Mobile Communications Ad-Hoc Networks & Wireless Sensor ...

Mobile Communications 

Ad-Hoc Networks 

& Wireless Sensor Networks 

Ad-hoc networks 

Motivation 

Routing 

Wireless Sensor Networks 

Motivation 

Routing 

Mobile Communications Ad-hoc Networks & Wireless Sensor Networks 1

Mobile ad hoc networks: Motivation 

Standard Mobile IP needs an infrastructure 

Home Agent/Foreign Agent in the fixed network 

DNS, routing etc. are not designed for mobility 

Sometimes there is no infrastructure! 

remote areas, ad-hoc meetings, disaster areas 

cost can also be an argument against an infrastructure! 

Without infrastructure, how can data reach destination node, which path is 

suitable? routing 

no default router available 

every node should be able to forward 

A B C 


Solution: Wireless & Mobile ad-hoc networks 

Network without infrastructure 

Use components of participants for networking 

Examples 

Single-hop: All partners max. one hop apart 

• Bluetooth piconet, PDAs in a room, 

gaming devices… 

Multi-hop: Cover larger distances, 

circumvent obstacles 

• Bluetooth scatternet, TETRA police network, 

car-to-car networks… 

Internet: MANET (Mobile Ad-hoc Networking) group 


MANET Characteristics I 

Highly dynamic network topology 

Device mobility plus varying channel quality 

Partitioning and merging of networks possible 

Asymmetric connections possible 

risk of packet loss 

N 7 N 6 

N 6 

N 7 

N 1 N 1 

N 2 

N 3 

N 4 

N 5 

N 4 

N 2 

N 5 

N 3 

time = t 1 time = t 2 

good link 

weak link 


MANET Characteristics II 

Wireless medium is broadcast medium 

Hidden and exposed nodes 

Limited battery capacities of mobile devices 

Amplified by signaling traffic, e.g., due to routing protocol messages 

Limited bandwidth 

Amplified by signaling traffic, e.g., due to routing protocol messages and by 

MAC protocol (collisions, hidden nodes, …) 

Time synchronisation of devices is difficult 

Energy saving becomes more difficult, e.g., periodic sleeping 

Security methods are more difficult to apply 

Interception of wireless channel 

Every device must be able to forward packets to other devices

Traditional routing algorithms 

Distance Vector 

periodic exchange of messages with all physical neighbors that contain 

information about who can be reached at what distance 

selection of the shortest path if several paths available 

Link State 

periodic notification of all routers about the current state of all physical links 

router get a complete picture of the network 

Example 

ARPA packet radio network (1973), DV-Routing 

every 7.5s exchange of routing tables including link quality 

updating of tables also by reception of packets 

routing problems solved with limited flooding 


Problems of traditional routing algorithms 

Dynamics of the topology 

frequent changes of connections, connection quality, participants 

Limited performance of mobile systems 

periodic updates of routing tables need energy without contributing to the 

transmission of user data, sleep modes difficult to realize 

limited bandwidth of the system is reduced even more due to the exchange 

of routing information 

links can be asymmetric, i.e., they can have a direction dependent 

transmission quality 


Routing in MANETs 

THE big topic in many research projects 

Far more than 50 different proposals exist 

The most simplest one: Flooding! 

Reasons 

Classical approaches from fixed networks fail 

• Very slow convergence, large overhead 

High dynamicity, low bandwidth, low computing power 

Metrics for routing 

Minimal 

• Number of nodes, loss rate, delay, congestion, interference … 

Maximal 

• Stability of the logical network, battery run-time, time of connectivity … 


Overview MANET routing protocols 

Flooding for data transport 

Simplest „protocol“: every node forwards every packet 

Huge overhead 

Table-driven / Proactive routing 

Maintain routes to all other nodes permanently 

Constant, high signalling overhead 

On-demand-driven / Reactive routing 

Routes are discovered if needed 

Delayed packet forwarding since route must be established first 

Signalling overhead depends on traffic patterns 

Hybrid routing 

Mixture of proactive and reactive routing 

There is not „one single best“ routing protocol for MANETs 

Decision about „best“ depends on scenario

Classification of MANET routing protocols 

Unicast routing protocols 

for MANETs 

(topologie-based) 

Table-driven/ 

pro-active 

Hybrid 

On-Demand 

-driven/reactive 

Cluster-based/ 

hierarchical 

Distance- 

Vector 

• DSDV 

• ... 

Link- 

State 

• OLSR 

• TBRPF 

• FSR 

• STAR 

• ... 

• ZRP 

• ... 

• DSR 

• AODV 

• TORA 

• ... 

not covered: position-based routing protocols 

• LANMAR 

• CEDAR 

• ...

Abbreviations MANET routing protocols 

DSDV 

OLSR 

TBRPF 

FSR 

STAR 

ZRP 

DSR 

AODV 

TORA 

LANMAR 

CEDAR 

Destination-Sequenced Distance Vector 

Optimized Link State Routing 

Topology Broadcast based on Reverse-Path Forwarding 

Fisheye State Routing 

Source Tree Adaptive Routing 

Zone Routing Protocol 

Dynamic Source Routing 

Ad Hoc On Demand Distance Vector 

Temporally-Ordered Routing Algorithm 

Landmark Ad Hoc Routing 

Core-Extraction Distributed Ad Hoc Routing

DSDV (Destination Sequenced Distance Vector) 

Early work 

on demand version: AODV 

Expansion of distance vector routing 

Sequence numbers for all routing updates 

assures in-order execution of all updates 

avoids loops and inconsistencies 

Decrease of update frequency 

store time between first and best announcement of a path 

inhibit update if it seems to be unstable (based on the stored time values) 


Dynamic source routing I 

Split routing into discovering a path and maintaining a path 

Discover a path 

only if a path for sending packets to a certain destination is needed and no 

path is currently available 

Maintaining a path 

only while the path is in use one has to make sure that it can be used 

continuously 

No periodic updates needed! 


Dynamic source routing II 

Path discovery 

broadcast a packet with destination address and unique ID 

if a station receives a broadcast packet 

• if the station is the receiver (i.e., has the correct destination address) then return 

the packet to the sender (path was collected in the packet) 

• if the packet has already been received earlier (identified via ID) then discard 

the packet 

• otherwise, append own address and broadcast packet 

sender receives packet with the current path (address list) 

Optimizations 

limit broadcasting if maximum diameter of the network is known 

caching of address lists (i.e. paths) with help of passing packets 

• stations can use the cached information for path discovery (own paths or paths 

for other hosts) 


DSR: Route Discovery 

Sending from C to O 

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(alternatively: [O,C/E/D,4711]) 



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Dynamic Source Routing III 

Maintaining paths 

after sending a packet 

• wait for a layer 2 acknowledgement (if applicable) 

• listen into the medium to detect if other stations forward the packet (if possible) 

• request an explicit acknowledgement 

if a station encounters problems it can inform the sender of a packet or 

look-up a new path locally 


Interference-based routing 

Routing based on assumptions about interference between signals 

N 1 

N 2 

R 1 

S 1 

N 5 

N 3 

N 4 

N 6 

R 2 

S 2 

N 9 

neighbors 

(i.e. within radio range) 

N 7 

N 8 


Examples for interference based routing 

Least Interference Routing (LIR) 

calculate the cost of a path based on the number of stations that can 

receive a transmission 

Max-Min Residual Capacity Routing (MMRCR) 

calculate the cost of a path based on a probability function of successful 

transmissions and interference 

Least Resistance Routing (LRR) 

calculate the cost of a path based on interference, jamming and other 

transmissions 

LIR is very simple to implement, only information from direct neighbors is 

necessary 


A plethora of ad hoc routing protocols 

Flat 

 

 

proactive 

• FSLS – Fuzzy Sighted Link State 

• FSR – Fisheye State Routing 

• OLSR – Optimised Link State Routing Protocol 

• TBRPF – Topology Broadcast Based on Reverse Path Forwarding 

reactive 

• AODV – Ad hoc On demand Distance Vector 

• DSR – Dynamic Source Routing 

Hierarchical 

CGSR – Clusterhead-Gateway Switch Routing 

 

 

 

HSR – Hierarchical State Routing 

LANMAR – Landmark Ad Hoc Routing 

ZRP – Zone Routing Protocol 

Geographic position assisted 

DREAM – Distance Routing Effect Algorithm for Mobility 

 

 

 

GeoCast – Geographic Addressing and Routing 

GPSR – Greedy Perimeter Stateless Routing 

LAR – Location-Aided Routing 


Further difficulties and research areas 

Auto-Configuration 

Assignment of addresses, function, profile, program, … 

Service discovery 

Discovery of services and service providers 

Multicast 

Transmission to a selected group of receivers 

Quality-of-Service 

Maintenance of a certain transmission quality 

Power control 

Minimizing interference, energy conservation mechanisms 

Security 

Data integrity, protection from attacks (e.g. Denial of Service) 

Scalability 

10 nodes? 100 nodes? 1000 nodes? 10000 nodes? 

Integration with fixed networks 


The next step: Wireless Sensor Networks (WSN) 

Commonalities with MANETs 

Self-organization, multi-hop 

Typically wireless, should be energy efficient 

Differences to MANETs 

Applications: MANET more powerful, more general 

↔ WSN more specific 

Devices: MANET more powerful, higher data rates, more resources 

↔ WSN rather limited, embedded, interacting with environment 

Scale: MANET rather small (some dozen devices) 

↔ WSN can be large (thousands) 

Basic paradigms: MANET individual node important, ID centric 

↔ WSN network important, individual node may be dispensable, data 

centric 

Mobility patterns, Quality-of Service, Energy, Cost per node … 


Properties of wireless sensor networks 

Sensor nodes (SN) monitor and control the environment 

Nodes process data and forward data via radio 

Integration into the environment, typically attached to other networks over a 

gateway (GW) 

Network is self-organizing and energy efficient 

Potentially high number of nodes at very low cost per node 

SN 

SN 

GW 

Bluetooth, TETRA, … 

SN 

SN 

SN 

SN 

GW 

SN 

SN 

SN 

SN 

GW 

GW 

SN 

SN 


Promising applications for WSNs 

Machine and vehicle monitoring 

 

 

Sensor nodes in moveable parts 

Monitoring of hub temperatures, fluid levels … 

Health & medicine 

 

 

Long-term monitoring of patients with minimal restrictions 

Intensive care with relative great freedom of movement 

Intelligent buildings, building monitoring 

 

 

Intrusion detection, mechanical stress detection 

Precision HVAC with individual climate 

Environmental monitoring, person tracking 

 

 

 

Monitoring of wildlife and national parks 

Cheap and (almost) invisible person monitoring 

Monitoring waste dumps, demilitarized zones 

… and many more: logistics (total asset management, RFID), telematics … 

 

WSNs are quite often complimentary to fixed networks! 


Example: ScatterWeb Sensor Nodes 

Embedded Sensor Board 

Sensors 

• Luminosity, noise detection, gas, 

vibration, PIR movement detection, pressure… 

Microphone/speaker, camera, display, 

IR sender/receiver, precise timing 

Communication using 868 MHz radio transceiver 

• Range up to 2 km LOS, 500 m indoor 

Software 

• Simple programming (C interface) 

• Optional: operating systems TinyOS, Contiki … 

• Optional: TCP/IP, web server … 

• Routing, management, flashing … 

Embedded Sensor Board 

Modular Sensor Node 


Example: ScatterWeb Gateways 

USB 

Simple Integration PC world 

Enables over-the-air programming 

either point-to-point or broadcast 

including reliable multi-hop 

Ethernet 

RJ45 Adapter for 10/100 Mbit/s 

Power-over-Ethernet (802.3af) 

Standard Internet protocols (IP, TCP, HTTP, HTTPS, ARP, DHCP) 

Integrated Web server providing applets for sensor net control 

Secure access of ScatterWeb from any browser on the net 

All-in-one 

WLAN, Ethernet, Bluetooth, 

GPS, GSM/GPRS, USB, serial… 


Sensor Networks: Challenges and Research Areas 

Real-World Integration 

Gaming, Tourism 

Emergency, Rescue 

Monitoring, Surveillance 

Self-configuring networks 

Robust routing 

Low-power data aggregation 

Simple (indoor) Localization 

Managing wireless sensor networks 

Tools for access and programming 

Update distribution 

Long-lived, autonomous networks 

Use environmental energy sources 

Embed and forget 

Scalability, Quality of Service… 


Routing in WSNs is different 

No IP addressing, but simple, locally valid IDs 

Example: directed diffusion 

Interest Messages 

• Interest in sensor data: Attribute/Value pair 

• Gradient: remember direction of interested node 

Data Messages 

• Send back data using gradients 

• Hop count guarantees shortest path 

Sink 


Energy-aware routing 

Only sensors with sufficient energy forward data for other nodes 

Example: Routing via nodes with enough solar power is considered “for 

free” 


Solar-aware routing 

Solar-powered node 

Send status updates to neighbors 

• Either proactive or 

when sniffing ongoing traffic 

Have neighbor nodes 

reroute the traffic 


Today’s WSNs 

First generation of WSNs is available 

Diverse sensor nodes, several gateways 

Even with special sensors: cameras, body temperature… 

Basic software 

• Routing, energy conservation, management 

Several prototypes for different applications 

Environmental monitoring, industrial automation, wildlife monitoring … 

Many see new possibilities for monitoring, surveillance, protection 

Sensor networks as a cheap and flexible new means 

for surveillance 

Monitoring and protection of goods 

• Chemicals, food, vehicles, machines, containers, … 

Large application area besides military 

• Law enforcement, disaster recovery, industry, 

private homes, …

Mobile Communications Ad-Hoc Networks & Wireless Sensor ...

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