Weight based Multicast Routing Protocol for Ad hoc Wireless Networks

學生：陳信皇

教授：陳仁暉

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 In the hard state Link failure

Data packets drop Low packet delivery

Localized prediction techniqueovercome

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.