fiber-optic networks xavier fernando ryerson communications lab
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Fiber-Optic Networks
Xavier Fernando
Ryerson Communications Lab
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OSI – 7 Layer Model
This Course
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Network CategoriesOptical Networks are categorized in multiple ways:• All Optical (or Passive Optical) Networks Vs
Optical/Electrical/Optical Networks• Based on service area
– Long haul, metropolitan and access network– Wide area (WAN), metropolitan area (MAN) or local
area network (LAN)
• Depending on the Protocol– SONET, Ethernet, ATM, IP
• Number of wavelengths – single wavelength, CWDM or DWDM
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Long Haul Network
Long/Metro & Access Networks
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Global Network Hierarchy
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Who Uses it?
Span (km)
Bit Rate(bps)
Multi-plexing
Fiber Laser Receiver
Core/LongHaul
Phone Company, Gov’t(s)
~103 ~1011
(100’s of Gbps)
DWDM/TDM
SMF/ DCF
EML/ DFB
APD
Metro/Regional
Phone Company, Big Business
~102 ~1010
(10’s of Gbps)
DWDM/CWDM/TDM
SMF/ LWPF
DFB APD/ PIN
Access/LocalLoop
Small Business, Consumer
~10 ~109
(56kbps- 1Gbps)
TDM/ SCM/
SMF/ MMF
DFB/ FP PIN
LWPF : Low-Water-Peak Fiber, DCF : Dispersion Compensating Fiber, EML : Externally modulated (DFB) laser
CoreCore - Combination of switching centers and transmission systems connecting switching centers.
AccessAccess- that part of the network which connects subscribers to their immediate service providers
Different Network Specs
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Local Area / Access NetworksLocal-area networks• Interconnection on number of local terminals• Main technologies: Ethernet, Fast Ethernet, Gigabit
Ethernet (better for multiple access)• Usually passive star or bus networks
Access networks• The first (or last) network segment between customer
premises and a WAN or MAN– Usually owned by a Local Exchange Carrier
• PON is getting popular• Fiber-copper technologies: HFC (fiber-coaxial cable) or
DSL (fiber-twisted pair) • Fiber-wireless and free-space optics are also used
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Metropolitan-area/regional-area networks
• A MAN or RAN covers a North American metropolitan area, or a small to medium-sized country in Europe or Asia
• Optical ring/mesh topologies with adequate back-up and protection
• Main technologies: SONET, ATM, Gigabit & 10-Gigabit Ethernet, DWDM
• Non-optical technologies: T1, T3, Frame Relay• Several LANs could be connected to MAN
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Wide-Area Networks (WAN)• Long haul inter-city connections • Either government-regulated or in the public
network environment– WANS originated in telephony
• Main technologies: SONET/SDH, ATM, WDM– Voice circuits vs. data packets– Non-optical technologies:T1(1.544 Mb/s)/E1(2.048
Mb/s), DS-3 (44.736 Mb/s ), Frame Relay– Standards bodies include ITU-T, IETF, ATM Forum,
Frame Relay Forum, IEEE
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Fiber in the Access End
Fiber increasingly reaches the user
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PASSIVE OPTICAL NETWORKS
PON
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Passive Optical Networks• There is no O/E conversion in between the
transmitter and the receiver (one continuous light path)
• Power budget and rise time calculations has to be done from end-to-end depending on which Tx/Rx pair communicates
• Star, bus, ring, mesh, tree topologies
• PON Access Networks are deployed widely
The PON will still need higher layer protocols (Ethernet/IP etc.) to complete the service
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Passive Optical Network(PON) Topologies
BUS
RING
STAR
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Network Elements of PON• Passive Power Coupler/Splitter: Number of
input/output ports and the power is split in different ratios. – Ex: 2X2 3-dB coupler; 80/20 coupler
• Star Coupler: Splits the incoming power into number of outputs in a star network
• Add/Drop Bus Coupler: Add or drop light wave to/from an optical bus
• All Optical Switch: Divert the incoming light wave into a particular output
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Fig. 10-4: Fused-fiber coupler / Directional coupler
• P3, P4 extremely low ( -70 dB below Po)• Coupling / Splitting Ratio = P2/(P1+P2)• If P1=P2 It is called 3-dB coupler
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Definitions
2 1 2Splitting (Coupling) Rat = )i (o P P P
0 1 2=10 LogExcess Lo [ss ( ] )P P P
=1In 0 sert Log[ion Loss ] in outP P
3 0= 10 LoCrosstalk g( P P )
Try Ex. 10.2
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Star Coupler
• Incoming total power is equally split between N outputs
• Usually bidirectional
• Splitting Loss = 10 Log N
• Excess Loss = 10 Log (Total Pin/Total Pout)
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Star Network
Power Budget:
Worst case power budget need to be satisfied
Ps-Pr = 2lc + α(L1+L2) + Excess Loss + 10 Log N + System Margin
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Linear bus topology
,
10log ( 1) 2 ( 2) 2oC thru TAP i
L N
PN L NL N L L NL
P
Ex. 12.1
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Add-Drop Bus-Coupler Losses
Connector loss (Lc) = 10Log (1-Fc)Tap loss (Ltap) = -10 Log (CT) Throughput loss (Lth) = -20 Log (1-CT) Intrinsic loss (Li) = -10 Log (1-Fi)
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Star, Tree & Bus Networks• Tree networks are widely deployed in the
access front
• Tree couplers are similar to star couplers (expansion in only one direction; no splitting in the uplink)
• Bus networks are widely used in LANs
• Ring networks (folded buses with protection) are widely used in MAN
• Designing ring & bus networks are similar
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Linear Bus versus Star Network
• The loss linearly increases with N in bus (ring) connections while it is almost constant in start (tree) networks (Log(N))
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SONETSynchronous Optical Network
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Brief History• Early (copper) digital networks were
asynchronous with individual clocks resulting in high bit errors and non-scalable multiplexing
• Fiber technology made highly Synchronous Optical Networks (SONET) possible.
• SONET standardized line rates, coding schemes, bit-rate hierarchies and maintenance functionality
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Synchronous Optical Networks
• SONET is the TDM optical network standard for North America (called SDH in the rest of the world)
• De-facto standard for fiber backhaul networks
• OC-1 consists of 810 bytes over 125 us; OC-n consists of 810n bytes over 125 us
• Linear multiplexing and de-multiplexing is possible with Add-Drop-Multiplexers
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SONET/SDH Bandwidths
SONET Optical Carrier Level
SONET Frame Format
SDH level and Frame Format
Payload bandwidth (kbps)
Line Rate (kbps)
OC-1 STS-1 STM-0 50,112 51,840
OC-3 STS-3 STM-1 150,336 155,520
OC-12 STS-12 STM-4 601,344 622,080
OC-24 STS-24 – 1,202,688 1,244,160
OC-48 STS-48 STM-16 2,405,376 2,488,320
OC-192 STS-192 STM-64 9,621,504 9,953,280
OC-768 STS-768 STM-256 38,486,016 39,813,120
OC-3072 STS-3072 STM-1024 153,944,064 159,252,480
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Synchronous Optical Networks
• SONET is the TDM optical network standard for North America (It is called SDH in the rest of the world)
• We focus on the physical layer• STS-1, Synchronous Transport Signal
consists of 810 bytes over 125 us • 27 bytes carry overhead information• Remaining 783 bytes: Synchronous
Payload Envelope
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SONET/SDH Bit Rates
SONET Bit Rate (Mbps) SDH
OC-1 51.84 -
OC-3 155.52 STM-1
OC-12 622.08 STM-4
OC-24 1244.16 STM-8
OC-48 2488.32 STM-16
OC-96 4976.64 STM-32
OC-192 9953.28 STM-64
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Digital Transmission Hierarchy (T-Standards)
Additional framing bits stuffed at each level to achieve synchronization
Not possible to directly add/drop sub-channels
DS1
DS2
DS3
Predominant before optical era
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Fig. 12-5: Basic STS-1 SONET frame
STS-1=(90*8bits/row)(9rows/frame)*125 /frame 51.84 Mb/ss
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Fig. 12-6: Basic STS-N SONET frame
STS-N signal has a bit rate equal to N times 51.84 Mb/sEx: STS-3 155.52 Mb/s
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SONET Add Drop Multiplexers
ADM is a fully synchronous, byte oriented device, that can be used add/drop OC sub-channels within an OC-N signal
Ex: OC-3 and OC-12 signals can be individually added/dropped from an OC-48 carrier
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SONET/SDH Rings
• SONET/SDH are usually configured in ring architecture to create loop diversity by self healing
• 2 or 4 fiber between nodes
• Unidirectional/bidirectional traffic flow
• Protection via line switching (entire OC-N channel is moved) or path switching (sub channel is moved)
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2-Fiber Unidirectional Path Switched Ring
Ex: Total capacity OC-12 may be divided to four OC-3 streams
Node 1-2OC-3
Node 2-4; OC-3
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2-Fiber UPSR
• Rx compares the signals received via the primary and protection paths and picks the best one
• Constant protection and automatic switching
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4-Fiber Bi-directional Line Switched Ring (BLSR)
Node 13; 1p, 2p 31; 7p, 8p
All
sec
onda
ry f
iber
left
for
pro
tect
ion
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BLSR Fiber Fault Reconfiguration
In case of failure, the secondary fibers between only the affected nodes (3 & 4) are used, the other links remain unaffected
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BLSR Node Fault Reconfiguration
If both primary and secondary are cut, still the connection is not lost, but both the primary and secondary fibers of the entire ring is occupied
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Generic SONET networkLarge National Backbone
City-wide
Local Area
Versatile SONET equipmentare available that support wide range of configurations, bit rates and protection schemes
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DO THE REST
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Network Terminologies
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Some TermsTopology – logical manner in which nodes linked
Switching – transfer of information from source to destination via series of intermediate nodes;
Circuit Switching – Virtual circuit established
Packet Switching – Individual packets are directed
Switch – is the intermediate node that stream the incoming information to the appropriate output
Routing – selection of such a suitable path
Router – translates the information from one network to another when two different protocol networks are connected (say ATM to Ethernet)
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The Optical Layer
The OL is a wavelength based concept lies just above the physical layer
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Optical Cross Connects
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WDM Networks
• Single fiber transmits multiple wavelengths WDM Networks
• One entire wavelength (with all the data) can be switched/routed
• This adds another dimension; the Optical Layer
• Wavelength converters/cross connectors; all optical networks
• Note protocol independence
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WDM Networks• Broadcast and Select: employs passive
optical stars or buses for local networks applications– Single hop networks– Multi hop networks
• Wavelength Routing: employs advanced wavelength routing techniques– Enable wavelength reuse– Increases capacity
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WDM P-P Link
Several OC-192 signals can be carried, each by one wavelength
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Single hop broadcast and select WDM
• Each Tx transmits at a different fixed wavelength• Each receiver receives all the wavelengths, but
selects (decodes) only the desired wavelength• Multicast or broadcast services are supported• Dynamic coordination (tunable filters) is required
Star Bus
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A Single-hop Multicast WDM Network
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Multi-hop Architecture
Four node broadcast and select multihop networkEach node transmits at fixed set of wavelengths
and receive fixed set of wavelengthsMultiple hops required depending on destinationEx. Node1 to Node2: N1N3 (1), N3N2 (6) No tunable filters required but throughput is less
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Fig. 12-17: Data packet
In multihop networks, the source and destination information is embedded in the header
These packets may travel asynchronously (Ex. ATM)
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Shuffle Net
Shuffle Net is one of several possible topologies in multihop networks
N = (# of nodes) X (per node)
Max. # of hops = 2(#of-columns) –1
(-) Large # of ’s
(-) High splitting loss
A two column shuffle netEx: Max. 2 X 2 - 1= 3 hops
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Wavelength Routing
• The limitation is overcome by: reuse, routing and conversion
• As long as the logical paths between nodes do not overlap they can use the same
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12X12 Optical Cross-Connect (OXC) Architecture
This uses space switching
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Optical Cross Connects (OXC)
• Works on the optical domain
• Can route high capacity wavelengths
• Space switches are controlled electronically
• Incoming wavelengths are routed either to desired output (ports 1-8) or dropped (9-12)
• What happens when both incoming fibers have a same wavelength? (contention)
• Try Ex. 12.5
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Ex: 12.5: 4X4 Optical cross-connect
Wavelength switches are electronically configuredWavelength conversion to avoid contention