Weight based Multicast Routing Protocol
for Ad hoc Wireless Networks
教授：陳仁暉
學生：陳信皇
Introduction
Multicasting consists of concurrently
sending the same message from one
source to multiple destinations.
 Several multicast routing protocols have
been proposed for Ad hoc networks
which are classified as either mesh
based or tree based.

Introduction

In a mesh based multicast protocol,
there may be more than one path
between a pair of source and receiver,
thus providing more robustness
compared to tree based multicast
protocols.
Introduction
In a tree based multicast protocol, there
exists only a single path between a pair
of source and receiver, thus leading to
higher multicast efficiency.
 The construction of a multicast tree can
be done starting either from the
source(source-initiated) or from the
receiver(receiver-initiated).

Introduction
The Ad hoc environment suffers from
frequent path breaks due to mobility of
nodes, and hence efficient group
maintenance is necessary.
 Maintaining the multicast group can be
done by either soft state approach or
hard state approach.

Introduction
In the soft state approach, the multicast
group membership and associated
routes are refreshed periodically.
 In hard state approach, the routes are
reconfigured only when a link breaks.

Motivation

Bandwidth efficient multicast routing protocol
consumes the least bandwidth due to its hard
state tree maintenance scheme.
 When a receiver wants to join the multicast
group, it floods JoinReq control packets and
receives a number of Reply packets from the
forwarding nodes and receivers in the
multicast tree.
Motivation
Then the receiver sends a Confirm
packet to the nearest forwarding node
and joins the multicast group.
 Thus it minimizes the number of added
forwarding nodes and eventually
leading to a high multicast efficiency.

Protocol Description
Our protocol involves two phases
 1.Tree initialization phase
 2.Tree Maintenance phase

Tree Initialization Phase
A node desires to join the multicast
group.
 The aim here is to find the best point of
entry into the multicast group.
 The approach we have taken for this is
a receiver-initiated approach.

Tree Initialization Phase
When a new receiver R5 decides to
join the group, it broadcasts a JoinReq
packet with a certain time to live(TTL)
entry.
 These JoinReq packets are forwarde
until they are received by a tree node.
 Upon receiving a JoinReq packet, a tree
node say I1, send a Replay packet.

Tree Initialization Phase
The Replay packet initally contains the
distance of the node I1 from the source
S.
 Upon the reply packet receipt at node
R5 will have the hop distance of the
node R5 from node I1 and the hop
distance of node I from the source S.

Tree Initialization Phase
Tree Initialization Phase

The best replay minimizes the following
quantity:
Q=(1-joinWeight)*(hop distance of R5 from I1-1)
+
joinWeight*(hop distance of R5 from I1
+
hop distance of I1 from S)
joinWeight:0到1的值
Tree Maintenance Phase
Node move
Data packets drop
overcome
In the hard state
Low packet delivery
Localized prediction technique
Link failure
Tree Maintenance Phase

In which tree maintenance phase is executed
for TriggerHandoff time period before the link
is expected to break.
 The triggerHandoff is the time duration after
which the downstream tree node starts the
handoff procedure to reconfigure the
multicast tree before the link breaks(link
between downstream node and its parent
node).
Tree Maintenance Phase
Tree Maintenance Phase
In this scheme, each node maintains a
Neighbor Multicast Tree table(NMT).
 A node refreshes the NMTExistence
timer when it receives data packets
from tree node.

Tree Maintenance Phase

When the downstream tree node
receives data packets from its parent
node, the node can predict the time
duration for which the parent node
would remain within its transmission
range.
Tree Maintenance Phase

After receiving the data packets if the
link life period is less than the
TriggerHandoff time period , then the
downstream node transmits the data
packet after setting InitiateHandoff bit.
Tree Maintenance Phase

When a neighbor node promiscuously
receives a data packet with InitateHandoff bit
set,it sends Handoff control packet if the
following two conditions are satisfied.
 1.the neighbor node has tree node inforation
for that particular multicast group in NMT
table.
 2.the NodeDistance value of the
corresponding tree node entry in NMT be less
than the distance of the node which requests
for handoff procedure.
Tree Maintenance Phase

If the above two conditions are satisfied , then
the neighbor node sends Handoff control
packet to the interested tree node.
 When the tree node receives many Handoff
control packets,it chooses the Handoff control
packet with least NodeDistance value and
immediately sends back a HandoffConf
control packet to the neighbor node.
Tree Maintenance Phase

After receiving the HandoffConf control
packet,the neighbor node forwards it to
the tree node to rejoin the multicast tree.
Tree Maintenance Phase
There may be more than one neighbor
which satisfy the above two conditions.
 They are also eligible to send Handoff
control packets to the interested tree
node to reconfigure the multicast tree.
 Due to this reason,there is a chance
that these Handoff packets collide and
not reach the destination node.

Tree Maintenance Phase
Sending Handoff control packets by
many neighbor nodes may lead to
increased control overhead.
 If any neighbor node hears a
HandoffConf control packet,just before
sending the Handoff control packet,then
it discards its Handoff control packet.

Tree Maintenance Phase

There is no neighbor node satisfying the two
conditions.
 Hence the downstream node in this case
does not get any Handoff control packet from
any neighbor nod,resulting in a link break.
 When such a situation arises, the
downstream node of the broken link has to
take measures to rejoin the multicast group.
Tree Maintenance Phase

To find the new route to any forwarding
node in the multicast tree, the
downstream node floods JoinReq with
certain TTL value.
Performance Evaluation
A. simulation environment
 B. Metrics
 C. Simulation Results

Simulation environment





50 mobile nodes move within a 1000m x
1000m area.
The radio transmission range used is 250m.
Channel capacit is assumed as 2Mbits/sec.
The network traffic load is kept at
10packets/sec.
Source and receivers are chosen randomly
and join the multicast seeion at the beginning.
Metrics

Data Packet Delivery Ratio:the percentage
of data packets received by the receivers.
 Number of Control Packets Transmitted
per Data Packet Received:the degree of
control overhead.
 Number of Data Packets Received per
Data Packet Transmitted:the multicast
routing efficiency.
Simulation Results
Simulation Results
Simulation Results
Simulation Results
Simulation Results
Simulation Results
Simulation Results
Simulation Results
Simulation Results
Conclusions
We consider not only the number of
forwarding nodes but alst the distance
between source and receiver.
 It makes the protocol efficient as well as
robust.
 We use localized prediction
scheme,hence it achieves high packet
delivery ratio.
