I was thinking that there is also some difference in the physical header
to support the larger PPU?
On 03/07/2016 11:53 AM, Don Sturek wrote:
Hi Michael,
I was not clear on what you were asking. Here are a couple of points:
1) IEEE 802.15.4g was an amendment to IEEE 802.15.4-2011 where the main
contributions were to the PHY (not so much the MAC). There is nothing in
4g that would make it incompatible with IEEE 802.15.4-2011
2) IEEE 802.15.4-2011 has a field called "frame version" that denotes
special processing for the 2003, 2006 and 2011 versions of the
specification. That is one place where a packet may be dropped but that
would not apply to MAC versions that are based on 2011 alone
3) If you were asking whether a 4g MAC/PHY implementation could send
payloads of varying sizes then I think the answer is "yes" with the
following caveats:
I. Since IEEE 802.15.4 never had a propoer protocol dispatch
until IEEE 802.15.9 came along, there would have to be some special vendor
extensions to denote where a full IPv6 frame was present or when a 6LoWPAN
fragment was present. It is possible with the Multiplex ID/EtherType in
IEEE 802.15.9 to make that distinction.
I think in some implementations you would see a varying payload size. For
example, when transferring packets over a good radio link, the payload
size might be set to 1280 bytes or better and a full IPv6 frame would be
present. In cases where the link is poor, the two communicating devices
may choose to use shorter packets and 6LoWPAN to fragment/reassemble,
however, keep in mind there are only MAC retries to ensure delivery.
Don
On 3/7/16 8:25 AM, "6lo on behalf of Michael Richardson"
<6lo-bounces@xxxxxxxx on behalf of mcr+ietf@xxxxxxxxxxxx> wrote:
Robert Moskowitz <rgm-ietf@xxxxxxxxxxxxxxx> wrote:
> The difference is in the header bits. A 802.15.4-2011 device would
see
> the bits set in the header that 4g uses and drop the packet
> immediately. Pat would have to pipe in here, and there may be some
> issues around super frames and intergap timings that result in
> interesting behaviour, better to be avoided.
Right, but the question is:
1) is it physically possible for a 15.4g device to send both 15.4g
frames and 15.4-2011 frames?
Another email suggests that this can never happen because frequencies
are never the same. If so, end of problem.
2) if the answer to question 1 is yes, then 15.4g devices need to know
if they are speaking to 15.4-2011 devices, and
a) adjust their frame header bits appropriately.
b) to 6lowpan fraglettation.
--
Michael Richardson <mcr+IETF@xxxxxxxxxxxx>, Sandelman Software Works
-= IPv6 IoT consulting =-
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