1. Wireless Embedded Systems (0120442x) IPv6 over Low-Power Wireless Personal Area Networks (6LoWPAN)
Chaiporn Jaikaeo
Department of Computer Engineering Kasetsart University

2. Outline 6LoWPAN IPv6 overview Header compression tecniques Routing
JenNet-IP
The 6lo Working Group

3. 6LoWPAN IPv6 over Low-power Wireless Personal Area Networks
Nodes communicate using IPv6 packets
An IPv6 packet is carried in the payload of IEEE data frames

4. Example 6LoWPAN Systems

5. IPv6 Overview Larger address space compared to IPv6 Autoconfiguration
232 vs. 2128
Autoconfiguration
Supporting both stateful (DHCPv6) and stateless operations
Simplified headers
Fixed header with optional daisy-chained headers
Mandatory security

6. IPv6 Header Minimum header size = 40 bytes
Header compression mechanism is needed
Bit 4 8 12 16 20 24 28
Ver
Traffic Class
Flow Label 32
Payload Length
Next Header
Hop Limit 64
Source Address 96
128
160
192
Destination Address
224
256
288

7. Next header = 43 (routing)
IPv6 Extended Headers
More flexible than IPv4’s option fields
Example 1: no extended header
Example 2: with a routing header
Next header = 6 (TCP)
TCP hdr + payload
Next header = 43 (routing)
Next header = 6 (TCP)
TCP hdr + payload

8. Prefix provided by service provider
IPv6 Addressing
Global unicast addresses
Start with 001
Host ID usually incorporates MAC address
001
Prefix provided by service provider
Subnet ID
Host ID 48 16 64

9. IPv6 Address Scopes Global addresses Link-local addresses
Globally routable
Link-local addresses
Only used within directly attached network
Belonging to FE80::/10 subnet
Interface ID 96 db c9 FF FE 00 16 fe
10 bits
xxxxxxUx
U = 0: not unique U = 1: unique 94 db c9 00 16 fe

10. IEEE 802.15.4 Revisited Allows 127 bytes MTU
Good for buffering cost and low packet error rate
Supports both 16-bit and 64-bit addresses
Supports both star and mesh topologies
Usually operates in an ad hoc fashion with unreliable links
IEEE networks are considered Low-power and Lossy Networks (LLN)

11. 6LoWPAN Adaptation Layer
Needs to make IEEE comply with IPv6’s MTU size of 1280 bytes
IEEE ’s MTU is 127 bytes
MAC header: ≤ 25 bytes
Optional security header: ≤ 21 bytes
Provides three main services
Packet fragmentation and reassembly
Header compression
Link-layer forwarding

12. 6LowPAN Header Stack

13. Header Dispatch Byte

14. Mesh Address Header (1) Used with mesh-under routing approach
Only performed by FFDs

15. Mesh Address Header (2) Hop left field is decremented by one every hop
Frame is discarded when hop left is 0
Address fields are unchanged
Header
Mesh Header
Header
Mesh Header B A A D
Data D C A D
Data
Dst
Src
Orig
Final
Dst
Src
Orig
Final
Originator
Final A B C D

16. Mesh-under vs. Route-over Routing
Application
Application
Transport
Transport
Network (IPv6)
Network (IPv6)
Routing
6LoWPAN Adaptation
6LoWPAN Adaptation
MAC
MAC
PHY
PHY
Mesh-under routing
Route-over routing

17. Fragment Header
Fragmentation is required when IPv6 payload size exceeds that of IEEE payload limit
All fragments are in units of 8 bytes
(in 8-byte units)

18. IPv6 Header Compression
Can be either stateless or stateful
Independent of flows

19. HC1 Compression (1) Optimized for link-local addresses
Based on the following observations
Version is always 6
IPv6 address’s interface ID can be inferred from MAC address
Packet length can be inferred from frame length
TC and flow label are commonly 0
Next header is TCP, UDP, or ICMP
Ver
Traffic Class
Flow Label
Payload Length
Next Header
Hop Limit
Source Address
Destination Address

20. HC1 Compression (2)

21. HC2 Compression Compress UDP header
Length field can be inferred from frame length
Source and destination ports are shortened into 4 bits each
Given that ports fall in the well-known range of – 61631

22. HC1 + HC2 Compression

23. IPHC Compression (1)
HC1 and HC2 are only optimized for link-local addresses
Globally routable addresses must be carried non-compressed
IPHC will be the main compression technique for 6LoWPAN
HC1 and HC2 will likely be deprecated

24. IPHC Compression (2) TF: Traffic class and flow label NH: Next header
HLIM: Hop limit (0NC, 11,264,3255)
CID: Context Identifier
SAC/DAC: Src/Dst address (stateful or stateless)
SAM/DAM: Src/Dst mode

25. IPHC’s Context Identifier
Can be used to derive source and destination addresses
Not specified how contexts are stored or maintained

26. RPL – Routing Protocol for Low-power and Lossy Networks

27. Low-power and Lossy Networks
Abbr. LLN
Packet drops and link failures are frequent
Routing protocol should not over-react to failures
Not only applied to wireless networks
E.g., power-line communication
Packet delivery ratio

28. Routing Requirements
IETF formed a working group in 2008, called ROLL (Routing over Low-power and Lossy Networks) to make routing requirements
Major requirements include
Unicast/multicast/anycast
Adaptive routing
Contraint-based routing
Traffic characteristics
Scalability
Auto-configuration and management
Security

29. LLN Example

30. Different Objective Functions
- Minimize low and fair quality links
- Avoid non-encrypted links
- Minimize latency
- Avoid poor quality links and battery-powered node

31. RPL Protocol IPv6 Routing Protocol for Low-power and Lossy Networks
Designed to be highly modular for flexibility
Employing distance vector mechanism

32. RPL Operations
DODAG (Destination Oriented Directed Acyclilc Graph) is created
Based on the objective function
LBR
LBR 1 1 11 12 13 11 12 13 21 22 23 24 21 22 23 24 31 32 33 34 35 31 32 33 34 35 41 42 43 44 45 46 41 42 43 44 45 46

33. Multiple DODAGs (1)
Provide alternate routes for different requirements

34. Multiple DODAGs (2) - High reliability (no battery-powered node)
- Low latency

35. JenNet IP Jennic’s implementation of 6LoWPAN Supports tree topology
Routing is performed over a tree

36. https://datatracker.ietf.org/wg/6lo/charter/
The 6lo Working Group
Works on IPv6 over networks of constrained nodes, such as
IEEE
ITU-T G.9959
Bluetooth LE

37. References
G. Montenegro, N. Kushalnagar, J. Hui, and D. Culler. Transmission of IPv6 Packets over IEEE Networks, RFC 4494, September 2007.
NXP Laboratories. JenNet-IP WPAN Stack User Guide (JN-UG-3080 v1.3)
Jean-Philippe Vasseur and Adam Dunkels. Interconnecting Smart Objects with IP: The Next Internet. Morgan Kaufmann