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

Routing in Wireless Networks 4-11
RREP
RREQ
S
RREP
RREP
RREP
RREP
RREP
RREP
D
FIGURE 4.5
ADOV route discovery procedure.
this breakage. Finally, the node must send the route error (RERR) message to the corresponding neighbors.
The RERR message can be broadcasted if there are many neighbors that need that information
or unicasted if there is only one neighbor. The sequence numbers for the entries in the routing table for
the unreachable destinations must be set to invalid lifetime. When the link breakage happens, then the
host can try to locally repair the link if the destination is no further than a specified amount of hops.
If the RREP message is not received, then it changes the routing table status for the entry to “invalid.” If
the host receives the RREP message, then the hop count measurement is compared. If the hop measurement
from the message is greater than the previous one, then the RERR with the N field that is set up is
broadcasted. The N field in the RERR message indicates that the host has been locally repaired, and the
link and the entry in the table should not be deleted.
An additional feature is the use of “Hello” messages (periodical broadcast) to inform a mobile node
about every neighboring node. These are a special kind of not-requested RREPs, whose sequence number
is equal to the last RREP sent (the sequence number is not increased) and that have a time-to-live
(TTL) = 1 to not flood the net. They can be used for the network route maintenance.
4.5.5 Dynamic MANET On-Demand Routing Protocol
DYMO [ChP08] is a reactive protocol that inherits most of its functionality from its predecessors, AODV
and DSR. It is intended for use by mobile nodes in wireless multi-hop networks. It offers adaptation to
changing network topology and determines unicast routes between nodes within the network. One of
the main features of this protocol is path accumulation, which consists of the following mechanism.
During the RREQ dissemination process, each intermediate node records a route to the originating
node. When the target node receives the RREQ, it responds with a RREP unicast toward the originating
node. It is expected that since intermediate nodes learn routes gratuitously from RREQs and RREPs,
protocol overhead will be small since part of the route discovery processes is avoided.
In Table 4.1, there is a comparison of the five routing protocols for ad hoc networks presented in this
section. This table also summarizes the routing algorithm used and the family protocol of every routing
protocol presented.
TABLE 4.1
Routing Protocols in Wireless Sensor Networks
Routing Protocols in Wireless Sensor Networks
SPIN LEACH GAF
Routing algorithm Resource
adaptative
Cluster based Energy aware
location based
Routing protocol family Flat Hierarchical Location based
© 2011 by Taylor and Francis Group, LLC