compensation for creating and maintaining it. Countless hours over many years have gone into the this. If you have problems, the author will try to help if possible, please have no expectations for support. There is no online group, such as DVSwitch or groups.io that is an "official" outlet for information. The only definitive source of information is me. Beware of others claiming to be authoritative. User-based mutual support is great, and I'm all for it. But please understand, this is what they are, and I have not sanctioned anyone to be the "home" of my software packages.

GitHub "Issues"

Do not use GitHub issues for support. Genuine bugs are accepted as issues. Before opening one, make sure that it is a true problem with the software and not merely a misconfiguration, or contention around a feature that was not supported. Isssues should never be used to ask for or recommend features. Issues that do not include complete details, relevent tracebacks, error messages, configuration snippets, operatrional conditions surrounding the event, etc. will be closed without action.

---

0x49 DE N0MJS

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