Answers to Questions from Alex Kritikos - Sub-committee meeting 28/4/2022

[Simon Johnson <simon.johnson@u-blox.com>]

Thank you Alex for your questions at the last committee meeting. Please find below my thoughts on the questions posed. We can discuss any feedback on these points at the next committee meeting.

Question 1: The session expiry interval format on the CONNECT packet

The session expiry interval format on the CONNECT packet is a 4 Byte (32-bit) Integer representing how long a disconnected session will exist on a gateway. It follows the definition of a Four Byte Integer in section 1.7.3. ACTION: Add the sentence "The Session Expiry Interval is a four byte integer time interval measured in seconds." to the start of the field definition in section 3.1.4.5.

Question 2: Should the format of the reason String in the DISCONNECT packet by a UTF string?

The reason string field on the DISCONNECT packet is the last field. For consistency I believe we should ensure that the String is a valid UTF8 string per the specified definition in section 1.7.4 (this is an optional field and so will only incur the extra 2 bytes of length data in the field if supplied. ACTION: Change the sentence in section 3.1.24.4 to "A UTF8 string representing a clear text description of disconnection"

Question 3: Can you clarify the meaning of the retain behaviour in the WillTopicMsg

The retain flag on the WillTopicMsg denotes the retain behaviour of any WillMsg set on a topic. It is consistent with the retain behaviour set out by MQTT v5.0; that is; "This bit specifies if the Will Message is to be retained when it is published." The will state in an aggregating gateway should be managed by the gateway since it is the source of knowledge for connected devices. The will state in a transparent gateway should be managed the broker. ACTION: We should have some conformance statements about will management lifecycle given the difference between aggregating and transparent gateways.

Thank you for the valuable feedback Alex.

Best,

Simon