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

Outline

Introduction Preliminaries Leader Election and Initialization

Protocols Simulation Results Conclusion Discussion

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

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

Preliminaries(2)

The Leader Election Protocol by contention probability: ½, ¼,…… do until a host is declared as a leader

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

Preliminaries(4)

Type 2: by contention partition tree

{a, b, c, d}

{a, d}

{b, c}

{d}

{a}

{b, c}

{b}

{c}

Ø

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

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

Protocol 1 (2)

The Leader Election Protocol (cont.) flow chart of one election round Ha: the host first broadcast its MAC

address successfully

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

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

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

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

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

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

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

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

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

Simulation Results(2)

proposed protocols

K: with the knowledge of the number of hosts

U: without it

Simulation Results(3)

Simulation Results(4)

Simulation Results(5)

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

Discussion

Simulation results In single-hop with multiple channels Tone

for leader’s ack for omitting The Leader Election Protocol

s In multihop MANETs