Download Optical Networks

Optical Networks
2008
Topics
• Optical Links
– Light Sources, Detectors and Receivers
– Optical Fiber Channel
– Optical Amplifiers
• Digital Optical Communications
– Time and Wavelength Multiplexing
– Optical Cross-Connects (OXC)
• Optical Networks
– First Generation Optical Networks and SONET
– Second Generation Optical Networks
• Multi Protocol Lambda Switching
• DWDM optoelectrical metro network
Review of Optics
• What is a monochromatic wave
• Polarization of light
• Interaction between Light and Matter
Total Internal Reflection and Absorption
• Diffraction
• Interference
Light Sources
• LED -- Light emitter diodes
• Laser diodes
• Single mode laser diodes
Detectors and Receivers
• Solid state detectors
• PIN diode
• Circuit noise and signal to noise ratio in a
receiver
• Direct detection and bit error rate
• Avalanche photodiodes (APD)
Detectors and Receivers (cont.)
Optical Fiber Channel (1)
• Total internal reflection in a optical fiber
• Telecommunications industry uses two windows:
1310 & 1550 nm
– 1550 window is preferred for long-haul
applications (Less attenuation, Wider window,
Optical amplifiers)
Optical Fiber Channel (2)
• Multimode fibers and their limitations
Optical Fiber Channel (3)
• Single mode fibers and limitations
• Non-linearities in fibers
• Coupling light in a fiber and connecting
two fibers
Fiber Amplifiers
erbium doped fiber amplifiers (EDFA)
Semiconductor Optical Amplifiers (SOA)
Topics
• Optical Links
– Light Sources, Detectors and Receivers
– Optical Fiber Channel
– Optical Amplifiers
• Digital Optical Communications
– Time and Wavelength Multiplexing
– Optical Cross-Connects (OXC)
• Optical Networks
– First Generation Optical Networks and SONET
– Second Generation Optical Networks
• Multi Protocol Lambda Switching
• DWDM optoelectrical metro network
Digital Optical Communications
• Signal Quantization / Coding: from analog to
digital signal and vice versa
• Digital Modulation: Amplitude, Phase, and
Frequency Modulation
• Multiplexing to increase the bandwidth of an
optical channel
– Time Division Multiplexing
– Wave Division Multiplexing (WDM)
• WDM vs. DWDM
Digital Optical Communications (cont)
DWDM
2.488 Gbps (1)
1310/1510 nm
2.488 Gbps (16)
λ1 λ2 λ3 λ4 λ5
λ16
1530-1565 nm ramge
1310/1510 nm
16 uncorrelated wavelengths
16*2.488 Gbps = 40 Gbps
16 stabilized, correlated
wavelengts
Fiber Optics Transmission
Optical Switch
• 1-input 2-outoput illustration with four
wavelengths
Input & Output fiber
array
Wavelength
Dispersive Element
1-D MEMS
Micro-mirror
Array
Input Fiber
Output Fiber 1
1011
Digital Mirror
Control
Electronics
Output Fiber 2
• 1-D MEMS (micro-electromechanical system) with
dispersive optics
– Dispersive element separates the ’s from inputs
– MEMS independently switches each 
– Dispersive element recombines the switched ’s
into outputs
All-Optical Switching
• Optical Cross-Connects (OXC)
– Wavelength Routing Switches (WRS)
– route a channel from any I/P port to any O/P port
• Natively switch s while they are still multiplexed
• Eliminate redundant optical-electronic-optical
conversions
DWDM
Demux
DWDM
Fibers
in
DWDM
Mux
DWDM
Fibers
out
All-optical
DWDM
Demux
OXC
DWDM
Mux
Optical Add-Drop Multiplexor (OADM)
1
2
1
OADM
2
3
’3
3
’3
Wavelength () Converters (WC)
improve utilization of available wavelengths
on links
needed at boundaries of different networks
all-optical WCs being developed
greatly reduce blocking
probabilities
3
3
2
2
WC
1
1
New request
1 3
New request
1 3
No Wavelength converters With Wavelength converters
Topics
• Optical Links
– Light Sources, Detectors and Receivers
– Optical Fiber Channel
– Optical Amplifiers
• Digital Optical Communications
– Time and Wavelength Multiplexing
– Optical Cross-Connects (OXC)
• Optical Networks
– First Generation Optical Networks and SONET
– Second Generation Optical Networks
• Multi Protocol Lambda Switching
• DWDM optoelectrical metro network
Optical Networks
•
1 st Generation: optical fibers substitute copper as
physical layer
– Submarine Systems
– SONET (synchronous optical) in TDM
– FDDI for LAN, Gbit Ethernet etc.
• 2 nd Generation: optical switching and
multiplexing/ WDM
– broadcast-and-select networks
– WDM rings
– wavelength routing networks
•
3 th Generation: optical packet switching???
Big Picture
Data
Center
SONET
SONET
DWD
M
DWD
M
SONET
SONET
Access
Metro
Long Haul
Metro
Access
SONET
• Encode bit streams into optical signals
propagated over optical fiber
• Uses Time Division Multiplexing (TDM) for
carrying many signals of different capacities
– A bit-way implementation providing end-to-end
transport of bit streams
– All clocks in the network are locked to a
common master clock
– Multiplexing done by byte interleaving
Practical SONET Architecture
ADM – Add-Drop Multiplexer
DCS – Digital Crossconnect
Protection Technique Classification
• Restoration techniques can protect network against:
– Link failures
• Fiber-cables cuts and line devices failures
– Equipment failures
• OXCs, ADMs, electro-optical interface.
• Protection can be implemented
– In the optical channel sublayer (path protection)
– In the optical multiplex sublayer (line protection)
• Different protection techniques are used for
– Ring networks
– Mesh networks
Path Protection / Line Protection
Normal Operation
Path Switching:
restoration is handled
by the source and the
destination.
Line Switching: restoration
is handled by
restoration
is handled
the nodesby
adjacent
the
nodestoadjacent
the failure.
to the
Span Protection: if
failure.
additional fiber is available.
Line Protection.
Shared Protection
Normal Operation
1:N Protection
• Backup fibers are used for protection of
multiple links
• Assume independent failure and handle
single failure.
• The capacity reserved for protection is
greatly reduced.
In Case of Failure
Protection in Ring Network
(Unidirectional Path
Switched Ring)
1+1 Path
Protection
Used in access rings
for traffic aggregation
into central office
(Bidirectional Line
Switched Ring)
1:1 Span and Line
Protection
Used in metropolitan or
long- haul rings
1:1 Line
Protection
Used for interoffice
rings
Protection in Mesh Networks
• Network planning and survivability design
– Disjoint path idea: service working route and its
backup route are topologically diverse.
– Lightpaths of a logical topology can withstand
physical link failures.
Working Path
Backup Path
Trend: IP over DWDM
•
•
•
•
IP is good for routing, traffic aggregation, resiliency
ATM for multi-service integration, QoS/signaling
SONET for traffic grooming, monitoring, protection
DWDM for capacity
IP over DWDM: Why?
•
•
•
•
•
IP and DWDM => Winning combination
– IP for route calculation, traffic aggregation,
protection
– DWDM => Cheap bandwidth
– Avoid the cost of SONET/ATM equipmnt
IP routers at OC-192 (10 Gbps)
=> Don't need SONET multiplexing
Optical layer for route provisioning,
protection, restoration
Coordinated restoration at optical/IP level
Coordinated path determination at optical/IP
level
•
MPS
MPS = Multi-Protocol Lambda Switching
– MPLS + OXC
– Combining MPLS traffic eng control with OXC
• All packets with one label are sent on one wavelength
• Next Hop Forwarding Label Entry (NHFLE)
– <Input port,  > to <output port,  > mapping
DWDM Summary
•
•
•
•
•
•
DWDM => Switching Bottleneck => O/O/O
switches
High speed routers => IP directly over DWDM
Data and control plane separation => IP
Control Plane
Data will be circuit switched in the core
IP needs to be extended to provide addressing,
signaling, routing, and protection for
lightpaths
High-speed point-to-point Ethernet => LANWAN convergence
The Current Home Service System
Copper pair
telephone line
Satellite dish
The Optoelectrical Multip-Service System
Telepnone To telephone
company backbone
Satellite dish
Internet Router To the Internet
for modem
connections
Satellite
dish
Satellite
dish
Copper pair
telephone line
Copper pair
telephone line
Coxial cable
(50/75 O)
To telephone
backbone
Internet RouterTo the Internet
for cable
modems
Sigle mode
Fiber cable
Coxial cable
(75 O)
Cable TV
company
Multip-Service
Company
To cable TV
network
To the Internet
To cable TV
network
Why Optical Networks?
DWDM optoelectricl metro network