Optical Networks Introduction - · PDF fileOptical Networks Introduction 27 August 2012, Belem, Para, ... Quiz (10 mins short ... WDM is the favorite multiplexing technology for optical

Optical Networks Introduction

27 August 2012, Belem, Para, Brazil Universitade Federal do Para (UFPA)

Dr. Cicek Cavdar, [email protected]

University of California, Davis

Istanbul Technical University

Optical Networks Lab (ONLab) Royal Institute of Technology, Stockholm, Sweden

Special thanks to Biswanath Mukherjee from UC-Davis and Aysegul Yayimli from ITU for the class material.

Optical Networks Introduction, Çiçek Çavdar

Course Program n  Optical Communication Networks: Introduction (Dia

27/08); n  Enabling Technologies (Dia 29/08); n  Optical access networks (passive optical networks

(PONs), Metro Optical Networks (Dia 31/08); n  Switched (Wavelength-Routed) Networks: Virtual

Topology Design (Dia 3/09); n  Routing and Wavelength Assignment (RWA) and

Wavelength Conversion (Dia 4/09); n  Survivability (Dia 5/09).


Evaluation and class material n  Class assignments n  Quiz (10 mins short questions before the class) n  Text Book: Optical WDM Networks, Biswanath Mukherjee, Springer n  Course material and all information to be found

at the course web site. Please visit frequently: http://www.lea.ufpa.br/index.php?option=com_content&view=article&id=418:curso-de-redes-opticas-dra-cicek-cavdar&catid=22:noticias&Itemid=39

Internet Traffic from 2006 to 2025

Source: Telegeography Optical Networks Introduction, Çiçek Çavdar

No. 8: Unsymmetry between Upstream and Downstream will be reduced or even disappeared

Sharing instead of downloads

?

Source: Picture from Mark Wegleitner @ verizon


World Internet Distribution 2007

Source: Miniwatts Marketing Group


Installed Volume of Optical Fiber is Fast Increasing

Source: Telegeography about submarine fiber system


Installed Fiber from now to 2025


Source: E.Desurvire @ Alcatel

Ethernet will play new roles in Optical Networks

1. Two Key Requirements in Core Networks n  Service availability n  Network survivability 2. Ethernet will reduce boundaries between metro/access

and core networks


From OTN (Optical Transport Networks) to SON (Service oriented Optical Networks)

Core networks will provide services, not only for transport; Services will be more diverse than ever. Source: Picture from Ovum RHK


Overview of Network Architecture


Hierarchical view §  Long haul

§  100s-1000s km §  Mesh

§  Metro (interoffice) §  10s of km §  Rings

§  Access §  a few km §  Hubbed rings, PONs

§  Users


Network Architecture

CERN

University

ISP

SLA SLA SLA SLA

User Requests

Management Plane

Applications and Services: L1-VPN, Grid Serv., VoD, IPTV, Video Conferencing

OC-48 OC-12

1

2

OC-24

Virtual Topology

Physical Topology

Virtual Channels

Data Plane

Provisioning Physical Channels

Provisioning Virtual Channels

Physical Topology

Virtual Topology

Virtual Channels

Control Plane


yesterday

today

tomorrow

5 Years

5 Years

Access Metro Backbone

Copper Optical with EB

DSL

Optical with EB

additional: color filter and optical amplifier

additional: optical switch, color converter, electronic bottleneck

Bottleneck is Shifting from Core to Metro/Access

Optical bottleneck (OB) will have more influence on network than electronic bottleneck (EB)

Optical Bottleneck additional: colorless converter

Optical Core additional: intelligent


Metro and Access are Merging



TE vs. NE vs. NP n  Traffic Engineering:

“Put the traffic where the bandwidth is” n  Network Engineering:

“Put the bandwidth where the traffic is” n  Network Planning:

“Put the bandwidth where the traffic is forecasted to be”


Traffic Engineering

n  Essentially a routing problem ¨ packets, packet flows, circuits

n  on-line dynamic problem, quick decision making n  Metric: blocking probability


Network Engineering n  As a network continues its operation, traffic

builds up, certain parts of the network becomes congested.

n  Additional capacity is needed to relieve the congestion.

n  Decision-making time is on the order of weeks/months.

n  Capacities may be asymmetric. n  Metric: exhaustion probability


Network Planning n  Planning network from scratch n  Decision-making timescale: years n  Given a set of traffic demands between nodes

design the network for minimum cost: ¨ Determine how much capacity to put on each link ¨ Route the traffic

n  Topology may or may not be given. n  Traffic forecasts are usually not “one snapshot”

event. n  A network planner may be given an annual

traffic forecast over an N-year period.


What is an Optical Network? n  Transmission: optical n  Switching:

¨ optical or electronic or hybrid ¨ circuit or packet or burst

n  Not necessarily all optical n  Most promising approach today:

¨ Connect any two routers with a direct bandwidth pipe of any capacity

¨  Increase or decrease or delete the capacity on demand

¨ Dynamically control the topology connecting routers


Advantages of Optics n  Fantastic for transmission

¨ Optical amplifier can simultaneously amplify all of the signals on all channels (~160) on a single fiber

n  Huge bandwidth: 50 Tbps on single fiber ¨ Compare it to electronic data rates of few Gbps

n  Low signal attenuation n  Low signal distortion n  Low power requirement n  Low cost


Optics-Electronics Mismatch n  50 Tbps vs. 10 Gbps n  How to exploit the fiber’s huge capacity?

¨  Introduce concurrency among multiple users ¨  Wavelength or frequency division multiplexing: WDM

n  WDM is the favorite multiplexing technology for optical

networks: ¨  End-user equipment needs to operate at the bitrate of the WDM

channel. ¨  Channel bitrate can be chosen arbitrarily: peak electronic

processing speed.


WDM n  The optical transmission spectrum is carved up

into a number of non-overlapping wavelength bands.

n  Each wavelength supports a single communication channel operating at any electronic speed.

n  Challenge is to design and develop appropriate network architectures, protocols, and algorithms.


Research on Optical WDM Networks n  Considerable activity over the past years.

¨ Check out the magazines and transactions: IEEE Communications, IEEE Network, ToN, JSAC, JLT, Optical Networking Magazine, Jrn. Photonic Networks, …

n  Overwhelming attendance at the WDM centered conferences and workshops. ¨  ICC, Globecom, Infocom, OFC, ECOC, ONDM, …

n  Many experimental prototypes are being deployed and tested by telecom providers in US, Europe and Japan.


Point to Point WDM Systems


Wavelength Add/Drop Multiplexers n  The WADM can be inserted on a physical fiber

link.


Passive Router

n  The wavelength on which an input port gets routed to an output port depends on a ‘routing matrix’ that is fixed.


Active Switch


Optical Transmission in Fiber n  Fiber is a thin filament of glass which acts as a

waveguide. Waveguide: A physical medium which allows the propagation of

electromagnetic waves like light.

n  Due to total internal reflection, light propagates the length of the fiber with little loss.

n  Light speed in vacuum: c = 3·108 m/s. n  Light can also travel through any transparent

material, but the speed is slower. n  The ratio of the speed of light in vacuum to that

in a material is the material’s refractive index n. nmat = c / cmat


Optical Transmission in Fiber n  When light travels from material of a given

refractive index to a material of a different refractive index, ¨  the angle at which the light is transmitted in the

second material depends on: n  the refractive indices and n  the angle at which light strikes the interface.

§  Snell’s Law: nasin Θa = nbsin Θb

§  If na > nb and Θa is greater than some critical value, the rays are reflected back into material a from its boundary with material b.

Θb

Θa

nb

na


Optical Transmission in Fiber n  Fiber consists of a core completely surrounded by a

cladding. n  Core and cladding consist of glass of different refractive

indices.

For light to travel down a fiber, the light must be inci-dent on the core-cladding surface at an angle greater than θcrit.


Critical Angle n  Typical delay of light in optical fiber is 5 µs/km

n  Single-mode vs. multimode fiber


Optical Transmitter n  Lasers are used as optical transmitter. n  The transmitters used in WDM networks often

require the capability to tune to different wavelengths.

n  Some primary characteristics of interest for tunable lasers are: ¨  the tuning range, ¨  the tuning time, ¨ whether the laser is continuously tunable (over its

tuning range) or discretely tunable (only to selected wavelengths).

Laser: Light Amplification by Stimulated Emission of Radiation


Types of Transmitters n  The table summarizes tuning range and time of

different types of lasers.

n  An alternative to tunable lasers is the laser array: A set of fixed-tuned lasers which are integrated into a single component, with each laser operating at a different wavelength.


Optical Receivers n  Optical filters transform the optical signal into electronic

signal. n  There are different types of tunable optical filters. n  These filters are characterized primarily by their tuning

range and tuning time. n  The tuning range specifies the range of wavelengths

which can be accessed by a filter. n  A wide tuning range allows systems to utilize a greater

number of channels. n  The tuning time of a filter specifies the time required to

tune from one wavelength to another.


Tunable Filters n  The table shows various types of filters and their

tuning range and time.


Alternate Receiving Devices n  An alternative to tunable filters is to use fixed

filters or grating devices. n  Grating devices typically filter out one or more

different wavelength signals from a fiber. n  Such devices may be used to implement optical

multiplexers and demultiplexers or receiver arrays.


Optical Amplifiers n  Although an optical signal can propagate a long distance -typically

80 km- before it needs amplification, for longer-distance links, it can benefit from optical amplifiers.

n  In a WDM system with electronic amplification: ¨  Each wavelength would need to be separated before being amplified

electronically, ¨  then recombined before being retransmitted.

All-optical amplification: n  To eliminate the need for optical multiplexers and demultiplexers in

amplifiers, optical amplifiers must boost the optical signals without first converting them to electrical signals.

Drawback: n  Optical noise, as well as the signal, will be amplified. n  Also, the amplifier introduces spontaneous emission noise.


Optical Amplifiers n  All-optical amplification may differ from opto-electronic

amplification in that it may act only to boost the power of a signal, not to restore the shape or timing of the signal. This type of amplification is known as 1R (regeneration/reamplifying).

n  In 2R (regeneration and reshaping), the optical signal is converted to an electronic signal which is then used to directly modulate a laser.

n  The optical signals may be amplified by first converting the information stream into an electronic data signal, and then retransmitting the signal optically. Such amplification is referred to as 3R (regeneration, reshaping, and reclocking/retiming).


Types of Amplifiers n  Semiconductor laser amplifier

¨ Fabry-Perot ¨ Traveling-wave

n  Doped-fiber amplifier ¨ EDFA ¨ PDFFA

n  Raman amplifier


Switching Elements n  According to the signal carriers, there are

¨ optical switching and ¨ electronic switching.

n  In the switching granularity point of view, there are two basic classes, ¨ circuit switching corresponding to wavelength routing, ¨ cell switching corresponding to optical packet

switching and optical burst switching. n  As far as the transparency of signal is

considered, there are ¨ opaque switching and ¨  transparent switching.


Optical Cross-connect (OXC) n  An optical cross-connect (OXC) switches optical signals

from input ports to output ports. n  A basic cross-connect element is the 2 × 2 crosspoint

element. n  It routes optical signals from two input ports to two output

ports and has two states: cross state and bar state.


1024x1024 Clos Fabric


MEMS n  Micro-electro mechanical systems. n  Believed to be the most promising technology for large-scale optical

cross-connects. n  Based on mirrors, membranes, and planar moving waveguides. n  The two major approaches are 2-Dimensional and 3-Dimensional

approaches. n  The 3-D Optical MEMS based on mirrors is popular because it is

suitable for compact, large-scale switching fabrics. ¨  The optical signals passing through the optical fibers at the input port

are switched independently by the MEMS mirrors with two-axis tilt control and then focused onto the optical fibers at the output ports.

¨  In the switch, any connection between input and output fibers can be accomplished by controlling the tilt angle of each mirror.

¨  The 3D MEMS-based OOO switches is in sizes ranging from 256 x 256 to 1000 x 1000 bi-directional port machines.

¨  Encouraging research show that 8000 x 8000 ports will be practical within the foreseeable future.


3D MEMS Optical Switch

？

For questions please send e-mail to [email protected]

Note: In the presentation, most material are cited from related sources. Since some material cited here may be confidential, or not be allowed to be circulated, please directly contact their own sources if you will use them.


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Optical Networks Introduction - · PDF fileOptical Networks Introduction 27 August 2012, Belem, Para, ... Quiz (10 mins short ... WDM is the favorite multiplexing technology for optical