Multicast routing protocol for ad-hoc networks with
route aggregation and transmission power control
Katsuhiro Naito, Michitaka Fujii, Kazuo Mori, and Hideo Kobayashi
Department of Electrical and Electronic Engineering, Mie University,
1577 Kurimamachiya, Tsu, 514-8507, Japan
Email: {naito, kmori, koba}@elec.mie-u.ac.jp
Abstract— In this paper, we propose a multicast routing protocol
for ad-hoc networks to reduce packet collisions. Packet collisions
are one of the degradation factors in wireless communications.
In the ad-hoc multicasting, some forwarder nodes forward data
packets from a source node to a lot of destination member
nodes. Moreover, forwarding timing of data packets is almost
same instance because forwarder nodes with a same hop count
receive data packets at same instance from their an upstream
node. Therefore, the ad-hoc multicasting tends to suffer from
packet collisions due to multiple forwarding of data packets at
same instance. In the proposed routing protocol, each forwarder
node informs a number of its downstream nodes. Then, neighbor
downstream nodes select a forwarder node with maximum number of downstream nodes to aggregate multicast routes. Hence,
the proposed protocol can reduce redundant packet forwarding
due to a lot of existence of forwarder nodes. Additionally,
forwarder nodes control transmission power of data packets
according to information from downstream nodes. As the results,
the proposed protocol can reduce packet collisions due to hidden
terminal problems. From the simulation results, we can find
that the proposed protocol can reduce the packet collisions and
improver the delivery ratio.
Keywords— Ad-hoc networks, Routing protocol, Multicast,
Collision, Hidden terminal problems, transmission power control
I. I NTRODUCTION
In wireless ad-hoc networks, each node behaves as a router
as well as an end host. Hence, end-to-end communication
is performed by multi-hop communication. Routing protocols
are most important mechanisms for multi-hop communication
because packet forwarding is decided by routing protocols. In
conventional researches, several routing protocols have been
proposed for ad-hoc networks [1].
In ad-hoc networks, various applications have been proposed. Meanwhile, these applications can be categorized into
three types: unicast communication, multicast communication,
and broadcast communication. In this paper, we focus on
the multicast communication because multicast communication is required for new type applications such as a video
streaming, an Internet radio, etc. In conventional multicasting
researches, several challenges due to changes in network
topology and features in wireless communication environment
are performed. Since conventional multicast routing protocols
for wired networks cannot apply to ad-hoc networks, new
routing protocols for ad-hoc networks have been proposed [2],
[3].
IEEE 802.11 is a well-known wireless device to achieve adhoc networks [4]. IEEE 802.11 has special mechanisms named
RTS (Request To Send) / CTS (Clear To Send) for hidden node
problems. Meanwhile, RTS/CTS mechanisms are not used for
multicast communication because multicast communication
employs broadcast modes in IEEE 802.11 systems. Therefore,
it is difficult to avoid collisions due to hidden node problems
because nodes only perform channel sensing in the broadcast
modes [5], [6], [7]. Moreover, some data packets are forwarded
hop by hop from a source node. Therefore, some forwarder
nodes with a same hop count transmit the data packets at
almost same instance. Hence, multicast communication tends
to suffer from packet collisions due to hidden node problems.
Additionally, almost all multicast routing protocols construct
a tree-based topology. As the result, packet collisions at upstream nodes cause many packet loses on their all-downstream
nodes in multicast communication[8].
In order to achieve reliable broadcast communication, some
Media Access Control protocols for multicasting have been
proposed [9], [10]. In these researches, authors extended
RTS/CTS mechanism in IEEE 802.11 for broadcast communication. Meanwhile, these extensions require modifications
of frame formats or hardware. In addition, few researches of
routing protocols have been proposed for solving these issues
[11].
In this paper, we propose a multicast routing protocol for adhoc networks to reduce packet collisions due to hidden node
problems. In the proposed routing protocol, each forwarder
node informs a number of its downstream nodes. Then,
neighbor downstream nodes select a forwarder node with the
maximum number of downstream nodes to aggregate multicast
routes. Hence, the proposed protocol can reduce redundant
packet forwarding due to a lot of existence of forwarder nodes.
Additionally, forwarder nodes control transmission power of
data packets according to information from downstream nodes.
As the results, the proposed protocol can reduce packet
collisions due to hidden node problems. From the simulation
results, we can find that the proposed protocol can reduce the
packet collisions and improver the delivery ratio.
N1
S
Hidden nodes
N6
II. ODMRP
In the proposed routing protocol, we employ an On-Demand
Multicast Routing Protocol (ODMRP) [12] as a base multicast
routing protocol. ODMRP is a well-known mesh based routing
protocol for ad-hoc multicasting. ODMRP constructs treebased routes from source nodes to some destination member
nodes. Then, a soft-state approach is taken to maintain multicast members.
When a multicast source node has packets to send, it broadcasts a Join-Query message to an entire network. Join-Query
messages are periodically broadcast to inform its multicast
service and to refresh membership information and to update routes. When intermediate nodes receive the Join-Query
messages, they store a source node address and a sequence
number in their message cache to detect any duplicate JoinQuery messages. An upstream node address of the Join-Query
message is registered into the routing table for a reverse
path back to the source node. If Join-Query packets are not
duplicate and a Time-To-Live (TTL) value is greater than zero,
they will be rebroadcast to neighbor nodes.
When destination nodes, which are multicast member, receive Join-Query messages, they create and transmit a JoinReply message to their upstream node. When intermediate
nodes receive the Join-Reply messages, they check whether
their own node address matches the next hop node address
within the Join-Reply messages. If they can confirm that the
Join-Reply messages are transmitted to own node, they should
be forwarding group nodes, which forward data packets from
the source node. The Join-Reply messages are propagated by
each forwarding group nodes until they reach the multicast
source node.
Figure 1 shows the example of route construction in
ODMRP. In the example, one source node exists, and ten
multicast group member nodes also exist in the network. The
locations between node N1 and N4, node N4 and N5, and
node N4 and N3 are hidden nodes situation. Therefore, each
node cannot sense the other node’s signals due to hidden
node problems. Solid arrows mean the constructed routes
by ODMRP. Dot arrows mean the interference signals from
corresponding hidden nodes. Dot circles mean the transmission
region of full transmission power.
N3
N4
Packet collisions
Hidden nodes
N2
Hidden nodes
N8
N7
Fig. 1.
N10
N5
Packet collisions
N9
Packet collisions
Selected routes
Interference signals
Transmission range
Example route construction in ODMRP
In ODMRP, nodes select an upstream route for first arriving Join-Query message. As the results, several routes are
constructed in the network. In the example, node N6 selects
node N1, node N7 selects node N4, node N8 selects node
N2, node N9 selects node N5, and node N10 selects node
N3 as the upstream node. In data delivery phase, nodes N1,
N2, N4, N5 and N3 forward same data packets at almost
same instance because the hop count of these nodes is same.
Moreover, node N6 can receive signals form nodes N1 and N4,
node N8 can receive signals from nodes N2, N4 and N5, and
node N10 can receive signals from nodes N5 and N3. As the
results, nodes N6, N8 and N10 suffer from packet collisions
due to interference from hidden nodes. In multicast delivery,
packet collisions at upstream nodes mean packet losses at all
corresponding downstream nodes. Therefore, packet collisions
at upstream nodes become one of the serious degradation
factors in multicast delivery.
III. P ROPOSED PROTOCOL
In order to reduce hidden nodes in ad-hoc networks, we
focus on number of FG nodes and transmission area. Hence,
the proposed protocol intends to aggregate routes from a
source node to reduce the number of FG nodes. Moreover,
each node controls transmission power according to desired
signal-to-interference and noise power ratio (SINR) to reduce
redundant transmission area. As the results, the proposed
protocol can reduce the number of hidden nodes.
Meanwhile, the proposed protocol extends the frame formats of Join-Query and Join-Reply messages to carry the
Reserved
Type
Time To Live Hop Count
Multicast Group IP Address
Sequence Number
Source IP Address
Last Address
Previous Hop IP Address
Previous Hop X Coodinate
Previous Hop Y Coodinate
Previous Hop Moving Speed
Type
Frame format of Join-Query messages
Count
R F Reserved
Multicast Group IP Address
Previous Hop IP Address
Sequence Number
Last Address
Required Transmission Power
Hop Count
Sender IP Address[1]
Next Hop IP Address[1]
Route Expiration Time[1]
Yes
Clear the transmission power list
Calculate route transmission power
per candidate downstream nodes
Add Pnode and next hop address
into own transmission power list
Select the minimum Pnode from own transmission list
and update the next hop address in own routing table
Estimate a SINR value of the Join-Query message
Calculate required transmission power : Preq
Proute = Proute + Ptx
Multicast member
node ?
Sender IP Address[n]
Next Hop IP Address[n]
Route Expiration Time[n]
When nodes receive Join-Reply messages, they confirm
that the own hop count is greater than the hop count of
the received Join-Reply message. If the Join reply messages
Yes
No
Increment the hop count &
decrement the TTL
The TTL is
larger than 0
No
Yes
Rebroadcast the Join-Query message
Discard the Join-Query message
Fig. 4.
In order to reduce the number of FG nodes, the proposed
protocol employs the number of candidate downstream nodes
at FG nodes as the selection criteria of upstream nodes. Figure
5 shows the flowcharts for Join-Reply messages.
Timer is expired ?
Transmit a Join Reply message to
a node with minimum Preq
Frame format of Join-Reply messages
required information. Figure 2 shows the frame format of JoinQuery messages. In the extensions, the fields for the number of
downstream nodes and the route transmission power are added.
Figure 3 shows the frame format of Join-Reply messages. In
the frame format, the fields for the required transmission power
and the hop count are added.
Yes
No
*
*
*
Fig. 3.
No
Sequence number
is updated ?
Previous Hop Moving Direction
Minimum Link Expiration Time
Number of Downstream Nodes
Route Transmission Power
Fig. 2.
Receive a Join-Query message
Flowchart for Join-Query messages
are transmitted from downstream nodes, nodes update the
candidate downstream nodes list, which include node address
of own downstream nodes. Then, they update the number of
candidate downstream nodes, which is informed to neighbor
downstream nodes via Join-Query messages.
When nodes confirm that the received Join-Reply messages
are transmitted to own node, they should become FG nodes,
and rebroadcast the Join-Reply messages to their upstream
node with the minimum route transmission power per downstream nodes.
Figure 4 shows the flowchart for Join-Query messages.
When intermediate nodes receive Join-Query messages, they
Receive a Join-Reply message
The Join-Reply is
transmitted
from downstream
nodes ?
N1
N3
S
No
Hidden nodes
Hidden nodes
Yes
Update the candidate downstream nodes list
N6
N4
Update the number of candidate downstream nodes
Own IP address is
included in the next hop
IP address ?
No
N2
Hidden nodes
N8
N7
Yes
Set a FG flag
Rebroadcast the Join-Reply message to
the upstream node with minimum route
transmission power per downstream nodes
Fig. 6.
N10
N5
N9
Selected routes
Interference signals
Transmission range
Example route construction in Proposed protocol
Discard the Join-Reply message
Fig. 5.
Flowchart for Join-Reply messages
confirm the sequence number. If the sequence number is
updated, clear the transmission power list and the node list to
refresh the conventional routes. Then, they calculate the route
transmission power per candidate downstream nodes Pnode ,
and add Pnode and next hop address into own transmission
power list. They select the minimum Pnode , which is the most
effective forwarding node, and update the next hop address in
own routing table. Next, they estimate a SINR value of the
received Join-Query messages. Then, they calculate required
transmission power according to the estimated SINR value. In
order to inform the own route transmission power, they add the
own transmission power to the route transmission power in the
received Join-Query message. Finally, the received Join-Query
messages are rebroadcasted.
When the nodes are multicast member, they collect some
Join-Query messages to explore the better candidate upstream
nodes for certain period. After the certain period, they transmit
a Join-Reply message to their upstream node with the minimum required transmission power Preq .
•
•
•
IV. E XAMPLE OPERATIONS
Figure 6 shows the example route construction in the
proposed protocol. The assumed situation in Fig. 6 is same as
Fig. 1. In the proposed protocol, nodes constructs the different
route by following procedures.
•
The source node S broadcasts Join-Query messages to
•
the whole network. The Join-Query messages include the
initial route transmission power Proute (S) and the initial
number of downstream nodes Ndown (S). The initial value
of Proute (S) is the full transmission power of the node
S. The initial value of Ndown (S) sets to 1.
The nodes N1, N2, N3, N4, and N5 receive the broadcasted Join-Query messages from the source node S. They
estimate the SNR of the received Join-Query messages,
and calculate the required transmission power Preq . Additionally, they calculate the route transmission power per
candidate downstream nodes Pnode according to the route
transmission power Proute (S) and the number of downstream nodes Ndown . Then, they register Pnode , Preq , and
corresponding upstream node into the transmission power
list.
The nodes N1, N2, N3, N4, and N5 select the minimum
Pnode from own transmission list and update the next hop
address in own routing table. Then, they reply the JoinReply messages to the selected upstream node when they
are member of multicasting.
The nodes N1, N2, N3, N4, and N5 calculate the new
route transmission power Proute by adding Proute (S)
and the own transmission power Ptx . For example,
Proute (N 1) = Proute (S) + Ptx (N 1). Then, they broadcast the own Join-Query messages including the new
route transmission power Proute and the own number of
downstream nodes Ndown .
The nodes N6, N7, N8, N9 and N10 receive the JoinQuery messages from the nodes N1, N2, N3, N4 and
•
•
•
N5. They proceed in the same operations such as the
operations of the nodes N1, N2, N3, N4 and N5. Finally,
they reply the Join-Reply messages to the upstream node.
The nodes N1, N2, N3, N4 and N5 can receive the JoinReply messages from the nodes N6, N7, N8, N9 and
N10. Therefore, they can count the candidate number
of downstream nodes, and update Ndown . Additionally,
nodes, that receive the Join-Reply messages including
own address, can update the own transmission power Ptx
according to the Preq of the downstream nodes. If the
number of downstream nodes is not one, they select the
maximum Preq for the own transmission power Ptx .
The nodes N1, N2, N3, N4 and N5 can update the route
transmission power Proute (S) when the source node
rebroadcast the next Join-Query messages. As the results,
Pnode (N 4) and Pnode (N 5) are less than Pnode (N 1),
Pnode (N 2) and Pnode (N 3). Therefore, nodes N6, N7 and
N8 can select the node N4 as their upstream node, and
nodes N9 and N10 can select the node N5 as their upstream node. Finally, multicast routes can be aggregated
through the nodes N4 and N5. Then, packet collisions at
the nodes N6 and N10 can be avoided according to the
route aggregation.
In the data delivery phase, the nodes N4 and N5 transmit data packets with the minimum transmission power
Ptx (N 4), and Ptx (N 5). As the results, the transmission
regions of the nodes N4 and N5 are reduced like as Fig.
6. Then, packet collisions at the nodes N8 can be avoided
according to the transmission power control.
V. N UMERICAL RESULTS
In this section, we compare the performance for the proposed protocol with that for the conventional ODMRP protocol. The simulations are performed by the network simulator
QualNet[13]. In the simulations, we assume the IEEE 802.11g
as the wireless communication device, and the transmission
rate is fixed at 54 [Mbps]. 100 nodes are placed randomly in
1000 × 1000 [m] area. The source and the member nodes are
selected randomly. The application is CBR (Constant Bit Rate)
and data packets with the length of 1 [KB] are transferred
for 300 [s]. We consider the additive white gaussian noise
(AWGN) environment and the free space propagation model.
A target SINR in the proposed protocol is set to 20 [dB]. The
simulation results are an average of 100 simulation trials.
Figure 7 shows the number of collisions per member nodes.
From the results, we can find that our proposed protocol can
reduce the packet collisions. This is because, the proposed protocol can reduce FG nodes by aggregating multicast delivery
routes and control transmission power to avoid hidden node
TABLE I
S IMULATION
PARAMETERS
Simulator
Simulation period
Simulation area
Number of nodes
Node position
Mobility
Data packet length
Transmission interval
Wireless device
Transmission rate
Wireless environment
Application
Routing protocol
Simulation trials
Buffer period of Join-Query messages
Target SINR
Qualnet 4.5
300 [s]
1000 × 1000 [m]
100
Random
None
1048 [byte]
65 [ms]
IEEE 802.11g
54 [Mbps]
Free space
CBR 128 [kbps]
ODMRP, Proposed
100
10[ms]
20[dB]
problems.
Figure 8 shows the packet delivery ratio at member nodes.
From the results, the proposed protocol can improve the packet
delivery ratio because our protocol can reduce hidden nodes
and improve performance degradation due to hidden node
problems.
Figure 9 shows the number of route change per data packets.
From the results, we can find that the proposed protocol can
also reduce the number of route change. This is caused by
the aggregation mechanisms of the proposed protocol. On
the contrary, ODMRP select some neighbor nodes randomly.
Therefore, the number of route change in ODMRP increases.
Figure 10 shows the average number of FG nodes in the
network. From the results, we can find that the number of FG
nodes is reduced in the proposed protocol. The reason is that
the proposed protocol can aggregate multicast route according
to the route transmission power per candidate downstream
nodes.
VI. C ONCLUSIONS
This paper proposed the new multicast routing protocol
for ad-hoc networks. The proposed protocol is based on the
ODMRP, which is the most well-known multicast protocol.
The features of the proposed protocol are to improve hidden
nodes problems by aggregating multicast routes and controlling transmission power. From the simulation results, we
confirmed that the hidden node problem is the one of the
degradation factors for ad-hoc multicasting, and our protocol
can improve the packet delivery ratio and route stability.
2.6
ODMRP
proposed
0.31
Number of Route change
Normalized collosions
[collisions/transmission/node]
0.32
0.3
0.29
0.28
0.27
0.26
2.4
2.2
2
1.8
1.6
1.4
1.2
ODMRP
proposed
1
0.8
0.25
10
20
30
40
50
60
70
80
90
100
10
20
30
Number of member nodes
Fig. 7.
50
60
70
80
90
100
90
100
Number of member nodes
Normalized collisions
Fig. 9.
94
Normalized number of route changes
55
92
50
Number of FG nodes
Packet delivery ratio[%]
40
90
88
86
84
82
45
40
35
30
80
ODMRP
proposed
78
76
20
10
20
30
40
50
60
70
80
90
100
Number of member nodes
Fig. 8.
ODMRP
proposed
25
Packet delivery ratio
ACKNOWLEDGMENT
This work was supported by the Telecommunications Advancement Foundation and MEXT KAKENHI(23700075).
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