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2NANOG 5/24/99 www.cisco.com
OutlineOutline
Optical Transmission Fundamentals
DWDM Systems
IP over DWDM
3NANOG 5/24/99 www.cisco.com
Its Analog Transmission
AttenuationDispersion
Nonlinearity
Waveform after 1000 kmTransmitted data waveform
Reflectance
4NANOG 5/24/99 www.cisco.com
Fiber AttenuationFiber Attenuation
Telecommunications industry uses two windows: 1310 & 1550
1550 window is preferred for long-haul applications
Less attenuation
Wider window
Optical amplifiers
1310window
1550window
5NANOG 5/24/99 www.cisco.com
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)
6NANOG 5/24/99 www.cisco.com
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
7NANOG 5/24/99 www.cisco.com
Polarization Mode DispersionPolarization Mode Dispersion
Most severe in older fiber
Caused by several sources
Core shape
External stress
Material properties
Becomes an issue at OC-192
8NANOG 5/24/99 www.cisco.com
Four-Wave Mixing (FWM) 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
9NANOG 5/24/99 www.cisco.com
OutlineOutline
Optical Transmission Fundamentals
DWDM Systems
IP over DWDM
10NANOG 5/24/99 www.cisco.com
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
11NANOG 5/24/99 www.cisco.com
EDFA SchematicEDFA 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
12NANOG 5/24/99 www.cisco.com
DWDM System Design
1550
1551
1552
1553
1554
1555
1556
1557
01234567
01234567
Amplify DW
DM
Filt
er
Op
tic
al C
om
bin
er
15xx nm 1310 nmReamplifyReshapeRetime
Rx Tx1310 nm
Rx
Ex
tern
al
Mo
du
lato
r
Laser
15xx nm
13NANOG 5/24/99 www.cisco.com
DWDM State-of-the-ArtDWDM 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!
14NANOG 5/24/99 www.cisco.com
OutlineOutline
Optical Transmission Fundamentals
DWDM Systems
IP over DWDM
15NANOG 5/24/99 www.cisco.com
Synchronization for IP over DWDMSynchronization 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
16NANOG 5/24/99 www.cisco.com
Protection for IP over DWDMProtection 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
17NANOG 5/24/99 www.cisco.com
Ciena 40 DWDMCiena 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
18NANOG 5/24/99 www.cisco.com
Nortel 16 DWDM and OC-192 RingNortel 16 DWDM and OC-192 Ring
PRS
Working
Protect
Lack of transponders prohibits direct connections at OC-192
19NANOG 5/24/99 www.cisco.com
Conclusion - IP over DWDM 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
