“Improving Fairness for Multi-Hop Bursts in

Optical Burst Switching Networks”

Tananun Orawiwattanakul Yusheng Ji Yongbing Zhang

Asia Pacific Advanced Network 2007, 27-31 August 2007, Xi’An, People’s Republic of China.

Topics

• Optical Burst Switching (OBS) Networks

• Hop Based Preemption (HBP)

• Numerical results

• Future works

LAN

Optical Burst Switching (OBS)

Core Switch Core SwitchEdge Switch Edge Switch

Users

LAN

UsersOBS Network

Optical Burst Switching (OBS)

Control Wavelengths

Data Wavelengths

Optical Burst Switching (OBS)

DB

C

Control Wavelengths

Data WavelengthsElectronic

IP Packets

Optical

Optical Burst Switching (OBS)

DB

C

Offset Time

Control Wavelengths

Data Wavelengths

Optical Burst Switching (OBS)

DB

Offset Time

C

Optic Electronic Process

Optic

C

Reserve this wavelength for the incoming data burst

Control Wavelengths

Data Wavelengths

Optical Burst Switching (OBS)

C

Optic Electronic Process

Optic

C C

DB

Full Wavelength Conversion

DB

Offset Time

Control Wavelengths

Data Wavelengths

Optical Burst Switching (OBS)

DB

Offset Time

C

Control Wavelengths

Data Wavelengths

Optical Burst Switching (OBS)

DB

Optical Electronic

IP Packets

General Networks

S5

S1

S2 S3

S4

Buffer

General Networks -> Electrical Buffer Loss occurs only during high traffic load

DB4

Data ChannelsDB1

DB3

DB2

Time

Control Channels

C1 C2

C3

C4

T1 T2 T3 T4 T5

Offset Time1

Offset Time1

Offset Time1

Offset Time1

Offset Time1

C5DB5

Offset Time5

No Buffer -> Contention occurs -> High Losses even in the light traffic load

The longer path -> The higher probability of Loss -> Unfairness

Challenge of OBS

Hop Based Preemption (HBP)

• The objective of HBP is to improve fairness for multi-hop 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

DB4

Data Channels

DB1

DB3

DB2

Time

Control Channels

C1 C2

C3

C4

T1 T2 T3 T4 T5

Offset Time1

Offset Time1

Offset Time1

Offset Time1

C5DB5

Offset Time5 Contending Burst

HBP Scheme Parameters

Parameters Description

Hp No. of hops between ingress switch of burst and corresponding switch.

HoNo. of hops between corresponding switch and egress switch of burst.

Wp Weight of Hp ( >=0)

Wo Weight of Ho ( >=0)

MThe 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

DB4

DB1

DB3

DB2

DB5

Contending BurstI5

I4

I1

I3

I2

Scheduled Bursts

DB5

Contending BurstI5

Source5 Destination5

Hp = 3 Ho = 3

Contending will be dropped if

HpContending / (HpContending + HoContending) < M M = 1/23/ (3+3) = 1/2

HBP

DB4

DB1

DB3

DB2

DB5

Contending Burst

I5 = 0Scheduled Bursts

DB5

Contending Burst

Source5 Destination5

Hp = 3 Ho = 3

I = (Hp * Wp ) - (Ho * Wo )

Wp = Wo = 1

I of the contending burst = 3-3 (Hp-Ho) = 0

HBP

DB4

DB1

DB3

DB2

DB5

Contending Burst

I5 = 0Scheduled Bursts

DB5

Contending Burst

Source5 Destination5

Hp = 3 Ho = 3

I4 = 1

I1 = -1I3 = 3

I2 = 0

Least I

The contending burst can preempt the channel of the original burst if

I5 – I1 >= TWhen T = 10-(-1) = 1

The contending burst wins the contention.

HBP

The corresponding switch cancels the original wavelength reservation for the original burst and instead allocates the

wavelength for the contending burst.

DB4

Data ChannelsDB3

DB2

Time

Control Channels

C2

C3

C4

T2 T3 T4 T5

Offset Time1

DB1

C1

T1

Offset Time1

Offset Time1

Offset Time1

C5DB5

Offset Time5 Contending Burst

DB5

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

1100

600

1600

1000

2000 1200

2000

900500

300

300

800

24002800

800500

1

0

2

34

6

7

5

8 13

12

9

1110

600800

1100

700

7001100

600

1600

1000

2000 1200

2000

900500

300

300

800

24002800

800500

11

00

22

3344

66

77

55

88 1313

1212

99

11111010

600800

1100

700

700

NSF Network

0

0.01

0.02

0.03

0.04

0.05

0.06

3 4 5 (General OBS)

3 4 5 1:1:1

3 4 5 1:1:2

3 4 5 1:0:1

3 4 5 1:0:2

No. of hops(Wp:Wo:T )

Burst lossprobability (%)

NSF Network

0.025

0.0255

0.026

0.0265

0.027

0.0275

General_OBS 1:1:1 1:1:2 1:0:1 1:0:2Wp:Wo:T

Total burst lossprobability (%)

ARPA Network

1

2

5 12

15

18

20

4

0

3

7

6

8 9

1014

13

11 17

16

1911

22

55 1212

1515

1818

2020

44

00

33

77

66

88 99

10101414

1313

1111 1717

1616

1919

ARPA Network

0

0.05

0.1

0.15

0.2

0.25

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)

3 4 5 6 7 8 9 (1:0:1)

3 4 5 6 7 8 9 (1:0:2)

No. of hops(Wp:Wo:T )

Burst lossprobability (%)

ARPA Network

0.05

0.052

0.054

0.056

0.058

0.06

0.062

0.064

General_OBS 1:1:1 1:1:2 1:0:1 1:0:2

Wp:Wo:T

Total burst lossprobability (%)

Future works

• Resolve more complicated unfairness issues, such as unfairness caused by bottle-neck links.

• Provide flow level fairness

• Decrease the total loss probability.