Draft Quality of Service X.509 extension for Delivery Authorization certificates

[gnarea]

Executive summary

Since relays like couriers and public gateways have a limited amount of disk space they can allocate to each private gateway, they'll be forced to stop accepting messages for those gateways once their quota is reached. With a Quality of Service mechanism in place, messages could be prioritised so that relays can make room for messages with a higher priority by deleting less critical messages when necessary.

Describe the solution you'd like

I propose that we attach it to the sender's certificate in the form of a non-critical X.509 extension. And when we calculate the priority for a message, we take the lowest priority in the sender's certificate chain.

The priority value would be an integer in the range [-2, 2] and would default to 0.

We'll probably have to get the desktop/Android gateway to check with the user if an app requests to use the highest priority. At least when the Internet is unavailable.

Describe any alternatives you've considered

Generally speaking, the priority field could be attached to the RAMF message (as a new field), the sender or both. However, it'd be problematic to attach it to RAMF messages because it'd only be applicable to cargo and parcel messages, but it wouldn't apply to messages like a Parcel Collection Acknowledgement, for example.