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Optimal 6loWPAN Configuration
-----------------------------
1. Link local IP addresses:
128 112 96 80 64 48 32 16
fe80 0000 0000 0000 xxxx xxxx xxxx xxxx
2. MAC-based IP addresses:
128 112 96 80 64 48 32 16
---- ---- ---- ---- ---- ---- ---- ----
xxxx xxxx xxxx xxxx xxxx 00ff fe00 MMMM 2-byte Rime address IEEE 48-bit MAC
fe80 0000 0000 0000 NNNN NNNN NNNN NNNN 8-byte Rime address IEEE EUI-64
Where MMM is the 2-byte rime address XOR 0x0200. For example, the MAC
address of 0xabcd would be 0xa9cd. And NNNN NNNN NNNN NNNN is the 8-byte
rime address address XOR 02000 0000 0000 0000
3. MAC based link-local addresses
128 112 96 80 64 48 32 16
---- ---- ---- ---- ---- ---- ---- ----
fe80 0000 0000 0000 0000 00ff fe00 MMMM 2-byte Rime address IEEE 48-bit MAC
fe80 0000 0000 0000 NNNN NNNN NNNN NNNN 8-byte Rime address IEEE EUI-64
4. Compressable port numbers in the rangs 0xf0b0-0xf0bf
5. IOBs: Must be big enough to hold one IEEE802.15.4 frame (CONFIG_NET_6LOWPAN_FRAMELEN,
typically 127). There must be enough IOBs to decompose the largest IPv6
packet (CONFIG_NET_6LOWPAN_MTU, default 1294, plus per frame overhead).
Fragmentation Headers
---------------------
A fragment header is placed at the beginning of the outgoing packet when the
payload is too large to fit in a single IEEE 802.15.4 frame. The fragment
header contains three fields: Datagram size, datagram tag and datagram
offset.
1. Datagram size describes the total (un-fragmented) payload.
2. Datagram tag identifies the set of fragments and is used to match
fragments of the same payload.
3. Datagram offset identifies the fragment’s offset within the un-
fragmented payload (in units of 8 bytes).
The length of the fragment header length is four bytes for the first header
(FRAG1) and five bytes for all subsequent headers (FRAGN). For example,
this is a HC1 compressed first frame of a packet
c50e 000b ### 4-byte FRAG1 header
01 08 01 0000 3412 ### 7-byte FCF header
42 ### SIXLOWPAN_DISPATCH_HC1
fb ### RIME_HC1_HC_UDP_HC1_ENCODING
e0 ### RIME_HC1_HC_UDP_UDP_ENCODING
00 ### RIME_HC1_HC_UDP_TTL
10 ### RIME_HC1_HC_UDP_PORTS
0000 ### RIME_HC1_HC_UDP_CHKSUM
4f4e452064617920 48656e6e792d7065 6e6e792077617320 7069636b696e6720 ### 80 byte payload
757020636f726e20 696e207468652063 6f726e7961726420 7768656e2d2d7768
61636b212d2d736f 6d657468696e6720 g
This is the second frame of the same transfer:
e50e 000b 0a ### 5 byte FRAGN header
01 08 01 0000 3412 ### 7-byte FCF header
6869742068657220 75706f6e20746865 20686561642e2027 476f6f646e657373 ### 88 byte payload
2067726163696f75 73206d6521272073 6169642048656e6e 792d70656e6e793b
202774686520736b 79277320612d676f 696e6720746f2066
The payload length is encoded in the LS 11-bits of the first 16-bit value:
In this example the payload size is 0x050e or 1,294. The tag is 0x000b. In
the second frame, the fifth byte contains the offset 0x0a which is 10 << 3 =
80 bytes, the size of the payload on the first packet.
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