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Re: [6tisch] slot schedluing

worley@ariadne.com (Dale R. Worley) Thu, 08 December 2016 20:38 UTC

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To: Randy Turner <rturner@amalfisystems.com>
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Cc: 6tisch@ietf.org
Subject: Re: [6tisch] slot schedluing
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Randy Turner <rturner@amalfisystems.com> writes:
> Just re-confirming an assumption -- from a TSCH perspective, slot
> scheduling assumes any single transmission "cannot" exceed a slot
> boundary -- if transmissions require a certain amount of time, then the
> slot width is increased to deal with this ( or possibly increase the
> TX bit rate if possible )
>
> Is this correct ?

As others have noted, extending the slot width can only be done when the
network is initialized.  In practice, packets that do not fit within a
slot time are fragmented.  My understanding is that all such packets are
IP packets, and are fragmented using using the layer 2 fragmentation
defined in RFC 6282 (not the one defined in RFC 4944).  Thus, the
minimum (layer 3) IPv6 MTU of 1280 bytes is supported.

As far as I know, there is no fragmentation mechanism for the EB
(extended beacon) layer-2 packets.  But that does not seem to be a
problem in practice.

Dale

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