CHAPTER 4

EFFICffiNT CROSS LAYER CONGESTION CONTROL

ROUTING PROTOCOL FOR MOBILE AD HOC NETWORKS IN

CONSTRAINED ENVIRONMENT

4.1 OVERVIEW

Ad hoc networks are a specialized class of networks comprising of hundreds of nodes which are

able to communicate among each other in a dynamic arbitrary manner. Ubiquitous computing is

intertwined with the ad hoc networking. In this type of environment the devices make use of the

resources provided in their current setup. Also the mobile nodes are crippled with the amount of

power used in mobility and for sending and receiving the messages. Infrastructure less setup of

ad hoc networks can be used in military deployment and emergency operations. Ad hoc network

being a wireless network has no fixed infrastructure. Nodes in the Ad hoc networks are mobile in

nature. If any two nodes are out of range then connectivity is estidilished by hoj^ing through

various intermediate nodes. If any two nodes are within the transmission range of each other then

the connectivity is established in a peer to peer manner. Ad hoc wireless networics are composed

of mobile stations communicating solely through wireless channels [55, 56]. Ad hoc wireless

networks are expected to play an increasingly important role in future civilian and military

setting. Ad hoc networks are useful for providing communication support where no fixed

infrastructure exists or the deployment of a fixed infrastructure is not economically profitable,

and movement of communicating parties is allowed. In ad hoc wireless networks, a message sent

by a mobile may be received simultaneously by all of its neighbors. Messages directed to

mobiles not within the sender's transmission range must be forwarded by neighbors, which thus

44

act as routers. Due to mobility it is not possible to establish fixed paths for message delivery

through the network. Therefore, a number of routing protocols have been proposed for ad hoc

wireless networks [57-64], derived fi-om distance-vector [65] or link-state [66, 67] routing

algorithms. Such protocols are classified as proactive or reactive, depending on whether they

keep routes continuously updated, or whether they react on demand. This approach is not

suitable for large networks because many unused routes still need to be maintained and the

periodic updating may incur overwhelming processing and communication overiiead.

The on-demand approach is more efficient in that a route is discovered only when needed for a

transmission and released when the transmission no longer takes place. However, when a link is

disconnected due to failure or node mobility, which occurs often in MANETs, the delay and

overhead due to new route estabUshment may be significant. To address this problem, multiple

paths to the destination may be used as in multipath routing protocols [68-71]. The alternative

path can be found immediately in case the existing is broken. The multipath has lot of overhead

in maintaining the multiple paths.

The routing protocols can also be categorized based on ccmgestion-adaptive versus congestion-

non adaptive routing. The congestion unawareness in routing in MANETs may lead to the

following issues.

Maximum delay to find a new route: Traditional routing protocol takes maximum time for

congestion to be detected by the congestion control mechanism. In severe congestion situations,

it may be better to use a new route. The problem with an on-demand routing protocol is the delay

it takes to search for the new route.

45

Huge routing overhead: In case a new route is needed, it takes processing and communication

effort to discover it. If multi-path routing is used, though an alternate route is readily found, it

takes effort to maintain multiple paths.

Heavy packet loss: Many packets may have ab^ady been lost by the time congestion is detected.

A typical congestion control solution will try to reduce the traffic load, either by decreasing the

sending rate at the sender or dropping packets at the intennediate nodes or doing both. The

consequence is a high packet loss rate or a small throughput at the receiver.

The above problems become more visible in large-scale transmission of traffic intensive data

such as multimedia data, where congestion is more probable and the negative impact of packet

loss on the service quality is more of significance. Our proposed Efficient Congestion Control

Adaptive Routing Algorithm (e-CARA) protocol tries to prevent congestion from occurring in

the first place and be adaptive should a ccmgestion occur. The ns-2 [54] simulation results show

that e-CARA significantly improves the packet loss rate and end-to-end delay while enjoying

small protocol overhead and high-energy efficiency as compared to AODV [72], DSR [73],

DSDV [74] and TORA [75].

46

4.2 REVIEW OF ROUTING PROTOCOLS FOR MANETs

Routing Protocols can be classified based on their proactive and reactive nature. In Proactive or

Table driven routing protocols, periodic exchange of routing table information takes place

between the nodes in the network. Routing information is extracted from these routing tables to

establish path between source node and the destination node. In a Reactive or On Demand

routing protocol routes are established by flooding the messages throughout the network. This is

done only when the routes needs to be established. In this chapter, brief reviews of four routing

protocols used in this research work are discussed.

4.2.1 Topology Control

Topology Control is absolute requirement in a multi-hop network like ad hoc network which

consists of mobile nodes. Topology control ensures that the netwOTk maintains certain degree of

connectivity in the topology so that the overall network does not suffer performance degradation

due to dynamic movements of nodes. Topology refers to the availability of the routes between

various nodes. The establishment of routes depends on various factors like location of the nodes,

availability of energy in each node, transmission range and the direction of antennas.

Mismanagement of network topology can lead to various problems are discussed. A network

with less number of nodes in a topology may result in network partition, less throughput and

higher delay in the network. If the network gets partitioned then no routes are available to reach

the destination. Dense node t(^)ology increases the number of routes available in the network

which may result in collision of packets. This again leads to more utilization of energy.

Topology Control in ad hoc network is carried out through power control and through

hierarchical organization. In the power control nodes the amount of energy required for

transmission and receiving of packets is done on a per node basis. In hierarchical organization

47

various clusters are formed to manage topology. Topology based on clustering mechanism leads

to less number of links but maintains high connectivity thereby conserving the amount of energy

spent in establishing routes in the network.

In literature majority of the papers argue that there should be a minimum transmission range to

maintain a topology where all the nodes are connected. The authors argue that this minimum

transmission range connected topology may lead to reduced performance in ad hoc networks.

Through experiments it is proved that high throughput is achieved for less number of nodes in a

network at minimum transmission range. When the nodes are increased the throughput reduces

even when the transmission range is kept at minimum.

Interference among neighboring nodes can be reduced by apfM-c riately configuring the topology

of a network. A critical neighbor scheme improves the overall network performance by

adaptively varying the transmission power of the nodes in the network based on route and traffic

demands. This critical neighbor scheme is based on measuring the critical range, estimating and

adjusting of ideal power.

4.2^ Ad hoc On Demand Distance Vector Routing Protocd (AODV)

AODV (Ad hoc On-demand Distance Vector) is a dynamic, self-starting, multi-hop on-demand

routing protocol for mobile wireless ad hoc networks. AODV discovers paths without source

routing and maintains table instance of route cache. This is loop free and uses destination

sequence numbers. The mobile nodes to respond to link breakages, changes in network topology

in a timely manner. AODV also maintains active routes only while they are in use and delete the

stale (unused) route. AODV routing protocol is a reactive routing protocol. Route discovery is

initiated by the soiuxie node by broadcasting the RouteRequest (RREQ) packet throughout the

network. A node receiving the RREQ packet forwards the packet only if it has not sent the

48

packet previously. This RREQ message consists of unique RREQ ID and the sequence number

for the destination node. This unique RREQ ID helps in eliminating the duplicate RREQ packets.

A route is established between the source node and the destination node through RouteReply

(RREP) packets. An intermediate node sends the RREP packet back to the source if the sequence

number of the destination node mentioned in the RREQ packet is greater than the sequence

number of the intermediate node. The RREQ packets create temporary route entries for the

reverse path through every node it passes in the network. When it reaches the destination a

RREP is sent back through the same path the RREQ was transmitted.

( 2 ''; -A 5 K,. '•• "•

* 4 ! " i ,^'^-- _ _ — K..^-^ •» — _ — •^..>t — _ >-,

3 : ' 7 r

Figure 4.1 Route Establishment in AODV Routing Protocol

Figure 4.1 shows the establishment of the route from the source node 2 to the destination node 8.

Routes between the source node and the destination node are maintained using the HELLO

messages which are sent periodically. Whenever a route is used to forward the data packet the

route expiry time is updated to the current time plus the Active Route Timeout. An active

neighbor node list is used by AODV at each node as a route entry to keep track of the

neighboring nodes that are using the entry to route data packets. These nodes are notified with

RouteError (RERR) packets when the link to the next hop node is broken. If a link is broken then

it is invalidated by the node which finds the broken route by sending the RERR to all its

49

neighboring nodes. Every node maintains a route table entry which updates the route expiry time.

A route is valid for the given expiry time, after which the route entry is deleted from the routing

table [72].

4.23 Dynamic Source Routing Algorithm (DSR)

DSR is an On Demand Reactive routing protocol [73]. DSR is different from other routing

protocols as it does not require sending of periodic HELLO messages for the maintenance of

neighboring nodes. The RouteRequest (RREQ) message is broadcasted throughout the network

by the source node. This RREQ message consists of unique RREQ ID and a list of all the

intermediate nodes. A RREQ is forwarded if the node has not sent the RREQ message previously

and if the address is not intended to itself. This duplicate RREQ messages are detected using the

unique RREQ ID. When an intermediate node forwards the packets it adds it address to the list.

This address indicates the path the RREQ packet has traversed through various intermediate

nodes to reach the destination node. When the destinaticm node 5 receives the RREQ packet then

the route from the source node 1 to the destination node 5 is established through different paths

as shown in Figure 4.2. The destination node 5 then generates a RouteReply (RREP) packet. This

RREP packet then reaches the source node by making use of the address of the various

intermediate nodes found in the list of the RREQ packet. When node 2 receives the RREP from

the destination node 5, it also contains the information about the various routes that are

established between source node and the destination node. The different paths between source

node 1 and destination node 5 are 1-2-3-5 and 1-2-4-5. The source node then makes entry of all

the available routes between the source node and the destination node in its route cache.

50

Figure 4.2: Route Establishment in DSR Routing Protocol

Figure 4.3: Packet Confirmation for Neighboring Nodes

Whenever a packet is sent from a node to its neighboring node, then the sender node decides

whether the receiving node has received the packet successfully or not by applying the following

mechanism. Consider Figure 4.3. Here, node 1 confirms that node 2 has received the packet

when it hears 2 sending a packet to node 4. If a path between any two nodes in the route is

broken then a RouteError (RERR) is generated which is sent back to the source node. Various

optimizations are incorporated for discovering the route and for its maintenance. If a route to the

source node is present in the route cache of the destination node, then the destination node can

make use of it to send the RREP packets back to the source node. Also, by piggybacking on the

RREP messages the destination node can establish a route to the source node. DSR can operate

in promiscuous mode and then extract the information from the various packets that are

generated in the network and by using this information it can establish a route between the

source node and the destination node.

51

4.2.4 Destination Sequence Distance Vector Routing Algorithm (DSDV)

The Destination Sequence Distance Vector Routing Algoritlim proposed in [74] is based on the

Bellman-Ford algorithm. Each of the nodes in the network maintains its own routing table. The

packets are transmitted by making use of the information stored in the routing table. The routing

table consists of the available destination nodes and the number of hops required in reaching the

destination. Each of the routing table is paired with a sequence number that is generated by the

destination node. Any node that generates a sequence number will be an even number. If an odd

sequence number is generated then it indicates that it is oo metric. On finding new significant

iirformation, the routing information is broadcast throughout the network by using packets. In

DSDV a node advertises its routing table to all its neighboring nodes so that the available

information is latest and the node is able to locate all the other nodes in the network. The packets

broadcast by the source node consist of the addresses of the destination node, the number of hops

needed to reach the destination node and the sequence number generated by the destination node.

A node checks its routing information available in the packet and compares the information with

its routing table. If the destination address does not match with its own, then it increments the

number of hops and passes the packet to the next available neighboring node. A broken link is

indicated is the QO metric for the next hop destination. This information is updated throughout the

network by broadcasting the packets. The routing information for a table can be updated either as

a "full dump" or through "incremental" way. The incremental update makes use of one network

protocol data unit (NPDU) while, full dump update requires multiple network protocol data

units. When a node receives routing information its sequence number is compared with the

sequence number available in the table. If the sequence number available in the packet is greater

52

than the sequence number found in the table then the information is updated otherwise the

information is discarded.

4.2^ Temporally Ordered Routing Algorithm (TORA)

TORA comes under a category of algorithms called "Link Reversal Algorithms". TORA is an

on demand routing protocol. Unlike other algorithms the TORA routing protocol does not use

the concept of shortest path for creating paths fh)m source to destination as it may itself take

huge amount of bandwidth in the network. Instead of using the shortest path for computing the

routes the TORA algorithm maintains the "direction of the next destination" to forward the

packets. Thus, a source node maintains one or more "downstream paths" to the destination node

through multiple intermediate neighboring nodes. TORA reduces the control messages in the

network by having the nodes to query for a path only when it needs to send a packet to a

destination. In TORA, three steps are involved in establishing a network. A) Creating routes

from source to destination, B) Maintaining the routes and C) Erasing invalid routes. TORA uses

the concept of "directed acyclic graph (DAG) to establish downstream paths to the destination".

This DAG is called as "Destination Oriented DAG". A node marked as destination oriented

DAG is the last node or the destination node and no link originates from this node. It has the

lowest height. Three different messages are used by TORA for establishing a path: the Query

(QRY) message for creating a route. Update (UPD) message for creating and maintaining routes

and Clear (CLR) message for erasing a route. Each of the nodes is associated with a height in the

network. A link is established between the nodes based on the height. The establishment of the

route from source to destination is based on the DAG mechanism thus ensuring that all the routes

are loop free. Packets move from the source node having the highest height to the destination

node with the lowest height. It's the same top to down approach. When there is no directed link

53

from source to destination, the source node trigger the QRY packet. The source node (node 1)

broadcasts the QRY packet across all the nodes in the network. This QRY packet is forwarded

by all the intermediate nodes which may contain a path to the destination.

Figure 4.4: Directed Path in TORA

Consider Figure 4.4 (a). When the QRY packet reaches the destination node (node 9) then the

destination node replies with a UPD message. Each node receiving this UPD message will set the

value of the height to a value greater than the height of the node from which it had received. This

results in the creation of the directed link from the source to the destination. This is the concept

involved in the link reversal algorithm. This enables to establish a number of multiple routes

from the source to destination. Assume that the path between node 5 and node 6 is broken

(Figure 4.4 (b)). Then node 6 generates an UPD message with a new height value within a given

"defined time". Node 3 reverses its link on receiving the UPD message. This reverse link

indicates that the path to destination through that directed link is not available. If there is a break

between node 1 and node 3, then it results in partition of the network where the resulting invalid

routes are erased using the CLR message [75].

54

4.3 PROBLEM OBSERVED IN CONSTRAINT SITUATION

The experiments are conducted with six CBR traffic sources sessions between common

destination using AODV, DSR, DSDV and TORA. We have considered three performance

metrics such as Packet Delivery Ratio, Average End-to-End Delay and Routing Overhead. In

normal case AODV outperforms better than other three routing protocols. The TORA performs

better than DSDV. Figure 4.5 shows the performance comparison of the routing protocols in

Normal Situation

i't-1" 0.8 •

1 °-6 1 '•'-8 0.2 •

* -JL_—-l-:zi~:

1 2 3 4

Sessions

—•—AODV

* DSR

TORA

DSDV

Figure 4.5: Performance of Routing Protocols in Normal Situation

But under constraint situation the same routing protocols behave differently. With the six CBR

traffic sources to a common destination, AODV suffers degradation up to 35% whereas DSR

suffers only 10% compared to normal situation. TORA suffers degradation of 45% whereas

DSDV suffers only 15%. On comparing their performances, it was observed that DSR performs

better than other three routing protocols.

The main reason for performance degradation in packet delivery ratio is due to packet drops by

the routing algorithm after being failed to transfer the data in the active routes. There are several

reasons for packet drops such as network partitioning, link break, collision and congestion in the

ad hoc networks. The important property of routing algorithm is quick link recovery through

55

efficient route maintenance. Therefore, the DSR routing protocol has fast reaction for link

recovery and finds alternative path (during congestion) when compared with AODV and other

routing protocols in the given situation. This is shown in the Figure 4.6.

S 0.8 •

§ 0.6 -I 0.5 • S 0.4 • % 0.3 • •g 0.2 £ 0.1 •

"—~~ ~m~~-^ "

1 2 3 4

Sessions

—•—DSR

— • AODV

DSDV

TORA

Figure 4.6: Performance of Routing Protocols in Constraint Situation

AODV keeps only the active and removes the stale ones. Therefore, unavailability of the

alternate routes leads to route discovery by the source node. The congestion will be high when

multiple CBR sources send data to a single destination. In AODV, the intermediate nodes are

unable to send the data packets, link break situation perceived by AODV sends route error of

finding new route through source will result in packet drops resulting in degradation of packet

delivery ratio, increase in Average End-to-End delay and increase in Routing Overhead. In DSR,

the routes caches have more alternative routes and in the constrained environment when most of

the routes are fresh, therefore the route repair is localized. DSR also has provision of more than

one mechanism for local route repairs such as replying to Route Requests using Cached Routes,

Packet Salvaging and Queued Packets Destined over Broken Link besides route maintenance.

DSDV is proactive routing protocol and has more alternate paths than TORA. Thus, performance

of DSDV is better than TORA in a Constraint environment. The delay for establishing route is

less when compared to TORA. Routing Overhead is very high in reactive protocols AODV and

DSR when compared to DSDV and TORA.

56

4.4 PROPOSED CROSS LAYER APPROACH FOR CONGESTION

CONTROL

In cross layer approach, the advantage of exchanging information among interlayer is

considered. The rate control may be used as congestion metric by the node in the MAC layer

uses queue length from the network layer. Queue length is used as metrics for making

transmission decision. The congestion control only at sender is not sufficient. This is because

whenever congestion occurs based the level of queue length threshold, the sender will try to send

out all the packets and chooses high data rate. When we consider on the receiver side, it is

vulnerable to reduce the data rate to avoid and limit more incoming packets waiting in its already

congested queue. It is very much required to balance the data rate between sender and receiver to

avoid congestion occurring at any end. This is because that the overall network performance will

not come down. The data rate is selected based on the queue length of the sender and receiver.

In ad hoc networks, the data forwarding load is more or higher in some areas when compared to

other areas. The nodes in the middle of the network carry high loads when routing protocol make

use of shortest path strategy. The performance can be improved by using the congestion

information from MAC, Network and Transport layer. The routing protocol uses congestion

information for the purpose of selecting route through the congestion area. The congestion level

measure may be applicable for several modifications of TCP based on the ECN (Explicit

Congestion Notification) bit in a packet IP header. Thus, motivated by the idea of cross layer

approach for congestion aware and adaptive protocol which makes use of rate adaption to

improve the overall perfcamance of the network, an efficient Cross layer congestion control

adaptive protocol (e-CARA) was developed.

57

4.4.1 Protocol Design

The e-CARA protocol designed to ensure the high availability of alternative routes and reduce

the rate of stale route. This can be achieved by increasing the parameters of routing protocols

(especially in AODV) that normally take more time for link recovery. The parameters such as

active_route_time-out, route_reply_wait_time, reverse_route_life, TTL_start, TTL_increment,

TTL_threshold and delete_period.

-AODV

AODV*

DSDV

DSDV*

Figure 4.7: Performance of AODV/DSDV with improved routing parameters

The overall performance of routing protocols is increased to 8 to 15% in constrained situation. In

Figure 4.7 it is observed that AODV and DSDV outperform other routing protocols in

constrained situation.

Every node appearing on a route warns its previous node when there is congestion. The previous

node uses "non congested" route to the node on the main route as shown in Figure 4.8. The thick

line represents congestion and dashed line represents non congested route.

Figure 4.8: Ad hoc Network with congested/non-congested route

58

The congestion may result in any of the following reasons:

• Lack of buffer space

• Link load exceeding the carrying capacity

• Redundant broadcasting packets

• Number of packets timeout and retransmitted

• Average Packet Delay/ Standard Deviation of Packet delay

• Increase in Number of nodes

4.4.2 Status Indicator Algorithm

By checking the occupancy of link layer buffer of node periodically the congestion status Cg can

be estimated.

Cs = Number of packet buffered in Buffer / Buffer Size.

Congestion can be indicated by three statuses "Go", "Careful" and "Stop"

"Go" indicates that there is no congestion with Cs < Vi

"Careful" indicates that the status likely to be congested with V < Cs < % and

"Stop" indicates that the status already congested, % < Cs< 1.

4.43 Main Route Discovery Phase

Broadcast RREQ packet toward the receiver and receiver responds to the RREQ by sending back

a RREP packet. Each node has two routing tables: Main Table denoted by MnTab and non

congestion Table denoted by NcTab. MnTab is used to direct packets on main route and NcTab is

used to direct packets on non congested routes. NcTab = 0 indicates that no non congested route

available for any connection at that moment. The table format for MnTab and NcTab are shown

in Table 4.1 and 4.2 respectively.

59

Table 4.1. MAIN ROUTING TABLE (MnTab)

Attribute

Nc_clest

Nc_status

Nc_hop

Prob

Go_hop

Go metric Hop Dest

Description Destination of the non congested route Congestion status of the non congested route Next node on the ncm congested Probability to forward a packet to the main link

Next "Go" node on the main route

Distance to Go_hop in hops Next mode on the main route E)estination

Table 4.2. NON CONGESTED ROUTING TABLE (NcTab)

Attribute

Nc_src

hop

status

Dest

Description

Start node of non congested route

Next node on non congested route

Congestion status of non congested route Destination

Every entry in the table is unique to a destination. MnTab [N, D] specify the entry for destination

D in the routing table of node N and MnTab [N, DJ.attr specify the value for the attribute attr.

The traffic can be reduce by dropping RREQ packets when congestion status is "stop" and also

stop broadcasting RREQ packets.

4.4.4 Non Congested Discovery Algorithm

Step 1: [Set the Main Routing table metric attribute.]

MnTab [N, D].nc_metric = 1.

Step 2: [Set the Destination node and Its congestion status as "Go"]

60

MnTab [N, DJ.ncJiop = D andMnTab [N, D].hop_status = "Go"

Step 3: [for every other node, Set Main Table has no congested node]

MnTab [N, D].nc_hop = -1

Step 4: [Node N receives a Update packet from its next main node Nnext ]

If MnTab [N„ext> D].nc_status = "stop" and MnTab [N„ext, D].nc_status = "careful" then node N

initiate nan congested route discovery process toward node of N obtained from the update

packet.

Step 5: [Non congested route search]

(i) Non congested request packets set TTL to 2 x k. where k is distance between Node N and

non-congested Node P on the main route.

(ii) Drop non congested request if arriving at a node already present on the Main route.

Step 6: Remove the entries in the NcTab if timeout occurs after certain period.

Step 7: [Traffic splitting effectively reduces the congestion status at the next main node.]

(i) If next Main node MnTab [N, Dj.hop = "stop" the incoming packets will follow Main Link N

-^ MnTab [N, Dj.hop and with probability p - MnTab [N, DJ.prob = 0.5

(ii) Non congested link N -^ MnTab [N, DJ.ncJiop will have equal chance (1-p = 0.5)

61

4.5 SIMULATION ENVIRONMENT

This protcxjol is implemented using Network Simulator NS-2 [54] version 3.34. A comparison of

e-CARA to DSR, AODV, DSDV and TORA, the most popular MANET routing protocols are

discussed in the following sections.

4.5.1 Performance Metrics

We have considered three important metrics were considered for the analysis of the results

obtained.

The packet delivery ratio (PDR) which is defined as the ratio between payload packets delivered

to the destination and those generated by the source nodes;

The average packet delay is defined as the delay for sending packets from source node to the

destination node. This metrics includes all the possible delays caused by buffering during the

route discovery latency, queuing at the interface queue, retransmission delays at the MAC layer,

and propagation and transfer times;

The routing overhead defined as the number of packets carrying control messages for route

discovery and routing to the number of packets carrying payload.

4.5.2 Simulation Setup

The network consists of 25 nodes in a 1500m x 800m rectangular and 1000m x 1000m square

field. The MAC layer was based on IEEE 802.11 CSMA and interface queue at MAC layer

could hold 50 packets. The nominal bit rate is 2 Mbps and transmission range is 250m. The

routing buffer at the network layer could store up to 128 data packets. The random waypoint

model [76] was used with maximum node speed of 4m/s as suggested in [77]. The traffic loads

were illustrated either varying the number of connections with fixed packet rate or varying the

packet rate with fixed number of connections. The simulations were run for 900 seconds with 25

62

connections generated. For each connection, the source generated 512-byte data packets at a

constant bit rate (CBR). This rate was varied among 1,5,10,15,20,30,40,50 packets/sec. With

fixed packet rate of 20 packets/sec number of connections were varied among 1,5,10,15,20,25

connections.

4.6 RESULTS AND DISCUSSIONS

The results were collected as average values over 15 runs of each simulation setting by keeping

the fixed connections to 20 and varying the packet rate. The improvement of e-CARA with

Packet Delivery Ratio over other routing protocols is shown in Figure 4.9.

0 0.8

•? 0.6

% 02

1 0

-V ^

-e-CAfV^ AOOV DSR DSDV

-TOIV.

1 5 10 20 40

pacK« rate p«r *ource (pacKMs/sec)

Figure 4.9: Packet Delivery Ratio Vs Packet Rate

In regard of Packet Delivery Ratio, both AODV and e-CARA outperforms DSR, DSDV and

TORA. This is because packets are lost due to congestion in DSR were more compared with

other routing protocols. When packets rate was small, AODV delivered more packets than e-

CARA. This is due to reduction in network load. With increase in the traffic of packet rate 20

packets/s, 30 packets/s and 40 packets/s, e-CARA successfully delivered packets more than

AODV and other routing protocols. Similarly, for end-to-end delay worst case computed, shown

in Figure 4.9. The e-CARA is improved over AODV by 63.76%, DSR even better by 77.42%,

DSDV by 79.12% and TORA by 80.67% in worst case. The delay variation was less than that of

63

AODV and DSR makes e-CARA more suitable for multimedia kind of applications as shown in

Figure 4.10.

-6-CARA

-AODV

DSR

DSDV

-TORA

Packet rale per source (packett/sec|

Figure 4.10: Average End-to-End Delay Vs Packet Rate.

The routing overhead incurred by e-CARA is very less when compared to other routing protocol.

This is shown in Figure 4.11.

-e•CAR^

-AOOV DSR -DSDV -TDRA

1 5 10 20 40

Packet rate per source (pacfcets^ec)

Figure 4.11. Normalized Routing Overiiead Vs Packet Rate.

When packet rate was 50 packets/sec, the e-CARA incurred less routing head and delivered

21.34% more data than AODV. This because, upon link breakage, AODV tried to establish a

new route to the destination by broadcasting RREQ and RREP packets, e-CARA tried to make

use of non congested available route and uses route request packets very often. The overhead to

maintain non congested paths in e-CARA is kept small by minimizing the use of multiple paths.

64

In the next scenario, the packet rate was fixed to 20 packets per seconds and varied the number

of connections. Even in this scenario, there was an improvement of e-CARA over other routing

protocols. The improvement of e-CARA with Packet Delivery Ratio is shown in Hgure 4.12.

1 OB-

1 OB­'S ^ 0 . 4 -

1 02-a.

0 ^

'•V-" ^ ^ ^ ^

^ ^ ^ ^ ^ ^ ^

t 5 19 15 20

Number of connMtom

-^B-CARA -<^-ADDV

DSR — DSDV

Figure 4.12. Packet Delivery Ratio Vs Number of Connections

With respect to Packet Delivery Ratio measured against varying the number of ccwmections, both

AODV and e-CARA outperforms DSR, DSDV and TORA. This is because packets are lost due

to congestion in DSR were more compared to other routing protocols. When packets rate was

small, AODV delivered more packets than e-CARA. This is due to reduced network load. With

increase in the traffic of packet rate 20 packets/s, 30 packets/s and 40 packets/s, e-CARA

successfully delivered packets more than AODV and other routing protocols.

For end-to-end delay, computations were made by varying the number of connections as shown

in Figure 4.13. The e-CARA improved over AODV by 65.36%, DSR by 79.25%, DSDV by

80.15% and TORA by 80.78% in worst case. The delay variation is less than that of AODV and

DSR makes e-CARA more suitable for multimedia kind of q)plications.

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10

5 8

^ 6 e •T 1 4

i'

-e-CARA

-AOOV

DSR

-DSDV

-TOFW

1 5 10 15 20

numD«r oi connaciions

Figure 4.13: Average End-to-End Delay Vs Number of Connections

The routing overhead incurred by e-CARA is very less when compared to other routing protocol.

When number of connections was 20 the e-CARA incurred less routing head and delivered

18.45% more data than AODV. This because, upon link breakage, AODV tried to establish a

new route to the destination by broadcasting RREQ and RREP packets, e-CARA tried to make

use of non congested available route and uses route request packets very often. The overhead to

maintain non congested paths in e-CARA is kept small by minimizing the use of multiple paths.

In all these measures, e-CARA outperformed AODV, DSR, DSDV and TORA, especially when

the network is heavily loaded. In case of DSR, every data packet carry the entire route

information, thus making network severely congested. The DSDV contains all the routes for

possible destinations and suffers buffer overflow as the packet rate increases due to congestion.

AODV would result in a less congested network because neither data nor control packets are

needed to include route information. As soon as the traffic load is increased, AODV fails in

handling the congestion. In contrast, e-CARA efficiently distributes traffic over the main routes

and non congested routes. It resolves the congestion in a better way and offers high PDR,

shortest end-to-end delay and less routing overhead.

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4.7 SUMMARY

The proposed e-CARA congestion control protocol enjoys fewer packet losses than routing

protocols in a constraint situation. Most of the MANET protocols are not adaptive to congestion

and cannot handle the heavy traffic load while offering services to multimedia applications. The

non congested route concept in e-CARA help next node that may go congested. If a node is

aware of congestion ahead, it finds a non congested route that will be used in case congestion is

about to occur. The part of incoming traffic is split and sent on the non congested route, making

the traffic coming to the congested node less. Thus, congestion can be avoided. e-CARA does

not incur heavy overhead due to maintaining of non congested paths. It also offers high Packet

Delivery Ratio when the traffic in heavy. The maintenance cost is reduced because non

congested is short and main node can only create at most one non congested route. The end-to-

end delay and queuing delay is less because e-CARA makes network less congested. The delay

incurred while establishing is low because of using existing non congested paths. Thus the

proposed e-CARA is congestion aware and congestion adaptive efficient routing protocol for

mobile ad hoc networks especially designed for multimedia applications.

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