S-72.3340 Optical Networks Course Lecture 12: The … links •Satellite links Radio relay stations...

S-72.3340 Optical Networks Course

Lecture 12: The Course Recap

Edward MutafungwaCommunications Laboratory, Helsinki University of Technology,

P. O. Box 2300,FIN-02015 TKK, Finland

Tel: +358 9 451 2318, E-mail: [email protected]

Apr 26, 2007 EMu/S-72.3340/TheRecap Slide 2 of 54

1. Introduction

Electrical communications

Light or optical communications

..011010..DataSource

Electrical signal source

Electrical signal

..011010..DataSource

Electrical signal source

Light source

Electrical signal

Optical signal


1. IntroductionElectrical repeaterMetallic cable

• Copper Links

• Terrestrial radio links

•Satellite links Radio relay stations

Orbiting satellite

•Fiber links

Electrical repeater

Electrical to Optical

converter

O → E E → O

Optical to electrical converterFiber


1. Introduction

Advantages of the fiber transmission media Low transmission loss (typically 0.2-0.5 dB/km) Large information carrying capacity (multi Gbit/s) Immunity to electromagnetic interference More secure to eavesdropping or wiretapping Smaller size and weight


Link performance is limited by:

Loss

Receiver

Spreading

1 0 1 1 1 1 1 1

Receiver

1 0 1 1 1 1 1 1

1. Introduction


1. Introduction

Graphical representation of fiber limitations

Distance

Bit

Rat

e

Dispersion & Loss LimitedDispersion Limit

Loss Limit

Costly!

Feasible Regime


2. Wavelength-Division Multiplexing

Optical amplifier

WDM fiber link with optical amplification

Space-division multiplexing fiber link with electrical regeneration

O → E E → O

O → E E → O

O → E E → O

Electrical repeater

Electrical to Optical

converter

Optical to electrical converter

Fiber

O → E E → O

O → E E → O

O → E E → O

O → E E → O

O → E E → O

WDM fiber link with electrical regeneration


Third window“1550-nm”

2. Wavelength-Division MultiplexingAmplified optical communications systems

Optical amplification enables WDM in 1550 nm window Less attenuation than 850 nm and 1300 nm windows

First window“850-nm”

Second window“1300-nm”

6000.1

λ (nm)

0.2

0.5

1.0

2.0

5.0

10

Atte

nuat

ion

(dB/

km)

800 1000 1200 1400 1600 1800

Standard fiber

Low water-peakFiber

Less loss and zero dispersion

Optical signal sources available Optical amplification,

even lower loss


2. Wavelength-Division Multiplexing Coarse WDM (CWDM)

ITU-T G.694.2/695 grid with 2500 GHz or 20 nm channel spacing 18 channels spanning O-, E-, S-, C- and L-bands (1260-1625 nm)

Source: F. Audet, “Understanding CWDM,”EXFO application note.


2. Wavelength-Division Multiplexing DWDM enables many channels with amplification,

...but requires stable transmitters and good filtering (sharp skirts and precise center frequency)

CWDM simplifies filter and transmitter design (cheaper) ...but no amplification and few channels

Source: F. Audet, “Understanding CWDM,”EXFO application note.


2. Wavelength-Division Multiplexing A typical amplified WDM link includes:

Optical transmitters and receivers (1 each per wavelength) Wavelength multiplexer and demultiplexers Optical amplifiers

• Boost amplifier: to increase the output power • Line amplifier: to compensate for fiber losses• Preamplifier: to improve receiver sensitivity


2. Modulation/Demodulation

Two popular optical modulation schemes On-off keying (OOK) modulation Subcarrier modulation (SCM)


2.1 On-Off Keying (OOK) Modulation

It is possible to directly or externally modulate (i.e. turn off and on) a light source (laser or LED) Direct modulation ⇒ simple, chirp External modulation ⇒ more complex, less chirp


NRZ

1

Time

0 1

T

Binary Data 1

Time

0 1

TPo

wer

Pow

er

TimeTime

TTFWHM

RZ Duty Cycle = TFWHM/T where TFWHM is full width at half maximum of power

2.1 On-Off Keying (OOK) ModulationNon-Return-to-Zero (NRZ) format

Return-to-Zero (RZ) format


Subcarrier modulated (SCM) systems Multiplex multiple data streams onto one optical signal Each data stream assigned a unique subcarrier frequency

⇒ subcarrier multiplexing

×~

f1

Data stream 1

×~

f2

Data stream 2

×~

f3

Data stream 3

Laserfc

2.2 Subcarrier Modulation

5 signal subcarrier multiplexing


Data signal recovery is a two step process(1) Recovering the clock (2) Determining whether a “0” or “1” bit was sent in a bit

interval direct detection⇨

2.3 Demodulation


Figure: Block diagram showing various functions and noise components in a receiver

Regeneratedoutput pulsesPhotocurrent +

photodetector noise

Photodetector Shot noise, Dark current, Thermal noise

Incident optical pulses

PhotodetectorAmplifier & filter

Sampler &

Decision circuit

Clock/timing recovery

2.3 Demodulation

Current to voltage conversion

P isignal + ishot + ithermal + idark


* For optically preamplified receiver, a noise figure of 6dB assumed

* Optical bandwidth Bo =50 GHz

2.3 Demodulation


2.3 Demodulation Also performance improvements with electrical DSP

techniques Equalizers Error detection and correction (forward error correction)

Receiver Sensitivity (dBm)

BER

Source: G. Barlow, “A G.709 Optical Transport Network Tutorial,” Innocor white paper.


3. Transmission System Engineering

Link power budget

FiberReceiverReceiverTransmitterTransmitter

dB valueValueItem dB valueValueItem

1a) Average output power

2a) Propagation losses (10 km)

Receiver:3a) Signal power at receiver3b) Receiver sensitivity

Link Margin (Power Margin)

Transmitter:

Channel:

1.0 mW

0.2 dB/km

= (3a – 3b)

0.0 dBm

-20.0 dB

-20.0 dBm-30.0 dBm

+10.0 dB



Power penalty analysis

Received optical power (dBm)

Log(

BER

)

- 31 - 30 - 29 - 28 - 27 - 26 - 25 - 24

- 3

- 4

- 5

- 6

- 7

- 8- 9

- 10- 11- 12- 13- 14- 15- 16

Signal without impairment

Signal with impairment

Power Penalty



Power penalty analysis

Impairment Allocation (dB) Ideal Q-factor 17 Transmitter 1 Crosstalk 1 Dispersion 2 Nonlinearities 1 Polarization dependent losses 3 Component ageing 3 System margin 3 Required Q-factor 31


4. SDH/SONET

Dominant standard for optical transmission and multiplexing for high-speed signals Single master clock ⇒ synchronous multiplexing

• Easier and cheaper multiplexers and demultiplexers

Extensive management information Standard optical interfaces enable interoperability Network topologies and protection switching for high

availability service Basic transmission rates

• SDH ⇒ 155 Mb/s STM-1 (synchronous transport module-1)• SONET ⇒ 51.48 Mb/s (STS-1)


Layer (except physical layer) has associated overhead bytes POH for path layer, MSOH for multiplexer section layer and RSOH for

regenerator section layer

4. SDH/SONET

STM-N frame structure

STM-1 Payload Capacity (VC-4)

POHSOH

261xN Bytes270×N Bytes

9 Row

sRS

OH

MSO

HAU

Po

inte

r


4. SDH/SONET

Regenator Section

Overhead

Multiplexer Section

Overhead

Framing A1

Framing A1

Framing A1

Framing A2

Framing A2

Framing A2

Ident J0

Datacom D1

Sync stat. S1

Growth Z1

Growth Z1

Growth Z2

Growth Z2

Trans err. M1

Orderwire E2

Datacom D2

Datacom D3

Datacom D4

Datacom D5

Datacom D6

Datacom D7

Datacom D8

Datacom D10

Datacom D11

Datacom D12

Datacom D9

APS K1 B2 B2 B2

BIP 24 APS K2

Pointer H1

Pointer H1

Pointer H1

Pointer H2

Pointer H2

Pointer H2

Pointer H3

Pointer H3

Pointer H3

BIP 8 B1

Orderwire E1

User F1

Figure: SDH section overhead bytes. Crossed bytes are auxiliary bytes

AU

P

oin

ter

Automatic Protection Switching

Bit Interleaved

Parity


4. SDH/SONET

VC-11

VC-12

VC-3

STM-1

STM-1

VC-N

DS1

E1

E3

STM-1

STM-N

STM-N

STM-N

VC-N interface

Timeslot Multiplexer

High Speed Interface

VC-12 VC-3 VC-4 STM-N

STM-N bus

E1 E3 E4 STM-N

STM-N STM-NSTM-N TU-12 TU-3 AU-4 STM-NSTM-N

VC-12 VC-3 VC-4 STM-N

Switch Matrix

E1 E3 E4 STM-N

STM-N

STM-N

STM-N

STM-N

STM-NSTM-N

Terminal Multiplexer Add/Drop Multiplexer

Digital Cross-Connect System

Path Terminating Equipment used in the SDH networks


4. SDH/SONETResilient SDH network topologies

TM

Point-to-point configuration

ADM

TM

TM TM

Drop Add

ADM

Drop Add

Linear add/drop configuration

Working fiberProtection fiber

TM: Terminal MultiplexerADM: Add/Drop Multiplexer


4. SDH/SONETResilient SDH network topologies

SNCP ring


ADM

Drop

Add

ADM

Drop

Add

ADM

Drop Add

ADM

Drop Add

ADM

Drop Add

ADM

Drop Add

ADM

Dro

pAd

d

ADM

Dro

pAd

d

TM: Terminal MultiplexerADM: Add/Drop Multiplexer

2-fiber MS-SPRing

ADM

Drop

Add

ADM

Drop

Add

ADM

Drop Add

ADM

Drop Add

ADM

Drop Add

ADM

Drop Add

ADM

Dro

pAd

d

ADM

Dro

pAd

d ADM

Drop

Add

ADM

Drop

Add

ADM

Drop Add

ADM

Drop Add

ADM

Drop Add

ADM

Drop Add

ADM

Dro

pAd

d

ADM

Dro

pAd

d

4-fiber MS-SPRing


5. Multiservice Optical Networks

Multiservice networks provide more than one distinct communications service type Voice, data, Internet etc. Over a common physical infrastructure e.g. fiber

Increased prominence of data-centric protocols ATM, IP/MPLS, Ethernet, SAN protocols etc.

SDH originally defined to carry voice traffic Unsuitable for asynchronous packet-switched bursty data

traffic Four-fold capacity increase increments (e.g. from STM-1

to STM-4) ⇒ Inflexible provision of capacity to users


5. Multiservice Optical NetworksUpgrade current systems with next-generation

SDH/SONET (NG-SDH) solutions Virtual Concatenation (ITU-T G.7043) Link Capacity Adjustment Scheme (ITU-T G.7042) Generic Framing Procedure (ITU-T G.7041)

These upgrades only needed at source and destination terminal equipment of required service Intermediate equipment do not need to be aware and

can interoperate with upgraded equipment Enables operater to make only partial network upgrades

on as-needed basis


5. Multiservice Optical Networks Example ways of transporting IP packets over optical

(WDM) networks via SDH/NG-SDH

IP

10GbE, GbE, Ethernet

Frame-Mapped GFP

Optical (WDM)

Transparent-Mapped GFP

SDH/NG-SDH

DVB, Fiber Channel, ESCON10GbE, AAL5(ATM), PDH PPP/HDLC, PoS

Fiber Link

λ 1

λ 2

λ 3

STM-N

STM-N

Ethernet, IP/MPLSPDH, ATM

FC, FICON, ESCON

DWDM SDH Services

STM-N


5. Multiservice Optical Networks Optical WDM network with open interfaces simplifies direct

access to fiber capacity sharing by different clients

Fiber Link

λ1

λ2

λ3

STM-N

Ethernet

PDH, ATM

IP/MPLS

DWDM Services



Optical Transport Network (OTN) ITU-T G.709, G.872 Truly global standard unlike SDH/SONET Enables SDH-like Operations, Administration,

Maintenance and Provisioning for WDM networks• Reduces the requirement to run every service through

SDH/SONET to benefit from the management features

More efficient multiplexing, provisioning, and switching of high-bandwidth (≥ 2.5 Gbit/s) services

Improved multivendor and inter-carrier interoperability Forward error correction (FEC) from the beggining Less complex than NG-SDH ⇒ easier to manage


5. Multiservice Optical NetworksD

igit

al

(ele

ctri

cal)

Opt

ical



Supported interfaces Electrical (DS1, E1, E3, STM-1E etc.) SDH (up to STM-64) CWDM and DWDM (OTN) Ethernet (up to GbE) SAN (Fiber Channel and FICON) Video (D1 video, HDTV)

Cross-connection levels DS1/E1 up to STM-64

Cisco ONS 15454

Multiservice provisioning platforms e.g. Cisco’s ONS 15454



MSPP

MSPP

MSPP

MSPP

10/100/1000 Mbit/s Ethernet

ATM

Metro Access /Edge

ATM/Ethernet

IP/MPLS

IP/MPLS

10/100/1000 Mbit/s Ethernet

PBX

IP/MPLS

MSPP: Multiservice Provisioning PlatformPBX: Private Branch ExchangeMPLS: Multiprotocol Label SwitchingATM: Asynchronous Transfer ProtocolMSC: Mobile Switching CenterBSC: Base Station Controller

NIU

NIU

MSC/BSC

Storage Center

Public WiFi

2G/3G/WiMAXWireless local loop

PDH/Ethernet/

ATM

FC, FICON, iSCI

Figure: Example service mix supported by deployment of MSPPs


7. Optical Network Design

IP Router

ATM Switch

SDH DigitalCross-Connect

Voice Switch

PSTN

IP/ATMNetworkClient Equipment/

Networks

Optical Node

Optical Network

Open OpticalInterface

FiberLink

A

B

Optical connections


7. Optical Network DesignW

DM

D

EMU

X WD

M

MU

X

Drop(a) Parallel

λ 1 λ 2 …λ W

Add

λ 1

λ 2

λ W

λ 1 λ 2 …λ W

WD

M

DEM

UX W

DM

M

UX

Drop(a) Parallel

λ 1 λ 2 …λ W

Add

λ 1

λ 2

λ W

λ 1 λ 2 …λ W

Example fixed OADM

(b) Fully tunable OADM using a large multiport optical switch

WD

M

DEM

UX W

DM

M

UX

λ 1 λ 2 …λ W

Any λ

λ 1 λ 2 …λ W

Optical switch

Any λAny λ

Any λ

Example reconfigurable OADM

The example OXC scaled to handle 4 wavelength channels on each fiber port

WD

M

DEM

UX

WD

M

MU

Xλ 1 λ 2 λ 3 λ 4

λ 1

λ 2

λ 4

λ 1 λ 2 λ 3 λ 4λ 3

WD

M

DEM

UXλ 1 λ 2 λ 3 λ 4

λ 1

λ 2

λ 4

λ 3

WD

M

MU

X

λ 1 λ 2 λ 3 λ 4

Inpu

t Fi

bers

Out

put

Fibe

rs

Example fixed OXC


7. Optical Network Design A WDM network may be realized by solving:

Physical topology design (PTD) problem Lightpath topology design (LTD) problem Routing and wavelength assignment (RWA) problem

1

4

2

3

A

B

C

D

Solve RWA Problem

1

4

2

3

A

B

C

Dλ 1

λ 2

λ 3

1

4

2

3

A

B

C

Dλ 1

λ 2

λ 3

B

AC

D

B

AC

D

AC

D

1

4

2

3

A

B

C

D

Solve LTD Problem


8. Test and Measurement

Digital Test Modules

SDH (up to STM-64)

PDH

Ethernet (up to 10GbE)

OSA (OSNR, LED/laser/EDFA test)

Q-factor meter

CWDM/DWDM Testing

Source:

Talk set (communication & file transfer)

CD/PMD Testing

OTDR/Power meter

Connection checklist tester

Fiber characterization

Software tools (result post-processing, report generation)

Example: Acterna MTS-8000 Tester


8. Test and Measurement

Figure: Example OTDR measurement for a fiber link to customers’ optical termination unit (ONU) Source: “Introduction to Optical Communications,” by L. Hart, Althos Publishing


9. Network Management and Survivability

Subnetwork connection protection (SNCP) rings

SNCP ring


ADM

Drop

Add

ADM

Drop Add

ADM

Drop Add

ADM

Dro

pAd

d

Working traffic

Before Failure

SNCP ring

ADM

Drop

Add

ADM

Drop Add

ADM

Drop Add

ADM

Dro

pAd

d

After Failure

Traffic on protection fiber selected

Duplicate traffic



IP/MPLS network protection schemes When failure detected packets could be rerouted on new

setup LSP

LSR

LSR

LSRPenultimate

LSRIngress

LER

Egress LSR

LSPLER: Label Edge RouterLSR: Label Switched-RouterLSP Label Switched Path

Customer Site A

Customer Site B

IP/MPLS Network

New LSP



OXC

Fiber

OXC

OXC

OXC

SDH ADM 1

(a) Normal operation before failure. SDH connection realized using lightpaths provided by optical layer between ADMs

SDH ADM 3

SDH connectionLightpath

SDH

AD

M 4 SD

H

ADM

2

Example of SDH protection involving optical layer

OXC

OXC

OXC

OXC

SDH ADM 1

SDH ADM 3

SDH

AD

M 4 SD

H

ADM

2

(c) Fiber fails and OXCs perform optical layer restoration and reroute lightpath. SDH carries on with normal operation awaiting another failure



Classical network management constitutes “FCAPS” functions Fault management: detecting failures and isolating failed component Configuration management: managing orderly network changes e.g.

equipment addition/removal Accounting management: billing and developing component lifetime

histories Performance management: monitoring and managing various

network performance metrics Security management: user authentication, control access to

network elements, user data protection etc. Safety management: (specifically for optical networks) ensure that

optical radiation conforms to eye safety requirements.



Optical Node 1

Interaction between optical and client layers (IP, SDH etc.) is important aspect of connection management protocols

Different control plane models proposed for interconnecting optical layer control plane and client layer control plane Overlay model Overlay+ model Augmented (dynamic overlay) model Peer model

IP router A

IP router B

Optical Node 2

IP connection provided via lightpath in optical layer

Fiber

Figure: Example of client layer connection provision via the optical layer


10. Deployment Considerations Selected fiber cable deployment method depends on various

factors Geographical topography of an area Availability of rights-of-way Time constraints Operator’s business strategy

Figure: Fiber cables deployed on power transmission lines (source: Alcatel)

Figure: Fiber cables deployed on power transmission lines (source: Alcatel)


10. Deployment Considerations


10. Deployment Considerations

2006 BMW X5

Flexray

Example: Avionics Full-Duplex Ethernet/ARINC 664 standard 10 Mb/s (Copper), 100 Mb/s

(Copper or Fiber), GbE (future) Planned for A380s, 787s

Airbus A380

Fiber-optic communications now used in diverse areas


10. Deployment Considerations Wireless or free space optics communications now also

available

Sources: Waseda University, Hamamatsu Photonics, IEEE/ConTEL conference

Figure: Rooftop FSO installation

Earth

RF linkRF link

Optical/infrared link

Satellite Satellite

Earthstation

Earthstation


11. Future Directions of Optical Net.

*Ref: J. Kahn & K. Ho, Proceedings of SPIE, Vol. 4872, July 2005

(Cap

acit

y x

Dis

tan

ce)/

Cos

t

Time

Optical Amplifiers

-

Optical Technologies

Non-Optical Technologies

WDM

FDM/SCM

Compensation

Adaptive Threshold, Transversal Filters

Error-Correction Coding

Non-Binary Modulation

Current Optical Comm. Systems

Adaptive Equalization

Coded Modulation

(Cap

acit

y x

Dis

tan

ce)/

Cos

t

Time

Optical Amplifiers

OEO Transponders

-

Optical Technologies

Non-Optical Technologies

WDM

FDM/SCM

Optical Dispersion

Adaptive Threshold, Transversal Filters

Error-Correction Coding

Non-Binary Modulation

Current Optical Comm. Systems

Adaptive Equalization

Coded Modulation


11. Future Directions of Optical Net. Still need for optical digital signal processing (> 40 Gb/s)

with photonic integrated circuits

Figure: A typical photonic crystal PIC envisioned for the future (source: Nature Photonics, pp. 11, Jan 2007).


About the Exam

Please note that YOU CAN ONLY DO ONE(1) EXAM. That is if you do Exam A, you will not do Exam B, OR if you do Exam B you will not do Exam A. Exam A: Day: Ma/Mon 14.05.2007, Time: 13-16,

Place: S1,S4 Exam B: Day: Ke/Wed 16.05.2007, Time: 16-19,

Place: S4 Each exam will have five questions, whereby

Question 1 is compulsory, and you can choose to do any three out of Questions 2 to 5.


?Thank You and Good luck!

S-72.3340 Optical Networks Course Lecture 12: The … links •Satellite links Radio relay stations...

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Transcript of S-72.3340 Optical Networks Course Lecture 12: The … links •Satellite links Radio relay stations...