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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. Asynchronous Data Rates. Digital Signal Level 0 DS0 64 Kb/s

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Optical networking part 2

Optical Networking (part 2)

Mark E. Allen, Ph.D.

mark.allen@ieee.org


Optical networking part 2

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


Asynchronous data rates
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

    • intra office only (600 ft limit)

  • 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


Asynchronous digital hierarchy
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
Asynchronous NetworkingManual DS1 Grooming/Add/Drop

D

S

X

1

D

S

X

1

D

S

X

3

D

S

X

3

LW

LW

M13

M13

DS3

DS3

DS1

  • Manually Hardwired Central Office

  • No Automation of Operations

  • Labor Intensive

  • High Operations Cost

  • Longer Time To Service


Some review questions
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
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


Sonet rates ds3s are sts 1 mapped
SONET RatesDS3s are STS-1 Mapped

DS0 (a digitized analog POTS circuit @ 64 Kbits/s)

STS-1

51.84 Mbits/s

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


Optical networking part 2

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

PTE

PTE

STE

STE

PTE

PTE

LTE

LTE

PTE

PTE

SONET Layering for Cost Effective Operations

DS-3

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
SONET Point-to-Point Network

Repeater

Repeater

TM

TM

Section

Line

Path

Section

Overhead

STS-1

Frame

Format

STS-1 Synchronous

Payload Envelope

STS-1 SPE

Path

Overhead

Line

Overhead


Protection schemes 1 1
Protection Schemes: 1 + 1

Network Protection

Working Facility

Protection Facility

(Source)

(Destination)

1 + 1 Protection Switching

(50% bandwidth utilization)


1 for n 1 n

.

.

.

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
Protection and Restoration

Path Protection

Line Protection (Loopback)

D1

D1

D2

D2

S

S

1 + 1

1:n


Optical networking part 2
UPSR

Rx

Tx

Rx

Work

Protect

Tx

Rx

Unidirectional/Path Switched Ring (UPSR)


Optical networking part 2
BLSR

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
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
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

First Driver for DWDMLong Distance Networks

BLSR Fiber Pairs

BLSR Fiber Pairs

WDM NE

  • Limited Rights of Way

  • Multiple BLSR Rings Homing to a few Rights of Way

  • Fiber Exhaustion


Optical networking part 2

40km

40km

40km

40km

40km

40km

40km

40km

40km

TERM

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

TERM

TERM

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

TERM

TERM

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

TERM

TERM

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

TERM

TERM

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

TERM

TERM

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

TERM

TERM

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

TERM

TERM

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

1310

RPTR

TERM

Conventional Optical Transport - 20 Gb/s

OC-48

OC-48

OC-48

OC-48

OC-48

120 km

OC-48

120 km

120 km

OC-48

OC-48

OLS

TERM

OLS

RPTR

OLS

TERM

OLS

RPTR

OC-48

OC-48

OC-48

OC-48

OC-48

OC-48

OC-48

OC-48

Fiber Amplifier Based Optical Transport - 20 Gb/s

Key Development for DWDM Optical Fiber Amplifier

Increased Fiber Network Capacity


Transporting broadband across transmission networks designed for narrowband

Transporting Broadbandacross Transmission Networksdesigned for Narrowband


Optical networking part 2

Core

Router

Core

Router

RAS

RAS

Core

Router

RAS

Access

Router

RAS

RAS

Access

Router

Core

Router

RAS

ATM

Switch

ATM

Switch

RAS

RAS

RAS

Core

Router

ATM

Switch

ATM

Switch

RAS

RAS

Access

Router

RAS

Core

Router

RAS

Access

Router

RAS

RAS

RAS

Access

Router

ATM

Access

ATM

Access

ATM

Access

ATM

Access

Data SP

Public/Private

Internet Peering

EtherSwitch

EtherSwitch

ATM Access

ATM Access

Backbone

SONET/WDM

T1/T3 IP

Leased-Line

Connections

RAS Farms

ATM

Switch

T1/T3 FR

and ATM IP

Leased-Line

Connections

T1/T3/OC3

FRS and CRS


High capacity path networking
High Capacity Path Networking

IP router

  • 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 router

IP router

STS-12c/48c/...

STS-3c

Existing SDH-SONET Network


Ip sonet wdm network architecture

SONET

NMS

SONET

XC

SONET

SONET

ADM/LT

ADM/LT

WDM

WDM

LT

LT

IP/SONET/WDM Network Architecture

OC-3/12

[STS-3c/12c]

OC-3/12

[STS-3c/12c/48c]

OC-48

EMS

EMS

Access

OC-12/48

.

.

Routers/

Core IP

Node

.

Core IP

Node

SONET Transport Network

.

Enterprise

.

Servers

.

OTN

NMS

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

l1

l1

l2

l2

lN

lN

Optical Network Evolution mirrorsSONET Network Evolution

Point-to-Point WDM Line System

Multipoint NetworkWDM Add/Drop

WDMADM

WDMADM

li

lk

Optical Cross-ConnectWDM Networking

OXC


Ip otn architecture
IP/OTN Architecture

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

Core Data

Node

.

mc

Optical Transport Network

.

Enterprise Servers

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
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
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



Terminology
Terminology

  • Protection

    • 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



Reactive proactive
Reactive / Proactive

  • Reactive

    • 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
Link Based vs. Path Based

  • Link-based

    • Shorter restoration time

    • Less efficient.

    • Can only fix link failures

  • Path-based

    • longer restoration time

    • More efficient.


Dedicated vs multiplexed backup
Dedicated vs. Multiplexed Backup

  • Dedicated backup

    • More robust

    • Less efficient.

  • Backup multiplexing

    • Less robust

    • More efficient.


Primary backup mux
Primary Backup MUX

  • Wavelength channel to be shared by a primary and one or more backup paths


Resilience in optical networks
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
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
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.



Blsr 4 fiber
BLSR - 4 Fiber

  • Fibers

    • 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 after a link failure
4-Fiber WDM Ring After a Link Failure


4 fiber wdm ring after a node failure
4-Fiber WDM Ring After a Node Failure


Path layer mesh protection
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
    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.



    Protection cycles cont d
    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






    P cycles
    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
    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 cycles1
    P - cycles


    Wdm recovery
    WDM Recovery

    • Fiber based restoration

      • 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
    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 guidelines
    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


    Optical networking part 2

    WDM

    Network Architecture


    Classes of wdm networks
    Classes of WDM Networks

    • Broadcast-and-select

    • Wavelength routed

    • Linear lightwave


    Broadcast and select
    Broadcast-and-Select

    w0

    Passive

    Coupler

    w1


    Wavelength routed
    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
    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

    H

    OXC

    I

    G

    SONET

    F

    O

    J

    1

    B

    IP

    2

    A

    1

    3

    K

    E

    2

    1

    N

    C

    D

    1

    L

    IP

    SONET

    M

    A WR Network


    Linear lightwave networks
    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
    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
    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
    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
    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
    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
    Wavelength Assignment under Wavelength Continuity Constraint

    • First-Fit (FF)

    • Least-Used (LU)

    • Most-Used (MU)

    • Max_Sum (MS)

    • Relative Capacity Loss (RCL)


    First fit
    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

    Least-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

    Least-Used and Most-Used


    Max sum and rcl
    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

    Applications for Free Space Optics (FSO)

    Mark E. Allen

    SignalWise LLC

    mallen@signalwise.com


    Outline
    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
    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
    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
    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

    Range ~3km

    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 and Wireless


    Fso impairments
    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
    Visibility and corresponding loss

    lossdB(L)10 * L/Visibility


    Scintillation heat waves
    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
    Other impairments

    • Mispointing 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

    4dB

    Required receiver sensitivity

    -30dBm

    Available weather margin

    27dB

    Sample budget



    Ex computing expected uptime
    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
    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.