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Powerline Connection Speed Monitoring via `pla-util`

<time datetime="2023-08-16 00:00:00 &#43;0000 UTC">16 August 2023</time><span class="px-2 text-primary-500">&middot;</span><span>1204 words</span>

First off, if you can have a real network cable, use that. As temporary measure I set up a powerline connection between the apartment and basement. Connection speeds vary quite a bit and I wanted to be able to monitor reported network speeds.

tl;dr use pla-util to query your powerline adapters. I made a Docker image:

Similar to Wi-Fi, network speeds reported and achieved are quite different. The adapter shows 200-300 MBit/s, while realistically you might end up getting about 50MBit/s. Either way it’s fine for daily work and video conferences – or at least this what the experiment is about.

My Setup #

I am using the TP-Link TL-PA7017 for connections.

If you are planning to buy adapters, get the pass-through versions and plug other electronic devices into them. The signal and data rate will be much better.

It is based on the Broadcom BCM60355 chip and does support the HomePlug AV 2.0 standard.

TP-Link offers their tool tpPLC via their support site. It is only available for MacOS and Windows, not Linux.

Screenshot of TP-Link&rsquo;s tpPLC tool
TP-Link’s tpPLC

Linux Based Tools #

My goal was to add continuous metrics into my monitoring setup, so I can see how the data rate develops throughout the day and with different devices switched on or off. I set off to find a command line utility for Linux that gets me this data.

I found the following:

  1.  qca/open-plc-utils - Those tools would be great, but they are for Qualcomm Atheros based chips only. TP-Link does not use those, but it might still be helpful for someone else.
  2.  jbit/powerline - A Rust library for interacting with Qualcomm and Broadcom Powerline chips. Currently, it does not support retrieving the reported network speed.
  3.  serock/pla-util - A tool based on ADA, specifically for Broadcom Powerline chips.

After getting pla-util to compile and run on a Raspberry Pi without any issues, I got the information I want:

pla-util -i eth0.1 get-network-stats:

Number of stations: 1
Station 1:
  Destination Address (DA):  c0:c9:e3:21:0d:3b
  Avg PHY Data Rate to DA:   222 Mbps
  Avg PHY Data Rate from DA: 319 Mbps

Metrics Capturing #

The next step is to get these values continuously. I’m using OpenWRT on my Raspberry Pi 4 Router.

The router has Docker available and currently uses collectd to collect metrics into an InfluxDB / Grafana setup.

The goal is then to run something that can call pla-util automatically. collectd supports the exec plugin that allows to write a script

Docker Image and Container for pla-util #

First off, pla-util needs to run on the target host, which in this case is the Raspberry Pi. I chose to run the tool in Docker because I don’t want to deal with installing the ADA runtime libraries in OpenWRT.

The installation instructions for pla-util are great and get you a running executable on the platforms relevant for me:

  • x86_64 (the Mac),
  • arm64 (Raspberry Pi 4),
  • arm/v7 (newer Raspberry Pi < 4)

The various compilers and libraries needed for it add up to ≈180 MB in the Docker image.

Looking at the libraries that the resulting tool actually needs, you can figure out, which runtime dependencies are needed:

ldd /bin/pla-util: (0x0000007f99ddf000) => /lib/aarch64-linux-gnu/ (0x0000007f99c20000) => /lib/aarch64-linux-gnu/ (0x0000007f997e0000) => /lib/aarch64-linux-gnu/ (0x0000007f997a0000) => /lib/aarch64-linux-gnu/ (0x0000007f995f0000)
/lib/ (0x0000007f99da2000) => /lib/aarch64-linux-gnu/ (0x0000007f99570000) => /lib/aarch64-linux-gnu/ (0x0000007f994d0000) => /lib/aarch64-linux-gnu/ (0x0000007f993e0000) => /lib/aarch64-linux-gnu/ (0x0000007f993b0000) => /lib/aarch64-linux-gnu/ (0x0000007f992a0000) => /lib/aarch64-linux-gnu/ (0x0000007f99250000) => /lib/aarch64-linux-gnu/ (0x0000007f99190000) => /lib/aarch64-linux-gnu/ (0x0000007f99140000) => /lib/aarch64-linux-gnu/ (0x0000007f990f0000)

Dockerfile #

This results in a two-stage Dockerfile, where the builder stage has all the build tools and is ultimately discarded.

The final stage takes the pla-util binary from the builder stage, installs the runtime requirements identified above and makes a nice slim image with just the libraries you need to run the tool, not to compile it.

FROM debian:12-slim as build

COPY . /pla-util
RUN apt update && \
    apt install -y gprbuild gnat git libpcap-dev && \
    cd pla-util && \
    gprbuild -p -P pla_util.gpr

FROM debian:12-slim

# Install all dependencies for running `pla-util`, and net-tools to have access to `ifconfig`.
RUN apt update && apt install -y \
    libgnat-12 \
    libgpg-error0 \
    liblz4-1 \
    libzstd1 \
    liblzma5 \
    libgcrypt20 \
    libcap2 \
    libsystemd0 \
    libpcap0.8 \
    libdbus-1-3  \
    libgcc-s1 \

COPY --from=build /pla-util/bin/pla-util /bin

collectd metrics scripts for the exec plugin #

Some important notes about collectd exec scripts:

  • The script can be a one-off and will be executed at the desired interval. This is great for debugging.
  • The script may be a loop and create a series of entries. collectd will just stream all the results. If the script exits, it’s restarted again anyway.
  • Metric names must follow the convention of hostname/item/metric, where metric may either be a name from the types.db, or can encode an alternative type.

The last bit cost me a bit of time. With the metric name router/pla/bytes-rx, you end up with the following data in InfluxDB:

  • Metric: pla_value:

In Grafana you can then set up a query for pla_value and create separate series by type_instance, which leads you to this beautiful graph:

Screenshot of the Powerline Throughput Graph in Grafana
Powerline Throughput Graph in Grafana

pla-stats script for collectd #

This script assumes a docker-compose setup with a service called pla that has the pla-util container running.

#! /usr/bin/env ash


while :; do
    RESULT=$(docker compose -f /root/docker-compose.yml exec pla pla-util -i "$INTERFACE" get-network-stats)
    if [ $? -ne 0 ]; then
    TX=$(echo "$RESULT" | sed -n -E 's/.*Avg PHY Data Rate to DA:\s+(\d+) Mbps/\1/p')
    RX=$(echo "$RESULT" | sed -n -E 's/.*Avg PHY Data Rate from DA:\s+(\d+) Mbps/\1/p')

    echo "PUTVAL \"$HOSTNAME/pla/bytes-rx\" interval=$INTERVAL N:$(( RX * 1024 * 1024 ))"
    echo "PUTVAL \"$HOSTNAME/pla/bytes-tx\" interval=$INTERVAL N:$(( TX * 1024 * 1024 ))"

    sleep "$(printf "%.0f" $INTERVAL)"

This script is quite limited. It only supports a single result. pla-util happens to default to finding your local network segment’s powerline adapter and query that one.

Powerline Network Analysis with Wireshark #

In case you want to check out the network traffic for Powerline, all control data is exchanged as additional Ethernet protocol.

Wireshark Dissectors:

While trying to find a tool that would help me get the same data as tpPLC, I was very close to writing something myself that would send the few commands and get the network statistics data back. Fortunately I found ready-made tools, because the protocol is quite complex.

Conclusion #

The Powerline setup is temporary until I get a CAT7 cable into the basement.

Accordingly, the monitoring setup is aimed at a single point-to-point Powerline network with one other endpoint. The script shows the concept and can be adapted and extended as needed. Getting additional tags on the data could require a different approach, such as telegraf.

Eventually I plan to migrate all metrics collection from collectd to telegraf anyway. collectd is convenient as it comes nicely integrated in OpenWRT via luci. It has its limits though, and I am using telegraf on some of the other machines already.

Telegraf has the same mechanism of capturing data via the exec and execd (for streamed data) plugins.