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
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)
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 (3)• Single mode fibers and limitations
• Non-linearities in fibers
• Coupling light in a fiber and connecting two fibers
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
DWDM
1310/1510 nm
1310/1510 nm
16 uncorrelated wavelengths
λ1 λ2 λ3 λ4 λ5 λ16
2.488 Gbps (1)
2.488 Gbps (16)
16*2.488 Gbps = 40 Gbps
1530-1565 nm ramge
16 stabilized, correlated wavelengts
Optical Switch• 1-input 2-outoput illustration with four
wavelengths
• 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
1-D MEMSMicro-mirror
Array
Digital MirrorControl
Electronics1011
Wavelength Dispersive Element
Input Fiber
Output Fiber 1
Output Fiber 2
Input & Output fiber array
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
DWDMFibers
in
DWDMDemux
DWDMDemux
DWDMFibers
out
DWDMMux
DWDMMux
All-optical
OXC
Wavelength () Converters (WC)improve utilization of available wavelengths
on linksneeded at boundaries of different networksall-optical WCs being developedgreatly reduce blocking probabilities
No Wavelength converters
1
2 3
New request 1 3
With Wavelength converters
1
2 3
New request 1 3
WC
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???
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
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 Switching: restoration is handled by the source and the destination.
Normal Operation
Line Switching: restoration is handled by the nodes adjacent to the failure. Span Protection: if additional fiber is available.
Line Switching: restoration is handled by the nodes adjacent to the failure.
Line Protection.
Path Protection / Line Protection
Shared Protection
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.
Normal Operation
In Case of Failure
Protection in Ring Network
1+1 Path Protection
Used in access rings for traffic
aggregation into
central office
1:1 Line Protection
Used for interoffice rings
1:1 Span and Line Protection
Used in metropolitan or long- haul rings
(Unidirectional Path Switched Ring) (Bidirectional Line
Switched Ring)
Protection in Mesh Networks
Working Path
Backup Path
• Network planning and survivability design – Disjoint path idea: service working route and its bac
kup route are topologically diverse.– Lightpaths of a logical topology can withstand physi
cal link failures.
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 l
evel
MPS• MPS = 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 sw
itches• High speed routers => IP directly over DWDM• Data and control plane separation => IP Contr
ol 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 => LAN-WAN convergence
Telepnonecompany
Cable TVcompany
Satellite dish
Satellite dish
Copper pairtelephone line
Coxial cable(75 O)
The Current Home Service System
Internet Router for modemconnections
Internet Router for cablemodems
To telephonebackbone
To cable TVnetwork
To the Internet
To the Internet
Satellite dish
Satellite dish
Coxial cable(50/75 O)
Multip-ServiceCompany
Sigle modeFiber cable
The Optoelectrical Multip-Service System
To telephonebackbone
To the Internet
To cable TVnetwork
Copper pairtelephone line
Copper pairtelephone line