Abstract: We demonstrate a 40 Gb/s self-synchronizing, all-optical packet
clock recovery circuit designed for efficient packet-mode traffic. The circuit
locks instantaneously and enables sub-nanosecond packet spacing due to the
low clock persistence time. A low-Q Fabry-Perot filter is used as a passive
resonator tuned to the line-rate that generates a retimed clock-resembling
signal. As a reshaping element, an optical power-limiting gate is
incorporated to perform bitwise pulse equalization. Using two preamble
bits, the clock is captured instantly and persists for the duration of the data
packet increased by 16 bits. The performance of the circuit suggests its
suitability for future all-optical packet-switched networks with reduced
transmission overhead and fine network granularity.
Abstract: The efficient use of resources and the lossless transfer of data bursts in future opticalnetworks requires the accurate knowledge of the available bandwidth for each network
link. Such information is important in monitoring congestions and can be used by
appropriate load balancing and congestion avoidance mechanisms. In this paper we
propose a mechanism for monitoring and subsequently managing bandwidth resources,
using the Simple NetworkManagement Protocol (SNMP). In the proposed mechanism,
link bandwidth availability is not a scalar parameter, but a function of time that records
the future utilization of the link. For every output port, each agent-node maintains a
simple data structure in the form of a table that records the utilization profile of that
outgoing link. With the addition of new objects in the Management Information Base
(MIB) of each agent-node and proper synchronization, SNMP can be used to update
and retrieve the reservations made on the links in order to obtain an instant picture of
the network traffic situation.
Abstract: Core networks of the future will have a
translucent and eventually transparent optical
structure. Ultra-high-speed end-to-end connectiv-
ity with high quality of service and high reliability
will be realized through the exploitation of opti-
mized protocols and lightpath routing algorithms.
These algorithms will complement a flexible con-
trol and management plane integrated in the
proposed solution. Physical layer impairments
and optical performance are monitored and
incorporated in impairment-aware lightpath rout-
ing algorithms. These algorithms will be integrat-
ed into a novel dynamic network planning tool
that will consider dynamic traffic characteristics,
a reconfigurable optical layer, and varying physi-
cal impairment and component characteristics.
The network planning tool along with extended
control planes will make it possible to realize the
vision of optical transparency. This article pre-
sents a novel framework that addresses dynamic
cross-layer network planning and optimization
while considering the development of a future
transport network infrastructure.
Abstract: The efficient use of resources and the lossless transfer of data bursts in future opticalnetworks requires the accurate knowledge of the available bandwidth for each network
link. Such information is important in monitoring congestions and can be used by
appropriate load balancing and congestion avoidance mechanisms. In this paper we
propose a mechanism for monitoring and subsequently managing bandwidth resources,
using the Simple NetworkManagement Protocol (SNMP). In the proposed mechanism,
link bandwidth availability is not a scalar parameter, but a function of time that records
the future utilization of the link. For every output port, each agent-node maintains a
simple data structure in the form of a table that records the utilization profile of that
outgoing link. With the addition of new objects in the Management Information Base
(MIB) of each agent-node and proper synchronization, SNMP can be used to update
and retrieve the reservations made on the links in order to obtain an instant picture of
the network traffic situation.
Abstract: We design and implement a multicost impairment- aware routing and wavelength assignment algorithm for online traffic. In transparent opticalnetworks 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: In this paper, we present a new hybrid optical burst switch architecture (HOBS) that takes advantage of the pre-transmission idle
time during lightpath establishment. In dynamic circuit switching (wavelength routing) networks, capacity is immediately hardreserved
upon the arrival of a setup message at a node, but it is used at least a round-trip time delay later. This waste of resources
is significant in optical multi-gigabit networks and can be used to transmit traffic of a lower class of service in a non-competing
way. The proposed hybrid OBS architecture, takes advantage of this idle time to transmit one-way optical bursts of a lower class of
service, while high priority data explicitly requests and establishes end-to-end lightpaths. In the proposed scheme, the two control
planes (two-way and one-way OBS reservation) are merged, in the sense that each SETUP message, used for the two-way lightpath
establishment, is associated with one-way burst transmission and therefore it is modified to carry routing and overhead information
for the one-way traffic as well. In this paper, we present the main architectural features of the proposed hybrid scheme and further
we assess its performance by conducting simulation experiments on the NSF net backbone topology. The extensive network study
revealed that the proposed hybrid architecture can achieve and sustain an adequate burst transmission rate with a finite worst case
delay.
Abstract: This paper presents an overview of Quality of Service (QoS) differentiation mechanisms proposed for Optical Burst Switching (OBS) networks. OBS has been proposed to couple the benefits of both circuit and packet switching for the “on demand” use of capacity in the future optical Internet. In such a case, QoS support imposes some important challenges before this technology is deployed. This paper takes a broader view on QoS, including QoS differentiation not only at the burst but also at the transport levels for OBS networks. A classification of existing QoS differentiation mechanisms for OBS is given and their efficiency and complexity are comparatively discussed. We provide numerical examples on how QoS differentiation with respect to burst loss rate and transport layer throughput can be achieved in OBS networks.
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 routing and wavelength assignment (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: This paper reviews the work performed under the
European ESPRIT project DO_ALL (Digital OpticAL Logic
modules) spanning from advanced devices (semiconductor optical
amplifiers) to all-optical modules (laser sources and gates) and
from optical signal processing subsystems (packet clock recovery,
optical write/store memory, and linear feedback shift register) to
their integration in the application level for the demonstration of
nontrivial logic functionality (all-optical bit-error-rate tester and
a 2 2 exchange–bypass switch). The successful accomplishment
of the project’s goals has opened the road for the implementation
of more complex ultra-high-speed all-optical signal processing
circuits that are key elements for the realization of all-optical
packet switching networks.
Abstract: Avertical perspective, ranging from management
and routing to physical layer options, concerning dynamic
network monitoring and compensation of impairments
(M&C),is given.Feasibility, reliability,and performance
improvements on reconfigurable transparent networksare
expected to arise from the consolidated assessment of network management and control specifications, as a more accurate evaluation of available M&C techniques. In the network
layer,physical parameters aware algorithms are foreseen to
pursue reliable network performance. In the physical layer,
some new M&C methods were developed and rating of the state-of-the-art reported in literature is given. Optical monitoring implementation and viability is discussed.
Abstract: Motivated by the wavelength assignment problem in WDM opticalnetworks, we study path coloring problems in graphs. Given a set of paths P on a graph G, the path coloring problem is to color the paths of P so that no two paths traversing the same edge of G are assigned the same color and the total number of colors used is minimized. The problem has been proved to be NP-hard even for trees and rings.
Using optimal solutions to fractional path coloring, a natural relaxation of path coloring, on which we apply a randomized rounding technique combined with existing coloring algorithms, we obtain new upper bounds on the minimum number of colors sufficient to color any set of paths on any graph. The upper bounds are either existential or constructive.
The existential upper bounds significantly improve existing ones provided that the cost of the optimal fractional path coloring is sufficiently large and the dilation of the set of paths is small. Our algorithmic results include improved approximation algorithms for path coloring in rings and in bidirected trees. Our results extend to variations of the original path coloring problem arizing in multifiber WDM opticalnetworks.
Abstract: The study of the path coloring problem is motivated by the allocation of optical bandwidth to communication requests in all-opticalnetworks that utilize Wavelength Division Multiplexing (WDM). WDM technology establishes communication between pairs of network nodes by establishing transmitter-receiver paths and assigning wavelengths to each path so that no two paths going through the same fiber link use the same wavelength. Optical bandwidth is the number of distinct wavelengths. Since state-of-the-art technology allows for a limited number of wavelengths, the engineering problem to be solved is to establish communication minimizing the total number of wavelengths used. This is known as the wavelength routing problem. In the case where the underlying network is a tree, it is equivalent to the path coloring problem.
We survey recent advances on the path coloring problem in both undirected and bidirected trees. We present hardness results and lower bounds for the general problem covering also the special case of sets of symmetric paths (corresponding to the important case of symmetric communication). We give an overview of the main ideas of deterministic greedy algorithms and point out their limitations. For bidirected trees, we present recent results about the use of randomization for path coloring and outline approximation algorithms that find path colorings by exploiting fractional path colorings. Also, we discuss upper and lower bounds on the performance of on-line algorithms.
Abstract: We propose and evaluate fast reservation (FR)
protocols for Optical Burst Switched (OBS) networks. The
proposed reservation schemes aim at reducing the end-to-end
delay of a data burst, by sending the Burst Header Packet (BHP)
in the core network before the burst assembly is completed at the
ingress node. We use linear prediction filters to estimate the
expected length of the burst and the time needed for the
burstification process to complete. A BHP packet carrying these
estimates is sent before burst completion, in order to reserve
bandwidth at each intermediate node for the time interval the
burst is expected to pass from that node. Reducing the total time
needed for a packet to be transported over an OBS network is
important, especially for real-time applications. Reserving
bandwidth only for the time interval it is actual going to be used
by a burst is important for network utilization efficiency. In the
simulations conducted we evaluate the proposed extensions and
prove their usefulness.
Abstract: In this article, we present a detailed performance
evaluation of a hybrid optical switching (HOS)
architecture called Overspill Routing in OpticalNetworks
(ORION). The ORION architecture combines
(optical) wavelength and (electronic) packet switching,
so as to obtain the individual advantages of both switching
paradigms. In particular, ORION exploits the possible insertions/extractions, to reduce the necessary
interfaces, do not deteriorate performance and thus the
use of traffic concentrators assure ORIONs economic
viability.
idle periods of established lightpaths to transmit
packets destined to the next common node, or even
directly to their common end-destination. Depending
on whether all lightpaths are allowed to simultaneously
carry and terminate overspill traffic or overspill is restricted
to a sub-set of wavelengths, the architecture
limits itself to constrained or un-constrained ORION. To
evaluate both cases, we developed an extensive network
simulator where the basic features of the ORION architectureweremodeled,
including suitable edge/core node
switches and load-varying sources to simulate overloading
traffic conditions. Further, we have assessed various
aspects of the ORION architecture including two
basic routing/forwarding policies and various buffering
schemes. The complete network study shows that
ORION can absorb temporal traffic overloads, as intended,
provided sufficient buffering is present.We also
demonstrate that the restriction of simultaneous packet
Abstract: Ever-increasing bandwidth demands and higher flexibility are the main challenges for the next generation optical core networks. A new trend in order to address these challenges is to consider the impairments of the lightpaths during the design of opticalnetworks. In our work, we focus on translucent opticalnetworks, where some lightpaths are routed transparently, whereas others go through a number of regenerators. We present a cost analysis of design strategies, which are based either on an exact Quality of Transmission (QoT) validation or on a relaxed one and attempt to reduce the amount of regenerators used. In the exact design strategy, regenerators are required if the QoT of a candidate lightpath is below a predefined threshold, assuming empty network conditions. In the relaxed strategy, this predefined threshold is lower, while it is assumed that the network is fully loaded. We evaluate techno-economically the suggested design solutions and also show that adding more flexibility to the optical nodes has a large impact to the total infrastructure cost.
Abstract: In this paper we present the efficient burst reservation protocol (EBRP) suitable
for bufferless optical burst switching (OBS) networks. The EBRP protocol is a
two-way reservation scheme that employs timed and in-advance reservation of
resources. In the EBRP protocol timed reservations are relaxed, introducing a
reservation time duration parameter that is negotiated during call setup phase.
This feature allows bursts to reserve resources beyond their actual size to
increase their successful forwarding probability and can be used to provide
quality-of-service (QoS) differentiation. The EBRP protocol is suitable for
OBS networks and can guarantee a low blocking probability for bursts that can
tolerate the round-trip delay associated with the two-way reservation.We present
the main features of the proposed protocol and describe in detail the timing
considerations regarding the call setup phase and the actual reservation process.
Furthermore, we show evaluation results and compare the EBRP performance
against two other typical reservation schemes, a tell-and-wait and a tell-and-go
(just-enough-time) like protocol. EBRP has been developed for the control plane
of the IST-LASAGNE project.
Abstract: Orthogonal Frequency Division Multiplexing (OFDM)
has recently been proposed as a modulation technique for opticalnetworks, 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 Routing and Wavelength Assignment (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) routing and 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: An enhanced impairment-aware path computation element (EPCE) for dynamic
transparent opticalnetworks is proposed and experimentally evaluated. The obtained results show
that by using the EPCE, light-path setup times of few seconds are achieved.
Abstract: Core opticalnetworks 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
routing and wavelength assignment 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: This paper evaluates a centralised impairment-aware path restoration approach for GMPLScontrolled
transparent opticalnetworks. Experimental results on a 14-node network test-bed show successful
QoT compliant path restoration of around 3.6 seconds.
Abstract: Motivated by the problem of allocating optical bandwidth in tree–shaped WDM networks, we study the fractional path coloring problem in trees. We consider the class of locally-symmetric sets of paths on binary trees and prove that any such set of paths has a fractional coloring of cost at most 1.367L, where L denotes the load of the set of paths. Using this result, we obtain a randomized algorithm that colors any locally-symmetric set of paths of load L on a binary tree (with reasonable restrictions on its depth) using at most 1.367L+o(L) colors, with high probability.
Abstract: We consider the offline version of the routing and
wavelength assignment (RWA) problem in transparent all-opticalnetworks. 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: In translucent (or managed reach) WDM opticalnetworks, regenerators are employed at specific nodes. Some of
the connections in such networks are routed transparently, while
others have to go through a sequence of 3R regenerators that serve
as “refueling stations” to restore their quality of transmission
(QoT). We extend an online multicost algorithm for transparent
networks presented in our previous study [1], to obtain an IA-RWA
algorithm that works in translucent networks and makes use,
when required, of the regenerators present at certain locations
of the network. To characterize a path, the algorithm uses a
multicost formulation with several cost parameters, including the
set of available wavelengths, the length of the path, the number of
regenerators used, and noise variance parameters that account for
the physical layer impairments. Given a new connection request
and the current utilization state of the network, the algorithm calculates
a set of non dominated candidate paths, meaning that any
path in this set is not inferior with respect to all cost parameters
than any other path. This set consists of all the cost-effective (in
terms of the domination relation) and feasible (in terms of QoT)
lightpaths for the given source-destination pair, including all the
possible combinations for the utilization of available regenerators
of the network. An optimization function or policy is then applied
to this set in order to select the optimal lightpath. Different optimization
policies correspond to different IA-RWA algorithms.
We propose and evaluate several optimization policies, such as the
most used wavelength, the best quality of transmission, the least
regeneration usage, or a combination of these rules. Our results
indicate that in a translucent network the employed IA-RWA
algorithm has to consider all problem parameters, namely, the
QoT of the lightpaths, the utilization of wavelengths and the
availability of regenerators, to efficiently serve the online traffic.
Abstract: We propose new burst assembly schemes and fast reservation (FR) protocols for Optical Burst Switched (OBS) networks that are based on traffic prediction. The burst assembly schemes aim at minimizing (for a given burst size) the average delay of the packets incurred during the burst assembly process, while the fast reservation protocols aim at further reducing the end-to-end delay of the data bursts. The burst assembly techniques use a linear prediction filter to estimate the number of packet arrivals at the ingress node in the following interval, and launch a new burst into the network when a certain criterion, different for each proposed scheme, is met. The fast reservation protocols use prediction filters to estimate the expected length of the burst and the time needed for the burst assembly process to complete. A Burst Header Packet (BHP) packet carrying these estimates is sent before the burst is completed, in order to reserve bandwidth at intermediate nodes for the time interval the burst is expected to pass from these nodes. Reducing the packet aggregation delay and the time required to perform the reservations, reduces the total time needed for a packet to be transported over an OBS network and is especially important for real-time applications. We evaluate the performance of the proposed burst assembly schemes and show that a number of them outperform the previously proposed timer-based, length-based and average delay-based burst assembly schemes. We also look at the performance of the fast reservation (FR) protocols in terms of the probability of successfully establishing the reservations required to transport the burst.
Abstract: We propose new burst assembly techniques that aim at reducing the average delay experienced by the packets during the burstification process in optical burst switched (OBS) networks, for a given average size of the bursts produced. These techniques use a linear prediction filter to estimate the number of packet arrivals at the ingress node in the following interval, and launch a new burst into the network when a certain criterion, which is different for each proposed scheme, is met. Reducing the packet burstification delay, for a given average burst size, is essential for real-time applications; correspondingly, increasing the average burst size for a given packet burstification delay is important for reducing the number of bursts injected into the network and the associated overhead imposed on the core nodes. We evaluate the performance of the proposed schemes and show that two of them outperform the previously proposed timer - based, length - based and average delay-based burst aggregation schemes in terms of the average packet burstification delay for a given average burst size.
Abstract: We consider the offline version of the routing and
wavelength assignment (RWA) problem in transparent all-opticalnetworks. 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 opticalnetworks, it is
important to consider the impact of physical impairments in the
routing and wavelengths 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-OpticalNetworks, Multi Objective Optimization.
Abstract: This article studies the transmission control
protocol (TCP) synchronization effect in optical burst
switched networks.Synchronization of TCP flows appears
when optical bursts with segments from different flows inside
are dropped in the network causing flow congestion windows decreasing simultaneously. In this article,this imminent
effect is studied with different assembly schemes and network scenarios.Different metrics are applied to quantitatively assess synchronization with classical assembly
schemes.A new burst assembly scheme is proposed that
statically or dynamically allocates flows to multiple assembly queues to control flow aggregation within the assembly
cycle.The effectiveness of the scheme has been evaluated,
showing a good improvement in optical link utilization
Abstract: We propose and evaluate an impairment-aware multi-parametric routing and wavelength assignment algorithm for online traffic in transparent opticalnetworks. 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: The authors demonstrate an optical buffer architecture which is implemented using quantum dot semiconductor optical amplifiers (QD-SOAs) in order to achieve wavelength conversion with regenerative capabilities, for all optical packet switched networks. The architecture consists of cascaded programmable delay stages that minimise the number of wavelength converters required to implement the buffer. Physical layer simulations have been performed in order to reveal the potential of this scheme as well as the operating and device parameters of QD-SOA-based wavelength converters. The results obtained have indicated that, up to three time-slot interchanger (TSI) cascaded stages show good performance at 160 Gb/s in the 1550 nm communication window.
Abstract: Switching in core opticalnetworks is currently being
performed using high-speed electronic or all-optical
circuit switches. Switching with high-speed electronics
requires optical-to-electronic (O/E) conversion of the
data stream, making the switch a potential bottleneck
of the network: any effort (including parallelization) for
electronics to approach the optical speeds seems to be
already reaching its practical limits. Furthermore, the
store-and-forward approach of packet-switching does
not seem suitable for all-optical implementation due to
the lack of practical optical random-access-memories
to buffer and resolve contentions. Circuit switching on
the other hand, involves a pre-transmission delay for
call setup and requires the aggregation of microlows
into circuits, sacriicing the granularity and the control
over individual lows, and is ineficient for bursty traf-
ic. Optical burst switching (OBS) has been proposed
by Qiao and Yoo (1999) to combine the advantages of
both packet and circuit switching and is considered a
promising technology for the next generation optical
internet.
Abstract: The objective of this research is to propose two new optical procedures for packet routing and forwarding in the framework of transparent opticalnetworks. The single-wavelength label-recognition and packet-forwarding unit, which represents the central physical constituent of the switching node, is fully described in both cases. The first architecture is a hybrid opto-electronic structure relying on an optical serial-to-parallel converter designed to slow down the label processing. The remaining switching operations are done electronically. The routing system remains transparent for the packet payloads. The second architecture is an all-optical architecture and is based on the implementation of all-optical decoding of the parallelized label. The packet-forwarding operations are done optically. The major subsystems required in both of the proposed architectures are described on the basis of nonlinear effects in semiconductor optical amplifiers. The experimental results are compatible with the integration of the whole architecture. Those subsystems are a 4-bit time-to-wavelength converter, a pulse extraction circuit, a an optical wavelength generator, a 3 x 8 all-optical decoder and a packet envelope detector.
Abstract: In this paper, we demonstrate optical transparency
in packet formatting and network traffic offered by all-optical
switching devices. Exploiting the bitwise processing capabilities
of these “optical transistors,” simple optical circuits are designed
verifying the independency to packet length, synchronization
and packet-to-packet power fluctuations. Devices with these attributes
are key elements for achieving network flexibility, fine
granularity and efficient bandwidth-on-demand use. To this end, a
header/payload separation circuit operating with IP-like packets,
a clock and data recovery circuit handling asynchronous packets
and a burst-mode receiver for bursty traffic are presented. These
network subsystems can find application in future high capacity
data-centric photonic packet switched networks.
Abstract: We consider path protection in the routing and
wavelength assignment (RWA) problem for impairment
constrained WDM opticalnetworks. 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 demonstrate the use of impairment constraint routing
for performance engineering of transparent metropolitan area
opticalnetworks. Our results show the relationship between
blocking probability and different network characteristics such
as span length, amplifier noise figure, and hit rate,and provide
information on the system specifications required to achieve
acceptable network performance.
Abstract: We present a detailed performance evaluation of a
hybrid optical switching architecture called Overspill Routing in
OpticalNetworks (ORION). The ORION architecture combines
wavelength and (electronic) packet switching, so as to obtain the
advantages of both switching paradigms. We have developed an
extensive network simulator where the basic features of the
ORION architecture were modeled, including suitable loadvarying
sources and edge/core node architectures. Various aspects
of the ORION architecture were studied including the routing
policies used (i.e. once ORION always ORION and lightpath reentry)
and the various options available for the buffer
architecture. The complete network study shows that ORION can
absorb temporary traffic overloads, as intended, provided
sufficient buffering is present.
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
routing and wavelength assignment (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: In this paper we present a signaling protocol for
QoS differentiation suitable for optical burst switching networks.
The proposed protocol is a two-way reservation scheme that
employs delayed and in-advance reservation of resources. In this
scheme delayed reservations may be relaxed, introducing a
reservation duration parameter that is negotiated during call
setup phase. This feature allows bursts to reserve resources
beyond their actual size to increase their successful forwarding
probability and is used to provide QoS differentiation. The
proposed signaling protocol offers a low blocking probability for
bursts that can tolerate the round-trip delay required for the
reservations. We present the main features of the protocol and
describe in detail timing considerations regarding the call setup
and the reservation process. We also describe several methods
for choosing the protocol parameters so as to optimize
performance and present corresponding evaluation results.
Furthermore, we compare the performance of the proposed
protocol against that of two other typical reservation protocols, a
Tell-and-Wait and a Tell-and-Go protocol.
Abstract: A key problem in networks that support advance reservations is the routing and time scheduling of connections with flexible starting time and known data transfer size. In this paper we present a multicost routing and scheduling algorithm for selecting the path to be followed by such a connection and the time the data should start and end transmission at each link so as to minimize the reception time at the destination, or optimize some other performance criterion. The utilization profiles of the network links, the link propagation delays, and the parameters of the connection to be scheduled form the inputs to the algorithm. We initially present a scheme of non-polynomial complexity to compute a set of so called non-dominated candidate paths, from which the optimal path can be found. We then propose two mechanisms to appropriately prune the set of candidate paths in order to find multicost routing and scheduling algorithms of polynomial complexity. We examine the performance of the algorithms in the special case of an Optical Burst Switched network. Our results indicate that the proposed polynomial-time algorithms have performance that is very close to that of the optimal algorithm. We also study the effects network propagation delays and link-state update policies have on performance.
Abstract: A key problem in networks that support advance reservations is the routing and time scheduling of
connections with flexible starting time and known data transfer size. In this paper we present a multicost
routing and scheduling algorithm for selecting the path to be followed by such a connection and the time the
data should start and end transmission at each link so as to minimize the reception time at the destination,
or optimize some other performance criterion. The utilization profiles of the network links, the link
propagation delays, and the parameters of the connection to be scheduled form the inputs to the algorithm.
We initially present a scheme of non-polynomial complexity to compute a set of so-called non-dominated
candidate paths, from which the optimal path can be found. We then propose two mechanisms to
appropriately prune the set of candidate paths in order to find multicost routing and scheduling algorithms of
polynomial complexity. We examine the performance of the algorithms in the special case of an Optical
Burst Switched network. Our results indicate that the proposed polynomial time algorithms have performance that is very close to that of the optimal algorithm. We also study the effects network
propagation delays and link-state update policies have on performance.
Abstract: A key problem in networks that support advance
reservations is the routing and time scheduling of connections
with flexible starting time. In this paper we present a multicost
routing and scheduling algorithm for selecting the path to be
followed by such a connection and the time the data should start
so as to minimize the reception time at the destination, or some
other QoS requirement. The utilization profiles of the network
links, the link propagation delays, and the parameters of the
connection to be scheduled form the inputs to the algorithm. We
initially present a scheme of non-polynomial complexity to
compute a set of so-called non-dominated candidate paths, from
which the optimal path can be found. By appropriately pruning
the set of candidate paths using path pseudo-domination
relationships, we also find multicost routing and scheduling
algorithms of polynomial complexity. We examine the
performance of the algorithms in the special case of an Optical
Burst Switched network. Our results indicate that the proposed
polynomial time algorithms have performance that it is very close
to that of the optimal algorithm.
Abstract: Orthogonal Frequency Division Multiplexing (OFDM)
has been recently proposed as a modulation technique for opticalnetworks, 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 Routing and Spectrum Allocation
(RSA) problem, as opposed to the typical Routing and
Wavelength Assignment (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) routing and (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: Random scaled sector graphs were introduced as a generalization of random geometric graphs to model networks of sensors using optical communication. In the random scaled sector graph model vertices are placed uniformly at random into the [0, 1]2 unit square. Each vertex i is assigned uniformly at random sector Si, of central angle {\'a}i, in a circle of radius ri (with vertex i as the origin). An arc is present from vertex i to any vertex j, if j falls in Si. In this work, we study the value of the chromatic number {\^O}(Gn), directed clique number {\`u}(Gn), and undirected clique number {\`u}2 (Gn) for random scaled sector graphs with n vertices, where each vertex spans a sector of {\'a} degrees with radius rn = \~{a}ln n/n. We prove that for values {\'a} < {\^I}, as n ¨ w.h.p., {\^O}(Gn) and {\`u}2 (Gn) are {\`E}(ln n/ln ln n), while {\`u}(Gn) is O(1), showing a clear difference with the random geometric graph model. For {\'a} > {\^I} w.h.p., {\^O}(Gn) and {\`u}2 (Gn) are {\`E} (ln n), being the same for random scaled sector and random geometric graphs, while {\`u}(Gn) is {\`E}(ln n/ln ln n).
Abstract: Recent advances in the all-optical signal processing
domain report high-speed and nontrivial
functionality directly implemented in the optical
layer. These developments mean that the alloptical
processing of packet headers has a future.
In this article we address various important control
plane issues that must be resolved when
designing networks based on all-optical packetswitched
nodes.
Abstract: Digital optical logic circuits capable of performing bit-wise signal processing are critical building blocks for the realization of future high-speed packet-switched networks. In this paper, we present recent advances in all-optical processing circuits and examine the potential of their integration into a system environment. On this concept, we demonstrate serial all-optical Boolean AND/XOR logic at 20 Gb/s and a novel all-optical packet clock recovery circuit, with low capturing time, suitable for burst-mode traffic. The circuits use the semiconductor-based ultrafast nonlinear interferometer (UNI) as the nonlinear switching element. We also present the integration of these circuits in a more complex unit that performs header and payload separation from short synchronous data packets at 10 Gb/s. Finally, we discuss a method to realize a novel packet scheduling switch architecture, which guarantees lossless communication for specific traffic burstiness constraints, using these logic units.
Abstract: We study computationally hard combinatorial problems arising from the important engineering question of how to maximize the number of connections that can be simultaneously served in a WDM optical network. In such networks, WDM technology can satisfy a set of connections by computing a route and assigning a wavelength to each connection so that no two connections routed through the same fiber are assigned the same wavelength. Each fiber supports a limited number of w wavelengths and in order to fully exploit the parallelism provided by the technology, one should select a set connections of maximum cardinality which can be satisfied using the available wavelengths. This is known as the maximum routing and path coloring problem (maxRPC).
Our main contribution is a general analysis method for a class of iterative algorithms for a more general coloring problem. A lower bound on the benefit of such an algorithm in terms of the optimal benefit and the number of available wavelengths is given by a benefit-revealing linear program. We apply this method to maxRPC in both undirected and bidirected rings to obtain bounds on the approximability of several algorithms. Our results also apply to the problem maxPC where paths instead of connections are given as part of the input. We also study the profit version of maxPC in rings where each path has a profit and the objective is to satisfy a set of paths of maximum total profit.
