wireless networks routing2003

7/27/2019 Wireless Networks Routing2003

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Wireless Networks Routing

國立屏東教育大學資訊科學系王朱福教授



Outlines

Wireless networks architectures

Routing protocols for wireless networks

Mobile ad-hoc Networks (MANETs)

Wireless Sensor Networks (WSNs)

Vehicle ad-hoc networks (VANETs)



Wireless Communications

Wireless networks use radio frequency channels as

their physical medium for communications.

Each node in the network broadcast information

which can be received by all nodes within its direct

transmission range.



Wireless network architectures

Infrastructure-based wireless networks

Fixed base stations / access points areused.

Infrastructure-less wireless networks(Ad-hoc networks)

No fixed infrastructure support are

available. Hybrid wireless networking

architecture



Wireless network architectures (cont.)

Infrastructure-based wireless networks

Uses fixed base stations / access points which are responsible

for coordinating communication between the hosts.

Single-hop communication



Ad-hoc networks

Consists of nodes which communicate with each other through

wireless medium without any fixed infrastructure.

Multi-hop communications

Wireless network architectures (cont.)



Properties of ad-hoc networks

No pre-build infrastructure

All nodes are wireless capable

Base stations are not necessary

Ease of deployment

Quickly deploy



Some emerging types of wireless networks

MANETs (Mobile Ad-hoc Networks)

WSNs (Wireless Sensor Networks)

VANET (Vehicle Ad-hoc Networks)

WMN (Wireless Mesh Networks)

…



Routing protocols for wireless networks –

MANETs

A dynamically reconfigurable ad-hoc network.

Main issues in the design and operation of MANETs.

(1) MANETs are more unstable than wired-networks because

of the lack of a centralized entity.



(2) Mobility will cause network topology to change,

which results in a great change in connection between

two hosts.

(3) The connectivity between network nodes is not

guaranteed, so intermittent connectivity is common.


MANETs (cont.)



1

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6

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3

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10

The main routing

problems for MANETs

Node mobility

Routing path broken

frequently



Traditional ad-hoc routing protocols



Routing protocols for MANETs

Flooding-type routing protocol (flooding)

Table-driven routing protocol (proactive)

On-demand routing protocol (reactive)

Hybrid routing protocol



Flooding-type routing protocol

(Flooding)

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Advantage: They do not need to maintain network

topology, or is looking for data transmission path, so

they can quickly transfer information.

Disadvantage: Node receives information after, must

repeat broadcast, making it fast consumes its batteryenergy, and produces broadcast storm .

Flooding-type routing protocol

(Flooding)



Table-driven routing protocol (proactive):

They maintain the global topology information in the

form of tables at every node. These tables are updated frequently in order to

maintain consistent and accurate network state

information. For example, DSDV , WRP, and STAR.

Routing protocols for MANETs (cont.)



The DSDV routing protocol is an enhanced version of the distributed Bellman-Ford algorithm where each

node maintain a table that contain the shortest distanceand the first node on the shortest path to every other node in the network.

Table-driven routing protocol — Destination Sequenced Distance Vector routing (DSDV)



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Dest NextNode Dist seqNo

2 2 1 22

3 2 2 26

4 5 2 325 5 1 134

6 6 1 144

7 2 3 162

8 5 3 170

9 2 4 186

10 6 2 142

11 6 3 176

12 5 3 190

13 5 4 198

14 6 3 214

15 5 4 256

Routing table for Node 1

Table-driven routing protocol – DSDV (cont.)

Example:




Each node, upon receiving an update, quickly

disseminates it to its neighbors in order to propagatethe broken-link information to the whole network.

Thus a single link break leads to the propagation of

table update information to the whole network.



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Routing table for Node 1

Dest NextNode Dist seqNo 2 2 1 22 3 2 2 26 4 5 2 32 5 5 1 134 6 6 1 144 7 2 3 162 8 5 3 170 9 2 4 186 10 6 2 142 11 5 4 180 12 5 3 190 13 5 4 198 14 6 3 214 15 5 4 256




Advantage：

It can be applied to MANETs with few modifications.The updates are propagated throughout the network in

order to maintain an up-to-date view of the network

topology at all the nodes.




Disadvantage：

(1) The DSDV suffers from excessive control

overhead that is proportional to the number of nodes in the network and therefore is notscalable in MANETs, which have limited

bandwidth and whose topologies are highly

dynamic.




(2) In order to obtain information about a particular

destination node, a node has to wait for a tableupdate message initiated by the same destination

node. This delay could result in stale routing

information at nodes.




On-demand routing protocol (reactive):

They execute the path-finding process and exchange

routing information only when a path is required by anode to communicate with a destination.

For example, AODV and DSR .

Routing protocols for MANETs (cont.)



AODV, a route is established only when it is required

by a source node for transmitting data packets.

In AODV, the source node and intermediate nodes

store the next-hop information corresponding to each

flow for data packet transmission.

On-demand routing protocol – Ah-hoc On-demand Distance-Vector Routing Protocol (AODV)



The major difference between AODV and other on-

demand routing protocol is that it uses a destination

sequence number ( DestSeqNum) to determine an up-

to-date path to the destination.

A node updates its path information only if the

DestSeqNum of the current packet received is greater than the last DestSeqNum stored at the node.

On-demand routing protocol – AODV (cont.)



AODV utilizes routing tables to store routing

information.

The routing table stores:

destination

addr

next-hop

addr

destination

sequence

hop count life time




1. If a node wants to send a packet to some destination. At

first, it checks its routing table to determine whether it has

a current route to the destination or not.

=>If yes, it forwards the packet to next hop node of the route.

=>If no, it initiates a route discovery process.

The AODV routing procedure



The Route discovery process :

It begins with the creation of a RouteRequest (RREQ) packet.Broadcasting is done via flooding.

Broadcast ID gets incremented each time a source node uses

RREQ.

Broadcast ID and source IP address form a unique identifier for

the RREQ.Type Reserved Hop Count

Broadcast ID

Destination IP Address

Destination Sequence Number

Source IP Address

Source Sequence Number

Time Stamp

RREQ packet format

The AODV routing procedure (cont.)



2. Sender S broadcasts a RREQ to all its neighbors, each node

receiving RREQ forwards RREQ to its neighbors.*Sequence numbers help to avoid the possibility of forwarding the same packet more than once.

3. An intermediate node (not the destination) may also send a

RouteReply (RREP) packet provided that it knows a morerecent path than the one previously known to sender S.

Type Reserved Hop Count

Destination IP Address

Destination Sequence Number

Source IP Address

Life Time

RREP packet format




4. As an intermediate node receives the RREP packet,

it sets up a forward path entry to the destination in

its routing table.

5. The source node can begin data transmission upon

receiving the first RREP.




Illustration of route establishment in AODV

1. Node S needs a routing path to node D.

2. Node S creates a RREQ packet

RREQ [D’s IP addr, seq#, S’s IP addr, seq#, hopcount]

Node S broadcasts RREQ to its neighbors.

S A

B

C

D

RREQ{D, D’seq, S, S’seq, 0}



2. Node A rebroadcasts RREQ to all its neighbors.

S A

B

C

D



Illustration of route establishment in AODV (cont.)



3. Since, node C known a route to D. Node C creates a RREP packet and unicasts RREP to A.

Set forward path in node C’s routing table.

S A

B

C

D

RREP{D, D’seq, S, S’seq, 1}


C’s Routing table

dest nexthop hopcount

D D 1



3. Node A creates a RREP packet and unicasts RREP to S.

4. Set forward path in node A’s routing table.

S A

B

C

D


C’s Routing table


D D 1

RREP{D, D’seq, S, S’seq, 2}

A’s Routing table


D C 2



4. Set forward path in node S’s routing table.

S A

B

C

D


C’s Routing table


D D 1

A’s Routing table


D C 2

S’s Routing table


D A 3



1. If intermediate nodes or the destination move.The next hop links break.

Routing tables are updated for the link failures.

All active neighbors are informed by RouteError (RRER) packet.

2. When a source node receives an RRER, it can

reinitiate the route discovery process.

3. It can be also dealt with by a local fix scheme.

Route maintenance in AODV (Path broken due to host mobility)



Assume link between C and D breaks.

Node C invalidates route to D in route table.

Node C creates RRER packet and sends to its upstream

neighbors.

Node A sends RRER to S. Node S rediscovers route if still needed.

S A

B

C

DRRER

Illustration of route maintenance in AODV

RRER



Advantage:

The routes are established on demand and the destination

sequence number can find the latest route to the

destination.

Disadvantage:

The intermediate nodes can lead to inconsistent routes if

the source sequence number is very old. The periodic beaconing leads to unnecessary bandwidth

consumption.




DSR designed to restrict the bandwidth consumed

by control packets in ad hoc wireless networks by

eliminating the periodic table-update messagesrequired in the table-driven approach.

On-demand routing protocol –

Dynamic Source Routing Protocol (DSR)



Route Discovery

(broadcasting the RREQ packets)

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8<1>

<1,2> <1,3,5,7>

<1,4>

<1,4,6>

<1,3,5>

<1,3><1>

<1>

Source

Destination



Route Discovery (cont.)

(propagating the RREP packets back to source)

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<1,4,6>

<1,4,6>

<1,4,6>

Source

Destination

<1,3,5, 7>

<1,3,5, 7>

b id i l



Hybrid routing protocol –

Zone Routing Protocol (ZRP)

A hybrid routing protocol which effectively combines

the best features of both proactive and reactive routing

protocols.

The key concept employed in ZRP is to use a

proactive routing scheme within a limited zone in the

γ-hop neighborhood of every node, and use a reactiverouting scheme for nodes beyond this zone.



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Routing Zone with Radius = 1


Routing Zone for Node 8

Routing zone for node 8 in ZRP

Performing the Proactive Routing for node 8



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Routing Zone for Node8

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RouteRequest

RouteReply


Performing the Proactive Routing for node 8

(destination=node 16)



Advantage:

By combining the best features of proactive and

reactive routing schemes, ZRP reduces the control

overhead.

Disadvantage:

But in the absence of a query control, ZRP tends to

produce higher control overhead than the previously

schemes.

Hybrid routing protocol – ZRP (cont.)



Other routing issue for MANET – The Intermittent connected routing problem

In case of the nodes density of a MANET is sparse, it

will cause the intermittent connected routing problem,

and consequently the traditional routing protocols will

be no longer fit.



Intermittent connected routing problem



Epidemic routing protocol

Epidemic is a simple routing protocol to resolve the

intermittent connected routing problem.

The nodes adopt store-carry-forward communication

scheme.

A node can carry the messages in its cache if no any direct

routing path to the destination is available. If a node moves into the node’s transmission range, they

will exchange the carried messages between them.



S

3

2

14

5

(Epidemic routing)



A sensor network is composed of a large number of

multifunctional and small sensor nodes.

WSN allows random deployment in inaccessible

terrains or disaster relief operations.

Sensor nodes are fitted with an onboard processor, itconsists of sensing, data processing, and

communicating components.


WSNs



Introduction to WSNs -- Communication architecture

Internet or

satelite

User

Task manager node

Sink

Sensor field



Sink

Satelite

Introduction to WSNs -- Communication architecture (cont.)



The sensor nodes are usually scattered in a sensor

field.

Sensor nodes can collect data and route data back tosink.

The sink may communicate with the task manager

node via Internet or Satellite.

Introduction to WSNs -- Communication architecture (cont.)



The number of sensor nodes in a sensor network

can be several orders of magnitude higher.

Sensor nodes are densely deployed.

Sensor nodes are prone to failures.

Sensor nodes are limited in power, computational

capacities, and memory.

Introduction to WSNs – The differences between WSNs and ad-hoc networks



Sensor nodes mainly use a broadcast communication

paradigm, whereas most ad hoc networks are based

on point-to-point communications.

Sensor nodes may not have global identification (ID)

because of the large amount of overhead and large

number of sensors.

Introduction to WSNs – The differences between WSNs and ad-hoc networks (cont.)



Introduction to WSNs – Sensor node



Aqua node

Introduction to WSNs – Sensor node (cont.)



Aqua node




Mobilizer Location Finding System Power Generator

Power Unit

Sensor ADC

Processor

Storage

Transceiver

Sensing Unit Processing Unit Transmission Unit




Introduction to WSNs – Design factors

Production costs

The cost of each sensor node should be much less

than US $1 in order for the sensor network to be

feasible.

Transmission media

In a multi-hop sensor network, communicating

nodes are linked by radio, infrared or optical

media.



Introduction to WSNs – Design factors (cont.)

Environment

Sensor network usually work unattended in remote

geographic areas, such as large machinery, ocean,

biologically and chemically contaminated field.

Hardware

A sensor node is made up of four basic components:

sensing unit, processing unit, transceiver unit,

power unit, and also have additional application-dependent components.



Three phases of WSNs deployment Pre-deployment phase

Sensor nodes can be either thrown in mass

or placed one by one in the sensor field.

Post-deployment phase

After deployment, topology changes are

due to change in sensor nodes’

Position available energy

malfunctioning

Introduction to WSNs – Network deployment



Re-deployment phase

Additional sensor nodes can be re-deployed at

any time to replace the malfunctioning nodes

or due to changes in task dynamics.

Addition of new nodes poses a need to re-

organize the network.

Introduction to WSNs – Network deployment (cont.)



Node deployment

In manual deployment, the sensors are

manually placed and data is routed through

predetermined paths.

Energy consumption without losing accuracy

Sensor nodes can use up their limited energy

performing computations and transmitting

information.

Introduction to WSNs – Routing challenges and design

issues



Data reporting method

Data reporting can be categorized as either time-

driven, event-driven, query-driven, or a hybrid.

The time-driven method is suitable for

applications that require periodic data.

Event-driven and query-driven methods, sensor

nodes react immediately to sudden and drasticchanges in the value of a sensed attribute


issues (cont.)



Coverage

A given sensor’s view of the environment is

limited in both range and accuracy.

Area coverage is an important design

parameter.

Quality of service

Bounded latency for data delivery is another

condition for time-constrained applications.

As energy is depleted, the network may be

required to reduce the quality of results in

order to reduce energy dissipation.


issues (cont.)



Routing protocols for WSNs (cont.)

Flat-based

All nodes are typically assigned equal roles or

functionality.

Hierarchical-based

Nodes will play different roles in the network.

Location-based

Sensor node’s positions are exploited to route

data in the network.

R i l f WSN ( )




Flat-based routing

Each node typically plays the same role andsensor nodes collaborate to perform the sensing

task.

This consideration has led to data-centric routing,where the BS sends queries to certain regions and

waits for data from the sensors located in the

selected regions.

Early work on data centric routing were shown to

save energy through data negotiation and

elimination of redundant data.



Flat-based routing exampleSPIN (Sensor Protocols for Information via Negotiation)

ADV REQ DATA

ADV REQ DATA

A

1. Data is described by meta-message (ADV).

2. Send ADV to neighbors.

3. If neighbor do not have the data, sends REQ; otherwise, do nothing.4. As the REQ received by sender, then it sends the data to the

neighbor.

Fl t b d ti l



Flat-based routing exampleSPIN (cont.)

Advantage

Each node only needs to know its one-hop

neighbors.

Disadvantage

Data advertisement cannot guarantee the

delivery of data.

R i l f WSN ( )



Hierarchical routing is two-layer routing where one

layer is used to select cluster heads and the other for

routing.

Higher-energy nodes can be used to process and sendthe information, while low-energy nodes can be used

to perform the sensing in the proximity of the target.

The creation of clusters and assigning special tasks tocluster heads can greatly contribute to overall system

scalability, lifetime, and energy efficiency.


Hierarchical-based routing



Proactive clustering.

Node transmits sensed data only if both of the following

conditions hold:

1. The sensed value is greater than a Hard Threshold .2. The sensed value differs from last transmitted value

by more than a Soft Threshold .

Hi hi l b d ti l



Hierarchical-based routing exampleTEEN (Threshold-Sensitive Energy Efficient Sensor Network Protocol)

Node

1st cluster head

2nd cluster head

Sink

Cluster

S

D

Hi hi l b d ti l



Advantage

Good for time-critical applications.

Disadvantage Inappropriate for periodic monitoring,

e.g., habitat monitoring.

Ambiguity between packet loss and

unimportant data.

Hierarchical-based routing exampleTEEN (cont.)



Routing compare

Hierarchical-based routing Flat-based routing

Reservation-based scheduling Contention-based scheduling

Collisions avoided Collision overhead present

Reduced duty cycle due to periodic

sleeping

Variable duty cycle by controlling

sleep time of nodes

Data aggregation by cluster head Node on multi-hop path aggregatesincoming data from neighbors

Simple but non-optimal routingRouting can be made optimal but

with an added complexity

Requires global and local

synchronization

Links formed on the fly without

synchronizationOverhead of cluster formation

throughout the network

Routes formed only in regions that

have data for transmission

Lower latency as multiple hops

network formed by cluster heads

always available

Latency in waking up intermediate

nodes and setting up the multipath

Routing protocols for WSNs (cont )




Location-based routing

The location of nodes may be available directly by

communicating with a satellite using GPS if nodes

are equipped with a small low-power GPS receiver.

Relative coordinates of neighboring nodes can beobtained by exchanging such information between

neighbors.

To save energy, some location-based schemesdemand that nodes should go to sleep if there is no

activity.



Vehicular Ad hoc Network (VANET) is a special case of

MANET.

The direct communication between vehicular using Adhoc network.


VANETs



Applications in a VANET fall into two categories

comfort applications

safety applications

Comfort applications aim to improve the driving comfortand the efficiency of the transportation system

on-board Internet access

high data rate content download

driving through payment

Introduction to VANETs



Safety applications aim to provide driver’s informationabout future critical situations

inter-vehicle danger warning

intersection collision avoidance

work zone safety warning

Introduction to VANETs (cont.)



Safety applications



VANETs provide the following three communications:

Inter-Vehicle Communication (IVC)

Roadside-to-Vehicle Communication (RVC)

Hybrid-Vehicular Communication (HVC)

V2V

V2R

RSU

Emergency Event




Vehicles mobility is restricted to one-dimensional road

geometry.

Factors affect the mobility of vehicles such as

road configuration

traffic laws

safety limits

physical limits




Vehicle mobility creates a highly dynamic topology.

VANETs are potentially large-scale networks.

Vehicles can provide more resources than other types of

mobile networks such as： large batteries

antennas

processing power




The connectivity of the network is affected by factors that

include

transmitter power

environmental conditionsobstacles

mobility




Factors such as the vast number of nodes that lack inherent organization, as well as

frequent topological changes




To enhance the safety of drivers

To provide the comfortable driving environment

The message for different purpose need to be sent to

vehicles through the inter-vehicle communications.Unicast routing

Multicast and Geocast

Broadcast

Routing for VANETs



Unicast routing is a fundamental operation for vehicle toconstruct a source-to-destination routing in a VANET

From Reference 1.

Routing for VANETs -- Unicast



Routing objective:Min-Delay

The goal of min-delay routing protocols is to transmit

data packets to destination as soon as possible. Relative routing protocols：VADD、CAR、 DIR

Routing for VANETs -- Unicast



Unicast routing example for VANETsVehicle-Assisted Data Delivery (VADD)

Carry-and-forward for data delivery from a moving

vehicle to a static destination.

VADD is to select a forwarding path with the smallest

packet delivery delay.

i i l f



Two Paths： (1) Ia => Ic => Id => Ib

(2) Ia => Ib

Disconnected due to sparse

Delayacdb < Delayab

Unicast routing example for VANETsThe VADD (cont.)

i i l f A



1. Transmit through wireless channels as much as possible.

2. If the packet has to be carried through certain roads, the

road with higher speed should be chosen.


U i i l f VANET



3. Due to the unpredictable nature of vehicular ad-hoc

networks, so dynamic path selection should

continuously be executed throughout the packet

forwarding process.− The routing cannot expect the packet to be successfully

routed along the pre-computed optimal path




To overcome the limitation of the static destination.

The CAR protocol establishes a routing path from source

to destination by setting the anchor points at intermediate

junctions.

Unicast routing example for VANETsConnectivity-Aware Routing (CAR)

i i l f



CAR protocol sends the searching packets to find the

destination.

Each forwarding vehicle records its ID, hop count, and

average number of neighbors in searching packets.

Once the searching packets reach the destination, thedestination chooses a routing path with the minimum

delivery delay time and replies it to the source.

Unicast routing example for VANETsThe CAR (cont.)

U i i l f VANET



While destination sends the reply packet to the source, the

junctions passed through by the reply packet are set as the

anchor point.

After the path set up, data packets are forwarded in a

greedy forwarding.

Greedy forwarding example:

x: the current message holder.

Assume y is the closest neighbor of x to D,

then x sends the message to y.

y

D

x

Unicast routing example for VANETsThe CAR (cont.)

U i i l f VANET



Vehicle V S tries to send data to vehicle V D , the anchor

points are set at I 1,1 , I 2,1 , I 2,2 , I 3,2 , I 3,3 , and I 3,4.

Data is forwarded according to order in the list of anchor points.

Unicast routing example for VANETsAn example for CAR (cont.)

Unicast routing example for VANETs



To improve the CAR protocol.

DIR protocol constructs a series of diagonal intersections

between the source and destination vehicles.

Auto-adjustability is achieved that one sub-path with low

data packet delay, between two neighboring diagonal

intersections, is dynamically selected to forward data packets.

Unicast routing example for VANETsDiagonal-Intersection-based Routing (DIR)

Unicast routing example for VANETs



To reduce the data packet delay, the route is automatically

re-routed by the selected sub-path with lowest delay.

DIR protocol constructs a series of diagonal intersections between vehicles V S and V D.

Unicast routing example for VANETsThe DIR (cont.)

U i t ti l f VANET



DIR protocol may set the fewer number of anchors than

CAR protocol.

DIR protocol can automatically adjust routing path for

keeping the lower packet delay, compared to CAR

protocol.

Unicast routing example for VANETsThe comparisons between CAR and DIR



Multicast is defined by delivering multicast packets from

a single source vehicle to all multicast members by multi-hop communication.

Geocast routing is to deliver a geocast packet to a specificgeographic region.

Geocast

Routing

Routing for VANETs – Multicast and Geocast



Broadcast protocol is utilized for a source vehicle sends

broadcast message to all other vehicles in the network.

Routing protocol type：

Broadcast methods for V2V communication

Advertisement Publicity Broadcast

Broadcast routing for VANETs



The purpose of emergency information is to announce anurgent event by broadcasting for surrounding vehicles.

emergency-vehicle-approach

traffic accident information dissemination

Broadcast outing for VANETs (cont.)



Emergency-vehicle-approach Emergency-vehicle-approach information is used to

announce the urgent event to those vehicles in front of the

current vehicle, so the emergency information is only

disseminated ahead. Traffic accident information dissemination

Traffic accident information is used to announce the urgent

event to those vehicles behind the current vehicle, the

emergency information is only disseminated behind.

Broadcast routing for VANETs (cont.)

Broadcast ro ting for VANETs



1. Vehicle V A broadcasts the emergency message to therestricted direction.

2. Vehicle V D does nothing.

Broadcast routing for VANETs(emergency message distribution)

Broadcast routing for VANETs



3. Vehicle V B is located in the relay range, it re-broadcasts theemergency information.

4. Vehicle V C is located in notification range but not in relay

range, V C just receives the emergency information and not

to re-broadcast.

Broadcast routing for VANETs --emergency message distribution (cont.)

References



References

I. F. Akyildiz, W. Su, Y. Sankarasubramaniam, and E. Cayirci, "Wireless

sensor network: a survey", Computer Networks, Vol. 38, pp. 393-422,2002.

I. F. Akyildiz, W. Su, Y. Sankarasubramaniam, and E. Cayirci, "A survey

on sensor networks", IEEE Communications Magazine, Vol. 40, issue 8,

pp. 102-114, Aug. 2002.

J. N. Karaki, A. E. Kamal, "Routing techniques in wireless sensor

networks: a survey", IEEE Wireless Communications, pp. 6-28, Dec.

2004.

J. Zhao and G.Cao, ―VADD: vehicle-assisted data delivery in vehicular

ad hoc networks,‖ IEEE Computer Communications, pp. 1-12, 2006.

V. Naumov and T. Gross, ―Connectivity-aware routing (CAR) in

vehicular ad hoc Networks,‖ in Proceedings of IEEE International

Conference on Computer Communications, pp.1919-1927, 2007.

Y. W. Lin, Y. S. Chen and S. L. Lee, ―Routing protocols in vehicular ad

hoc networks: a survey and future perspectives,‖ Journal of Information

Science and Engineering 26, pp.1-20, 2010.

References



References

M. S. Bouassida and M. Shawky, ―A cooperative congestion control approachwithin VANETs : formal verification and performance evaluation,‖ EURASIP

Journal on Wireless Communications and Networking, Vol. 2010, 2010.

http://commonsense.epfl.ch/COMMONSense/description.htm

http://groups.csail.mit.edu/drl/wiki/index.php/AMOUR_(Autonomous_Modula

r_Optical_Underwater_Robot)

http://russnelson.com/wisan/Sensor-node-front.jpg http://www.ece.ncsu.edu/wireless/Images/sensor.gif

http://blogs.iium.edu.my/jaiz/2008/12/22/what-is-vehicular-network/

http://www.ece.ncsu.edu/wireless/Images/sensor.gif









http://www.ece.ncsu.edu/wireless/Images/sensor.gif

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