Optical Networking (part 2) Mark E. Allen, Ph.D. mark.allen@ieee.org

Review of Transmission (Transport) Technologies, Architectures and Evolution (Adapted from Shikuma (RIT) Notes 3

Asynchronous Data Rates Digital Signal Level 0 DS0 64 Kb/s internal to equipment Digital Signal Level 1 DS1 1.544 Mb/s intra office only (600 ft limit) Digital Signal Level 3 DS3 45 Mb/s T1 Electrical (Copper) Version of DS1 1.544 Mb/s repeatered version of DS1 sent out of Central Office T3 Electrical (Copper) Version of DS3 45 Mb/s repeatered version of DS3 sent out of Central Office 7

Asynchronous Digital Hierarchy DS0 (a digitized analog POTS circuit @ 64 Kbits/s) DS3 DS1 DS0 24 DS0s = 1 DS1 28 DS1s = 1 DS3 Asynchronous Optical Line Signal N x DS3s Asynchronous Lightwave Systems typically transport traffic in multiples of DS3s i.e.... 1, 3, 12, 24, 36, 72 DS3s

Asynchronous Networking Manual DS1 Grooming/Add/Drop X 3 D S X 1 D S X 1 D S X 3 LW M13 M13 LW DS3 DS3 DS1 Manually Hardwired Central Office No Automation of Operations Labor Intensive High Operations Cost Longer Time To Service 16

Some Review Questions What does the acronym SONET mean? What differentiates SONET from Asynchronous technology? What does the acronym SDH mean?

The Original Goals of SONET/SDH Standardization Vendor Independence & Interoperability Elimination of All Manual Operations Activities Reduction of Cost of Operations Protection from Cable Cuts and Node Failures Faster, More Reliable, Less Expensive Service to the Customer 5

SONET Rates DS3s are STS-1 Mapped DS0 (a digitized analog POTS circuit @ 64 Kbits/s) 51.84 Mbits/s STS-1 DS1 DS0 DS3 24 DS0s = 1 DS1 (= 1 VT1.5) 28 DS1s = 1 DS3 = 1 STS-1 SONET Optical Line Signal OC-N = N x STS-1s N is the number of STS-1s (or DS3s) transported

SONET and SDH OC level STM level Line rate (MB/s) OC-1 - 51.84 OC-3 STM-1 155.52 OC-12 STM-4 622.08 OC-48 STM-16 2488.32 OC-192 STM-64 9953.28

SONET Layering for Cost Effective Operations DS-3 STE LTE PTE STE LTE PTE DS-3 DS-3 DS-3 DS-3 DS-3 OC-3 TM OC-3 TM SONET Section SONET Line SONET Path PTE = Path Terminating Element LTE = Line Terminating Element STE = Section Terminating Element TM = Terminal Multiplexor DS = Digital Signal

SONET Point-to-Point Network Repeater Repeater TM TM Section Line Path STS-1 Frame Format Section Overhead STS-1 Synchronous Payload Envelope STS-1 SPE Path Overhead Line Overhead 13

1 + 1 Protection Switching (50% bandwidth utilization) Protection Schemes: 1 + 1 Network Protection Working Facility Protection Facility (Source) (Destination) 1 + 1 Protection Switching (50% bandwidth utilization)

1:n Protection Switching (Bandwidth Efficiencies) 1 for N (1:N) Network Protection Working Facility 1 2 . 3 Protection Facility (Source) (Destination) 1:n Protection Switching (Bandwidth Efficiencies)

Protection and Restoration Path Protection Line Protection (Loopback) D1 D1 D2 D2 S S 1 + 1 1:n

Unidirectional/Path Switched Ring (UPSR) Rx Tx Rx Work Protect Tx Rx Unidirectional/Path Switched Ring (UPSR)

BLSR Bidirectional/Line Switched Ring (BLSR) Work Protect 4 fiber supports span switching 2 fiber doesn’t Work Protect Bidirectional/Line Switched Ring (BLSR) 2 fiber, 4 fiber

Typical Deployment of UPSR and BLSR in RBOC Network Regional Ring (BLSR) BB DACs Intra-Regional Ring (BLSR) Intra-Regional Ring (BLSR) WB DACs Access Rings (UPSR) WB DACS = Wideband DACS - DS1 Grooming BB DACS = Broadband DACS - DS3/STS-1 Grooming Optical Cross Connect = OXC = STS-48 Grooming DACS=DCS=DXC

Emergence of DWDM Some Review Questions What does the acronym DWDM mean? What was the fundamental technology that enabled the DWDM network deployments?

First Driver for DWDM Long Distance Networks WDM NE BLSR Fiber Pairs BLSR Fiber Pairs WDM NE Limited Rights of Way Multiple BLSR Rings Homing to a few Rights of Way Fiber Exhaustion

Increased Fiber Network Capacity Key Development for DWDM Optical Fiber Amplifier 120 km OC-48 OLS TERM RPTR Fiber Amplifier Based Optical Transport - 20 Gb/s Conventional Optical Transport - 20 Gb/s 1310 40km Increased Fiber Network Capacity 9 120

Transporting Broadband across Transmission Networks designed for Narrowband

Data SP Public/Private Internet Peering Backbone SONET/WDM T1/T3 IP Core Router Core Router RAS RAS Core Router EtherSwitch Access Router RAS RAS RAS Access Router ATM Switch ATM Switch Core Router RAS EtherSwitch RAS RAS RAS ATM Switch RAS ATM Access Access Router RAS Core Router RAS RAS Access Router RAS ATM Access RAS Backbone SONET/WDM RAS Access Router T1/T3 IP Leased-Line Connections RAS Farms ATM Switch ATM Access ATM Access ATM Access ATM Access T1/T3 FR and ATM IP Leased-Line Connections T1/T3/OC3 FRS and CRS

High Capacity Path Networking IP router IP router STS-12c/48c/... IP router STS-3c Existing SDH-SONET Network Existing SONET/SDH networks are a BOTTLENECK for Broadband Transport Most Access Rings are OC-3 and OC-12 UPSRs while most Backbone Rings are OC-48. Transport of rates higher than OC-48 using the existing SONET/SDH network will require significant and costly changes. Clearly upgrading the SONET/SDH network everytime broadband data interfaces are upgraded based increased IP traffic is not an appropriate solution.

IP/SONET/WDM Network Architecture OC-3/12 [STS-3c/12c] SONET NMS OC-3/12 [STS-3c/12c/48c] SONET XC OC-48 EMS SONET ADM/LT SONET ADM/LT EMS Access . OC-12/48 Routers/ Core IP Node . . Enterprise SONET Transport Network Core IP Node . Servers . . OTN NMS WDM LT WDM LT OC-3/12/48 [STS-3c/12c/48c] OC-3/12/48 [STS-3c/12c/48c] l1, l2, ... Pt-to-Pt WDM Transport Network LT = Line Terminal EMS = Element Management System NMS = Network Management System IP = Internet Protocol OTN = Optical Transport Network ADM = Add Drop Multiplexor WDM = Wavelength Division Multiplexing

Optical Network Evolution mirrors SONET Network Evolution Point-to-Point WDM Line System l1 l2 lN Multipoint Network WDM Add/Drop WDM ADM WDM ADM li lk Optical Cross-Connect WDM Networking OXC

IP/OTN Architecture IP = Internet Protocol EMS . Core Data Node . . mc: multi-channel interface (e.g., multi-channel OC-12/OC-48) mc OTN NMS OXC EMS EMS OXC OXC . mc Access Routers . Core Data Node . Enterprise Servers Optical Transport Network mc Core Data Node . mc . . IP = Internet Protocol OTN = Optical Transport Network OXC = Optical Cross Connect WDM = Wavelength Division Multiplexing EMS = Element Management System NMS = Network Management System

Restoration on the backbone SONET rings Simple and do the job today Inefficient and inflexible Diversely routed working and protect Next generation options “Virtual rings” Mesh with shared protect Optical rings Optical mesh

What are the restoration requirements? Recovery from failures Equipment failures Cable cuts Four 9’s? Down 52 minutes per year. Five 9’s? Down 5 minutes per year. Need to satisfy the users requirements: Service Level Agreement (SLA) Service degradation varies by application 911 calls, voice, video, ATM, Frame, IP Do customers want to pay for 50ms recovery from a cut? Wide area rings vs. Local area

Protection & Restoration of Optical Networks

Terminology Protection Restoration Survivability Uses pre-assigned capacity to ensure survivability Restoration Reroutes the affected traffic after failure occurrence by using available capacity Survivability Property of a network to be resilient to failures

Classification of Schemes

Reactive / Proactive Reactive Proactive When an existing lightpath fails, a search is initiated to find a new lightpath which does not use the failed components. (After the failure happens) It cannot guarantee successful recovery, Longer restoration time Proactive Backup lightpaths are identified and resources are reserved along the backup lightpaths at the time of establishing the primary lightpath itself. 100% restoration guarantee Faster recovery

Link Based vs. Path Based Shorter restoration time Less efficient. Can only fix link failures Path-based longer restoration time More efficient.

Dedicated vs. Multiplexed Backup Dedicated backup More robust Less efficient. Backup multiplexing Less robust More efficient.

Primary Backup MUX Wavelength channel to be shared by a primary and one or more backup paths

Resilience in Optical Networks Linear Systems 1+1 protection 1:1 protection 1:N protection Ring-based UPSR: Uni-directional Path Switched Rings BLSR: Bi-directional Line Switched Rings Mesh-based Optical mesh networks connected by optical cross-connects (OXCs) or optical add/drop multiplexers (OADMs) Link-based/path-based protection/restoration Hybrid Mesh Rings Physical: mesh Logical: ring

Unidirectional WDM Path Protected Rings 1+1 wavelength path selection Signal bridged on both protection and working fiber. Receiver chooses the better signal. Failure: Destination switches to the operational link. Revertive /Non revertive switching No signaling required.

Bidirectional Line switched Ring Shares protection capacity among all the spans on the ring Link failure Working traffic from 1 fiber looped back onto opposite direction. Signaling protocol required Node failure Line switching performed at both sides of the failed node.

2-Fiber WDM Ring

BLSR - 4 Fiber Fibers Protection fiber: no traffic unless failure. 2 working 2 protection Protection fiber: no traffic unless failure. Link Failure. APS channel required to coordinate the switching at both ends of a failure.

4-Fiber WDM Ring.

4-Fiber WDM Ring After a Link Failure

4-Fiber WDM Ring After a Node Failure

Path Layer Mesh Protection Protect Mesh as a single unit Pre-computed routes 1+1 path protection Protection route per light path Protection route per failure. On the fly route computation. Centralized route computation and coordination Route computation and coordination at end nodes. Distributed route computation at path ends. Decompose into protection domains. Pure rings P cycles

Mesh Topologies Fibers organized in protection cycles. Computed offline 4 fibers of each link is terminated by 4 2X2 protection switches Before link failure, switches in normal position. After failure, switches moved to protection state and traffic looped back into the protection cycles.

2X2 Switch

Protection Cycles (cont’d) Criterion for protection cycles. Recovery from a single link failure in any optical network with arbitrary topology and bi-directional fiber links All protection fibers are used exactly once. In any directed cycle both protection fibers in a pair are not used unless they are in a bridge

Protection Cycles

Protection Cycles (cont’d)

Network With Default Protection Switching

Network After a Link Failure

P –cycles Ring like restoration needed for some client signals. Mesh topologies: bandwidth efficient. P –cycles:Ring like speeds, Mesh like capacity. Addresses the speed limitation of mesh restoration.

P –cycles (cont’d) Cycle oriented pre configuration of spare capacity. Can offer up to 2 restoration paths for a failure scenario. Span Failure On cycle: similar to BLSR Off the cycle: 2 paths. Time needed for calculating and connecting restoration path is needed in non-real time.

P - cycles

WDM Recovery Fiber based restoration WDM based recovery Entire traffic carried by a fiber is backed by another fiber. Bi-directional connection - 4 fibers. WDM based recovery Protection for each wavelength. Bi-directional connection - 2 fibers Allows flexibility in planning the configuration of the network. Recovery procedure similar to BLSR.

Resilience in Multilayer Networks Why resilience in multilayer networks? Avoid contention between different single-layer recovery schemes. Promote cooperation and sharing of spare capacity

PANEL: Protection Across Network Layers

PANEL Guidelines Recovery in the highest layer is recommended when: Multiple reliability grades need to be provided with fine granularity Recovery inter-working cannot be implemented Survivability schemes in the highest layer are more mature than in the lowest layer Recovery in the lowest layer is recommended when: The number of entities to recover has to be limited/reduced The lowest layer supports multiple client layers and it is appropriate to provide survivability to all services in a homogeneous way Survivability schemes in the lowest layer are more mature than in the highest layer It is difficult to ensure the physical diversity of working and backup paths in the higher layer

WDM Network Architecture

Classes of WDM Networks Broadcast-and-select Wavelength routed Linear lightwave

Broadcast-and-Select w0 Passive Coupler w1

Wavelength Routed An OXC is placed at each node End users communicate with one another through lightpaths, which may contain several fiber links and wavelengths Two lightpaths are not allowed to have the same wavelength on the same link.

WRN (cont’d) Wavelength converter can be used to convert a wavelength to another at OXC Wavelength-convertible network. Wavelength converters configured in the network A lightpath can occupy different wavelengths Wavelength-continuous network A lightpath must occupy the same wavelength

A WR Network B A C D E F G H I J K L M N O 1 2 3 OXC IP SONET

Linear Lightwave Networks Granularity of switching in wave bands Complexity reduction in switches Inseparability Channels belonging to the same waveband when combined on a single fiber cannot be separated within the network

Routing and Wavelength Assignment (RWA) To establish a lightpath, need to determine: A route Corresponding wavelengths on the route RWA problem can be divided into two sub-problems: Routing Wavelength assignment Static vs. dynamic lightpath establishment

Static Lightpath Establishment (SLE) Suitable for static traffic Traffic matrix and network topology are known in advance Objective is to minimize the network capacity needed for the traffic when setting up the network Compute a route and assign wavelengths for each connection in an off-line manner

Dynamic Lightpath Establishment (DLE) Suitable for dynamic traffic Traffic matrix is not known in advance while network topology is known Objective is to maximize the network capacity at any time when a connection request arrives at the network

Routing Fixed routing: predefine a route for each lightpath connection Alternative routing: predefine several routes for each lightpath connection and choose one of them Exhaust routing: use all the possible paths

Wavelength Assignment For the network with wavelength conversion capability, wavelength assignment is trivial For the network with wavelength continuity constraint, use heuristics

Wavelength Assignment under Wavelength Continuity Constraint First-Fit (FF) Least-Used (LU) Most-Used (MU) Max_Sum (MS) Relative Capacity Loss (RCL)

First-Fit All the wavelength are indexed with consecutive integer numbers The available wavelength with the lowest index is assigned

Least-Used and Most-Used Record the usage of each wavelength Pick up a wavelength, which is least used before, from the available wavelength pool Most-Used Record the usage of each wavelength Pick up a wavelength, which is most used before, from the available wavelength pool

Max-Sum and RCL Fixed routing MAX_SUM Chooses the wavelength, such that the decision will minimize the capacity loss or maximize the possibility of future connections. RCL will choose the wavelength which minimize the relative capacity loss.

Applications for Free Space Optics (FSO) Mark E. Allen SignalWise LLC mallen@signalwise.com

Outline Where does FSO fit in the network? FSO design issues What is the performance of FSO? Applications for FSO Future directions

Intro to FSO The last-mile problem continues to be an issue. Fiber doesn’t exist everywhere. Trenching new fiber can cost upwards of $250K /mile Often impossible in congested metro areas Not cost effective in sparse areas Nobody has any money left DSL / Cable / Copper ? DSL/T1/DS3 (when available) are limited in speed and distance (~1.5M for DSL/T1), (45M for DS3) Provisioning times/errors often a problem Monthly recurring charges can be substantial

Lasers through the air Laser sources normally in the 850nm, 1310 or 1550 ranges. Some debate on what’s best, 1550 generally more eye-safe Receiver optics capture the light and converts back to electrical signal (OEO) Several factors can impair the signal as it propagates through the air.

Two major markets for FSO Enterprises looking for: Increased bandwidth and connectivity throughout the campus Reduced monthly recurring costs from Telco Unconstrained expansion of their GigE LANs Service providers want: Access to more customers Reduced capital infrastructure costs Military has also been very interested in “LaserCom”

FSO and Wireless FSO Wireless Range ~3km Range ~ 5-25km 10 – 100 Mbps More than 1Gbps No rain fade Fog interferes No license required Indoor (through window) or outdoor installation No licensing required 3-4 nines typical Line of sight Wireless Range ~ 5-25km 10 – 100 Mbps Rain fade Fog OK Outdoor installation Licensing may be required 3-4 nines typical Line of sight required? No (MHz carrier) Yes (GHz carrier)

FSO Impairments Atmospheric Impairments Scattering of light from particles Fog,smoke have diameter in the micron range Turns out visibility and FSO path loss are directly correlated On a clear day, FSO path will incur low loss, but must be engineered for worst case.

Visibility and corresponding loss lossdB(L)  10 * L/Visibility

Scintillation (heat waves) These are caused by localized changes in the density of the air. Can be mitigated Multiple beams Aperture averaging (large beam) Adaptive Optics (time-varying corrective lens) Other than fog, this is the biggest challenge for FSO.

Other impairments Mispointing losses Divergence losses Inaccuracy or building shake/vibration can cause signal dropouts Active control systems can correct this. $$$ Divergence losses As the beam travels, it spreads out. Can be tightened, but this complicates the mispointing problem.

Sample budget Description FSO Transmit power +20dBm Internal losses (total for both ends) 8dB Window losses 6dB Path attenuation (clear air) 0dB Scintillation loss 4dB Mispointing loss 1dB Geometric spreading loss Required receiver sensitivity -30dBm Available weather margin 27dB

The statistics of visibility

Ex: Computing expected uptime Assume link with 27dB “weather” margin 1km in length 400m visibility >> 27dB/km of loss So: The 1km link goes down when visibility drops below 400m. Statistics of different cities vary widely. 2-3 “nines” are usually attainable for shorter links.

FSO Applications Metro Fiber Extension Services providers extending their reach into areas where they don’t have (or can’t lease) fiber OC-N mux can be terminated at the end of the FSO system 1+1 Redundancy with fiber can also used.