Optical Networking (part 2)

1
Optical Networking (part 2)

• Mark E. Allen, Ph.D.
• mark.allen_at_ieee.org

2
Review of Transmission(Transport)
Technologies,Architectures and
Evolution(Adapted from Shikuma (RIT) Notes
3
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

4
Asynchronous Digital Hierarchy
DS0 (a digitized analog POTS circuit _at_ 64
Kbits/s)
DS3
DS1
DS0
Asynchronous Optical Line Signal N x DS3s
28 DS1s 1 DS3
24 DS0s 1 DS1
Asynchronous Lightwave Systems typically
transport traffic in multiples of DS3s i.e.... 1,
3, 12, 24, 36, 72 DS3s
5
Asynchronous NetworkingManual DS1
Grooming/Add/Drop
D S X 1
D S X 1
D S X 3
D S X 3
LW
LW
M13
M13
DS3
DS3
DS1

• Manually Hardwired Central Office
• No Automation of Operations
• Labor Intensive
• High Operations Cost
• Longer Time To Service

6
Some Review Questions

• What does the acronym SONET mean?
• What differentiates SONET from Asynchronous
  technology?
• What does the acronym SDH mean?

7
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

8
SONET RatesDS3s are STS-1 Mapped
DS0 (a digitized analog POTS circuit _at_ 64
Kbits/s)
STS-1 51.84 Mbits/s
DS1
DS0
DS3
SONET Optical Line Signal OC-N N x STS-1s N is
the number of STS-1s (or DS3s) transported
28 DS1s 1 DS3 1 STS-1
24 DS0s 1 DS1 ( 1 VT1.5)
9
SONET and SDH
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
10
SONET Layering for Cost Effective Operations
DS-3
DS-3
DS-3
DS-3
DS-3
DS-3
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
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SONET Point-to-Point Network
Repeater
Repeater
TM
TM
Section
Line
Path
Section Overhead
STS-1 Frame Format
STS-1 Synchronous Payload Envelope STS-1 SPE
Path Overhead
Line Overhead
12
Protection Schemes 1 1
Network Protection
Working Facility
Protection Facility
(Source)
(Destination)
1 1 Protection Switching (50 bandwidth
utilization)
13
1 for N (1N)
Network Protection
Working Facility
1
2
3
Protection Facility
(Source)
(Destination)
1n Protection Switching (Bandwidth Efficiencies)
14
Protection and Restoration
Path Protection
Line Protection (Loopback)
D1
D1
D2
D2
S
S
1 1
1n
15
UPSR
Rx
Tx
Rx
Work Protect
Tx
Rx
Unidirectional/Path Switched Ring (UPSR)
16
BLSR
4 fiber supports span switching 2 fiber doesnt
Work Protect
Bidirectional/Line Switched Ring (BLSR) 2 fiber,
4 fiber
17
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
DACSDCSDXC
18
Emergence of DWDM

• Some Review Questions
• What does the acronym DWDM mean?
• What was the fundamental technology that enabled
  the DWDM network deployments?

19
First Driver for DWDMLong Distance Networks
BLSR Fiber Pairs
BLSR Fiber Pairs
WDM NE

• Limited Rights of Way
• Multiple BLSR Rings Homing to a few Rights of
  Way
• Fiber Exhaustion

20
Key Development for DWDM Optical Fiber Amplifier
Increased Fiber Network Capacity
21
Transporting Broadbandacross Transmission
Networksdesigned for Narrowband
22
Data SP
Public/Private Internet Peering
EtherSwitch
EtherSwitch
ATM Access
ATM Access
Backbone SONET/WDM
T1/T3 IP Leased-Line Connections
RAS Farms
ATM Switch
T1/T3 FR and ATM IP Leased-Line Connections
T1/T3/OC3 FRS and CRS
23
High Capacity Path Networking
IP router
IP router
IP router
STS-12c/48c/...
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.

24
IP/SONET/WDM Network Architecture
OC-3/12 STS-3c/12c
OC-3/12 STS-3c/12c/48c
OC-48
EMS
EMS
Access
OC-12/48
.
.
Core IP Node
Routers/
.
Core IP Node
SONET Transport Network
.
Enterprise
.
Servers
.
OTN NMS
OC-3/12/48 STS-3c/12c/48c
OC-3/12/48 STS-3c/12c/48c
l1, l2, ...
Pt-to-Pt WDM Transport Network
LT Line Terminal EMS Element Management
System NMS Network Management System
IP Internet Protocol OTN Optical Transport
Network ADM Add Drop Multiplexor WDM
Wavelength Division Multiplexing
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Optical Network Evolution mirrorsSONET Network
Evolution
Point-to-Point WDM Line System
Multipoint NetworkWDM Add/Drop
WDMADM
WDMADM
li
lk
Optical Cross-ConnectWDM Networking
OXC
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IP/OTN Architecture
EMS
.
Core Data Node
.
.
mc multi-channel interface (e.g., multi-channel
OC-12/OC-48)
mc
OTN NMS
OXC
EMS
EMS
OXC
OXC
mc
.
.
Access Routers
Core Data Node
Core Data Node
.
mc
.
Optical Transport Network
Enterprise Servers
mc
.
.
IP Internet Protocol OTN Optical Transport
Network OXC Optical Cross Connect WDM
Wavelength Division Multiplexing
EMS Element Management System NMS Network
Management System
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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

28
What are the restoration requirements?

• Recovery from failures
• Equipment failures
• Cable cuts
• Four 9s?
• Down 52 minutes per year.
• Five 9s?
• 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

29
Protection Restoration of Optical Networks
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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

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Classification of Schemes
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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

33
Link Based vs. Path Based

• Link-based
• Shorter restoration time
• Less efficient.
• Can only fix link failures

• Path-based
• longer restoration time
• More efficient.

34
Dedicated vs. Multiplexed Backup

• Dedicated backup
• More robust
• Less efficient.

• Backup multiplexing
• Less robust
• More efficient.

35
Primary Backup MUX

• Wavelength channel to be shared by a primary and
  one or more backup paths

36
Resilience in Optical Networks

• Linear Systems
• 11 protection
• 11 protection
• 1N 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

37
Unidirectional WDM Path Protected Rings

• 11 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.

38
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.

39
2-Fiber WDM Ring
40
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.

41
4-Fiber WDM Ring.
42
4-Fiber WDM Ring After a Link Failure
43
4-Fiber WDM Ring After a Node Failure
44
Path Layer Mesh Protection

• Protect Mesh as a single unit
• Pre-computed routes
• 11 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

45
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.

46
2X2 Switch
47
Protection Cycles (contd)

• 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

48
Protection Cycles
49
Protection Cycles (contd)
50
Network With Default Protection Switching
51
Network After a Link Failure
52
P cycles

• Ring like restoration needed for some client
  signals.
• Mesh topologies bandwidth efficient.
• P cyclesRing like speeds, Mesh like capacity.
• Addresses the speed limitation of mesh
  restoration.

53
P cycles (contd)

• 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.

54
P - cycles
55
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.

56
Resilience in Multilayer Networks

• Why resilience in multilayer networks?
• Avoid contention between different single-layer
  recovery schemes.
• Promote cooperation and sharing of spare capacity

57
PANEL Protection Across Network Layers
58
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

59
WDM

• Network Architecture

60
Classes of WDM Networks

• Broadcast-and-select
• Wavelength routed
• Linear lightwave

61
Broadcast-and-Select
w0
Passive Coupler
w1
62
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.

63
WRN (contd)

• 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

64
A WR Network
65
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

66
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

67
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

68
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

69
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

70
Wavelength Assignment

• For the network with wavelength conversion
  capability, wavelength assignment is trivial
• For the network with wavelength continuity
  constraint, use heuristics

71
Wavelength Assignment under Wavelength Continuity
Constraint

• First-Fit (FF)
• Least-Used (LU)
• Most-Used (MU)
• Max_Sum (MS)
• Relative Capacity Loss (RCL)

72
First-Fit

• All the wavelength are indexed with consecutive
  integer numbers
• The available wavelength with the lowest index is
  assigned

73
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

74
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.

75
Applications for Free Space Optics (FSO)

• Mark E. Allen
• SignalWise LLC
• mallen_at_signalwise.com

76
Outline

• Where does FSO fit in the network?
• FSO design issues
• What is the performance of FSO?
• Applications for FSO
• Future directions

77
Intro to FSO

• The last-mile problem continues to be an issue.
• Fiber doesnt 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

78
Lasers through the air

• Laser sources normally in the 850nm, 1310 or 1550
  ranges.
• Some debate on whats 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.

79
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

80
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)

81
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.

82
Visibility and corresponding loss
lossdB(L) ? 10 L/Visibility
83
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.

84
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.

85
Sample budget
86
The statistics of visibility
87
Ex Computing expected uptime

• Assume link with 27dB weather margin
• 1km in length
• 400m visibility gtgt 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.

88
FSO Applications

• Metro Fiber Extension
• Services providers extending their reach into
  areas where they dont have (or cant lease)
  fiber
• OC-N mux can be terminated at the end of the FSO
  system
• 11 Redundancy with fiber can also used.