Overview

Comms is the OpenMANET push-to-talk (PTT) voice subsystem. It runs as part of openmanetd and carries live audio between nodes over the mesh using Opus-encoded RTP on multicast UDP. A node can run one or more parallel talk groups (each on its own multicast address/port), enforce half-duplex within each group, and source PTT events from any of four selectable control sources. A browser-only web mode is also available for nodes that have no sound card at all.

At a glance

Parameter Value
Codec Opus, 48 kHz, mono, VoIP profile
Bitrate 32 kbps
Frame size 20 ms (960 samples)
Encoder complexity 5 (default; configurable 1–10)
In-band FEC Enabled, adaptive (packetLossPerc floor = 20, ramps to 30 / 40 under loss)
DTX Disabled
Transport RTP over multicast UDP
RTP payload type 111 (dynamic, Opus)
RTP MTU 1400 bytes
Multicast TTL 32 (sized for multi-hop batman-adv + VXLAN + Tailscale paths)
RTCP Sender Report interval 5 s (outbound only; inbound RTCP not processed)
Default playback / capture latency hint 60 ms each

Control sources

Comms supports four PTT control sources, selected by the comms.controlSource config key:

  • openvlm (default) — OpenVLM USB HID dongle. GPIO3 on the dongle is the PTT button: press → PTTDown, release → PTTUp (hold-to-talk). VOL+ / VOL− buttons on the dongle also drive the system ALSA mixer via a built-in alsa.Controller aux event handler.
  • web — Browser-driven PTT. The browser owns audio I/O and the malgo audio backend is bypassed entirely, so this mode works on nodes with no sound card.

In this section

  • How comms works — operator-level walkthrough of the audio pipeline, talk groups, half-duplex, and the adaptive FEC loop.
  • Setting up comms — enable comms on a node, pick a control source, wire the hardware, and verify it’s working.

See also

Table of contents