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Mobile Communications Ad-hoc Networks & Wireless Sensor Networks 1

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 2

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

Mobile Communications Ad-hoc Networks & Wireless Sensor Networks 3

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

Mobile Communications Ad-hoc Networks & Wireless Sensor Networks 5

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

good link weak link time = t1 time = t2 N1 N4 N2 N5 N3 N1 N4 N2 N5 N3 N6 N7 N6 N7

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

Mobile Communications Ad-hoc Networks & Wireless Sensor Networks 7

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

Mobile Communications Ad-hoc Networks & Wireless Sensor Networks 8

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

• f routing information

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

transmission quality

Mobile Communications Ad-hoc Networks & Wireless Sensor Networks 9

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 On-Demand

• driven/reactive

Hybrid

• DSDV
• ...
• ZRP
• ...
• DSR
• AODV
• TORA
• ...

Distance- Vector Link- State

• OLSR
• TBRPF
• FSR
• STAR
• ...

Cluster-based/ hierarchical

• LANMAR
• CEDAR
• ...

not covered: position-based routing protocols

Abbreviations MANET routing protocols

DSDV Destination-Sequenced Distance Vector OLSR Optimized Link State Routing TBRPF Topology Broadcast based on Reverse-Path Forwarding FSR Fisheye State Routing STAR Source Tree Adaptive Routing ZRP Zone Routing Protocol DSR Dynamic Source Routing AODV Ad Hoc On Demand Distance Vector TORA Temporally-Ordered Routing Algorithm LANMAR Landmark Ad Hoc Routing CEDAR Core-Extraction Distributed Ad Hoc Routing

Mobile Communications Ad-hoc Networks & Wireless Sensor Networks 13

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)

Mobile Communications Ad-hoc Networks & Wireless Sensor Networks 14

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!

Mobile Communications Ad-hoc Networks & Wireless Sensor Networks 15

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)

Mobile Communications Ad-hoc Networks & Wireless Sensor Networks 16

DSR: Route Discovery

B A C G I D K L E H F J Q P M N O R Sending from C to O

Mobile Communications Ad-hoc Networks & Wireless Sensor Networks 17

DSR: Route Discovery

Broadcast B A C G I D K L E H F J Q P M N O R [O,C,4711] [O,C,4711]

Mobile Communications Ad-hoc Networks & Wireless Sensor Networks 18

DSR: Route Discovery

B A C G I D K L E H F J Q P M N O R [O,C/G,4711] [O,C/G,4711] [O,C/B,4711] [O,C/E,4711]

Mobile Communications Ad-hoc Networks & Wireless Sensor Networks 19

DSR: Route Discovery

B A C G I D K L E H F J Q P M N O R

[O,C/G/I,4711] [O,C/B/A,4711] [O,C/B/D,4711] [O,C/E/H,4711] (alternatively: [O,C/E/D,4711])

Mobile Communications Ad-hoc Networks & Wireless Sensor Networks 20

DSR: Route Discovery

B A C G I D K L E H F J Q P M N O R

[O,C/B/D/F,4711] [O,C/G/I/K,4711] [O,C/E/H/J,4711]

Mobile Communications Ad-hoc Networks & Wireless Sensor Networks 21

DSR: Route Discovery

B A C G I D K L E H F J Q P M N O R

[O,C/E/H/J/L,4711] (alternatively: [O,C/G/I/K/L,4711]) [O,C/G/I/K/M,4711]

Mobile Communications Ad-hoc Networks & Wireless Sensor Networks 22

DSR: Route Discovery

B A C G I D K L E H F J Q P M N O R

[O,C/E/H/J/L/N,4711]

Mobile Communications Ad-hoc Networks & Wireless Sensor Networks 23

DSR: Route Discovery

B A C G I D K L E H F J Q P M N O R

Path: M, K, I, G

Mobile Communications Ad-hoc Networks & Wireless Sensor Networks 24

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

Mobile Communications Ad-hoc Networks & Wireless Sensor Networks 25

Interference-based routing

Routing based on assumptions about interference between signals

S1 N5 N3 N4 N1 N2 R1 R2 N6 N8 S2 N9 N7 neighbors (i.e. within radio range)

Mobile Communications Ad-hoc Networks & Wireless Sensor Networks 26

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

Mobile Communications Ad-hoc Networks & Wireless Sensor Networks 27

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

Mobile Communications Ad-hoc Networks & Wireless Sensor Networks 28

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

Mobile Communications Ad-hoc Networks & Wireless Sensor Networks 30

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 GW SN SN SN SN SN SN SN SN SN SN GW GW GW Bluetooth, TETRA, … SN

Mobile Communications Ad-hoc Networks & Wireless Sensor Networks 31

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!

Mobile Communications Ad-hoc Networks & Wireless Sensor Networks 32

Mobile Communications Ad-hoc Networks & Wireless Sensor Networks 33

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

Mobile Communications Ad-hoc Networks & Wireless Sensor Networks 34

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…

Mobile Communications Ad-hoc Networks & Wireless Sensor Networks 35

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…

Mobile Communications Ad-hoc Networks & Wireless Sensor Networks 36

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

Mobile Communications Ad-hoc Networks & Wireless Sensor Networks 37

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”

Mobile Communications Ad-hoc Networks & Wireless Sensor Networks 38

Solar-aware routing

Solar-powered node

 Send status updates to neighbors

 Either proactive or

when sniffing ongoing traffic

 Have neighbor nodes

reroute the traffic

Mobile Communications Ad-hoc Networks & Wireless Sensor Networks 40

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, …