wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

4-8 Industrial Communication Systems
After this, a new one is explained—Dynamic MANET On-Demand (DYMO), which has been published
as Standard Track RFC.
Along similar lines, three more routing protocols used in WSNs are explained. These are Sensor
Protocols for Information via Negotiation (SPIN), which are classified as flat routing protocols, and Low
Energy Adaptive Clustering Hierarchy (LEACH) protocol, and Geographic Adaptive Fidelity (GAF),
which is a location-based routing protocol.
4.5.1 Optimized Link-State Routing Protocol
OLSR [JMC01] is a proactive routing protocol based on the link state algorithm. It is in experimental
state in the IETF Working Group [CJ03].
Each node maintains a route to the rest of the nodes in the ad hoc network. The nodes forming
the network exchange messages about the link state periodically, but they use the multipoint relaying
(MPR) strategy to minimize both, the routing message size and the number of nodes that resend the
routing messages in broadcast mode. In the MPR [BCGS04] strategy, each node uses “Hello” messages
to find out which nodes are placed at one hop distance and a list is created, see Figure 4.3.
Each node selects in that list a subset of neighbor nodes able to reach every node at a distance of
two hops from the node that is making the selection. Only these selected neighbor nodes will be used
to retransmit the routing messages, and these are called multipoint relays. The rest of the neighboring
nodes will process the routing messages they receive, but they will be unable to retransmit them. Each
node determines the best route (in number of hops) for each destination, using the information stored
(in the routing table of the topology and in that of their neighbors) [AWD04], and stores that information
in a routing table, so that it is available at the precise moment when a node wants to start sending
data. This protocol selects bidirectional links to send messages [ChCL03], dispensing with unidirectional
links. OLSR is well suited to large, dense mobile networks. Because of the use of MPRs, larger and
denser networks link state routing offers optimum performance.
4.5.2 topology Dissemination Based on Reverse Path Forwarding
Topology Dissemination Based on Reverse-Path Forwarding [OTL04] is a proactive, link-state routing
protocol designed for mobile ad hoc networks, which provides hop-by-hop routing along shortest
paths to each destination. Each node running TBRPF computes a source tree based on partial topology
information stored in its topology table, using a modification of Dijkstra’s algorithm. To minimize overhead,
each node reports only part of its source tree to neighbors. TBRPF uses a combination of periodic
and differential updates to keep all neighbors informed of the reported part of its source tree. Each
node also has the option to report additional topology information, to provide improved robustness
B
MPR nodes
Source node
A
S
C
FIGURE 4.3
OLSR multipoint relay selection.
© 2011 by Taylor and Francis Group, LLC