1 Optical Packet Switching Techniques Walter Picco MS Thesis Defense December 2001 Fabio Neri, Marco...

1

Optical Packet Switching Techniques

Walter Picco

MS Thesis Defense December 2001

Fabio Neri, Marco Ajmone Marsan

Telecommunication Networks Group

http://www.tlc-networks.polito.it/

2

Overview

• Introduction and motivations

• Goals of the thesis

• State-of-the-art and enabling technologies

• SIMON: an optical network simulator

• Optical networks design

• Obtained results

3

The need of optics

Future network requirements:• High bandwidth capacity• Flexibility, robustness• Power supply and equipment footprint

reduction

Optics offers a good evolution perspective

4

Optical framework today

• Point to point communications• Circuit switching with packet switching

electronic control

why ?

• Optical packet switching:

– no optical memories

– slow optical switches

5

Optical packet switching

Bandwidth is not a problem

Network cost is in the commutation

New protocols and architectures needed

• New tools to measure performance• New design techniques

more

6

Overview







7

Goals

• New optical network simulator

Topology Simulation Performance

8

Goals

• New analysis and design method for optical networks

Resources Analysis Topology

9

Overview







10

Transmitting data

Wavelength Division Multiplexing: the huge bandwidth of an optical fiber is divided in many channels (colors)

Each channel occupies a

different frequency slot

11

Storing data

• Optical RAM is not available yet• Fiber Delay Lines (FDLs) are used instead

FDLs

Forward usage Feedback usage

FDL

12

Processing data

• Electronics limits the speed in data forwarding• Optical 3R regeneration (and wavelength

conversion) is now possible

• Physical layer is not a matter of concern• All-optical solutions are currently at the study

3R1 2

13

Switching data

• Tomorrow (a possibility): Micro Electro Mechanical Systems

• Today: Semiconductor Optical Amplifiers

14

Overview







15

• Fixed routing implementation

Not good for WDM

The starting simulator: CLASS

• Simulator of ATM networks• Topology independent

Adaptable tool

} fiber

channel

16

CLASS modifications

• Dynamic routing strategy

• Each WDM channel must be listed in the network description file

Maximum flexibility in the network description

} fiber

channel

17

SIMON node architecture

n n

1 1

n-1 n-1

SWITCHCONTROL UNIT

3R3R

3R

3R3R

3R

3R3R

3R

11

2 2

m m

18

Time division

• Slotted network:

t

t

t

C1

C2

C3t 0

timeslot

P1

P2

t 1

19

Overview







20

Designing WDM networks

• Given:

Network topology and the traffic matrix• Find:

Number of WDM channels on each link • Optimizing:

Network throughput• Meeting a cost constraint:

Network cost

commutation

Fixed number of ports for all the switches

21

The optimization problem

• Mathematical statement:

Find minimum (maximum) of a non-linear function in the discrete domain, meeting

some constraints

NP-complete problem

Only heuristic solutions are possible

22

Proposed approach

1)Find:

– Ptot : packet loss probability of the whole network

– ni : number of WDM channels on link i

2)Elaborate a heuristic solution to find the minimum of Ptot

Mtot nnfP 1

23

Link model

• Classical queueing theory: M/M/L/k queue

• server WDM channel• buffer slot FDL

k1

2

L

serversbuffer

more

24

Node model

Inputfibers

Outputfibers

25

• FDLs can’t be modeled as a simple buffer– discrete storage time– noise addition at each recirculation

• All the FDLs of a node are shared among the different queues

Model limitations

channel

FDLAB

ttt

SNRSNR

AB

AB

26

Network model

• The packet loss probability (Pf) of a flow is:

• The packet loss probability (Ptot) of the whole network results:

• First step completed

Fff

Ffff

tot t

Pt

P Mtot nnfP 1

fLi

if PP 11

27

• Cost constraint:

(channel ports + FDLs ports) = constant• optimum balance optimum solution

Searching the minimum

Network connectivity(number of channel ports)

Storage capacity(number of FDLs)

Level

28

Heuristic approach

• Starting topology: maximum connected

• Iteration steps:– the current topology is perturbed

– if the perturbed topology has a lower Ptot

the topology is modified

Highest possible level

29

Heuristic approach

• Topology perturbation: – all the links are analyzed

– the link that modified gives the lower Ptot is memorized

cancelled

added

30

Overview







31

General backbone: topology

Node

User

1 2

34

5

6 7

8

9

1011

12

32

General backbone: throughput

0 2 4 6 8 10 12 14 16 180.85

0.9

0.95

1

Total network load [Gbps]

Fra

ctio

n o

f pac

kets

su

cces

sfu

lly tr

an

sfe

rre

d

1 2 3 4 M/M/L/k (4 MR)M/M/L/k ( MR)

33

General backbone: delay

0 2 4 6 8 10 12 14 16 180

1

2

3

4

5

6

7

8

9

Pa

cke

ts n

et d

ela

y

1 2 3 4 M/M/L/k (4 MR)M/M/L/k ( MR)


34

USA backbone: topology

28

27

26

25

24

23

22

21

20

19

1815

1611

10

12

13

17149

85

6

7

3

42

1

35

USA backbone: throughput

0 5 10 15 20 25 30 35 400.86

0.88

0.9

0.92

0.94

0.96

0.98

1

1 2 3 M/M/L/k (4 MR)M/M/L/k ( MR)


Fra

ctio

n o

f pac

kets

su

cces

sfu

lly tr

an

sfe

rre

d

more

36

Conclusions

Two key elements:

• A new tool capable to simulate the next generation optical networks

• A new optimization target in the optical networks design giving good results

more

37

E S

38

Optical Burst Switching

• Packets are assembled in the network edge, forming bursts

• Advantages:– More efficient exploitation of the bandwidth– Possibility to implement Service

Differentiation• Disadvantages:

– More complicated network structure– More complicated forwarding process

continue

39

Link model• Packet loss probability P on the link:

– link capacity– link traffic load– offered load [Erlangs],

1 if 1!!

1 if 1

1

!1

1

0

11

0

1

0

rkLi

rr

r

i

LL

i

i

L

i

ki

continue

Lr

40

Japan backbone: topology1

2 3

4

5 6

78

9 10

11

41

Japan backbone: throughput

0 5 10 15 20 25 300.9

0.91

0.92

0.93

0.94

0.95

0.96

0.97

0.98

0.99

1

1 2 3 M/M/L/k (4 MR)M/M/L/k ( MR)


Fra

ctio

n o

f pac

kets

su

cces

sfu

lly tr

an

sfe

rre

d

continue

42

Future work

• Simulator:– Support for different architectures– FDLs of variable length

• Heuristic approach:– More detailed model for FDLs

continue

43End of presentation

1 Optical Packet Switching Techniques Walter Picco MS Thesis Defense December 2001 Fabio Neri, Marco...

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