wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

6LoWPAN: IP for Wireless Sensor Networks and Smart Cooperating Objects 51-5
MAC
sublayer
Octets:
2 1 4–20
Frame
control
Sequence
number
MAC header (MHR)
Addressing
fields
n
MAC payload
MAC service data unit (MSDU)
MAC protocol data unit (MPDU)
2
Frame check
sequence
(FCS)
MAC footer
(MFR)
Octets:
4 1 1
5 + (4–20) + n
PHY
layer
Preamble
sequence
Start of frame
delimter
Synchronization header (SHR)
Frame
PHY payload
length
PHY header
(PHR)
PHY service data unit (PSDU)
PHY protocol data unit (PPDU)
11 + (4–20) + n
FIGURE 51.3
IEEE 802.15.4 PHY and MAC frame format.
51.4 802.15.4 and 6LoWPAN
The number of wireless networking nodes is expected to rise in future, whereby low power and low cost
“are essential enablers toward their deployment in networks” [IETF6LoW]. These networks are characterized
by significantly more devices than current LANs, severely limited code and RAM space, and
unobtrusive but very different user interfaces for configuration [IETF6LoW]. The assumptions for IEEE
802.15.4 made above like peer-to-peer network topology and limited frame size require further efforts
to enable emerging IPv6 [RFC2460] on top of 802.15.4 as MAC and PHY layers. Thus, the IETF founded
the 6LoWPAN [IETF6LoW] working group (IPv6 over low-power WPAN), which has produced currently
two RFCs:
• IPv6 over low-power wireless personal area networks (6LoWPANs): overview, assumptions,
problem statement, and goals (RFC4919)
• Transmission of IPv6 packets over IEEE 802.15.4 networks (RFC4944)
The RFC4919 document describes the requirements that have to be considered for realizing IPv6 in
low-power wireless networks and focuses on IEEE 802.15.4 based on application scenarios of 6LoWPAN
protocols. The RFC4944 instead describes different dedicated compression formats and required adaptations
and enhancements for IPv6 on IEEE 802.15.4.
Additionally, the working group has published four documents “to ensure interoperable implementations
of 6LoWPAN networks” and to “define the necessary security and management protocols and
constructs for building 6LoWPAN networks, paying particular attention to protocols already available”
[IETF6LoW]. These documents and further efforts in and around the 6LoWPAN working group focus
on applicability of, e.g., neighbor discovery (ND), MIB, and SNMP. Reuse of existing technologies and
protocols is a core characteristic of 6LoWPAN and related efforts. The 6LoWPAN working group and
miscellaneous draft documents are still active at the time of writing this section. Therefore, this section
concentrates on the existing RFCs, explanations of the core concepts, and not on still active and intensively
discussed drafts. Routing protocols for 6LoWPAN networks are not focused by the 6LoWPAN
working group at all and will be defined by the routing over low-power and lossy networks (ROLL)
[IETFROLL] working group. Hence, the 6LoWPAN working group defines only recommendations for
the ROLL working group based on their experiences and provides header fields that may be used by
future routing protocols. Further deployments of existing and adopted application layer protocols like
HTTP, SOAP, etc., are examined in the 6LoWAPP activities of the IETF. 6LoWAPP is not an IETF working
group, but the intention is the creation of new working groups or further activities, which will lead
to specifications, for 6LoWPAN networks.
© 2011 by Taylor and Francis Group, LLC