1

Optical Networks

Jason JueThe University of Texas at Dallas

Course Details

Instructor: Jason JueE-mail: jjue@utdallas.edu URL: http://www.utdallas.edu/~jjue/optical/

Lectures: Thursday 2-5 pm

Course Description: Introduction to optical networks. Topics include: enabling technologies, wavelength-division multiplexing, wavelength-routed optical networks, virtual topology design, routing and wavelength assignment, network control and management, protection and restoration, traffic grooming, optical packet switching, optical burst switching, optical access networks.

Course References

Textbook: • B. Mukherjee, Optical WDM Networks, Springer, 2006

Additional References: • R. Ramaswami and K. Sivarajan, Optical Networks: A Practical

Perspective, second edition, Morgan Kaufmann 2001• Selected papers from research literature

Grading

• Assignments: 25%• Exam: 25%• Project: 50%

Course Project

• The project will involve selecting a topic in optical networks and evaluating protocols, architectures, or schemes related to the selected topic.

• Projects may involve one or more of the following:– Implementation of optical network protocols or applications in C,

C++, Java, etc.– Development of a computer simulation to study optical network

characteristics and to evaluate optical network architectures and protocols

– Development of an analytical model for evaluating network behavior and performance

– Formulation and solution of network optimization problems

• Project presentations will be held at the end of the semester.

Outline of Course• Introduction

– Overview and motivation– Historical evolution– Research issues

• Optical components and technology• Wavelength-routed (circuit-switched) optical networks

– Static network design – RWA, logical topology design, traffic grooming– Dynamic network design – RWA, signaling, blocking probability analysis– Protection and restoration

• Optical burst switching– Signaling– Contention resolution– Scheduling– QoS

• Photonic packet switching– Contention resolution – buffering, deflection, wavelength conversion– QoS

• Optical metro and access networks

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The Need for More Bandwidth

• Growing bandwidth demands driven by– Growth of the Internet

• Number of hosts and users increasing exponentially• Higher access rates

– Emerging high-bandwidth applications• Scientific/GRID computing – petabytes of information• File-sharing – composes majority of Internet traffic• IPTV – killer app for fiber to the home?• IP telephony, video conferencing

• In addition to providing raw bandwidth, network must also provide services to support needs of applications

Optical Networks

• Optical networks are critical for satisfying these growing demands– What is an optical network?– How can an optical network provide the necessary bandwidth and

services?– What is the state of technology and deployment?

What is an Optical Network?• Network in which data is transmitted using

optical signals• Elements of an optical network

– Optical transmission system• Transmission medium• Transmitters (lasers, LEDs)• Receivers (photodetector)

– Switching/interconnection elements• Electronic

– Circuit-based (SONET,SDH)– Packet-based (IP, Ethernet)

• Optical– Circuit-based (Optical cross-connect)– Packet-based – Burst-based

– Software and protocols• Routing, connection establishment,

contention resolution, protection, etc.

Optical Communications

• Communication system characterized by:– Frequency (wavelength) of signal– Propagation medium

• Wavelength:• Optical communication systems

– Frequency range: 1014 – 1015 Hz (3 μm to .3 μm)– Medium: Optical fiber, free-space optics

;λ fc= m/s103 8×=c

Why Optical Communications?

• Optical communication systems provide high bandwidth and low attenuation (power loss)– Typical copper media bandwidth:

• Telephone line - 1.1 MHz• CAT5 cable (Ethernet) - 100 MHz• Coaxial cable - 1 GHz

– Typical copper media attenuation:• CAT5 – 200 dB/km at 100 MHz• Coaxial cable – 10-20 dB/km (90% - 99% loss/km)

– Potential fiber bandwidth: ~50 THz– Fiber attenuation: 0.2 dB/km

• Other benefits of fiber– Resistant to electromagnetic interference– Resistant to corrosion

Attenuation of Light in Fiber

• Amount of attenuation (loss per km) depends on wavelength of light– dB = 10 log (Pin/Pout)– At 1.5 μm: 0.2 dB/km ~ 5% loss/km

• Bandwidth:

Hz)1075.3( 14× Hz)1067.1( 14×

λλ2

Δ⋅=Δcf

3

Utilizing Fiber Bandwidth

• Problem: Peak electronic transmission rates limited to 40 Gbps• Approaches for increasing bandwidth:

– Increase transmission rates (100 Gbps and beyond)– Install more fiber– Multiplex signals from different sources onto a single fiber

• Multiplexing Approaches:– Optical Time Division Multiplexing (OTDM)

• Interleave bits of different electronic signal streams• Requires synchronization

– Wavelength Division Multiplexing (WDM)• Signals on different wavelengths multiplexed onto same fiber• Each wavelength can operate at peak electronic rates

Cable and Fiber Deployment(10000’s-km)

• Source: KMI Research

Annual Fiber Deployment (Thousands of Miles)

• Source: KMI Corp.

1,3056,7112,1132006

1,0255,4681,5532005

9324,2251,2432004

8083,3559322003

7462,6419322002

2,889 5,5672,4852001

5,2826,1846,0762000

CLECILECIXCYear

IXC = Interexchange Carrier (AT&T, Sprint, MCI)ILEC = Incumbent Local Exchange Carrier (SBC, GTE)CLEC = Competitive Local Exchange Carrier

Optical TDM

• Interleave bits of different electronic signal streams• Requires synchronization• Dispersion

Wavelength Division Multiplexing

• Signals on different wavelengths multiplexed onto same fiber• Each wavelength can operate at peak electronic rates

404040

Evolution of Optical Fiber Communication

• 1950’s - Fibers used for medical imaging applications– Loss of 1 dB/m (20% loss/m or 99% loss after 20 m)

• 1960 - Invention of laser– Development of free-space optical communication systems

• 1966 - Charles Kao proposes optical fiber for communications• 1970 - First low-loss fiber developed at Corning by Maurer,

Keck, and Schultz– Attenuation of 17 dB/km

• 1977 - First commercial system deployed by AT&T– Multimode fiber– Attenuation of 2 dB/km– 45 Mbps over 7 km distance – limited by modal dispersion

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Evolution of Optical Fiber Communication

• Early 80’s - Deployment of single-mode systems– Attenuation of 0.5 dB/km for 1300 nm laser– 180 Mbps over 20-40 km distance – limited by attenuation

• Mid 80’s - Deployment of 1550 nm single-mode systems– Attenuation of 0.2 dB/km– 400 Mbps over 40-80 km – limited by chromatic dispersion

• Early 90’s - Development of Erbium-doped fiber amplifiers (EDFA)– Enabled all-optical amplification of signals in 1550 nm band– 2.5 Gbps over 600 km

• Mid 90’s - WDM systems deployed– 40 wavelengths at 2.5 Gbps per wavelength– Emerging systems capable of 100’s wavelengths at 40 Gbps per

wavelength

Telecommunication Network Overview

Optical Network Architecture Evolution

• Long-haul, metro, metro access– Point-to-point systems– Add-drop systems– Wavelength-routed networks– Optical packet/burst-switched networks

• Last-mile access– Twisted pair– Coax– Hybrid fiber coax networks– Passive optical networks (PONs) for FTTH/FTTP– Broadcast-and-select optical networks?

• Local area networks– Ethernet– Wireless– Ethernet over fiber

Point-to-Point Systems• Point-to-point systems

– Fiber replaces copper– Switching still done electronically– Deployed in most long-haul backbone networks

• Electronic switching: SONET – OC-192 (10 Gb/s), OC-48 (2.5 Gb/s)– Can be used for Ethernet connections

• Design issue – how to increase link capacity– Multifiber solution – best for short distances– WDM solution – best for longer distances (> 50 km)– Higher electronic speed solution, e.g. OC-768 (40 Gb/s)

Add-Drop Systems

• Add-drop systems– Typically used in ring or linear network topologies– Wavelengths can traverse node all-optically– Reduces cost (number of transmitters/receivers at each node)– Reduces electronic processing requirements

Add-Drop Systems

• Reconfigurable optical add-drop multiplexers (ROADMS)– Allow add-drop function to be reconfigured dynamically– Increasingly being deployed in long haul and metro networks– Provides greater flexibility to service providers

• Reconfiguration can be automated• Quick activation of new services

– Partially driven by prospect of IPTV in metro networks

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Optical Circuit-Switched (OCS) Networks

• Wavelength-routed systems– Optical switching of wavelengths from input fibers to output fibers– Optical cross-connects provide switching at wavelength granularity– Configuration of optical cross-connect may be either static or dynamic

Wavelength-Routed Networks

• Can establish lightpaths – optical end-to-end connections • Spatial re-use of wavelengths• Switching may be all-optical (transparent) or may involve

conversion of the signal to electronics (opaque)• In absence of wavelength converters, lightpath must occupy

same wavelength on entire route – wavelength continuity constraint

Optical Cross-Connect (OXC) Configurations

O/E E/OO/E/O O/E/OElectrical

coreElectrical-core OXC

O/E/O O/E/OO/E/O O/E/OOptical

core

Optical-core OXC(Opaque)

O/E/O O/E/OOptical

coreFully-optical OXC

(Opaque)

Opticalcore

All-Optical Network(Transparent)

• Opaque OXCs have been deployed in long haul networks

“Opaque” vs. “Transparent” OXC

• Opaque– Allows regeneration of signal– Allows conversion from one wavelength to another– Must be aware of bit rate and signal format– OXC and interfaces more expensive

• Transparent– Bit-rate-independent: can increase bit rate without upgrading

equipment– Lower-cost interfaces– Imposes wavelength-continuity constraint if no all-optical

wavelength converters are available– Optical signal quality issues: limits to how far a signal can be

transmitted all-optically

Design Issues in OCS Networks

• Static design problems: design a network given traffic demands

• Dynamic design problems: allocate resources for dynamically arriving and departing requests

• Network dimensioning: grow existing network to meet expected traffic growth

Design Issues in OCS Networks

• Logical topology design– What lightpaths to set up to meet a given traffic demand

• Routing and wavelength assignment– Given one or more lightpath requests, find a route and assign a wavelength

to each request• Traffic grooming

– Establish lightpaths and assign traffic to lightpaths• Objectives:

– Efficient allocation of resources - minimize cost, maximize utilization– Fast provisioning of resources– Guarantees with respect to service

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Design Issues in OCS Networks

• Control and signaling– Maintaining and distributing network state information– Reserve network resources for a given lightpath– GMPLS deployment issues

• Survivability– Reserve spare capacity to protect against network failures

Optical Network Survivability

• Protection– Reserve back-up resources in advance– Guarantees survivability for any single link failure– Costly in terms of resources used

• Restoration– Find spare resources after failure has occurred– No need to reserve extra resources in advance– No guarantee that resources will be available

• Partial protection/Maximum survivability– Consider probability of link failures– Reserve resources to maximize probability of survivability

Emerging Problems in OCS Networks

• Advanced reservation/Scheduled lightpaths• Cross-layer design

– Physical impairment-aware network design– Multi-layer and cross-layer survivability

• Service differentiation– Differentiated QoS– Differentiated reliability/survivability

• Optical multicast

• Goal: Provide services to support requirements of emerging applications

Optical Packet/Burst Switching

• Optical packet/burst switching– Data switched all-optically on packet-by-packet or burst-by-burst basis– Control/header information may be processed electronically

• Design issues– Contention – multiple packets head to same output at same time

• Problem: lack of optical storage technology– Quality of Service – meeting delay and loss requirements

Issues in Optical Burst Switching (OBS)

• Benefits– Flexible allocation of network

bandwidth– Reduced control overhead

• Challenges– Compensation for lack of optical

buffers– Support for different applications

and classes of traffic (QoS)

BurstAssembly

Scheduling

ContentionResolution

RoutingSignaling

OBS Research Directions

• Suitability of OBS for emerging traffic and applications– On-demand bulk data transfer – Grid computing– Storage area networks– Voice over IP– Video and multimedia

• Comparison of OBS with alternative architectures– Optical packet switching– Electronic packets over optical circuits– Hybrid optical burst/circuit switched networks

• Interaction of OBS with higher-layer protocols– TCP/UDP over OBS– SONET over OBS

• Proof of concept– Experiments and testbeds

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Optical Packet Switching (OPS)

Optical Packet-Switched Network

• Packet consists of payload (data) and header• Packets switched directly in the optical domain• Reconfigure switch on packet-by-packet basis based on packet headers• Higher degree of multiplexing

Packet

Challenges for OPS

• Fast switching time in order of ns– At 10 Gbps, 1500 bytes, 1.2 us– At 40 Gbps, 1500 bytes, 0.3 us– Technologies

• MEMs: 10 ms• Liquid crystal: 4 ms• SOA: 1 ns• Electro-Optic: 4-10 ns

• Synchronization • Header processing

– Lack of optical processing • Contention Resolution

– Lack of optical RAM storage• Fiber delay line buffer architectures

– Switching times

Optical Access Networks: Hybrid Fiber Coax

Diagram: http://www.cabledatacomnews.com/cmic/diagram.html

Optical Access Networks: PONs

• Passive optical networks (PONs) for last-mile access• Recent deployments:

– AT&T U-Verse– Verizon FiOS (Fiber Optic Service)

Broadcast-and-Select Optical Networks

• Passive Star Coupler – optical broadcast device• Nodes equipped with one or more transmitters and one or more

receivers• Transmitters and receivers may either be fixed to a single

wavelength or tunable to different wavelengths• Receiving node must have receiver fixed/tuned to same

wavelength as sending node’s transmitter

Challenges for Access Networks

• MAC protocols• Dynamic bandwidth allocation• Scheduling

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Outline of Course• Introduction

– Overview and motivation– Historical evolution– Research issues

• Optical components and technology• Wavelength-routed (circuit-switched) optical networks

– Static network design – RWA, logical topology design, traffic grooming– Dynamic network design – RWA, signaling, blocking probability analysis– Protection and restoration

• Optical burst switching– Signaling– Contention resolution– Scheduling– QoS

• Photonic packet switching– Contention resolution – buffering, deflection, wavelength conversion– QoS

• Optical metro and access networks

Resource Reservation for Distributed Computing Applications over Optical Networks

• Many emerging distributed computing applications– Grid computing– Storage area networking– Distributed content distribution

• Distributed computing applications require– Network resources for transferring data– End-node resources for computation, storage, etc.

Distributed Computing Jobs

• Jobs can be divided into tasks• Task properties

– Amount of data– Starting time constraints– Ending time constraints (deadline)– Required processing time– Independent vs. dependent– Parallel vs. sequential– Shared data vs. partitioned data

Scheduling/Resource Reservation Problem

• Schedule/reserve network resources– Immediate reservation

• Reserve if resources available now, otherwise block– Advance reservation

• Schedule/reserve resources at earliest available time• Schedule/reserve computing resources

– Immediate reservation• Reserve if resources available now, otherwise block

– Advance reservation• Schedule/reserve resources at earliest available time

– Queue tasks• Wait in queue for resource to become available

• Joint vs. independent network/computing resource reservation

Network Resource Reservation

• Routing problem– Fixed routing – independent of state of network and computing resources– Adaptive routing – depends on state of network and/or computing resources

• Adaptive to network resources• Adaptive to computing resources• Adaptive to both

• State information distribution for adaptive– Centralized vs. distributed– Global vs. local information– Accuracy of state information

• Frequency of updates

Computing Resource Reservation

• Destination selection problem– Fixed

• Depends on physical topology, total amount of network resources, total amount of computing resources at each node

– Closest destination(s)– Destination with most resources

– Adaptive• Depends on current state/availability of resources

– Shortest available paths– Most available resources– State information update issues

• Resource selection problem– How many resources to request from each destination

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Objectives

• Minimize resources consumed• Minimize completion time

Unicast and Multicast

• Unicast– Given

• Network• Source node• Destination node

– Find• Route from source to destination

• Multicast– Given

• Network• Source node• Set of destination nodes

– Find• Routes (spanning tree) from source to destinations

Anycast and Manycast

• Anycast– Given

• Network• Source node• Set of candidate destinations

– Find• One destination out of candidate destinations• Route from source to selected destinaiton

• Manycast– Given

• Network• Source node• Set of candidate destinations• Number of required destinations, k

– Find• Selection of k destinations out of set of candidate destinations• Routes from source to selected k destinations

Optical multicast

• Optical multicasting through optical splitters– From one input to multiple outputs – Fixed or adjustable optical splitters

• Optical multicast vs. IP multicast– No expensive O/E/O conversion– No expensive electronic switches– Higher degree of data transparency– More efficient in data replication

Optical splitter

Multicast capable OXCs Manycasting over OBS networks

• Problem definition– Given: a WDM OBS network and bursty dynamic manycast requests – Find: a subset of the destinations and a route for the requests– Objective: minimize data loss probability

• Related work– The manycast problem is proven to be NP-hard– Routing algorithms to minimize the cost of the tree– No work has been done on supporting manycasting over OBS

networks

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Our solution

• Challenges– Finding an optimal solution is NP-hard– Real time demand on routing– Data loss due to burst contention

• Our focus– Not on optimal routing for each manycast request– Instead on the data loss issue of OBS networks

• Our solution– A shortest-path tree based routing algorithm– Two new schemes to reduce data loss

New schemes

• Static over-provisioning (SOP)– Instead of selecting K destinations, we select k + k’ destinations – Even the burst to some destinations are lost, the total number of

destinations which actually receive the burst may still be K or more

• Dynamic membership (DM)– K destinations are not decided at the source node– If some destinations are blocked along the route tree, we will try to

send the burst to some other destinations.

Static over-provisioning Dynamic membership with SOP

Plain manycast

DM

SOP & DM

Multi-Resource Manycast over Optical Burst Switched Networks

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Distributed Computing Architecture

• Optical network– Links and switching nodes– Circuit-switched, packet-switched, or burst-switched

• Destination-node resources– Computing or storage devices– With or without queueing– Different destination nodes may have identical resources

Multi-Resource Manycast (MRM)• Given

– A network– The number of available resources at each destination node– A multi-resource manycast request (s, Dc, r )

• s - the source node • Dc - the set of destination nodes which have available computing

resources• r - the number of computing resources required by the request

• Find– A selected set of destination nodes– The number of resources requested from each selected destination– The routes from the source to each selected destination node

• Objective– Minimize resource blocking rate

• Blocking due to contention in the OBS network• Blocking due to contention for resources at destination nodes

Destination Selection Heuristics

• Closest Destination First (CDF)– Source node first selects nearest destination which has available

resources

• Most Available First (MAF)

• Random Selection (RS)

B

A

E

D

(0)

(3) (4)

(2)(0)

Request (A , {C, D, E}, 6)

CC

D

E

Destination Selection Heuristics Cont.

• Closest Destination First (CDF)

• Most Available First (MAF)– Source node first selects destination nodes that have greatest

number of available resources

• Random Selection (RS)

B

A

E

D

(0)

(3) (4)

(2)(0)

Request (A , {C, D, E}, 6)

CC E

Destination Selection Heuristics Cont.

• Closest Destination First (CDF)

• Most Available First (MAF)

• Random Selection (RS)– Randomly chooses a destination with uniform probability among

the destinations with available resources

Resource Selection Policy

• Greedy– Reserve maximum possible number of resources from each

destination

• Limit per Destination (LpD)– Sets a limit on the maximum number of allocated resources per

destination– Td = maximum fraction of destination’s resources that can be

requested by a job

B

A

E

D

(0)

(6) (4)

(2)(0)Request (A , {C, D, E}, 4) , Td= 50%

C→ (3) → (2)

→ (1)

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Produced Bursts per Request(with Greedy Resource Selection)

2.132292.07191.924951.8352RS

1.813551.80781.780011.81392MAF

2.218742.08841.979051.86456CDF

7 request/ms5 request/ms3 request/ms1 request/msRequest Arrival Rate

Resource Blocking Rate(with Greedy Resource Selection)

Resource Blocking Rate with Limit per Destination