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Re: [core] A couple of late comments on Hop-Limit

Carsten Bormann <cabo@tzi.org> Wed, 16 October 2019 11:37 UTC

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From: Carsten Bormann <cabo@tzi.org>
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Date: Wed, 16 Oct 2019 13:37:16 +0200
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To: Christer Holmberg <christer.holmberg@ericsson.com>
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Subject: Re: [core] A couple of late comments on Hop-Limit
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(Responding just to that specific item now:)

> On Oct 16, 2019, at 13:26, Christer Holmberg <christer.holmberg@ericsson.com> wrote:
> 
>> Specific response codes are useful if you want specific state machine transitions to happen
> 
>    Specific response codes are also very useful for debugging - especially in this case where one probably should start by looking at the network/routing configurations instead of the endpoint implementations.

When designing CoAP, we made a very conscious decision to separate protocol elements such as response codes from diagnostic information.  Creating a new response code just for better diagnostics would be out of character for CoAP.

(Frugality in assigning response codes is a prerequisite to getting by with a small code space, e.g., only 32 possible codes for client errors.  Moreover, the design guideline pointed out above is generally a good idea, as it keeps the state machine clean and also allows permissionless innovation in diagnostic information.)

Grüße, Carsten

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