[mqtt-comment] application layer

Hi all,

A number of new elements have been introduced to the protocol that address application layer concerns. User Property, Correlation Data and Reply Topic are examples. These extensions make server code more complicated, while only presenting limited use for more advanced deployments. As an example, while IoT devices might be connected to a server via MQTT, the corresponding backend application logic may potentially not receive messages via MQTT, but rather use some other technology such as a queuing or streaming solution to better run at scale. Even larger IoT-like devices such as vehicle that might be using MQTT as an off-board protocol are often using other protocols internally, with messages being transferred from internal to external protocols by a generic gateway on the vehicle. The corresponding backend applications will not be able to access information that is stored in the MQTT header without this information being copied from the MQTT layer into an application layer within the MQTT server (by a plugin, for instance). In addition, information that can be used to authenticate the original publisher, such as a signed message payload, cannot be applied to the header information, making this information a target for spoofing and other attacks.

It would be preferable to keep the transport protocol simple, and provide other application-layer functionality on top. Of course, these layers too can be standardised, but it is not clear what the benefit is from doing so within the MQTT protocol.

Cheers,

David Katz

BMW Car IT GmbH
David Katz

Moosacher Straße 86
80809 München

Web: http://www.bmw-carit.de
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