Download Optical Burst Switching (OBS)

“Improving Fairness for Multi-Hop Bursts in
Optical Burst Switching Networks”
Asia Pacific Advanced Network 2007, 27-31 August 2007,
Xi’An, People’s Republic of China.
Tananun Orawiwattanakul
Yusheng Ji
Yongbing Zhang
Topics
• Optical Burst Switching (OBS) Networks
• Hop Based Preemption (HBP)
• Numerical results
• Future works
Optical Burst Switching (OBS)
L
A
N
Users
Edge Switch
Core Switch
OBS
Network
Core Switch
Edge Switch
L
A
N
Users
Optical Burst Switching (OBS)
Control Wavelengths
Data Wavelengths
Optical Burst Switching (OBS)
C
Control Wavelengths
Electronic
Optical
DB
IP Packets
Data Wavelengths
Optical Burst Switching (OBS)
C
Control Wavelengths
Data Wavelengths
DB
Offset Time
Optical Burst Switching (OBS)
Optic
Electronic Process
Optic
C
C
Control Wavelengths
Reserve this wavelength for the incoming data burst
Data Wavelengths
DB
Offset Time
Optical Burst Switching (OBS)
Optic
Electronic Process
Optic
C
C
C
Control Wavelengths
DB
Full Wavelength
Conversion
DB
Offset Time
Data Wavelengths
Optical Burst Switching (OBS)
C
Control Wavelengths
DB
Offset Time
Data Wavelengths
Optical Burst Switching (OBS)
Optical
Electronic
DB
IP Packets
General Networks
S1
Buffer
S4
S2
S5
S3
General Networks -> Electrical Buffer
Loss occurs only during high traffic load
Challenge of OBS
Offset Time1
Offset Time5
C1
C2
C4
C5
DB5
Control Channels
C3
Offset Time1
Offset Time1
Offset Time1
Offset Time1
T1
T2
T3
T4
DB4
DB1
DB3
Data Channels
DB2
T5
Time
No Buffer -> Contention occurs -> High Losses even in the light traffic load
The longer path -> The higher probability of Loss -> Unfairness
Hop Based Preemption (HBP)
• The objective of HBP is to improve fairness for multihop bursts in OBS networks.
• The burst that has traveled through many nodes
and has a high possibility to arrive at a destination can
preempt a channel from other scheduled bursts.
• HBP support non/full/limited wavelength conversion
networks.
• HBP is implemented only in core switches.
HBP
Offset Time5
Contending Burst
DB5
C1
C2
C4
C5
Control Channels
C3
Offset Time1
DB4
Offset Time1
DB1
Offset Time1
Data Channels
DB3
Offset Time1
DB2
T1
T2
T3
T4
T5
Time
HBP Scheme Parameters
Parameters
Description
Hp
No. of hops between ingress switch of burst and
corresponding switch.
Ho
No. of hops between corresponding switch and egress
switch of burst.
Wp
Weight of Hp ( >=0)
Wo
Weight of Ho ( >=0)
M
The minimum ratio of No. of hops that burst has traveled
through and No. of hops between burst’s ingress and egress
switches
I
Hop Index
T
Threshold ( >=0)
HBP
Contending will be dropped if
HpContending / (HpContending + HoContending) < M
Hp = 3
M = 1/2
3/ (3+3) = 1/2
Ho = 3
Contending Burst
DB5
Source5
I5
Scheduled Bursts
DB4
DB1
DB3
DB2
I4
I1
I3
I2
Destination5
HBP
I = (Hp * Wp ) - (Ho * Wo )
Wp = Wo = 1
I of the contending burst = 3-3 (Hp-Ho) = 0
Hp = 3
Ho = 3
Contending Burst
DB5
Source5
I5 = 0
Scheduled Bursts
DB4
DB1
DB3
DB2
Destination5
HBP
The contending burst wins the contention.
Hp = 3
Ho = 3
Contending Burst
DB5
Source5
I5 = 0
Destination5
Scheduled Bursts
DB4
I4 = 1
DB1
I1 = -1
DB3
DB2
Least I
I3 = 3
I2 = 0
The contending burst can preempt the channel of the original burst if
I5 – I1 >= T
When T = 1
0-(-1) = 1
HBP
The corresponding switch cancels the original wavelength
reservation for the original burst and instead allocates the
wavelength for the contending burst.
Offset Time5
Contending Burst
DB5
C1
C2
C4
C5
Control Channels
C3
Offset Time1
DB4
Offset Time1
DB5
DB1
Offset Time1
Data Channels
DB3
Offset Time1
DB2
T1
T2
T3
T4
T5
Time
Numerical Results
• Simulated on Optical Internet Research Center’s
(OIRC) optical burst switching simulator based on
ns-2.
• Based on NSF and ARPA networks
• No losses in control channels
• Bandwidth per wavelength = 1 Gbps and the
processing time of a BCP at each switch = 0.01
msec
• Hybrid burst assembly
NSF Network
800
2400
2800
0
1100
7
1600
800
3
1
1000
600 4
1100
600
2
2000
5
6
10
800
500
700
8
300
13
500
700
900
300
12
2000
1200
11
9
NSF Network
Burst loss
probability (%)
0.06
0.05
0.04
0.03
0.02
0.01
0
3 4 5
(General OBS)
3
4 5
1:1:1
3
4 5
1:1:2
No. of hops
(Wp:Wo:T )
3
4 5
1:0:1
3
4 5
1:0:2
NSF Network
Total burst loss
probability (%)
0.0275
0.027
0.0265
0.026
0.0255
0.025
General_OBS
1:1:1
1:1:2
Wp:Wo:T
1:0:1
1:0:2
ARPA Network
0
5
8
9
3
1
16
18
13
10
6
7
19
14
4
2
12
11
15
17
20
ARPA Network
Burst loss
probability (%)
0.25
0.2
0.15
0.1
0.05
0
3 4 5 6 7 8 9
(General OBS)
3 4 5 6 7 8 9
(1:1:1)
3 4 5 6 7 8 9
(1:1:2)
No. of hops
(Wp:Wo:T )
3 4 5 6 7 8 9
(1:0:1)
3 4 5 6 7 8 9
(1:0:2)
ARPA Network
Total burst loss
probability (%)
0.064
0.062
0.06
0.058
0.056
0.054
0.052
0.05
General_OBS
1:1:1
1:1:2
Wp:Wo:T
1:0:1
1:0:2
Future works
• Resolve more complicated unfairness issues,
such as unfairness caused by bottle-neck links.
• Provide flow level fairness
• Decrease the total loss probability.