WSN Programming Course

TinyOS Lab: Lesson 05: Advanced Protocols

Manuel Fernández

UAH, 18th September 2013

• Introduction to advanced protocols • Trends • Exercises

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Contents

• Up to now, we have only used single hop transmission, or very basic multi hop • The interest of wireless networks is their ability to form multi hop networks

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Advanced Protocols

The Collection Tree Protocol (CTP)

• CTP is a tree-based collection protocol. • Some number of nodes in a network advertise themselves as tree roots. • Nodes form a set of routing trees to these roots. •CTP is address-free in that a node does not send a packet to a particular root; instead, it implicitly chooses a root by choosing a next hop. • Nodes generate routes to roots using a routing gradient.

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Overview of Existing Protocols (I)

How does CTP choose a neighbour?

• CTP uses expected transmissions (ETX) as its routing gradient. • A root has an ETX of 0. The ETX of a node is the ETX of its parent plus the ETX of its link to its parent. • This additive measure assumes that nodes use link-level retransmissions. • Given a choice of valid routes, CTP SHOULD choose the one with the lowest ETX value.

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Overview of Existing Protocols (II)

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Overview of Existing Protocols (III)

Main features:

• AODV, that stands for “Ad hoc On-Demand Distance Vector (AODV) Routing”, is a reactive routing protocol : establishes route only on demand.

• AODV is specially adequate for wireless sensor networks, as it effectively creates mesh or star networks.

Single hop

Multi-hop mesh

GW

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Overview of Existing Protocols (IV)

AODV explanation:

• Based on IETF RFC3561 standard.

• There are three basic message types: – RREQ: Route requests.

– RREP: Route replies.

– RERR: Route error.

• As it is a reactive routing algorithm, a route is only searched for whenever it is needed.

• The best path metric used is the LEAST number of hops.

• CTP is very robust and has a high packet delivery rate, but no built in low power operation: not suitable for battery deployments • Asynchronous low power listening exists for CTP, has many bugs • TRENDS:

• Network Synchronization Algorithms reduce consumption • IPv6 layer implementation Interoperability • TDMA based protocols for industrial environments

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Trends

1. Cooperative application with the java test project. Try to find out the motes path.

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Exercises

Contact Info: Manuel Fernández

manuel.fernandez@advanticsys.com

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