Internship end

6LoWPAN border router :
Internship

Maxime D ENIS

UMONS

6 December 2012

´
Masters : Sebastien DAWANS Director : Pr. Bruno Q UOITIN
Laurent D ERU

Maxime D ENIS (UMONS) 6LoWPAN border router : Internship 6 December 2012 1 / 41

Summary

Outline

1 Introduction

2 Evaluation phase

3 Implementation

4 Using the testbed

5 Contiki on Linux

6 Master thesis

7 Conclusion


Introduction Internship subject

Starting point
CETIC border router prototype
The CETIC border router interconnects a WLAN (IPv6) and a WSN
(6LoWPAN) using RPL for routing.

F IGURE 1 : The border router in a typical topology.

Modes
Router, hybrid bridge and full bridge.


Phases of the internship

1 Documentation :
a state of the art ;
b documentation of the current implementation.
2 Evaluation :
a scenarios : use cases with sequence diagrams ;
b performance ;
c mobility ;
d etc.
3 Implementation :
a optimizations ;
b adding functionalities.



Platforms

F IGURE 2 : Redwire Econotag [1] and ENC28J60[2] Ethernet controller (left),
Crossbow Telos B [3] (right).
Conﬁguration
Redwire Econotag running the CETIC BR application and an UDP
server on Contiki ;
Crossbow Telos B running a simple webserver (Sky websense)
and an UDP sender on Contiki.


Testbed

F IGURE 3 : CETIC testbed topology allowing multi-hop routing.


Introduction Notions

6LoWPAN and RPL

6LoWPAN[4, 5]
Constitutes an adaption layer between IPv6 and IEEE 802.15.4. It
introduces packets fragmentation and reassembly, header
compression and Link layer forwarding (in case of mesh under
networks).
RPL [6, 7]
Lightweight distance vector
protocol destined to WSN. It
builds a DODAG [8]
representing the network.
RPL performs a covering of
the NDP functionalities
(Messages : DIO, DIS, DAO).
F IGURE 4 : Example of RPL DODAG.


Introduction Notions

Contiki
Description
Real time operating system [9], for embedded platforms. Contiki made
to use only one interface : introduction of a Packet Filter.
What Contiki brings
uIP stack : small IPv6 (or IPv4) compliant stack, few RAM ;
Protothreads : light threads stackless (blockable).

F IGURE 5 : Changes between standard IPv6 stack and 6LoWPAN stack.


Introduction CETIC prototype

Structure and modes

1 Packet ﬁlter : difference
between WSN and ethernet
RPL
data ;
2 Full bridge mode : switch,
uIPv6
forward and translating
ll-addresses ;
PacketFilter 3 Hybrid bridge mode : switch,
ND proxy and multi-hop (in
ENC28J60 802.15.4
route-over) ;
4 Router : Preﬁx announcement,
routing, forwarding (two
F IGURE 6 : CETIC prototype separated subnets).
structure.



Structure and modes

RPL
data ;
2 Full bridge mode : switch,
uIPv6
Translation
ll-addresses ;
RPL
ENC28J60 802.15.4 Traffic route-over) ;
Data 4 Router : Preﬁx announcement,
Traffic
structure.



Structure and modes

RPL
data ;
Multi-hop ND-Proxy 2 Full bridge mode : switch,
uIPv6
Translation
ll-addresses ;
NDP RPL
Messages
ENC28J60 802.15.4
Messages route-over) ;
Traffic
structure.



Structure and modes

RPL
data ;
Routing Multi-hop 2 Full bridge mode : switch,
Table
uIPv6
Translation
ll-addresses ;
NDP RPL
Messages
ENC28J60 802.15.4
Messages route-over) ;
Traffic
structure.


Evaluation phase

Outline

1 Introduction

2 Evaluation phase
Example of basic scenario
The restart
Sensors mobility
Transparent gateway

3 Implementation

4 Using the testbed

5 Contiki on Linux

6 Master thesis

Evaluation phase

Organization of the evaluation phase

F IGURE 7 : Flowcharts of the evaluation phase.

During the phase
1 Twelve scenarios deﬁned and explained in documentation,
declined in the three modes of the border router ;
2 When a issue was encountered, solutions were designed to
improve prototype.


Evaluation phase Example of basic scenario

Description

F IGURE 8 : Actors of the scenario.

In a one-sensor topology with border router in hybrid bridge and
manual conﬁguration
1 Wait for the DODAG to be built (typically when a DAO is received
by the border router) ;
2 Plug the computer to the border router ;
3 Start sending pings to the sensor and wait for response.



Results
Computer BR 802.15.4 Sky
(router)
User DAD(fe80::250:c2a8:cb76:d81b)

1
DAD(fe80::250:c2a8:cb76:d81b)

DAD(fe80::250:c2ff:fea8:ced0)


DAD(aaaa::250:c2a8:cb76:d81b)

DIO

NS(aaaa::212:7400:1465:f55e)

NA

DIO

DAO

Computer connection Ethernet

DAD(fe80::223:dfff:fe97:2492)
RA(bbbb::/64)
DAD(bbbb::223:dffff:fe97:2492)

Ping to Sky NS(bbbb::100)
NA

13s Echo Request(seq=0)
before
Echo Reply(Seq=0)

F IGURE 9 : Ping from Computer to Sensor (Sky) through the border router.


Results
(router)

DAD(fe80::250:c2a8:cb76:d81b)




DIO

NS(aaaa::212:7400:1465:f55e)

NA

DIO

DAO

2

DAD(fe80::223:dfff:fe97:2492)
RA(bbbb::/64)

Ping to Sky NS(bbbb::100)
NA

before
Echo Reply(Seq=0)



Results
(router)

DAD(fe80::250:c2a8:cb76:d81b)




DIO

NS(aaaa::212:7400:1465:f55e)

NA

DIO

DAO


DAD(fe80::223:dfff:fe97:2492)
RA(bbbb::/64)

Ping to Sky

NS(bbbb::100)
3
NA

before
Echo Reply(Seq=0)


Evaluation phase The restart

Bridge in autoconf mode restarting in stable network
Issue encountered
When restarting, the border router requests a DODAG (using a DIS
message) and a preﬁx on the wired network. If it receives a DIO ﬁrst, it
becomes leaf and root at the same time : loop.

F IGURE 10 : DODAG representation of the network before and after
restarting.

Evaluation phase The restart

Solution

Changes to implementation
Increment the version number of the DODAG : the incremented
number makes the network restarting ;
Construct a prefixless DODAG (using link-local address as
DODAG ID instead of global address) in autoconfiguration mode ;
When a prefix is received from the wired network, add it to the
DIO (in Prefix Information Option) and propagate it.

Changes to Contiki
The prefix treatment in a sensor already in a DODAG was defective
and had to be modified to handle new prefix announced.


Evaluation phase Sensors mobility

Loss in wireless sensors networks
How can a loss occur ?
Sensor problem, interferences, collisions ;
Moving topology.

F IGURE 11 : DODAG representation of the network before and after a sensor
loss.

Deal with losses
Losses in WSN can occur a lot of time : ETX metric used in RPL.

Evaluation phase Sensors mobility

Dealing with lost destinations

Before implementation
The lifetime attribute of the route is used. When lifetime expires, the
associated route is tested and can be removed from the table. This
mechanism prevent any kind of quick mobility among several subnets.

Proposal
Use the ETX for descending routes, and remove routes when some
condition are encountered :
The ETX of the neighbor becomes greater than a threshold value ;
No-ack penalties are encountered.


Evaluation phase Transparent gateway

Bridge mode to simplify subnets

F IGURE 12 : Several subnets visible as one subnet with bridge.

Issue encountered with full bridge
On-link preﬁx announced as off-link, and poorly propagated.

Implementation

Outline

1 Introduction

2 Evaluation phase

3 Implementation

4 Using the testbed

5 Contiki on Linux

6 Master thesis

7 Conclusion


Implementation

Features added

1 On-link preﬁx management and propagation (bit set and correctly
managed by the sensor) ;
2 Incremented DODAG version number correctly managed by the
sensors when restart ;
3 Preﬁx Information Option propagation and management by the
sensors ;
4 Route Information Option management by the border router.


Implementation

Route Information Option management
Option of NDP’s RA message[10] used to set routes in routing tables.

Type Length Pref Len R P R
Route lifetime

Prefix (variable length)

F IGURE 13 : Route Information Option message format as speciﬁed in [10].

Before implementation
Border router managing RA but ignoring RIOs.

After implementation
When a RIO is received from an IPv6 router, announced preﬁxes are
added to the routing table of the border router, and not spread to the
WSN.

Using the testbed

Outline

1 Introduction

2 Evaluation phase

3 Implementation

4 Using the testbed
Application
Evaluation

5 Contiki on Linux

6 Master thesis

7 Conclusion

Using the testbed Application

Scenario
Two applications
1 UDP client running on the sensors, and sending to a server
frequent messages identifying them (each 15s) ;
2 UDP server running on the border router, sending an
acknowledgment when receiving a message from a node.

F IGURE 14 : Testbed topology used for the scenario.

Using the testbed Evaluation

Metrics
What is measured ?
PRR from testbed to server : the amount of messages (UDP
packets) sent is compared to the amount of messages received at
the UDP server (running on the border router) ;
PRR from server to testbed : the amount of messages
Acknowledgment sent by the server compared to the amount of
messages received on the sensors ;
TCPIP forwarding : the amount of forwards done at each sensor ;
CSMA : the amount of CSMA errors encountered at each sensor
and through time.

How ?
The packet trip is observable using traces all along the stacks (in the
application, in the uIP stack and in CSMA).



Results

F IGURE 15 : Metrics.


Analysis

PRRs
Metric Average value
PRRTB→S 99.75%
PRRS→TB 98.01%

TABLE 1 : Average results of metrics.

RPL is optimized for collecting data (ascendant trafﬁc).

TCPIP forwarding
Nodes T2 and T3 used for forwarding by T8 and sometimes by T5.



RPL routing
RPL is an asymmetric routing protocol which relies on a sink system
for ascendant traffic and on routes for descendant traffic.

From sensor to border router
The current implementation
uses the default router to
forward the packet.

From border router to sensor
A lookup is performed to find
the best route to forward the
packet.

F IGURE 16 : Example of traffic on a RPL
DODAG.

Contiki on Linux

Outline

1 Introduction

2 Evaluation phase

3 Implementation

4 Using the testbed

5 Contiki on Linux

6 Master thesis

7 Conclusion


Contiki on Linux

Successful portage of the Contiki’s app to Linux

Platform
Beaglebone using a 700Mhz ARM Cortex A8 [11], relying on the
Angstrom distribution [12].

RADVD
RPL
....
BR
Linux Server

TAP IP Tables
Eth Telos Beaglebone Eth
SLIP
RAW
802.15.4 Raw or Ctrl (MAC, channel, Ack...)

F IGURE 17 : Linux portage and platform structure.


Master thesis

Outline

1 Introduction

2 Evaluation phase

3 Implementation

4 Using the testbed

5 Contiki on Linux

6 Master thesis
Subject
Concrete applications

7 Conclusion

Master thesis Subject

Subject

What ?
Multiple border router problematic : maintain a state between
several border router ;
Make border router more simple : using on an higher root
(outside the RPL network, in WPAN).

Why ?
Redundancy or Trafﬁc engineering ;
Run several QoS ;
Invisible sink changes (mobility).


Master thesis Concrete applications

Redundancy paths and trafﬁc engineering
Load balancing, robustness, etc.

F IGURE 18 : One QoS on same subnet : one instance and several DODAGs.


Several QoS
Collecting data, request data, energy-saving paths, etc., on same
network

F IGURE 19 : Two QoS on same subnet : several instances.


Invisible sink changes
Same QoS on two separated subnets.

F IGURE 20 : Invisible mobility.


Conclusion

Outline

1 Introduction

2 Evaluation phase

3 Implementation

4 Using the testbed

5 Contiki on Linux

6 Master thesis

7 Conclusion


Conclusion

Internship achievements
1 Increased border router stability : some optimizations and
bugfixes ;
2 Paper :
State of the art (the border router solutions) ;
Complete description of the border router and scenarios detailed.
3 Features added :
Border router more easily deployable ;
Autoconfiguration ;
Stability increased.

Master thesis perspectives
1 RPL root outside WSN ;
2 Mobility, redundancy, traffic engineering.


Conclusion

Questions ?


Conclusion

Demonstration

F IGURE 21 : Conﬁguration.

Summary
Border router web interface, pings, etc.

References

[1] “Redwire Econotag.”
http://redwirellc.com/store/node/1 (last access :
26/09/12).
[2] “ENC28J60.” http://www.microchip.com/wwwproducts/
Devices.aspx?dDocName=en022889 (last access : 26/09/12).
[3] Crossbow, “Telos b.”
http://www.xbow.jp/TelosbCatalog.pdf (last access :
1/10/12).
[4] “6LoWPAN Backbone Router.” http://tools.ietf.org/
html/draft-thubert-6lowpan-backbone-router-02
(last access : 2/10/12).
[5] L. M. Ara, “Neighbor Discovery Proxy-Gateway for
6LoWPAN-based Wireless Sensor Networks.” KTM Information
and Communication Technology.


References

[6] “RFC 6550 : RPL : IPv6 Routing Protocol for Low-Power and
Lossy Networks.”
https://datatracker.ietf.org/doc/rfc6550/ (last
access : 2/10/12).
[7] J.-P. Vasseur and A. Dunkels, Interconnecting smart objects with
IP.
Morgan Kauffman, 2012.
[8] S. Kuryla, “RPL : IPv6 Routing Protocol for Low power and Lossy
Networks.” http://cnds.eecs.jacobs-university.de/
courses/nds-2010/kuryla-rpl.pdf (last access :
20/09/12), 2010.
[9] “Contiki 2.6 Doxygen.”
http://contiki.sourceforge.net/docs/2.6/ (last
access : 17/09/12).


References

[10] “RFC 4191 : Default Router Preferences and More-Speciﬁc
Routes.” https://datatracker.ietf.org/doc/rfc4191/
[11] “Beaglebone ﬂyer.”
http://beagleboard.org/static/flyer_latest.pdf
[12] “Angstrom distribution.”
http://linuxtogo.org/gowiki/AngstromManual (last
access : 3/12/12).


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