ip over dmdw

1© 1999, Cisco Systems, Inc.

IP over DWDMNANOG May 24, 1999

Larry [email protected]

2NANOG 5/24/99 www.cisco.com

Outline

Optical Transmission Fundamentals

DWDM Systems IP over DWDM


Its Analog Transmission

AttenuationDispersion

Nonlinearity

Waveform after 1000 kmTransmitted data waveform

Reflectance


Fiber Attenuation

Telecommunications industry uses two windows: 1310 & 1550

1550 window is preferred for long-haul applications

Less attenuation Wider window Optical amplifiers

1310window

1550window


Fiber Dispersion

Wavelength

Dis

pers

ion

ps/

nm-k

m

18

01310 nm 1550nm

Normal fiberNon-dispersion shifted fiber (NDSF) >95% of deployed plant

Reduced dispersion fibersDispersion shifted fiber (DSF)Non-zero dispersion shifted fibers (NZDSF)


Dispersion

Dispersion causes the pulse to spread as it travels along the fiber

Chromatic dispersion is important for singlemode fiber

Depends on fiber type and laser used Degradation scales as (data-rate)2

Modal dispersion limits use of multimode fiber to short distances

Interference


Polarization Mode Dispersion

Most severe in older fiber

Caused by several sources

Core shape External stress Material properties

Becomes an issue at OC-192


Four-Wave Mixing (FWM)

Creates in-band crosstalk that can not be filtered

Problem increases geometrically with

Number of s Spacing between s Optical power level

Chromatic dispersion minimizes FWM


Outline




EDFAs Enable DWDM

40-80 km

Terminal

Regenerator - 3R (Reamplify, Reshape and Retime)

Terminal

120 km

TerminalTerminal

EDFA - 1R (Reamplify)

Terminal

EDFA amplifies all s

Terminal

Terminal

Terminal

Terminal

Terminal


EDFA Schematic

EDFAs amplify all s in 1550 window simultaneously Key performance parameters include

Saturation output power, noise figure, gain flatness/passband

......

980PumpLaser

WDMCoupler

WDMCoupler

EDF

DCF

OpticalIsolator

1480PumpLaser

OpticalFilter

OpticalIsolator

EDF


DWDM System Design

15501551155215531554155515561557

01234567

01234567

Amplify DW

DM

Filt

er

Opt

ical

Com

bine

r

15xx nm 1310 nmReamplifyReshapeRetime

Rx Tx1310 nm

Rx

Exte

rnal

M

odul

ator

Laser

15xx nm


DWDM State-of-the-Art

Data

Rate

Point-to-point systems 40 x OC-48 deployed 16 x OC-192 deployed 160 x OC-192 announced

Configurable OADMs Metro rings

1-10 Tbps per fiber is just around the corner!


Outline




Synchronization for IP over DWDM

OC-48c

Ethernet

Gig-Ethernet

Ethernet

DS1

• Point-to-point application • Synchronization driven from router• Router interface internal timed

T1 OC-12c

~~~~~~ ~~~~~~OC-48c

FIBER

REGEN

WDM

OC-3c

PRS

SONETNETWORKOC-48c OC-48c

• SONET network application • Synchronization driven from network• Router interface timed to PRS via Rx OC-48c


Protection for IP over DWDM

Optical protection is not sufficient Only protects transmission infrastructure

Layer 3 must provide path restoration Opportunity for differentiation at the service level

Optical Cloud


Ciena 40 DWDM

TX RC

TX

500 km

100 km25 dB RC

TX

TX

RC

RCGSR 12000

SR OC-48 PoS

1

2

3

Error-free transmission over 20,000 kms without SONET regeneration

TX RC

GSR 12000SR OC-48 PoS


Nortel 16 DWDM and OC-192 Ring

PRS

Working

Protect

Lack of transponders prohibits direct connections at OC-192


Conclusion - IP over DWDM

Transmission is an analog problem Proprietary solutions abound

DWDM provides 100s Gbps of capacityTransponders are required for an open architecture

Large scale deployments have been achieved IP directly over DWDM is a reality

ip over dmdw

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