Add mandatory support in Join Proxy for Uri-Path-Abbrev CoAP Option for handling CoAP discovery messages?

[EskoDijk]

See definition in: https://datatracker.ietf.org/doc/html/draft-ietf-core-uri-path-abbrev-02

To reduce message size, it's advantageous to use the Uri-Path-Abbrev Option by the Pledge when doing CoAP discovery of JPs.
This only works of course if it's a MUST support for the Join Proxy. Should we add this?

[EskoDijk]

FYI @mcr @toerless

[EskoDijk]

Issue has been presented for discussion at IETF 124, Montreal, in slides: https://datatracker.ietf.org/meeting/124/materials/slides-124-anima-01-constrained-brski-cbrski-and-join-proxy-00

It's remarked there that the size savings for the request message is modest. Besides,

• the request only travels over a single hop, so there is no accumulated savings over multiple hops.
• the request fits in a single 6LoWPAN frame anyhow - there's no potential reduction in 6LoWPAN fragments by applying the option.
• the savings in power and reduced RF channel use (for a typical 250 kbps 802.15.4 6LoWAN) for an action only used during onboarding time, are very minimal over the entire device lifetime.
• it would require a constrained device to support the Option -- a JP, as opposed to a Registrar as for the case of cBRSKI where this Option is applied see link.
• a particular profile of cBRSKI, that defines its own discovery methods, can still introduce the option if they need it.

Given all these considerations, it's proposed to not require the Uri-Path-Abbrev option for discovery. And not make a text update.