Optical Packet Switching Techniques

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

• Introduction and motivations
• Goals of the thesis
• State-of-the-art and enabling technologies
• SIMON an optical network simulator
• Optical networks design
• Obtained results

7
Goals

• New optical network simulator

Topology
Simulation
Performance
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Goals

• New analysis and design method for optical
  networks

Resources
Analysis
Topology
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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

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
FDL
Forward usage
Feedback usage
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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

l1
l2
3R
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Switching data

• Today Semiconductor Optical Amplifiers

• Tomorrow (a possibility) Micro Electro
  Mechanical Systems

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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

15
The starting simulator CLASS

• Simulator of ATM networks
• Topology independent
• Adaptable tool

• Fixed routing implementation
• Not good for WDM

fiber
channel
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CLASS modifications

• Dynamic routing strategy
• Each WDM channel must be listed in the network
  description file
• Maximum flexibility in the network description

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SIMON node architecture
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Time division

• Slotted network

timeslot
P
2
C
t
1
P
C
1
t
2
C
t
3
t
t
0
1
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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

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
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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

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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

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Link model

• Classical queueing theory M/M/L/k queue
• server ? WDM channel
• buffer slot ? FDL

k
1
2
buffer
L
servers
more
24
Node model
Input fibers
Output fibers
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Model limitations

• FDLs cant 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

FDL
B
A
channel
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Network model

• The packet loss probability (Pf) of a flow is
• The packet loss probability (Ptot) of the whole
  network results

• First step completed

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Searching the minimum
Storage capacity (number of FDLs)
Level
Network connectivity (number of channel ports)

• Cost constraint
• (channel ports FDLs ports) constant
• optimum balance ? optimum solution

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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
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Heuristic approach

• Topology perturbation
• all the links are analyzed

added
cancelled

• the link that modified gives the lower Ptot is
  memorized

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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

31
General backbone topology
Node
6
7
User
1
2
5
8
3
4
9
12
10
11
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General backbone throughput
1
0.95
Fraction of packets successfully transferred
0.9
l
1
l
2
l
3
l
4
M/M/L/k (4 MR)

M/M/L/k (
MR)
0.85
0
2
4
6
8
10
12
14
16
18
Total network load Gbps
33
General backbone delay
9
8
l
1
l
2
7
l
3
l
4
M/M/L/k (4 MR)
6

M/M/L/k (
MR)
5
Packets net delay
4
3
2
1
0
0
2
4
6
8
10
12
14
16
18
Total network load Gbps
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USA backbone topology
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1
17
8
5
9
14
22
24
18
15
10
6
4
2
25
19
16
11
3
26
20
7
12
27
13
21
28
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USA backbone throughput
1
0.98
0.96
0.94
Fraction of packets successfully transferred
0.92
0.9
l
1
l
2
l
3
0.88
M/M/L/k (4 MR)

M/M/L/k (
MR)
0.86
0
5
10
15
20
25
30
35
40
Total network load Gbps
more
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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
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E S
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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
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Link model

• Packet loss probability P on the link
• m link capacity
• a link traffic load
• offered load Erlangs,

continue
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Japan backbone topology
1
2
3
4
5
6
8
7
9
10
11
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Japan backbone throughput
1
0.99
0.98
0.97
0.96
Fraction of packets successfully transferred
0.95
0.94
0.93
l
1
l
2
0.92
l
3
M/M/L/k (4 MR)
0.91

M/M/L/k (
MR)
0.9
0
5
10
15
20
25
30
Total network load Gbps
continue
42
Future work

• Simulator
• Support for different architectures
• FDLs of variable length
• Heuristic approach
• More detailed model for FDLs

continue
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End of presentation