Atmel AVR2070 C.6 6LoWPAN Compressed Header

AVR2070

8240B-AVR-06/09

Traffic Class and Flow Label encoding

A message will be properly parsed by end-nodes regardless if traffic class and flow

label is compressed or uncompressed. However the value itself is not read, hence to

avoid wasting space all messages should have the traffic class and flow label set to

zero.

Address Compression

The code supports carrying all 128 bytes; or compressing an address down to 64, 16,

or 0 bytes of extra payload.

Next Header Compression

Only a UDP packet will have the next header field compressed, any other type will

have the next header field carried in full.

Hop Limit Compression

A hop limit of 255, 64, or 1 will result in the hop limit being compressed. Any other

value will result in the hop limit field being carried in full.

UDP Header Compression

UDP Header compression is supported by this implementation.

C.6 6LoWPAN Compressed Header

If sniffing a 6LoWPAN network, it can be useful to understand the header. Note that

the 802.15.4 payload will be the RUM frame, which includes some additional fields.

The 6LoWPAN header described here is actually the RUM payload. Table C-6-1

illustrates this relationship.

Table C-6-1 Understanding the relationship between 6LoWPAN, RUM, and 802.15.4 Frames.

802.15.4 Frame

802.15.4 Header 802.15.4 Payload

RUM Data Header RUM Data Payload

FCF Seq PID Dest Src Final

Dest Origin Type 6LoWPAN Frame

0x8821 0x12 0x1234 0x0006 0x0007 0x0000 0x0007 0x05 …..

The 6LoWPAN Frame contains three bytes of interest at the beginning. The first is the

‘dispatch’ which is always set to 0x03, which corresponds to the header compression

used. The HC01 Encoding is specified in two bytes, and a detailed description of this

field is given at http://tools.ietf.org/html/draft-ietf-6lowpan-hc-01 in section C.5.1.

Additionally the source code for the avr_sixlowpan.c file in the

sixlowpan_hc01_process() function provides a reference for decoding the

compressed 6LoWPAN header.

Table C-6-2 6LoWPAN Frame

6LoWPAN

Dispatch

HC01

Encoding Compressed IPv6 Header / IPv6 Payload

1 byte 2 bytes Variable