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
WDM Network Design
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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
3
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
10 -5
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
WDM Network Design
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
4
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
WDM Network Design
(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.
WDM Network Design
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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
WDM Network Design
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
WDM Network Design
Passive Optical Muliplexer
850 nm
8
WDM System Function
1
EO Converter
OE Converter
1
2
EO Converter
OE Converter
2
n
EO Converter
OE Converter
n
WDM Network Design
Mux & Demux
Mux & Demux
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Wavelength Switching in WDM Networks
1
2
1
2
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The concept of lightpath Example: A European WDM Network
Helsinki
Madrid
WDM Network Design
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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
WDM Network Design
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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
WDM Network Design
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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
WDM Network Design
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Different OXC configurations
*Jane Simmons, “Optical network design and planning”
WDM Network Design
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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
WDM Network Design
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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
WDM Network Design
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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)
WDM Network Design
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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