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)

Time and Wavelength Multiplexing (cont)

DWDM 1310/1510 nm 16 uncorrelated wavelengths λ1λ1 λ2λ2 λ3λ3 λ4λ4 λ5λ5 λ Gbps (1) Gbps (16) 16*2.488 Gbps = 40 Gbps nm ramge 16 stabilized, correlated wavelengts

Fiber Optics Transmission

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 MEMS Micro-mirror Array Digital Mirror Control Electronics 1011 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 DWDM Fibers in DWDM Demux DWDM Demux DWDM Fibers out DWDM Mux DWDM Mux All-optical OXC

Optical Add-Drop Multiplexor (OADM) OADM ’ 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 No Wavelength converters New request 1  3 With Wavelength converters 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 ???

Big Picture SONET Data Center SONET DWD M Access Long Haul Access Metro

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 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

1+1 Protection Traffic is sent over two parallel paths, and the destination selects a better one In case of failure, the destination switch onto the other path Pros: simple for implementation and fast restoration Cons: waste of bandwidth

1:1 Protection During normal operation, no traffic or low priority traffic is sent across the backup path In case failure both the source and destination switch onto the protection path Pros: better network utilization Cons: required signaling overhead, slower restoration

1:1 Ring Protection Each channel on one ring is protected by one channel on the other ring When faults  loop around ADM

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 backup route are topologically diverse. –Lightpaths of a logical topology can withstand physical 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

Multi-layer Stack: Problems Functional overlap: –Muxing: DWDM =  STM=  VC=  flows=  packets –Routing: DWDM, SONET, ATM, IP –QoS/Integration: ATM, IP Failure affects multiple layers: –1 Fiber => 64 => 1000 OC-3 => 10 5 VCs => 10 8 flows Restoration at multiple layers: –DWDM => SONET => ATM => IP SONET – Manual (jumpers) => months/connection Any layer can bottleneck –Intersection of features + union of problems

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) – to 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 => LAN- WAN convergence

Why Optical Networks? DWDM optoelectricl metro network