Transcript Optical Transport - CS Course Webpages

Transmission Technology:
what’s the big deal?
Hint: We are not talking about “manual” or
“automatic” transmissions for cars!
– Data goes in, data comes out
– No complex operations, no settings
– Just a piece of glass
Cisco
Catalyst 6509
10GE
“Transmission System”
Fiber pair <80km
(Transmit and Receive)
Cisco
Catalyst 6509
Systems
Systems
Transmission Technology
• The simplest transmission system is a fiber
jumper from one piece of client equipment
to another
Essentially a Semaphore
Power
11111010101
Time
• The transmitter turns a laser on
and off 10 billion times per
second. The receiver converts
the light back to an electrical
signal.
• For non-WDM systems, the
source laser is a nontemperature controlled source
that consumes a broad spectral
bandwidth.
1550nm
Power
20nm
“Wavelength”
• Nominal frequencies are
typically 1310 or 1550.
Optical Limitations
• Attenuation in fiber (dB loss)
• Chromatic Dispersion (CD)
• Polarization Mode Dispersion (PMD)
• Non-linear Optical Fiber effects
Due to non-linear index of refraction:
• Four Wave Mixing (FWM)
• Self Phase Modulation (SPM)
• Cross Phase Modulation (XPM)
Due to stimulated scattering:
• Raman
• Brillouin
• Ultimately: Optical Signal to Noise Ratio (OSNR)
Fraction of Power
Remaining
Fiber Loss
1
0.8
0.6
80 km  100x loss
0.4
0.2
0
0
20
40
60
80
Distance (km)
100
Optical Amplifiers Compensate Loss
80-100km
Input
Amplifier
After Loss
After Amplifier
Added Noise
Power
Wavelength
Chromatic Dispersion
300
20
250
Time/Distance
200
150
10
Frequency (GHz)
0
100
50
-10
0
-20
0.8
0.6
0.4
Frequency components
of modulated signal
travel at different
velocities in fiber
0.2
0
Power
Data distortion from dispersion
Propagation Distance
10101
0110
010
160 km
80 km
1’s
0 km
0’s
Time
NRZ distortion very pattern dependent!
Dispersion Compensation
• For longer reaches, dispersion compensation
devices provide dispersion of opposite sign
and slope to the transmission fiber
• The precision required in these devices
scales as the square of the bit rate
• Compensation is incorporated in systems
and is available for common fiber types
• To get more information on a single fiber, use more
wavelengths!
• DWDM systems use temperature controlled lasers to
lock laser wavelength to a very specific frequency.
Power (dBm)
0
-10
-20
-30
1570
1580
1590
Wavelength (nm)
1600
DWDM
0.6nm
Example Fiber Nonlinearity (FWM)
Input
•25 km Dispersion-Shifted Fiber
•3 mW/Channel
Output
Number of Mixing Terms:
M = ½(N3 – N2)
= 31,200 terms for 40ch.
Optical System Limitations
• Optical amplifiers generate noise
– Total noise is proportional to number of amplifiers x gain
of each amplifier
• Various effects limit the amount of optical power
that can be launched
• At the receiver, the signal power must be some
fixed ratio larger than the noise (OSNR)
Combined, these effects constrain the length
and capacity of a given system.
Transmission System Building Blocks
•Fiber
•Optronics
•In-Line Amplification (ILA)
•Erbium-Doped Fiber Amplifiers (EDFA)
•Dispersion Compensation
•Gain Equalization
•Optical Add/Drop Multiplexing (OADM)
•Terminal
•Optical Muxing/DeMuxing
•Transceivers
•Tributaries
Transmission Technology and Fiber Choice
• Fiber Choice
– 100s of thousands of fiber miles and multiple national
networks were installed over the last several years
• New fiber types, large count cables
• Factors affecting performance
– Chromatic Dispersion (CD)
– Polarization-Mode Dispersion (PMD)
– Fiber Non-linearity (FWM, SPM, XPM, Raman, etc)
Commonly Available Fiber Types
Type
Dispersion @1550
Vintages
SMF
17 ps/nm/km
1980-
E-LEAF
4 ps/nm/km
1996-
TrueWave RS
4.5 ps/nm/km
1996-
TrueWave Classic
2 ps/nm/km
1992-1996
DSF
0 ps/nm/km
1990-1992
SMF-LS
-1 ps/nm/km
1992-1995
Fibers before 1993 may have significant PMD!
1550nm Low-Loss Wavelength Band
30
Dispersion (ps/nm)
Fiber Loss (dB/km)
1300nm
20
1550nm
window
10
0
-10
-20
-30
1250
1350
1450
1550
1650
Wavelength (nm)
At 1550nm, wide region of low-loss wavelengths is irresistible for
WDM systems even with high dispersion.
Conventional Single-Mode Fiber (SMF)
30
20
Dispersion (ps/nm)
• First single-channel systems
operated at 1310nm (good
laser materials)
S C L
10
• Zero dispersion point at
1310nm.
0
• WDM systems moved to
1550nm: wide low-loss
window, but higher dispersion
-10
-20
-30
1250
1350
1450
1550
1650
• Disp.-Limit = 1000 km at
2.5Gb/s in SMF, so not really
a problem for OC-48.
Wavelength (nm)
D(1530-1565nm) = 16 - 19 ps/nm*km
DD = 0.065 ps/nm2km
Aeff = 85 um2
Dispersion-Shifted Fiber (DSF) – Oops!
30
S C L
Dispersion (ps/nm)
20
• Move the zero dispersion point
to 1550nm, so no dispersion
compensation required for
1550nm signals, even at 10G.
10
0
• However, lack of dispersion at
1550 aggravates FWM and
severely limits optical power
levels for C-band DWDM
systems. Thus, DSF was a
“bad idea” for DWDM.
-10
-20
-30
1250
1350
1450
1550
Wavelength (nm)
1650
• Substantial amounts of DSF in
some U.S. networks.
• Small effective core area, so
very nonlinear.
Dispersion-Shifted Fiber
S-Band
C-Band
L-Band
Dispersion (ps/nm)
20
16
12
8
4
0
-4
1510
1530
1550
1570
1590
1610
Wavelength (nm)
L-band systems attractive for DSF
because of reasonable dispersion values
Lucent TrueWave “Classic”
S-Band
C-Band
L-Band
Dispersion (ps/nm)
20
• Some dispersion is good
for DWDM systems
because the optical power
is reduced, thus reducing
FWM.
16
12
8
4
0
-4
1510
1530
1550
1570
1590
1610
Wavelength (nm)
SMF-28
DSF
TWC
D(1550nm) = ~ 2 ps/nm*km
Lucent TrueWave - RS
S-Band
C-Band
L-Band
• If some dispersion is good
for DWDM, then more
must be even better!
Dispersion (ps/nm)
20
16
12
• Increase dispersion from
2ps to 4ps/nm*km @ 1550
8
• Significantly reduced
dispersion slope…
4
0
• But small effective area
-4
1510
1530
1550
1570
1590
1610
Wavelength (nm)
SMF-28
DSF
TWC
TWRS
D(1530-1565nm) = 2.6 – 6.0 ps/nm*km
D(1565 – 1600nm) = 4.0 - 8.6 ps/nm*km
DD = 0.045 ps/nm2km
Aeff = 55 um2
Corning E-Leaf
Dispersion (ps/nm)
S-Band
C-Band
L-Band
20
• 4 ps/nm*km average dispersion
16
• Larger dispersion slope, but
12
• Increased effective core area to
equal SMF
8
4
0
-4
1510
1530
1550
1570
1590
1610
Wavelength (nm)
SMF-28
DSF
TWC
TWRS
E-LEAF
D(1530-1565nm) = 2.5 - 6 ps/nm*km
DD ~ 0.083 ps/nm2km
Aeff = 75 um2
Transmission System Building Blocks
•Fiber
•Optronics
•In-Line Amplification (ILA)
•Erbium-Doped Fiber Amplifiers (EDFA)
•Dispersion Compensation
•Gain Equalization
•Optical Add/Drop Multiplexing (OADM)
•Terminal
•Optical Muxing/DeMuxing
•Transceivers
•Tributaries
Most sites in inter-city deployments are
In-Line Amplifiers (ILAs)
Boston
ILA
Ann Arbor
ILA
ILA
ILA
New York
ILA
ILA
ILAs include:
ILA
Chicago
ILA
ILA
Princeton
Philadelphia
ILA
ILA
Baltimore
•Optical Amplification
•Dispersion Compensation
•Gain Equalization
•Management
ILA
Washington DC
107
ILA
97
Richmond
90
ILA
Memphis
75
Nashville
103
90
ILA
ILA
104
ILA
Dallas100
ILA
ILA
89
105
108
ILA
ILA
95
ILA
108
89
ILA
Birmingham
105
95
90
101
ILA
Atlanta
ILA
91
ILA
Raleigh
Charlotte
ILA
101
91
Huntsville
ILA
102
ILA
96
101
95
89
83
91
ILA
109
80
90
ILA
81
ILA
Little Rock
ILA
104
ILA
ILAGE
Terminal
OADM
Splice
Spools of
Erbium-doped
fiber are gain
medium.
Erbium-Doped Fiber Amplifier (EDFA)
Stage 1
Stage 2
EDF
EDF
Pump
Pump
Pump
Pump
G
F
F
VOA
Two-stage EDFA
Laser pumps
provide power.
Dispersion
Compensator
DCM
Compensates for accumulated
chromatic dispersion.
Distributed Raman Amplifier
Plant fiber is
gain medium!
Couples pump power (800mW to 1W)
in counter-propagating direction.
Coupler
Pump
Pump
Pump
Pump
Compensates for accumulated
chromatic dispersion.
Dispersion
Compensator
Laser pumps provide power.
Pump frequencies 100nm < ls
DCM
Gain Equalization
Gain equalization is required due to:
•Amplifier gain is frequency (channel) dependent
•Fiber attenuation is frequency (channel) dependent
•Channels interact with each other in fiber (FWM, Raman, etc.)
Channels accumulate power variations resulting in reduced OSNR!
1000 km Spectrum with DSE
1000 km Spectrum without DSE
10
0
-2
5
-4
-6
Optical Power (dBm)
Optical Power (dBm)
0
-8
-10
-12
-5
-10
-14
-16
-15
-18
-20
1565
1570
1575
1580
1585
1590
1595
1600
1605
1610
-20
1565
1570
1575
1580
1585
1590
1595
1600
1605
1610
Gain equalization restores optimal channel power across the spectrum.
Various mechanisms are available:
•Demux-VOA-Mux
•Grating-LCD
Wavelength (nm)
Wavelength (nm)
DGE Architecture
Ingress composite
signal
Egress composite
signal
Collimating
Lens
Collimating
Lens
First grating disperses
wavelengths.
Imaging
Lens
LCD
Array
Grating
Grating
Imaging
Lens
LCD array selectively
attenuates individual
wavelengths under
software control.
Second grating converges
wavelengths.
Sites can also be Terminals or OADM.
Boston
ILA
Ann Arbor
ILA
ILA
ILA
New York
ILA
ILA
ILA
Chicago
ILA
ILA
Princeton
Philadelphia
ILA
ILA
Terminals and OADMs include:
Baltimore
ILA
Memphis
75
103
90
ILA
ILA
104
ILA
Dallas100
ILA
ILA
ILA
97
Richmond
90
ILA
ILA
108
89
105
ILA
ILA
108
89
Birmingham
105
95
90
101
ILA
Atlanta
ILA
ILA
Raleigh
Charlotte
ILA
101
91
ILA
95
91
91
Huntsville
ILA
102
83
ILA
ILA
104
Nashville
95
89
Washington DC
107
96
101
ILA
109
80
90
ILA
81
ILA
Little Rock
•Optical Muxing and De-muxing
•Amplification and Dispersion Compensation
•Channel termination on client equipment
•Regeneration
•Management
ILA
ILAGE
Terminal
OADM
Splice
Terminals provide for:
Terminals
•Optical amplification and dispersion compensation
•Optical muxing, de-muxing, and gain equalization
•OE/EO termination/generation of line-side optical wavelengths
•FEC generation/recovery and performance monitoring
•Electrical muxing/de-muxing of tributary signals
•OE/EO termination/generation of client connections (tributaries)
•OEO Regeneration
•Management
Terminals exist at:
•Locations at the end of a route
•Locations where regeneration is required
•Locations at intermediate sites on a route via OADM or GOADMTM
•Locations in a metro area via Distributed TerminalsTM
Basic Terminal Architecture
Client
Optical
Optical
Dispersion
Equipment Tributaries Transceivers ITU l Muxing Amplification Compensation
DCM
10GE
Transceiver
OC-192
Transceiver
ATM
4xOC48
Transceiver
Ethernet
4x1GE
Transceiver
Trib-side
Line-side
MUX
TDM
Post
Amp
Mgmt
De-MUX
Router
PreAmp
DCM
Regeneration
Regeneration is required in traditional long-haul (LH) systems to extend reach
beyond a single system’s capabilities.
•On LH systems, regeneration is generally required every 500-600km.
•Required due to OSNR limitations in LH system’s optical design:
•No or limited FEC
•Simple NRZ modulation
•Simplistic dispersion compensation
•No gain equalization
•Operation in C-band or multiple bands
Ultra-Long-Haul (ULH) systems achieve reaches of 2000 to 6000km, thus
eliminating the need for most regeneration.
Regeneration takes two basic forms:
Regeneration
1. “Back-to-Back” terminals with patches between tributaries.
DCM
PostAmp
Terminal
MUX
DCM
Transceiver
Transceiver
Transceiver
Transceiver
Transceiver
Transceiver
Transceiver
Transceiver
Transceiver
Transceiver
Transceiver
Transceiver
Transceiver
Transceiver
Transceiver
MUX
De-MUX
Post
Amp
Transceiver
Post
Amp
DCM
De-MUX
DCM
PreAmp
Terminal
Regeneration takes two basic forms:
Regeneration
1. “Back-to-Back” terminals with patches between tributaries.
2. Special “regeneration” modules.
DCM
DCM
Regenerator Module
Regenerator Module
Regenerator Module
MUX
De-MUX
Post
Amp
Post
Amp
Regenerator Module
DCM
Regenerator Module
Regenerator Module
Regenerator Module
Regenerator
De-MUX
Regenerator Module
MUX
PostAmp
DCM
PreAmp
Regeneration adds cost and complexity to networks!
Boston
ILA
Ann Arbor
ILA
ILA
ILA
New York
ILA
ILA
ILA
Chicago
ILA
ILA
Princeton
Philadelphia
ILA
ILA
Example of LH system with 5-span reach:
Baltimore
•12 regeneration sites have been added
•Some systems are “short” due to city placement
•Some regens are in locations that are difficult to service (MoNLA)
•Provisioning express wavelengths becomes very difficult
•Incremental wavelengths become very expensive
ILA
Washington DC
107
ILA
97
Richmond
90
ILA
Memphis
75
Nashville
103
90
ILA
ILA
104
ILA
Dallas100
ILA
MoNLA
89
105
108
ILA
ILA
95
ILA
108
89
ILA
Birmingham
105
95
90
101
ILA
Atlanta
ILA
91
ILA
Raleigh
Charlotte
ILA
101
91
Huntsville
ILA
102
ILA
96
101
95
89
83
91
ILA
109
80
90
ILA
81
ILA
Little Rock
ILA
104
ILA
ILAGE
Terminal
OADM
GOADMTM
Splice
Optical Add/Drop Multiplexers (OADM)
On LH or ULH systems, OADMs are utilized to add and/or drop wavelengths at
intermediate sites (non-terminals) while allowing “express” wavelengths to
continue in the optical domain.
Terminal
Terminal
OADM
TXR
TXR
ILAs
TXR
TXR
TXR
Site “A”
OADM
TXR
Site “B”
TXR
TXR
Site “C”
There are two basic types of OADM architectures:
•Static (a.k.a. “Fixed” or “Banded”)
•Dynamic
Site “D”
Static OADM
“Fixed” or “banded” OADM designs pre-determined which wavelengths are
added/dropped based on static filters placed during the initial installation:
•Advantages: Cheap capital costs.
•Disadvantages:
Requires precise fore-knowledge of add/drop configuration
Non-flexible static configuration that is difficult to change
“Express” wavelengths in add/drop band are regen’d at OADM sites
OADM
TXR
TXR
OADM
ILAs
Channels are statically
dropped via filters
during the initial
installation.
TXR
TXR
TXR
TXR
TXR
TXR
Static OADM
Non-dropped wavelengths
are optically passed
through.
Static Thin-Film Filter
(TFF) selects specific
wavelengths to be
dropped.
TFF
TFF
EDF
EDF
DCM
Pump
G
F
F
VOA
Pump
Pump
Pump
OADM
Typically, 4 to 8 specific
channels are dropped.
Terminal
Dmx
Mux
Wavelengths are
optically de-muxed.
RRR
x x x
TTT
x x x
Receivers perform OEO
conversion to client
signal.
R
“Express” wavelengths
that are dropped must be
regen’d (OEO).
Dynamic OADM
“Dynamic” OADMs allow wavelengths to be added/dropped on an individual
wavelength basis via dynamically re-configurable devices:
•Advantages:
Wavelength topology can be dynamically changed to match needs.
Minimization of unnecessary OEO of express wavelengths
Minimized operational costs (no visits to intermediate sites)
•Disadvantages: More expensive capital costs.
OADM
TXR
TXR
OADM
ILAs
Individual channels are
dynamically dropped via
software control of
switching devices.
TXR
TXR
TXR
TXR
TXR
TXR
3dB coupler splits optical
power and “broadcasts” all
wavelengths to drop port.
DCM
EDF
Software controlled DGE blocks
dropped channels and gain equalizes
“through” channels
Dynamic OADM
Coupler
EDF
DGE
Coupler
EDF
Pump
Pump
Pump
Pump
Pump
Pump
OADM
All wavelengths appear on drop
port!
Wavelengths are
optically de-muxed.
Receivers perform OEO
conversion to client signal only
for “dropped” wavelengths.
Terminal
Dmx
Mux
RRR
x x x
TTT
x x x
R
Only “added” wavelengths
are coupled back into
route.
Transmitters perform OEO
conversion from client signal
only for “added” wavelengths.
Generalized OADM (GOADMTM)
“Generalized” OADMs allow individual wavelengths to be cross-connected
between different routes without leaving the optical domain.
•Useful at fiber junctions.
•Cost effective at high express channel counts
TXR
Channels are dynamically
cross-connected via
software control of
switching device.
TXR
GOADMTM
OADM
TXR
TXR
TXR
ILAs
TXR
TXR
TXR
TXR
TXR
Washington DC becomes a GOADMTM
Boston
ILA
Ann Arbor
ILA
ILA
ILA
New York
ILA
ILA
ILA
Chicago
ILA
ILA
Princeton
Philadelphia
ILA
ILA
Wavelengths can be provisioned, completely optically,
between any two points without regeneration up to the
maximum system reach.
Baltimore
ILA
Washington DC
107
ILA
97
Richmond
90
ILA
Memphis
75
Nashville
103
104
ILA
90
ILA
Dallas100
ILA
ILA
89
105
108
ILA
ILA
95
ILA
108
89
ILA
Birmingham
105
95
90
101
ILA
Atlanta
ILA
91
ILA
Raleigh
Charlotte
ILA
101
91
Huntsville
ILA
102
ILA
96
101
95
89
83
91
ILA
109
80
90
ILA
81
ILA
Little Rock
ILA
104
ILA
•
ILA
ILAGE
Terminal
OADM
GOADMTM
Splice
DCM
MUX
Transceiver
Transceiver
DCM
De-MUX
PreAmp
MUX
Terminal
50km
Post
Amp
DCM
Transceiver
Transceiver
Metro Solutions - Distributed TerminalTM
Transceiver
Transceiver
DCM
MUX
Transceiver
Transceiver
Terminal
PreAmp
Terminal
DCM
De-MUX
Transceiver
Transceiver
Post
Amp
Transceiver
De-MUX
Transceiver
DCM
Post
Amp
PreAmp
Distributed Terminals allow sets of wavelengths to
be extended into a metropolitan area up to 50km.
Metro Solutions - Tributary Extension
Tributary interfaces may be optically extended to remote locations via:
•Extended reach tributary optics for single channel over dark fiber:
• IR-1 (20km@1310), IR-2 (40km@1550)
• LR-1 (40km@1310), LR-2 (80km@1550)
10GE
• 10GE LR (40km) and ER (80km)
• GigE 1000Base-ZX (100km)
•CWDM
•8 wavelengths of GigE/OC-48 up to 80km
•Passive external muxing
•GBICs and SFFPs available
•ITU DWDM
•Up to 32 channels of 10GE/OC192 up to 80km
•Passive external muxing
•ITU Grid DWDM MSAs available
Transceiver
OC-192
Transceiver
4xOC48
Transceiver
8x1GE
Transceiver
Eliminates separate metro systems for distribution in metro area.
Metro Solutions - GOADMTM (Metro Switching Application)
Metro connectivity can be achieved with
GOADMTM:
• Supports Metro connectivity and ULH
connectivity completely optically.
To DEN
DALLAS
To ATL
Gateway
ULH
Path
• More cost-effective “Metro-reach”
transceivers can be utilized within a city for
terminal-to-terminal connectivity.
• “ULH/XLH-reach” transceivers can be
Working
Path
Protection
Path
Metro
Locations
utilized for inter-city wavelengths.
• Both card variations can exist in same
system simultaneously.
• Diverse Metro routes can be supported for
protection applications.
Metro
Xcvr
ULH
Xcvr
Metro
Xcvr
Terminal
Regen
GOADM
Router/BXC
Metro Xcvr
ULH Xcvr
It’s a Complex Problem
• Long haul systems are impacted by a variety of
effects
• The design of these systems requires a mix of
experts
– Optical effects
– Electronics
– Software