Abstract: We design and implement a multicost impairment- aware routingandwavelengthassignment algorithm for online traffic. In transparent optical networks the quality of a transmission degrades due to physical layer impairments. To serve a connection, the proposed algorithm finds a path and a free wavelength (a lightpath) that has acceptable signal quality performance by estimating a quality of transmission measure, called the Q factor. We take into account channel utilization in the network, which changes as new connections are established or released, in order to calculate the noise variances that correspond to physical impairments on the links. These, along with the time invariant eye impairment penalties of all candidate network paths, form the inputs to the algorithm. The multicost algorithm finds a set of so called non-dominated Q paths from the given source to the given destination. Various objective functions are then evaluated in order to choose the optimal lightpath to serve the connection. The proposed algorithm combines the strength of multicost optimization with low execution time, making it appropriate for serving online connections.

Abstract: We consider the problem of planning a mixed line
rates (MLR) wavelength division multiplexing (WDM) transport
optical network. In such networks, different modulation formats
are usually employed to support the transmission at different line
rates. Previously proposed planning algorithms, have used a
transmission reach limit for each modulation format/line rate,
mainly driven by single line rate systems. However, transmission
experiments in MLR networks have shown that physical layer
interference phenomena are more significant between
transmissions that utilize different modulation formats. Thus, the
transmission reach of a connection with a specific modulation
format/line rate depends also on the other connections that copropagate
with it in the network. To plan a MLR WDM network,
we present routingandwavelengthassignment (RWA)
algorithms that take into account the adaptation of the
transmission reach of each connection according to the use of the
modulation formats/line rates in the network. The proposed
algorithms are able to plan the network so as to alleviate
interference effects, enabling the establishment of connections of
acceptable quality over paths that would otherwise be prohibited

Abstract: Optical network design problems fall in the broad
category of network optimization problems. We give a short
introduction on network optimization and general algorithmic
techniques that can be used to solve complex and difficult
network design problems. We apply these techniques to address
the static RoutingandWavelengthAssignment problem that is
related to planning phase of a WDM optical network. We present
simulation result to evaluate the performance of the proposed
algorithmic solution.

Abstract: Orthogonal Frequency Division Multiplexing (OFDM)
has recently been proposed as a modulation technique for optical networks, because of its good spectral efficiency, flexibility, and tolerance to impairments. We consider the planning problem of an OFDM optical network, where we are given a traffic matrix that includes the requested transmission rates of the connections to be served. Connections are provisioned for their requested rate by elastically allocating spectrum using a variable number of OFDM subcarriers and choosing an appropriate modulation level, taking into account the transmission distance. We introduce the Routing, Modulation Level and Spectrum Allocation (RMLSA) problem, as opposed to the typical RoutingandWavelengthAssignment (RWA) problem of traditional WDM networks, prove that is also NP-complete and present various algorithms to solve it. We start by presenting an optimal ILP RMLSA algorithm that minimizes the spectrum used to serve the traffic matrix, and also present a decomposition method that breaks RMLSA into its two
substituent subproblems, namely, (i) routingand modulation level, and (ii) spectrum allocation (RML+SA), and solves them sequentially. We also propose a heuristic algorithm that serves connections one-by-one and use it to solve the planning problem by sequentially serving all the connections in the traffic matrix. In the sequential algorithm, we investigate two policies for defining the order in which connections are considered. We also use a simulated annealing meta-heuristic to obtain even better orderings. We examine the performance of the proposed algorithms through simulation experiments and evaluate the spectrum utilization benefits that can be obtained by utilizing OFDM elastic bandwidth allocation, when compared to a traditional WDM network.

Abstract: Core optical networks using reconfigurable optical
switches and tunable lasers appear to be on the road towards
widespread deployment and could evolve to all-optical mesh
networks in the coming future. Considering the impact of physical
layer impairments in the planning and operation of all-optical
(and translucent) networks is the main focus of the DICONET
project. The impairment aware network planning and operation
tool (NPOT) is the main outcome of DICONET project, which
is explained in detail in this paper. The key building blocks of
the NPOT, consisting of network description repositories, the
physical layer performance evaluator, the impairment aware
routingandwavelengthassignment engines, the component
placement modules, failure handling and the integration of
NPOT in the control plane are the main contributions of this
work. Besides, the experimental result of DICONET proposal for
centralized and distributed control plane integration schemes and
the performance of the failure handling in terms of restoration
time is presented in this work.

Abstract: We consider the offline version of the routingandwavelengthassignment (RWA) problem in transparent all-optical networks. In such networks and in the absence of regenerators, the signal quality of transmission degrades due to physical layer
impairments. We initially present an algorithm for solving the static RWA problem based on an LP relaxation formulation that tends to yield integer solutions. To account for signal degradation due to physical impairments, we model the effects of the path length, the path hop count, and the interference among ligthpaths by imposing additional (soft) constraints on RWA. The objective of the resulting optimization problem is not only to serve the
connection requests using the available wavelengths, but also to minimize the total accumulated signal degradation on the selected lightpaths. Our simulation studies indicate that the proposed RWA algorithms select the lightpaths for the requested connections so as to avoid impairment generating sources, thus dramatically reducing the overall physical-layer blocking when compared to RWA algorithms that do not account for impairments.

Abstract: We consider the online impairment-aware routingandwavelengthassignment (IA-RWA) problem in transparent
WDM networks. To serve a new connection, the online algorithm,
in addition to finding a route and a free wavelength (a lightpath),
has to guarantee its transmission quality, which is affected by
physical-layer impairments. Due to interference effects, the establishment
of the new lightpath affects and is affected by the other
lightpaths. We present two multicost algorithms that account
for the actual current interference among lightpaths, as well as
for other physical effects, performing a cross-layer optimization
between the network and physical layers. In multicost routing,
a vector of cost parameters is assigned to each link, from which
the cost vectors of the paths are calculated. The first algorithm
utilizes cost vectors consisting of impairment-generating source
parameters, so as to be generic and applicable to different physical
settings. These parameters are combined into a scalar cost
that indirectly evaluates the quality of candidate lightpaths. The
second algorithm uses specific physical-layer models to define
noise variance-related cost parameters, so as to directly calculate
the -factor of candidate lightpaths. The algorithms find a set of
so-called nondominated paths to serve the connection in the sense
that no path is better in the set with respect to all cost parameters.
To select the lightpath, we propose various optimization functions
that correspond to different IA-RWA algorithms. The proposed
algorithms combine the strength of multicost optimization with
low execution times, making them appropriate for serving online
connections

Abstract: We consider the offline version of the routingandwavelengthassignment (RWA) problem in transparent all-optical
networks. In such networks and in the absence of regenerators,
the signal quality of transmission degrades due to physical layer
impairments. Because of certain physical effects, routing choices
made for one lightpath affect and are affected by the choices made
for the other lightpaths. This interference among the lightpaths
is particularly difficult to formulate in an offline algorithm since,
in this version of the problem, we start without any established
connections and the utilization of lightpaths are the variables of
the problem.We initially present an algorithm for solving the pure
(without impairments) RWA problem based on a LP-relaxation
formulation that tends to yield integer solutions. Then, we extend
this algorithm and present two impairment-aware (IA) RWA algorithms
that account for the interference among lightpaths in their
formulation. The first algorithm takes the physical layer indirectly
into account by limiting the impairment-generating sources. The
second algorithm uses noise variance-related parameters to directly
account for the most important physical impairments. The
objective of the resulting cross-layer optimization problem is not
only to serve the connections using a small number of wavelengths
(network layer objective), but also to select lightpaths that have
acceptable quality of transmission (physical layer objective).
Simulations experiments using realistic network, physical layer,
and traffic parameters indicate that the proposed algorithms can
solve real problems within acceptable time.

Abstract: In future transparent optical networks, it is
important to consider the impact of physical impairments in the
routingandwavelengths assignment process, to achieve efficient
connection provisioning. In this paper, we use classical multi-
objective optimization (MOO) strategies and particularly genetic
algorithms to jointly solve the impairment aware RWA (IA-
RWA) problem. Fiber impairments are indirectly considered
through the insertion of the path length and the number of
common hops in the optimization process. It is shown that
blocking is greatly improved, while the obtained solutions truly
converge towards the Pareto front that constitutes the set of
global optimum solutions. We have evaluated our findings, using
an Q estimator tool, that calculates the signal quality of each path
analytically.
Index Terms RWA, Genetic Algorithm, All-Optical
Networks, Multi Objective Optimization.

Abstract: We propose and evaluate an impairment-aware multi-parametric routingandwavelengthassignment algorithm for online traffic in transparent optical networks. In such networks the signal quality of transmission degrades due to physical layer impairments. In the multiparametric approach, a vector of cost parameters is assigned to each link, from which the cost vectors of candidate lightpaths are calculated. In the proposed scheme the cost vector includes impairment generating source parameters, such as the path length, the number of hops, the number of crosstalk sources and other inter-lightpath interfering parameters, so as to indirectly account for the physical layer effects. For a requested connection the algorithm calculates a set of candidate lightpaths, whose quality of transmission is validated using a function that combines the impairment generating parameters. For selecting the lightpath we propose and evaluate various optimization functions that correspond to different IA-RWA algorithms. Our performance results indicate that the proposed algorithms utilize efficiently the available resources and minimize the total accumulated signal degradation on the selected lightpaths, while having low execution times.

Abstract: We consider path protection in the routingandwavelengthassignment (RWA) problem for impairment
constrained WDM optical networks. The proposed multicost
RWA algorithms select the primary and the backup lightpaths by
accounting for physical layer impairments. The backup lightpath
may either be activated (1+1 protection) or it may be reserved and
not activated, with activation taking place when/if needed (1:1
protection). In case of 1:1 protection the period of time where the
quality of its transmission (QoT) is valid, despite the possible
establishment of future connections, should be preserved, so as to
be used in case the primary lightpath fails. We show that, by using
the multicost approach for solving the RWA with protection
problem, great benefits can be achieved both in terms of the
connection blocking rate and in terms of the validity period of the
backup lightpath. Moreover the multicost approach, by providing
a set of candidate lightpaths for each source destination pair,
instead of a single one, offers ease and flexibility in selecting the
primary and the backup lightpaths.

Abstract: We present a network operation tool called Impairment Aware Lightpath Computation Engine
(IALCE) that incorporates an impairment-aware routingandwavelengthassignment (RWA) algorithm.
We perform experiments illustrating the flexibility of the engine and the performance of the algorithm

Abstract: We consider the problem of planning a mixed line rate
(MLR) wavelength division multiplexing (WDM) transport
optical network. In such networks, different modulation formats
are usually employed to support transmission at different line
rates. Previously proposed planning algorithms have used a
transmission reach bound for each modulation format/line rate,
mainly driven by single line rate systems. However, transmission
experiments in MLR networks have shown that physical layer
interference phenomena are more severe among transmissions
that utilize different modulation formats. Thus, the transmission
reach of a connection with a specific modulation format/line rate
depends also on the other connections that co-propagate with it
in the network. To plan a MLR WDM network, we present
routingandwavelengthassignment (RWA) algorithms that
adapt the transmission reach of each connection according to the
use of the modulation formats/line rates in the network. The
proposed algorithms are able to plan the network so as to
alleviate cross-rate interference effects, enabling the
establishment of connections of acceptable quality over paths that
would otherwise be prohibited.

Abstract: Orthogonal Frequency Division Multiplexing (OFDM)
has been recently proposed as a modulation technique for optical
networks, due to its good spectral efficiency and impairment
tolerance. Optical OFDM is much more flexible compared to
traditional WDM systems, enabling elastic bandwidth
transmissions. We consider the planning problem of an OFDMbased optical network where we are given a traffic matrix that
includes the requested transmission rates of the connections to be
served. Connections are provisioned for their requested rate by
elastically allocating spectrum using a variable number of OFDM
subcarriers. We introduce the Routingand Spectrum Allocation
(RSA) problem, as opposed to the typical RoutingandWavelengthAssignment (RWA) problem of traditional WDM
networks, and present various algorithms to solve the RSA. We
start by presenting an optimal ILP RSA algorithm that minimizes
the spectrum used to serve the traffic matrix, and also present a
decomposition method that breaks RSA into two substituent
subproblems, namely, (i) routingand (ii) spectrum allocation
(R+SA) and solves them sequentially. We also propose a heuristic
algorithm that serves connections one-by-one and use it to solve
the planning problem by sequentially serving all traffic matrix
connections. To feed the sequential algorithm, two ordering
policies are proposed; a simulated annealing meta-heuristic is also
proposed to obtain even better orderings. Our results indicate
that the proposed sequential heuristic with appropriate ordering
yields close to optimal solutions in low running times.

Abstract: In this work we add a training phase to an Impairment Aware RoutingandWavelengthAssignment (IA-RWA) algorithm so as to improve its performance. The initial IA-RWA algorithm is a multi-parametric algorithm where a vector of physical impairment parameters is assigned to each link, from which the impairment vectors of candidate lightpaths are calculated. The important issue here is how to combine these impairment parameters into a scalar that would reflect the true transmission quality of a path. The training phase of the proposed IA-RWA algorithm is based on an optimization approach, called Particle Swarm Optimization (PSO), inspired by animal social behavior. The training phase gives the ability to the algorithm to be aware of the physical impairments even though the optical layer is seen as a black box. Our simulation studies show that the performance of the proposed scheme is close to that of algorithms that have explicit knowledge of the optical layer and the physical impairments.