A network you can trace, shape and rebuild.

Method

Five things that decide whether it works

1. One clock master, everything else slaved

   PTP provides the reference; do not let every device free-run and hope. If your audio hardware also has a word-clock input, keep that hierarchy consistent with the PTP hierarchy instead of creating two competing authorities.

2. Hardware timestamping on the NIC

   Software timestamping adds jitter that no buffer setting can remove. Check with ethtool -T and pick a NIC that reports hardware transmit and receive timestamping.

3. Its own VLAN and a DSCP class

   Put audio in a dedicated VLAN, mark it DSCP EF, and make the switch trust those markings. Never let a backup job share a queue with a live stream.

4. A stated latency target

   AES67 is comfortable at about 1 ms of network latency at 48 kHz — 48 samples per channel — and many devices also offer 125 µs to 250 µs packet times. Decide the target, then size buffers to meet it rather than guessing.

5. Measure the round trip

   Use a loopback measurement, not your ears. jack_iodelay reports actual round-trip latency, and pw-top shows whether the graph is keeping up or quietly dropping cycles.

Configuration

PTP and an AES67 stream from a desktop

# Clocking. One grandmaster, everyone else slave-only.
ptp4l -i eno1 -f /etc/ptp4l.conf -m      # grandmaster
ptp4l -i eno1 -s -m                      # slaves: -s = slave only
phc2sys -s eno1 -c CLOCK_REALTIME -w -m  # align the system clock

# Confirm the NIC timestamps in hardware, not in software.
ethtool -T eno1

# Energy-efficient Ethernet adds latency and drops packets.
ethtool --set-eee eno1 eee off

# ~/.config/pipewire/pipewire.conf.d/20-aes67.conf
# Argument names have changed between PipeWire releases —
# check the module documentation for the version you run.
context.modules = [
  { name = libpipewire-module-rtp-sap
      args = {
        local.ifname        = "eno1"
        sap.ip              = "239.255.255.255"
        sap.port            = 9875
        net.mtu             = 1500
        sess.latency.msec   = 1
        audio.format        = "S24LE"
        audio.rate          = 48000
        audio.channels      = 8
        source.ip           = "10.20.50.10"
        source.props = {
          node.name        = "aes67-output"
          node.description = "AES67 8-channel output"
        }
      }
  }
]

Restart the PipeWire daemon, then confirm the node appears with pw-link -o or pw-cli ls Node. If the stream is silent, check multicast group membership and the switch's IGMP snooping configuration before touching the audio settings.