Networking Reference
In-Depth Information
the RREQ packet is assigned to 1 first then increased as the area of interest in
which the source is centred is widened.
- Other protocols depend on exploiting the location and speed information to limit
the RREQ flooding to a certain zone. An example is the Location Aided Routing
(LAR) protocol [ 17 ] in which this zone is known as the request zone. In LAR,
for route discovery, the source first estimates the zone where the destination is
expected to be within. This zone is calculated based on the last known position
for the destination, the last time to hear from that destination, the current time,
and the speed of that destination. The flooding of RREQs is limited to the
request zone which includes the expected zone and the location of the source
node. Nodes out of the request zone discard the RREQ packets.
- Network congestion is one of the major problems that multi-hop networks suffer
from especially if there are some intermediate nodes kept as a part of the routing
path for multiple transmissions. Network congestion leads to performance
degradation due to the increase in packet loss rate and the end-to-end delay. The
Congestion Free Routing (CFR) protocol [ 18 ] was proposed to consider this
problem, utilize the network resources efficiently, and keep the congestion level
as low as possible. CFR depends on exchanging RREQs and RREPs for dis-
covering a route, and considers only the non-congested neighbors for estab-
lishing a route. A node's congestion level is monitored by calculating the
average queue length at each node. Another protocol whose primary objective is
to avoid congested routes is the Node Centric Load Balancing Routing
(NCLBR) protocol [ 19 ]. NCLBR works similar to AODV for discovering a
route but with some minor changes to the format of the RREQ packets. As well,
NCLBR divides nodes in a network into three types based on their role and
connectivity: terminal, trunk, and normal nodes. In NCLBR, each node is
responsible for avoiding congestion and diverting any over load to other routes
in the network.
For hybrid route discovery, most protocols depend on deploying a proactive
technique for reaching local nodes and a reactive one for reaching remote nodes:
- For example, the Zone Routing Protocol (ZRP) [ 20 ] divides the network into
zones. The zone of a node comprises the nodes that are up to h hops from that
node. ZRP employs two different routing approaches for the intra-zone and the
inter-zone packets. Inside a routing zone, a proactive IntrA-zone Routing Pro-
tocol (IARP) is used. For communication with nodes in different zones, a
reactive IntEr-zone Routing Protocol (IERP) is used. Both the IARP and the
IERP perform route discovery as specified by the used proactive and reactive
protocols, respectively.
- Another example is the Zone-based Hierarchical Link State (ZHLS) routing
protocol [ 21 ] which assumes that the nodes know their physical location and
divides them into zones based on the geographical information. Each node
periodically broadcasts information about its neighbors to the nodes in the same
zone and this information is stored in an intra-zone routing table. When a node
has a packet to send, it checks first its intra-zone table. If the destination is out of
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