1. OLPC Mesh network improving
Arina Rudakova
(Saint-Petersburg Elelectrotechnical University «LETI»)
3rd FRUCT seminar
Saint-Petersburg
23 May 2008

2. Agenda
 Introduction
 Problem definition
 Domain analysis
 Solution
 Project timeline

3. I. Introduction

4. One Laptop Per Child

Home: http://laptop.org

The mission of the One Laptop
per Child association is to
develop a low-cost laptop—the
"XO Laptop"— to revolutionize
how we educate the world's
children. Goal is to provide
children around the world with
new opportunities to explore,
experiment, and express
themselves.

5. XO laptops hardware

Dimensions: 242mm × 228mm × 32mm

CPU x86-compatible processor AMD Geode LX-700 433 Mhz, 64KB each L1 I and D
cache; at least 128KB L2 cache

DRAM memory: 256 MiB dynamic RAM

BIOS: 1024KiB SPI-interface flash ROM

Mass storage: 1024 MiB SLC NAND flash, high-speed flash controller

Display: Liquid-crystal display: 7.5” dual-mode TFT display

Keyboard: 80+ keys, 1.0mm stroke; sealed rubber-membrane key-switch assembly

Gamepad: Two sets of four-direction cursor-control keys

Touchpad: Dual capacitance/resistive touchpad; supports written-input mode

Audio: AC’97 compatible audio subsystem

Integrated color video camera: 640 x 480 resolution at 30 FPS

Wireless Networking: Integrated 802.11b/g (2.4GHz) interface; 802.11s (Mesh)
networking supported; dual adjustable, rotating antennas support diversity reception;
capable of mesh operation when CPU is powered down;

6. XO laptops software

Operating system: Linux Kernel: Linux 2.6.22; Fedora 7 base environment.

User environment: Sugar GUI, written in Python, on top of the X Window and the Matchbox WM

Programming environments (main):
− Python (Version 2.5);
− JavaScript;
− Csound, music programming language;
− Etoys, an implementation of Squeak using Smalltalk, an object-based programming
language;
− Turtle Art, a graphical programming environment;
− Adobe's Flash Player, Java, Gnash

Libraries
− Mozilla Gecko/Xulrunner (the Firefox web engine);
− GUI toolkit (GTK+) (Gnome);
− Matchbox window manager;
− X Window System X.org Foundation;
− Multimedia framework: GStreamer and RealNetworks;
− Gettext, the GNU internationalization library

7. Neighborhood:
Collaboration interface
The Neighbourhood view
displays all the connected
XO laptops within a child’s
community, and what
activities they are sharing.
Each child is represented by a
different colour
If there is a shared document
or activity being
collaborated on by a
number of children, it will
show up within this view.

8. XO Mesh goals

Ability to act as a mesh point when laptop's main CPU is off.

Support for asymmetric links/paths.

Incremental releases—mesh networking is available immediately
on XO; Upgrades will continue to improve functionality and
adherence with standards.

Simultaneously acts as a mesh point and an infrastructure node.

Standards Compliance: follow 802.11s draft when possible.

9. II. Problem definition

10. Mesh network types

Infrastructure wireless mesh networks: Mesh
routers form an infrastructure for clients.

Client wireless mesh networks: Client nodes
constitute the actual network to perform routing
and configuration functionalities.

Hybrid wireless mesh networks: Mesh clients can
perform mesh functions with other mesh clients as
well as accessing the network

11. Distinguishing features

dynamics

structure

12. Routing mechanism in mesh

Redundante links usage
− Fault tolerance
− Load sharing

Traffic analysis

Network diversity

Route aggregation

13. Routing overhead reasons

Nodes number influence on the amount
of control traffic

Network changes dynamics influence on
the amount of control traffic

Route length influence on the amount of
control traffic

14. Project Goals

Reducing Routing overhead

OLPC implementation

15. III. Domain analysis

16. Ad-hoc Routing types

Pro-active or Table-driven

Reactive Routing or On-demand

Flow Oriented

Adaptive Routing or Situation-Aware

Hybrid (Pro-Active and Reactive)

17. Industrial and open source
implementations

AWDS (Ad-hoc Wireless Distribution Service) http://awds.berlios.de/

DSDV (Highly Dynamic Destination-Sequenced Distance Vector routing
protocol) – based on Bellman-Ford Routing Protocol

AODV (Ad-hoc On-demand Distance Vector)

Mobile Ad-hoc On-Demand Data Delivery Protocol

MPRDV (Multipoint Relay Distance Vector protocol)

SSR (Signal Stability Routing protocol)

PLBR (Preferred link based routing)

TORA (Temporally-Ordered Routing Algorithm routing protocol)

HRPLS (Hybrid Routing Protocol for Large Scale Mobile Ad-Hoc Networks
with Mobile Backbones)

HSLS (Hazy Sighted Link State routing protocol)

ZRP (Zone Routing Protocol)

18. IV. Solution

19. Solution components

Routing area restriction

Dynamic selection of optimization radius

External definition of routing overhead

20. Routing overhead chart

m — tree arity

n — nodes number

R — dynamics

21. Possible reasons of
routing overhead increase

Number of nodes increase

Network dynamics increase

Network radius increase

Using aggressive updating strategy

22. Routing area restriction
For effective routing area definition we should
introduce some definitions.
G(t)=<V,E>, where V – set of nodes, E – arches
G(t) describes network topology
d(vi,vj) – distance between vi and vj
vi: Ri>0, G (vi , Ri ) ⊂ G (t ), d (vi , v j ) ≤ Ri
Choose Ri with regard to time needed for collection
of information about G(vi,Ri)
G(vi,Ri) - effective routing area for vi, G (vi , Ri ) ≡ R(vi )

23. External and internal
routing records

External routing
records (only in
edge nodes)

Internal routing
records (always
true)

24. Routing optimization area

Local optimization

Global optimization

Optimization in restricted area

25. Local sample

Information collection – 1 hop

Route defining – 1 hop

«Trust» zone – 1 hop

Control traffic is minimum

26. Global sample

Information collection –
whole net

Route defining – whole net

«Trust» zone – whole net

Control traffic is maximum

27. Restricted sample

Information collection is
restricted with R

Route defining – within R
radius

«Trust» zone – within R
radius

Control traffic is restricted

28. Failure detection

At first only one
router knows
about a route
failure

After the
message to
sender about
the
impossibility of
passing, the
whole effective
routing area is
informed

The sender gets
informed when
its timer is over

29. Routing overhead analysis

30. V. Project timeline

31. Global plan
The past

2007 Autumn, generic task definition, domain investigation

2008 Winter, getting XO devices, experience XO system
programming
The future

2008 Summer, public presentation our of solution ideas
(conference proceedings or paper)

2008 Autumn, implement modules for NS2 and simulations

2008 Winter, contribute some code for XO laptops

2009 Spring, defence of the master thesises at LETI

32. Thank you.
Any questions?