The MQTT gateway is not a broker. It is a client.

Let me try to explain MQTT architecture to my understanding. MQTT is just a protocol for which clients talk to each other. However, in order for clients to talk, they need a server. This server is called the broker which can be mosquitto or RabbitMQ, etc.

MQTT gateway is a client(A publishing one) which publishes messages to the server(RabbitMQ). Any other clients(Subscribing ones) who wish to receive messages will have to subscribe to the topic through the server(RabbitMQ). In any case, if a subscribing client wants to listen to a publishing client, the subscribing client has to subscribe to the same topic the publishing client publishes to. Both clients have to connect to a broker(RabbitMQ).

I have already implemented my design as in the diagram above and it works. I guess what you mean is that if your client does not understand the messages coming from the MQTT gateway by MySensors, then you would need another client who republishes the message in a format that your clients understand.

I might have seen this issue as well when I have nodes that are not directly connected to the gateway. Ie going through repeaters. I did not investigate though. Are you using repeaters as well? Or are your nodes connected directly to the gateway?

@TD22057 said:

See here: http://forum.mysensors.org/topic/1034/mqtt-gateway-openhab-mosquitto/2 which connects mosquitto to the gateway using the bridge input. Bridging is used for connecting two brokers together (see http://mosquitto.org/man/mosquitto-conf-5.html "configuring bridges").

I think MySensor's MQTT Gateway is already a broker by itself where clients like OpenHab can connect to. However, if there is a need, you can use a bridge which forwards the messages from a remote broker(MySensor's MQTT Gateway) to a local broker(Mosquitto). Then clients could now also connect to Mosquitto.

@TD22057 said:

https://github.com/mysensors/Arduino/blob/master/libraries/MySensors/examples/MQTTGateway/MQTTGateway.ino

In that gateway code is the TCP_IP and TCP_PORT the external broker IP and port numbers? The comments say those are the static IP and a port to listen on. I read that as saying it's the static IP of the gateway and the port for the broker to listen on but perhaps they mean the remote IP/Port of the broker to connect to.

I have'nt used MySensors's MQTT Gateway, but if I am not wrong, TCP_IP is the IP you want your arduino to have. TCP_Port is the port you want others to connect to your arduino. Using these two parameters, your arduino will create a ethernet server for others to connect to.

The MQTT gateway is not a broker. It is a client.

Let me try to explain MQTT architecture to my understanding. MQTT is just a protocol for which clients talk to each other. However, in order for clients to talk, they need a server. This server is called the broker which can be mosquitto or RabbitMQ, etc.

MQTT gateway is a client(A publishing one) which publishes messages to the server(RabbitMQ). Any other clients(Subscribing ones) who wish to receive messages will have to subscribe to the topic through the server(RabbitMQ). In any case, if a subscribing client wants to listen to a publishing client, the subscribing client has to subscribe to the same topic the publishing client publishes to. Both clients have to connect to a broker(RabbitMQ).

I have already implemented my design as in the diagram above and it works. I guess what you mean is that if your client does not understand the messages coming from the MQTT gateway by MySensors, then you would need another client who republishes the message in a format that your clients understand.

I always had a problem with ethernet gateway. So i used serial gateway instead to connect with my nodejs application on my RPI. Inside that node js application, i converted all messages into my own MQTT topics and publish them to a MQTT server(Mosquitto) on my RPI. On the openhab side, i just bind items to these MQTT topics.
You can take a look at my system diagram.