Sensor Network

1.IntroductionGoal Wireless Sensor NetworkUbiquitous ComputingUbiquitous Network SocietyHuman-centric

1.IntroductionUbiquitousUbiquitous7AAnytimeAnyoneAnywhereAny DeviceAffordableAll SecurityAny Information/Service

1.IntroductionGeneral PurposeA wireless sensor network (WSN) is a wireless network using sensors to cooperatively monitor physical or environmental conditionsThe development of wireless sensor networks was originally motivated by military applications. Wireless sensor networks are now used in many wide-range application areas.

1.IntroductionSensorsImage Sensor Modules (885.7mm)Ultrasonic Magnetic Sensor (22.522.539mm)WII sensor (2403515mm)

1.IntroductionTypical Sensor NetworksensorsensorsensorsensorsensorsensorCenterRelaynodeRelaynodeData gatheringData transmitting processing

1.Introductionsensor characteristics Wireless sensors are small devices that gather information. Pressure, Humidity, TemperatureSpeed, Location

Wireless sensors have some characteristics:Low powerSmall sizeLow cost

Kizza - Guide to Computer Network SecurityDesign Factors in Sensor Networks Several factors influence the design philosophy of sensor networks. Among these factors are first whether the nodes are stationary or moving and whether the network is deterministic or self-organizing. Most sensor network applications use stationary nodes. In a deterministic topology, the positions of the nodes and the routes in the network are pre-determined and the nodes are manually placed. In self-organizing topology, node positions are random and the routes are also random and unreliable. Routing in these networks, therefore, becomes the main design concern. These demand a lot of energy, direct routing is not desirable and multi-hop routing is more energy efficient.

Kizza - Guide to Computer Network Security

Kizza - Guide to Computer Network SecurityFactors that influence the design philosophy of sensor networks are:Routing - communication in wireless sensor networks, is based on a protocol stack with several layersPower Consumption - most sensor networks are entirely self-organizing and operate with extremely limited energy and computational resources. The functionality of the network, therefore, depends on the consumption rate of energy by node units.

Kizza - Guide to Computer Network Security

Kizza - Guide to Computer Network SecurityFault Tolerance in case of anyone sensor node failure, the network should sustain all its functionalities. Scalability - the addition of more nodes to the network should not have any diverse effects to the functionality of the networkProduction Costs the unit cost of each individual sensor node plays a crucial role in determining the overall costs of the entire sensor network. The network should have a least unit cost for individual nodes

Kizza - Guide to Computer Network Security

Kizza - Guide to Computer Network SecurityNature of Hardware Deployed - A sensor node consists of four basic parts: the sensing unit, the processing unit, the transceiver unit, the power unit. All these units must be packaged in a very small, match-box-sized package. And consumer very low power.Topology of Sensor Networks - a normal sensor network may contain thousands of sensor nodes deployed randomly throughout the field of observation, resulting in uneven densities depending on how the nodes where deployed. Transmission Media nodes in wireless sensor network are linked by a wireless medium. The medium could be by radio like RF and Bluetooth, infrared or optical waves. The functionality of the network may depend on these media

Kizza - Guide to Computer Network Security

1.Introductionsensor network characteristicsPrimary FunctionSample the environment for sensory informationPropagate data back to the infrastructure

Traffic pattern in sensor networkLow activity in a long periodBursting data in short timeHighly correlated traffic

1.Introductionsensors categoriesSensors can be classified into two categories:Ordinary SensorsData gathering Ordinary Sensors require external circuitry to perform some dedicated tasks like data analyzing. Smart SensorsData gathering and processing Smart Sensors have internal circuitry to perform dedicated tasks.

1.IntroductionRelated WorkRelated work

CSMATo improve the energy consumption by avoiding overhearing among neighboring nodesTDMANo contention-introduced overhead and collisionsNot easy to manage the inter-cluster communication and interferenceNot easy to dynamically change its frame length and time slot assignment

1.IntroductionRelated WorkPAMASPower off radio when not actively transmitting and receiving packet.ZigbeeCombined with IEEE 802.15.4 (Low-Rate Wireless Personal Area Network, LR-WPAN)Low rate: 250kbpsShort distance: 50-300mLow power consumptionfrequency band:Global: 2.4GHz ,16 channelsAmerica: 915MHz, 10 channelsEurope: 868MHz, 1 channel.

1.IntroductionZigbee stackZigbee Platform Stack and IEEE802.15.4PHY LayerMAC LayerNetwork / SecurityLayersApplication FrameworkApplication/ProfilesIEEE 802.15.4ZigBee or OEMZigBeeAlliancePlatform

1.IntroductionZigbee ApplicationReference: NTPZigBee

2.MAC for Sensor NetworkSensor Network MAC ProtocolCarrier SensingOnly during low traffic load.BackoffBackoff in application layer is desired other than in MAC layer.ContentionRTS-CTS only during high traffic load.

2.MAC for Sensor NetworkSources of Energy WastageThe major sources of energy wastage are:CollisionsOverhearingControl packet overheadIdle listening

Achieving good scalability and collision avoidance capability is necessary.

2.MAC for Sensor NetworkS-MACSensor-MAC (S-MAC): Medium Access Control for Wireless Sensor Networks

S-MAC is a medium-access control (MAC) protocol designed for wireless sensor networks.

Sensor networks are deployed in an ad hoc fashion, with individual nodes remaining largely inactive for long periods of time, but then becoming suddenly active when something is detected.

2.MAC for Sensor NetworkS-MACThese characteristics of sensor networks and applications motivate a MAC that is different from traditional wireless MACs such as IEEE 802.11 in almost every wayEnergy conservation and self-configuration are primary goals.Per-node fairness and latency are less important.

2.MAC for Sensor NetworkThree techniques in S-MACS-MAC uses three techniques to reduce energy consumption.

Nodes go to sleep periodically.Nearby nodes form virtual clusters to synchronize their wake-up and sleep periods to keep the control packet overhead of the network low.Message passing is used to reduce the contention latency and control overhead.

2.MAC for Sensor NetworkThree techniques in S-MACPeriodic Listen and Sleep:

Nodes do not waste energy by listening to an empty channel or when a neighboring node is transmitting to another node.Nodes use RTS and CTS to talk to each other and contend for the medium.

2.MAC for Sensor NetworkThree techniques in S-MAC Collision and Overhearing Avoidance:S-MAC adopts a contention-based scheme to avoid collisions.A duration field is introduced in each transmitted packet which indicates how much longer the transmission will last.When a node receives a packet, it will not transmit any packets for at least the time that is specified in the duration field.

2.MAC for Sensor NetworkThree techniques in S-MACCollision and Overhearing Avoidance:Overhearing is avoided by letting the nodes, which get RTS and CTS packets which are not meant for them, go to sleep.All immediate neighbors also go to sleep till the current transmission is completed after a sender or receiver receives the RTS or CTS packet.

2.MAC for Sensor NetworkThree techniques in S-MACMessage Passing:Long messages are fragmented into smaller messages and transmitted in a burst.To avoid the high overhead and delay encountered for retransmitting when message is lost.ACK messages are used to indicate if a fragment is lost at any time.The sender can resend the fragment again.The ACK message also have the duration field to reduce overhearing and collisions.

3. ChallengesChallenges:1. Energy Efficiency:Power consumptions are crucial to wireless sensor network applications because sensor nodes are not connected to any energy source.Energy efficiency is a dominant consideration no matter what the problem is. Sensor nodes only have a small and finite source of energy. Many solutions, both hardware and software related, have been proposed to optimize energy usage.

3. Challenges2. Ad hoc deployment:

Most sensor nodes are deployed in regions which have no infrastructure.We must cope with the changes of connectivity and distribution.

3. Unattended operation:

Generally, once sensors are deployed, there is no human intervention for a long time. Sensor network must reconfigure by itself when certain errors occur.

3. Challenges

4. Dynamic changes:As changes of connectivity due to addition of more nodes or failure of nodes, Sensor network must be able to adapt itself to changing connectivity.

4.CoverageCoverage can be classified into three types:Area coveragedeployment of sensors to cover a given area Point coveragedeployment of sensors to cover a set of pointsBarrier coverageThe goal is to minimize the probability of undetected penetration through the barrier.To find a path in a region For any point on the path, the distance to the closest sensor is minimized.

4.Coverage Area coverageArea coveragedeployment of sensors to cover a given area

4.Coverage Point coveragePoint coveragedeployment of sensors to cover a set of points

4.Coverage Point coverageBarrier coverageTo find a path from A to BFor any point on the path, the distance to the closest sensor is minimized.

AB

5.LocalizationIn sensor networks, nodes are deployed without priori knowledge about their locations.

Estimating spatial-coordinates of the node is referred to as localization.

5.LocalizationGPSGlobal Positioning System (GPS) is an immediate solution.There some factors against the usage of GPS:GPS can work only outdoors.GPS receivers are too expensive to unsuitable for wide-range deployment. It cannot work in the presence of obstructions.

5.LocalizationCategoriesLocalization can be classified into two categories:Fine-grainedBased on timing / signal strength Coarse-grainedBased on proximity

5.LocalizationProximity base localizationTrilateration / Multilateration techniqueProximity based localization:Some nodes which can know their position through some technique (ex. GPS) broadcast their position information.Other nodes listen to these broadcast messages and calculate their own position.A simple method would be to calculate its position as the centroid of all the positions it has obtained.This method leads to accumulation of localization error.

5.LocalizationTrilateration ExampleTrilaterationA is 5m from BA is 10m from CA is 8m from DBCD

5.LocalizationTrilaterationTrilateration is a geometric principle which allows us to find a location if its distance from other nodes are known.The same principle can be extended to three-dimensional space.Four spheres would be needed to locate certain point in 3D space.

5.Localization Fine-grained methodSignal strength methodAttenuation happens when signals are propagated. We can use the degree of attenuation to calculate the distance.

Timing methodThe distance between two nodes is determined by the time of flight of the signal.

6.Routing CategoriesRouting protocols can be divided into two types.Proactive routing protocolProactive routing protocol maintain consistent updated routing information between all nodes.To update routing table periodically.Reactive routing protocolRoutes are created only when they are needed.

6.RoutingThree types in sensor networkBecause of the energy constrained nature of sensor networks, conventional routing protocols have many limitations when being applied to sensor networks.Three types of routing protocol in sensor network:Data-centricHierarchicalLocation-based

6.RoutingData-centricData-centric:Managers broadcast a Query message to the network.If a sensor observes some events related to the Query message, it sends the data to the data center.Data aggregation:sensor1sensor2Relaynode1DataCenter

6.Routing Data-centricData centric: FloodingFlooding is one of basic data transmitting methods.If any sensor receives or generates some packets, it will broadcast these packets to all its neighbors.Nodes may receive duplicate data.More power consumption.

6.Routing Data-centricData centric: Sensor Protocols for Information via Negotiation (SPIN)

There are three messages in SPIN:Advertisement (ADV): When a node has some data to send, it sends an ADV message to its neighbors containing data descriptor (meta-data).Request (REQ): When a node wants to receive some data. It sends an REQ message first.DATA: Actual data message with a meta-data header.

6.Routing Data-centricNode1Node6Node3Node2Node4Node5Node7SPIN:

6.Routing Data centricData centric: Directed DiffusionThis is a destination-initiated reactive routing technique.Routes are established when requested.A interest is propagated throughout the network for named data by a node and data which matches this interest is then sent toward this nodes.Interests are described by a list of attribute-value pairs.Example: type=birds & response=20 ms

6.Routing Data centricDirected DiffusionThe propagation of data and its aggregation at intermediate nodes on the way to the request originating node are determined by the messages which are exchanged between neighboring nodes within some distance.

6.Routing Data centricNode6Forward interest Directed Diffusion:

6.Routing Data centric Directed Diffusion:Sender can choose the best return path.EX: minimum response time, least hops

6.Routing HierarchicalHierarchical: Low Energy Adaptive Clustering Hierarchy (LEACH)LEACH is a two-tier protocol.Cluster headCluster memberEvery node runs a random algorithm periodically to decide its identity. (cluster head or not)

6.Routing HierarchicalLEACHAll cluster heads broadcast Advertisement (ADV) message and other nodes decide which cluster they belong to according the strength of ADV message. Cluster members only send data to their cluster head. Then, cluster heads reply data to Sinks.

6.Routing HierarchicalNode1Node4Node2Node3SinkNode5Cluster Head1Cluster Head2Cluster Head3Node7Node6Node9Node10Node8Node12Node13Node11Cluster 1Cluster 2Cluster 3LEACH Example

6.Routing Location-basedLocation-based: Geographic Adaptive Fidelity (GAF)GAF divides the network into several virtual grids.For adjacent virtual grids A and B, every node in A can directly connect with every node in B.In GAF, every node has three types of status:Active DiscoverySleep

6.Routing Location-basedGAF:Initially, every node is in discovery status and tries to find out nodes belong to the same grid with itself.Every node in discovery status sets a timer Td. Once the Td timer ends, Nodes broadcast discovery message and get into active status.

6.Routing Location-basedGAF:When a node is in active status, it will start a timer Ta. Data transmission is allowed until Ta timer ends.In active status, nodes will periodically broadcast discovery message at Td intervals.Once Ta timer ends, nodes return to discovery status.

6.Routing Location-basedGAF:If a node in discovery status receives a discovery message sent from the node which is in the same grid and has higher ranking, it will get into sleep status.After a Ts timer, it will return to discovery status.Ranking can be done by remaining power or ID sequence.

Need for securityWSNs are becoming a cost effective, practical way to go about deploying sensor networks.Large range of applications from civilian to military purposes.Pose different challenges as compared to traditional networks. Hence different mechanisms must be brought about.Enormous research potential.

Main AspectsObstacles to WSN security.Requirements of a Secure WSN.Attacks.Defensive Measures.

Obstacles to WSN SecurityVery limited resources: Limited memory and Storage space : A typical sensor has a 16 bit 8 Mhz CPU with 10K RAM, 48K Program Memory and 1M flash storage. Power limitation

Obstacles to WSN Security -continuedUnreliable Communication : Unreliable Transfer : Packet-based routing of the sensor network is connectionless hence unreliable. Conflicts: Even if the channel is reliable, the communication may still be unreliable due to broadcast nature of WSN. Latency: Multi-hop routing, network congestion and node processing can lead to greater latency in the network.

Obstacles to WSN Security continued..againUnattended Operation: Exposure to Physical Attacks. Managed Remotely: Hard to detect physical tampering. No Central Management Point: Ideally a WSN should have no central management point. However, if the network is designed incorrectly it may lead to greater congestion.

Security RequirementsShares some common points with traditional networks but also presents unique problems of its own.Data confidentiality: Most important issue in any network.Data integrity: Inability to modify data.Data freshness: Ensures that no old messages have been replayed. Essential for shared key schemes.

Security Requirements - continuedAvailability: Adjusting existing encryption algorithms to fit within a WSN has costs : Additional computation consumes more energy. Additional communication consumes more energy. Threat of a single point failure if a central management point scheme is used.

Security Requirements continued..againSelf Organization: A WSN is typically an ad hoc network which requires every node to be self organizing and self healing. Time Synchronization: e.g. to calculate the end to end delay time of packets between nodes. Secure localization: Ability to accurately and automatically locate each sensor in the network.Authentication

Attacks Vulnerable to a multitude of attacks such as DoS, traffic analysis, privacy violation, physical attacks and so on. DoS: Jamming a node or set of nodes by transmission of a radio signal that interferes with radio frequencies being used. Violate the communication protocol thus depleting valuable battery life.

More attacksSybil attack: Defined as a malicious device illegitimately taking on multiple identities.Originally used against peer to peer networks but may also be used to disrupt routing algorithms, data aggregation etc.Traffic Analysis Attacks: Take over the base station/nodes closest to base station.

Yet more attacksNode replication attacks.Attacks against privacy.Physical attacks.

Defensive MeasuresKey Establishment.Secure Broadcasting and Multicasting.More efficient routing protocols.Intrusion Detection.