This document summarizes and compares different multicast routing protocols for ad hoc wireless networks. It reviews tree-based protocols like AMRoute and AMRIS that build multicast trees, as well as mesh-based protocols like ODMRP and CAMP that build multicast meshes. It finds that mesh-based protocols generally outperform tree-based protocols because the multiple routes in a mesh make it more robust to node mobility and channel fading. The document presents simulation results showing how different protocols are affected by parameters like node speed, number of multicast sources, group size, and network traffic load. ODMRP is found to be the most robust to mobility and have the lowest overhead.
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Multicast in computer Architecture
1. Multicast ad hoc networks
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Review of M ulticasting in wired networks
Tree based wireless multicast
M esh based wireless multicast – ODMRP
Performance comparison
Reliable, congestion controlled multicast
Scalable multicast, M-LANM AR
2. Multicast Routing
• M ulticast: delivery of same packet to a group
of receivers
• M ulticasting is becoming increasingly
popular in the Internet (video on demand;
whiteboard; interactive games)
• M ultiple unicast vs multicast
3. Multicast Group Address
• M -cast group address installed in all
receivers in the group
• Internet uses Class D address for m-cast
• M -cast address distribution etc. managed by
IGMP Protocol
4. The Multicast Tree problem
• Problem: find the best (e.g., min cost) tree
which interconnects all the members
5. Multicast Tree options
• GROUP SHARED TREE: single tree; the root
(node C below) is the “CORE” or the
“Rendez Vous” point; all messages go
through the CORE
• SOURCE BASED TREE: each source is the
root of its own tree connecting to all the
members; thus N separate trees
6. Group Shared Tree
• Predefined CORE for given m-cast group (eg, posted
on web page)
• New members “join” and “leave” the tree with explicit
join and leave control messages
• Tree grows as new branches are “grafted” onto the
tree
• CBT (Core Based Tree) and PIM Sparse-Mode are
Internet m-cast protocols based on GSTree
• All packets go through the CORE
7. Source Based Tree
• Each source is the root of its own tree: the tree of
shortest paths
• Packets delivered on the tree using “reverse path
forwarding” (RPF); i.e., a router accepts a packet
originated by source S only if such packet is
forwarded by the neighbor on the shortest path to S
• In other words, m-cast packets are “forwarded” on
paths which are the “reverse” of “shortest paths” to S
8. Per-Source Tree Multicast
Each source supports own
separate tree
“Probing and Pruning” tree
maintenance
Reverse Path Forwarding (to
avoid endless packet
circulation)
“Fast Source” problem
S2
S1
R2
R1
9. RP-based Shared Tree Multicast
RP (Rendezvous Point)based “Shared” tree
Tree maintenance:
soft state
“off-center” RP
longer paths than
shortest path tree
RP
S1
10. Shared Tree vs. Per-source Tree
Shared Tree:
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+
−
−
scalability
less sensitive to fast source
longer path
off center RP
R2
R3
Per-Source Tree:
+
+
+
−
−
shortest path
traffic distribution
no central node
scalability problem
fast source problem
RP
S2
R4
R1
S1
11. Wireless Tree Multicast Limitations in High Mobility
RP
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In a mobile situation, tree is fragile: connectivity loss,
multipath fading
Need to refresh paths very frequently
High control traffic overhead
12. Proposed solution: Forwarding Group Multicast
Forwarding Group
FG
FG
FG
FG
FG
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All the nodes inside the “bubble” forward the M-cast packets via
“restricted” flooding
Multicast Tree replaced by Multicast “Mesh” Topology
Flooding redundancy helps overcome displacements and fading
FG nodes selected by tracing shortest paths between M-cast
members
13. Forwarding Group Concept
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A set of nodes in charge of forwarding multicast packets
Supports shortest paths between any member pairs
Flooding helps overcome displacements and channel
fading
14. ODMRP (On Demand Multicast
Routing Protocol)
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Forwarding Group Multicast concept
Tree replaced by Mesh
On-demand approach
Soft state
15. FG Maintenance
(On-Demand Approach)
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A sender periodically floods control messages when it has data to
send
All intermediate nodes set up route to sender (backward pointer)
Receivers update Member Tables ; periodically broadcast Join
Tables
Nodes on path to sources set FG_Flag; FG nodes broadcast Join
Tables
16. Soft State Approach
• No explicit messages required to join/leave
multicast group (or FG)
• An entry of a receiver’s Member Table expires
if no Join Request is received from that sender
entry during MEM _TIMEOUT
• Nodes in the forwarding group are demoted to
non-forwarding nodes if not refreshed (no Join
Tables received) within FG_TIMEOUT
18. Simulation Environment
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Written in PARSEC within GloMoSim Library
50 nodes placed in 1000m X 1000m space
Free space channel propagation model
Radio range: 250 m
Bandwidth: 2 Mb/s
MAC: IEEE 802.11 DCF
Underlying unicast : Wing Routing Prot (for AMRoute & CAMP)
Multicast members and sources are chosen randomly with
uniform probabilities
Random waypoint mobility
19. Goal
• Compare mesh- and tree-based multicast
protocols
– Mesh-based: ODMRP, CAMP, Flooding
– Tree-based: AMRoute, AMRIS
• Evaluate sensitivity to the following
parameters:
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Mobility (ie, speed)
Number of multicast sources
Multicast group size
Network traffic load
20. Multicast Protocols
• Adhoc Multicast Routing (AMRoute)
– Bidirectional shared tree with a core
– Relies on unicast protocol to provide routes between multicast
members and to handle mobility
– Suffers from temporary loops and non-optimal trees
21. Multicast Protocols (cont’d)
• Ad hoc Multicast Routing protocol utilizing
Increasing id-numberS (AMRIS)
– Each node is assigned an ID number to build a tree
– The increasing id is used in tree maintenance and localized repair
– Beacons are sent by each node to neighbors
• Core-Assisted Mesh Protocol (CAMP)
– A shared mesh for each multicast group
– Cores are used to limit the flow of join requests
– Relies on certain underlying unicast protocols (e.g., WRP, ALP, etc.)
22. Packet Delivery Ratio as a Function
of Mobility Speed
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20 members
5 sources each
send 2 pkt/sec
Mesh protocols
outperform tree
protocols
Multiple routes
help overcome
fading and node
displacements
23. Packet Delivery Ratio as a Function
of # of Sources
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20 members
1 m/sec of mobility
speed
Total traffic load of
10 pkt/sec
Increasing the
number of sender
makes mesh richer
for ODMRP and
CAMP
24. Packet Delivery Ratio as a Function of M ulticast
Group Size
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5 sources each send 2
pkt/sec
1 m/sec of mobility
speed
Flooding and ODMRP
not affected by group
size
CAMP builds massive
mesh with growth of
the members
25. Packet Delivery Ratio as a Function of Network
Load
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20 members and
5 sources
no mobility
AMRIS is the
most sensitive to
traffic load due to
large beacon
transmissions
26. Conclusions
Tree schemes:
Too fragile to mobility
lower throughput in heavy load
lower control O/H
Meshed Based scheme (CAMP):
Better than tree schemes (mesh more robust)
Mesh requires increasing maintenance with mobility
ODMRP:
most robust to mobility& lowest O/H
Lessons learned:
– Mesh-based protocols outperform tree-based protocols
– Multiple routes help overcome node displacements and fading