Can we use keep alive, given that the Awake state is bracketed by PINGREQ and PINGRESP? We can use another Packet Identifier, so is having nested PINGREQ/PINGRESPs valid?

For example, if the PUBLISH packets from the server are all QoS 0, what does the client do if it doesn't receive the PINGRESP? Send the PINGREQ again presumably? It has to be in retry mode as the PINGRESP is the response to the PINGREQ.

We aren't expecting any interval in PUBLISH sending from the Server, so is the only timer active Retry - no Keep Alive?