Wireless Embedded Systems

(0120442x)

IPv6 over Low-Power Wireless Personal Area

Networks(6LoWPAN)

Chaiporn Jaikaeochaiporn.j@ku.ac.th

Department of Computer EngineeringKasetsart University

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

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6LoWPAN IPv6 over Low-power Wireless

Personal Area Networks Nodes communicate using IPv6

packets An IPv6 packet is carried in the

payload of IEEE 802.15.4 data frames

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Example 6LoWPAN Systems

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IPv6 Overview Larger address space compared to

IPv6 232 vs. 2128

Autoconfiguration Supporting both stateful (DHCPv6) and

stateless operations Simplified headers

Fixed header with optional daisy-chained headers

Mandatory security

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IPv6 Header Minimum header size = 40 bytes

Header compression mechanism is needed

Ver

Bit 0 4 8 12 16 20 24 28

0 Traffic Class Flow Label

Payload Length Next Header Hop Limit

Source Address

Destination Address

32

64

96

128

160

192

224

256

288

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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) TCP hdr + payloadNext header = 6 (TCP)

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IPv6 Addressing Global unicast addresses

Start with 001

Host ID usually incorporates MAC address

Prefix provided byservice provider

Subnet ID

48 16

Host ID001

64

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IPv6 Address Scopes Global addresses

Globally routable Link-local addresses

Only used within directly attached network

Belonging to FE80::/10 subnet0 Interface ID

1111 1110 10

10 bits

96 db c9 FF FE 00 16 fe

94 db c9 00 16 fe

U = 0: not uniqueU = 1: unique

xxxxxxUx

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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 802.15.4 networks are considered Low-power and Lossy Networks (LLN)

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6LoWPAN Adaptation Layer Needs to make IEEE 802.15.4

comply with IPv6’s MTU size of 1280 bytes IEEE 802.15.4’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

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6LowPAN Header Stack

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Header Dispatch Byte

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Mesh Address Header (1) Used with mesh-under routing

approach Only performed by FFDs

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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

A B C

Originator Final

802.15.4Header

MeshHeader

BOrig FinalDst Src

A A D Data

D

802.15.4Header

MeshHeader

DOrig FinalDst Src

C A D Data

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Mesh-under vs. Route-over Routing

Application

Transport

Network (IPv6)

6LoWPAN Adaptation

802.15.4 MAC

802.15.4 PHY

Application

Transport

Network (IPv6)

6LoWPAN Adaptation

802.15.4 MAC

802.15.4 PHY

Mesh-under routing Route-over routing

Routing

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Fragment Header Fragmentation is required when IPv6

payload size exceeds that of IEEE 802.15.4 payload limit

All fragments are in units of 8 bytes

(in 8-byte units)

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

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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

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HC1 Compression (2)

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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 61616 – 61631

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HC1 + HC2 Compression

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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

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IPHC Compression (2)

TF: Traffic class and flow label NH: Next header HLIM: Hop limit (0NC, 11,264,3255) CID: Context Identifier SAC/DAC: Src/Dst address (stateful or stateless) SAM/DAM: Src/Dst mode

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IPHC’s Context Identifier Can be used to derive source and

destination addresses Not specified how contexts are

stored or maintained

RPL – Routing Protocol for Low-power and Lossy Networks

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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

Pac

ket

del

iver

y ra

tio

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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

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LLN Example

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Different Objective Functions

- Minimize low and fair quality links- Avoid non-encrypted links

- Minimize latency- Avoid poor quality links and battery-powered node

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RPL Protocol IPv6 Routing Protocol for Low-power

and Lossy Networks Designed to be highly modular for

flexibility Employing distance vector

mechanism

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DODAG (Destination Oriented Directed Acyclilc Graph) is created Based on the objective function

RPL Operations

1

1211

23 24

13

21 22

3534333231

4241 4443 45 46

LBR1

1211

23 24

13

21 22

3534333231

4241 4443 45 46

LBR

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Multiple DODAGs (1) Provide alternate routes for different

requirements

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Multiple DODAGs (2)

- Low latency- High reliability (no battery-powered node)

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

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The 6lo Working Group Works on IPv6 over networks of

constrained nodes, such as IEEE 802.15.4 ITU-T G.9959 Bluetooth LE

https://datatracker.ietf.org/wg/6lo/charter/

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References G. Montenegro, N. Kushalnagar, J. Hui, and

D. Culler. Transmission of IPv6 Packets over IEEE 802.15.4 Networks, RFC 4494, September 2007.

NXP Laboratories. JenNet-IP WPAN Stack User Guide (JN-UG-3080 v1.3). 2013.

Jean-Philippe Vasseur and Adam Dunkels. Interconnecting Smart Objects with IP: The Next Internet. Morgan Kaufmann. 2010.