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3.3 Survey of IoT Routing Protocols: RPL and LEACH

Lesson 17 of 31 in the free Internet of Things (IoT) notes on Siksha Sarovar, written by Rohit Jangra.

3.3.1 Routing in Low-power and Lossy Networks (LLNs)

IoT networks are unique because links are unstable (lossy) and nodes are energy-constrained. Standard internet routing (OSPF/BGP) is too "Chatty" and heavy.

3.3.2 Classification of IoT Routing Strategies

  • Flat Routing: Every node is equal. Use for small networks (e.g., AODV, DSDV).
  • Hierarchical Routing: Nodes organized into clusters. Data is aggregated at the "Cluster Head" to save energy (e.g., LEACH, TEEN).
  • Geographical Routing: Using physical coordinates (GPS or RSSI trilateration) to route data towards the destination without needing global routing tables.

3.3.3 The RPL Standard (IETF RFC 6550) - The Industry standard

RPL is the IPv6 distance-vector routing protocol for LLNs.

  1. DODAG: Destination Oriented Directed Acyclic Graph (A tree structure rooted at the gateway).
  2. Rank: A scalar value representing the node's "cost" to reach the root. Prevents routing loops.
  3. Objective Function (OF): The algorithm that calculates the best path. (e.g., MRHOF minimizes Expected Transmission Count).

3.3.4 LEACH Protocol (Cluster-based Routing theory)

LEACH (Low-Energy Adaptive Clustering Hierarchy):

  • Nodes elect a "Cluster Head" (CH) based on probability.
  • Non-CH nodes send data to CH; CH aggregates and sends a single packet to the Gateway.
  • Key Feature: CH role rotates among all nodes every "Round" to balance energy consumption.

3.3.5 Routing Metrics Technical comparison

Metric NamePurposeSelection CriteriaTarget Application
ETXReliabilityLink with fewest retriesIndustrial Safety
EnergyLongevityNodes with most batteryEnvironmental
LatencySpeedShortest path timeAlarm Systems
LQISignal QualityStrongest RSSI linkIndoor Smart Home