Multicast Routing Protocols in Adhoc Networks

T S Pradeep KumarVIT Chennai

http://www.nsnam.com http://www.pradeepkumar.org

Medium Access Control (MAC Layer)◦ Transmission and reception of packets is the main

service ◦ Also arbitration to access the channel ◦ Three modules are handled

Transmission Module Receiving Module Neighbor list handler

Reference Model for Multicast Protocols

Routing Layer ◦ Formation and maintaining the unicast

session/multicast group◦ Uses a set of tables, timers and route cache◦ Unicast Routing information handler◦ Multicast Routing information handler◦ Forwarding module◦ Tree/Mesh construction module◦ Session Maintenance Module◦ Route cache maintenance module

Reference Model for Multicast Protocols

Application Layer ◦ Data packet transmit/receive controller◦ Multicast session initiator/terminator◦ Joining a group◦ Data packet propagation◦ Route Repair

Reference Model for Multicast Protocols

Reference Model for Multicast Protocols

Type of Node Active ModulesSource/Receiver All ModulesIntermediate Nodes All modules of MAC and routing

LayersOther Nodes Modules 2,3,8 and optionally

module 4

Multicast Routing protocol

Application Independent / Generic◦ Based on Topology

Tree based Source Tree and Shared Tree

Mesh based◦ Based on initialization of multicast session

Source initiated Receiver initiated

◦ Based on topology maintenance mechanism Soft state approach Hard state approach

Classification of Multicast Protocols

Tree based ◦ Source Tree based

The source is at the root◦ Shared Tree based

All the sources share the common tree with a core node at the root

If there is a single point of failure (if core node failed), the route construction should happen again

Based on Topology

Source initiated Receiver initiated

Based on initialization of multicast session

Soft state approach◦ Control packets are flooded periodically to refresh

the route◦ Packet delivery ratio is high

Hard state approach◦ Control packets are flooded only during a link

break◦ Packet delivery ratio is low because low control

overhead

Based on Topology maintenance

Source Tree based Shared Tree BasedA single multicast tree maintained per source

A single tree is shared by all sources in the tree

Less scalable (increase in number of sources leads to increase in trees which affects the bandwidth)

More scalable (performance will not be degraded when more multicast sessions or more souces are added)

More memory is needed at the source nodes

Less memory is needed as the tree is shared between the sources

Source Tree Vs Shared Tree

Tries to find the nearest forwarding node rather than the shortest path between source and receiver

Reduces number of data transmissions Uses hard state approach (to rejoin

multicast group, the control packets are sent only during link breaks)

Bandwidth Efficient Multicast Routing Protocol (BEMRP)

Tree initialisation Phase◦ Join packets

A receiver node floods the join control packets◦ Reply Packets

The existing members of the tree, on receiving join packets, respond with Reply control packets

◦ Reserve Packets When many such reply packets comes to the

receiver nodes, then the receiver node select the minimum hop count route and send a Reserve Control packet to the member node.

Bandwidth Efficient Multicast Routing Protocol (BEMRP)

BEMRP - Tree Initialization phase

BEMRP - Tree Maintenance phase

Node R3 Moves, I3 Broadcasts

R3 receives and send a Reserve packet

Broadcast multicast scheme

When the node moves, the upstream node is responsible for finding a new route by flooding with broadcast-multicast packets

BEMRP - Tree Maintenance phase

R3, I3 Links fails, R3 sends join and I3 reply

R3 Send Reserve packets and rejoin the group

Local Rejoin Scheme The corresponding

sends the join packet if there is any break in the link.

It is similar like tree initialization phase

BEMRP – Route optimisation phase

R3 Receives from I2 before I5 and R3 Sends a Reserve packet

I5->I4->I3->I2, sends a Quit packet and thus a path is pruned

When a tree node or receiver nodes comes within the transmission range of other tree nodes, the unwanted tree nodes are pruned by sending the Quit messages.