Subject: [core] Protocol Constants section of coap-08

From: Thomas Herbst <[email-masked]>
Date: Sat, 18 Feb 2012 10:27:50 -0800

Trying to come up with a better way to deal with the protocol constants
section.

Obvious first edit is that all three values - Timeout, random factor and
max retransmits should be configurable.

Next step might be to state that these are configurable, but the
configuration is out of scope of this document.

Deployment guidance could be that the numbers should be constant for any
given network, though I can think of several cases where I might have
different constants for different node types, but that is me playing with
my own rope.

On the specific numbers, 2 seconds is way too short of a default for our
networks, but I understand having everyone use our constants for their
smaller networks may make the smaller networks slower than necessary.

Someone putting an unconfigured device on a network should work.  Best
case would be the unconfigured device would work efficiently.

Tom
------------------------------------------

9. Protocol Constants
This section defines the relevant protocol constants defined in this
document:
RESPONSE_TIMEOUT 2 seconds
RESPONSE_RANDOM_FACTOR 1.5
MAX_RETRANSMIT 4
Future specifications are expected that will allow implementations to use
other sources for initializing RESPONSE_TIMEOUT. The RESPONSE_TIMEOUT
variable MAY be configured with a different value for special environments
that exhibit very short or very long RTTs.

---

From: Zach Shelby <[email-masked]>
Date: Sun, 19 Feb 2012 15:21:45 +0200

Tom,

Agreeing with you on all points. The intention has been that those constants are configurable. Could you propose some new text?

Regarding RESPONSE_TIMEOUT, I would like to find a default value that works for the majority of LoWPANs at least. Don't see a problem in increasing that somewhat, for example to 3-4 seconds. With a longer starting timeout, it may make sense to reduce MAX_RETRANSMIT to 3.

Zach

On Feb 18, 2012, at 8:27 PM, Thomas Herbst wrote:

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-- 
Zach Shelby, Chief Nerd, Sensinode Ltd.
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