Multicast in Wireless Mesh Network

1
Multicast in Wireless Mesh Network

• Xuan (William) Zhang
• Xun Shi

2
Outline

• Introduction to multicast in WMNs
• Defining the cost of multicast tree
• Ruizs MNT protocol
• Chous MDM protocol
• Conclusion

3
Outline

• Introduction to multicast in WMNs
• Defining the cost of multicast tree
• Ruizs MNT protocol
• Chous MDM protocol
• Conclusion

4
What is Multicast?

• Point-to-multipoint" or "multipoint-to-multipoint
  
• Different from broadcast and unicast

(a) Broadcast
(b) Multicast
(c) Unicast
5
Advantages of Multicast

• Delivery to destinations simultaneously
• Deliver the messages over each link of the
  network only once
• Only create copies when the links to the
  destinations split

6
Wireless Mesh Networks

• Mesh routers are generally stationary
• Multi-hop forwarding
• High speed
• Reliable power supply

7
Internet multicast protocols

• Feature
• Wired / Powerful / Reliable
• Maintain a large and fixed topology
• Shortest path algorithms
• simpler to implement
• simpler to support frequent joins/leaves
• lowest delay

8
Drawbacks of Internet multicast in WMNs

• Routing metrics do not aim at minimizing the cost
  of multicast tree
• Not using broadcast nature

9
MANET multicast protocols

• Feature
• Maintaining a smaller and mobility network
  topology
• Relying on flooding mechanism
• On-demand routing protocols
• Suitable for mobility
• Low power consumption

10
Drawbacks of MANET multicast in WMNs

• Complexity of computation
• High mobility
• High Power consumption

11
Multicast protocols in WMNs

• WMNs multicast is between Internet and MANET
  multicast
• Fixed topology
• Broadcast nature
• Mobility and power are not problems

12
Outline

• Introduction to multicast in WMNs
• Defining the cost of multicast tree
• Ruizs MNT protocol
• Chous MDM protocol
• Conclusion

13
Traditional definition of cost

• Measured by hops, delays, etc.
• Minimum Steiner tree problem
• NP-complete
• Heuristic algorithms polynomial time
• Shortest path tree
• Sub-optimal shared tree
• MST algorithm 2optimal approximation
• Zelikovsky algorithm 11/6optimal approximation

14
Define the cost in WMNs

• Cost number of transmissions
• Minimize the number of transmissions
• Maximize the forwarding nodes which are shared by
  sender-receiver paths
• This problem is NP-complete

15
Problem with Steiner Tree

• Steiner Tree minimum edge cost
• Broadcast node can send neighbors data in one
  transmission
• Our goal minimizing the number of transmissions!!

16
Outline

• Introduction to multicast in WMNs
• Defining the cost of multicast tree
• Ruizs MNT protocol
• Chous MDM protocol
• Conclusion

17
Ruizs Algorithm

• Purpose find minimal data overhead tree
• Contributions
• Theorem 1 Prove Steiner tree is not optimal in
  WMNs with respect to the number of transmissions
• Theorem 2 Prove minimal data overhead tree is
  NP-Complete
• Proposed heuristics to compute trees with
  minimizing the number of transmissions

18
Problem statement

• Define t is multicast delivery tree
• Define Ct(t) is the number of transmissions
  required to deliver a message from sender s to
  receiver set R
• Problem statement Minimize the Ct(t)
• Ct(t)1Ft
• Minimize the number of forwarding nodes

19
Theorem 1 Steiner tree not minimal

• Steiner multicast tree (minimal edge cost) is not
  the minimal data-overhead multicast tree.
• Proof by example

20
Theorem 2 NP-Complete

• Proof by including a particular case
• Special case RV-s, find the smallest
  forwarding nodes covers the rest of nodes in V-s

Vertex cover problem NP-complete
21
Heuristic Algorithm

• Goal approximate minimal data overhead multicast
  tree
• Reduce the number of forwarding nodes
• While increase the number of leaf nodes
• Centralized greedy-based heuristic algorithm
• Distributed heuristic algorithm

22
Greedy minimal data overhead Alg.

• Centralized WMNs
• Greedily build cost-effective sub-trees
• A node v is selected a forwarding node only if it
  covers two or more nodes

23
Greedy minimal data overhead Alg. cont.

• Steps
• Construct a cost-efficient sub-trees
• Build a Steiner tree among the roots of the
  sub-trees

24
Alg Demo
Stop!! All nodes in V now only cover at most 1
receiver
V (unvisited nodes)
M1, R1, R2, R3, R4, R5, R6
M2, M3, M1, R1, R2, R3, R4, R5, R6
M2
M3
M3, M1, R1, R2, R3, R4, R5, R6
aux (nodes to cover list)
minimal data overhead tree! Hehe!!
S, R5, R6, M2
S, M2, M3
S, R2, R3, R4, R5, R6,
MF (multicast forward node list)
e
M2, M3
M2
MST heuristics to build Steiner tree
25
Performance Evaluation

• Compared Algs
• SPT source path tree Alg
• MST Steiner tree Alg
• MNT centralized proposed Alg
• MNT2 distributed proposed Alg
• Simulations
• Number of Tx required
• Mean number of hops
• Number of Tx with density

26
Performance Evaluation cont.

• Number of transmissions required

The total number of packets transmitted either by
the source or any relay node in path. MNT,
MNT2 MST SPT
Theorem 2, Steiner tree is not minimum
data-overhead.
Do not aim at minimize the cost of the tree.
27
Performance Evaluation cont.

• Mean path length (Mean number of hops)

The number of multicast hops from a receiver to
the source averaged over the total number of
receivers. MNT, MNT2 MST SPT
Aim at minimize the length of the tree.
28
Performance Evaluation cont.

• Number of transmissions with density

Examine reduction of Tx numbers when increase the
density. Proposed heuristic MNT, MNT2 reduced
more than SPT and MST!
29
Summary of Ruizs Algorithm

• Steiner tree does not suitable in WMNs
• The proposed Algorithm is NP-complete
• Heuristic Algorithm
• Centralized Algorithm
• Distributed Algorithm
• Evaluation
• the higher the density, the higher are the
  Heuristic Alg performance

30
Outline

• Introduction to multicast in WMNs
• Defining the cost of multicast tree
• Ruizs MNT protocol
• Chous MDM protocol
• Conclusion

31
Resilient Forwarding Mesh

• Makes multicast robust to node or link failure
• 2 paths
• Increases PDR and throughput

32
Resilient Forwarding Mesh Example
(a) Network topology (b) Optimal
solution (c) Suboptimal solution
33
Node-Disjoint Paths

• Parallel routes that connect the source and the
  destination
• Do not have any node in common except the source
  and destination
• Deliver packets simultaneously

34
Optimal Resilient Forwarding Mesh

• Each source-destination pair is connected by two
  node-disjoint paths
• Total number of broadcast transmissions is
  minimized
• Minimizing the number of broadcast transmissions
  is NP-complete
• Use heuristic algorithms to obtain approximate
  solutions

35
Heuristic Approximation Algorithms

• Tree-based
• Node-Disjoint Tree Algorithm (NDT)
• Revised Node-Disjoint Tree Algorithm (RNDT)
• Path-based
• Shared Disjoint Mesh Algorithm (SDM)
• Minimal Disjoint Mesh Algorithm (MDM)

36
Node-Disjoint Tree Algorithm (NDT)

• Build a multicast tree PT with minimal number of
  transmissions using the MNT
• Remove all intermediate nodes of PT from node set
  V
• Find a new minimal multicast tree BT in the new V
• Add all intermediate nodes of PT and BT to RFM

37
NDT Example
S
S
S
M1
M2
M1
M2
M3
M3
M3
R1
R2
R1
R2
R1
R2
38
NDT Example
S
S
S
M1
M2
M1
M2
M3
M3
M3
R1
R1
R2
R2
R2
39
Shared Disjoint Mesh Algorithm

• Find a shortest path P
• Remove all intermediate nodes of P from V, and
  find another shortest path B which is
  node-disjoint to P
• Update out-flow links of all intermediate nodes
  to zero
• Add all intermediate nodes of PT and BT to RFM
• Repeat above steps for all receivers

40
SDM Example
S
1
2
2
0
0
M1
M2
M2
2
2
0
0
M3
1
2
2
0
0
2
2
0
0
R1
R2
5
5
41
Minimal Disjoint Mesh Algorithm

• Improves SDM in the way of building the
  node-disjoint path pair
• Use Suurballes algorithm to find node-disjoint
  path pair with minimal cost at the same time

42
Suurballes Algorithm Example
S
S
1
10
1
10
1
1
M1
M3
M2
M1
M3
M2
10
1
10
1
10
1
100
10
1
100
R
R
Cost 3 101
Cost 11 12
43
Comparison of the 4 Protocols

• Simulated in QualNet
• Manually calculate optimal solution up to session
  size of 10
• Performance is measured by the number of
  transmissions as a function of multicast session
  size

44
Performance Comparison
NDT
Number of Transmissions
RNDT
SDM
MDM
Multicast Session Size
45
Summary

• NDT and RNDT are tree-based heuristic algorithms
• SDM and MDM are mesh-based heuristic algorithms
• MDM used Suurballes algorithm to find
  node-disjoint path pair with minimal cost
• Total Number of transmissions MDMltSDMltRNDTltNDT

46
Compare MNT with MDM
47
Compare MNT with MDM cont.

• MDM needs additional transmissions to provide
  resilience
• MDM needs more transmissions when session size is
  small
• When session size increases, the MDM is more
  likely to find the disjoint paths that share more
  common intermediate nodes

48
Outline

• Introduction to multicast in WMNs
• Defining the cost of multicast tree
• Ruizs MNT protocol
• Chous MDM protocol
• Conclusion

49
Lecture Summary

• Ruizs
• The MNT is NP-complete
• Heuristic Algorithm
• Centralized Algorithm
• Distributed Algorithm
• Chous
• Tree-based NDT and RNDT
• Path-based SDM and MDM
• Total number of transmissions MDMltSDMltRNDTltNDT

50
References

• Heuristic algorithms for minimum bandwidth
  consumption multicast routing in wireless mesh
  networks, P. M. Ruiz, and A. F. Gomez-Skarmeta,
  Proceedings of ADHOC-NOW, 2005.
• Protecting Multicast Sessions in Wireless Mesh
  Networks, X. Zhou, J. Guo, C.T. Chou, and S. Jha,
  IEEE Conference on Local Computer Networks, 2006.
  
• Simulation Study of Diverse Routing and
  Protection Algorithm in Mesh WDM Network, X. Yao,
  and C. Chen, 2004.
• A Performance Comparison Study of Ad Hoc Wireless
  Multicast Protocols, S.J. Lee, W. Su, J. Hsu, M.
  Gerla, and R. Bagrodia, Proceedings of IEEE
  INFOCOM, 2000.
• A Fast Algorithm for Steiner Trees, L. Kou, G.
  Markowsky, and L. Berman, Acta Informatica, No.
  15, vol. 2, 1981, pp.141-145.