Re: [Roll] WG Last Call draft-ietf-roll-trickle-mcast-04

[Philip Levis <[e-mail]>]

On Mar 15, 2013, at 4:34 AM, JP Vasseur (jvasseur) wrote:

> Dear all,
> 
> All issues raised during the previous WG LC have been successfully addressed in draft-ietf-roll-trickle-mcast-04.
> That said, since we made several changes, this starts a 2-week WG LC that will end on March 29 at noon ET.
> Thanks.

I missed the last call, but this is a comment rather than a suggested change.

I worry a bit about the default value for DATA_MESSAGE_IMAX. Setting IMAX to the same as IMIN misses one very useful property of exponentially increasing timers, which is that they quickly find the right randomization interval under heavy congestion. The original motivation for the exponential timer in Trickle was to find the right randomization interval (much as, say, Ethernet CSMA/CD does). The challenge with having IMAX equal IMIN is that if IMIN is too small, you'll end up with a lot of congestion and link-layer collisions.

I don't think this needs any change to the document because it's just a default. If experience and practice shows that you don't want IMAX to be equal to IMIN, then I'm sure people will adjust best practices and recommendations appropriately. Just wanted to point out that keeping an eye on this might be valuable.

Phil