Design of Optical WDM Networks using Integer Linear Programming

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Check: http://www.thefoa.org/tech/ref/basic/SMbands.html ... Converter. EO. Converter. Passive Optical. Muliplexer. 1300 nm. 1310 nm ..... psd connections between s and d. ▫ Path-related constraints. – Routing can be easily constrained (e.g. ...
Design of Optical WDM Networks using Integer Linear Programming Network Design and Planning (2016) Massimo Tornatore Dept. Electronics and Information Politecnico di Milano Piazza Leonardo da Vinci 32 - 20133 Milan, Italy [email protected]

Outline

 Introduction to WDM optical networks and network design  WDM network design and optimization – Integer Linear Programming approach – Physical Topology Design • Unprotected case • Dedicated path protection case • Shared path & link protection cases – Notes on Traffic Grooming – Heuristics

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Success of optical communications Main technical reasons  Optical fiber advantages – – – – – – – –

Huge bandwidth (WDM) Long range transmission (EDFA optical amplifiers) Strength Use flexibility (transparency) Low noise Low cost Interference immunity ….

 Optical components – Rapid technological evolution – Increasing reliability (not for all…) – Decreasing costs (not for all…)

 Ok, but from a network perspective? – Convergence of services over a unique transport platform WDM Network Design

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Spectrum of the main transmission media Lunghezza d'onda [m] Wavelength 104

10 3

102

10 1

Radio AM

100

Radio FM

10 -1

10-2

10 -3

10-4

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10-6

Microonde

Luce visibile

Satellite

Fibra ottica

TV Cavo coassiale

v  f

Doppino

v  c  3  108 m / s 104

LF

MF

HF

VHF

10 5

106

10 7

108

EHF

THF

10 9 1010 10 11 Frequency Frequenza [Hz]

1012

LF = Low Frequency MF = Medium Frequency HF = High Frequency

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UHF

SHF

10 13

1014

10 15

VHF = Very High Frequency UHF = Ultra High Frequency SHF = Super High Frequency EHF = Extremely High Frequency THF = Tremendously High Frequency

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All-Wave Fiber… low-loss region + WDM (a) All-wave fiber (true wave, Leaf, etc.)

• Removal of water molecule absorption peak. Check: http://www.thefoa.org/tech/ref/basic/SMbands.html

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(b) Traditional fiber

WDM = wavelengthdivision multiplexing (wavelength = channel) 5

The ITU-T grid for WDM

Check: ITU-T G.694.1 Spectral grids for WDM applications: DWDM frequency grid, Feb 2012.

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WDM optical networks: a “layered vision”  WDM layer fundamentals – Wavelength Division Multiplexing: information is carried on highcapacity channels of different wavelengths on the same fiber – Switching: WDM systems transparently switch optical flows in the space (fiber) and wavelength domains  WDM layer basic functions – Optical circuit (LIGTHPATH) provisioning for the electronic layers – Common transport platform for a multi-protocol electronic-switching environment ...

Electronic layers

SDH

ATM

IP

WDM Layer

Optical layers

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Optical transmission

...

Lightpath connection request

Lightpath connection provisioning

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What’s a WDM System?

EO Converter

Ch 1 1300 nm

EO Converter

Ch 2 1310 nm

EO Converter

Ch n

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Passive Optical Muliplexer

850 nm

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WDM System Function

1

EO Converter

OE Converter

1

2

EO Converter

OE Converter

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n

EO Converter

OE Converter

n

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Mux & Demux

Mux & Demux

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Wavelength Switching in WDM Networks

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2

1

2

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The concept of lightpath Example: A European WDM Network

Helsinki

Madrid

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Outline

 Introduction to WDM network design and optimization

 Integer Linear Programming approach  Physical Topology Design – Unprotected case – Dedicated path protection case – Shared path & link protection cases  Heuristic approach

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WDM networks: basic concepts Logical topology Electronic-layer connection request

CR1 CR3

Electronic switching node (DXC, IP router, ATM switch, etc.) CR2 Optical network access point

WDM LOGICAL TOPOLOGY

CR4

WDM network WDM network nodes

   

Logical topology (LT): each link represent a lightpath that could be (or has been) established to accommodate traffic A lightpath is a “logical link” between two nodes Full mesh Logical topology: a lightpath is established between any node pairs LT Design (LTD): choose, minimizing a given cost function, the lightpaths to support a given traffic

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WDM networks: basic concepts Physical topology

WDM optical-fiber link

Optical path termination

Optical Cross Connect (OXC) Wavelength converter

WDM PHYSICAL TOPOLOGY

 Physical topology: set of WDM links and switching-nodes  Some or all the nodes may be equipped with wavelength converters  The capacity of each link is dimensioned in the design phase

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Different OXC configurations

*Jane Simmons, “Optical network design and planning”

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WDM networks: basic concepts Mapping of the logical over the physical topology Mapping is different according to the fact that the network is not (a) or is (b) provided with wavelength converters

CR1

CR2

CR4

LP1 LP = LIGHTPATH 1 2 3

CR3

LP1 LP2

LP3

LP2 (a)

LP3

(b)

LP4

LP4

Optical wavelength channels

 Solving the resource-allocation problem is equivalent to perform a

mapping of the logical over the physical topology – Also called Routing Fiber and Wavelength Assignment (RFWA)  Physical-network dimensioning is jointly carried out WDM Network Design

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Illustrative Example NY

WA

MI

NJ

PA UT CA1

CO NE

IL MD CA1

IL

CA2 GA TX

TX

UT

PA

WA NJ

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Static WDM network planning Problem definition  Input parameters, given a priori – Physical topology (OXC nodes and WDM links) – Traffic requirement (logical topology) • Connections can be mono or bidirectional • Each connection corresponds to one lightpath than must be setup between the nodes • Each connection requires the full capacity of a wavelength channel (no traffic grooming)

 Parameters which can be specified or can be part of the problem – Network resources: two cases • Fiber-constrained: the number of fibers per link is a preassigned global parameter (typically, in mono-fiber networks), while the number of wavelengths per fiber required to setup all the lightpaths is an output • Wavelength-constrained: the number of wavelengths per fiber is a preassigned global parameter (typically, in multi-fiber networks) and the number of fibers per link required to setup all the lightpaths is an output WDM Network Design

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Static WDM network planning Problem definition (II)  Physical constraints – Wavelength conversion capability • Absent (wavelength path, WP or transparent) • Full (virtual wavelength path, VWP or opaque) • Partial (partial virtual wavelength path, PVWP)

– Propagation impairments • The length of lightpaths is limited by propagation phenomena (physicallength constraint) • The number of hops of lightpaths is limited by signal degradation due to the switching nodes

– Connectivity constraints • Node connectivity is constrained; nodes may be blocking

 Links and/or nodes can be associated to weights – Typically, link physical length is considered

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Static WDM network optimization Problem definition (III)

 Routing can be – Constrained: only some possible paths between source and destination (e.g. the K shortest paths) are admissible • Great problem simplification

– Unconstrained: all the possible paths are admissible • Higher efficiency in network-resource utilization

 Cost function to be optimized (optimization objectives) – Route all the lightpaths using the minimum number of wavelengths (physical-topology optimization) – Route all the lightpaths using the minimum number of fibers (physicaltopology optimization) – Route all the lightpaths minimizing the total network cost, taking into account also switching systems (physical-topology optimization)

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Static WDM network optimization Complexity  Routing and Wavelength Assignment (RWA) [OzBe03] – The capacity of each link is given – It has been proven to be a NP-complete problem [ChGaKa92] – Two possible approaches • Maximal capacity given  maximize routed traffic (throughput) • Offered traffic given  minimize wavelength requirement

 Routing Fiber and Wavelength Assignment (RFWA) – The capacity of each link is a problem variable – Further term of complexity  Capacitated network – The problem contains multicommodity flow (routing), graph coloring (wavelength) and localization (fiber) problems – It has been proven to be a NP-hard problem (contains RWA)

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Optimization problems Classification  Optimization problem – optimization version – Find the minimum-cost solution  Optimization problem – decision version (answer is yes or no) – Given a specific bound k, tell me if a solution x exists such that x