SLKGHIJABCDEEach node S in the network has a routing zone. This isthe proactive zone for S as S collects informationabout its routing zone in the manner of the DSDVprotocol.
The routing in ZRP is divided into twoparts› Intrazone routing : First, the packet is sentwithin the routing zone of the source node toreach the peripheral nodes.› Interzone routing : Then the packet is sentfrom the peripheral nodes towards thedestination node.SDintrazoneinterzone
5#Intrazone Routing• Each node collects information about allthe nodes in its routing zone proactively.This strategy is similar to a proactiveprotocol like DSDV.• Each node maintains a routing table forits routing zone, so that it can find a routeto any node in the routing zone from thistable.• Each node periodically broadcasts amessage similar to a hello messageknown as a zone notification message.
6#• A hello message dies after one hop, i.e.,after reaching a node´s neighbours.• A zone notification mesage dies after khops, i.e., after reaching the node´sneighbours at a distance of k hops.• Each node receiving this messagedecreases the hop count of the messageby 1 and forwards the message to itsneighbours.
7#SCAEFBDS performs routediscovery for DDenotes route request
8#SCAEFBDS performs routediscovery for DDenotes route replyE knows route from E to D,so route request need not beforwarded to D from E
9#SCAEFBDS performs routediscovery for DDenotes route taken by Data
10#• The interzone routing discovers routesto the destination reactively.• Consider a source (S) and adestination (D). If D is within the routingzone of S, the routing is completed inthe intrazone routing phase.• Otherwise, S sends the packet to theperipheral nodes of its zone throughbordercasting.
11#• S sends a route request (RREQ) messageto the peripheral nodes of its zonethrough bordercasting.• Each peripheral node P executes thesame algorithm.– First, P checks whether the destination D iswithin its routing zone and if so, sends thepacket to D.– Otherwise, P sends the packet to theperipheral nodes of its routing zone throughbordercasting.
12#• The bordercasting to peripheral nodescan be done mainly in two ways :– By maintaining a multicast tree for theperipheral nodes. S is the root of this tree.– Otherwise, S maintains complete routingtable for its zone and routes the packet tothe peripheral nodes by consulting thisrouting table.
If a node P finds that the destination D iswithin its routing zone, P can initiate a routereply. Each node appends its address to the RREQmessage during the route request phase.This is similar to route request phase in DSR. This accumulated address can be used tosend the route reply (RREP) back to thesource node S.14#
An alternative strategy is to keep forwardand backward links at every node´s routingtable similar to the AODV protocol. Thishelps in keeping the packet size constant. A RREQ usually results in more than oneRREP and ZRP keeps track of more than onepath between S and D. An alternative pathis chosen in case one path is broken.15#
When there is a broken link along anactive path between S and D, a localpath repair procedure is initiated. A broken link is always within the routingzone of some node.16#SD
Hence, repairing a broken link requiresestablishing a new path between twonodes within a routing zone. The repair is done by the starting node ofthe link (node A in the previous diagram)by sending a route repair message tonode B within its routing zone. This is like a RREQ message from A with Bas the destination.17#
Interzone routing may generate manycopies of the same RREQ message if notdirected correctly. The RREQ should be steered towards thedestination or towards previouslyunexplored regions of the network. Otherwise, the same RREQ message mayreach the same nodes manytimes, causing the flooding of thenetwork. 18#
Since each node has its own routingzone, the routing zones of neighbouringnodes overlap heavily. Since each peripheral node of a zoneforwards the RREQ message, themessage can reach the same nodemultiple times without proper control. Each node may forward the same RREQmultiple times.19#
20#The search explores new regions of the network.
When a node P receives a RREQmessage, P records the message in its listof RREQ messages that it has received. If P receives the same RREQ more thanonce, it does not forward the RREQ thesecond time onwards. Also P can keep track of passing RREQmessages in several different ways.21#
In the promiscuous mode of operationaccording to IEEE 802.11 standards, a nodecan overhear passing traffic. Also, a node may act as a routing nodeduring bordercasting in the intrazonerouting phase. Whenever P receives a RREQ messagethrough any of these means, it rememberswhich routing zone the message is meantfor.22#
23#P receives a RREQ from Q since P is a peripheral node for the routingzone of Q.PQABCNXP does not bordercast the RREQ to A,B,...,N but only to X which is not inits list.
Suppose P has a list of nodes A, B,C,...,Nsuch that the RREQ message has alreadyarrived in the routing zones of the nodesA, B, C, ...,N. Now P receives a request to forward aRREQ message from another node Q. This may happen when P is a peripheralnode for the routing zone of Q.24#
The optimal zone radius depends on nodemobility and route query rates. When the radius of the routing zone is 1, thebehaviour of ZRP is like a pure reactiveprotocol, for example, like DSR. When the radius of the routing zone isinfinity (or the diameter of the network), ZRPbehaves like a pure proactive protocol, forexample, like DSDV.25#
In the intrazone routing, each node needsto construct the bordercast tree for its zone. With a zone radius of r, this requirescomplete exchange of information over adistance of 2r-1 hops. For unbounded networks with a uniformdistribution of nodes, this results in O( )intrazone control traffic.26#2r
However, for a bounded network, thedependence is lower than . There is no intrazone control traffic whenr=1. The intrazone control traffic grows fast inpractice with increase in zone radius. So,it is important to keep the zone radiussmall.27#2r
When the zone radius is 1, the control trafficis maximum since ZRP degenerates intoflood search. In other words, every RREQ messagepotentially floods the entire network. This isdue to the fact that all the neighbours of anode n are its peripheral nodes. However, control traffic drops considerablyeven if the zone radius is just 2.28#
The control traffic can be reduceddrastically with early query termination,when a RREQ message is prevented fromgoing to the same region of the networkmultiple times. However, the amount of control trafficdepends both on node mobility and queryrate. The performance of ZRP is measured bycompairing control traffic with call-to-mobility (CMR) ratio.29#
The call-to-mobility ratio (CMR) is the ratioof route query rate to node speed. As CMR increases, the number of controlmessages is reduced by increasing theradius of the routing zones. This is because, it is easier to maintain largerrouting zones if mobility is low. Hence, routediscovery traffic also reduces.30#
On the other hand, CMR is low if mobility ishigh. In such a case, the routing zonemaintenance becomes very costly andsmaller routing zones are better forreducing control traffic. An optimally configured ZRP for a CMR of500 [query/km] produces 70% less trafficthan flood searching.31#
For a fixed CMR, the route queryresponse time decreases initially withincreased zone radius. However, after a certain radius, theresponse time increases with zone radius. This is due to the fact that the networktakes longer time to settle even withsmall changes in large routing zones.32#
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Presentation on Zone Routing protocol (Hybrid Protocol ) in Mobile Ad Hoc Network course,2013