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Optical Networking (part 2). Mark E. Allen, Ph.D. [email protected]. Review of Transmission (Transport) Technologies, Architectures and Evolution (Adapted from Shikuma (RIT) Notes. Asynchronous Data Rates. Digital Signal Level 0 DS0 64 Kb/s - PowerPoint PPT Presentation
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Review of Transmission(Transport) Technologies,
Architectures and Evolution(Adapted from Shikuma (RIT) Notes
Asynchronous Data Rates
•Digital Signal Level 0 DS0 64 Kb/s– internal to equipment
•Digital Signal Level 1 DS1 1.544 Mb/s– intra office only (600 ft limit)
•Digital Signal Level 3 DS3 45 Mb/s – 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
DS1 DS3
Asynchronous Optical Line SignalN x DS3s
28 DS1s = 1 DS324 DS0s = 1 DS1
DS0 (a digitized analog POTS circuit @ 64 Kbits/s)
Asynchronous Lightwave Systems typically transport traffic in multiples of DS3s i.e.... 1, 3, 12, 24, 36, 72 DS3s
DS0
Asynchronous NetworkingManual DS1 Grooming/Add/Drop
LW M13
DSX3
DS1
M13
DSX1
DSX1
DSX3
LW
• Manually Hardwired Central Office• No Automation of Operations• Labor Intensive• High Operations Cost• Longer Time To Service
DS3 DS3
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 RatesDS3s are STS-1 Mapped
DS3STS-1
51.84
Mbits/s
SONET Optical Line SignalOC-N = N x STS-1s
N is the number of STS-1s (or DS3s) transported
28 DS1s = 1 DS3 = 1 STS-124 DS0s = 1 DS1
(= 1 VT1.5)
DS1
DS0 (a digitized analog POTS circuit @ 64 Kbits/s)
DS0
OC level STM level Line rate (MB/s) OC-1 - 51.84 OC-3 STM-1 155.52 OC-12 STM-4 622.08 OC-48 STM-16 2488.32 OC-192 STM-64 9953.28
SONET and SDH
STESTELTE
LTE
PTEPTEPTEPTEPTEPTE
STESTELTELTE
PTEPTEPTEPTEPTEPTE
DS-3DS-3
DS-3DS-3
DS-3DS-3DS-3DS-3DS-3DS-3DS-3DS-3
OC-3 TMOC-3 TMOC-3 TMOC-3 TM
SONET LineSONET Path
SONET Section
TM = Terminal MultiplexorDS = Digital Signal
PTE = Path Terminating ElementLTE = Line Terminating ElementSTE = Section Terminating Element
SONET Layering for Cost Effective Operations
SONET Point-to-Point NetworkRepeater Repeater
TM TM
Section
Line
Path
STS-1FrameFormat Line
Overhead
SectionOverhead Path
Overhead
STS-1 Synchronous Payload Envelope
STS-1 SPE
Protection Schemes: 1 + 1
(Source) (Destination)
Working Facility
Protection Facility
1 + 1 Protection Switching(50% bandwidth utilization)
Network Protection
1 for N (1:N)
(Source) (Destination)
Working Facility
Protection Facility
1:n Protection Switching(Bandwidth Efficiencies)
...
123
Network Protection
Protection and Restoration
D1
S
D2
1 + 1
D1
S
D2
1:n
Path Protection Line Protection (Loopback)
UPSR
Unidirectional/Path Switched Ring (UPSR)
WorkProtect
Rx
Rx
TxRx
Tx
BLSR
Bidirectional/Line Switched Ring (BLSR)2 fiber, 4 fiber
WorkProtect
4 fiber supports span switching2 fiber doesn’t
Typical Deployment of UPSR and BLSR in RBOC Network
Regional Ring (BLSR)
Intra-Regional Ring (BLSR) Intra-Regional Ring (BLSR)
Access Rings (UPSR)
WB DACs
BB DACs
WB DACS = Wideband DACS - DS1 GroomingBB DACS = Broadband DACS - DS3/STS-1 GroomingOptical 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?
First Driver for DWDMLong Distance Networks
WD
M N
EW
DM
NE W
DM
NE
WD
M N
E
• Limited Rights of Way• Multiple BLSR Rings Homing to a few Rights of Way• Fiber Exhaustion
BLSR Fiber PairsBLSR Fiber Pairs
Key Development for DWDM Optical Fiber Amplifier
120 km
OC-48
OLSTERM
OLSRPTR
OLSRPTR
OLSTERM
120 km 120 km
Fiber Amplifier Based Optical Transport - 20 Gb/s
OC-48OC-48
OC-48
OC-48OC-48
OC-48OC-48
Conventional Optical Transport - 20 Gb/s
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTRTERM TERM
40km 40km 40km 40km 40km 40km 40km 40km 40km
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTRTERM TERM1310
RPTR1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTRTERM TERM1310
RPTR1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTRTERM
TERM1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTRTERM TERM1310
RPTR1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTRTERM TERM1310
RPTR1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
TERMTERM1310
RPTR1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTR
1310RPTRTERM
TERM
OC-48OC-48
OC-48OC-48
OC-48OC-48
OC-48OC-48
Increased Fiber Network Capacity
Transporting BroadbandTransporting Broadbandacross Transmission across Transmission
NetworksNetworksdesigned for Narrowbanddesigned for Narrowband
T1/T3/OC3FRS and CRS
ATMAccess
ATMAccess
ATMSwitch
Public/PrivateInternet Peering
ATMAccess
ATMAccess
AccessRouter
T1/T3 IPLeased-LineConnections
CoreRouter
CoreRouter
AccessRouter
AccessRouter
ATM Access
ATM Access
RAS
RAS
RAS
RAS
RAS
RAS
RAS
RAS
AccessRouter
AccessRouter
EtherSwitch
EtherSwitch
RAS
RAS
RAS
RAS
RAS
RAS
RAS
RAS
CoreRouter
CoreRouter
BackboneSONET/WDM RAS Farms
T1/T3 FRand ATM IPLeased-LineConnections
ATM Switch
ATMSwitch
ATMSwitch
ATMSwitch
CoreRouter
CoreRouter
Data SP
High Capacity Path Networking
•Existing SONET/SDH networks are a Existing SONET/SDH networks are a BOTTLENECKBOTTLENECK for Broadband Transport 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 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.and costly changes. Clearly upgrading the SONET/SDH network everytime broadband data interfaces are upgraded based increased IP traffic is not an appropriate solution.
Existing SDH-SONET Network
IP router
IP router IP router
STS-3c
STS-12c/48c/...
IP/SONET/WDM Network Architecture
Core IPNode
EMS
.
.
.
SONETADM/LT
OC-3/12[STS-3c/12c]
OC-12/48
OC-3/12[STS-3c/12c/48c]
SONET Transport Network
SONETNMS
Core IPNode
EMS
.
.
.
Access Routers/EnterpriseServers
OC-48
SONETADM/LT
SONETXC
WDMLT
WDMLT1, 2, ...
OC-3/12/48[STS-3c/12c/48c]
Pt-to-Pt WDM Transport Network
OC-3/12/48[STS-3c/12c/48c]
OTNNMS
IP = Internet ProtocolIP = Internet ProtocolOTN = Optical Transport NetworkOTN = Optical Transport NetworkADM = Add Drop MultiplexorADM = Add Drop MultiplexorWDM = Wavelength Division MultiplexingWDM = Wavelength Division Multiplexing
LT = Line TerminalLT = Line TerminalEMS = Element Management SystemEMS = Element Management SystemNMS = Network Management SystemNMS = Network Management System
Optical Network Evolution mirrorsSONET Network Evolution
Multipoint NetworkWDM Add/Drop
Point-to-Point WDM Line System
Optical Cross-ConnectWDM Networking OXC
i
WDMADM
WDMADM
k
IP/OTN Architecture
Core DataNode
EMS
.
.
.
OXC
mc: multi-channel interface(e.g., multi-channel OC-12/OC-48)
mcmcOptical Transport Network
OTNNMS
Core Data Node
EMS
.
.
.Access RoutersEnterprise Servers
OXC
OXC
Core Data Node
EMS
.
.
.
mc
mc
IP = Internet ProtocolIP = Internet ProtocolOTN = Optical Transport NetworkOTN = Optical Transport NetworkOXC = Optical Cross ConnectOXC = Optical Cross ConnectWDM = Wavelength Division MultiplexingWDM = Wavelength Division Multiplexing
EMS = Element Management SystemEMS = Element Management SystemNMS = Network Management SystemNMS = Network Management System
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 single-
layer 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
Couplerw1
w0
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
B
A
CD
E
FG
HI
J
K
LM
N
O
1
2
32
1
1
1
OXC
IP SONET
SONET
IP
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 sub-problems:– 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.
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
60200 m
128100 m
21500 m
38
27
9.3
4
1.2
dB loss / km
400 m
300 m
1 km
2 km
5 km
Visibility
60200 m
128100 m
21500 m
38
27
9.3
4
1.2
dB loss / km
400 m
300 m
1 km
2 km
5 km
Visibility
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
95
96
97
98
99
100
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Visibility (km)
Cum
ulat
ive
Tim
e (%
)
Tulsa, OK
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.
