AD HOC WIRELESS
MUTICAST ROUTING
Multicasting in wired networks
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In wired networks changes in
network topology is rare
But for mobile ad hoc networks
changes are frequent
Multicasting in wired networks
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If two communications nodes are
within radio range of each other
these connections can be direct
connections
Otherwise, use multi-hop
connections
Multicasting in wired networks
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Because every mobile node can
move, changes in network topology
are frequent.
The bandwidth of wireless links is an
order of magnitude lower than that
of wired links.
Multicasting in wired networks
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New routing protocols for both
unicast and multicast
communications are required.
Highly adaptive to be able to cope
with highly dynamic network
conditions.
Low control overhead and power
consumption.
Multicasting in wired networks
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IP multicast architecture
MBone[60]
IP multicast architecture
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In 1989, Deering[61] proposed.
Enable point to multipoint
communications in TCP/IP networks.
Multicast group is identified by a
single IP address.
IP multicast architecture
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Receiver needs to join and become a
member of a particular multicast
group. But sender doesn’t need.
Deliveries of multicast packets from
multicast senders to all intended
multicast members are handled by
network, with help from multicast
routing protocol.
IP multicast architecture
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All routers in the network are
required to support multicast routing.
the fact that multicast senders have
no control over the multicast delivery
process can make administrative and
security policies cumbersome.
Multicast Tunnels and MBone
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The requirement that every router in
the network must be multicastenabled has prohibited large-scale
multicast deployment in the internet.
Multicast traffic is encapsulated in
unicast packets and transmitted from
one multicast network to another
network, where it is decapsulated
and process as multicast packets.
Multicast Tunnels and MBone
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The connection through which the
encapsulated packets are
transmitted is called the multicast
tunnel, or mtunnel.
Shown in figure 10.1
Multicast Tunnels and MBone
Multicast routing algorithms
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Source-base shortest-path multicast
tree
• Broadcast-and-prune technique
• RPF (reverse path forwarding)
mechanism
Reverse path forwarding
Multicast routing algorithms
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Single shared tree per multicast
group
• CBT( Cored Based Trees)
• PIM-SM( Protocol Independent Multicast
Sparse Mode)
Multicast routing in mobile ad hoc
networks
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Based on multicast delivery structure
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flooding
Sourced-Based Multicast Tree
Core-Based Multicast Tree(CBT)
Multicast Mesh
Group-Based Multicast Forwarding
Flooding
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Multicast packet is globally flooded to
all nodes in network.
Well suited to networks with high
mobility.
Bandwidth is wasted and
unnecessary forwarding of duplicate
data.
Source-Based Multicast Tree(SBT)
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Multicast tree is established for each
multicast source node.
Each multicast packet is forwarded
along the most efficient path from
the source to each member.
A lot of overhead is incurred in
establishing multicast tree.
Source-Based Multicast Tree
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DVMRP
MOSPF
PIM-DM
Core-Based Multicast Tree(CBT)
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A single shared tree is used to
connect all multicast group members.
A special node is designated as the
cored node.
The tree can be either unidirectional
or bidirectional.
Core-Based Multicast Tree(cont.)
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In unidirectional shared tree,
multicast packets must be unicast to
the core node.
In bidirectional shared tree,multicast
packets can enter the tree at any
point.
Core-Based Multicast Tree(cont.)
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More efficient in communication
performance and forwarding
overhead.
Result in high tendency for
congestion at the shared links.
CBT, PIM-SM, AmRoute[71], AMRIS,
and AODV[26].
Multicast Mesh
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Establish a mesh for each multicast
group.
A mesh is different from a tree since
each node can have multiple parents.
Provide multiple redundant path,
avoiding frequent mesh
reconfigurations.
Unnecessary forwarding of multicast
packets.
Group-Based Multicast Forwarding
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A group of nodes acts as multicast
forwarding nodes for each multicast
group.
A group of nodes is maintained
instead of the links that constitute
the tree or mesh.
Group-Based Multicast Forwarding
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Multicast packets are forwarded only
by forwarding nodes.
All received multicast packets that
are not duplicated are rebroadcast
by the forwarding nodes to their
neighbors.
Group-Based Multicast Forwarding
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Few states are kept at each
intermediate node and redundant
paths are available.
ODMRP(On Demand Multicast
Routing Protocol).
Ad hoc multicast routing protocol
DVMRP with Wireless Extension
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To function more efficient in a
mobile ad hoc environment.
These extensions are:
a.
b.
c.
leaf-node detection
Dynamic grafting/pruning
The use of packet duplication
DVMRP with Wireless Extension
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Flooding the whole network with the
multicast traffic.
The leaf node which is not interest in
that particular multicast group will
send prune message upstream.
DVMRP with Wireless Extension
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The intermediate node receiving this
prune message will mark that
particular link as “pruned-off” and will
not forward any subsequent
multicast packets of the
corresponding session onto that link.
DVMRP with Wireless Extension
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Once this prune message is
completed, the optimal source-base
tree is established.
Join/leave operation
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Periodically , the timer on the pruned
branch will expire and the multicast
traffic will be flooded again.
This mechanism incurs latency when
new members wish to join the group
since a new member has to wait until
the next flooding period.
Grafting /pruning
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Dynamic grafting is provided to allow a
member to quickly join the multicast
group.
In dynamic grafting/pruning, when a node
detects that the shortest path back to the
multicast source node has changed, it will
send a prune message to the current
upstream node and a graft message to the
new upstream node.
ODMRP
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Flooding-based multicast routing
protocol for mobile ad hoc network.
Data is flooded only throughout the
forwarding group.
Forwarding group is a set of ad hoc
nodes specially chosen to forward
multicast traffic for a particular
multicast group.
ODMRP
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ODMRP depends on the following
operations:
a) multicast sender advertisement
b) JOIN-TABLE broadcast by multicast
receivers.
ODMRP
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When a multicast sender has data to
send , it starts the periodic broadcast
of JOIN-REQUEST message.
Each node , upon receiving the JOINREQUEST message, will update
routing table with the address of the
node from which the JOIN-REQUEST
message is received.
ODMRP
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When a multicast receiver receives
the JOIN-REQUEST message , it will
update its member table with of the
multicast sender and periodically
broadcast JOIN-TABLE message.
Only the node listed as the next-hop
in the JOIN-TABLE message will
process the JOIN-TABLE message.
ODMRP