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LIDS
Optical Networks
and
Wavelength Division Multiplexing (WDM)
Eytan Modiano
Eytan Modiano
Slide 1
Laboratory for Information and Decision Systems
Outline
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LIDS
•
Introduction
–
–
•
All optical networks
–
–
•
LANs
WANs
Hybrid optical-electronic networks
–
–
–
Eytan Modiano
Slide 2
SONET
WDM
IP over WDM
Protection
Topology design
Laboratory for Information and Decision Systems
Communications Evolution
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1980’s-1990’s
1930’s-1970’s
LIDS
Electronic
Electronic
Electronic
Switch
Switch
Switch
Electronic
Electronic
Electronic
Switch
fiber
Switch
fiber
Switch
Electronic
Electronic
2000+
Electronic
Switch
Switch
Optical
Switch
Eytan Modiano
Slide 3
Optical
fiber
Switch
Optical
fiber
Switch
Laboratory for Information and Decision Systems
Switch
Synchronous Optical Network
(SONET)
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•
Standard family of interfaces for optical fiber links
–
Line speeds
n x 51.84 Mbps
n=1,3,12,48,192, 768
–
TDMA frame structure
125 µsec frames
–
Multiplexing
Basic unit is 64 kbps circuit for digitized voice
–
Protection schemes
Ring topologies
Eytan Modiano
Slide 4
Laboratory for Information and Decision Systems
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LIDS
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SONET Line Rates
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LIDS
Backbone
Speeds
1995
2000
Eytan Modiano
Slide 5
Fiber
Synchronous
Optic
Transport
Signal
Signal
OC Level STS Level
Synchronous
Transport
Mode
STM Level
Equivalent
Channels
Line Rate
DS0
DS1
51.84 Mbps
672
28
1
DS3
(64 KBPS) (1.54 Mbps) (44.74 Mbps)
OC1
STS-1
OC3
STS-3
STM-1
155.52 Mbps
2016
84
3
OC12
STS-12
STM-4
622.08 Mbps
8064
336
12
OC48
STS-48
STM-16
2488.320 Mbps 32256
1344
48
OC-192
STS-192
STM-64
9953.280 Mbps 129024
5376
192
OC-768
STS-768
STM-256
39813.12 Mbps 516096
21504
Laboratory for Information and Decision Systems
768
Multiplexing Frame Format
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LIDS
810 bytes x 8000 frame/sec x 8 bits = 51,840,000 bits
OH
PAYLOAD
OH
PAYLOAD
OH
PAYLOAD
STS-1
Synchronous
Payload
Envelope
9 rows
90 columns (87 columns of payload)
3 columns of
transport overhead:
Section overhead
Eytan Modiano
Slide 6
Path overhead
Line overhead
Laboratory for Information and Decision Systems
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STS-1 Multiplexing
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LIDS
3 x 51.840 Mb/s = 3 x STS1 = STS-3 = 155.520 Mb/s (OC-3)
STS-1 Signal A
STS-1 Signal B
STS-1 Signal C
Eytan Modiano
Slide 7
SONET
MUX
EQUIPMENT
Time Slots
STS-3 Combined Signal
Laboratory for Information and Decision Systems
Transmission medium
(Low Loss Windows)
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LIDS
0.5
Attenuation (dB/km)
0.4
0.3
1550
window
1310 nm
0.2
1550 nm
0.1
1100
1300
1500
Wavelength (λ)
Eytan Modiano
Slide 8
Laboratory for Information and Decision Systems
1700
Network Elements and Topologies
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LIDS
•
Add Drop Multiplexers (ADMS)
–
•
(De) multiplex lower rate
circuits into higher rate stream
ADM
ADM
Digital Cross-connects (DCS)
–
Switch traffic streams
ADM
Ring
Central Office
Work
Ring #2
Ring #1
Protect
Linear (pt-to-pt)
DCS
Eytan Modiano
Slide 9
Laboratory for Information and Decision Systems
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Traditional SONET Ring Architecture
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LIDS
DCS
OC-3/OC12
DSO-based
services
DS1/DS3
DCS
OC-48
Sonet
ADM
Sonet
ADM
4-Fiber
BLSR
DCS
Sonet
ADM
Sonet
ADM
Working Fiber Pair
DCS
Eytan Modiano
Slide 10
Laboratory for Information and Decision Systems
Protect Fiber Pair
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Link protection schemes
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LIDS
Working fiber
1+1
Simultaneous
transmission
(Source)
Protection
(Destination)
Working fiber
1:1
Switched
recovery
(Source)
Protection
50 % bandwidth inefficiency
Eytan Modiano
Slide 11
Laboratory for Information and Decision Systems
(Destination)
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Protection Schemes: 1:n
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LIDS
Working fibers
..
.
(Source)
Protection Fibers
1:n Protection Switching
Eytan Modiano
Slide 12
Laboratory for Information and Decision Systems
1
2
3
(Destination)
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Path vs. line protection
LIDS
Path Protection
Line Protection (Loopback)
D1
D1
D2
S
Eytan Modiano
Slide 13
D2
S
Laboratory for Information and Decision Systems
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Protection Schemes: UPSR
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LIDS
Rx
Tx
Rx
1+1 protection
60 ms restoration time
Working
Tx
Rx
protection
Unidirectional/Path Switched Ring (UPSR)
Eytan Modiano
Slide 14
Laboratory for Information and Decision Systems
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Protection Schemes: BLSR
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LIDS
Shortest path routing
Span and path protection
2 and 4 fibers
protection
working
Bidirectional/Line Switched Ring (BLSR)
Eytan Modiano
Slide 15
Laboratory for Information and Decision Systems
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Architectures and Topologies
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LIDS
LongDistance
Backbone
MESH
OC-48/192/768
COLLAPSED
RING
Metro,
InterOffice
Access
and
Enterprise
OC-12/48
RINGS
Business
Access
Ring
Collection and
Distribution Network
CO
OC-3/12/48
Feeder
Network
Collection and
Distribution Network
Gigabit LAN
TREE
FDDI, Fiber Channel, Gigabit Ethernet
Eytan Modiano
Slide 16
Laboratory for Information and Decision Systems
Scaling Options
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LIDS
Option 1:
Overbuild Fiber
Option 2:
Upgrade SONET
Option 3:
Introduce DWDM
OC-12
OADM
OC-48
OC-192
λ1λ2••• λ8
Eytan Modiano
Slide 17
Laboratory for Information and Decision Systems
λ8
WAVELENGTH DIVISIION MULTIPLEXING
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LIDS
• EXPLOITS
- ENORMOUS BANDWITH OF SILICA FIBER
FIBER LOSS (DB/km)
- HIGH-GAIN WIDEBAND OPTICAL AMPLIFIERS
Wavelength
Eytan Modiano
Slide 18
(µm)
Laboratory for Information and Decision Systems
Optical Amplifiers
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LIDS
λ1 λ2 λ3
λn
…..
λn
λ1λ2 λ3 …..
...
Attenuated wavelengths
•
•
•
•
•
•
Eytan Modiano
Slide 19
Amplified wavelengths
No O/E, E/O conversion
Greater bandwidth than electronic repeaters
Transparent to bit rates
Transparent to modulation formats
Simultaneous regeneration of multiple WDM signals
Low noise, high gain
Laboratory for Information and Decision Systems
WDM Benefits
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LIDS
Eytan Modiano
Slide 20
•
Increases bandwidth capacity of fiber
•
Addresses fiber exhaust in long-haul routes
•
Reduces transmission costs
•
Improves performance
•
Enhances protection (virtual and physical)
•
Enables rapid service deployment
•
Reduces network elements
Laboratory for Information and Decision Systems
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SONET over WDM
LIDS
1310nm
repeater
Before
1310nm
repeater
1310nm
repeater
1310nm
repeater
Sonet
Sonet
Sonet
Sonet
Sonet
Sonet
40 km
EDFA
Sonet
After
Sonet
Sonet
Eytan Modiano
Slide 21
λ1
λn
80 km
λ1 λn
Laboratory for Information and Decision Systems
λ1
Sonet
Sonet
λn
Sonet
All optical WDM networks
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LIDS
•
Network elements
–
–
–
–
•
WDM LANs
–
–
•
Passive networks
Broadcast star based
WDM WANs
–
–
–
Eytan Modiano
Slide 22
Broadcast star
Wavelength router
Frequency selective switch
Wavelength converters
Hierarchical architectures
Wavelength assignment
Wavelength conversion
Laboratory for Information and Decision Systems
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COMMON ALL-OPTICAL NODES
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LIDS
BROADCAST STAR
(PASSIVE)
FREQUENCY SELECTIVE SWITCH
(CONFIGURABLE)
Eytan Modiano
Slide 23
WAVELENGTH ROUTER
(PASSIVE)
FREQUENCY SELECTIVE SWITCH
WITH WAVELENGTH CHANGERS
(CONFIGURABLE)
Laboratory for Information and Decision Systems
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Broadcast star (passive)
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LIDS
OT
OT
OT
Σ
OT
OT
OT
combine
•
•
Each output contains all inputs
High loss
–
–
•
3 db per stage
Log N stages
No frequency reuse
–
•
•
split
Only one user per wavelength
Cheap and simple
Support W connections
3 db couplers
Eytan Modiano
Slide 24
Laboratory for Information and Decision Systems
Wavelength Router
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LIDS
λ11, λ12λ13λ14
2
2
2
2
λ1, λ 2λ3λ 4
λ31, λ32 λ33λ34
4
4
4 4
λ1, λ 2λ3 λ4
λ11, λ42λ33λ24
2
1
4
3
λ1, λ2λ3λ4
Passive
Wavelength λ31, λ22λ13λ44
4 3 2 1
Router
λ1, λ2λ 3λ4
2
2 2 2
λ 1, λ 2λ 3λ 4
•
Complete frequency reuse
–
–
•
Passive device
–
–
Eytan Modiano
Slide 25
Each input can use all wavelengths without interference
Can support N2 connections
All connections are static
Exactly one wavelength connecting an input-output pair
Laboratory for Information and Decision Systems
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Multiplexers and De-multiplexers
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LIDS
λ1
λ2
λ3
λ4
λ 1, λ2 λ 3 λ 4
Multiplexer
–
•
Single output of a router
Demultiplexer
–
Eytan Modiano
Slide 26
λ 1, λ2 λ 3 λ 4
multiplexer
Demultiplexer
•
λ1
λ2
λ3
λ4
Single input to router
Laboratory for Information and Decision Systems
Optical Add/Drop Multiplexers (ADM)
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LIDS
λ1
λ2
λ3
λ4
λ2
λ3
λ4
~
~
λ1
Wavelength
Multiplexer
λ4
•
An ADM can be used to “drop” one or more wavelengths at a node
–
–
–
–
Eytan Modiano
Slide 27
λ4
Wavelength
Demultiplexer
One input fiber and one output fiber plus local “drop” fibers
can be either static or configurable
Usually limited number of wavelengths
Loss proportional to number of wavelengths that can be dropped at a
node
Laboratory for Information and Decision Systems
Frequency Selective Switch
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LIDS
M
λ1λ 2
λw
λ1λ 2
λw
λ1λ 2
λ1
λ2
•
λw
•
•
•
λ1λ 2
λw
λ1λ 2
λw
MxM
switch
Mux
M input and M output fibers
Any wavelength can be switched from any input fiber to any
output fiber
Expensive device that offers a lot of configurability
–
Eytan Modiano
Slide 28
λw
λw
Demux
•
•
λ1λ 2
Switch times depend on implementation but are typically in the few
ms range
Laboratory for Information and Decision Systems
Frequency selective switch
with wavelength conversion
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λ1λ 2
λw
λ1λ 2
λw
Optical
λ1λ 2
λw
λ1λ 2
λw
λ1λ 2
λw
switch
λ1λ 2
λw
Demux
Mux
Wavelength converters
•
•
•
Wavelength conversion offers the maximum flexibility
Optical wavelength conversion not a mature technology
Electronic conversion is possible but very expensive
–
Eytan Modiano
Slide 29
Essentially requires a transceiver
Laboratory for Information and Decision Systems
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LIDS
FSS using an electronic cross-connect
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LIDS
λ1λ 2
λw
λ1λ 2
λw
Electronic
switch
λ1λ 2
λw
Receivers
λw
λ1λ 2
λw
Transmitters
Limited size
Not all optical
Not bit rate transparent (OC-48)
Most of the cost is in the transceivers
Most practical implementation
–
–
–
Eytan Modiano
Slide 30
λ1λ 2
Electronic cross-connects are less expensive
–
–
–
–
•
λw
Mux
Demux
•
λ1λ 2
Implemented on an ASIC
No need for optical wavelength conversion
Very fast switching times
Laboratory for Information and Decision Systems
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Wavelength Conversion
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LIDS
•
Fixed conversion
–
–
•
Convert from one wavelength to
another
Maybe useful for integrating
different networks
Fixed Wavelength
conversion
Limited conversion
–
–
Provides conversion to a limited
set of wavelengths
Drivers: cost and technology
Limited Wavelength
conversion
Limited range conversion
•
λ1
λ1
λ2
λ2
λ3
λ3
λ1
λ1
λ2
λ2
λ3
λ3
Full conversion
–
–
–
Eytan Modiano
Slide 31
Maximum flexibility
Costly
Optical to electronic to optical is
probably the most practical
implementation
Full Wavelength
conversion
λ1
λ1
λ2
λ2
λ3
λ3
Laboratory for Information and Decision Systems
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WDM ALL-OPTICAL NETWORKS
•
Low Loss / Huge Bandwidth
•
Transparency (rate, modulation, protocol)
•
Future Proofing
•
Multiple Protocols
•
Electronic Bottleneck
•
All-Optical nodes potentially cheaper
than high capacity electronic nodes
Eytan Modiano
Slide 32
Laboratory for Information and Decision Systems
LIDS
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Possible all-optical topologies
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LIDS
Metro
and access
LAN
Add/drops
Star
WAN
FSS
• Fiber cost
• Frequency reuse
• Scalability
Eytan Modiano
Slide 33
Laboratory for Information and Decision Systems
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WDM LAN
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LIDS
•
Passive star topology
–
–
•
Eytan Modiano
Slide 34
Low cost
Broadcast medium
Scalability issues
–
With broadcast star if two users
transmit on the same wavelength their
transmissions interfere (collisions)
–
A circuit switched network limits the
number of connections to the number of
wavelengths
–
A packet switched system can support
virtually an unlimited number of
connections (MAC)
–
Need MAC protocol to coordinate
transmissions across wavelengths
OT
OT
OT
Σ
OT
OT
OT
PROT.
PROC.
TR
FIFO
QUEUE
TT
Laboratory for Information and Decision Systems
λc,λ1..λ 32
λc,λ1..λ 32
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THE EVOLUTION OF LAN/MAN TECHNOLOGY
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LIDS
LAN/MAN TECHNOLOGY
SYSTEM CAPACITY
(BITS/SEC)
E+12
WDM ?
E+11
SWITCHED
ETHERNET
E+10
E+09
GBIT ETHERNET
E+08
FDDI
E+07
ETHERNET/TOKEN RING
APPLE TALK
E+06
1985
1990
2000
2005
YEAR
Eytan Modiano
Slide 35
Laboratory for Information and Decision Systems
ATM
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Partitioned WDM network
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LIDS
USER
Local traffic
blocking filter
∑
O PT
ICA
L
AM
P
USER
Partition into subnets
Frequency Selective Switch (FSS)
and λ-converters
–
•
Frequency reuse
USER
FSS
USER
USER
∑
USER
All- optical transport
–
–
Eytan Modiano
Slide 36
USER
∑
USER
•
•
FREQ
CONVERT
No electronic repeaters
Optical amplifiers
Laboratory for Information and Decision Systems
USER
Hierarchical All-optical Network (AON)
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LIDS
LEVEL 2
GLOBAL
FSS
FSS
FSS
FSS
FSS
OT
Star
OT
OT
Star
OT
USER
Eytan Modiano
Slide 37
Router
Router
Router
Star
METRO
OT
USER
Star
Star
OT
OT
OT
USER
Laboratory for Information and Decision Systems
USER
OT
LOCAL
Resolving Wavelength Conflicts
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LIDS
n
y
x
m
i
•
k
Approaches
–
Use wavelength converters
Everywhere or at select nodes
–
Wavelength assignment algorithm
Cleverly assign wavelengths to reduce conflicts
Eytan Modiano
Slide 38
Laboratory for Information and Decision Systems
Wavelength Changing Gain
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LIDS
•
Gain =
Offered load (with λ−changers)
Offered load (without λ−changers)
For same blocking probability pb = 0, 10-6..10-3
•
Important factors
–
H = Path length in hops
Large H increases need for wavelength changers
–
L = Interference length (average length of an interfering call)
Large L reduces benefit of wavelength changers
–
d = number of fibers per link
Large d reduces benefit of wavelength changers
Eytan Modiano
Slide 39
Laboratory for Information and Decision Systems
Simple Analysis
(Independence Approximation)
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•
Assume each wavelength is used on a link with probability p
–
–
Independent from link to link and wavelength to wavelength
approximation
•
Consider a call of length H
•
Without wavelength changers,
–
Pb = Pr(every wavelength is used on some link)
= [1 - P(wavelength is not used on any link)]W
= [1-(1-p)H]W
•
With wavelength changers,
–
Pb = 1 - Pr(every link has at least one unused wavelength)
=1
•
Eytan Modiano
Slide 40
- (1-pW)H
Analysis can be extended to include multiple fibers and account
for interference length
Laboratory for Information and Decision Systems
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LIDS
Wavelength Changing Gain
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LIDS
Pb = 10-3
4
H/L=10
3.5
Gain
3
H/L=5
2.5
2
1.5
H/L=2.5
1
0.5
0
1
5
10
15
20
25
30
Wavelengths
• Comparison to Random Wavelength Assignment
• d = 1 fiber per link, Poisson traffic
Eytan Modiano
Slide 41
Laboratory for Information and Decision Systems
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Wavelength Assignment Algorithms
LIDS
λ1
λ2
λ1
3 wavelengths
λ2
2 wavelengths
λ2
λ3
Let Ω = candidate wavelengths
bad assignment
good assignment
RANDOM: pick f ε Ω uniformly randomly
•
FIRST FIT: pick lowest number f ε Ω
•
MOST USED: pick f ε Ω used on the most links
•
LEAST LOADED ROUTING: pick f ε Ω with least congested
link along call path
•
MAX_SUM (MΣ): pick f ε Ω which maximizes remaining excess capacity
Eytan Modiano
Slide 42
Laboratory for Information and Decision Systems
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Example
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LIDS
1
2
3
4
5
6
7
λ4
λ1
•
New call between 4 and 5
–
–
–
–
All wavelengths are available
First Fit (FF) would select λ1 (red)
Most used would select λ2 (green)
Max sum would select λ4 (orange)
Disrupt the smallest number of potential future calls
–
Eytan Modiano
Slide 43
Random may choose say blue…
Laboratory for Information and Decision Systems
8
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Wavelength assignment performance
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LIDS
Single Fiber Ring (20 Nodes)
log(Pb)
1.0 Erlangs/wavelength
Wavelengths
Eytan Modiano
Slide 44
Laboratory for Information and Decision Systems
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Wavelength assignment performance
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LIDS
log(Pb)
10-Fiber ring (20 nodes)
1.6 Erlangs/wavelength
Wavelengths
Eytan Modiano
Slide 45
Laboratory for Information and Decision Systems
Status of Optical Networks
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LIDS
•
All-optical networks are primarily in experimental test-beds
•
WDM commercial marketplace is very active
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Point to point WDM systems for backbone networks
Systems with up-to 80 wavelengths
–
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WDM rings for access networks
WDM being used as a “physical” layer only
Network layer functions are done in electronic domain
E.g., IP/SONET/WDM
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Hybrid electronic/optical networks appear to be the way to go
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Eytan Modiano
Slide 46
IP over WDM
Laboratory for Information and Decision Systems
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IP-over-WDM
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•
Networks use many layers
–
•
Applications
Eliminate electronic layers
Preserve functionality
Joint design of electronic and
optical layers
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–
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Virtual topology design
Traffic grooming
Optical layer protection
WDM
IP router
Eytan Modiano
Slide 47
Applications
Goal: reduced protocol stack
–
–
•
Inefficient, expensive
TCP
TCP
IP
ATM
WDM-aware
IP
SONET
WDM
WDM
Laboratory for Information and Decision Systems
Optical layer protection
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•
Protection is needed to recover from fiber cuts, equipment
failures, etc.
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Some protection is usually provided at higher layers
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•
E.g., SONET loop-back
So, why provide optical layer protection?
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Sometimes higher layer protection is limited (e.g., IP)
Optical protection can be much faster
Optical layer protection can be more efficient
Restoring a single fiber cut is easier than 40 SONET rings
Once restored optically, SONET can protect from more failures
–
Eytan Modiano
Slide 48
Also, SONET is mainly used for its protection capability so if we can
provide protection at the optical layer we can eliminate SONET
equipment
Laboratory for Information and Decision Systems
Optical protection mechanisms
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•
Path protection
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Restore a lightpath using an alternative route from the source to the
destination
Wavelength by wavelength
•
Line protection
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Restore all lightpaths on a failed link simultaneously by finding a
bypass for that link (loop-back)
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In rings techniques such as 1+1,1:1,1:n still apply
•
In a mesh protection is more complicated
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Path protection requires finding diverse routes
Line protection requires finding ring covers
Sharing protection resources
Establish backup paths in such a way that minimizes network resources
If two lightpaths share a common fiber they cannot share protection
capacity
Eytan Modiano
Slide 49
Laboratory for Information and Decision Systems
Limitations of optical layer protection
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•
•
Cannot recover from electronic failures (e.g., line card)
Added overhead
–
–
As much as 50% for 1:1 schemes
This overhead is on top of whatever overhead is used by the higher
layer
For example, SONET uses an additional 50%
•
Compatibility with higher layer protection mechanism
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SONET must recover from a fault in 60 ms
SONET starts to responds after 2.5 ms of disconnect
Can the optical layer recover before SONET detects a failure?
•
Eytan Modiano
Slide 50
Joint design of optical and electronic protection mechanisms
Laboratory for Information and Decision Systems
Joint design of electronic and optical
protection (example)
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(2,1)
4
1
2
5
1
(1,3) 2
(1,3)
(5,2)
5
(2,1)
3
(3,4)
(4,5)
4
1
2
3
(5,2)
(3,4)
(1,3)
(1,3)
Bad
•
LIDS
Physical topology
Logical topology
3
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5
(4,5)
4
Good
How do we route the logical topology on the physical topology so
that we can keep the logical topology protected ?
–
Logical connections are lightpaths that can be routed in many ways
on the physical topology
–
Some lightpaths may share a physical link in which case the failure
of that physical link would cause the failure of multiple logical links
For rings (e.g., SONET) this would leave the network disconnected
–
Eytan Modiano
Slide 51
Need to embed the logical topology onto the physical topology to
maintain the protection capability of the logical topology
Laboratory for Information and Decision Systems
SONET/WDM network design
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Ungroomed
•
Groomed
Groom traffic onto wavelengths in order to minimize amount of
electronic equipment
–
–
“Drop” only those wavelengths that have traffic for that node
Assigns traffic to wavelengths to minimize the number of wavelengths
that must be dropped at each node
E.g., minimize number of SONET ADMs
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Eytan Modiano
Slide 52
Similar problem in the design of an IP/WDM network (minimize ports)
Laboratory for Information and Decision Systems
SONET Example
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•
Traffic grooming in a SONET ring network
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–
–
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•
Each wavelength can be used to support an OC-48 SONET ring
16 OC-3 circuits on each OC-48 circuit
Each time a wavelength is dropped at a node a SONET ADM is needed
Assign OC-3 circuits onto OC-48 rings using the minimum number of ADMs
Simple example:
–
–
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Unidirectional ring with 4 nodes
8 OC-3’s between each pair of nodes
traffic load:
6 node pairs
8 OC-3’s between each pair
Total load = 48 OC-3’s
3 full OC-48 rings
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Eytan Modiano
Slide 53
Each ring can support traffic between two node pairs
Laboratory for Information and Decision Systems
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Example, continued
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Node 1
–
12 ADMs needed
(n1 = n2 = n3 = n4 = 3)
Node 3
Assignment #2
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–
–
λ1: 1-2, 1-3
λ2: 2-3, 2-4
λ3: 1-4, 3-4
–
9 ADMs needed
(n1 = n2 = n4 = 2, n3=3)
Node 2
λ1: 1-2, 3-4
λ2: 1-3, 2-4
λ3: 1-4, 2-3
Node 4
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Node 1
Node 2
•
Assignment #1
Node 4
•
Node 3
Eytan Modiano
Slide 54
Laboratory for Information and Decision Systems
Future Trends
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•
Optical access
•
Optical flow switching
•
Logical topology (IP) reconfiguration
•
All-optical packet switching
Eytan Modiano
Slide 55
Laboratory for Information and Decision Systems
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Access Network Architecture
LIDS
TRANSPORT
BACKBONE
BACKBONE
NETWORK
NETWORK
CO
Optical
LAN
AN
Eytan Modiano
Slide 56
Optical
LAN
AN
FEEDER
FEEDER
NETWORK
NETWORK
AN
(configurable
optics
(configurable optics
and
andelectronics)
electronics)
AN
COLLECTION
COLLECTION&&
DISTRIBUTION
DISTRIBUTION
NETWORK
NETWORK
(Passive
(PassiveOptics)
Optics)
ACCESS
Access Node
Optical Switching
Electrical Switching
CO
Satellite
Station
Campus
Network
Laboratory for Information and Decision Systems
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Optical flow switching
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LIDS
Without
flow switching
IP router
IP router
IP router
WDM
WDM
WDM
IP router
IP router
IP router
WDM
WDM
WDM
IP router
IP router
IP router
WDM
WDM
WDM
Router initiated
flows
End-end flows
•
Optical flow switching reduces the amount of electronic
processing by switching long sessions at the WDM layer
–
–
Lower costs, reduced delays, increased switch capacity
Today: IP over ATM (e.g., IP switching, tag switching, MPLS)
dynamically set-up new ATM VC’s to switch a long IP session
Future: IP directly over WDM
dynamically configure new lightpaths to optically switch a long session
Eytan Modiano
Slide 57
Laboratory for Information and Decision Systems
Topology Reconfiguration
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Call Blocked
Call Admitted
Reconfigure
•
Reconfigure the electronic topology in response to changes in
traffic conditions
–
–
Eytan Modiano
Slide 58
Electronic switches are connected using lightpaths
Lightpaths can be dynamically rearranged using WADMs
Laboratory for Information and Decision Systems
Optical packet switched networks
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•
Wide area WDM networks are circuit (wavelength) switched
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•
•
Limits scalability
Packet switching is needed for scalable optical networks
In the LAN we saw that packet switching can be accomplished
using a MAC protocol
–
–
Requires fast tunable transceivers
This approach does not easily scale to wide areas
High latency
Broadcast
•
Optical packet switching is
needed for all-optical WANs
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–
–
•
Eytan Modiano
Slide 59
All-Optical
Processing
Header processing
Packet routing
Optical buffers
Do we really need all optical??
Laboratory for Information and Decision Systems
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Opening Up New Wavelength Bands
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LIDS
Loss
water-peak
C-band (conventional)
80 channels
1530 - 1562 nm L-band (long wavelength)
80 channels
1570 - 1620 nm
EDFAs
C-band L-band
1st
850
Eytan Modiano
Slide 60
350
2nd
460
5th
1260-1360
1365-1525
80
3rd
80
4th
# of waves
@ 50 GHz
1530-1562 1570-1604 (nm)
Laboratory for Information and Decision Systems
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WDM Network Evolution
LIDS
Early-Mid ‘90s
LINEAR
Early ‘90s
Mid ‘90s
Late ‘90s
Late ‘90s - Early ‘00s
RINGS
Early ‘00s
MESHES
400 GHz
200 GHz
100 GHz
50 GHz
Late ‘90s
Late ‘90s
Early ‘00s
Early ‘00s
Eytan Modiano
Slide 61
?
Fixed add/drops
Configurable add/drops
Configurable switches
Wavelength changers
Laboratory for Information and Decision Systems
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Select References
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LIDS
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R. Ramaswami and K. N. Sivarajan, Optical Networks, Morgan
Kaufmann, 1998
•
B. Mukherjee, Optical Communication Networks, McGraw-Hill, 1997
•
B. Mukherjee, WDM based Local Lightwave Networks, IEEE Network,
May, 1992
•
E. Modiano, WDM based Packet Networks, IEEE Communications
Magazine, March, 1999
•
V.W.S. Chan, et. al. "Architectures and Technologies for High-Speed
Optical Data Networks," IEEE Journal of Lightwave Technology,
December 1998.
Eytan Modiano
Slide 62
Laboratory for Information and Decision Systems