Lesson 05 slides for one day introductory course on wireless sensor networks and TinyOS, that took place at the University of Alcalá de Henares in Madrid Spain the 18th of September 2013. This course was jointly designed by the Electronics Department of the university and Advanticsys. Find source code for the lessons here: http://www.advanticsys.com/wiki/index.php?title=TinyOS%C2%AE_Course_at_UAH_18th_September_2013
3. • 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
3
Advanced Protocols
4. 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.
4
Overview of Existing Protocols (I)
5. 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.
5
Overview of Existing Protocols (II)
6. 6
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
7. 7
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.
8. • 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
8
Trends
