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
DS1
1.544 Mb/s
DS3
45 Mb/s
– internal to equipment
•Digital Signal Level 1
– intra office only (600 ft limit)
•Digital Signal Level 3
– 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
DS0 (a digitized analog
POTS circuit @ 64 Kbits/s)
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
LW
D
S
X
3
M13
D
S
X
1
D
S
X
1
DS3
DS3
DS1
• Manually Hardwired Central Office
• No Automation of Operations
• Labor Intensive
• High Operations Cost
• Longer Time To Service
M13
D
S
X
3
LW
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
•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
DS0 (a digitized analog
POTS circuit @ 64 Kbits/s)
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
SONET and SDH
OC level
OC-1
OC-3
OC-12
OC-48
OC-192
STM level
Line rate (MB/s)
STM-1
STM-4
STM-16
STM-64
51.84
155.52
622.08
2488.32
9953.28
SONET Layering for Cost
Effective Operations
DS-3
PTE
LTE
DS-3
PTE
STE
STE
LTE
DS-3
PTE
PTE
PTE
PTE
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
DS-3
DS-3
DS-3
SONET Point-to-Point Network
Repeater
Repeater
TM
TM
Section
Line
Path
STS-1
Frame
Format
Section
Overhead
Line
Overhead
Path
Overhead
STS-1 Synchronous
Payload Envelope
STS-1 SPE
Protection Schemes: 1 + 1
Network Protection
Working Facility
(Source)
Protection Facility
1 + 1 Protection Switching
(50% bandwidth utilization)
(Destination)
1 for N (1:N)
Network Protection
Working Facility
..
.
(Source)
Protection Facility
1:n Protection Switching
(Bandwidth Efficiencies)
1
2
3
(Destination)
Protection and Restoration
Path Protection
Line Protection (Loopback)
D1
D1
D2
S
D2
S
1+1
1:n
UPSR
Rx
Tx
Rx
Work
Protect
Tx
Rx
Unidirectional/Path Switched Ring (UPSR)
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
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
• Some Review Questions
– What does the acronym DWDM mean?
– What was the fundamental technology that
enabled the DWDM network deployments?
WDM NE
BLSR Fiber Pairs
WDM NE
First Driver for DWDM
Long Distance Networks
• Limited Rights of Way
• Multiple BLSR Rings Homing to a few Rights of Way
• Fiber Exhaustion
BLSR Fiber Pairs
Key Development for DWDM
Optical Fiber Amplifier
40km
40km
40km
40km
40km
40km
40km
40km
40km
1310
1310
1310
1310
1310
1310
1310
1310
TERM
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
TERM
1310
1310
1310
1310
1310
1310
1310
1310
TERM
TERM
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
1310
1310
1310
1310
1310
1310
1310
1310
TERM
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
TERM
1310
1310
1310
1310
1310
1310
1310
1310
TERM
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
TERM
1310
1310
1310
1310
1310
1310
1310
1310
TERM
TERM
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
1310
1310
1310
1310
1310
1310
1310
1310
TERM
TERM
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
1310
1310
1310
1310
1310
1310
1310
1310
TERM
TERM
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
1310
1310
1310
1310
1310
1310
1310
1310
TERM
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
TERM
Conventional Optical Transport - 20 Gb/s
OC-48
OC-48
OC-48
OC-48
OC-48
OC-48
OC-48
OC-48
120 km
120 km
OLS
TERM
OLS
RPTR
120 km
OLS
RPTR
OLS
TERM
Fiber Amplifier Based Optical Transport - 20 Gb/s
Increased Fiber Network Capacity
OC-48
OC-48
OC-48
OC-48
OC-48
OC-48
OC-48
OC-48
Transporting Broadband
across Transmission
Networks
designed for
Narrowband
Public/Private
Internet Peering
Data SP
Core
Core
Router
Router
RAS
RAS
EtherSwitch
Core
Access
Router
Router
RAS
RAS
RAS
Access
ATM
Switch
Core
ATM
Switch
RAS
Router
EtherSwitch
Router
RAS
RAS
RAS
ATM
Switch
Core
ATM
Switch
Router
RAS
ATM Access
Access
Router
RAS
RAS
Core
RAS
Router
Access
RAS
Router
ATM Access
RAS
RAS
Backbone
SONET/WDM
T1/T3/OC3
FRS and CRS
ATM
Access
Switch
Router
T1/T3 IP
Leased-Line
Connections
ATM
ATM
ATM
ATM
Access
Access
Access
Access
T1/T3 FR
and ATM IP
Leased-Line
Connections
RAS Farms
High Capacity Path
Networking
IP router
IP router
STS-12c/48c/...
IP router
STS-3c
Existing SDH-SONET Network
•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/SONET/WDM Network Architecture
OC-3/12
[STS-3c/12c]
OC-48
EMS
Access
Routers/
Enterprise
Servers
.
.
.
SONET
XC
SONET
NMS
SONET
ADM/LT
OC-3/12
[STS-3c/12c/48c]
SONET
ADM/LT
EMS
OC-12/48
SONET Transport Network
Core IP
Node
Core IP
Node
.
.
.
OTN
NMS
OC-3/12/48
[STS-3c/12c/48c]
WDM
LT
l1, l2, ...
WDM
LT
Pt-to-Pt WDM Transport Network
OC-3/12/48
[STS-3c/12c/48c]
LT = Line Terminal
IP = Internet Protocol
EMS = Element Management System
OTN = Optical Transport Network
NMS = Network Management System
ADM = Add Drop Multiplexor
WDM = Wavelength Division Multiplexing
Optical Network Evolution
mirrors
SONET Network Evolution
Point-to-Point WDM
Line System
Multipoint Network
WDM Add/Drop
Optical Cross-Connect
WDM Networking
l1
l2
lN
l1
l2
lN
WDM
ADM
WDM
ADM
li
lk
OXC
IP/OTN Architecture
EMS
Core Data
Node
mc: multi-channel interface
(e.g., multi-channel OC-12/OC-48)
.
.
.
mc
OTN
NMS
OXC
EMS
Access Routers
Enterprise Servers
.
.
.
Core Data
Node
EMS
OXC
OXC
mc
mc
Optical Transport Network
mc
Core Data
Node
.
.
.
IP = Internet Protocol
EMS = Element Management System
OTN = Optical Transport Network
NMS = Network Management System
OXC = Optical Cross Connect
WDM = Wavelength Division Multiplexing
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?
• 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
Protection & Restoration of
Optical Networks
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
Classification of Schemes
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
– Shorter restoration time
– Less efficient.
– Can only fix link failures
• Path-based
– longer restoration time
– More efficient.
Dedicated vs. Multiplexed
Backup
• Dedicated backup
– More robust
– Less efficient.
• Backup multiplexing
– Less robust
– More efficient.
Primary Backup MUX
• Wavelength channel to be shared by a
primary and one or more backup paths
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
• 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
• 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.
2-Fiber WDM Ring
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.
4-Fiber WDM Ring
After a Link Failure
4-Fiber WDM Ring
After a Node Failure
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
• 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.
2X2 Switch
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
Protection Cycles
Protection Cycles (cont’d)
Network With Default
Protection Switching
Network After a Link Failure
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)
• 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 - cycles
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
• Why resilience in multilayer networks?
– Avoid contention between different singlelayer recovery schemes.
– Promote cooperation and sharing of spare
capacity
PANEL: Protection Across
Network Layers
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
WDM
Network Architecture
Classes of WDM Networks
• Broadcast-and-select
• Wavelength routed
• Linear lightwave
Broadcast-and-Select
Passive
Coupler
w0
w1
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)
• 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
F
J
B
A
K
l1
l3
SONET
l
1
l2
IP
l1
IP
E
l2
l1
D
O
N
C
L
M
SONET
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)
• To establish a lightpath, need to determine:
– A route
– Corresponding wavelengths on the route
• RWA problem can be divided into two subproblems:
– Routing
– Wavelength assignment
• Static vs. dynamic lightpath establishment
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)
• 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
• 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
• 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
•
•
•
•
•
First-Fit (FF)
Least-Used (LU)
Most-Used (MU)
Max_Sum (MS)
Relative Capacity Loss (RCL)
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
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)
Mark E. Allen
SignalWise LLC
mallen@signalwise.com
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
• 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
• 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
• 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 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
dB loss / km
5 km
1.2
2 km
4
1 km
9.3
500 m
21
400 m
27
300 m
38
200 m
60
100 m
128
lossdB(L)  10 * L/Visibility
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
• 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
The statistics of visibility
Visibility vs. Cumulative Time
100
Cumulative Time (%)
99
98
97
96
95
0
0.2
0.4
0.6
0.8
1
Visibility (km)
Tulsa, OK
1.2
1.4
1.6
1.8
2
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
• 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.