Characterized By Wireless Connectivity Continuous Computer Science Essay

Published Date: 02 Nov 2017

I.INTRODUCTION

MANET is a kind of wireless ad hoc

network, and is a self-configuring network of mobile

routers connected by wireless links – the union of

which form an arbitrary topology. The routers are

free to move randomly and organize themselves

arbitrarily which leads to dynamic changing

topology. Each node will act as router in forwarding

the packets to the destination. The reliability of

packet delivery services provided by a network

influences the behavior of networked applications,

especially loss-sensitive ones. Thus it is important to

improve the reliability of packet delivery. The packet

loss in MANET are due to (i) Wireless channels in

MANETs may have low quality since noise and

external interference may be strong. Moreover, in

MANETs, multiple wireless hops generally share the

same medium, so intra-session interference

contributes a non-negligible portion in the total

interference. If the bit errors cannot be corrected by

the communication system's error-correction

mechanism, the entire data packet must be discarded.

(ii) Due to mobility and power limitations, links in

MANETs are opportunistic. Link failures may

happen at any time during the packet-transmission

process, which may disrupt the transmission of a data

packet. If no mechanism is employed to discover and

replace failed links, packet losses will occur.

II. ROUTING PROTOCOLS

Routing is the act of moving information

from a source to a destination in an internetwork.

During this process, at least one intermediate node

within the internetwork is encountered.

A. Proactive Protocol

Proactive Protocol is a table driven approach

where each node maintains a routing table and any

changes to the network topology should be updated

in each routing table and it is stored reliably. During

transmission, each and every node maintains a

routing information table that communicates all the

other nodes in the network to update the changes in

network topology and this information should be

reflected to all other nodes within the network.

Though it establishes the routes quickly with a small

delay, it requires larger resources and the major

disadvantage is that, there is a tendency of creating

loops within the network. Some of the proactive

protocols are DSDV (Destination Sequenced

Distance Vector), OLSR (Optimized Link State

Routing).

B. Reactive Protocol

It is an on-demand approach in which the

routes are being established only when there is a

request from the sender node. When there is no route

from one node to another it helps in establishing a

connection between them by creating a route. A route

is acquired through the route discovery function

which is initiated from the source node. The route is

being maintained through the route maintenance

function. When compared to Proactive Protocol, this

consumes more power with large delay. The flexible

operations are done through reduced routing loads

since it has no loop formation within the network.

Some of Reactive Protocols are AODV (Ad-hoc Ondemand

Distance Vector) routing, MABR (Modified

Associativity Based Routing).

MABR is the improved method of ABR

(Associativity Based Routing) protocol which uses

the stability of the node to establish the routes. The

stability can be measured from the interconnections

made in between the each nodes. Thus it reduces the

route overhead by having less route reconstruction.

The improvement of ABR is MABR which uses

position information of nodes.

C. Hybrid Protocol

It is the combination of proactive and

reactive approaches. Initially the route is established

through the routing information available in the

routing table (i.e. proactive) and uses the reactive

protocol which will serve for additional demands.

ZRP (Zone Routing Protocol) is a kind of hybrid

protocol. Here, the topology is divided into number

of zones and each zone uses any of the routing

protocol. Additional features of this protocol are

scalability and limited cost of searching.

D. Geographic routing

All the protocols described above are

susceptible to node mobility. Position-based or

geographic routing approaches were introduced to

eliminate some of the limitations of the topologybased

protocols in MANETs. These routing protocols

rely on having one piece of information and that is

the nodes’ physical location information. The

forwarding strategy in these protocols is based on

location information of the destination as well as the

one hop neighbor’s. It is probable that the forwarding

scheme fails if there is no one-hop neighbor whose

location is closer to the destination than that of the

forwarding node. In such cases, recovery strategies

are introduced to deal with such failures.[3]

Geographic routing protocols scale better for ad hoc

networks mainly for two reasons:

Up-to-date routing table is not required

No need to have a global view of the

network topology and its changes.

III. POSITION BASED OPPORTUNISTIC

ROUTING (POR)

Traditional routing protocols such as

AODV, DSDV , ZRP are susceptible to the link

failure as well as vulunerable to malicious node

attacks. Opportunistic routing which works in

connected static ad hoc network is a type of routing

protocol that determines the delivery of data in real

time.

POR takes the full advantage of broadcast

nature of wireless channel and opportunistic routing.

The packet transmission is done in a multicast

fashion with multiple forwarders. It is based on

geographic routing , where the node’s location

information is being exchanged through GPS. When

the source node wishes to transmit the packet to the

destination the destination location can be acquired

through any location service. The location of the

destination could be transmitted by low bit rate. The

location replies are being used when the request is

from the source. [15]

The POR is made robust and scalable from

the position based property. When a source node S

sends a packet to the destination node D, it calculates

the forwarder list according to the distance between

its neighbors and the destination, and the list is being

inserted into the packet header. The neighbor who is

nearer to the destination will have higher priority.

After that, the packet is sent out, taking the best

forwarder as the next hop. When a node receives a

packet and finds itself is not the first candidate in the

forwarder list, it will cache the packet for a period of

time according to its forwarding priority determined

by the forwarder list.

IV. ROBUST GEOGRAPHIC ROUTING (RGR)

RGR is similar to POR which is based on

geographic routing and opportunistic forwarding. The

nodes in this protocol are aware of own position and

position of the direct neighbors. The beacons are used

in knowing the location information. It has several

sub-optimal forwarders cache the packet that has

been received using MAC interception. If the best

forwarder does not forward the packet in certain time

slots, sub-optimal candidates will take turn to

forward the packet according to a locally formed

order. As long as one of the candidates succeeds in

receiving the packet, the data transmission will not be

interrupted, leading to RGR’s excellent robustness.

[14]

V. AD-HOC ON-DEMAND DISTANCE VECTOR

ROUTING (AODV)

AODV is an on-demand routing protocol

where the route is discovered when the packet has to

be transmitted to the destination. Destination

sequence number is used to find the up-to-date path

to the destination node. The source node floods the

Route request to find the route to destination node.

The Route request contains the source identifier,

destination identifier, broadcast identifier and time to

live (TTL). The destination sequence number is used

in identifying the freshness of the path. Thus using

this sequence number we can verify the validity of

the route. The intermediate node which has the valid

route to the destination sends its path to the source

node through Route reply message. The connection

setup delay is less in this protocol.[1]

VI. ANALYSIS OF ROUTING PROTOCOLS

The network simulator used is NS-2

simulation tool.

The various performance metrics which can

be used in comparing the protocols are: packet

delivery ratio, end-to-end delay, path length.

Packet delivery ratio: It is defined as the

total number of packets received by the

destination node that the source node has

been transmitted.

Fig 1: Packet Delivery Ratio (RGR)

It can be also said as the ratio of total

number of packets received by the

destination D to the packets send by source

node S. The below graph (packet delivery

ratio) shows that RGR performs better than

other protocols. The yellow line indicates

the RGR performance in Figure1.

Fig 2: Packet Delivery Ratio (POR)

End-to-End Delay: It is defined as a time

taken by the network to transmit a packet

from the source to the destination node in

the network.

Fig 3: End-to-End Delay

VII. CONCLUSION

In this paper we have analyzed different

MANET routing protocols on the basis of different

performance metrics such as packet delivery ratio,

transmission delay and path length. The traditional

routing protocols such as AODV are being compared

with the geographic-based routing such as POR and

RGR. From the analysis, the geographic based

routing performs better when compared to other

traditional routing protocols.