11.a study of congestion aware adaptive routing protocols in manet

Computer Engineering and Intelligent Systems www.iiste.org
ISSN 2222-1719 (Paper) ISSN 2222-2863 (Online)
Vol 3, No.4, 2012

A Study of Congestion Aware Adaptive Routing Protocols in
MANET
Shitalkumar Jain, Shrikant Kokate, Pranita Thakur, Shubhangi Takalkar
Maharashtra Academy of engineering, Alandi (D)
Email: sajain@comp.maepune.ac.in

Abstract

Routing protocols for mobile ad hoc networks (MANETs) have been explored extensively in last few years.
Much of this work is targeted at finding a feasible route from a source to a destination without considering
current network traffic or application requirements. Routing may let a congestion happen which is detected
by congestion control, but dealing with congestion in reactive manner results in longer delay, and
unnecessary packet loss and requires significant overhead if a new route is needed. Routing should not be
aware of, but also be adaptive to, network congestion. Adaptation to the congestion helps to increase both
the effectiveness and efficiency of routing. These problems are solved by the congestion-aware routing
protocols in certain degree. These protocols which are adaptive to congestion status of mobile ad-hoc
network can greatly improve the network performance. In this paper, we present the survey of congestion
adaptive routing protocols for mobile ad-hoc network. Finally, the future direction of congestion-aware
routing protocols is described.
Keywords: Ad hoc networks, congestion aware routing, Congestion metric, congestion adaptability
1. Introduction
Wireless ad-hoc network is usually defined as a set of wireless mobile nodes dynamically self organizing a
temporary network without any central administration or existing network infrastructure. The node in the
wireless ad-hoc network can serve as routers and hosts. So, they can forward packets for other nodes if they
are on route from source to destination. Routing is important problem in wireless ad-hoc network.
Traditional working protocols cannot work well in wireless ad-hoc network because of the characteristics
of the wireless ad-hoc networks. Since, mobile nodes have limited transmission capacity they mostly
intercommunicate by multihop relay. Multihop routing is challenged by limited wireless bandwidth, low
device power, dynamically changing network topology, high vulnerability to failure. To answer these
challenges, many routing algorithms in MANETs were proposed. There are different dimensions to
categorize them: proactive routing Vs reactive routing or single path routing Vs multipath routing. In
proactive protocols, route between every two nodes are established in advance even though no transmission
is in demand. In reactive protocols, route is discovered when needed transmission and released when
transmission no longer takes place. Congestion is one of the most important restrictions of wireless ad-hoc
network. It may deteriorate the performance of whole network. In the current design routing is not
congestion-adaptive. Routing may let the congestion happen which is detected by congestion control. But
dealing with congestion in reactive manner results in longer delay and an unnecessary packet loss and
requires significant overhead if the new route is needed. But, now there is another dimension for
categorizing for routing protocols: congestion adaptive Vs congestion un-adaptive routing. Our motivation
is that congestion is dominant cause for packet loss, long delay, and high overhead in MANETs.
These problems become visible in large scale transmission of traffic intensive data such as multimedia data
where congestion is more probable and negative impact of packet loss on the service quality is of more
significance. In this paper we studied congestion routing protocols like CRP(Congestion Adaptive Routing
Protocol)[7],ECARP (Efficient Congestion Adaptive Routing Protocol )[11],CARP(Congestion Aware
Routing Protocol),CADV(Congestion Aware Distance Vector)[12],CARA(Congestion Aware Routing plus
rate Adaptation)[12],CARM(Congestion Aware Routing Protocol for Mobile Ad-hoc Network)[12].

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The remaining part of the paper is organized as follows: In section II we provide the studied congestion
aware routing protocols. In section III comparison between these algorithms is presented. In section IV we
concluded the paper.

2. Algorithm

There are many routing algorithms in mobile ad-hoc networks for routing and congestion free networks.
Some of them are explained below:

2.1 Congestion Adaptive Routing Protocol (CRP):

Congestion Adaptive Routing is a congestion adaptive unicast routing protocol for mobile ad-hoc
network.CRP protocol tries to prevent congestion from occurring in the first place. In CRP, every node
appearing on a route warns its previous node when prone to be congested. So, CRP uses the additional
paths called as “bypass” for bypassing the potential congestion area to the first non congested node on the
primary route. It reduces packet delay. But, at the same time CRP tries to minimize bypass to reduce
protocol overhead. Hence, the traffic is split over bypass and primary and adaptively to network congestion.
Hence, 1) power consumption is efficient.2) Congestion is resolved beforehand and at the same time there
is small packet loss rate.

CRP is on-demand and consists of the following components.

2.1.1 Congestion Monitoring
When no. of packets coming to the node exceeds its carrying capacity, node becomes congested and its
starts losing packets. Various metrics are used for node to monitor congestion status. Main parameters are
percentage of all packets discarded for lack of buffer space, the average queue length, the no. of the packets
timed out and retransmitted, average packet delay. In all these parameters, rising number indicates growing
congestion.
2.1.2 Primary Route Discovery
Sender discovers the route to the receiver by broadcasting the REQ packet toward receiver. The receiver
responds REQ by sending the REP packet on same path that the REQ previously followed. This is called
primary route and nodes on this are called primary nodes. To reduce traffic due to the primary route
discovery and better deal with Congestion in the network, 2 strategies are adopted 1) REQ is dropped if
arriving at a node which is having congestion status as “red” 2) REQ is dropped I arriving at node already
having a route to destination .
2.1.3 Bypass Discovery
A primary node periodically broadcasts a UDT i.e. update packet. This packet contains the nodes
congestion status and set of tuples [destination D, next green node G, distance to green node, n] for each
node appearing as a destination in primary table. For this reason is when node P receives an update packet
from next primary node Pnext, about the destination D, P will be aware of congestion status of next. This
causes the congestion to know about the next green node of P which is n hops away from primary route.
But if the next hop is yellow or red, congestion will be there if data packets continue to be forwarded on
P Pnext. But, CRP tries to keep congestion from occurring in the first place, P node starts to select bypass
route toward G-the next green node of P known from the UDT packet. This bypass search is similar to
primary route search, except that 1)the bypass request packet’s TTL is set to 2*m and 2)bypass request is
dropped if arriving at node already present on primary route. It can be also possible that no bypass is found.
So, in such situation packets are delivered to destination by following primary route.
2.1.4 Traffic Splitting and Congestion Adaptability
When the bypass at a node is found, data packets coming to this node are not necessarily spread over

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bypass and primary route. To avoid the bypass from being congested no packet is forwarded on bypass
unless any primary node is red i.e. congested. The basic idea behind traffic splitting is that when primary
link consists of less congested node, traffic on primary link should be increased, otherwise it should be
reduced. Bypass and primary routes cannot include more than 2 common nodes, but different bypass paths
can share common node. This increases chance to discover a bypass. But, because of this bypass node may
become congested if it has to carry large loads of bypass traffic. But, this can be solved, by splitting
probability adjustment for congestion adaptation. The probability adjustment is as shown in TABLE I.
2.1.5 Multipath Minimization
To reduce the protocol overhead, CRP tries to minimize using multiple paths. If the probability p to forward
data on a primary link approaches 1.0, this means the next primary node is far from congested or the bypass
route is highly congested. In this case, the bypass at the current node is removed. Similarly, if the next
primary node is very congested (p approaches 0), the primary link is disconnected and the bypass route
becomes primary. To make the
protocol more lightweight, CRP does not allow a node to have more than one bypass. The protocol
overhead due to using bypass is also reduced partly because of short bypass lengths. Each bypass connects
to the first non-congested node after the congestion spot, which should be just a few hops downstream.
2.1.6 Failure Recovery
CRP is able to quickly resume connectivity after a link breakage by using bypass routes currently
available. There are 3 min cases of failure
2.1.6.1 Primary link failure
When one of link on primary route fails, the initial node sends a DISC packet towards sender along route.
This DISC goes on recording nodes and it stops at node having bypass. This node if finds that its bypass
destination is there in DISC, that bypass is not used and DISC is forwarded upstream towards sender till it
finds a node with bypass and not having failed node as its destination. If both these cases are not there
DISC is sent to the sender and it will find new primary route.

2.1.6.2 Bypass link or node fails
In this case bypass node which finds this failure sends a BPS_DISC packet through bypass route to
primary node and that bypass is removed.

2.1.6.3 Primary node fails
If node on the primary route fails, its previous node sends DISC packet along primary route. If the bypass
node detects some failure, it will also send BPS_DISC packet along bypass until reaching a primary node.
When primary node received both these packet, it removes bypass and DISC packet is forwarded along
primary route. Then this is handled same as first case. If BPS_DISC packet doesn’t arrive at the primary
node on time that bypass is used as primary route. But, if it comes late, it is ignored. But, route remains
broken but it will recover soon because another DISC packet will be sent back.
2.2. An Efficient Congestion Adaptive Routing Protocol for Mobile Ad Hoc Networks (ECARP):
An efficient congestion adaptive routing protocol is better than every other routing protocol during heavy
traffic loads. The ECARP, routing protocol ensures high availability of alternative routes and reduce the
rate of stale routes. ECARP is having mainly AODV as its base. This can be achieved by increasing the
parameters of routing protocols (especially in AODV) that normally take more time for link recovery.
These parameters are active_route_time-out, route_reply_wait_time, reverse_route_life, TTL_start,
TTL_increment, TTL_threshold and delete_period.

ECARP Congestion Control Algorithm
This algorithm provides solution to improve routing protocols due to constrained environment.
Step 1: Check the occupancy of link layer buffer of node periodically. Let Nc be the congestion status

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estimated.
Step 2: Compute Nc =Number of packet buffered in buffer/Buffer Size
Step 3: Set the status for congestion. It can be indicated by three statuses “Go”, “careful”, and “Stop”.
[ “Go” indicates there is no congestion with Nc ≤ ½ ], “carefull” indicates the status likely to be congested
with ½ ≤ Nc ≤ ¾ and “Stop” indicates the status already congested, ¾ ≤ Nc ≤ 1.]
Step 4: Invoke congestion control routine when link failed event has occurred in data transfer with using
active route or ¾ ≤ Nc ≤ 1.
Step 5: Assume that neighboring will have alternate route or non-congested route to the destination.
Step 6: Make Query to non-congested neighbors for route to destination
Step 7: after obtaining the routes from the neighbors, select route with minimum hops.
Step 8: Once route is finalized start sending the data packets through non-congested route.
Step 9: If there is no alternative route to destination then start splitting the traffic to the less congested
route.
Step 10: Traffic splitting effectively reduces the congestion status at the next main node.

2.3. Congestion aware routing plus Rate Adaptation (CARA):
The base use of CARA protocol is DSR. The route discovery mechanism of DSR is modified. This protocol
mainly aims to find the bypass route for congested zones or nodes. This can be achieved by combining the
average MAC utilization and the instantaneous transmission queue length to indicate the congestion level
of nodes in the network. When source wants to transmit data to the destination node, it broadcasts RREQ
packets. When intermediate code receives RREQ, it checks its congestion level. If the congestion level is
higher than it discards the RREQ. When RREQ arrives at the destination node, though destination node is
congested or not it handles the RREQ and replies RREP. So, route without congested node is established.
CARA uses two metrics to measure congestion information first is average MAC layer utilization. The
instantaneous MAC layer utilization is considered as 0 only when the medium around the node is available
at the beginning of a transmission and as 1 when the node is not idle. (e.g. detecting physical carrier or
detecting or back off due to virtual carrier sensing.) As, the instantaneous MAC layer utilization is either 1
or 0 the average value with in the period indicates the use of wireless medium around the node.
Second metric used is instantaneous transmission queue length. If the node has many packets waiting in the
queue, it causes long packet latency or even dropping of packets. So we can say that node is congested now.
The above mentioned metric can veraciously reflect the congestion conditions around the node. This
protocol tries to minimize the congestion in two ways: 1) It forbids the RREQ packets to propagate in the
congested area. 2) It guides the route around the congested area or nodes instead of across them.
As a result of this no conditional transmission burden generate in these areas.

2.4. Congestion Aware Routing protocol for Mobile ad hoc networks (CARM):
A congestion aware routing protocol for mobile ad hoc networks uses a metric incorporating data rates,
MAC overhead and buffer delay to control the congestion. The CARM protocol introduces a new
parameter called WCD (Weighted Channel Delay) to measure congestion level and adopts a route
ELDC(Effective link Data-rate Category) to avoid the MDRR(Mismatched data-rate route) problem. The
MDRR problem is shown in following fig.1
The data rate of route shown by dashed (A-B-D-G) is limited by teaming fast link (B-D) with slow link (A-
B and D-G).
As mentioned earlier, the CARM protocol introduces a new parameter called WCD (weighted channel
delay) to measure congestion and it is given as
WCD=a ΣτQ + (1+b)TMACALL+Tdata
where Q is the number of buffered packets for this link. Tdata=Ldata/ R is the data transmission time, Ldata is
the length of data in bytes or bits and R is the data rate of the link. TMACALL is total time spent at the MAC
layer. The constants a and b are parameters with values between 0 and 1 which are used to weight TMACALL.
By weighting TMACALL can avoid misjudgment of congestion as shown in fig.2

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In CARM, source node broadcasts RREQ packets with ELDC and WCD information when it attempts to

transmit data to the destination. Intermediate nodes compare source ID, source sequence, and ELDC of the

RREQ packets they receive from neighbors, and drop the RREQ packets whose source ID and source

sequence number are the same with that of other RREQ packets received earlier and ELDC is lower than

the earlier RREQ packets’. Only the destination node can responds to the RREQ packets by sending RREP
packets back to the source along the route from which they came. The route is established when the first

RREP arrives at the source. The subsequent RREP packets are cached for the spare routes. The utilization

of the congestion metric, WCD, is very special in CARM protocol. Because the priority of route packets is
higher than data packets, the route packets can be forwarded without queuing. That is, the congestion level

information inherent in queuing delays is lost. The author proposed a RREQ-delay scheme. An RREQ is

forwarded with a delay of the WCD that is calculated according to the WCD information in the RREQ at

the intermediate nodes. The lower the congestion level of link is, the smaller the delay of RREQ packets

are, the earlier the RREQ packets arrive at the destinations. This scheme ensures that the RREQ packets of

routes with lower congestion level arrive at the destination first and congested links are eliminated in the
routes. This all causes high overhead. So, overhead in case of CARM is very high.

2.5. Congestion-Aware Distance Vector (CADV):

The CADV protocol is based on proactive protocol, DSDV. In a distance vector routing protocol, every host

maintains a routing table contains a distances from itself to possible destinations. A mobile host in ad -hoc

network acts like a single server queuing system. Delay in sending packet is related with congestion. In

CADV, each entry is related with delay expected. This helps to measure congestion at the next hop. The

expected delay is computed follows:
∑
(1)
Where n is the number of sent packets & L is the length of MAC layer packet queue. E [D] estimates the

time. A newly arrived packet has to wait before it is send out.In CADV, routing decision is made based on
distance to the destination as well as the expected delay at the next hop showed in (1) CADV gives the

routes with low expected delay, higher priority. CADV tries to avoid congestion and tries to balance traffic

by giving priority to a route having low expected delay.

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CADV routing protocol consist of three components:

1) Traffic Monitor: It monitors traffic going out through the link layer. Currently it keeps track of average

delay for sending one data packet in receipt period of time. Time period is specified by route maintainance

component.

2) Traffic Control: It determines which packet is the next to send or drop. It reschedules packets if needed.

It supports a drop tail FIFO queue and provides functionality to queue packets.
3) Route maintainance: It is the main component. It performs the work of exchanging information with

neighbors, evaluation and maintaining routes. It manages the traffic monitor and traffic control component.

CADV better support for QoS. The real time performance of CADV is good, and end to end delay was

short. The over head of CADV is unacceptable when the network is large. Through put also decreases the

performance of CADV is may be well in the small & steady wireless ad- hoc network.

2.6. Congestion Aware routing Protocol (CARP)

CARP is an on-demand routing protocol. It uses information gathered from MAC layer to discover

congestion free routes. CARP uses combined weight matrix in its standard cost function to check for the

congestion level. The multiple paths are computed during the route discovery. Calculate node weight matrix

NM which assign a cost to each link in the network and select maximum throughput paths.

NM = (Lq * Drate)/(OHmac * Davg)

1) Route request: Consider the route

S-P1-P2-P3-D

To initiate congestion-aware routing discovery, the source node S sends a RREQ. When the intermediate

node P1 receives the RREQ packet, it first estimates all the node weight metrics.

The node P1 then calculates its node weight NMP1

RREQP1 P2

P2 calculates NMP2 and forward the RREQ packet

RREQP2 P3

Finally the RREQ reaches the destination node D with the sum of node weights

RREQP3 D

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2) Route Reply: The destination node D sends the route reply packet RREP along with total node weight

to the immediate upstream node P3

RREQD P3

Now P3 calculates its cost C based on the information from RREP as

CP3= (NMp1+NMp2+NMp3)-(NMp1+NMp2)

By proceeding in the same way, all the intermediate hosts calculate its cost .On receiving the RREP from

all the routes, the source selects the route with minimum cost value.

3. COMPARISONS

Congestion is a dominant reason for packet drops in ad hoc networks.CRP sends packets on both bypass

paths and primary routes simultaneously. So, incoming traffic is distributed on primary and bypass route

depending on current congestion status of network. Congestion is subsequently better resolved .In ECARP

some parameters of AODV such as TTL_start, TTL_increment are increased. So, it ensures the high

availability of alternative routes and reduces the rate of broken rut removal process. CADV is not

congestion adaptive. It offers no remedy when the existing route becomes heavily congested. So, CADV
improves AODV in delivery ratio only. The real time performance of the CADV is good and the End-to-

End delay is short. The disadvantage of the CADV is that since, each node maintains all the routes to the

nodes in the network and changes the route information periodically, the overhead for maintaining the

routing tables is huge. The overhead of the CADV is unacceptable when the network is large or the

topology changes frequently. The throughput decreases sharply at the same time. So, CADV may perform

well in the small, steady wireless ad -hoc network. By studying the algorithms of CARM, CARA and

CADV it is conclude that overhead of the CARM and CADV are higher than CARA, the delay of CADV is

shorter than the other two.

4. CONCLUSION

It is clear from algorithms available for having adaptive solution for congestion in the network as due to

vast pay load on networks, which may be due to flooding of packets or may be due to repeat requests on the

basis of error correction techniques. Congestion metrics still remains a great challenge for the future work.

It is quite important to obtain an optimal approach that combines related parameters collected from physical

layer, MAC layer to measure congestion. Finally we can conclude that congestion is the problem associated

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with the network and has to be countered by having compromised solution rather than elimination.

REFERENCES

[1] D. B. Johnson, D. A. Maltz, “Dynamic source routing in ad hoc wireless networks,” Mobile Computing,

pp. 153–181, 1996.

[2] Josh Broch, David A. Maltz, David B. Johnson, Yih-Chun Hu, Jorjeta Jetcheva. “A Performance

Comparison of Multi-Hop Wireless Ad Hoc Network Routing Protocols,” The Fourth Annual ACM/IEEE

International Conference on Mobile Computing and Networking, pp. 1-13, 1998

[3]Chen, X., H. M. Jones, A .D .S. Jayalath, “Congestion-Aware Routing Protocol for Mobile Ad Hoc

Networks,” Vehicular Technology Conference 2007, pp. 21-25, 2007

[4] S. Ramanathan, M. E. Steenstrup, “A survey of routing techniques for mobile communications
networks, mobile networks and applications,” Vol. 1, pp. 98–104, 1996.

[5] C. E. Perkins, “Ad hoc on demand distance vector (AODV) routing,” IEFT Internet Draft, November

1998,

[6] H. Raghavendra and D.A. Tran, “Congestion Adaptive Routing in Ad Hoc Networks (Short Version),”

Proc. ACM Int’l Conf. Mobile Computing and Networking (MOBICOM), Oct. 2004.

[7] H. Raghavendra and D.A. Tran, “Congestion Adaptive Routing in Ad Hoc Networks” IEEE

Transactions on Parallel and Distributed Systems, Vol. 17, No. 11, November 2006.

[8] D.A. Tran and H. Raghavendra, “Routing with Congestion Awareness and Adaptivity in Mobile Ad Hoc

Networks,” Proc. IEEE Wireless Comm. and Networking Conf. (WCNC), Mar. 2005.
[9] Xiaoqin Chen, Haley M. Jones and Jayalath, "Congestion-Aware Routing Protocol for Mobile Ad Hoc

Networks" IEEE 66th conference on Vehicle Technology, pp.21-25, October 2005.

[10] S. J. Lee and M. Gerla, “Dynamic load-aware routing in ad hoc networks,” Proceedings IEEE

International Conference on Communications, pp. 3206–3210, June 2001.

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TABLE I
Splitting probability distribution

Congestion Bypass status=green Bypass status=yellow Bypass status=red

Next primary node is green P:=p+(1-p)/4 P:=p+(1-p)/3 P:=p+(1-p)/2

Next primary node is yellow P unchanged P unchanged P:=p+(1-p)/4

Next primary node is red P:=p-(1-p)/2 P:=p-(1-p)/4 Find another bypass

Fig. 1 An example of MDDR problem

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Fig. 2 Two scenarios with the same overall delay but different MAC and transmission delay due to different

data-rates and congestion levels.

73

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