routing protocols for wsn and iot - gazi...

Gazi University

Wireless Sensor Networks and Data Mining Laboratory

Routing Protocols for WSN and IoT

Suat Özdemir

1.11.2016 w3.gazi.edu.tr/~suatozdemir/ 1

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Routing algorithms for ad hoc networks• Proactive strategy:

• also referred to as table driven, relies on periodic disseminationof routing information to maintain consistent and accurate routing tables across all nodes of the network.

• Reactive routing strategy:• establish routes to a limited set of destinations on demand. Do

not typically maintain global information across all nodes of the network.

• Hybrid strategy:• the network is organized into clusters. Proactive routing is used

within a cluster and reactive routing is used across clusters

• Routing protocol overhead typically increases dramatically with increased network size anddynamics.


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Routing in Wireless Sensor Networks


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Routing challenges and design issues• Node deployment

• Manual deployment• Sensors are manually deployed• Data is routed through predetermined path

• Random deployment• Optimal clustering is necessary to allow connectivity & energy-

efficiency• Multi-hop routing

• Fault tolerance

• Some sensors may fail due to lack of power, physical damage, or environmental interference

• Adjust transmission power, change sensing rate, reroute packets through regions with more power


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Routing challenges and design issues• Coverage

• An individual sensor’s view is limited

• Area coverage is an important design factor

• Data aggregation• Minimize the transmitted data along the path

• Quality of Service• Bounded delay

• Energy efficiency • For longer network lifetime


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Routing Protocols in WSNs

• Flat

• Hierarchical

• Location-based

• QoS-based


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Flat• Flooding

• Too much waste

• Implosion & Overlap


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Flat• Gossiping

• slightly enhanced version of flooding where the receiving node sends the packet to a randomly selected neighbor

• Data-centric routing• No globally unique ID

• Naming based on data attributes

• SPIN

• Directed diffusion


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Flat

• SPIN (Sensor Protocols for Information via Negotiation)


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Flat• SPIN (Sensor Protocols for Information via

Negotiation)

• Pros• Each node only needs to know its one-hop neighbors• Significantly reduce energy consumption compared to

flooding• Good for mobile nodes

• Cons• Data advertisement cannot guarantee the delivery of data

• If the node interested in the data are far from the source, data will not be delivered

• Not good for applications requiring reliable data delivery, e.g., intrusion detection


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Flat• Directed diffusion

• Data centric • Individual nodes are unimportant

• Request driven• Sinks place requests as interests• Sources satisfying the interest can be found• Intermediate nodes route data toward sinks

• Localized repair and reinforcement

• Multi-path delivery for multiple sources, sinks, and queries


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Hierarchical

• LEACH (Low Energy Clustering Hierarchy)

• Cluster-based protocol


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Hierarchical• LEACH (Low Energy Clustering Hierarchy)• Each node randomly decides to become a cluster

heads (CH)• CH broadcasts Adv; Each node decides to which

cluster it belongs based on the received signal strength of Adv

• CH creates a tranmission schedule for TDMA in the cluster

• CDMA between clusters• Nodes can sleep when its not their turn to transmit• CH compresses data received from the nodes in the

cluster and sends the aggregated data to BS• CH is rotated randomly


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Hierarchical

• LEACH (Low Energy Clustering Hierarchy)

• Pros• Distributed, no global knowledge required

• Energy saving due to aggregation by CHs

• Cons• LEACH assumes all nodes can transmit with enough

power to reach BS if necessary (e.g., elected as CHs)

• Each node should support both TDMA & CDMA


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Location-based

• GEAR (Geographic and Energy Aware Routing)

• Each query packet has target region specified in the original packet

• Each node knows its position (GPS) and remaining energy level

• Each node knows its neighbors’ position (beacon) and their remaining energy levels

• Links (Transmission) are bi-directional


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Location-based

• GEAR (Geographic and Energy Aware Routing)

• Restrict the number of interest floods in directed diffusion • Consider only a certain region of the network rather

than flooding the entire network

• Each node keeps an estimated cost & a learning cost of reaching the sink through its neighbors

• Estimated cost = f(residual energy, distance to the destination)


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QoS-aware• Energy Aware QoS Routing Protocol

• Basic settings• Gateways can communicate with each other• Sensor nodes in a cluster can only be accessed by the

gateway managing the cluster• Focus on QoS routing in one cluster• Real-time & non-real-time traffic exist

• Support timing constraints for RT• Improve throughput of non-RT traffic


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• Finds least cost and energy efficient paths that meet the end-to-end delay during connection• Link cost = f(energy reserve, transmission energy, error rate)

of nodes

• Class-based queuing model

used to support best-effort and

real-time traffic generated

by imaging sensors


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• Drawbacks• Transmission time is not considered to estimate E2E delay

• Assumes more powerful gateways • All communications are through gateways

• Gateways have to find paths and r to support QoS requirements


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Routing in IoT

• What makes it different?• Relatively close base station compared to WSNs• Once data reaches the BS the rest is Internet routing • Low power and Lossy Networks (LLNs)

• IETF working group focused on routing issues for LLNs

• Routing Over Low power and Lossy networks (ROLL)

• LLNs are composed of many embedded devices: • restricted in processing power, memory and energy

(battery); • interconnected by a variety of links, such as IEEE 802.15.4

or Low Power WiFi, characterized by high loss rates, low data rates and instability;


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RPL: IPv6 Routing Protocol for LLNs

• IETF working group focused on routing issues for LLNs: • routing requirements specification for various

application areas of LLNs

• evaluation of existing routing protocols in the scope of LLNs

• Routing Protocol for Low power and lossy networks (RPL)


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RPL: IPv6 Routing Protocol for LLNs• RPL is a distance vector routing protocol for

LLNs that makes use of IPv6.

• The protocol tries to avoid routing loops by computing a node’s position relative to other nodes with respect to the root.

• The RPL specification defines four types of control messages for topology maintenance and information exchange.

• Another important fact about the protocol’s design is the maintenance of the topology.


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• Definitions: • Directed Acyclic Graph (DAG) - a directed graph with

no cycles exist.

• Destination Oriented DAG (DODAG) - a DAG rooted at a single destination


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RPL Node Rank

• Defines a node’s relative position within a DODAG with respect to the DODAG root.


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• Assumption: most traffic in LLNs flows through few nodes • many-to-one

• one-to-many

• Approach: build a topology (Instance) where routes to these nodes are optimized (DODAG(s) rooted at these nodes)


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RPL Instance

• Defines Optimization Objective when forming paths towards roots based on one or more metrics

• Metrics may include both Link properties (Reliability, Latency) and Node properties (Powered on not)

• A network may run multiple instances concurrently with different optimization criteria


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RPL Control Messages

• RPL defines a new ICMPv6 message with three possible types: • DAG Information Object (DIO) - carries information

that allows a node to discover an RPL Instance, learn its configuration parameters and select DODAG parents

• DAG Information Solicitation (DIS) - solicit a DODAG Information Object from a RPL node

• Destination Advertisement Object (DAO) - used to propagate destination information upwards along the DODAG.


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DODAG Construction

• Nodes periodically send link-local multicast DIO messages

• Stability or detection of routing inconsistencies influence the rate of DIO messages

• Nodes listen for DIOs and use their information to join a new DODAG, or to maintain an existing DODAG

• Nodes may use a DIS message to solicit a DIO

• Based on information in the DIOs the node chooses parents that minimize path cost to the DODAG root

• Result: Upward routes towards the DODAG root


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DODAG Example

• Each node has a set of parent nodes

• A node has no knowledge about children → ONLY upward routes


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DODAG Repair

• Link between G and C fails: • Choose another parent with a lower rank


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DODAG Repair

• Makes use of DODAG Sequence Numbers


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Downward Routes and Destination Advertisement • Nodes inform parents of their presence and

reachability to descendants by sending a DAO message

• Node capable of maintaining routing state → aggregate routes

• Node incapable of maintaining routing state → attach a next-hop address to the reverse route stack contained within the DAO message


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Destination Advertisement -Example• H sends a DAO message to F indication the availability of H, F

adds the next-hop and forwards the message to I

• G sends a DAO message to F indication the availability of G, F adds the next-hop and forwards the message to I

• F sends a DAO message to I indication the availability of F

• I aggregates the routes and sends a DAO advertising (F-I)


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RPL Traffic Flows

• Up towards the DAG root for many-to-one

• Down away from the DAG root for one-to-many

• Point-to-point via up*down*


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RPL Summary

• Optimized for many-to-one and one-to-many traffic patterns

• Routing state is minimized: stateless nodes have to store only instance(s) configuration parameters and a list of parent nodes

• Takes into account both link and node properties when choosing paths

• Link failures does not trigger global network re-optimization


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