Re: [6lo] big frame support in 802.15.4G

[Robert Moskowitz <rgm-ietf@htt-consult.com>]

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@ietf.org on behalf of mcr+ietf@sandelman.ca> wrote:
>
>> Robert Moskowitz <rgm-ietf@htt-consult.com> 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@sandelman.ca>, Sandelman Software Works
>> -= IPv6 IoT consulting =-
>>
>>
>>
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>