Networking Reference
In-Depth Information
links are prone to failure due to node mobility, for example. It is considered a
crucial component in MANETs where nodes are highly mobile and the network
topology encounters frequent dynamic changes. Route maintenance includes route
refreshing, route failure handling, and route invalidation [ 1 ].
(a) Route Refreshing
Route refreshing aims at keeping the current routes valid by updating or using
them only for the sake of refreshing. Route refreshing can be handled by one
of three approaches depending on the category of the protocol: proactive,
reactive, or hybrid. In the proactive protocols, route refreshing is done
implicitly by having the nodes periodically or upon the occurrence of topology
changes exchange network topology information and update the routing tables
according to the current changes in the network. Therefore, in the proactive
protocols, routes in the routing table are always the most up-to-date. In the
reactive approach, routes are only touched on demand, so to keep routes usable
and ensure their validity, nodes can refresh routes either by use of control
packets (e.g., hello messages) or by using a data packet before the expiration
of the route. Hybrid protocols and hybrid route refreshing combine both the
proactive and reactive approaches.
(b) Route Failure Handling
In reactive routing, when an intermediate node finds that the next hop is
unreachable, it tries one of two options: (1) to find an alternate path locally
either by looking up its routing cache for an alternative or by initiating a route
discovery process to replace the failing link with a valid one, or (2) to send a
route error message to the source node with information about the failing link.
The source node can also look up its route cache for a different route. If there
is no alternative, it reinitiates the route discovery process while marking the
failing part in order not to include it again.
In proactive routing, route failure is handled by route refreshing. As the
routing tables have up-to-date routing information, route failure is handled by
automatic updates.
In the hybrid protocols, it is a combination between the proactive and reactive
route failure handling approaches.
(c) Route Invalidation
Route invalidation is the process of finding out stale routes and removing them
from the routing tables and caches. The stale routes are distinguished and
recognized by employing a lifetime period for each route, and if this route has
not been refreshed during that period, it will be marked as expired and will be
removed. Route Energy Efficiency
As some of the wireless multi-hop networks are comprised of devices with limited
resources, e.g., sensor nodes in WSNs, such networks have energy efficiency as
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