initialization protocols for ieee 802.11 based ad hoc networks c. – s. hsu and j. p. sheu...
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Initialization Protocols for IEEE 802.11 Based Ad Hoc Networks
C. –S. Hsu and J. P. Sheu International Conference on Parallel and Distributed Systems (IC
PADS), Dec. 2002
Speaker: Chien-Wen Chang
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Outline
Introduction Preliminaries Leader Election and Initialization
Protocols Simulation Results Conclusion Discussion
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Introduction
The leader can serve as a coordinator a relay point a reporter
The initialization protocol can assign each host a unique id
two contention-based protocols
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Preliminaries(1)
The Nakano-Olariu Protocols Type 1: with the collision detection capa
bility do the Initialization Protocol
Type 2: without the collision detection capability
do the Leader Election Protocol elect a leader to serve as a detector
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Preliminaries(2)
The Leader Election Protocol by contention probability: ½, ¼,…… do until a host is declared as a leader
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Preliminaries(3) The Initialization Protocol
Type 1: with the collision detection and the number of host in advance
Type 2: without the later knowledge Type 1:
get their ids by contention n-m+1 as its id
probability: 1/m, m is the number of hosts without ids
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Preliminaries(4)
Type 2: by contention partition tree
{a, b, c, d}
{a, d}
{b, c}
{d}
{a}
{b, c}
{b}
{c}
Ø
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Leader Election and Initialization Protocols
Two efficient protocols protocol 1
the number of hosts is known in advance protocol 2
without the knowledge of the number of hosts
For single-hop MANET
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Protocol 1 (1)
The Leader Election Protocol elect a leader to serve as coordinator help to initialize a MANET follows a DCF procedure to contend as
a leader CW is set according to the number of
hosts will not contend again until election
round is over
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Protocol 1 (2)
The Leader Election Protocol (cont.) flow chart of one election round Ha: the host first broadcast its MAC
address successfully
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Protocol 1 (3)other hosts
Ha
Sets backoff timer
no leader and backoff
timer has expired
broadcasts its
MAC addr.
receives the ack ?
waits for ack
waits SIFS and announces
itself as the new leader
the Leader Election
Protocol is completed
YES
NO
Set backoff timer
backoff timer has expired and
receive the Ha’s MAC addr.
return ack
(broadcast the Ha’s MAC addr.)
no collision ?
YES
NO
wait for
the Ha’s announce
contend to re-broadcast its MAC
addr. at the next election roundcontend to re-broadcast the ack
at the next election round if
all hosts failed to return ack
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Protocol 1 (4) Example
8 hosts: A, B, C, D, E, F, G, H CW: 8 ST (backoff time slot) the backoff timers of hosts
B, C: 0 ST F: 2 ST A, E: 3 ST D, H: 4 ST G : 6 ST
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Protocol 1 (5)
DIFS
BC
DIFS
F DIFS
AE
DIFS
DH
DIFS
G SIFS
F(complete)
backoff time slot 1 2 3 4 5 6
(broadcasts F’s MAC addr. successfully)
contend to serve as leader contend to broadcast the ack
F announces itself as the
leader
G sends ack successfully
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Protocol 1 (6) The Initialization Protocol
with the help of leader CW is set as described above follows DCF to send a request id message to
leader be repeatedly executed until all hosts have got
ids exception
r1: the number of hosts without ids before executing the protocol
r2: the number of hosts without ids after executing the protocol
12 /* rrmm
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Protocol 1 (7) Example
4 hosts: A, B, C, D Host A is the leader with id=1 CW: 2 ST (backoff time slot); 1 ST in the s
econd round the backoff timers of hosts
B: 2 ST; 1 ST in the second round C: 0 ST D: 2 ST; 0 ST in the second round
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Protocol 1 (8)
DIFS
C SIFS
Id(=2)
DIFS
BD
DIFS
D SIFS
Id(=3)
DIFS
B SIFS
Id(=4)
backoff time slot 1 2 1
|-- First round --|-- Second round --|
Host A broadcasts C’s id(2) mess. successfully)
send the request id mess. successfully
B, D reset their backoff timer
collision of two request id mess. send the request id
mess. successfully
13/)13(*2
/* 12
rrmm
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Protocol 2 (1)
follow the same protocol described in Protocol 1
The Leader Election Protocol exception
First, the CW value is predetermined the rule of setting the CW value
be doubled until 256
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Protocol 2 (2)
The Initialization Protocol exception
First, the CW value is also predetermined After a round, the CW value is set
according to the estimated number of hosts without ids
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Simulation Results(1)
develop a simulator using C transmission rate: 2M bits/sec DIFS: 50s SIFS: 10s ST: 20s the number of hosts: 20~100
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Simulation Results(2)
proposed protocols
K: with the knowledge of the number of hosts
U: without it
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Simulation Results(3)
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Simulation Results(4)
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Simulation Results(5)
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Conclusion proposed two Leader Election Protoc
ols and Initialization Protocols The first Protocols for IEEE 802.11-bas
ed single-hop MANETs more efficient than Nakano-Olariu Pro
tocols can be easily implemented in IEEE 802.
11-based WaveLAN cards
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Discussion
Simulation results In single-hop with multiple channels Tone
for leader’s ack for omitting The Leader Election Protocol
s In multihop MANETs