Eindhoven University of Technology MASTER 6LoWPAN

Eindhoven University of Technology MASTER 6LoWPAN
Eindhoven University of Technology
MASTER
6LoWPAN
IPv6 for battery-less building networks
Abbasi, N.A.
Award date:
2009
Disclaimer
This document contains a student thesis (bachelor's or master's), as authored by a student at Eindhoven University of Technology. Student
theses are made available in the TU/e repository upon obtaining the required degree. The grade received is not published on the document
as presented in the repository. The required complexity or quality of research of student theses may vary by program, and the required
minimum study period may vary in duration.
General rights
Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners
and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.
• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.
• You may not further distribute the material or use it for any profit-making activity or commercial gain
Take down policy
If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately
and investigate your claim.
Download date: 12. Sep. 2017
Technische Universiteit Eindhoven
Department of Mathematics and Computer Science
and Department of Electrical Engineering
6LoWPAN: IPv6 for Battery-less Building Networks
By
Naveed A. Abbasi
Supervisors
Prof. Dr. J.J. Lukkien
Dr. P.D.V. van der Stok
Dr. Ir. M.C. W. Geilen
Dr. Ir. P.H.F.M Verhoeven
August 2009
Contents
1 Introduction
1
1.1
Lighting Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1
1.2
Wireless Sensor Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
1.3
Wireless Lighting Control Networks . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
1.4
Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5
1.5
Outline of thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6
2 IEEE 802.15.4 MAC and PHY
7
2.1
Device Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7
2.2
Network Topologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8
2.3
MAC Frame Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9
2.4
PHY Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10
2.5
MAC Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11
2.5.1
MAC Data Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11
2.5.2
MAC Management Service . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12
2.6
Network Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13
2.7
PAN Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13
2.8
Robustness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15
3 Internet Protocol and ZigBee
3.1
3.2
Internet Protocol version 6
16
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16
3.1.1
Header Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17
3.1.2
Address types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17
3.1.3
Address Representation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19
ZigBee . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20
3.2.1
Device Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20
3.2.2
Traffic Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
21
3.2.3
Addressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
22
1
CONTENTS
3.3
2
IPv6 and ZigBee : A comparison of standards . . . . . . . . . . . . . . . . . . . . . .
4 6LoWPAN
22
23
4.1
IEEE 802.15.4 for IP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
23
4.2
Addressing Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24
4.3
Stateless Address Autoconfiguration . . . . . . . . . . . . . . . . . . . . . . . . . . .
24
4.4
Routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25
4.5
Constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
26
4.6
6LoWPAN Adaptation Layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
26
4.6.1
Header Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
27
4.6.2
Header Compression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
30
6LoWPAN Neighbor Discovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
32
4.7.1
Node Registration/Confirmation . . . . . . . . . . . . . . . . . . . . . . . . .
33
4.8
Router Solicitation Message . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
34
4.9
Router Advertisement Message . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
34
4.10 6LoWPAN-ND Message Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
34
4.11 6LoWPAN and ZigBee: A comparison . . . . . . . . . . . . . . . . . . . . . . . . . .
35
4.7
5 Development Environment
5.1
36
FreeRTOS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
36
5.1.1
Scheduler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
36
5.1.2
Inter-task Communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
37
5.1.3
Memory Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
38
5.2
SAND Node . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
38
5.3
BSN Node . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
39
5.4
MSPGCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
39
5.5
Debugging and Visualization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
40
6 Implementation
6.1
6.2
41
Pre-porting Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
41
6.1.1
The 6LoWPAN Stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
41
6.1.2
FreeRTOS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
42
6.1.3
Drivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
42
6.1.4
MAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
42
The 6LoWPAN Stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
43
6.2.1
sixLowPanLayer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
43
6.2.2
ipv6Layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
44
6.2.3
udpLayer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
44
CONTENTS
3
6.2.4
socket . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
44
6.2.5
buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
44
6.2.6
routingUnderIp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
45
6.2.7
routingTable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
45
6.3
Investigation Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
45
6.4
6LoWPAN Stack Extension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
45
6.4.1
6LoWPAN Adaptation Layer . . . . . . . . . . . . . . . . . . . . . . . . . . .
46
6.4.2
ICMPv6 Layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
46
UDP Chat Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
47
6.5.1
Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
47
WASP Demonstration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
48
6.6.1
51
6.5
6.6
Code Size Reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7 Self-powered Switch and Sensors
52
7.1
Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
53
7.2
Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
53
7.3
Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
55
7.4
Acknowledgment Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
58
7.5
Timing Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
58
7.5.1
MSP430 Timing Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
59
7.5.2
AquisGrain2 Timing Results . . . . . . . . . . . . . . . . . . . . . . . . . . .
59
7.5.3
Timing Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
60
7.6
Conclusion
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
60
8 Conclusion
62
A Header and Frame Formats
64
A.1 IPv6 Header . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
64
A.2 LOWPAN IPHC Details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
66
A.3 LOWPAN UDP Details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
67
A.4 Node Registration/Confirmation . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
68
A.5 Router Solicitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
70
A.6 Router Advertisement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
71
B Packet Details
73
B.1 Route Request/Reply Packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
73
B.2 UDP Packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
74
B.3 Router Solicitation and Router Advertisement . . . . . . . . . . . . . . . . . . . . . .
75
CONTENTS
C UDP Application
4
76
C.1 Client . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
76
C.2 Server . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
77
D Error Log
78
Bibliography
82
Bibliography
82
List of Figures
1.1
A Comparison on using different Physical Layer Architectures . . . . . . . . . . . . .
2
1.2
Wireless Lighting Network overview . . . . . . . . . . . . . . . . . . . . . . . . . . .
5
2.1
MAC Data Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12
2.2
The Association Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14
3.1
Unicast and Broadcast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18
3.2
Multicast and Anycast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19
3.3
The ZigBee Stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
21
4.1
6LoWPAN Stack Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
28
5.1
SAND Node and BSN Node . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
39
6.1
Directory Structure of the Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
42
6.2
Driver Abstraction of CC2420 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
43
6.3
The 6LoWPAN Stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
44
6.4
Network and Software Architecture of 6LoWPAN . . . . . . . . . . . . . . . . . . . .
49
6.5
BSN Node and PC Interaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
50
7.1
Battery-less Switch Based Lighting Network . . . . . . . . . . . . . . . . . . . . . . .
54
7.2
Battery-less Switch Circuitry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
55
7.3
MSP430 Timing Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
59
7.4
AquisGrain 2 Timing Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
60
B.1 Route Request Message . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
73
B.2 UDP Packet with short addresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
74
B.3 Router Solicitation and Router Advertisement . . . . . . . . . . . . . . . . . . . . . .
75
C.1 UDP Client Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
76
5
LIST OF FIGURES
C.2 UDP Server Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6
77
List of Tables
1.1
A Comparison of LR WPAN with other wireless technologies . . . . . . . . . . . . .
6
2.1
MAC Packet Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9
2.2
Frame Control Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10
3.1
IPv6 Address Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20
4.1
Dispatch Value Bit Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
27
4.2
Stack Comparison as in [1] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
35
6.1
Memory Utilization on BSN Node . . . . . . . . . . . . . . . . . . . . . . . . . . . .
51
A.1 IPv6 Header . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
65
A.2 LOWPAN IPHC Encoding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
66
A.3 LOWPAN UDP Encoding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
67
7
Abstract
6LoWPAN is a protocol specification to enable IPv6 packets to be communicated on top of low
power wireless networks, specifically IEEE 802.15.4. The rationale behind this protocol is that bulky
IPv6 headers can be compressed to only few bytes by introducing an adaptation layer between IP
stack’s link and network layer, therefore reducing IP overhead. The transmission of 1280 bytes
long IPv6 Maximum Transmission Unit (MTU) over IEEE 802.15.4 is also made possible using
fragmentation and reassembly provided by this adaptation layer.
Philips Lighting is particularly interested in IPv6 connectivity for battery-less switches. These
switches operate on the technology that converts the pressing action into small amount of energy.
This energy can then be used by a radio transceiver to transmit a signal to luminaries. Within
Philips Research a 6LoWPAN stack has been developed for the SAND node platform.
The purpose of the present assignment was to port the existing 6LoWPAN stack from the SAND
node platform to the MSP430 platform, to enhance the stack capabilities by providing support for
other features which were missing from existing implementation. Moreover the Neighbor Discovery
Protocol for 6LoWPAN was to be investigated and implemented. Apart from these, a demonstration
of 6LoWPAN based lighting network utilizing a self powered switch was also carried out as part of
this project.
Chapter 1
Introduction
Recent advancements in communication technologies and network equipment have greatly expanded
the horizons for business and residential connectivity for voice, internet and telecommunication.
Network components are available at affordable prices, configuration is easy and help is readily
available via websites and consulting services to install and manage such networks. The situation
in building automation systems (BAS) is however, much different.
A BAS describes the functionality provided by the control system of a building. A BAS is
an example of a distributed control system. It comprises a computerized, intelligent network of
electronic devices and a control system to automate various constituents of BAS. The difficulties
that are faced in BAS are:
• Many proprietary protocols are not open and their connectivity with other systems is cumbersome.
• The control network configuration is not flexible.
• Different systems exist next to each other and make it difficult to maintain and install.
When these networks employ different technologies, then the cost of installation and operation
increases. Moreover connectivity becomes complicated as well.
We will discuss Lighting Networks as a part of BAS in more detail.
1.1
Lighting Networks
Lighting Networks are an important constituent of BAS. Traditionally lighting control networks
have been operated via wired connections. Different standards evolved over time but their key
1
CHAPTER 1. INTRODUCTION
2
Figure 1.1: A Comparison on using different Physical Layer Architectures
characteristics remain the same. They are normally isolated from the external world and form a
small, independent control group. Two major wired lighting control systems are DMX512 and DALI.
DMX512 is a standard wired communication protocol used extensively in industrial lighting
applications, most commonly to control stage lighting and exhibition lighting. Developed by the
Engineering Commission of USITT, the standard started in 1986. With subsequent revisions in
1990, the standard was named as USITT DMX512/1990. The revised edition of standard namely
”Entertainment Technology USITT DMX512A Asynchronous Serial Digital Data Transmission
Standard for Controlling Lighting Equipment and Accessories”, was approved by ANSI in November
2004. This current standard is more commonly known as DMX512-A.
The physical interface consists of 3 to 5 wires, with 1 data signal constructed from two differential
lines (D+, D-), a common/ground and an optional second set of Data lines. It supports data rate
up to 250 kbit/sec. It can support up to 512 devices in one network. DMX512 is unidirectional and
does not include automatic error checking and correction, so it is not safe to use for applications
involving life safety, such as controlling pyrotechnics or laser lighting display where audience or
performer safety is involved [2].
DALI stands for Digital Addressable Lighting Interface. It is a standard wired communication
protocol used for home and building lighting applications. It is an open standard, being standardized
in accordance with International Electrotechnical Commission IEC 62386 [3].
The physical interface consists of two wires, DALI Power and DALI Data. The DALI system
consists of one DALI control module with up to 63 DALI devices. It supports data rate up to 1200
bits/sec.
The limitations with existing lighting control and communication systems is their limited inter
CHAPTER 1. INTRODUCTION
3
operability and their lack of connectivity with external world. A step towards improving connectivity is taken recently in the form of Architecture for Control Networks (ACN), a suite of network
protocols for theatrical lighting control, being developed by Entertainment Services and Technology
Association (ESTA). It may replace DMX as the control protocol for lighting systems. This protocol is designed to be layered on top of UDP/IP and therefore will run over standard, inexpensive
Ethernet and 802.11 network links.
With ACN it is possible to have connectivity with external world, directly. DALI networks
can connect to external networks via a gateway. However when it comes to flexibility and inter
operability, the Internet Protocol has a proven track record. IP can be used for connectivity of all
major systems and control protocols can be run on top of it, thus providing compatibility of various
control systems.
Lighting connectivity and control systems exist in wireless world as well. Z-Wave, EnOcean
and recently introduced ZigBee based control systems are some among those. Although all of them
operate on wireless networks, they are not inter operable due to the physical characteristics of
wireless networks as well as specifications of these protocols.
In a house with a different control network each for lighting, HVAC, security and automation,
the layout and installation is complicated. Moreover operating all these different control systems
will be a difficult task as well, as all of them will have different controllers. Having a common
communication protocol for all different networks will ease the procedure of installation, operation
and maintenance. Figure 1.1 depicts how cabling cost and configuration is simplified when using
integrated system [4].
Philips Lighting is particularly interested in utilizing wireless battery-less switches in lighting
networks. These switches operate on the principle of piezoelectric energy harvesting in which mechanical strain is converted into electrical current. Therefore whenever these switches are pressed,
they produce a small amount of current. A microcontroller based node containing a radio transceiver
utilizes this current to transmit wireless control messages to the luminaries. Philips Lighting in cooperation with Philips Research is also investigating the usage of IPv6 over Low Power Wireless
Personal Area Networks (6LoWPAN)[5] in these lighting applications employing battery-less switch,
thus standardizing and having connectivity with the Internet. These wireless networks are low powered, lossy, exhibit low data rates and have limited communication range. These lighting control
wireless networks are a special case of Wireless Sensor Networks (WSN).
CHAPTER 1. INTRODUCTION
1.2
4
Wireless Sensor Networks
A Wireless Sensor Network (WSN) is a network of spatially distributed small autonomous systems,
called sensor nodes which cooperate over a wireless medium to support at least one common application. These wireless sensor networks are used in various industrial and civilian application areas,
including but not limited to, process monitoring and control, environment and health monitoring,
healthcare applications, home automation and traffic control. In addition to sensors each node contains a radio transceiver, a small microcontroller and limited energy source, either a battery or an
energy scavenging device. Their sizes vary depending on the nature of application. Similarly their
costs also vary depending on the size of network, the size of business and the complexity required
for application.
WSN are different from traditional wireless networks, such as Mobile Ad Hoc Networks due
to various principle differences, mainly due to their nature of applications, environment interaction, scale of deployment, energy costs, self configurability, data centricity, resource scarceness and
mobility[6].
IEEE 802.15.4 is a standard which specifies physical and media access control layer for low
rate wireless personal area networks. It is maintained by the IEEE 802.15.4 working group. It
provides the basis for ZigBee[7], WirelessHART and MiWi specifications. It is also an active area
of investigation for provision of Internet Protocol version 6 (IPv6). The availability of IPv6 over
WSN ensures connectivity of such networks with the Internet. By supporting IPv6 these nodes will
be able to communicate with any IPv6 enabled host over the Internet, benefit from standardized
and already established services, network management tools and end-to-end reliable communication
through existing transport protocols. However IEEE 802.15.4 is ideal for low power and low data
rate networks, a comparison with other wireless networks is made in Table 1.1. IPv6 requires more
complicated headers which are large in nature, and impose heavy overhead. Therefore a tailored
version of IPv6, namely 6LoWPAN is being defined and implemented on IEEE 802.15.4.
1.3
Wireless Lighting Control Networks
Wireless Lighting Control Networks employ wireless communication between control systems installed in luminaries and switches. These control systems are microcontroller based devices containing transceivers. They are installed inside luminaries and can control them. The switches are
also built on similar principle, however unlike control systems in luminaries, they require human
interaction. A new generation of switches does not require batteries, instead they generate a small
amount of energy when pressed. This energy can be used to power-up the chip attached to the
switch and then using its radio, transmit the control packets to the luminary controllers.
In this assignment a battery-less switch was deployed in a lighting control network, which operates
on 6LoWPAN based network. The structure of the network is shown in Figure 1.2. Whenever the
CHAPTER 1. INTRODUCTION
5
Figure 1.2: Wireless Lighting Network overview
switch is pressed, it powers up the attached BSN node[8]. This BSN node then sends control packets
to the luminaries via 6LoWPAN stack. These luminaries can also be accessed through internet using
Edge Router, which provides interface from 6LoWPAN to the internet. Messages directed to the
luminaries pass through Edge Router and messages addressed to the nodes outside pass through it
as well. In practice, a user can check the status of the lightings anywhere just with the basic access
of the internet. User will send a command to the luminaries routed through Edge Router and in
reply, the luminaries will send status via Edge Router.
1.4
Objectives
Philips and TU/e are participating in a European Union project WASP, which stands for Wirelessly
Accessible Sensor Populations. This project is aimed at narrowing the mismatch between research
at the application level and the node and network level by covering complete technology chain from
sensor node hardware to the implementation of application [9].
Within WASP, a common platform for development is in the form of Imperial College BSN nodes
which are based on MSP430 microcontroller derivatives [8]. Every node contains a radio transceiver,
for which different MAC versions can be used. One such implementation employs MAC libraries
provided by Chipcon. Within Philips a 6LoWPAN stack with limited functionality was already
developed, for the Small Autonomous Network Devices (SAND)[10] architecture .
This thesis project has following objectives.
CHAPTER 1. INTRODUCTION
6
Table 1.1: A Comparison of LR WPAN with other wireless technologies
W LAN
BT − basedW P AN
LR WPAN
Range
˜ 100 m
˜ 10-100 m
10 m
Data throughput
˜ 2-11 Mb/s
1 Mb/s
less than 0.25 Mb/s
Power Consumption
Medium
Low
Ultra low
Size
Larger
Smaller
Smallest
• Port the existing 6LoWPAN stack implementation from the SAND node to the MSP430 architecture.
• Develop the stack so as to comply with predefined standard and proposed draft [11].
• Investigate and develop the Neighbor Discovery for 6LoWPAN nodes as proposed in [12].
• To provide the wireless IP based lighting demonstration to Philips Lighting employing a
battery-less switch as mentioned in 1.3.
• To assist in Philips-WASP project 6LoWPAN demonstration, i.e. inter operability of 6LoWPAN stack with IPv6 wired network.
1.5
Outline of thesis
The remaining report is structured as follows. Chapter 2 will give details about the IEEE 802.15.4
MAC and PHY protocol. In Chapter 3, Internet Protocol version 6 is discussed and compared
with ZigBee. Chapter 4 summarizes the 6LoWPAN standard and the challenges that needed to be
overcame in order for successful deployment over IEEE 802.15.4. Details about the environment are
given in Chapter 5. Implementation details and some applications are given in Chapter 6. Philips
Lighting project demonstration and details are given in Chapter 7. Results and concluding remarks
are given in the Chapter 8.
Chapter 2
IEEE 802.15.4 MAC and PHY
IEEE 802.15.4 is a standard which specifies the physical layer and media access layer for low-rate
wireless personal area networks (LR-WPANs). It is maintained by the IEEE 802.15 working group.
It is meant to operate at lower power for extended duration of time. The data rate for 802.15.4
varies from 20 to 250 kbps. These devices are designed to be of extremely low cost and small size.
Medium Access Control (MAC) provides addressing and channel control system. The fundamental task of a MAC protocol is to regulate the access of a number of nodes to a shared medium
in a way to meet some performance goal. In some networks these goals are throughput, delay and
fairness, while in WSN major criteria is energy.
Physical Layer (PHY) consists of basic hardware transmission technologies of a network, providing means to transmit raw bits rather than logical data packet. It mediates between the transmission
and the reception of wireless waveforms and the processing of digital data in the remaining higher
level layers.
The MAC protocol is the first protocol layer above PHY and consequently MAC protocols are
heavily influenced by its properties [6]. Therefore to achieve best possible performance, the MAC
layer is optimized for specific characteristics of underlying PHY layer for various parameters including
energy, delay, efficiency and throughput.
This chapter summarizes various features of the IEEE 802.15.4 MAC and PHY layer.
2.1
Device Types
IEEE 802.15.4 describes two device types:
• Full Function Device (FFD)
Such a device has implemented the all primitives and functions, which are defined in the standard. An FFD can act as Personal Area Network (PAN) coordinator, a (cluster) coordinator
7
CHAPTER 2. IEEE 802.15.4 MAC AND PHY
8
or an ordinary device.
• Reduced Function Device (RFD)
In contrast to FFD, the RFD only consists of minimal implementation of the standard. So it
is not possible for such a device to act as coordinator.
As a result, an FFD can talk to any device in the network, be it an RFD or another FFD,
whereas an RFD can only talk to an FFD. The use of RFDs is typically limited to simple application
scenarios in which individual nodes possess basic communication capability but little computational
capability. Hence for a FFD more memory capacity is needed and a consequence of that, the power
consumption and hardware costs are higher. An RFD has low power consumption and low hardware
requirements.
The distinction between these two device types offers the way to design systems in a flexible and
economic way.
2.2
Network Topologies
IEEE 802.15.4 standard supports multiple network topologies, including both star and peer-to-peer
networks. The topology is an application design choice; some applications which require low latency
will preferably be deployed using star topology however applications requiring large area coverage
may require peer-to-peer networking, as in perimeter security. Multiple address types, including
both physical (i.e. 64 bit IEEE) and short (i.e. 16 bit network assigned) are provided.
• Star Topology
In the networks with star topology, the communication is between devices and a single central
controller called the PAN coordinator. In this topology a device is either an initiator or the end
receiver of network communication. A PAN coordinator is an FFD. It can initiate, terminate
or route communication around the network. It is the primary controller of the network. If
a device wants to communicate with another device in the PAN it sends the message to the
PAN coordinator which then forwards the message to the destination device.
• Peer-to-Peer Topology
In a peer-to-peer network each device can communicate with every other device in its environment directly. It also has a PAN coordinator; however it is not the central point of
communication. The technology allows the more complex network formations to be implemented, include mesh topology. If a device wants to communicate with another device which
is not in its immediate environment, a routing scheme is employed.
CHAPTER 2. IEEE 802.15.4 MAC AND PHY
2.3
9
MAC Frame Format
Each MAC layer packet consists of the header, which provides administrative and security information, a variable length payload and a footer which contains the frame check sequence. The details
of the MAC layer packet structure are shown in Table 2.1.
Element
Header
Payload
Footer
Table 2.1: MAC Packet Structure
F ield
Length (in bytes)
Frame Control
2
Sequence Number
1
Destination PAN Identifier
0 or 2
Destination Address
0, 2 or 8
Source PAN Identifier
0 or 2
Source Address
0, 2 or 8
Auxiliary Security Header
0, 5, 6, 10 or 14
Frame Payload
Variable
Frame Check Sequence
2
The first field of the MAC header is the frame control field. It indicates the type of MAC
frame being transmitted, specifies the format of the address field and controls the acknowledgment.
Further details about the frame control field are given in Table 2.2. The values not used in the table
are reserved for future use.
The sequence number field contains the beacon sequence number, in case of a beacon frame,
or a data sequence number that is used to match an acknowledgment frame to the corresponding
data or MAC command frame. A frame transmission is considered successful only if the sequence
number in the acknowledgment frame is the same as in the data frame. The size of an address field
may vary between 0 and 20. For example, a data packet may contain both source and destination
address information, i.e. address and PAN identifier. While the return acknowledgment frame
does not contain any information at all. On the other hand a beacon frame may only contain the
source address information. In addition, short 16 bit or 64 bit IEEE addresses may be used. The
short address value of 0xFFFF is used for broadcast transmission, which should be accepted by all
devices currently receiving on that channel. A radio channel is a specific frequency, pair or band of
frequencies, named with a number. IEEE 802.15.4-2003 has 27 channels, numbered 0 through 26.
The payload field is variable in length; however the complete MAC frame may not exceed 127
bytes in length. The data contained in the packet is dependent on the frame type. IEEE 802.15.4
has four different frame types. These are the beacon frame, data frame, acknowledgment frame
and MAC command frame. Only the data and beacon frame actually contain information sent by
higher layers; the acknowledgment and MAC command frame are originated in MAC layer and are
used for MAC peer-to-peer communication. The FCS in an IEEE 802.15.4 MAC frame is a 16 bit
International Telecommunication Union - Telecommunication Standardization Sector (ITU-T)cyclic
CHAPTER 2. IEEE 802.15.4 MAC AND PHY
10
Table 2.2: Frame Control Field
BitN o. V alues Meaning
0-2
000
Beacon
001
Data
010
Acknowledgment
011
MAC Command
Security Enabled
3
1
Frame is protected
Frame Pending
4
1
more data is pending
Acknowledgment Request
5
1
Acknowledgment is requested
PAN ID Compression
6
1
Dest. and Source PAN ID equal
the latter can be omitted
Destination Addressing Mode
10-11
00
PAN ID and address not present
10
16 bit short addresses used
11
64 bit extended addresses used
Frame Version
12-13
00
Frame compliant with 2003 standard
01
Frame compliant with 2006 standard
Source Addressing Mode
14-15
00
PAN ID and address not present
10
16 bit short addresses used
11
64 bit extended addresses used
Subfield
Frame Type
redundancy check.
2.4
PHY Specification
The IEEE 802.15.4 PHY is responsible for the following tasks.
• Activation and deactivation of the radio transceiver
• Data transmission and reception
• Channel clear assessment (CCA) for CSMA/CA
• Link quality index (LQI) for received packets
• Energy Detection (ED) for current channel
The PHY provides an interface between MAC sublayer and physical radio channel, via RF
firmware and RF hardware. The PHY includes a management entity called the Physical Layer
Management Entity (PLME). This entity provides the layer management service interface through
which layer management functions may be invoked. The PLME is also responsible for maintaining
a database PHY PAN information base (PIB). This database contains information about managed
objects.
The PHY provides two services:
• the PHY data service
CHAPTER 2. IEEE 802.15.4 MAC AND PHY
11
• the PHY management service
Following are some of the PHY management services.
• Clear Channel Assessment
Before sending a frame, the PHY needs to do a clear channel assessment. This is part of
CSMA/CA, the collision management protocol. It prevents the sending of a frame when there
is already another frame being transmitted and thus avoids corrupting it.
• Get/Set PHY PIB
The PHY PAN Information Base (PIB) contains information related to the PHY configuration.
Most of these values are constants. Some of the values it contains are as following.
– Current Channel
– Channels Supported
– Transmit Power
• Set Tx/Rx State
This service allows the PHY transceiver to be enabled, disabled, set in Rx mode or set in Tx
mode.
2.5
MAC Specification
The IEEE 802.15.4 MAC is responsible for the following tasks.
• Generating network beacons if the device is a coordinator
• Synchronizing to the beacons
• Support PAN association and disassociation
• Employ CSMA/CA mechanism for channel access
The MAC provides two different types of service: the MAC data service and the MAC management service. These services utilize underlying PHY layer’s data and management services. An FFD
must implement the entire MAC data service, but there are some capabilities in MAC management
service that are optional for FFDs. There are a number of capabilities in both data and management
service that are optional for RFDs. A brief overview is given as follows.
2.5.1
MAC Data Service
The important primitives that supported and required by every application are as following.
CHAPTER 2. IEEE 802.15.4 MAC AND PHY
12
• Data Request
This is a transmit function. On calling this request, the data is taken from high level and put
into the outgoing FIFO of the radio.
• Data Confirm
When data is transmitted, then the sending radio gives some indication of the status to MAC.
The status information will tell whether data was transmitted successfully or it failed due to
interference or some other catastrophic failure.
• Data Indication
This is signaled by the Rx Data ISR. When data arrives in radio’s inbound FIFO, then it will
trigger the interrupt. From the ISR, MAC is normally signalled that data was received and
needs processing.
Figure 2.1 denotes a channel access by two nodes using MAC Data Service.
Figure 2.1: MAC Data Service
2.5.2
MAC Management Service
Some management services offered by the MAC layer are follows:
• Association and disassociation
• Beacon Notification
• Request data from coordinator
• Initiate a channel scan over a given list of channels
• Enable receiver for a finite period of time
Higher layers use these services to request PLME to perform above mentioned actions.
CHAPTER 2. IEEE 802.15.4 MAC AND PHY
2.6
13
Network Formation
The association is a process in which a device joins a network. The MAC layer provides the association procedures to the Network layer. The Network layer manages the network formation. IEEE
802.15.4 MAC layer provides four service primitives for MAC association procedure.
• Associate Request
This primitive is used by the Network layer of the device that requests joining a coordinator.
This request also provides the list of capabilities of the device that requests to join the network.
• Associate Indication
When the MAC of the coordinator receives Associate Request from a node, it uses Associate
Confirm primitive to inform its Network layer about the pending request.
• Associate Response
Upon receiving Associate Indication, Network layer uses Associate Response to inform about
the decision to its own MAC layer.
• Associate Confirm
The response from PAN coordinator is not sent immediately. Instead the requesting node
waits for a certain amount of time and then requests the result of association of request. The
MAC of coordinator responds with the result. Associate Confirm is used by the MAC layer of
requesting node to inform its own Network layer about the decision of PAN coordinator.
This procedure can be seen in Figure 2.2.
2.7
PAN Setup
When a device boots up, it can either become a coordinator or associate to another coordinator.
Coordinators can operate in a peer-to-peer fashion and multiple coordinators can form a Personal
Area Network (PAN). A PAN is identified by a 16-bit PAN identifier and one of its coordinators is
designated as a PAN coordinator.
Before a node can associate, it first needs to know about the reachable PANs and their link
quality which is determined by the scan process. This can be done by either active or passive scan.
In passive scan the device turns on its receiver and listens to the channel for a defined period of
time. After that it switches to another channel and performs the scan again. When all requested
channels are scanned, the MAC sublayer informs the next higher layer about all discovered PANs.
The active scan is quite similar to passive scan, however in this case the node transmits a beacon
request frame and waits for a definite period of time, for a beacon frame of the coordinator. Hence
the active scan is used for non beacon enabled PANs. If a PAN coordinator in a non-beacon enabled
PAN receives a beacon request, it will reply with a single beacon frame.
CHAPTER 2. IEEE 802.15.4 MAC AND PHY
14
Figure 2.2: The Association Procedure
When a device discovers a PAN coordinator through a scan, it can start the association process.
Before the request, the internal state of the device must be updated. A higher layer in the new
device sends an association request to its own MAC layer, which is relayed to the coordinator. If the
coordinator’s MAC layer receives this message, it informs the next higher layer. The higher layer
decides whether or not the association can be made. Depending on this decision, the coordinator’s
MAC layer sends a response to the device which requested the association. When the device receives
this message, it informs its higher layer. If the association was successful, the received short address
is stored into its internal data structure.
If a device wants to disassociate from a PAN, the next higher layer sends the disassociation
frame to MAC. The MAC layer generates the disassociation command frame and sends to the PAN
coordinator. After receiving the acknowledgment frame from the coordinator, the originating node’s
MAC layer informs the next higher layer about successful disassociation. If the device does not
receive an acknowledgment frame, it indicates disassociation anyway.
On the other hand, if a coordinator wants a device to be disassociated, it sends such request to its
own MAC layer. The MAC layer sends a disassociation notification to that node. This node should
send an acknowledgment frame back to the coordinator. Upon reception of such acknowledgment
frame, the MAC layer of the coordinator informs the next higher layer about the disassociation. If
no such acknowledgment is received, the MAC layer of the coordinator indicates the next higher
layer the disassociation anyway.
CHAPTER 2. IEEE 802.15.4 MAC AND PHY
2.8
15
Robustness
Robustness in an IEEE 802.15.4 based network is achieved by using various channel access mechanisms, data verification and optional acknowledgments. The channel access can be done either in
the beacon mode or non-beacon mode. In the beacon mode, the PAN coordinator regularly transmits frame beacon packets announcing the PAN identifier, a list of outstanding frames and other
parameters [6]. The frame beacon includes a superframe specification describing the length of various components of the superframe that follows the beacon frame. The superframe is divided into
active period and inactive period. During the inactive period all nodes including the coordinator can
switch off their transceivers and go to sleep mode. The active period is subdivided into a Contention
Access Period (CAP) and Guaranteed Time Slots (GTSs). During CAP slotted CSMA/CA is used.
In non-beacon networks, transmission is done using a unslotted CSMA/CA channel access mechanism. Whenever a node has to transmit a frame, it has to wait for a random period of time. After
that it checks if the channel is idle or not. If it is idle, the frame is transmitted. If the channel is busy,
the node will wait for another random period of time before retrying. Beacon enabled networks use
slotted CSMA/CA. The backoff slots are aligned with the start of beacon transmission. A device
wishing to transmit waits for a random number of backoff slots. If the channel is idle after this
waiting period, the packet is transmitted. In case the channel is busy, the node again waits for a
random number of slots. The data verification in 802.15.4 based network is done using CRC. It is
performed on every frame to detect bit errors. The acknowledgment frames can be requested by the
transmitter for data and command frames. GTS can be used for the data that requires timeliness
and real-time guarantees.
Chapter 3
Internet Protocol and ZigBee
LR-WPAN defines only two layers of the 7-layer OSI model: the physical layer and MAC sub layer.
The upper layers are left for developers to implement. A variety of host protocols can be implemented
on top of IEEE 802.15.4. Among them, ZigBee and IPv6 are two distinct and prominent choices.
The IPv6 implementation is only possible through an adaptation layer namely 6LoWPAN, which is
discussed in Chapter 4. ZigBee is a specification for a suite of high level communication protocols
to operate on top of the IEEE 802.15.4 standard. It is maintained by the ZigBee alliance. In this
chapter, we will discuss the Internet Protocol and ZigBee.
3.1
Internet Protocol version 6
Internet Protocol Version 6 is a best effort layer 3 network protocol. It neither guarantees delivery,
nor assures proper sequencing or avoid duplicate delivery. These aspects are taken care of by upper
layer protocols such as UDP and TCP. IPv6 is a successor of IPv4. IPv6 introduces changes in
address size, header formats and address assignment. Network security is integrated into the design
of IPv6.
IPv6 has a much larger address space than IPv4: addresses in IPv6 are 128 bits long, compared
to 32-bit addresses in IPv4. It also has a goal to reduce time required to configure and manage
systems. An IPv6 system can participate in stateless autoconfiguration, where it can create its
guaranteed unique IP address by combining its MAC address with a prefix provided by the network
router. Therefore DHCP is not needed in this configuration for address assignment, whereas in IPv4
it was a requirement. IPv6 headers are fixed size and more regular than IPv4 counterparts. Thus
resulting in improved performance and more extension possibilities. Multicast is a requirement in
IPv6 specifications and although supported in IPv4, not every router and host supports it. Moreover
Neighbor Discovery is a part of IPv6. It specifies a set of ICMPv6 messages, which replaces Address
Resolution Protocol, ICMP Router Discovery and ICMP Redirect used in IPv4.
16
CHAPTER 3. INTERNET PROTOCOL AND ZIGBEE
3.1.1
17
Header Format
An IPv6 packet includes an IPv6 header. It is placed at the beginning of the IPv6 packet and is 40
bytes long. The structure is given in Appendix A.1.
IPv6 contains optional information in separate extension headers. They are placed between the
IPv6 header and the IPv6 payload. The presence is indicated in the Next Header field. Every
extension header also has this field. Hence a sequence of headers can be formed. These headers
can contain Hop-by-Hop Options, Destination Options, Routing, Authentication and Destination
Options among many other possible options. The value 59 in Next Header field means that there
is nothing following that header.
The IPv6 layer requires the underlying layer to support an MTU of at least 1280 bytes.
3.1.2
Address types
IPv6 addresses are 128 bits long. Unlike IPv4, it does not use classes. However it defines three
different IP address types
• Unicast
A unicast address defines a single recipient and a packet addressed to such address is only
delivered to that specific recipient. IPv6 unicast addresses can be classified according to their
scopes. A scope determines the applicable area. An IPv6 unicast address can have global, sitelocal or link-local scopes. A global scope means that the address is valid for communication
with any node on the IPv6 internet. Site-local address is defined to be configured in a networked
site made up of several subnets. Link-local address is used within a link.
• Multicast
Multicast addresses are used to allow a single device to send a packet to a group of recipients.
These recipients must belong to a multicast group. The packet addressed to this group will
be delivered to all nodes belonging to this group. There is one-to-many relationship between
network addresses and network end points. Each destination identifies a set of receiver endpoints, to which all information is replicated.
IPv4 multicast address starts with 1110. Remaining 28 bits identify multicast group address.
In contrast, IPv6 start with 0xFF, 4 bits for Flags and 4 bits for Scope ID. Remaining 14 bytes
identify actual group address. Flags denote the nature of multicast address. Multicast addresses can be well-known when allocated by IANA or transient when they are not permanent.
Multicast address can have one of the following different scopes.
– Interface-local: meaning packet with this destination address may not be sent over any
network link, but must remain within current node. It is equivalent to unicast loopback
CHAPTER 3. INTERNET PROTOCOL AND ZIGBEE
18
address.
– Link-local: meaning packet with this destination address may only be sent to local neighbors.
– Admin-local: meaning packet with this destination address must be administratively
configured.
– Site-local is restricted to local physical network.
– Organization-local: restricted to networks used by the organization administrating the
local network.
– Global: eligible to be routed over the public internet.
In IPv4 a specific address, 0xFFFFFFFF is used for broadcast. IPv6 does not specify an address
for broadcast. This can be achieved by defining a link-local multicast group and sending a
multicast message on that address.
• Anycast
An anycast address is used to identify a set of recipients where a packet sent to the anycast
address is routed to the nearest recipients belonging to that group, depending on the distance
of the routing algorithm. While a unicast address requires the message to be sent to a specific
recipient and a multicast address requires the message to be sent to every member in that
multicast group, an anycast requires the message to be sent to one member of the anycast
group. The destination is chosen by router for efficiency in term of routing distance.
Like multicast, in anycast there is also one-to-many relationship between network addresses
and end points, only one of those end points is chosen at any given time to receive information
from any sender.
The above types are shown in Figure 3.1 and Figure 3.2.
Figure 3.1: Unicast and Broadcast
CHAPTER 3. INTERNET PROTOCOL AND ZIGBEE
19
Figure 3.2: Multicast and Anycast
3.1.3
Address Representation
A common representation of IPv6 address is xx:xx:xx:xx:xx:xx:xx:xx, where each x denotes a
byte. Also it can be represented as eight group of four hexadecimal digits. An example of an IPv6
address is as following
2001:1db8:85e3:0000:0000:8a2a:1370:2354
To shorten the writing and presentation of addresses, some simplifications to the notation are
permitted.
• Any leading zeroes in a group may be omitted, thus the above example becomes
2001:1db8:85e3:0:0:8a2a:1370:2354
• Furthermore consecutive groups of 0 values can be replaced by two colons ::.
2001:1db8:85e3::8a2a:1370:2354
However only one ”::” simplification is allowed in any address, to avoid ambiguity.
To represent a prefix, the format ipv6 address/prefix length is used. where
• ipv6 address is an IPv6 address in any of notations given above
• prefix length is a decimal value specifying how many of remaining most contiguous bits of
the address comprise of the prefix.
For example, the following are legal representations of 32-bit prefix 2001D0D0 (hexadecimal):
2001:D0D0:0000:0000:0000:0000:0000:0000/32
2001:D0D0:0:0:0:0:0:0/32
2001:D0D0::/32
CHAPTER 3. INTERNET PROTOCOL AND ZIGBEE
20
Table 3.1: IPv6 Address Types
Address Type
Binary Prefix
IPv6 Notation
Unspecified
00...00 128 bits
::/128
Loopback
00...01 128 bits
::1/128
Multicast
11111111
FF00::/8
Link-local Unicast
1111111010
FE80::/10
Global Unicast
Everything else
Empty
A list of IPv6 address prefixes and notation is given in Table 3.1.
The IPv6 header does not provide a checksum. However it provides a pseudo-header which can
be used by upper layers for checksum calculation. A pseudo-header contains IP source address,
destination address, protocol and length fields. A byte consisting of zeros is added to this header
and then this header is added to the actual message. Checksum is computed over the combination
of pseudo-header and real message and the value is placed in the checksum field. The pseudoheader is only used for computation of checksum and not transmitted along with real message. The
destination higher layer performs same action and computes a checksum to be compared in the
transmitted header.
3.2
ZigBee
ZigBee is built on top of the IEEE 802.15.4 standard. Therefore it is tied to this specification. It
uses standard’s functionalities and adds its own features on top of it. It provides specification for
network and application layer along with providing security features. It is maintained by the ZigBee
alliance. The ZigBee alliance was established in 2002. It is an association of companies working
together to enable reliable, cost-effective, low power and wirelessly networked products based on
IEEE 802.15.4. The ZigBee stack is shown in Figure 3.3.
3.2.1
Device Types
ZigBee distinguishes devices either on the basis of physical characteristics or logical role.
1. Physical Device Types
To provide low cost implementation options, the ZigBee Physical Device type distinguishes
the type of hardware on the basis of IEEE 802.15.4 definition of devices. These types are fully
functional device (FFD) and reduced function device (RFD).
2. Logical Device Types
The ZigBee Logical Device type distinguishes the Physical Device Types (FFD or RFD) on the
basis of their role in the ZigBee network. The device types are ZigBee Coordinators, ZigBee
Routers and ZigBee End Devices. The ZigBee coordinator initializes a network, manages
CHAPTER 3. INTERNET PROTOCOL AND ZIGBEE
21
network nodes and stores network information. The ZigBee router routes messages between
paired nodes. The ZigBee End Devices act as a leaf node in the network and can be either an
RFD or FFD.
A ZigBee network must have a coordinator, which along with routers must be mains-powered.
End nodes can be battery-powered.
Figure 3.3: The ZigBee Stack
3.2.2
Traffic Types
ZigBee networks support multiple traffic types with their own unique characteristics, which are as
follows.
• Periodic Data
This type of data is usually defined by sensor based applications. These sensors provide data
on timely intervals. Typically this type of traffic is handled using the beacon system, where
sensor nodes wake up at a set time, check for the beacon, synchronize, exchange data and go
back to sleep.
• Intermittent Data
This type of data is derived from the application or an external event, such as pressing a
wireless switch. Data can be handled in a beaconless or disconnected system. In disconnected
mode, the attachment to the system is only done when communication is required.
• Repetitive Low Latency Data
This type of data is handled using guaranteed time slots (GTS). A GTS is a part of contentionfree period (CFP) during which a node ensures the transmission without any contention. GTS
are managed by MAC. Applications requiring timeliness and critical data passage may include
medical alerts and security system.
CHAPTER 3. INTERNET PROTOCOL AND ZIGBEE
22
ZigBee networks are primarily intended for low duty cycle sensor networks. ZigBee applications
have the ability to quickly attach, send information, detach and go to sleep; which results in low
power consumption and extended battery life.
3.2.3
Addressing
The devices with IEEE 802.15.4-compliant radio have a 64-bit address. This is globally unique address made up of Organizationally Unique Identifier (OUI) and 40 bits assigned by the manufacturer
of that module. OUIs are obtained from the IEEE.
When a device joins ZigBee network, it gets a 16-bit address. This address is unique within the
network. Either of these, the 64-bit or 16-bit address can be used within the PAN to communicate
with the device. The coordinator always has the 16-bit address ’0’.
3.3
IPv6 and ZigBee : A comparison of standards
While ZigBee is a complete suite on top of a single PHY and MAC specification, IPv6 is just a layer
that theoretically can exist on top of any PHY and MAC. However we can compare the usefulness
of implementing IPv6 on sensor networks against an existing and quite mature ZigBee suite. Here
is a comparison between both existing technologies.
1. ZigBee is using a small scale and ad-hoc networking model. IPv6 is massively scalable and can
provide end to end connectivity to the internet.
2. ZigBee is limited to a single radio standard, i.e. IEEE 802.15.4, whereas IPv6 (or IP) is already
existing on various wired and wireless standards, e.g. IEEE 802.3 and IEEE 802.11.
3. ZigBee is a standard of an alliance, which is not open to non-members. IPv6 on the other
hand, is an open standardization group.
4. ZigBee has already defined service and device descriptions. No such descriptions are yet
available for IPv6 based networks.
An implementation of IPv6 on IEEE 802.15.4 is not a straightforward task and there are limitations of the underlying network. The version of IPv6 to be implemented on IEEE 802.15.4 is named
6LoWPAN, which will be discussed in chapter 4.
Chapter 4
6LoWPAN
6LoWPAN is an acronym for IPv6 over Low power Wireless Personal Area Networks. It is managed
by IETF 6lowpan working group. It defines the frame format for the transmission of IPv6 packets
over IEEE 802.15.4. Since IPv6 requires support for packet size larger than 802.15.4 can handle, an
adaptation layer is defined in this specification. It also defines the header compression and supports
fragmentation and reassembly below IP layer[5].
It is assumed that a PAN maps to a specific IPv6 link. A link is a medium over which nodes
can communicate at the link layer. Strictly speaking, in wireless networks a link is only single hop
- the radio range of one node. In a wired network a link contains all the nodes that share the
communication medium to a router. For example let us take three nodes A, B and C. In a wired
network if A can communicate to B directly and B can communicate directly to C, A can also
directly communicate to C. Therefore A and C are said be on the same link. In wireless network,
this is different. If A can communicate to B directly and B can communicate directly to C, it may
be possible that A can not communicate directly to C, due to factors such as radio range. In WSN
a link of a given node is limited to only one hop. A mesh is formed for multiple hop communication.
A 6LoWPAN network can also be seen as a mesh of various wireless links.
A PAN ID can also be used in an IPv6 address. One 6LoWPAN mesh (IPv6 link) maps to one
PAN ID.
4.1
IEEE 802.15.4 for IP
IPv6 packets must only be carried on data frames of IEEE 802.15.4, which can optionally request
that they may be acknowledged. It is recommended to do so (request acknowledgments) in order to
aid link-level recovery.
This specification does not require that IEEE 802.15.4 networks run in beacon enabled mode. It
23
CHAPTER 4. 6LOWPAN
24
is however, recommended in this specification that beacons to be configured so as to assist association
and disassociation events. This specification also requires both source and destination addresses to
be included in the IEEE 802.15.4 frame header. The source or destination PAN ID may also be
included.
4.2
Addressing Modes
IEEE 802.15.4 defines various addressing modes: it allows the use of either an IEEE 64-bit extended
address or a 16-bit short addresses unique within the PAN. These short addresses can only be used
after association with a PAN coordinator. This specification supports both addresses. It also assumes
that a PAN maps to a specific IPv6 link. IPv6 supports multicast but not broadcast whereas IEEE
802.15.4 does not support multicast natively. Instead multicast is performed on it using link-layer
broadcast. In order to do a multicast a node has to do a broadcast in a way that only a specific
multicast group is recipient of such messages. This is carried out as below.
1. The destination PAN ID in the frame header must match the PAN ID of the link.
2. The short destination address in frame header must match the broadcast address, i.e. 0xFFFF.
3. The nodes that receive this message, parse it at higher level and find out if that message was
intended for them or not.
A value of 0xFFFF refers to broadcast and must be accepted by all nodes. Additionally within
6LoWPAN networks, 16-bit addresses are divided into 5 different classes. Only two of these classes
are defined as of now, the others are reserved for future use. In following listing ’x’ is a place holder
for an unspecified address format.
1. 0xxxxxxxxxxxxxxx
The first bit (bit 0) shall be zero if 16-bit address is a unicast address. This leaves 15 bits for
actual address.
2. 100xxxxxxxxxxxxx
Bits 0, 1 and 2 shall follow the pattern above in case of multicast address. Remaining 13 bits
will contain the actual multicast address.
4.3
Stateless Address Autoconfiguration
6LoWPAN also provides support for stateless address autoconfiguration, which means that a host
can generate its own addresses using a combination of locally available information and information
advertised by routers, without making stateful binding with routers. Since every 802.15.4 device has
CHAPTER 4. 6LOWPAN
25
a unique EUI-64 identifier, an IPv6 interface identifier can be obtained from this EUI-64 identifier
using stateless autoconfiguration as explained in [13].
Although every device has a EUI-64 address, a 16-bit short address can also be given to such a
device after the association with PAN coordinator. These addresses should be unique within a PAN.
The specification of such addresses is given as following .
0
1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
16-bit short Address
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
It is also possible to use 16-bit addresses for autoconfiguration. In this case a pseudo 48-bit
address is formed by concatenating this 16-bit address with the 16-bit PAN ID (or 16 zero-bits in
case PAN is not known) and 16 zero-bits in following way.
16_bit_PAN:16_zero_bits:16_bit_short_address
Afterwards an interface identifier (64-bit) can be formed from above 48-bits using ”IP over
Ethernet” specification [13].
The IPv6 link-local addresses are formed by appending the interface identifier as defined above,
to the prefix FE80::/64 as below.
10 bits
54 bits
64 bits
+----------+-----------------------+----------------------------+
|1111111010|
(zeros)
|
Interface Identifier
|
+----------+-----------------------+----------------------------+
4.4
Routing
Network routing defines the ability to send a unit of information from one node to another by
determining a single path through the network while meeting certain efficiency criteria. Within a
6LoWPAN header format, routing protocols can be defined at two layers, which are as following.
1. Mesh-under Routing
The mesh-under routing supports routing under the IP link and is directly based on linklayer standard 802.15.4 standard. It utilizes 64-bit IEEE extended addresses or 16-bit short
addresses. This routing can only be used within a 6LoWPAN network.
CHAPTER 4. 6LOWPAN
26
2. Route-over Routing
The route-over routing lies at the network layer of 6LoWPAN stack. It utilizes IP addresses for
addressing and locating nodes. This routing can be used to access nodes outside the 6LoWPAN
as well as inside. This routing is essentially same as used in regular IP networks.
4.5
Constraints
The IPv6 maximum transmission unit (MTU) is 1280 bytes which is more than the largest possible
802.15.4 packet size. Depending on overhead, the 802.15.4 protocol data unit has different sizes.
Since maximum physical layer packet size aMaxPHYPacketSize is 127 bytes and maximum frame
overhead aMaxFrameOverhead is 25 bytes, 102 bytes are available for MAC layer. Moreover depending on application requirements link-layer security may or may not be implemented using AES.
However it is highly recommended to employ encryption. In case it is implemented it will impose
further overhead of 9, 13 or 21 bytes in case AES-CCM-32, AES-CCM-64 or AES-CCM-128 are used
respectively. In case AES-CCM-128 is used, only 81 bytes are available for the MAC payload. This
is obviously below the minimum IPv6 requirements and therefore a fragmentation and reassembly
adaptation layer must be provided at the layer below IP. The IPv6 header is 40 bytes long, resulting
in 41 bytes for the actual payload for upper layers, like UDP. Then the UDP layer has a 8 byte
header as well, leaving only 33 bytes for actual application data. This induces a huge overhead
for a bandwidth constrained medium. As already mentioned there is a need for the fragmentation
and the reassembly, in addition there is also need for header compression. This leads to following
observations.
1. The adaptation layer must be provided to comply with IPv6 minimum MTU requirements.
Although it is not expected from such devices to produce payloads with such large packets.
2. The header size of IPv6 must be reduced or adapted to minimize the overhead.
The above two issues lead to the requirement of an adaptation layer under layer 3.
4.6
6LoWPAN Adaptation Layer
The adaptation layer lies between layer 2 and layer 3, as depicted in Figure 4.1. This layer encapsulates IPv6 datagrams that need to be transmitted, by a header stack. This header is placed at
the beginning of the 802.15.4 MAC protocol data unit (PDU), the 6LoWPAN payload (e.g. an IPv6
packet) follows this header.
All 6LoWPAN encapsulated datagrams transported over IEEE 802.15.4 are prefixed by an encapsulation header stack. Each header in the stack starts with a dispatch value indicating the
CHAPTER 4. 6LOWPAN
27
header type. Zero of more headers follow after the dispatch value. A 6LoWPAN encapsulated IPv6
datagram looks like as follows.
+----------+-------------+---------+
| Dispatch | IPv6 Header | Payload |
+----------+-------------+---------+
Since this layer does header compression as well, LOWPAN IPHC compressed IPv6 datagram will
be written as following.
+-----------+----------------------+------------+
| Dispatch
| LOWPAN_IPHC Header
| Payload
|
+-----------+----------------------+------------+
Dispatch indicates which packet follows dispatch immediately. The different supported types
are summarized in Table 4.1.
Pattern
00 xxxxxx
00 000011
01
01
01
01
10
11
11
000001
000010
010000
111111
xxxxxx
000xxx
100xxx
Table 4.1: Dispatch Value Bit Pattern
Header Type
NALP - Not a LoWPAN frame
LOWPPAN IPHC - LOWPAN IPHC compressed IPv6
Provisional Value
IPv6 - Uncompressed IPv6 Addresses
LOWPPAN HC1 - LOWPAN HC1 compressed IPv6
LOWPPAN BC0 - LOWPAN BC0 broadcast
ESC - Additional Dispatch byte follows
MESH - Mesh Header
FRAG1 - Fragmentation Header (first)
FRAGN - Fragmentation Header (subsequent)
Values not mentioned in this table are reserved for future use.
4.6.1
Header Types
The header stack may contain three optional LoWPAN headers summarized as below.
1. Mesh Addressing header
Frames using mesh networking include a mesh addressing header. The structure is as following.
CHAPTER 4. 6LOWPAN
28
Figure 4.1: 6LoWPAN Stack Overview
1
2
3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1 0|V|F|HopsLeft| originator address, final address
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The details of fields are as following.
• V: This value is 0 if the Originator address (very first address) is an IEEE extended
address (64-bit) or 1 if it is a 16-bit short address.
• F: This value is 0 if the Final Destination address (very last address) is an IEEE extended
address (64-bit) or 1 if it is a 16-bit short address.
• HopsLeft: This 4-bit field will be decremented by each forwarding node before sending
this packet to next hop. The packet is not forwarded anymore if this value reaches 0. The
value 0xF is reserved and indicates 8-bit hop limit which will be immediately followed
after addresses, hence allowing hops more than just 14.
• Originator Address: This is the link-layer address of the Originator.
• Final Address: This is the link-layer address of the Final Destination within the mesh.
2. Broadcast header
The broadcast header is used whenever a packet is multicast or broadcast. The structure is as
following.
CHAPTER 4. 6LOWPAN
29
0
1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|1|LOWPAN_BC0 |Sequence Number|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Here sequence number is used to differentiate between duplicate packets. This 8-bit field is
incremented by the originator whenever it sends a new mesh broadcast or multicast packet.
3. Fragmentation header
If an entire payload fits within single 802.15.4 frame, no fragmentation is required. It is only
needed whenever the size of the payload is more than the effective MTU of IEEE 802.15.4.
This is done by breaking up the payload into multiple link fragments. Two different types of
fragmentation packets are used. One to mark the start of fragmented transmission and others
to mark the continuity of the fragmentation with an offset. Link bytes must be a multiples of
eight bytes in length. The first header is given below.
0
1
2
3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1 1 0 0 0|
datagram_size
|
datagram_tag
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The remaining headers are contain an offset value.
0
1
2
3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1 1 1 0 0|
datagram_size
|
datagram_tag
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|datagram_offset|
+-+-+-+-+-+-+-+-+
The fields are described as following.
CHAPTER 4. 6LOWPAN
30
• datagram size: This 11-bit field encodes the size of an entire IP packet before link-layer
fragmentation. This value stays the same for all fragmented packets. Although it is not
necessary to contain this value in every packet, doing so will assist in reassembly of the
packet on destination in the event that the 2nd or subsequent packet arrives earlier than
the first. This will enable buffer space reservation.
• datagram tag: This 16-bit value stays the same for all fragments of a payload. It will
be incremented by the sender for every successive fragmented datagrams. This value is
wrapped to zero whenever it reaches 65535.
• datagram offset: This field is present only in the second and subsequent fragments. It
specifies the offset from the beginning of the payload datagram in unit of 8 bytes. The
first packet has an offset of zero.
Upon reception of a link fragment, the receiver starts constructing the original unfragmented
packet, whose size is datagram size. It uses datagram offset to determine the position of
subsequent fragments within the original unfragmented packet. The size of the reassembly
packet is determined by the datagram size.
4.6.2
Header Compression
Along with optional header definitions, the adaptation layer provides stateless header compression
which significantly reduces IPv6 header overhead. It is stateless since it does not make binding with
any other node and is defined independent of the packet history. Any node operating within the
6LoWPAN can decompress this header.
The header compression changes the packet format, which is indicated by the dispatch value in
the encapsulation header preceding the LoWPAN payload. The header compression is done for the
IPv6 header and the next layer protocol. The term LOWPAN IPHC is used for the IPv6 encoding and
for higher layer protocols the term LOWPAN NHC is used. As of now, LOWPAN NHC is only defined for the
UDP header, namely LOWPAN UDP. ICMP and TCP packets are not compressed. The compression
details are described as below.
1. LOWPAN IPHC - IPv6 Header Encoding
LOWPAN IPHC can compress the 40-byte IPv6 header down to 7 bytes (2-byte LOWPAN IPHC, 1byte Hop Limit, 2-byte Source Address, and 2-byte Destination Address). To do so, following
considerations are made.
• Both Source and Destination Addresses have a link local prefix (FE80::/64) and their
last 64 bits can be inferred from link-layer addresses, in case the interface identifiers are
autoconfigured.
CHAPTER 4. 6LOWPAN
31
• The packet length can be inferred from the MAC layer or from datagram size, in case
fragmentation is used.
• Next header value is indicated as either ICMP, UDP or TCP.
• Hop Limit field is carried uncompressed 1 byte.
LOWPAN IPHC based encoding looks as follows:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
LOWPAN_IPHC encoding
| Non-Compressed fields follow...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LOWPAN IPHC encoding is a 2-byte value which determines how compression is done and what
values are following this header. The structure looks as follows.
0
0
1
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| T |VF |NH | HLIM
|
rsv
|
SAM
|
SAC
|
DAM
|
DAC
|
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
The values are explained in Table A.2.
2. LOWPAN UDP - UDP Header Encoding
LOWPAN NHC defines the compression scheme for headers following the IPv6 header. In this
case, so far compression is only done for UDP headers. LOWPAN NHC is a by that tells which
header is next. Bits 0-5 are used to identify the header type and 6-8 are used to set options.
The LOWPAN UDP looks as follows.
0
1
2
3
4
5
6
7
+---+---+---+---+---+---+---+---+
| 1 | 1 | 1 | 1 | 1 | 0 | S | D |
+---+---+---+---+---+---+---+---+
Table A.3 summarizes the LOWPAN UDP encoding starting from bit 0 to bit 7.
CHAPTER 4. 6LOWPAN
4.7
32
6LoWPAN Neighbor Discovery
The Neighbor Discovery protocol is a protocol in the Internet Protocol Suite used with IPv6. Nodes
use Neighbor Discovery to find other nodes on the link, to determine the link-layer addresses of
other on-link nodes, to find available routers and to maintain information on their reachability. If a
router or path to a router fails, the node actively searches for a functioning alternatives. The cached
values that become invalid are immediately purged.
The Neighbor Discovery protocol for IPv6 defines mechanisms for the following.
• Router Discovery: Nodes can locate routers that reside on an attached link.
• Prefix Discovery: Nodes can discover the set of address prefixes that are used to define their
globally unique addresses.
• Address Resolution: Mapping from IP to link layer address. This is not required in 6LoWPAN
since there is direct mapping between their globally unique address and the link-layer address.
• Next-hop Determination: Nodes can find next hop routers for a destination.
• Neighbor Unreachability Detection (NUD): Nodes can determine that a neighbor is no longer
available on the link.
• Duplicate Address Detection (DAD): Nodes can check whether an address is already in use.
• Address Autoconfiguration: Nodes can automatically configure their address without the use
of a stateful configuration protocol, such as Dynamic Host Configuration Protocol for IPv6
(DHCPv6).
Address resolution for neighboring nodes in LoWPAN is not effectively possible. Due to physical
mobility of nodes or varying radio strength, a node may often move from one router to another.
Moreover characteristics of LoWPAN are different from traditional networks, therefore standard
Neighbor Discovery is not suitable and a 6LoWPAN-specific ND is proposed. In this specification,
along with standard mechanisms for neighbor discovery, following new entities are introduced.
• Edge Router: An IPv6 router that connects a 6LoWPAN mesh to another IP network.
• Whiteboard: A conceptual data structure which is supported by Edge Routers. The Whiteboard is used for NUD and DAD across the entire 6LoWPAN mesh. The Whiteboard contains
information of a node regarding its Owner Interface Identifier, Owner Nonce, IPv6 address,
Transaction ID and remaining time of binding.
• Node Registration: A Method in which nodes in LoWPAN register with Edge Routers, therefore creating Whiteboard bindings of their all IPv6 addresses in LoWPAN.
CHAPTER 4. 6LOWPAN
33
Neighbor Discovery for 6LoWPAN (6LoWPAN-ND) defines additional message formats along
with modifying standard ND messages for IPv6. The following message types are used with modifications from [14].
• Router Solicitation: Nodes send this message to request a Router Advertisement immediately.
• Router Advertisement: Routers send this message either periodically or in response to Router
Solicitation. Router Advertisements contain various link and Internet parameters as well as
prefixes information.
• Neighbor Solicitation: Nodes send this message to determine the link layer address of their
neighbors or verify their reachability. Neighbor Solicitations are also used for Duplicate Address Detection. Only used in extended LoWPAN, i.e. an aggregation of multiple 6LoWPANs,
interconnected by a backbone link via Edge Routers and forming a single subnet as defined in
[15].
• Neighbor Advertisement: Nodes send this message in response to Neighbor Solicitation. They
can also send to announce link layer address change. Only used in extended 6LoWPAN. An
extended 6LoWPAN is an aggregation of multiple 6LoWPAN interconnected by a backbone
link via Edge Routers and farming a single subnet.
The following new message types are defined in Neighbor Discovery for 6LoWPAN.
• Node Registration: A node sends this message along with its IID and requested lifetime to
register at an Edge Router. This message can include possible options like the address option,
which can include the address the node wants to register.
• Node Confirmation: An Edge Router sends this message to the node in response to its Node
Registration. This is used to confirm the binding of the node at the Edge Router.
6LoWPAN-ND messages that are implemented in current assignment are explained in more detail
here after.
4.7.1
Node Registration/Confirmation
The Node Registration/Confirmation messages are used for the registration of a node at an Edge
Router and the confirmation of the binding. The Node Registration message is sent by a node to the
link-local unicast IPv6 address of an on-link Edge Router. When registering for the first time, the
sender IP address field contains the unspecified IPv6 address of the sending node. For subsequent
NR messages, the IP address field contains the link-local IPv6 address of the sending node. NR/NC
messages may be sent over multiple IP hops within a LoWPAN by relaying. When relaying, a new
message is created with an updated checksum and a code is used to indicate relaying.
CHAPTER 4. 6LOWPAN
34
The Node Registration/Confirmation message format is given in Appendix A.4.
Since Node Registration and Node Confirmation are ICMPv6 packets, there is an IP header
before them. This IP header contains following values:
• Source Address: The IPv6 address of the source. When registering for the first time, this must
be IPv6 unspecified address.
• Destination Address: The link-local unicast IPv6 address of an on-link Edge Router when sent
directly by node. The destination IPv6 address of an Edge Router or a well known anycast
address 6LOWPAN ER when relayed by another router. This address will be allocated by
IANA. A router is a node that can forward datagrams between arbitrary source-destination
pairs by performing IP routing.
• Hop Limit: 255
4.8
Router Solicitation Message
Routers send out their Router Advertisements periodically. However a node can request for an
immediate advertisement using Router Solicitation. The message format is given in Appendix A.5.
4.9
Router Advertisement Message
Routers send out their Router Advertisements periodically and upon receiving Router Solicitation.
The message format in Appendix A.6.
Along with above mentioned new message types, various new options are defined in 6LoWPANND which are as follows.
4.10
6LoWPAN-ND Message Options
Besides existing message options in [14], new message options were defined in [12]. Which are
summarized as below.
• Address Option: This option is used to indicate the address which a node wants to register
with the ER in a Node Registration message. Alternatively, this is used in Node Confirmation,
sent by the Edge Router, to indicate the success or failure of the binding.
• 6LoWPAN Prefix Information Option: This option carries the prefix information for 6LoWPAN. It also contains the lifetime of the validity of a prefix on a link.
CHAPTER 4. 6LOWPAN
35
• 6LoWPAN Prefix Summary Option: This option identifies the set of prefix information options
by sequence numbers, if there is a change in the sequence number, it denotes that prefix
information is likely changed.
• Owner Interface Identifier: This option is for uniquely identifying the binding in question and
match it with the Whiteboard entries. This option contains values of Owner Interface Identifier
and Owner Nonce.
4.11
6LoWPAN and ZigBee: A comparison
Although both networks operate on IEEE 802.15.4, still we can see some difference.
ZigBee and 6LoWPAN are different in multiple aspects. Firstly the layers are not compatible with
each other. 6LoWPAN employs standard IP at the network layer and UDP at the transport layer
whereas ZigBee contains its own descriptions for the network and the application frame work layers,
which are not included in 6LoWPAN. Application Framework layer is an execution environment for
application objects to send and receive data and it is specific to ZigBee devices only.
Secondly, ZigBee requires support from a mains-powered coordinator and routers. In 6LoWPAN
network, an Edge Router can also act as pan-coordinator, however it is not necessary that a mainspowered node is a pan-coordinator.
Moreover 6LoWPAN can be connected to other IP based networks using an Edge Router, ZigBee
requires a Gateway implementation to do so. Also 6LoWPAN supports a larger network size than
ZigBee.
Table 4.2 compares some features of 6LoWPAN and ZigBee stacks[1].
Table 4.2: Stack Comparison as in [1]
ZigBee
6LoWPAN
Code Size with Mesh
32K to 64K
22K
Code Size w/o Mesh
Not Possible
12K
RAM Requirements
8K
4K
Header overhead
8-16 bytes
2 to 11 bytes
Network Size
65K
2ˆ64
RF Radio Support
802.15.4
802.15.4++
Transport Layer
Within ZigBee
UDP/TCP
Internet Connectivity ZigBee Gateway Router/Bridge
Chapter 5
Development Environment
This chapter deals with the development environment, more specifically the operating system, i.e.
FreeRTOS and the hardware interfaced during this project.
5.1
FreeRTOS
FreeRTOS is an open source, portable, mini real time kernel. The porting is possible due to several
factors. Firstly the code size is small. It is composed of only three core files and an additional port
file for specific processor. Secondly most of the code is written in C. Only few lines of assembly code
are required to adapt to a specific platform. Finally FreeRTOS is heavily documented on the website
[16]. Due to already mentioned factors, it has been already ported to various hardware architectures
from 8-bit to 32-bit micro-controllers, including but not limited to, ARM7, ARM9, MSP430, AVR
and 8051.
It is licensed under a modified GPL and can be used in commercial applications under this
license. The code is freely available on the official website.
The following sections describe FreeRTOS main features utilized in this project.
5.1.1
Scheduler
FreeRTOS features a Round Robin, priority based scheduler. Each task is assigned a priority. The
tasks with the same priority share the CPU time in a Round Robin fashion.
Tasks in FreeRTOS can exist in one of the following states.
• Running
When a task is actually executing, it is said to be in running state. In this state, it is utilizing
CPU time.
36
CHAPTER 5. DEVELOPMENT ENVIRONMENT
37
• Ready
When a task is able to execute but not currently executing because a different task of equal
or higher priority is already in Running State, it is said to be a Ready Task.
• Blocked
A task is said to be in the Blocked state if it is currently waiting for either a temporal or
external event. A task can block waiting for queue and semaphore events. Additionally if we
a use delay statement in a task, it will be blocked until the delay period has expired. Tasks in
Blocked state always have a ’timeout’ period, after which the task will be unblocked. Blocked
tasks are not available for scheduling.
• Suspended
Tasks in Suspended state are also not available for scheduling. Tasks will enter this state only
if explicitly commanded to do so through API calls. They will resume via explicit API calls
as well. A ’timeout’ period can not be specified for Suspended tasks.
Each task is assigned a priority ranging from 0 to the maximal configured priority in FreeRTOS
configuration file. Low priority numbers denote low priority tasks, idle task priority is by default
defined to be 0.
The scheduler will ensure that a task with higher priority in the Ready or Running queue will
always be given processor time in preference to tasks of lower priority that are also in the same
queues. In essence the tasks given the processing time will always be the highest priority task
available for execution. Only one task can be in the running queue at a given time. If there are no
tasks ready to run, FreeRTOS makes a special task running, namely the idle task. The idle task has
the lowest priority. This task can be used to perform power management as it is running only when
there is no other task available.
The scheduler can be configured as preemptive or collaborative.
5.1.2
Inter-task Communication
FreeRTOS provides various mechanisms for inter-task communication, including message queues
and binary semaphores. The Queue mechanism can be used to send messages between tasks, and
between interrupts and tasks. A queue is a structured table, used to store and retrieve data, created
in the heap. It can be used by two tasks to send data between each other. Tasks and Interrupt
Service Routines (ISR) can also communicate through queues. For example a task can send a byte
in a queue and this byte can be later accessed by another task. In most cases these queues are used
as FIFO (First In First Out) buffers with new data being sent to the back of the queue. Queues
contain items with a fixed size. Items are placed into a queue by copy, not by reference.
Binary semaphores in FreeRTOS are used for both mutual exclusion and synchronization purposes. They are actually implemented as a special case of queue, i.e. a queue with one element. On
CHAPTER 5. DEVELOPMENT ENVIRONMENT
38
initialization the semaphore queue is full. The first task executing a section of mutual code takes
the semaphore. Any other task willing to execute this code will wait until the semaphore is released.
A task trying to receive a byte from an empty queue or willing to send a byte in a full queue will
be blocked by the kernel. A task decides the maximum time it allows the kernel to block. If a queue
becomes available within that time, the kernel will wake up the and run the task with the highest
priority. If the queue stays busy and maximum blocking time elapses, the kernel will get the task
ready again and return an error to it.
5.1.3
Memory Management
FreeRTOS provides three memory allocation schemes to allocate memory each time a task, queue
or semaphore is created.
• The first scheme is simplest of all schemes, it does not allow memory to be freed once it
has been allocated. A huge table in the memory is reserved, namely the heap. Every time
the memory allocation system call is used, the pointer for free space is incremented with the
allocation size and a pointer is returned to the application. The memory freeing call simply
does nothing.
• The second scheme is a more complex memory allocation system. It uses best fit algorithm
but it does not combine adjacent free blocks into a single block. It however allows previously
allocated blocks to be freed.
• The third scheme is merely a wrapper for standard memory allocation and free functions. This
scheme is not deterministic as well and may increase the kernel code size.
In our application, the first memory management scheme was chosen. This was done to avoid
the hassle of a garbage collection algorithm and to keep things simple. Moreover, our application
does not require memory freeing.
5.2
SAND Node
SAND (Small Autonomous Network Devices) is a low power and small size reconfigurable hardware
platform with a CoolFlux DSP [10]. CoolFlux is a 24-bit ultra low-low power, embedded DSP core,
originally developed for audio applications with low power requirements.
Programs for CoolFlux are compiled using CHESS Retargetable Compiler by Target Compiler
Technologies.
CHAPTER 5. DEVELOPMENT ENVIRONMENT
5.3
39
BSN Node
BSN (Body Sensor Network) Node is a hardware platform with an MSP430 microcontroller with a
CC2420 radio chip [8]. It provides a low-powered, miniaturized, stackable platform for the design and
development of pervasive health care applications and sensor networks. It may optionally contain
physiological sensors such as ECG, EEG, Sp02.
The version of BSN nodes in use are v2 and v3. Like predecessor these nodes are based on
an MSP430 microcontroller variant. However this new microcontroller has more resources. It has
10KB RAM and 48KB Flash Memory. It has two built-in 16-bit timers, two universal serial synchronous/asynchronous communication interfaces (USART) and 48 I/O pins.
Figure 5.1: SAND Node and BSN Node
5.4
MSPGCC
The source code for the BSN node is compiled using the MSPGCC compiler. MSPGCC is a port
of the GNU C and assembly language tool chain to the Texas Instruments MSP430 family of lowpower microcontrollers. The MSPGCC port of the GNU C compiler used in our project is based on
version 3.2.3 of GNU GCC. A FreeRTOS port for MSPGCC was used in our project. This version
of MSPGCC supports optimization for code size reduction. It supports all the current variants
of the MSP430 processor, and comes out with a full set of header files for the processors. Signed
and unsigned integers of 8, 16, 32 and 64 bit length are supported. Currently only the C language
is supported. Within Windows NT/XP environment, MSPGCC was run inside a Cygwin shell.
Cygwin is a Linux-like environment for Windows. It consists of two parts:
• A DLL (cygwin1.dll) which acts as a Linux API emulation layer providing substantial Linux
API functionality.
• A collection of tools which provide a Linux look and feel
CHAPTER 5. DEVELOPMENT ENVIRONMENT
40
Complete development in this assignment was done using MSPGCC compiler within the Cygwin
environment.
5.5
Debugging and Visualization
The debugging and visualization was done using two different techniques, which are as following:
• These nodes can be communicated from PC via Hyperterminal. This can be done using one
USART of the MSP430 microcontroller. Data in the form of text strings can be sent to these
nodes and vice versa. Hence for debugging purpose a variety of text strings were used which
were sent by the node to the user PC and later printed on the Hyperterminal. A unique code
is assigned to every error and these codes can be sent in case an error is produced. This
debug functionality induces an overhead on the code size but it can be removed from the final
application.
• A packet sniffer was used to visualize packets transmitted using the nodes. Chipcon CC2420DK
contains this functionality. When a packet is transmitted over a preset radio channel, the sniffer
is tuned to this channel and it can visualize the packet and its details. Therefore using this
packet sniffer and transmitting packets when needed, visualization of errors was made possible.
Chapter 6
Implementation
Philips Lighting is investigating the possibilities and the impacts of the IP based networking in the
lighting networks. Wireless networks have their limitations regarding packet size, power and MTU.
Therefore an adaptation was required to implement IP functionality in wireless networks. This was
done in the form of a 6LoWPAN stack.
Within Philips Research, a 6LoWPAN stack was developed for the SAND platform[10]. These
nodes have more RAM and code memory than the BSN nodes[8]. The stack supports DYMO-LOW
[17] routing protocol, which is a mesh-under routing protocol. This means it utilizes link layer
addresses for routing. It was developed for FreeRTOS environment and Chipcon MAC. The first
part of this assignment dealt with the porting of the code from SAND platform to BSN.
To successfully do the porting of the code to the target platform, first the knowledge of existing
architecture was required.
6.1
Pre-porting Analysis
Before porting the code to the BSN node, first an analysis and thorough understanding of the existing
code was carried out. The code consists of the following main parts. The directory structure of the
code is given in Figure 6.1.
6.1.1
The 6LoWPAN Stack
This section contains the core functionality of 6LoWPAN. It contains all the header and source files
required for packet compression, fragmentation and routing according to DYMO-LOW [17]. The
stack will be discussed in more detail in section 6.2.
41
CHAPTER 6. IMPLEMENTATION
42
Figure 6.1: Directory Structure of the Code
6.1.2
FreeRTOS
This module holds the FreeRTOS header and source files. This module consists of common files
used by all ports and port specific files.
6.1.3
Drivers
The drivers section contains the source files for the Timer, SPI and UART drivers.
6.1.4
MAC
The MAC section contains the header files and source files by Chipcon, necessary for MAC communication. It also contains the Hardware Abstraction Layer (HAL). The application and the operating
system do not need to know about the hardware. The functionalities of hardware are provided by
standard functions through the HAL. HAL is a platform specific layer. The structure of MAC is
given in Figure 6.2.
After familiarizing with the code structure, it is necessary to understand the different functionalities that code has to offer.
CHAPTER 6. IMPLEMENTATION
43
Figure 6.2: Driver Abstraction of CC2420
6.2
The 6LoWPAN Stack
From Figure 6.3 we can identify the main components of the 6LoWPAN stack. Since it is a layered
architecture, each layer’s functionality is contained in a different file.
Following are the details of different files available in the stack and their functionalities. Files
are named according to Figure 6.3.
6.2.1
sixLowPanLayer
This file is named after the 6LoWPAN adaptation layer itself. It contains the core of header compression and adaptation. It contains the functions to perform stateless address auto-configuration.
When a node boots up, it calls the function macToIpv6Translation() and passes its MAC address
as argument. The function returns a structure containing the link-local IPv6 address with prefix
FE80::/64. The remaining 64 bits are created by the PAN identifier and the short MAC address as
specified in [13]
On packet transmission this file adds the 6LoWPAN dispatch, LOWPAN IPHC and LOWPAN NHC.
Then it sends the packet to DYMO-LOW for routing the packet. On packet reception, depending on
the first byte, either this file handles the packet or it is processed by routingUnderIp and routingTable
using DYMO-LOW routing protocol. If sixLowPanLayer handles the packet, it processes mesh,
fragmentation and LOWPAN IPHC. A full IPv6 datagram is created by this layer and then sent to the
IP layer.
CHAPTER 6. IMPLEMENTATION
44
Figure 6.3: The 6LoWPAN Stack
6.2.2
ipv6Layer
This file contains the functions to process the IPv6 header. No functionalities were yet needed at
that stage so this file did not contain any extra functionalities.
6.2.3
udpLayer
This file contains the functions to handle the UDP transmission and reception. Upon transmission
it compresses the ports according to a specific format [11]. Upon reception it decodes the port values
and if they are similar, the payload will be delivered to the right socket where an application will
fetch it.
6.2.4
socket
This file contains basic socket functions like create and bind. With bind applications can bind
sockets to their IP address and application port number. This file also contains the code to initiate
transmission and reception from the udpLayer.
6.2.5
buffer
This file contains the functionality of creating a buffer, assigning buffers, writing data to them and
reading from them. These buffers are used by the socket interface as well as 6LoWPAN adaptation
CHAPTER 6. IMPLEMENTATION
45
layer to copy incoming packets from the MAC layer or the application layer and process them
throughout the stack. It uses the functionality provided by the underlying FreeRTOS kernel for
dynamic memory allocation.
6.2.6
routingUnderIp
This file contains the functionality of the packet transmission to the next hop according to the router
decisions, i.e. neighbor, not neighbor or even unknown route. If the packet size is greater than the
MTU, it breaks them down into fragments and transmits in successive link fragments.
6.2.7
routingTable
This file contains all the functions that are required to maintain the routing table. It contains
the core functionality of DYMO-LOW [17]. It handles Route Request and Route Reply messages,
updates routing table and checks the addresses in table to initiate Route Discovery.
6.3
Investigation Methodology
After familiarizing with the code structure, the next step was to find out the nature of the problems
that might arise. The list of these problems can be broken up into two categories.
1. Structural Issues
These are the issues that will be produced due to incompatibility of code and the new environment. The code will not effectively compile in this case.
2. Functional Issues
These are the issues that will be produced due to break up of code. The code will compile but
not work on the new platform, i.e. BSN nodes, as effectively as it is supposed to be.
Therefore to continue the investigation, the first aim was to compile the code with MSPGCC
without errors. After giving various errors and modifying code structure, code successfully compiled. At this stage, when it was possible to compile with new compiler, next aim was to test the
functionality of code against standard benchmark, i.e. a demo application that is shipped with
FreeRTOS.
During this phase various minor and major errors were found and handled. More detail of such
issues is given in Appendix D.
6.4
6LoWPAN Stack Extension
After the porting of code, the next step was to improve the compliance of the stack with the draft
[11]. The original code had limited functionality of the 6LoWPAN adaptation layer. It could not use
CHAPTER 6. IMPLEMENTATION
46
128-bit IPv6 addresses, i.e. there was no activity on the IPv6 layer. In this phase of the project, the
functionality of the IPv6 layer and the ICMPv6 layer on top of the adaptation layer was improved.
6.4.1
6LoWPAN Adaptation Layer
In the original implementation, the LOWPAN IPHC header always contained the compressed addressing
scheme. This limited the transmission of packets to within 6LoWPAN since all 128-bits of the
source address and all 128-bits of the destination address were elided. In order to transmit messages
outside 6LoWPAN, through the Edge Router, complete address support was required. During this
assignment, this support was added. Now in case the destination is outside 6LoWPAN then the full
128-bit address is carried inline. In case if the destination is within 6LoWPAN, IPv6 addresses are
elided. Short link layer addresses are used for routing in this case.
The procedure is as follows:
• When a UDP packet is created by the application layer, the destination address is passed as
an argument in a function call made to the udpLayer via socket. The udpLayer creates a
HC UDP2 header and after compressing ports and writing into a buffer, it passes the pointer
to the buffer to the ipv6Layer. The ipv6Layer in this scheme does not do anything but instead
it passes the pointer to the sixLowPanLayer which then checks the destination address. If the
destination address is within 6LoWPAN, 128-bit addresses are not used. If the destination
address is outside 6LoWPAN, it changes the header format for this packet (LOWPAN IPHC).
The IPv6 address of the destination is added to the packet and the value is indicated in
the header. Then sixLowPanLayer forwards this packet to the routingUnderIp, the mesh
destination address is the short address of the Edge Router.
• Upon reception of a packet, first it is checked whether it is a routing packet or a 6LoWPAN
data packet. This is done by comparing the first byte, the dispatch byte with a set of values. If
it is 6LoWPAN packet, the pointer is given to sixLowPanLayer. First it is checked that what
is value of LOWPAN IPHC. If it denotes that a 128-bit host address is carried, it is extracted from
the packet and an IPv6 datagram is created from that packet. If a short address is carried,
then the IPv6 address is created from the short address. An IPv6 datagram is constituted
from these autoconfigured addresses and this datagram is passed to higher layers.
An example of a UDP packet over 6LoWPAN is depicted in Appendix B.2. The above procedure
is also depicted in Figure C.1.
6.4.2
ICMPv6 Layer
In the original implementation, ICMPv6 only contained support for ECHO REQUEST and ECHO
REPLY [18]. Neighbor Discovery in IPv6 is done via ICMPv6 messages. Therefore these messages
CHAPTER 6. IMPLEMENTATION
47
were added and Neighbor Discovery support was added. The procedure of ICMPv6 message parsing
is as follows:
• When an ICMPv6 packet is created by icmpv6Layer, it is sent to the ipv6Layer. Creation
of ICMPv6 packet is done on a trigger from the application layer, a timer expiration or on
start up, depending on the nature of the packet being created. Along with existing support
for ECHO REQUEST and ECHO REPLY, support for the following ICMPv6 message types
is provided.
1. Router Solicitation
2. Router Advertisement
3. Node Registration
4. Node Confirmation
The above mentioned messages are used for Neighbor Discovery. Also support is provided for
parsing options which are as follows:
1. Address Option
2. Owner Interface Identifier Option
3. Prefix Summary Option
• When a packet is received at sixLowPanLayer, it is checked whether it is an ICMPv6 packet or
a UDP packet. If it is an ICMPv6 packet, it is sent to icmpv6Layer. This layer then processes
the packet, starting from the type of message. Upon finding out the type of message, respective
actions are preformed on this packet, ranging from the indication to the application layer to
silently dropping the packet.
An example of an ICMPv6 packet is given in Appendix B.3.
6.5
UDP Chat Application
The functionality of 6LoWPAN stack was checked with a UDP chat application. This application
requires minimum of two nodes, namely client and server. A user sends a message from client node
and the message is echoed back from the server application. The resulting message is shown on the
screen. The communication with the client node is done via Hyperterminal.
6.5.1
Operation
Initially two nodes (client and forwarder) are powered. The server node is not powered up.
The client node, running TestSixLowPanClient application is connected via UART to a PC. The
CHAPTER 6. IMPLEMENTATION
48
application starts with a fixed client and server address. After initialization, it waits for user input
via Hyperterminal. When user enters a character string, application copies it into a buffer. When
user enters a carriage return (Enter key), the buffer is forwarded to the udpLayer through socket
interface for further processing and transmission to the server. The udpLayer adds compressed
ports and LOWPAN UDP header and forwards the packet to the ipv6Layer, which in this case
does not add ip addresses as short link layer addresses are used. The packet is then passed to the
sixLowPanLayer, which add the LOWPAN IPHC header and dispatch. It sends the packet to the
routingUnderIp layer, which checks if the destination is known or not. In first transmission the
destination is not known and through routingTable a Route Request is generated. The packet is
meanwhile saved in a structure. After receiving Route Response and therefore a valid route to the
destination, the client node transmits the packet. Route Request is done over broadcast, while Route
Reply is via unicast.
When server node, running TestSixLowPanServer application receives the packet, it first checks if
it is a valid 6LoWPAN packet or not. If it is a 6LoWPAN packet, it is forwarded to sixLowPanLayer.
In this layer first dispatch byte is checked. After verifying that the packet is destined to this specific
node, an IP datagram is reconstructed. Based on the header values, this layer sets the values of the
IP datagram. Afterwards, the buffer is forwarded to ipv6Layer. Which in this particular application,
forwards to udpLayer. Compressed ports are extracted from the packet and the payload is copied
to the application via the socket interface.
This application can be tested on single hop or multiple hop. For multi-hop chat application,
another node is required which runs TestSixLowPanClient. This node receives the packets and just
forwards to the destined location. This forwarding is done below sixLowPanLayer.
The procedure can be seen in Appendix C.
6.6
WASP Demonstration
In this demonstration, an application based on the Event-Condition Action (ECA) programming
model was to be deployed on the BSN nodes with 6LoWPAN support. These nodes must be able
to communicate to the Edge Router. From Edge Router they can communicate to the Server over
IPv6 link.
The network consists of an Edge Router, implemented on a PC and equipped with a USB 802.15.4
dongle and several BSN nodes. The devices form a mesh network based at 802.15.4 MAC layer.
Within this mesh, the routing is done using DYMO-LOW.
On the BSN node side, the stack contains UDP and ICMP functionality. This stack allows
following tasks.
• Router Discovery using Neighbor Discovery Protocol
• Prefix assignment and global address assignment using Neighbor Discovery Protocol
CHAPTER 6. IMPLEMENTATION
49
• Ping application using ICMPv6
• UDP communication within 6LoWPAN using short link layer addresses. When addressing
outside 6LoWPAN, the stack uses full IPv6 address for the destination.
• Mesh-under routing using DYMO-LOW.
This stack does not support fragmentation for this particular demonstration. The fragmentation
support was removed to reduce code size, after assessing that it will not be utilized in this demonstration, since the message size will never exceed MTU. The network and software architecture of
this demonstration is shown in Figure 6.4. On the PC side, 6LoWPAN stack is integrated into the
Figure 6.4: Network and Software Architecture of 6LoWPAN
Windows OS through a kernel module implementing a driver that acts as Virtual Network Interface
CHAPTER 6. IMPLEMENTATION
50
Card. The communication to the mesh network from the PC is done through an 802.15.4 dongle
connected to a USB port.
When a new BSN node boots within mesh, it either waits for a Router Advertisement or sends
a Router Solicitation message to an Edge Router. On reception of Router Solicitation, the Edge
Router replies with the Router Advertisement, with the prefix option, as explained in Section 4.9.
The node receives the Prefix in Router Advertisement, configures it global address and sends Node
Registration message, with the address option containing the globally unique address for the node.
The Edge Router replies with a Node Confirmation message. After Node Confirmation, the BSN
node can communicate with external IP networks using its unique address, through Edge Router.
This procedure is shown in Figure 6.5.
Figure 6.5: BSN Node and PC Interaction
This ECA based application required support for UDP data transfer and Neighbor Discovery.
However the size of this application was 13K and there was not enough space available on these
nodes. To overcome this problem, the functionality of these nodes was reduced to the requirements
of the specific application.
CHAPTER 6. IMPLEMENTATION
6.6.1
51
Code Size Reduction
Table 6.1 depicts the code memory utilization of various aspects of the code. If the complete MAC
is compiled along with the complete 6LoWPAN stack, there will not be any space left for the
application on top of it. Therefore it is a big challenge to provide 6LoWPAN stack support for an
application with required functionalities. To do so, a number of design decisions were taken which
are as follows.
• A node can have a pre-programmed short address and PAN ID. Therefore PAN coordinator
support is not required. Moreover support for PAN association and disassociation is also not
required. Therefore this code can be stripped from the MAC code.
• The network is beaconless, so all the MAC code that supports beacons is stripped off as well.
• The size of packets being communicated is almost never more than MTU. Hence support for
fragmentation is not required in this implementation. The related code was removed to save
almost 1500 bytes.
• Debug support is not required for nodes in the field. Therefore all related debug code is also
not included in the build. Almost 900 bytes are saved in this process.
Due to the above modifications, the code size reduction to 35KB was possible.
Table 6.1: Memory Utilization on BSN Node
Code
FreeRTOS, Peripheral Drivers, MAC and Idle task
FreeRTOS, Peripheral Drivers, MAC and MAC test task
FreeRTOS, Peripheral Drivers and Idle Task
FreeRTOS and Idle Task
MAC and HAL (Original Size, with Beacon and PAN association )
6LoWPAN Stack (Original Size, with Fragmentation and debug)
MAC and HAL (without Beacon and PAN association)
6LoWPAN Stack (without Fragmentation)
FreeRTOS, Peripheral Drivers, MAC and 6LoWPAN (Final Version)
Size (Bytes)
36740
36744
13792
4330
22900
10000
16000
7300
35358
Chapter 7
Self-powered Switch and Sensors
A migration from a wired communication system to a wireless communication introduces new and
different components. Wireless battery-less self-powered switches and sensors are among these.
Such a switch or sensor does not require batteries or any kind of external power. It operates on the
technology that converts the pressing action of the switch or sensor into a small amount of energy.
This energy can then be used by a radio transceiver to transmit a signal to a destination, carrying
commands and data. A piezoelectric conversion mechanism is used in this type of switches or sensor,
that when applied with force, produce voltage across the material. The battery free switches can be
used to control lights in home and any other on/off devices, including HVAC, security systems, fans
and any automation system that require pressing a switch. The wireless nature of these switches
allow freedom of mobility and flexibility.
Existing wired building automation systems do not share common physical medium or network
protocols. They are vertically isolated, meaning they do not have anything common on any layer.
Co-existence of such systems creates complex building networks, which are difficult to install, have
expensive cabling layout and are hard to maintain. Introducing a common physical medium and a
common network protocol will make the co-existence of such networks easily possible. Just sharing
a physical medium will reduce cabling costs and ease installation and maintenance.
Wireless building automation systems offer advantages over their wired counter parts. Firstly
these networks are retrofit, that means addition of new components to the existing infrastructure
is possible and much easier than wired networks. Secondly they reduce the cabling costs. In wired
networks, cabling is an expensive factor. In wireless networks one time commissioning is required.
In wired network, new devices require cabling as well, whereas in wireless, just placing new the
components within the existing system’s range will make connectivity possible. Also wired building
automation systems are influenced by the positioning of the cables. Devices can only be placed
where cables are laid. In wireless building automation systems, sensors can be placed with more
freedom.
52
CHAPTER 7. SELF-POWERED SWITCH AND SENSORS
53
IP as a common network protocol offers very promising role in the interoperability of the exiting
building automation systems. Seeing the merits of wireless building automation systems, Philips
Research is investigating the possibilities regarding IP over wireless networks for building automation systems. This leads to the investigation of 6LoWPAN, i.e. IPv6 over Low Power Wireless
Personal Area Networks. Self powered switches are investigated for their role in lighting networks.
This assignment led to the investigation of 6LoWPAN for lighting networks employing battery-less
switches.
7.1
Requirements
The requirements from a battery-less switch based setup in a lighting network are as follows.
• Luminaries should be able to join multicast groups when they want.
• Switch may be used to turn luminaries on and off.
• Luminaries can be accessed from outside the lighting network through Edge Router.
• Switch and luminaries may have unique IP addresses.
7.2
Procedure
In a 6LoWPAN enabled lighting network, to trigger the luminaries with a battery-less switch requires
the switch to be connected to a node. The node must have a radio transceiver and the 6LoWPAN
stack. The luminaries should also have the 6LoWPAN stack running on their controllers. For a
complete 6LoWPAN based lighting network, presence of an Edge Router is necessary. This Edge
Router will provide a prefix to the nodes within the 6LoWPAN mesh for globally unique ID.
When a switch is pressed, it will turn on the attached node for a short duration. In this time, the
node configures its link-local address, sends Router Solicitation to an Edge Router and upon receiving
Router Advertisement, it registers its globally unique IPv6 address at Edge Router Whiteboard via
Node Registration message. The Edge Router replies with the Node Confirmation message.
The luminaries should be able to join a well-known link-local multicast address. The Edge Router
should be able to identify the listeners to this multicast group and keep their record. This can be
done with MLDv1 [19] and MLDv2 [20] messages. Whenever an Edge Router sends a multicast
listener query, luminaries interested in joining the group respond with the multicast listener report.
After configuration of globally unique IPv6 address, the switch can send messages to the luminary
multicast group via Edge Router. The message sent to the specific multicast group should be
forwarded by the Edge Router to all the luminaries that are subscribed to that address. Luminaries
can join or leave a multicast group at any time. The procedure is depicted in Figure 7.1.
CHAPTER 7. SELF-POWERED SWITCH AND SENSORS
54
Figure 7.1: Battery-less Switch Based Lighting Network
The above setup is explained for a proposed case when there are no timing constraints due to
the limited energy produced by switch. In such case, the switch can save the acquired values to flash
memory and turn off. When starting up next time, it will read values from the flash memory and
skip the registration process. This is however not possible yet. As we will see there are limitations
due to little amount of energy produced by switch.
While within a subnet, where neighborhood discovery is not required, above scenario can be
replaced by one given below.
• The switch is pressed.
• The node turns on and sends a Route Request broadcast message for a well known destination.
• Using Route Reply, it finds the route to the luminaries.
• The node then, using the discovered route, transmits the control signal (turn on/off) to the
luminary.
• The luminary node acknowledges the reception of control signal.
• In case the acknowledgment is not received, the switch node does multiple retries to transmit
that control signal as long as the node stays on.
CHAPTER 7. SELF-POWERED SWITCH AND SENSORS
55
Figure 7.2: Battery-less Switch Circuitry
The luminaries know their existing states. Whenever they receive a message, they toggle their
state. e.g. if a luminary is ON and it receives a control signal from the switch, it will turn OFF
and vice versa. The above setup is used in this assignment, i.e. Edge Router is not used in lighting
network. Therefore Neighbor Discovery is not implemented on switch based nodes due to the energy
and timing constraints, which will be discussed later in this chapter.
The battery-less switch is shown in Figure 7.2, where it is connected with AquisGrain 2 module.
This switch was also connected with MSP430 nodes for separated testing. An oscilloscope was
connected to the ports available on MSP430 and AquisGrain nodes for timing measurements. At
various points of interest, these ports were given high or low output. This output was measured
using oscilloscope and later analyzed.
7.3
Problems
The main issue with such implementation is that such type of switches provide very little energy.
This energy is in the range of millijoules. Therefore a series of packet transmission which is spread
over long time is not feasible. In our case the switch was able to provide 30mA @ 3.3V for more or
less 60 ms, depending upon how far it was pressed. Which results in total of 5.94 mJ energy.
Booting the BSN node running FreeRTOS and using its radio requires around 45ms. When a
node boots up, it does standard reset procedure, which is responsible for following tasks.
• Providing a default vector table
• Providing default interrupt handlers
• Initializing the watchdog timer
CHAPTER 7. SELF-POWERED SWITCH AND SENSORS
56
• Initializing the .data segment
• Initializing the .bss segment
• Jump to main
A jump is used in the last phase, instead of a call to main, to save space on the stack. Since
main is not supposed to return.
Every MSP430 device has its interrupt vectors table located at 0xffe0. This table looks like as
follows.
Disassembly of section .vectors:
0000ffe0 <InterruptVectors>:
ffe0: 3a 40
interrupt service routine at 0x403a
ffe2: 3a 40
interrupt service routine at 0x403a
ffe4: 9c 64
interrupt service routine at 0x649c
ffe6: 42 64
interrupt service routine at 0x6442
ffe8: e4 bc
interrupt service routine at 0xbce4
.
.
fff8: ba bd
interrupt service routine at 0xbdba
fffa: 12 bd
interrupt service routine at 0xbd12
fffc: 3a 40
interrupt service routine at 0x403a
fffe: 00 40
interrupt service routine at 0x4000
The reset vector
is located at address 0x4000. Whenever execution begins, the PC is loaded
with this address.
Disassembly of section .text:
00004000 <_reset_vector__>:
4000: b2 40 80 5a
mov #23168,&0x0120 ;#0x5a80
4004: 20 01
.
.
4020: 3f 40 7a 11
mov #4474,r15
;#0x117a
4024: 3d 40 fe 32
mov #13054,r13
4028: 0d 9f
cmp r15,r13
402a: 05 24
jz $+12
402c: cf 43 00 00
mov.b #0,0(r15) ;r3 As==00
4030: 1f 53
inc r15
;#0x32fe
;
;abs 0x4036
;
CHAPTER 7. SELF-POWERED SWITCH AND SENSORS
4032: 0f 9d
cmp r13,r15
4034: fb 2b
jnc $-8
4036: 30 40 40 40
br #0x4040
57
;
;abs 0x402c
;
00004040 <main>:
As a first step of the startup, the watchdog timer is initialized. Then the initialized global
variables are copied to RAM. After this the uninitialized global variables are cleared, i.e. put 0 as
their value. In the above excerpt from the application with an uninitialized data size of 8580 bytes,
we can see that all these bytes are initialized with 0.
Firstly the start and the end of the data are stored into two different registers, namely r15 and
r13 respectively. Then on every address contained in register r15, a 0 is copied. Afterwards this
address is incremented and compared with the maximum address. As long as current address does
not increase than the maximum, this loop continues. When this address increases beyond maximum
address, a flag is set and loop terminates. After this a jump to main is performed. In above case
main is located at 0x4040.
From above we can see that program startup depends heavily on the size of the initialized and the
uninitialized data. In our application, the heap size is set to 6000 bytes. This heap is used for dynamic
memory allocation for queues, tasks and semaphores. Due to this big size of heap, i.e. uninitialized
data, the startup time is increased - since during this phase, this memory is initialized with zeros. A
reduction in heap size leads to reduced startup time but it leads to abnormal application behavior.
After startup, Route Discovery takes a considerable amount of time (up to 100-200 ms) depending
on the response by different nodes in the network. This does not give us time to do useful transmission
of control packets. Therefore it was decided that for the demonstration of such a network, any node
capable of broadcasting a control packet when switch is pressed will do the job until the switch energy
output and BSN node boot-up time is reduced. The AquisGrain2 was used for above purpose.
This AquisGrain node is not running any RTOS. Instead it runs an application that transmits
packets in a specific format, satisfying requirements for UDP transmission over 6LoWPAN. The
MAC is provided by Chipcon. The recipient on the other hand, is a BSN node with a functional
6LoWPAN stack, FreeRTOS and Chipcon MAC. It will receive the packet and parse it accordingly.
In this case, it will trigger the lights whenever it receives a packet, based on its MAC address.
The switch is assigned to a specific luminaries, i.e. the address and PAN ID are fixed. In this
demonstration, an LED was soldered to the MSP node, therefore denoting the reception of the
packet.
CHAPTER 7. SELF-POWERED SWITCH AND SENSORS
7.4
58
Acknowledgment Requirements
Originally it was considered that a luminary upon reception of a packet, transmits an acknowledgment to the switch. This can be an application level or a MAC level acknowledgment. An application
level acknowledgment can be single hop or multi-hop. A MAC level acknowledgment is only single
hop. The acknowledgment is used to indicate successful transmission of packet. Following cases
arise when we consider the acknowledgment scenario.
• As of now, there is no way a switch can indicate the successful transmission of a packet to the
user. If it is successful, the luminary will turn on. If it is unsuccessful, the luminary will stay
off.
• If the transmitting node connected to the switch does not receive the acknowledgment, all it
needs to do is to retransmit same packet for a preset number of times.
• The waiting for acknowledgment takes a considerable amount of time, depending on factors
like number of hops and whether the MAC layer acknowledgment is sufficient or the application
layer acknowledgment is required. Following observations were made in this regard.
– MAC acknowledgment takes on average 2.7 ms in our set up.
– An application level acknowledgment takes on average 30 ms for one hop.
• During this waiting time, the switch is consuming precious energy, generated for a short time
and in a small quantity.
Considering above, we’ll have a look at two scenarios for the transmission of a packet.
• Successful Transmission - the luminary will turn on or off, no further evidence is required by
the user.
• Unsuccessful Transmission - the luminary state will remain the same. In this case the switch
will wait for the acknowledgment. In case there is no acknowledgment, the switch will retry
to send same packet.
It was decided that instead of waiting for acknowledgment, the sending node should send multiple
copies of same packet as many times as possible during the time it is powered on. This will ensure
the best possible results for transmission of one single packet. The receiver drops copies of same
message received within a fixed period of time.
7.5
Timing Results
Due to the timing constraints of the switch, both platforms i.e. MSP430 and AquisGrain were
benchmarked for two different applications. The timing measurements were taken using oscilloscope.
The results are discussed separately for both platforms.
CHAPTER 7. SELF-POWERED SWITCH AND SENSORS
7.5.1
59
MSP430 Timing Results
The UDP chat application timing was measured on MSP node. The timing results are depicted in
Figure 7.3.
Figure 7.3: MSP430 Timing Results
The details are as follows.
1. FreeRTOS startup and led = 85 ms
2. Route Request and Route Reply = 172 ms
3. Sending Packet = 102 ms
4. Packet Reception wait = 70 ms
5. Delay = 1000 ms
6. Route Request and Route Reply = 162 ms
7. Sending Packet = 138 ms
8. Packet Reception wait = 50 ms
7.5.2
AquisGrain2 Timing Results
The simple application running on AquisGrain does not take too much time to start up. Also the
processing does not take much time as well. Detailed timing results for the AquisGrain application
for first packet generation are given in Figure 7.4.
1. Button press to Led on = 1900 us
2. MAC Init() = 174 us
3. Radio Power Up() = 1355 us
CHAPTER 7. SELF-POWERED SWITCH AND SENSORS
60
Figure 7.4: AquisGrain 2 Timing Results
4. Reset MAC layer = 1075 us
5. Start as PAN coordinator (set PIB attributes) = 267 us
6. Send one packet = 253.6 us
The total time it takes from pressing the switch till first packet transmission is 5024.6 us.
7.5.3
Timing Analysis
The results from both nodes cannot be compared directly since both applications are different in
nature. Still it is evident that AquisGrain startup time and initialization time is quite promising.
Absence of FreeRTOS has an impact on these results. In MSP430 the timing results were not exactly
same on both occasions. The sending time of packet varied in both recorded tries. This difference
can be caused due to unavailability of channel. There is no stack used on AquisGrain. It runs a
simple C application on top of Chipcon MAC. The addresses and PAN ID are preset. These factors
contribute to the fact that within 5 ms we can transfer a packet to the luminary. In this case switch
does not wait for response from the luminaries. In case the response is expected from application
layer, it can take up to 50 ms. A link layer acknowledgment on the other hand, only takes 20 ms.
7.6
Conclusion
Due to the limited amount of current produced during the pressing action, it is difficult to operate
a fully functional node running an operating system with this energy. The start up time should be
minimized to utilize the energy harvested for actual transmissions. This can be achieved by using
tailored application for transmission of packets. The application on AquisGrain does not process
IPv6 packets. It can receive packets but it is not supposed to perform any action. The switch
CHAPTER 7. SELF-POWERED SWITCH AND SENSORS
61
is not given any processing tasks yet. In practical cases such switch will be utilized for only one
way communication to the luminaries. The messages sent from the switch have fixed destination
addresses, i.e. luminaries addresses are known in application. Luminaries are running full 6LoWPAN
stack, so that they can communicate with switches as well as nodes on external IPv6 network, using
Edge Router. So it is possible to monitor and control the luminaries from out side the LoWPAN,
since each luminary, when starts up for the first time, configures a link-local and a global address
as well. UDP messages sent from the switch are static, the luminaries toggle on every new message.
It is the responsibility of the luminaries to save the last state, ignore repetitive messages sent by
same switch and toggle only on new messages. The acknowledgments at the MAC level should be
sufficient for link level recovery of messages. In this scenario a fully functional 6LoWPAN stack that
supports ICMPv6 and the reception of UDP messages is not required. Moreover fragmentation is
also not utilized in this simple application. The MAC will not be required to perform power saving
as it will be only turned on when the switch is pressed, for a very short duration. Therefore above
application sufficed for IPv6 based addressing over wireless. Mesh-under routing suffices for such
example as a switch will only be able to access its link-local neighbors. If accessed from outside, the
Edge Router can translate from router-over routing to mesh-under routing.
In a real-world example, a switch should not have a fixed destination address since this will limit
the design options. The switch should find its neighbors using Neighbor Discovery Protocol via
Neighbor Solicitation and Neighbor Advertisement messages. These neighbors should be grouped
into multicast addresses based on the services they offer. The switch should address one of these
multicast addresses whenever pressed. Another possibility is that a fixed coordinator node is installed
in such system. This node keeps track of all the nodes in neighborhood, when a switch node turns
on, it detects this node and exchange the addresses of luminaries. These addresses can be used to
communicate with one of many luminaries. In order to make the switch address configurable using
Neighbor Discovery, the platform needs to be optimized for the harvested energy on pressing action.
The coordinator keeps track of all the switches in neighborhood as well as the luminaries.
Chapter 8
Conclusion
IP over Low Power Wireless Personal Area Networks is made possible through 6LoWPAN. It offers
new possibilities for networking, especially in Building Automation Systems. As first and second
objective of this thesis, the 6LoWPAN stack was ported to MSP430 based BSN nodes. Moreover,
additions were made into the existing stack according to the proposed standard draft [11].
The 6LoWPAN stack supports UDP and ICMPv6 messaging. Two different applications for
UDP and ICMPv6 were tested for proper functionality. Code size was reduced by stripping off
functionalities surplus to our requirements. Changes in the existing stack were done to improve
performance in terms of primary memory and code memory usage.
As a third objective Neighbor Discovery was implemented on the nodes as part of ICMPv6
messages. This implementation was done for simple LoWPAN; therefore Neighbor Solicitation and
Neighbor Advertisement messages were not included. In essence this implementation does router
discovery and prefix assignment. Although it has support for message parsing and options analysis,
such functionality is not required in our current configuration as of now.
As a further step, a battery-less switch based demonstration was carried out for lighting networks
which operate on IP addresses. Different challenges were faced during this phase, which are explained
in chapter 7 and how they were tackled. Finally, support was given for WASP demonstration by
providing IPv6 stack integration into WASP network and testing required functionalities.
Although 6LoWPAN has introduced a way to improve flexibility and scalability in communication, it also imposes various restrictions and has pit falls. Points raised during this project were
memory usage and code size. As already mentioned in chapter 6, the code size was reduced at
the cost of some MAC functionalities. If we have a fully functional MAC, then it is difficult to
implement an application utilizing 6LoWPAN stack even on a resource rich MSP430F1611 microcontroller based BSN node. Also memory utilization is another bottleneck. Typical nodes do not
have memory specifications as high as nodes in our use. Therefore if we need a 6LoWPAN based
network we need nodes with at least 10K RAM. Moreover the standard is still evolving so there will
62
CHAPTER 8. CONCLUSION
63
be more additions to the existing stack. Because of that even more resources will be required.
In the end, this will be decided by the network architect whether to use 6LoWPAN connectivity
or not. If it is required, more expensive nodes will be used.
Appendix A
Header and Frame Formats
A.1
IPv6 Header
The header format is as below.
0
1
2
3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| Traffic Class |
Flow Label
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
Payload Length
|
Next Header
|
Hop Limit
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|
+
+
|
|
+
Source Address
+
|
|
+
+
|
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|
+
+
|
|
+
Destination Address
+
|
|
+
+
64
APPENDIX A. HEADER AND FRAME FORMATS
|
65
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The details of these fields are given in Table A.1.
Field
Version
Traffic Class
Flow Label
Payload Length
Next Header
Hop Limit
Source Address
Destination Address
Table A.1: IPv6 Header
Meaning
4-bit field is set to be 6
8-bit field - To identify between
different classes and priorities
20-bit field - To identify between normal
and special QoS handling of packets
16-bit field - Length of IPv6 payload
8-bit field - Identifies type of next header
8-bit field - Decrements every time a packet is forwarded
128-bit address - Originator IPv6 address
128-bit address - Destination IPv6 address
APPENDIX A. HEADER AND FRAME FORMATS
A.2
LOWPAN IPHC Details
Subfield
T
Definition
Traffic Class
VF
Version and
Flow Label
NH
Next Header
HLIM
Hop Limit
rsv
SAM
Reserved
Source
Address
Mode
SAC
Source
Address
Context
Destination
Address
Mode
DAM
DAC
66
Destination
Address
Context
Table A.2: LOWPAN IPHC Encoding
BitN o.
V alues
Meaning
0
0
Full 8-bits carried in-line
1
Elided, implicitly 0
1
0
Full 4 bits for Version
and 20 bits for Flow Label carried in-line
1
Elided, Version is 6 and Flow Label is 0
2
0
Full 8 bits for next header carried in-line
1
Next Header compressed using LOWPAN NHC
3-4
00
All 8-bits of Hop Limit carried in-line
01
All 8-bits elided, Hop Limit assumed to be 1
10
All 8-bits elided, Hop Limit assumed to be 64
11
All 8-bits elided, Hop Limit assumed to be 255
5-7
Reserved for Future use
8-9
00
All 128 bits carried inline
01
64-bit compressed IPv6 address
10
16-bit compressed IPv6 address
11
All 128 bits are elided
10-11
00
Source Address is a link-local address
other values Reserved
12-13
14-15
00
01
10
11
00
other values
All 128 bits carried inline
64-bit compressed IPv6 address
16-bit compressed IPv6 address
All 128 bits are elided
Destination Address is a link-local address
Reserved
APPENDIX A. HEADER AND FRAME FORMATS
A.3
LOWPAN UDP Details
Subfield
S Source Port
D Destination Port
Table A.3: LOWPAN UDP Encoding
BitN o. V alues Meaning
0
0
Not compressed, all 16 bits carried inline
1
Compressed to 4 bits. The actual source port
is calculated as 0xF0B0 + short port value
4 bit short port value is carried inline
2
0
Not compressed, all 16 bits carried inline
1
Compressed to 4 bits. The actual destination port
is calculated as 0xF0B0 + short port value
4 bit short port value is carried inline
67
APPENDIX A. HEADER AND FRAME FORMATS
A.4
68
Node Registration/Confirmation
The message format is as below.
0
1
2
3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
Type
|
Code
|
Checksum
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
TID
|
Status
|P|
Reserved
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
Lifetime
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
+
|
Owner Interface Identifier
|
+
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
Owner Nonce
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
Registration option(s)...
+-+-+-+-+-+-+-+-+-+-+-+-+-+
The ICMPv6 packet fields are as follows.
• Type: Type is not defined in the draft yet. However provisional values are set within this
project. 200 for NR and 201 for NC.
• Code: Code is 0 if it is a direct message from a node to an Edge Router. It will be set to 1
when the message is relayed. Other values indicate error types.
• Checksum: The ICMP checksum is included in this field.
• TID: A unique Transaction ID for a Node Registration. When a node boots up, TID is set to
0 and increments with every NR message. When it reaches 0xFFFF, it is reset to 16. Values
from 0-15 are only used after first boot.
• Status: Values to be decided, 0 means success.
• P: 1 bit flag, set to denote that the router is the primary router of node.
• Reserved: Unused field, must be initialized with 0 and ignored at receiver’s end.
• Lifetime: A 32-bit integer, denoting the amount of time in seconds remaining before the binding
expires.
APPENDIX A. HEADER AND FRAME FORMATS
69
• Owner Interface Identifier: A globally unique identifier for requesting node’s interface.
• Owner Nonce: An Owner Nonce is a 32-bit number randomly generated by the node upon
booting and generated again each time the node re-boots. This number is used by Edge
Routers to detect duplicate Owner Interface Identifiers. It stays same as long as node stays
on, and is used to identify rouge or counterfeiting nodes.
• Options: Possible options include Address Option, for each address the node wants to bind.
APPENDIX A. HEADER AND FRAME FORMATS
A.5
70
Router Solicitation
The message format is as below.
0
1
2
3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
Type
|
Code
|
Checksum
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
Reserved
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
Options ...
+-+-+-+-+-+-+-+-+
The ICMP fields for this message are as follows.
• Type: Type is set to 133.
• Code: Code is 0.
• Checksum: The ICMP checksum.
• Reserved: Unused field, must be initialized with 0 and ignored at the receiver’s end.
• Options: Owner Interface Identifier Option must be included in a Router Solicitation message.
APPENDIX A. HEADER AND FRAME FORMATS
A.6
71
Router Advertisement
The message format is as below.
0
1
2
3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
Type
|
Code
|
Checksum
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cur Hop Limit |M|O|H|Prf|Rsrvd|
Router Lifetime
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
Reachable Time
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
Retrans Timer
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
The ICMP fields for this message are as follows.
• Type: Type is set to 134.
• Code: Code is 0.
• Checksum: The ICMP checksum.
• M: 1-bit ”Managed address configuration” flag, when set it mentions the availability of the
Edge Router. In standard ND, this flag mentions that DHCPv6 is used [14].
• O: 1-bit ”Other configuration” flag, when set it mentions other configuration information is
available via DHCPv6.
• H: 1-bit ”Home Agent” flag, when set it indicates that the Edge Router sending this advertisement is also acting as Mobile IPv6 home agent on this link [21].
• Preference: 2-bit signed integer indicating whether to prefer this router over others or not. It
should be set to 01 for Edge Routers. More details in [22].
• Reserved: Unused field, must be initialized with 0 and ignored at the receiver’s end.
• Router Lifetime: 16-bit unsigned integer denoting the lifetime associated with default router
in unit of seconds.
APPENDIX A. HEADER AND FRAME FORMATS
72
• Reachable Time: 32-bit unsigned integer denoting the availability of neighbor in milliseconds
after having received a reachability confirmation. Used in Neighbor Unreachability Detection
algorithm [14].
• Retrans Timer: 32-bit unsigned integer denoting the time in milliseconds between retransmitted neighbor solicitation messages. Zero means unspecified.
• Options: Options may include source link-layer address, .
Appendix B
Packet Details
B.1
Route Request/Reply Packet
A Route Request packet looks as in Figure B.1.
The details of the packet field are as following.
• 0x0c TYPE : set as WASP Route Request, value 0x10 is set is Route Reply
• 0x0c TTL
• 0x00 Route Cost
• 0xFF Flags
• 0x00 RREQ ID
• 0x0000 Destination address for whom Route is requested)
• 0x0011 Source address
Route Request is always sent on broadcast address, i.e. 0xFFFF.
Figure B.1: Route Request Message
73
APPENDIX B. PACKET DETAILS
B.2
74
UDP Packet
A UDP packet carrying a string as payload looks as in Figure B.2.
Figure B.2: UDP Packet with short addresses
The details of the packet fields are as following.
• 0xB4 Mesh header
• 0x0011 - Originator short address
• 0x0000 Final destination short address
• 0x03 IPHC Dispatch
• 0xF8DD IPHC with next header UDP
• 0xFB88 UDP header with ports carried inline
• 54657374 Text string, ”Test”
The values of IPHC and UDP header denote following.
• IPHC Header - 0xF8DD - Traffic Class is 0, version is IPv6, Flow Label is 0, Next Header is
compressed using LOWPAN NHC, Hop Limit is fixed to 255. Source address and destination
addresses are not carried.
• UDP Header - 0xFB88 - B denotes both source and destination UDP ports are compressed in
one nibble each. Original value of ports can be calculated by P + short port, where P is
61616 (0xF0B0). Short port is carried inline for both source and destination, i.e. 88 denotes,
source short port is 8 and destination short port is 8 as well.
APPENDIX B. PACKET DETAILS
B.3
75
Router Solicitation and Router Advertisement
Router Solicitation sent from a node to an Edge Router and Router Advertisement message sent
from an Edge Router to a node look as in Figure B.3.
Figure B.3: Router Solicitation and Router Advertisement
The details of the packet fields are as following.
1. 0xB4 - Mesh header
2. 0x0011 - Source short address
3. 0x0000 - Destination short address
4. 0x03 - Dispatch
5. 0xD8DD - IPHC with ICMP uncompressed next header field
6. 0x3A - ICMP header
7. 0x85 - Router Solicitation
8. 0xFD - Owner ID Option
9. 0x002A00FFFE000011 - Owner Address 64 bit comprise of PAN ID and 16-bit short address
10. 0x86 - Router Advertisement
11. 0xFB - Address Option
12. 0xFEBBCCDD00000000 - 64-bit Prefix
Appendix C
UDP Application
C.1
Client
Figure C.1: UDP Client Block Diagram
76
APPENDIX C. UDP APPLICATION
C.2
Server
Figure C.2: UDP Server Block Diagram
77
Appendix D
Error Log
The following are the issues that were faced in the initial phase of porting. Each issue includes
a description of problem, its severity, complexity, files involved and solution. Severity denotes
the impact of that bug on program execution, being expressed as low, medium, high or critical.
Complexity relates with the time consumed to find the bug and solve it, and not just the solution.
It is expressed as low, medium or high.
1. Problem: struct in6 addr declared inside parameter list.
Description: Original code had irregular use of typedef.
Severity: Medium
Complexity: Low
Files: sixLowPanLayer.c ipv6Layer.c udpLayer.c
Solution: structure redefined, typedef used at appropriate places to avoid same errors.
2. Problem: Request for member in something not a union or structure.
Description: If pointers are accessed like structures, the C compiler gives this error. Previous
code was inconsistent with usage of -¿ and . while calling members of pointer or structure.
Severity: Medium
Complexity: Low
Files: Various
Solution: Access of pointers and structure elements was made consistent throughout all code.
3. Problem: mactoIpv6Translation() return value inconsistent.
78
APPENDIX D. ERROR LOG
79
Description: This function returns a pointer of structure in6 addr and not a structure it self.
The access was inconsistent through different files.
Severity: Low
Complexity: Low
Files: sixLowPanLayer.c sixLowPanLayer.h Test6LowPanLayerClient.c Test6LowPanLayerServer.c
Test6LowPanLayerForwarder.c
Solution: Now function returns a structure instead of pointer. To make it consistent with
code. It can also be modified to return pointer though.
4. Problem: Variable declaration inconsistent with C99.
Description: Variables are not allowed to be declared inside case statement.
Severity: Low
Complexity: Low
Files: routingUnderIp.c icmpv6.c
Solution: Variable declaration was moved to start of function.
5. Problem: UART0 inaccessible.
Description: In port code of FreeRTOS, the UART0 description was not available. The baud
rate setting were disabled.
Severity: Medium
Complexity: Medium
Files: All files requiring debugging
Solution: UART1 was used instead.
6. Problem: Variable declaration inconsistent with C99.
Description: Variables are not allowed to be declared inside loops.
Severity: Low
Complexity: Low
Files: Various
Solution: Declarations moved earlier in respective functions.
APPENDIX D. ERROR LOG
80
7. Problem: Stack size for tasks was not sufficient.
Description: Minimal stack size for tasks was specified, which was insufficient for task operation.
Severity: High
Complexity: High
Files: Mac.c Test6LowPanLayerClient.c Test6LowPanLayerServer.c Test6LowPanLayerForwarder.c
Solution: Stack size was increased to next optimal size.
8. Problem: Problem with buffer memory allocation.
Description: When a buffer is declared, using malloc memory should be allocated. However
it was not done, resulting in corrupt data at every access.
Severity: High
Complexity: Medium
Files: Buffer.c
Solution: Memory access was done using malloc where necessary.
9. Problem: IPv6ToMacTranslation return type inconsistent.
Description: Some pointer values were assigned to struct types.
Severity: Medium
Complexity: Low
Files: Various
Solution: Return type changed. Code modified accordingly.
10. Problem:In buffer.c, function writeInBuffer() does not update the value of the pointer to
current location after writing new characters into the buffer.
Description: The buffer pointer should always point to the head of the buffer. It is initialized
with the last address of the declared buffer. To explain further, buffer writing procedure is as
follows.
• Declare a buffer of amount MAX BUFFER SIZE.
• The pointer of buffer is pointing at the last address.
• Whenever there is a value added in buffer, pointer is decremented.
APPENDIX D. ERROR LOG
81
• This pointer in the end will point to the head of message.
This function had a bug that after writing the string, the pointer again pointed to the original
value. Therefore at next call, it would overwrites existing data.
Severity: Critical
Complexity: High
Files: buffer.c
Solution: Function was modified as per requirements.
11. Problem: Memory allocation for struct sockeraddr in6 * was wrong.
Description: The memory allocated was not sizeofstruct sock addr in6.
Severity: High
Complexity: Medium
Files: Test6LowPanLayerClient.c Test6LowPanLayerServer.c Test6LowPanLayerForwarder.c
Solution: Code modified accordingly. Memory allocated of correct size.
12. Problem: MAC Acknowledgment not transmitting.
Description: Some conditional statements used variables from part of code commented to
reduce size. Therefore these conditional terms were never evaluated to true.
Severity: High
Complexity: High
Files: mac rx engine.c
Solution: Code modified accordingly so that these conditions become true when ACK is
pending.
Bibliography
[1] Geoff Mulligan. The 6lowpan architecture. In EmNets ’07: Proceedings of the 4th workshop on
Embedded networked sensors, pages 78–82, New York, NY, USA, 2007. ACM.
[2] Wikipedia. http://en.wikipedia.org/wiki/dmx512-a, July 2009.
[3] DALI-AG. http://www.dali-ag.org/, July 2009.
[4] Continental Automated Buildings Association. http://www.caba.org/standards-protocols.
[5] G. Montenegro, N. Kushalnagar, J. Hui, and D. Culler. Transmission of IPv6 Packets over
IEEE 802.15.4 Networks. RFC 4944 (Proposed Standard), September 2007.
[6] Holger Karl and Andreas Willig. Protocols and Architectures for Wireless Sensor Networks.
John Wiley & Sons, 2005.
[7] Patrick Kinney. Zigbee technology: Wireless control that simply works, October 2003.
[8] Imperial College London. http://vip.doc.ic.ac.uk/bsn/index.php?article=926, September 2006.
[9] WASP. http://www.wasp-project.org/, July 2009.
[10] Martin Ouwerkerk, Frank J. Pasveer, and Nur Engin. Sand: a modular application development
platform for miniature wireless sensors. In BSN, pages 166–170, 2006.
[11] J. Hui and D. Culler. Compression format for ipv6 datagrams in 6lowpan networks. draft-hui6lowpan-hc-01, 2008.
[12] Ed. Z. Shelby, P. Thubert, J. Hui, and S. Chakrabarti. 6lowpan neighbor discovery. draft-ietf6lowpan-nd-04, 2009.
[13] M. Crawford. Transmission of IPv6 Packets over Ethernet Networks. RFC 2464 (Proposed
Standard), December 1998.
[14] T. Narten, E. Nordmark, W. Simpson, and H. Soliman. Neighbor Discovery for IP version 6
(IPv6). RFC 4861 (Draft Standard), September 2007.
82
BIBLIOGRAPHY
83
[15] N. Kushalnagar, G. Montenegro, and C. Schumacher. IPv6 over Low-Power Wireless Personal
Area Networks (6LoWPANs): Overview, Assumptions, Problem Statement, and Goals. RFC
4919 (Informational), August 2007.
[16] Richard Barry and FreeRTOS Team. http://www.freertos.org/, January 2006.
[17] Ed. K. Kim, G. Montenegro, Ed. S. Park, I. Chakeres, and C. Perkins. Dynamic manet
on-demand for 6lowpan (dymo-low) routing. draft-montenegro-6lowpan-dymo-low-routing-03,
2007.
[18] A. Conta and S. Deering. Internet Control Message Protocol (ICMPv6) for the Internet Protocol
Version 6 (IPv6) Specification. RFC 2463 (Draft Standard), December 1998. Obsoleted by RFC
4443.
[19] S. Deering, W. Fenner, and B. Haberman. Multicast Listener Discovery (MLD) for IPv6. RFC
2710 (Proposed Standard), October 1999.
[20] R. Vida and L. Costa. Multicast Listener Discovery Version 2 (MLDv2) for IPv6. RFC 3810
(Proposed Standard), June 2004.
[21] D. Johnson, C. Perkins, and J. Arkko. Mobility Support in IPv6. RFC 3775 (Proposed Standard), June 2004.
[22] R. Draves and D. Thaler. Default Router Preferences and More-Specific Routes. RFC 4191
(Proposed Standard), November 2005.
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Related manuals

Download PDF

advertisement