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Fiber-Optic Networks. Xavier Fernando Ryerson Communications Lab. OSI – 7 Layer Model. This Course. Network Categories. Optical Networks are categorized in multiple ways: All Optical (or Passive Optical) Networks Vs Optical/Electrical/Optical Networks Based on service area

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Fiber optic networks

Fiber-Optic Networks

Xavier Fernando

Ryerson Communications Lab

Network categories
Network Categories

Optical 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

Long metro access networks

Long Haul Network

Long/Metro & Access Networks

Different network specs
Different Network Specs

Core - Combination of switching centers and transmission systems connecting switching centers.

Access- that part of the network which connects subscribers to their immediate service providers

LWPF : Low-Water-Peak Fiber, DCF : Dispersion Compensating Fiber, EML : Externally modulated (DFB) laser

Local area access networks
Local Area / Access Networks

Local-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

Metropolitan area regional area networks
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

Wide area networks wan
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

Fiber in the access end
Fiber in the Access End

Fiber increasingly reaches the user

Passive optical networks


Passive Optical Networks

Passive optical networks1
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

Passive optical network pon topologies
Passive Optical Network(PON) Topologies




Network elements of pon
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 OpticalSwitch: Divert the incoming light wave into a particular output

Fig 10 4 fused fiber coupler directional coupler
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


Try Ex. 10.2

Star coupler
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)

Star network
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

Add drop bus coupler losses
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)

Star tree bus networks
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 & busnetworks are similar

Linear bus versus star network
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))

Brief history
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

Synchronous optical networks
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

Synchronous optical networks1
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

Digital transmission hierarchy t standards
Digital Transmission Hierarchy (T-Standards)

Additional framing bits stuffed at each level to achieve synchronization

Not possible to directly add/drop sub-channels




Predominant before optical era

Fig 12 6 basic sts n sonet frame
Fig. 12-6: Basic STS-N SONET frame

STS-N signal has a bit rate equal to N times 51.84Mb/s

Ex: STS-3  155.52 Mb/s

Sonet add drop multiplexers
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

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)

2 fiber unidirectional path switched ring
2-Fiber Unidirectional Path Switched Ring

Node 1-2


Node 2-4; OC-3

Ex: Total capacity OC-12 may be divided to

four OC-3 streams

2 fiber upsr
2-Fiber UPSR

  • Rx compares the signals received via the primary and protection paths and picks the best one

  • Constant protection and automatic switching

4 fiber bi directional line switched ring blsr
4-Fiber Bi-directional Line Switched Ring (BLSR)

All secondary fiber left for protection

Node 13; 1p, 2p 31; 7p, 8p

Blsr fiber fault reconfiguration
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

Blsr node fault reconfiguration
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

Generic sonet network
Generic SONET network

Large National Backbone


Local Area

Versatile SONET equipment

are available that support wide

range of configurations, bit rates

and protection schemes

Some terms
Some Terms

Topology – 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)

The optical layer
The Optical Layer

The OL is a wavelength based concept lies just above the physical layer

Wdm networks
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

Wdm networks1
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

Wdm p p link
WDM P-P Link

Several OC-192 signals can be carried,

each by one wavelength

Single hop broadcast and select wdm
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



Multi hop architecture
Multi-hop Architecture

Four node broadcast and select multihop network

Each node transmits at fixed set of wavelengths and receive fixed set of wavelengths

Multiple hops required depending on destination

Ex. Node1 to Node2: N1N3 (1), N3N2 (6)

No tunable filters required but throughput is less

Fig 12 17 data packet
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)

Shuffle net
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 net

Ex: Max. 2 X 2 - 1= 3 hops

Wavelength routing
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 

12x12 optical cross connect oxc architecture
12X12 Optical Cross-Connect (OXC) Architecture

This uses space


Optical cross connects oxc
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

Ex 12 5 4x4 optical cross connect
Ex: 12.5: 4X4 Optical cross-connect

Wavelength switches are electronically configured

Wavelength conversion to avoid contention