Optimized Multicast Routing Algorithm Based on Tree

NETWORK TECHNOLOGY AND ApPLICATIONS

Optimized Multicast Routing Algorithm Based on Tree

Structure in MANETs

LI Xut, LIU Tianjiaot, LIU Yingt, TANG Van!

lState Key Laboratory of Rail Traffic Control and Safety, School of Electronic and Information Engineering, Beijing Jiaotong University,

Beijing 100044, China

Abstract: M o b i l e A d h o c N e t w o r k s

(MANETs) p lay an important role in

emergency communications where network

needs to be constructed temporarily and

quickly. Since the nodes move randomly,

routing protocols must be highly effective

and reliable to guarantee successful packet

delivery. Based on the data delivery structure,

most of the existing multicast routing protocols

can be classified into two folders: tree-based

and mesh-based. We observe that tree-based

ones have high forwarding efficiency and

low consumptions of bandwidth, and they

may have poor robustness because only one

link exists between two nodes. As a tree

based multicast routing protocol, MAODV

(Multicast Ad hoc On-demand Vector) shows

an excellent performance in lightweight ad hoc

networks. As the load of network increases,

QoS ( Quali ty of Service) is degraded

obviously. In this paper, we analyze the impact

of network load on MAODV protocol, and

propose an optimized protocol MAODV-BB

(Multicast Ad hoc On-demand Vector with

Backup Branches), which improves robustness

of the MAODV protocol by combining

advantages of the tree structure and the mesh

structure. It not only can update shorter tree

branches but also construct a multicast tree

with backup branches. Mathematical analysis

and simulation results both demonstrate

that the MAODV-BB protocol improves

the network performance over conventional

MAODV in heavy load ad hoc networks.

China Communications· February 2014

Key words:multicast routing, MAODV, tree

structure, backup branch

I. INTRODUCTION

Mobile ad hoc networks[1-2] (MANETs) are

self-organizing wireless networks without any

fixed infrastructure and centralized manage

ment. All the nodes move randomly, which

communicate with each other through multi

hop wireless links. If two mobile nodes are

not within radio range, the communication

between them can be established through one

or more intermediate nodes. Multicast is an ef

ficient way to transmit packets from one point

or multi-points to multi-points, which can re

duce the consumptions of network bandwidth

and host power by sending the same data to

multiple recipients. Consequently, multicast

ing plays an important role for communication

in MANETs, where group tasks are often de

ployed.

Based on the structure used for data deliv

ery, most of the existing multicast routing pro

tocols[3-4] can be classified into two catego

ries: tree-based and mesh-based protocols. In

tree-based multicast routing protocols, all the

routers form a tree structure with the source

node as the root, thus there is only one single

path between every pair of source and receiv

er. In contrast with tree-based protocols, the

mesh-based multicast routing protocols main

tain more than one path between each pair

of source and receiver, and provides a more

90

The key idea of MA

ODV -BB is to make

full use of GRPH mes

sages that the group

l e a d e r b r o a d c a s t s

periodically to update

shorter tree branches

and construct a multi

cast tree with backup

branches, resulting

i n o p t i m i z e d t r e e

structure and reduced

frequency of tree re

construction.

91

robust data delivery path; however, it brings

on more control overhead to maintain multiple

paths.

The study[5] reviews the operation of tree

based and mesh-based multicast routing using

MAODV[6] (Multicast Ad hoc On-demand

Vector) and ODMRP[7] (On-Demand Mul

ticast Routing Protocol) as examples of tree

based and mesh-based protocols, respectively.

Comparing MAODV with ODMRP, the gen

eral trend we observe from the simulation re

sults is that, especially at high mobility, ODM

RP exhibits better (by roughly 10%) packet

delivery ratios than MAODY. Since MAODV

delivers packet along a multicast tree, a single

packet drop upstream can prevent a large num

ber of downstream multicast receivers from

receiving the packet. The absence of redundant

routes affects performance greatly as node

mobility results in frequent link breakages and

packet drops. In this experiment, we can also

conclude that ODMRP has a greater routing

overhead than MAODV on account of the

mesh structure. Routing protocol overhead can

be especially harmful in typical MANET sce

narios where nodes are both bandwidth-con

strained and energy-constrained.

Considering the advantages of tree-based

multicast routing protocols that high forward

ing efficiency and low consumptions of band

width, several researchers have managed to

optimize existing tree-based multicast routing

protocols and improve robustness of the pro

tocols in various methods[8-13]. In this paper,

we consider a tree-based case and propose

an optimized protocol MAODV-BB (Backup

Branches) to improve the performance of MA

ODV in heavy load ad hoc networks. The key

idea of MAODV-BB algorithm is to make full

use of GRPH (Group-hello) messages that the

group leader broadcasts periodically to update

shorter tree branches and construct a multi

cast tree with backup branches. The shorter

branches reduce the resource occupied and

the existence of backup branches avoids large

numbers of tree reconstructions and enhanc

es robustness of the protocol. The improved

protocol not only doesn't bring extra control

overhead, but also ensures high packet deliv

ery ratio and low end-to-end delay.

The rest of the paper is organized as fol

lows: Section 2 introduces related researches;

Section 3 abstracts MAODV protocol and ana

lyzes the impact of network load on MAODV;

Section 4 describes the optimized protocol

MAODV-BB in detail; Section 5 proves in

non-formal methods and derives the mathe

matical model; Section 6 presents simulation

results; and Section 7 concludes the paper.

II. RELATED WORK

To provide reliable multicasting suitable for

mobile ad hoc networks, several researchers

have kept trying to optimize existing multi

cast routing protocols. The main approaches

to improve the robustness of tree-based mul

ticast routing protocols are the optimization

of selecting route mechanism, node mobility

prediction, the establishment of multiple trees,

the utilization of multipath routing and so on.

Ref. 8 presents an Entropy-based long-life

multicast routing protocol in MAODV (E-MA

ODV ). It uses entropy concepts to develop

an analytical modeling, and selects the long

life multicast routing according to entropy

metric. This improvement reduces the number

of route reconstruction and ensures the route

stability in dynamic mobile networks, but it

increases complexity of route establishments.

Furthermore, this paper takes no extra measure

to repair broken tree branches. NMP-MAO

DV[9] (Node Mobility Prediction-MAODV)

ensures non-disconnection communication by

active-link switch before mobile node breaks

away from upstream node's signal range. The

multicast group members set the unified cycle

and calculate the predicted departure time.

If the result is less than threshold, then turn

to the active-link switch process. If the link

switch process fails, it will initiate the MAO

DV repair process. The improved protocol can

operate properly in highly mobile network, but

it increases additional control overhead due to


broadcasting S-marked MACT and M-marked

MACT messages.

In Ref. 10, a Reliability of the Multicast

Ad Hoc On-Demand Distance Vector (RMA

ODV) routing protocol is proposed, which is

based on a protocol relay concept. The basic

schemes for reliable communication can be

classified as sender initiated and receiver

initiated approaches. In the receiver initiated

approach, each receiver maintains receiving

records and requests retransmission via a neg

ative acknowledgement (NACK ) when errors

occur. In RMAODV, we use the receiver ini

tiated approach and protocol relays are placed

along the multicast tree. Each relay node has

only one upper relay to request a retransmis

sion. However, one relay node may have sev

eral lower relay nodes. When a relay node de

tects a loss, it sends a NACK back to its upper

relay node. The improved protocol has a better

performance for packet delivery ratio and re

duces the number of packet retransmissions,

but it increases the probability of receiving

data duplication to the receivers in a multicast

group.

Ref. I I introduces an optim ized routing

protocol MT-MAODV (Multiple Tree-MA

ODV ), which concentrates on issue related

to video multicast over mobile ad hoc net

works. In order to maintain continuous video

streaming, it propose an extension to MAO

DV to construct two highly-disjoint trees. In

MT-MAODV, the video is divided into two

independent sub-streams and is transmitted

separately along these trees. In light of this,

the video source must have a connection to

both trees so that the traffic allocator can split

the traffic accordingly. However, if a node

that attempts to join the multicast group has

only one option to be connected to the multi

cast group, which is through another node u,

considering that connectivity is giving higher

concern than tree disjointedness, node u must

become the forwarding node for both tree-\

and tree-2. Obviously, this method can signifi

cantly reduce the correlation of packet loss if

the multicast trees are highly disjoint. But if

China Communications' February 2014

the tree disjointedness cannot be maintained at

a high level, the performance of improved pro

tocol will be under the restrictions. MP-MA

ODV[12] (Multipath Routing-MAODV) ex

tends MAODV to establish two node-disjoint

routes to improve network efficiency and

balances the network loads. It adds two extra

control messages MACT-S (multicast activa

tion with the flag S) and RREP-S (route reply

the flag S) for selecting and establishing dis

joint paths. Actually, the backup path is built

from the source node to the multicast tree, so

it has nothing to do with the effectiveness of

the multicast tree structure. However, it is still

only one link between two on-tree nodes. Fur

thermore, when the structure of multicast tree

is a large-scale, the problem of heavy network

load cannot be solved effectively.

Above all, almost no effective improvement

focusing on the tree structure itself has been

taken to optimize tree-based multicast routing

protocols. To overcome such inefficiency, we

combine advantages of the tree structure and

the mesh structure to optimize the multicast

tree structure, including updating shorter tree

branches and constructing a mu Iticast tree

with backup branches to improve reliability of

the protocol.

III. MAODV PROTOCOL INTRODUCTION

MAODV is an on-demand routing protocol

based on distance vector, which is recom

mended by IETF MANET. In this section, we

firstly give a brief description of route mecha

nism in MAODV and then discuss the impact

of network load on the MAODV protocol.

3.1 Route mechanism

MAODV is a routing protocol designed es

pecially for ad hoc networks. In addition to

unicast routing, MAODV supports multicast

and broadcast as well. MAODV protocol

constructs a shared delivery tree to support

multiple senders and receivers in a multicast

session. The route mechanism in MAODV

mainly consists of route establishments and

route maintenances.

92

/ Group Member Tree Member

......• RREQ ......• RREP

Non·tree Member ----. MACT

- - Broken link � Multicast data

Fig.l Impact a/network load on MAODV

93

As a tree-based multicast routing protocol,

MAODV relies on flooding through the whole

network to discover the routing path and es

tablish the multicast tree. When a source node

wants to join a multicast group or has data to

send to the multicast group, it will broadcast

a route request (RREQ) message. Intermedi

ate nodes establish reverse route and forward

the RREQ message. After receiving a RREQ

message, the members of multicast group re

ply a route reply (RREP) message to setup a

forward path. [f the source node receives one

or more RREP messages from the destina

tion nodes before timeout, it chooses one of

the routes with the largest sequence number

and the smallest hop count. Then it activates

the route by unicasting a multicast activation

(MACT) message to the next hop and starts to

send multicast data packets.

[n MAODV, when an on-tree node detects

a link broken, it will start the route recovery

immediately. Firstly, it needs to determine

whether the broken link is upstream or not. [f

it is, the node will delete the upstream node in

its next-hop list, drop multicast data packets

which should be sent and then send RREQ

message with the flag J to reconstruct anew

tree branch. Otherwise, the node will delete

the downstream node in its next-hop list and

then set pruning timer.

3.2 Impact of network load on the MAODV protocol

In light load ad hoc networks, the above mech-

anism of multicast route recovery is effective.

Because most applications allow a small

amount of packets lost before the multicast

route recovery is completed. However, when

the network is highly loaded, large number of

packets will be discarded and poor robustness

of the tree-based protocols appears. Therefore,

only depending on the original route mainte

nance in MAODV cannot ensure the network

performance.

As shown in figure 1, in order to illustrate

the impact of network load, we simply set two

source nodes to send multicast packets. Node

S I and node S2 both establish the routes to

the multicast tree. When any one of multicast

group members receives multicast packets, it

will broadcast along the multicast tree branch

es. Due to mobile nodes moving randomly, the

structure of established multicast tree may be

destroyed partly. [t needs to take some time

to repair the broken link. During this period,

large amounts of multicast data packets arrive

in the multicast tree continuously. As a result

of the invalid link, the multicast group member

C cannot receive any multicast packets from

node A and cannot forward multicast packets

successfully to other group members, which

results in packet delivery ratio decreased.

IV. IMPROVEMENT OF MULTICAST

ROUTING

To overcome the impact of network load and

improve robustness of the MAODV protocol,

we extend MAODV protocol to construct a

multicast tree with backup branches from two

aspects. One is the process of backup branches

selection and addition, the other is the mecha

nism of multicast tree maintenance ..

4.1 GRPH message expansion

[n MAODV, the group leader periodically

broadcasts GRPH messages to update or main

tain the multicast group information. In order

to select and add backup branches correctly,

we extend original GRPH (Group-hello) mes

sages with the number of active downstream


branches in MAODV-BB (Backup Branches).

In our experiments, we set an upper limit with

the value of three. In practice, when the num

ber of downstream branches is larger than the

upper limit, the performance of protocols will

not be improved further. The format of the ex

tended GRPH messages is showed in Table 1.

4.2 Backup branches selection and addition

In MAODV protocol, when an on-tree

node firstly receives a GRPH message with

the same multicast group leader address and

multicast group address, it updates the mul

ticast group information in its group leader

table and multicast routing table. Usually, the

GRPH message is identified as the multicast

group leader address and the multicast group

address. We add one backup routing table for

each on-tree node to save the information of

its backup tree branch in MAODV-BB. In

order to accomplish the improvement, the

operation after receiving a GRPH message is

modified as followed:

(a)lf it is the first time for the on-tree node

to receive the GRPH message, then turn to b),

otherwise discard the GRPH message;

(b) Determine whether the GRPH message

is received from its upstream node or not. If it

is, the node needs to perform the same opera

tion as MAODV, otherwise tum to c);

(c )If the hop to the group leader in the

GRPH message is less than that in multicast

routing table and the number of active down

stream branches is under the limit, then update

the tree branch, otherwise tum to d);

(d)Judge whether there is a available back

up branch or not. If there is, turn to e), other

wise add a new backup branch in the backup

routing table;

(e )If the hop to the group leader in the

GRPH message is less than that in the backup

routing table, then update its backup branch,

otherwise abandon the GRPH message.

For example, in figure 2, node K firstly

receives a GRPH message from node B and

then determines that the hop to the group


Table I The format ofGRPH message in MAODV-BB.

Type Flag Reserved

Multicast group leader IP address

Multicast group IP address

Multicast group ID

Hop count

The number of downstream branches for previous node

o Group Member o Tree Member o Non-tree Member

-----. Branch updated ._-_. __ ..• Back-up branch ====> GRPH

Fig.2 Backup branches selection and addition

leader in the GRPH message is less than that

in multicast routing table. Node K updates the

shorter tree branch and replaces node E with

node B as the new upstream node. The shorter

tree branches can reduce control traffic and

average delay. Furthermore, node H, node I

and node J respectively add backup branches

in their backup routing tables. Without dam

aging the tree structure, the addition of backup

branches improves robustness of the network

and ensures the network performance.

4.3 Multicast tree maintenance

During the phase of multicast tree mainte

nance, when the upstream node detects the

link broken, it will delete the downstream

node in its next-hop list and set pruning timer.

When the downstream node detects the link

broken, it needs to determine whether there

is an available backup branch in its backup

routing table. If there is, the downstream node

sends a multicast activation message with

the flag J to enable the backup branch. At the

same time, the downstream node needs to send

a multicast activation message with the flag P

to prune the original upstream and deletes the

94

95

original upstream node in its next-hop list. The

existence of backup branches avoids the pro

cess of route recovery and ensures multicast

data packets to transmit continuously.

v. MATHEMATICAL PROVING AND

DERIVATION

In this session, we firstly prove that group

members own smaller hops to the multicast

group leader in MAODV-BB, due to adding

the update operation of tree branches. The

smaller the hop is, the less resource is occu

pied. Secondly, we derivate the mathematic

model to prove that the interval time between

two route recoveries obviously increases in the

multicast tree with backup branches.

5.1 The updating operation of tree branches

Here we take non-formal methods to prove.

Theorem 1. The update operation of tree

branches can ensure an appropriate path from

a group member to the group leader.

Proof. There is no essential difference in the

route mechanism between the improved pro

tocol MAODV-BB and MAODY. Only during

the process of multicast tree maintenances,

we add a hop factor to determine whether to

update a shorter tree branch. The update oper

ation can provide a shorter path from a group

member to the group leader. Consequently, an

appropriate path from a group member to the

group leader can be ensured.

Theorem 2. The hops from group members

to the group leader in other route mechanism

improved protocols are not less than that in

MAODY. After adding the update operation of

tree branches, the hops from group members

to the group leader in MAODY-BB are less

than or equal to that in MAODY.

Proof. Utilize reduction to absurdity. We

assume that the hops from group members

to the group leader in other route mechanism

improved protocols are less than that in MAO

DY. Base on the principle of MAODY, we can

conclude that it is a minimum-hop protocol.

But this is in contradiction with the assump

tion. In MAODV-BB, if a shorter path to the

group leader is detected during the process of

multicast tree maintenances, the node will up

date the multicast tree branch. Therefore, the

improved protocol MAODY-BB optimizes the

tree structure with shorter branches during the

phase of multicast tree maintenance.

5.2 The existing of backup branches

The mathematical model is derived as follows:

We describe mobile ad hoc networks as a

graph G=(N, E), where N and E respective

ly represent the node sets and the link sets.

Assume that a branch P from anon-tree node

to the multicast group leader consists of n

wireless links. The i-th link in the branch is

denoted by Lj and its lifetime is defined as Xr./ If any one of the wireless links in the branch

breaks, the on-tree node will break away from

the multicast tree. So the lifetime of a branch

P considering of n wireless links can be ex

pressed as Xp, where Xp=min{XLI,xL2 ..... XL) .

It is well known that XI' is an exponentially

distributed random variable. Therefore, its

probability density function and cumulative

distribution function are expressed as: fx,Ct) = ke-h

t

Fx,(t) = I !x,(t)dt =1 - e-kt

(1)

(2)

where k is a parameter associated with n.

Consider an on-tree node which has an

available backup branch to the multicast group

leader, where the lifetime of the tree branch is

denoted by Xp, and the lifetime of the backup

branch is denoted by Xp,. Assume that Xp, and

XP• are independent. Then the interval time

between two route recoveries in the multicast

tree is described as a random variable T, where

T=max{Xp,xp }. The probability density func-I 2

tion of T is calculated as: fT(t) = peT :;;; t) = P(max{Xp" Xp, } :;;; t) (3)

where kl and k2 are the parameters respec

tively associated with the tree branch and the

backup branch, further, k] ::; k2. Then we can derive the mathematical ex

pectation of T:


f I 1 1 f I E[T] = t!T(t)dt = � + k, -

k, + k2 � E[XpJ = t!x" (t)dt = �

According to Eq. (4), it is not difficult to

conclude that the existence of backup branch

es makes the interval time between two route

recoveries in the multicast tree longer. It not

only reduces the frequency of tree reconstruc

tion but also ensures high packet delivery ratio

in heavy load ad hoc networks. The addition

of backup branches improves robustness of

the tree-based multicast routing protocols and

shows the advantages of both tree-based and

mesh-based protocols.

VI. SIMULATION RESULTS AND

EVALUATION

We run simulations with NS-214 to analyze

and compare MAODV-BB with MAODV in

heavy load ad hoc networks. NS-2 provides

substantial support for simulation of TCP,

routing and multicast protocols over wired and

wireless networks.

6.1 Simulation environment

In the following simulation, 20 nodes move

randomly in a square area about 500 x 500

meters. Select 6 nodes to join the multicast

group. Radio propagation range for each node

is 250 meters and channel capacity is 2 Mbps.

Each simu lation is executed for 910 seconds

of simulation time. A traffic generator is devel

oped to simulate CBR sources. The size of the

data payload is 512 bytes. Each source node

sends out 5 packets per second. In order to test

the influence of network loads on the protocol

performance, load of network is set to 5, 10,

15 and 20 packets per second respectively.

Two-ray ground propagation model is used in

our experiments, and the MAC layer protocol

is IEEE 802.11. Table 2 lists the simulation

parameters.

6.2 Impact of network load

As a tree-based multicast routing protocol,

MAODV shows an excellent performance in

light load ad hoc networks. However, as the


load of network increasing, QoS is degraded

obviously. In order to illustrate the impact of

network load on the performance of MAODV,

we select packet delivery ratio, control over

head and average end-to-end delay to evaluate

the performance of protocols.

Packet Delivery Ratio Measure related to

the reliability of communication, the delivery

ratio R is defined as:

R= (5)

Where ndata-, is the number of multicast

data packets received at all multicast group

members, and ndata-s is the number of multicast

packets that a source node generated, besides

n is the number of multicast group members.

Control Overhead Control overhead reflects

the degree of network congestion and the effi

ciency of protocols, the control overhead C is

defined as: c = nc/rl-s

ndata-r (6)

Where n data-s is the number of transmissions

of control packets in the whole network, and

ndma_r is the same as abovementioned.

End to end average delay End to end aver

age delay is usually used to evaluate the effec

tiveness of routing. Furthermore, it concludes

whether the routing is easy to be built. The

end to end average delay T is defined as:

T=� ndota-I

Table II Simulation parameters.

Number of nodes

Scene range

Load of network

Number of group members

Channel bandwidth

Data payload

N ode pause time

Transmission range

Simulation time

Propagation model

(7)

20

500mx500m

5,10,15,20 packet/s

6

2 Mbps

512 bytes/packet

0-10 seconds

250 m

910 seconds

Two-ray ground

(4)

96

3 0.8

0 .,.; '" '" :.. 0.6 ;>. :.. " > ,.; ..,

0.4 " "0 '" "

"'"' u '" 0.2 0-

0 5

Where ttotal is the total time which multicast

data packets take from the source node to mul

ticast group members, and ndma_r is the same as

abovementioned.

[n the simulation, load of network is set to

5, [0, 15 and 20 packets per second respec

tively. Furthermore, three curves in figure 3, 4

and 5 respectively represent simulation results

with the speed of I mis, 5m/s, 10m/s. Obvious

ly, as network load increases, the MAODV's

packet delivery rate decreases. Moreover, as

network load increases, routing overhead also

decreases due to the total number of data bytes

received by MAODV receivers increasing.

However control data transmitted, remains

fairly constant with increased network load

there by reducing the routing overhead. [t is

10 15 20

load of netwol-k (packets/51

Fig.3 Impact on packet delivery ratio

0.5

� 0.4 "0 '" " .<: ... " 0.3 > 0 '" "

"'" u 0.2 '" 0-..., 0 t c 0.1 0 u

0 5 10 15 20

load of netwQl-k (packets/51

Fig.4 Impact on control overhead

97

obvious to see that node mobility makes great

er negative impact on the protocol's perfor

mance. [n short, the performance of MAODV

is degraded obviously in heavy load ad hoc

networks. Therefore, the improvement in this

paper is very necessary.

6.3 Simulation results and performance evaluation

At first, we simulate to prove that packet de

livery ratio will not be improved further when

the number of downstream branches is larger

than the upper limit, as is shown in figure 6.

In our experiments, we set an upper limit with

the value of three.

The average hop from group members to

the group leader reflects the optimization of

the multicast tree structure. Figure 7 shows

the comparison of average hop from group

members to the group leader. We observe from

the simulation result that MAODV-BB owns

the smallest average hop. On one hand, the

updating operation of tree branches optimizes

the tree structure. On the other hand, backup

branches can provide more effective routing

information for group members. The load of

network nearly has no effect on the multicast

tree structure, so the average hop under differ

ent load of network remains almost the same.

As follows, we analyze and compare MA

ODV-BB with MAODV in heavy load ad hoc

networks by using packet delivery ratio and

average end-to-end delay.

Figure 8 shows the impact of network load

on packet delivery ratio. With the increasing

of the network load, the MAODV's packet

delivery rate has descended obviously. When

the load of network is 20 packets per second,

the packet delivery rate of MAODV is about

10 percent lower than that in the network with

5 packets per second. Only adding the updat

ing operation to MAODV improves the packet

delivery ratio when the network load is light.

However, MAODV-BB's packet delivery is

always maintained at a high level even when

the network load is heavy. In MAODV-BB,

the existence of backup branches reduces the


frequency of tree reconstruction and ensures

high packet delivery ratio in heavy load ad hoc

networks.

The average end-to-end delay of MAO

DV-BB is least, as is shown in figure 9. As the

increasing of the network load, the packet de

livery delays become longer. This is because

that the recovery procedure takes a long time

to repair the partition and makes a bad effect

on data transmitting. It is obvious to see that

the delay of MAODV-BB is always lower

than MAODV's. The update operation of tree

branches optimizes the tree structure and re

duces delay.

VII. CONCLUSION

This paper proposes an optimized protocol

MAODV-BB based on MAODV, which im

proves robustness of the MAODV protocol

by combining advantages of the tree struc

ture with the mesh structure. The key idea of

MAODV-BB is to make full use of GRPH

messages that the group leader broadcasts

periodically to update shorter tree branches

and construct a multicast tree with backup

branches. It not only optimizes the tree struc

ture but also reduces the frequency of tree re

construction. Mathematic modeling derivation

and simulation results both demonstrate that

MAODV-BB protocol improves the network

performance over conventional MAODV in

heavy load ad hoc networks, which meets QoS

requirements for communication in a MANET.

As further work, we intend to study the

reliability of tree-based multicast routing pro

tocols in varying conditions such as node mo

bility, group size. We also consider enhancing

our protocol with a global congestion control

mechanism to slow the data rate of the senders

when the network is highly loaded.

ACKNOWLEDGEMENT

This work is supported by the NSFC (National

Natural Science Foundation of China) No.

61371068 and No. 61172130, the National 863

program No.2011AAIIAI02-04-02 and Shen-


0.05

.3 ;>. '" ,..., 0.04 " '0 " OIl '" '"' 0.03 " > '"

'0 " " I 0 0.02

-' I

'0 " " -' om "

"" u '" '"

0 5 10

1 hlAODV: 1m/

,s

hlAODV: 5m/s �IAODV:lOm/s

15

load of netwo,'k (packets/ s)

Fig.S Impact on average end-to-end delay

0.96

g 0.95

0 "D '" 0.94 :-'" <-" 0.93 > � " '0 '-' 0.92 "

"" u '" "- 0.91

0.9 5

MAODV-BB downstl'eam size <� 2 MAODV-BB (downstream

-size <� 3)

MAODV-BB (downst,'eam:':size <� 4) 10 15

load of netwol'k (packets/s)

Fig.6 Illustration about the number of downstream branches

5

if; "-0 .:5 4

1 hlAODV

MAODV-BB MAODI' (update branch)

<-0 '0 '" 0 ,..., 0- 3 " 0 <-'" 0 2 '" "-0 .<: " "" co '-" > '"

0 5 10 15

load of network (packets/ s)

Fig.7 Average hop to the group leader

=:=1

20

20

=:=1

20

98

? 0.9

0 .� <tl <- O.S >-

5 >-.,., ""

0.7 " "D

., "

"" u <tl 0.6 0-MAODY

MAODY-BB

0.5 "'AODI' (update branch)

5 10 15 20

load of network (packets/ s)

Fig.8 Comparison of packet delivery ratio

0.04

� 1 "'AODI'

=:= 1 "'AODY-BB >. MAODV (update bl-anch) <tl "" " "0 0.03 " 00 <tl <-" >-<tl

"0 0.02 c " I 0 '"' I "0 c 0.01 "

'"' "

"'" u '" 0-

0 5 10 15 20

load of netwOl-k (packets/s)

Fig.9 Comparison of average end-to-end delay.

99

zhen Technology Research and Development

Program No. CXZZ20120830100839333.

References [1] Internet Engineering Task Force (IETF), Mobile

Ad Hoc Networks (MANET) Working Group

Charter 2006, http://www.ietf.org/html.charters/

manet-charter.html.

[2] Conti M, Giordano S. Multihop Ad hoc net

working: the theory[J]. IEEE Communications

Magazine, 2007, 45 (4): 78-86.

[3] Luo Junhai, Ve Danxia, Xue Liu and Fan Mingyu,

"A survey of multicastrouting protocols for mo

bile ad-hoc networks," IEEE Communications

Surveys & Tutorials, vol. 11, no. 1, pp. 78-91,

2009.

[4] Soni S.K. and Aseri T.Ci, "A review of current

multicast routing protocol of mobile ad hoc

network," in Proc. Second Int. Conf. Computer

Modeling and Simulation ICCMS' 10, vol. 3, pp.

207-211, 2010.

[5] K. Viswanath, K. Obraczka, and G. Tsudik, "Ex

ploring mesh and tree based multicast routing

protocols for manets," vol. 5, no. 1, pp. 28-

42,2006.

[6]

[7]

[8]

[9]

[10]

[11]

E. M. Royer and C. E. Perkins, "Multicast ad hoc

on-demand distance vector (maodv) routing,"

draft-ietf-manet-maodv-OO.txt, 2000.

W. S. Vunjung Vi Sung-Ju Le and M. Gerla,

"On-demand multicast routing protocol (odm

rp) for ad hoc networks," draft-ietf-manet-odm

rp-04.txt, 2002.

Hua Chen, Zhengxiang. Van, Baolin Sun, Vue

Zeng, Xianying He, An Entropy-Based Long

life Multicast Routing Protocol in MAODV.2009

ISECS International Colloquium on Computing,

Communication, Control, and Management,

2009, Page(s): 314 -317.

Mingyang Zhong, Vunqing Fu, Xinqiang Jia.

"MAODV multicast routing protocol based on

node mobility prediction ", E -Business and E

-Government (ICEE), 2011 International Confer

ence, June, 2011.

Baolin Sun, Hua Chen, and Layuan Li, "A Reli

able Multicast Routing Protocol in Mobile Ad

Hoc Networks", In Proceedings of the 16th In

ternational Conference on Computer Commu

nication (ICCC2004), Beijing, China, September,

2004, pp. 1123-1129.

CheeOnn Chow, Hiroshi Ishii. Video multicast

over mobile ad hoc networks: Multiple-Tree

Multicast Ad Hoc On-demand Distance Vector

Routing Protocol (MT -MAODV). The 18th An

nual IEEE International Symposium on Personal,

Indoor and Mobile Radio Communications

(PIMRC07). Sept. 2007.

[12] Hong Tang, Fei Xue, Peng Huang. MP-MAODV:

a MAODV-Based Multi-path Routing Algorithm.

IFIP International Conference on Network and

Parallel Computing. 2008 , Page(s): 296- 301.

[13] Xiaohua Chen, Qiu Zhong, Danpu Liu, An Im

proved MAODV Based on Mobility Prediction

and Self-pruning Flooding, In Proceedings of

IEEEICCMC -2009, China, Jan, 2009, pp.127 -131.

[14] The Network Simulator - NS-2: http://www.isi.

edu/ nsnam/ns.

Biographies LI Xu, is a professor of School of Electronic and In

formation Engineering and Laboratory of Rail Transit

Control and Security and is Director of Lab of Broad

band Self-organizing Networks, She has directed

or participated in more than ten National Natural

Science Foundation projects, and international/do

mestic cooperation projects, Professor U's research

interests are wireless communication, personal com

munication, self-organizing networks, WSN, etc. and

she focuses on the overall design and modeling of

wireless communication systems and self-organizing

networks as well as key algorithms.


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