Transcript Multilevel VPN ( 2 Level )

A Scheduled/Bandwidth
Reservation/Fairness MAC protocol
for Voice/Data over WLAN
Wang Ming An
Advised by Dr. Sunshin An
Major in Electronics Engineering
Graduate School
Korea University
Korea Univ.
Contents
 802.11 WLAN standard introduction
 Accessing the wireless Medium
 Existed protocols & The main problem of existed MAC
protocol
 Idea of SBRFP
 Design of SBRFP
 Simulation
 Conclusion and future work
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2
802.11 WLAN standard Introduction (1/4)
 IEEE 802.11 WLAN standard
 Two type of data transmission

distributed coordination function (DCF)
 carrier sense multiple access with collision avoidance (CSMA/CA)
 request-to-send (RTS)
 clear-to-send (CTS)
 distributed, contention-based protocol
 point coordination function (PCF)
 contention free period (CFP)




contention period (CP)


Central control
Contention free
polling
CSMA/CA
Central, contention-free, Polling-based protocol
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802.11 WLAN standard Introduction (2/4)
 IEEE 802.11 WLAN standard MAC architecture

PCF is on the top of DCF
Contentionfree
Contentionbased
Point
Coordination
MAC Function(PCF)
Extent
Distributed
Coordination
Function(DCF)
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802.11 WLAN standard Introduction (3/4)
 Distributed Coordination Function(DCF)

uses a Carrier Sense Multiple Access with Collision Avoidance
(CSMA/CA) algorithm to mediate access to the shared medium.
DIFS
Sender
CW
Ack
Receiver
Others
DIFS: DCF Interframe Space
ACK: Acknowledgement packet
NAV: Network Allocation Vector
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SIFS
Data
CW
NAV
SIFS: Short Interframe Space
CW: Contention Window
Data
5
802.11 WLAN standard Introduction (4/4)
6
 Point Coordination Function(PCF)
Contention-Free Repetition Interval
Contention-Free Period
SIFS
SIFS
SIFS
PIFS
SIFS
Contention Period
B
D1+poll
D3+ack+poll
D2+poll+ack
U1+ack
u2+ack
No
PIFS
SIFS

Response
to CF-POLL
SIFS
E
D4+poll
u4+ack
CF-end
SIFS
Reset NAV
NAV
CF_Max_Duration
Dx=Frames sent by Point Coordinator
CFP: Contention-free period
B: beacon
NAV: Network Allocation Vector
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Ux=Frames sent by polled stations
CP: contention period
E: CF-End
Accessing the Wireless Medium
 Carrier Sense Multiple Access with Collision
Avoidance (CSMA/CA) protocol
 backoff procedure
 Black-burst (BB) protocol
 Access procedures of real-time stations
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Accessing the Wireless Medium(1/6)
 CSMA/CA Protocol
Start
NAV=0
?
while ( NAV = 0 )
{
sense the medium;
NO
YES
Sense the
medium
Medium
Idle?
NO
Random
Backoff Time
If ( medium idle )
send (data);
else
backoff ( );
YES
Transmit
frame
Collision?
YES
NO
Success
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If ( collision )
backoff ( );
}
8
Accessing the Wireless Medium(2/6)
 Binary exponential backoff
CW = random ( 0 , min (2n-1 , CWmax))
255 255
CW max
127
63
31
CW min
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9
Accessing the Wireless Medium(3/6)
 Backoff procedure
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Accessing the Wireless Medium(4/6)

11
BB protocol

stations first sort their access rights by jamming the channel with pulses of
energy
 The length of a BB transmitted by a real-time station is an increasing
function of the contention delay experienced by the node
DIFS
Sta A
Frame
DIFS
PIFS listen
Frame
rt-Sta B
DIFS
listen
listen
listen
Frame
Sta C
listen
Frame
Sta D
listen
listen
Frame
Sta E
pulse
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pulse
pulse
Accessing the Wireless Medium(5/6)
 Enhanced algorithm on Binary Exponential Backoff for BB
CW = random ( max(0, 2n-1 -1), min (2n-1 , CWmax))
255
CW max
127
63
31
CW min
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255
12
Accessing the Wireless Medium(6/6)
13
 A time diagram of the access procedures of real-time
stations

it transmits a packet that must last for at least tpkt seconds,and
 it schedules the next access instant to occur tsch seconds in the
futrure
tmed tobs
tmed tobs tmed tobs
x1
STAx
x2
y2
tsch
STAy
tsch
Access
instant
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Data packet
y1
Scheduled
Access instant
Transmission of a
black burst
Existed protocols &
The main problem of existed MAC protocol
 “A Bandwidth Allocation/Sharing/Extension Protocol for
Multimedia Over IEEE 802.11 Ad Hoc Wireless LANs” IEEE
Communications
 “Real-time traffic over the IEEE 802.11 medium access control
layer,” Bell Labs Technical Journal
 “Distributed Control Algorithms for Service Differentiation in
Wireless Packet Networks”, INFOCOM 2001. Proceedings. IEEE
 Kanghee Kim and Seokjoo Shin, “A Novel MAC Scheme for
Prioritized Services in IEEE 802.11a Wireless LAN”, ATM (ICATM
2001) and High Speed Intelligent Internet Symposium, 2001.
 “Distributed fair scheduling in a wireless LAN”, in Proc. ACM
MOBICOM’00, Boston
 How to assign appropriate weights for real-time and nonreal-time flows is still an open issue
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Idea of SBRFP
 Reduce the collision
 Provide fairness for nrt-data service
 Provide bandwidth reservation for rt-data service
 Use little redundant data to provide perfect
service
 Scheduled/Bandwidth Reservation/Fairness
protocol (SBRFP)
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Design of SBRFP(1/8)
 Contents

Format of Schedule Table, Beacon and EF frame
 nrt-data Transmission Procedure
 Rt-data Transmission Procedure
 Error processing
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Design of SBRFP(2/8)
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 Schedule Table

Each station catches the same Schedule Table
 The first station recorded in the Schedule Table would broadcast the
beacon packet to each station at the beginning of every CYCLE that
contains the Schedule Table to keep them to be the same
Bits:
8
STA ID
STA ID:
Link Type:
Last Success Time:
Extension Flag:
Idle counter:
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1
7
1
2
Link Last Success Extension
Idle
Type
Time
Flag
counter
5
Reserved
Station Identifier
0 for real-time data and 1 for non-real-time data
the time record in millisecond when received ACK last time
has more data to transfer
if it reaches 3 this note would be deleted from Schedule table
Design of SBRFP(3/8)
18
 Beacon frame format

It will be broadcasted at the begging of each CYCLE
 It contains the schedule table
Octets: 2
2
Frame Duration/
Control
ID
Bits: 2
Protocol
Version
Type:
Subtype:
26
Other fields
MAC header
2
4
8
Other
Type Subtype
fields
00
1000
0-2312
Management
Beacon
Octets: 8
Timestamp
4
Frame Body
FCS
2
Beacon interval
Information
Octets: 1
Element ID
1
Length
Length
Schedule table
Element ID: 7
Length: active station number * 2
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Reserved
Length of Schedule table
Design of SBRFP(4/8)
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 EF (Extension Flag) frame format
If a station can’t finish its transmission in scheduled time the EF
field of the station in the Schedule Table would marked
 EF will be broadcasted after all of the rt-data stations transmit their
data once in a CYCLE
 EF frame contains only the SID field of the marked stations in
Schedule Table

Octets: 2
2
Frame Duration/
Control
ID
Bits: 2
Protocol
Version
Type:
Subtype:
26
Other fields
MAC header
2
4
8
Other
Type Subtype
fields
00
0111
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0-2312
Management
Reserved
Octets: 1
Length
Frame Body
4
FCS
Length
Extension Flag marked Stations
Design of SBRFP(5/8)
20
 Non-real-time data transfer
The smaller value the “last success time” is, the earlier it will be transmit
 During the CFP in the CYCLE it allows only one station to transmit data
continually.
 CP only used for those stations that haven’t been recorded to apply for
being recording into the Schedule Table
 Those stations that have been recorded will not contend the medium during
CP

CYCLE
CYCLE
CFP
B
STAx data transfer
NAV
CFP
CP B
STAy data transfer
CP
NAV
B: Beacon frame
Stax data transfer: used for only one station to transfer data continuously
CP: contention period, used for those stations which haven’t noted in schedule table
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An Example
Schedule table
Station A
Station B
Station C
Station D
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DIFS
B
1
4160
beacon
data
B
1
4360
ACK
NAV
NAV
CFP
data
B
1
4960
B
C
1
1
4960
5160
PIFS/
DIFS
ACK
CP
NAV
apply
RIFS
beacon
CFP
B
C
1
1
5960
5160
PIFS/
DIFS
CP
B
C
A
B
C
A
1
1
1
1
1
1
5960
5160
6160
5960
6960
6160
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NAV
NAV
RIFS
data
data
ACK
pulse
Design of SBRFP(6/8)
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 Real-time data transfer

Each station can not exceed scheduled time
 If all allocated bandwidth fully fill the CYCLE period the CP would be given
up, so no new real-time station will be allowed to be added into the
schedule table
B STAx rt-data
CYCLE
STAy rt-data
STAz rt-data CF_end CP
NAV
CYCLE
B STAx rt-data
STAz rt-data STAm nrt-data CP
STAy rt-data
NAV
Not fully filled
CYCLE
B STAx rt- data
STAy rt-data
NAV
Fully filled
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STAz rt-data
Have not
nrt-data station
Have at least one
nrt-data station
Design of SBRFP(7/8)
23
 Real-time data transfer
 Extension Flag
If (STAy (last success time) + frame (duration) >
STAz (last success time) +Tcycle )
then Set (Extension Flag)
CYCLE
B STAx rt-data
STAy
rt-data
CYCLE
STAz rt-data CP B STAx rt-data
STAy
STAy rt-data STAz rt-data EF rt-data
≤CYCLE
B: Beacon frame
STAx data transfer: used for only one station to transfer data continuously
CP: contention period, used for those stations which haven’t noted in schedule table
EF: Extension Flag frame
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Design of SBRFP(8/8)
24
 Error processing
SIFS, RIFS, PIFS and DIFS

CYCLE
Station A
Station B
CP
CFP
RIFS
B
PIFS/DIFS
ACK
Frame 1
SIFS
ACK
Frame 2
SIFS SIFS
NAV
Frame 2
RIFS
ACK
SIFS SIFS
ACK NAV
SIFS
SIFS
Frame 1
Station C
NAV
PIFS
Station D
Others
Marked with “finished”
NAV
Frame 1
NAV
pulse
Apply frame
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A
Simulation(1/2)
25
number of collision
delay time
200
9
180
8
174
collisions
140
128
120
sbrfp
100
802.11
80
60
66
57
40
total delay time(s)
160
7
6
5
802.11
4
sbrfp
3
2
1
20
0
0
5
0
10
0
20
node number
Number of collision
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0
30
0
5
10
20
node number
Delay time
30
Simulation(2/2)
26
thoughput
2500
throughput
2000
1500
sbrfp
802.11
1000
500
0
5
10
20
node number
Throughput
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Conclusion and Future work
27
 Advancement of SBRFP

Reduce the collision greatly
 Stronger than 802.11 WLAN standard MAC protocol
 Provide bandwidth reservation for real-time data transference
 Provide fairness to non-real-time data transference
 Forward work

Ad hoc network routing algorithm for real-time data transfer base on
SBRFP
 Coexist with the bluetooth
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