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1
An Energy Efficient, Load Balanced Multicast Protocol with Probabilistic Anycast for ZigBee Wireless Sensor Networks
Advisor : Prof. Yu-Chee TsengStudent : Yi-Chen Lu
2009/06/26
3
Introduction
A WSN is composed of numerous inexpensive wireless sensor nodes, each of which is normally powered by batteries and has limited computing ability
Wireless sensor nodes are capable of not only collecting, storing, processing environmental information, but also communicating with neighboring nodes
Many research works have been dedicated to WSNs, such as routing, self-organization, deployment, and localization
4
Introduction
Multicast is a fundamental routing service of network communication
In WSN, a single message can be delivered to multiple destinations efficiently via multicast communication
In WSN, members may dynamically join and leave the groups
Fruits Area
Drinks Area
Join banana group
Join coke group
5
Introduction
ZigBee is a cost-effective wireless networking solution that supports low data-rates, low-power consumption, security, and reliability
Most WSN industries have adopted ZigBee as their communication protocol and developed numerous products
6
ZigBee Multicast
In ZigBee, multicast members are physically separated by a hop distance of no more than MaxNonMemberRadius
ZigBee multicast exploits regional flooding to deliver the multicast message
Region bounded by MaxNonMemberRadius
Member Another Member
Drawbacks of ZigBee multicast Heavy traffic
overhead High energy cost Unreliable
7
Outline
IntroductionRelated Work
Overlay Multicast Geographic Multicast Relay-Selection Multicast
MotivationGoalProtocol DesignSimulationConclusion
8
Overlay Multicast
PAST-DM (Wireless Networks 2007) Applying unicast leads to excessive
energy consumption and redundant transmissions
AOM (ICPPW 2007) Applying broadcast eliminates
redundant transmissions Packet header overhead
Overlay multicast needs extra cost to support dynamic member actions
Fixed delivery paths lead to single-node failure problem
redundant
6 transmissions
4 transmissions
Destination List & Forwarder List
9
Geographic Multicast
GMREE (COMCOM 2007) Cost over progress ratio
Drawbacks Packet header overhead Location information must be available Suffer from the face routing cost Do not support dynamic member
joining/leaving Single-node failure problem
S SS
S
S
S
S
S
S
S
S
S
S
S
SS
S
10
Relay-Selection Multicast
Steiner-tree based multicast BIP and MIP (MONET 2002)▪ Based on Prim’s algorithm to find a minimum-cost spanning tree
NJT and TJT (COMCOM 2007 ) ▪ Minimum cost set cover heuristics
Single-node failure problem Computing complexity is high Centralized algorithm must keep global
information Do not support dynamic member joining/leaving Source tree construction overhead
12
Motivation
Due to the limited power resource, energy efficient multicast is a critical issue in WSN
ZigBee multicast is not only energy inefficient but also unreliable
Many approaches have been proposed to study on the energy efficient multicast issues in WSN
13
Motivation
However, these proposed approaches either have significant drawbacks or are not compatible with ZigBee Single-node failure problem (all) Do not support dynamic member joining/leaving
(all) Packet header overhead (overlay & geographic) Location information (geographic) High computing complexity (geographic & relay) Must keep global information (relay-selection)
15
Goal
Propose a multicast routing protocol which has the following features ZigBee Compatible Energy efficient▪ Less energy consumption
Reliable▪ Higher delivery ratio
Load balanced▪ Avoid single-node failure problem▪ Prolong the network lifetime
Support dynamic member joining/leaving
Protocol Overview
17
S
S
S
S
S
S
SS
S
Probabilistic
Anycast
Random Backoff
Packet Forwardin
g
Coverage Over Cost Ratio
Residual Energy
Forwarding Strategy
Ack Mechanism
Multicast Informatio
n Table (MIT)
S
S
S
S
S
S
18
Protocol Flow
MIT Maitenance
Radom Backoff
Discard
Forward
Rebroadcast
Ack Mechanis
m
Forwarding Strategy
Initiate A Multicast
Receive A Multicast Packet
Coverage Over Cost Ratio
Residual Energy
Wait for twait
Backoff for tb
Multicasting
19
Outline
Introduction Related Work Motivation Goal Protocol Design
MIT Maintenance Multicasting
Simulation Conclusion
20
MIT Maintenance
Multicast Information Table (MIT) Reachable members within
MaxNonMemberRadius hops Hop distances to the reachable members
MIT
Member Hop Count
m1 h1
m2 h2
… …
mn hn
21
MIT Maintenance Example
1
5
8
15
21
MIT 21
15 2
MIT 1
5 2
8 2
15 3
MIT 5
1 2
8 3
MIT 8
1 2
5 3
15 3
MIT 15
1 3
8 3
21 2
MaxNonMemberRadius = 2
MIT keeps the information of only the members located within the region bounded by MaxNonMemberRadius hops
22
Outline
Introduction Related Work Motivation Goal Protocol Design
MIT Maintenance Multicasting
Simulation Conclusion
23
Multicasting
MIT Maitenance
Radom Backoff
Discard
Forward
Rebroadcast
Ack Mechanis
m
Forwarding Strategy
Initiate A Multicast
Receive A Multicast Packet
Coverage Over Cost Ratio
Residual Energy
Wait for twait
Backoff for tb
Multicasting
24
Multicasting
Our protocol adopts a probabilistic anycast mechanism based on the coverage over cost ratio and each node’s residual energy
Our protocol is similar to the relay-selection approaches
However, the selection of relay nodes is determined by the receivers, rather than by the senders
25
Probabilistic Anycast
Random Back-off
Packet Forwarding
Probabilistic Anycast
•Coverage Over Cost Ratio• Residual Energy
•Forwarding Strategy•Ack Mechanism
26
Initiating A Multicast
Packet
M H
m1 2
m2 2
m3 3
Eavg
S
•Multicast to {m1, m2, m3}•Hop distance to them is {2, 2, 3 }•The average residual energy of my
neighbors is Eavg
Destination Set M = {m1, m2, m3}Distance Set H = {2, 2, 3 }
Average residual energy of the neighbors = Eavg
MIT
m1 2
m2 2
m3 3
27
Upon Receipt of A Multicast Packet
Packet
M H
m1 2
m2 2
m3 3
Eavg(S)
S
MIT
m1 1
m2 3
m3 2
S XPacke
t
M H
m1 1
m2 3
m3 2
Eavg(X)
Remove member originator/previous hop to avoid
loop
Remove the members which are further from me
than from the previous hop to avoid detours
MIT
m1 2
m2 2
m3 3
Generate a random Backoff period
28
Random BackoffRandom Backoff
Packet Forwarding
Probabilistic Anycast
•Coverage Over Cost Ratio• Residual Energy
29
Coverage Over Cost Ratio Coverage Over Cost Ratio
The coverage over cost ratio is targeted at reaching as many member nodes as possible while consuming as little energy as possible
ontransmissibroadcast single one ofcost energy the:
MIT theofentry each in counts hop of sum the: TL
MIT in the members reachable ofnumber the: D
(1) 1DTL
D
tx
tx
E
Ef
X
A
B
Y C
B
A
Number of covered
members
Estimated energy cost Superior
in forwarding
30
Radom Backoff
The backoff timer interval tb is generated randomly within the range [0, T]
With greater f value, T should be smaller The single-node failure problem is still
unsolved
erRadiusMaxNonMembEf
E
Nf
ff
ff
TT
tx
tx
max
1
)1(
min
max
minmax
min
max
Normalize f to a parameter α to show the influence of coverage over cost ratio on the backoff interval
31
Random Backoff
We further introduce the idea of load balance to our protocol
Therefore, a node which has more energy and covers more destination members with less energy cost has a better chance to generate a shorter backoff interval
The data delivery paths are dynamically adjusted during each propagation according to the instant network condition
(2) )1( maxr
avg
E
ETT S
S
S
S
Superior in forwarding
32
Packet Forwarding
Random Back-off
Packet Forwarding
Probabilistic Anycast
•Forwarding Strategy•Ack Mechanism
33
Forwarding Strategy
During the backoff period, any member covered by other nodes is removed from M
When the backoff period expires, and M is not Φ
Rebroadcast the packet with up-to-date M, H and Eavg
34
ACK Mechanism
After sending out the multicast packet, the sender waits for a period
of time twait to confirm the forwarding
status of the destination members If not all the members in set M of the
sender are forwarded when twait
expires, the sender retransmits the multicast packet
36
Simulation
Simulation Environment
Simulation Duration 105 sec
Area 35m * 35m
Number of Nodes 100~500 (Random deployment)
Number of Members 10 (Randomly generated)
MaxNonMemberRadius 5
Transmission Range 6m
MAC IEEE 802.15.4 MAC with unslotted CSMA-CA
Max Backoff Interval 5ms
Transmission Rate 250Kbps
37
Simulation
100 200 300 400 5000
5
10
15
20
25
30
ZigBee Proposed protocol
Network size
Late
ncy (
ms)
100 200 300 400 5000
100
200
300
400
500
600
700
800
900
1000
ZigBee Proposed protocol
Network Size
Nu
mb
er
of
packets
39
Conclusion
Energy efficient multicast is a critical issue in WSN Many approaches have been proposed, but they fail
to achieve energy efficiency and load balance at the same time
We propose a ZigBee compatible multicast protocol Energy efficient Load balanced Reliable Support dynamic member joining/leaving
Simulation result shows that our protocol outperforms ZigBee in energy consumption and latency