Dear 6LoWPANers,
Though HC1 and HC2 provide us with the capability to express any
combination of compression, the most expected (or at least shot for)
case does not lead to a better compression of the HC headers themselves.
Seems that we could define an HC3 that would compress the pair of HC1
and HC2 for that best case. My proposal for doing this would be to:
- define a new dispatch
| 01 000011 | LOWPAN_HC3 - LOWPAN_HC3 compressed IPv6 and
transport
- define HC3 itself to:
- implicitly say that the first 5 bits of HC1 are all ones
- carry HC1 bits 5 and 6 (Next Header)
- replace HC2 so bit 7 of HC1 is useless
- provide transport specific bits such as those defined for
HC-UDP,
then again assuming a predefined best case if room is missing
An example of what the HC3 octet could be:
bits 0 1 2-3
4-7
+------------------+-------------+-----------------+--------------------
---------------------+
| reserved | reserved | Next Header | transport
specific control bits |
+------------------+-------------+-----------------+--------------------
---------------------+
Next header: as defined in HC1, bits 5 and 6
transport specific control bits for UDP:
bit 4 echoes HC-UDP bit 0 on UDP source port
bit 5 echoes HC-UDP bit 1 on UDP destination port
bit 6 echoes HC-UDP bit 2 on UDP length
bit 7 is reserved
What do you think?
Pascal
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