tx: messages transmitted
rx: messages received
tx_expired: messages that the MUX was not able to transmit (no connection to the channel)
tx_pending: messages already on time to be sent out through the channel (waiting for a connection)
rx_expired: messages that didn't get a response
rx_pending: messages we are still waiting for a response
rx_unhandled: messages received that didn't match any request
rx_forwarded: messages forwarded to the unhandled queue
connected: status of the MUX (connected, unconnected)
last: timestamp (in millis) of the last messages received