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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
8
Goals
• New analysis and design method for optical networks
Resources Analysis Topology
9
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
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
• 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
• 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
• 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
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
• 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
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)
Total network load [Gbps]
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)
Total network load [Gbps]
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)
Total network load [Gbps]
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