Post on 14-Dec-2015
Wireless Embedded Systems
(0120442x)
IPv6 over Low-Power Wireless Personal Area
Networks(6LoWPAN)
Chaiporn Jaikaeochaiporn.j@ku.ac.th
Department of Computer EngineeringKasetsart 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 802.15.4 data frames
4
Example 6LoWPAN Systems
5
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
6
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
7
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)
8
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
9
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
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 802.15.4 networks are considered Low-power and Lossy Networks (LLN)
11
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
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
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
16
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
17
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)
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 61616 – 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 (0NC, 11,264,3255) 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
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
Pac
ket
del
iver
y ra
tio
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
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
33
Multiple DODAGs (1) Provide alternate routes for different
requirements
34
Multiple DODAGs (2)
- Low latency- High reliability (no battery-powered node)
35
JenNet IP Jennic’s implementation of 6LoWPAN Supports tree topology Routing is performed over a tree
36
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/
37
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.