MQTT subscriber keepalive timeouts

[frazieje]

I'm using an nrf52dk (pca10040) to develop an mqtt subscriber application.

I'm using the IoT softdevice, with the IoT 0.9.0 sdk example for subscriber as a starting point, with armgcc and eclipse.

Raspberry pi 1b+ running jessie with radvd & 6lowpan module to act as a gateway / border router

After establishing a 6lowpan link, I am able to connect to my broker (RabbitMQ with MQTT plugin) on the cloud directy using the example code for mqtt subscriber, and I can subscribe to the 'led/state' topic.

When I publish messages to the topic from other clients, the led on the nrf52dk reflects the state published. This is working as expected.

Problem:

I have noticed that eventually the nrf52832 will become disconnected from the broker due to keepalive timout. There doesn't seem to be any direct cause for this, Im just noticing that it eventually happens and disconnects clients after a period of time, usually within 10 minutes.

Using tcpdump on my broker, I'm able to observe keepalive exchanges taking place every ~60s when things are operating normally. However, eventually one will be missed and the broker will disconnect the session. Once this happens, I merely need to press button 0 to reconnect, and then button 1 to subscribe, and all is well again for a while...

The raspi ble router and the nrf52dk are about 2 feet from eachother and stationary during these tests, so I assume the 6lowpanconnection is reliable.

This same behavior happens when I use the mosquitto broker instead.

Question:

Is this something normal to expect to happen or are there known issues with keepalive timeout? Any recommendations to determine why the keepalive ping is missed? What recommendations does anyone have to work around this and create a more reliable mqtt connection?

[bjorn-spockeli]

Hi Frazieje,

the IoT SDK team has done major improvements to the MQTT library of the IoT SDK since the v0.9.x release. I have attached the latest MQTT library files from our internal repo below, could you try to replace the mqtt library and see if that resolves the issue?

MQTT Library files: mqtt.zip

I have also attached a minimal version of IoT SDK with only the mqtt examples that uses the updated mqtt files.

IoT SDK with updated MQTT files: nrf5_iot_sdk_3288530_mqtt.zip

Note, I've only tested the examples using a non-secure connection, i.e. used the following configuration

#define APP_MQTT_BROKER_PORT             1883
m_app_mqtt_client.transport_type       = MQTT_TRANSPORT_NON_SECURE;
m_app_mqtt_client.p_security_settings  = NULL;

[frazieje]

Hi Bjørn, thanks for the reply.

I have created a new project based around the mqtt library you've provided above.

I have an active connection to the broker using the new mqtt client and will monitor over the next day or so to see if the stability has improved.

[bjorn-spockeli]

Great, keep me posted :)

[frazieje]

It has been 24 hours.

I did have one keep alive timeout occur during the night. I'm still unsure if it was a network hiccup or power failure or the same problem as before.

Other than that things are much much better. I have had it subscribed for about 12 hours without any issues. I will reply back in the morning with more resuls.

[frazieje]

ok after another 10 hours, it's still connected and happily listening for mqtt application events :)

I think it's safe to mark this as the answer. Thanks for the help!