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8/3/2019 13. Perspectivas Futuras Das Redes Opticas (Artigo)
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4684 JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 24, NO. 12, DECEMBER 2006
Future Optical NetworksMichael J. OMahony, Senior Member, IEEE, Christina Politi, Student Member, IEEE,
Dimitrios Klonidis, Member, IEEE, Reza Nejabati, Member, IEEE, andDimitra Simeonidou, Member, IEEE
Invited Paper
AbstractThis paper presents views on the future of optical net-working. A historical look at the emergence of optical networkingis first taken, followed by a discussion on the drivers pushing for anew and pervasive network, which is based on photonics and cansatisfy the needs of a broadening base of residential, business, andscientific users. Regional plans and targets for optical networkingare reviewed to understand which current approaches are judgedimportant. Today, two thrusts are driving separate optical networkinfrastructure models, namely 1) the need by nations to provide
a ubiquitous network infrastructure to support all the futureservices and telecommunication needs of residential and businessusers and 2) increasing demands by the scientific community fornetworks to support their requirements with respect to large-scaledata transport and processing. This paper discusses these networkmodels together with the key enabling technologies currently beingconsidered for future implementation, including optical circuit,burst and packet switching, and optical code-division multiplex-ing. Critical subsystem functionalities are also reviewed. The dis-cussion considers how these separate models might eventuallymerge to form a global optical network infrastructure.
Index TermsOptical communications, optical networks.
I. INTRODUCTIONEMERGENCE OF
OPTICAL NETWORKING
THE INVENTION of the laser by Schawlow and Townes
in 1958, followed by the work of Kao and Hockham
on optical fibers in 1965, and the subsequent demonstration
of optical fiber as a practical communication medium by
Maurer et al. in 1970 brought into being a technology plat-
form capable of supporting national and global communication
requirements for the 21st century and beyond. In the late
1970s, fiber began to replace coaxial cable as the transmission
medium in the trunk systems of telecommunication networks,
bringing many advantages both technical and economic. The
creation of the Internet (with Transmission Control Protocol
(TCP)/IP) in 1983 and subsequently the World Wide Web in1993 sparked the growth of data traffic on the network, and
Manuscript received April 19, 2006; revised September 20, 2006.M. J. OMahony, R. Nejabati, and D. Simeonidou are with the Photonic Net-
works Research Laboratory, University of Essex, CO4 3SQ Colchester, U.K.(e-mail: mikej@essex.ac.uk; mejabati@essex.ac.uk; dsimeo@essex.ac.uk).
C. Politi was with the Photonic Networks Research Laboratory, Universityof Essex, CO4 3SQ Colchester, U.K. She is now with the National TechnicalUniversity of Athens, 10682 Athens, Greece (e-mail: tpoliti@telecom.ntua.gr).
D. Klonidis was with the Photonic Networks Research Laboratory, Uni-versity of Essex, CO4 3SQ Colchester, U.K. He is now with the AthensInformation Technology Centre, 19002 Athens, Greece (e-mail: dikl@ait.gr).
Color versions of Figs. 25 are available online at http://ieeexplore.ieee.org.Digital Object Identifier 10.1109/JLT.2006.885765
Fig. 1. Evolution of transport and service bit rates.
in 2002, or thereabouts, the amount of network data traffic
exceeded that of voice traffic. In the decade from 1985 to
1995, four significant events heralded the possibility of optical
networking, where both transmission and switching might be
based on optics. These were 1) the realization of optical am-
plifiers allowing 2) the economic deployment of wavelength
division multiplexing (WDM), 3) the demonstration of an
optical cross-connect (OXC) enabling the rapid reconfigura-
tion of lightpaths based on wavelength channels, and 4) the
convergence of service and transport transmission rate.
Early visions of optical networking considered, for example,
the deployment of OXCs to form an extension to the exist-
ing synchronous digital hierarchy/synchronous optical network
(SDH/SONET) network layersthe optical layer. In this paper,
an OXC is defined as a general wavelength switch that can be
realized in an all-optical (transparent) manner [optical input,
optical switch fabric, optical output (OOO)] or in an opaque
manner [optical input, electrical switch fabric, optical output
(OEO)] through choice of technologies. The optical layer wouldenable long-haul transit traffic to bypass the main switch nodes
and hence reduce the size and cost of the digital cross-connects
(DXCs). Demonstrations of such reconfigurable networks were
carried out in Europe and the United States in 1994 [1], [2].
The convergence of service and transport wavelength bit
rates around the year 2000 (Fig. 1), at a bit rate of 10 Gb/s,opened the possibility of direct interfacing between, for exam-
ple, an IP network and an optical transport network employing
WDM and OXCs, where the granularity of the network directly
matched the router interface rate. The figure also shows that
convergence at 40 Gb/s occurred in 2005 with the availability of
40-Gb/s routers and engineered 40-Gb/s dense WDM (DWDM)
0733-8724/$20.00 2006 IEEE
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Fig. 2. Schematic of telecommunications network.
transmission systems [3]. Each wavelength, of course, supports
many traffic streams.
Fig. 2 shows a schematic of the possible future telecommuni-
cations network showing core, metro, and access layers, which
builds on earlier concepts and will be used to discuss views
of future optical networks. The core cloud represents an opti-
cal network comprising a number of nodes interconnected by
amplified fiber links employing DWDM. The nodes comprise
an OXC in conjunction with a network service element (SE).
The OXC supports the bypass function and allows specific
wavelength channels to be dropped to the SE, which, for exam-
ple, could be an IP/multiprotocol label switching (IP/MPLS)
router, an SDH/SONET DXC, or an optical burst, packet,
or Ethernet switch, as discussed later. At the network edge,
traffic is mapped onto the network services via an edge inter-
face/router, which can perform either user network interface
(UNI) or network node interface (NNI) functionality as definedby the optical internetworking forum [4], depending on what is
connected to the core. A control plane is required to establish
paths across the data plane as requested at the network edge,
mapping, for example, an IP/MPLS stream from the metropoli-
tan area network onto a specific wavelength; path establishment
can be done in a centralized or distributed manner.
Fig. 2, however, shows only one of a number of network
models, based on optical technology, currently being developed
to satisfy an increasing diversity of users with greatly differing
service requirements; networks to support scientific users are
another example and are discussed below. Currently, operator
business models do not encourage the development of a ho-mogeneous network, and so, interoperability issues are arising
between these different (heterogeneous) networks. This paper
addresses two developing optical network models, representing
residential/business (telco) and scientific users, to understand
their requirements and evolution paths. The key (optical layer)
functionalities required in these networks are considered (rather
than the detail of all the technology issues that inevitably are
part of any evolution) with a view to understanding how a
future interoperable global heterogeneous optical network with
end-to-end connectivity and possibly eventually transparent
(homogeneous) networking might be achieved. It is recognized
that a number of functions, for example, dispersion compen-
sation, are currently migrating to the electronic domain, butthese topics are not considered here. As discussed earlier,
TABLE IRESIDENTIAL SERVICE REQUIREMENTS
optical networking includes the concept of OXCs (wavelength
switches) using either an OEO switching or OOO approach; the
latter is currently a more futuristic approach supporting network
transparency, which may well solve many problems including
cost issues related to the reduction in the required number ofOEO interfaces. However, recent approaches by Infinera [5],
where all the interfaces are integrated on a chip, challenge this
simple viewpoint.
In this paper, Section II looks at applications and their
requirements, Section III considers the importance of future
networks together with regional plans for optical infrastruc-
tures, Sections IV and V look at two emerging network models
as represented by national telecommunication networks and na-
tional research and educational networks (NRENs), Sections VI
and VII consider key networking approaches and technologies,
Section VII looks at a possible future global heterogeneous
optical network serving all users, and Section VIII summa-rizes. Here, it should be noted that the views in this paper
are essentially research led, and the adoption of many of the
approaches and technologies highlighted are, as always, subject
to commercial considerations that can change rapidly, as seen
in the year 2000.
II. 21ST CENTURY: EDGE OF THE DATA TSUNAMI
Between the years 2000 and 2003, the volume of data grew
from 3 billion to 24 billion gigabytes, with 93% of all data
being born digitally [6]. This highlights the start of a huge wave
of data to be expected over the next five to ten years as many
traditional services and industries move from analog to digital
(e.g., TV broadcasting and movie making), and the spread
and development of e-services across government, health, and
security become more available and acceptable. In addition
to the increased expectations from residential and business
users, new requirements from scientific users are driving the
deployment of high-performance optical networking. Examples
of these drivers are as follows.
A. Residential Users
The bandwidth requirements for fixed home users have been
estimated at 100 Mb/s (downstream) in the near future, asshown in Table I [7], the main demand arising from Triple
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Play services (already launched in a number of EU countries)
that include voice data and video, and mobile users will also
require high bandwidth access, estimated as 30 Mb/s in this
model. These figures would be greatly increased if, as ex-
pected in Japan, superhigh-definition TV would also become a
broadcast service, moving access speed requirements into the
gigabits per second regime.
B. Large Business/Enterprise Users
Large business/enterprise users require access to high sym-
metric bandwidths (e.g., up to 10 Gb/s) for virtual private
networks, disaster recovery, storage, etc.
C. Scientific Users (Currently Served by NRENs)
Application examples include the following.
1) High-Energy Particle Physics: The next generation of
experiments at the Large Hadron Collider in CERN will pro-
duce data sets measured in tens of petabytes per year that canonly be processed and analyzed by globally distributed com-
puting resources. Experiments require deterministic transport
of 10- to 100-TB data sets, and a 100-TB data set requires a
throughput of 10 Gb/s for delivery within 24 h. Thus, optical
network services will be crucial to this discipline where dedi-
cated and guaranteed bandwidth is required for periods of days.
2) Very Long Baseline Interferometry (VLBI): VLBI is used
by radio astronomers to obtain detailed images of cosmic radio
sources, where the combination of signals from two or more
widely separated radio telescopes can effectively create an
instrument with a resolving power proportional to their spatial
separation. e-VLBI [8] will use high-speed networks to transfer
telescope data to a correlator, and the availability of opticalnetwork services at multi-gigabits per second (1040 Gb/s)
throughput will greatly increase the capability.
3) e-Health: Remote mammography poses challenges for
the deployment of supporting IT systems due to both the size
and the quantity of images, with networks required to transport
1.2 GB of data every 30 s. The availability of optical network
services offering real-time guarantees is important in this field.
All these applications, whether residential, scientific, or
business related, look for high bit rate access, wavelength
and subwavelength granularity, and quality-of-service (QoS)
guarantees; these qualities can be delivered through optical
networking.
III. MOVE TOWARD PERVASIVE AND UBIQUITOUS
NETWORKSR EGIONAL PLANS
In the face of this wave of new data-oriented services, the tra-
ditional telecommunications network is seen as transforming to
a generic and data-centric communications network optimized
for data. Most regions of the world have a vision of moving to
a situation that in Japan is called ubiquitous network society
and in Europe is called ambient intelligence. By this is meant
an environment (comprising wired and wireless network) where
one can communicate effortlessly and access key information
resources in a straightforward manner. To achieve these ideals,the ultimate network will have as its main building blocks
a fixed optical network platform accessed through wireless
(Wi-Fi, WiMax, UMTS) and wired infrastructures, such as fiber
to the premises (FTTP). Moving to such an all-pervasive net-
worked society, however, puts increased demands on network
reliability and security; it must be there when it is needed and
have the ability and flexibility to interface and integrate multiple
technologies and service requirements.The importance of future national network infrastructures is
mirrored in the ongoing discussions on how a new Internet
might be realized. It has been commented [9] that the Inter-
net is expanding from an information service to a critical
infrastructure for all aspects of society, and so, new network
architectures must evolve to overcome many of the problems
inherent in the current Internet. NRENs and experimental net-
work testbeds are currently being used (in part) to understand
how a new Internet might be constructed. The inference is
that at all levels, communication networks are no longer just
desirable but critical for a nations development and security.
Regional views on expected growth in capacity demands,
traffic profiles of new services, and the need to move to data-
centric networking are reflected in the scope of the major
research programs and their associated projects funded by
regional governments.
In Europe, the European Commission (EC) periodically re-
leases tranches of funding for R&D. Currently, there are no
overarching roadmaps for future networks, but a number of very
large integrated projects identify their own vision of the
future. The NOBEL project [10], for example, studies the
evolution of core and metropolitan optical transport networks,
supporting end-to-end QoS, with intelligent data-centric solu-
tions based on automatic switched optical network (ASON)
and generalized MPLS (GMPLS) [3] together with optical burstswitching (OBS) and optical packet switching (OPS).
The investigation of OPS has had long-term support within
EU and national programs with projects such as ATMOS,
KEOPS, DAVID [11], and OPSNET/OPORON [12], [13]
developing the technology and its application over a period of
about 15 years; however, it is still seen as a very future tech-
nology. On the other hand, OBS and GMPLS approaches are
viewed as realistic possibilities for more near-term deployment,
and research in these areas is also echoed in national funding in
many countries.
Recently, BT (U.K.) has committed itself to moving to a
converged national network solution (BT 21CN Network) withan IP/MPLS core [14]. This change is also under way in other
countries (Netherlands and Australia) and is significant in that
the architecture opens the path to a full optical transport net-
work at some point in the future, with the possible replacement
of OEO switches and regenerators with OOO technologies.
Europe is also characterized by a large number of NRENs
that exist in most member countries. These networks are na-
tionally funded and commonly used for research into scientific
applications (of the type discussed above). The EC funds an
overlay network GEANT [15] that provides interconnections
between these national networks and provides international
connections, for example, to the United States. These networks
look to lambda networking based on scheduled or dynamicprovision of lightpaths.
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The Pacific Rim countries of Japan and Korea are well known
for their ambitious plans in relation to broadband deployment
and enhanced network infrastructures.
Japan has well-defined R&D programs; some are initiated
by the Japanese government with a view to evolving a legacy
telecommunications network to an IP over WDM network.
Such programs move in tandem with operator plans; forexample, NTT plans to migrate 30 million customers to FTTP
and IP telephony by 2010. The most recent program focused on
developing an all-optical transport network with terabit capa-
bility [16]. This paper comprised the study and development
of photonic nodes such as fast OXC based on microelectro-
mechanical system (MEMS) together with control plane (such
as GMPLS), OBS, and high-bit-rate ultralong transmission
based on DWDM (up to 1000 channels) and optical time
division multiplexing (OTDM). For photonic routing, targets
are related to the feasibility of 100-Tb/s routers and network
architectures appropriate to a terabit-class wavelength-routed
optical network. The current program seeks to understand how
this optical platform can support new bandwidth demanding
applications such as grid computing and real-time applications
like video, digital cinema, and network storage. It is anticipated
that broadcasting and streaming of high-quality video using
high- or superhigh-definition TV (4.5 Gb/s) together with grid
computing and e-science applications may need to be sup-
ported, many of these on FTTP. Key targets include 160-Gb/s
multilevel transmission systems using differential quadrature
phase shift keying/quadratic-amplitude modulation, etc., aim-
ing at bandwidth utilization of more than 2 bits/Hz by 2010.
Ultrafast signal processing functions such as optical gating,
optical-3R, OTDM, optical multiplexing/demultiplexing, and
optical wavelength conversion are seen as important.South Korea is known to (currently) have the worlds highest
(> 60%) penetration of broadband (> 4 Mb/s) Internet access.
The broadband convergence network (BcG) is the Korean
vision of the ITU-T next-generation (NG) network defining
future transport and access architectures and is expected to sup-
port 20 million users by the year 2010. In the access network,
technologies will be FTTP with E-passive optical network
(E-PON) and WDM-PON. The BcG transport network will be
a managed optical network with support for end-to-end QoS
provisioning. BcG is seen as a ubiquitous network that will also
support grid applications.
China has a number of optical network testbeds for ASONand OBS, which investigate the support of future IP-based
services. Moreover, there is a strong interest in optical grid
networking with associated research into architectures, control
plane functions, and interfaces [21].
In the USA, funding for research (nonindustrial) is through
the National Science Foundation and for large projects often
through DARPA. Current major photonic activities include
studies on optical code-division multiplexing (OCDM) and
terabit router technology; the latter represented by projects
IRIS [17] and LASOR [18] whose goal is to realize 100-Tb/s
routers. Both projects take the route of OPS, which offers
attractions in terms of footprint and power requirements.
The strong interest in optical networking in the USA isreflected in the existence of a number of national testbeds,
Fig. 3. Network evolution.
which enable the interconnection of scientific users and sup-port research into future networks. For example, the National
Lambda Rail (NLR) [19] is a high-speed national computer
network that is also used as a network testbed for experimen-
tation with NG large-scale networks. Links in the network
use DWDM at 10-Gb/s/channel. NLRs services are already
in use by many network research projects, for example, the
NSF OptIPuter project and Internet 2s Hybrid Optical Packet
Infrastructure (HOPI) project, which looks at a future in-
frastructure comprising an IP core network together with an
optically switched wavelength set, for the dynamic provisioning
of high-capacity paths. Currently being proposed is a new na-
tional facility GENI [20], which includes a global experimental
facility designed to explore new network architectures with
the broad scope of understanding new paradigms for Internet-
type networks.
IV. EVOLUTION TOWARD NATIONAL OPTICALTELECOMMUNICATION NETWORKS
Fig. 3 outlines a possible evolution route for the network
structures and technologies that may appear in the future op-
tical (transport) network; a version of many such diagrams
have been presented over the years. Progress toward optical
networking has been much slower than envisaged in the late
1990s, and currently, the first real steps toward networkingare seen in the deployment of reconfigurable optical adddrop
multiplexers (ROADMs), in particular those based on a mul-
tiport wavelength selective switch (WSS) [22]. These devices
have the functionality of OXCsan exciting development. In
the following discussion, the evolution is examined from three
viewpoints.
A. Transmission Speed
Current networks employ amplified DWDM systems with
individual channel bit rates up to 10 Gb/s to connect main
switching centers, and the industry is on the verge of deploying
40-Gb/s systems. There are many reasons for believing that bitrates will increase beyond 10 Gb/s and perhaps even to 160 Gb/s
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(Fig. 3). For example, 1) in the past, it has always been
advantageous to move to high bit rates from a cost viewpoint;
2) although optical amplifiers are reasonably bit rate agnostic,
most of the more advanced functions currently considered for
future networks such as all-optical regeneration, wavelength
conversion, dispersion compensators, etc., can only operate on
a single wavelength; and 3) when future OOO switches aredeployed, then increasing the bit rate can help in reducing the
port count required of the switch fabrics [23], as large OOO
switch fabrics are difficult to realize, for example, in the case
of an OPS where it is difficult to scale fabrics; for wavelength
switching, waveband approaches [24] can be used to mitigate
these technological issues. Increasing the bit rate, however,
leads to a more demanding requirement for system design to
minimize the effects of dispersion (chromatic and polarization)
and nonlinear effects; thus, there is the increasing interest in
modulation techniques such as differential phase-shift keying
(DPSK), which is more robust to transmission impairments than
intensity modulation.
B. Network Switching
Much research has focused on moving from the traditional
circuit-based switching to a more dynamic and data-centric
network enabling rapid lightpath reconfiguration and providing
subwavelength granularity, as needed by the new applications
discussed above. In its present form, the network has a complex
layering to allow the simultaneous support of data and voice
services; in this mode, data (IP) may be encapsulated into
asynchronous transfer mode (ATM) cells (or SDH/SONET
frames) for transmission across the point-to-point connections
between DXCs. Currently, the network is changing to a moredata-oriented version of SDH/SONET (NG SDH/SONET).
Fig. 3 illustrates the possible further stages in the network
switching evolution. Fig. 3(a) represents the move to a more
data-centric and dynamic switching model using an ASON
[4] architecture, which would allow automated lighpath pro-
visioning and supports NG-SDH/SONET with DXC or OXC
(OEO) switching in the data plane. Fig. 3(a) also shows that
a move to IP/MPLS (i.e., IP routers) or GMPLS (with OEO
or OOO wavelength switches) architectures is foreseen, which
provides an enhanced dynamic capability GMPLS to allow all
transport modes, circuits, burst, and packets to be supported and
can be deployed in either a centralized or a distributed mode.This represents one of the options to build a converged net-
work, where the backbone is a multitechnology IP/GMPLS/
OEO/OOO network supporting all services (voice, data, video),
which may overtake the ASON architecture. It is also the
case that in recent times carrier Ethernet [25] (based on native
Ethernet or MPLS) looks increasingly attractive across all
layers of the network. Indeed, within the U.K., some (small)
network providers already operate national converged networks
with Ethernet switching elements. The move toward 100 GbE
standards illustrates the importance of this technology and
hints of future major roles in NG networks. Fig. 3(b) rep-
resents a move to a user-centric design based on OBS with
GMPLS (OBS/GMPLS); this technology provides subwave-length granularity and is also of interest to future optical grid
networks [26]. Finally, Fig. 3(c) represents the move to an
OPS network, where MPLS provides a common (across elec-
trical/optical domains) control plane. OPS offers the finest
granularity and is still seen as the ultimate switching technique,
but its success will depend on many technological advances;
these options are discussed in more detail in Section VI.
The metro/aggregation network (Fig. 2) delivers data fromthe access to the edge device for processing and will likely use
DWDM supporting, for example, carrier Ethernet, but it is the
access network that provides the key to the future, in particular,
the move toward FTTP.
C. Access PONs
FTTP supports the PON concept, which has been studied
for over 20 years but now increasingly deployed. PONs offer
multiservice (voice, data, video, and telemetry) and multiproto-
col (IP, TDM, and ATM) support and thus are a very flexible
infrastructure. A number of possibilities have been studied,
which exploit the basic PON concept but with a view to reduce
costs. Two examples follow.
Long-Reach PONs: Some operators [27] see the possibility
of merging metro and access in a long-reach (amplified) PON.
Optical amplification is included to boost the power budget and
increase bandwidth, range, and number of splits. Long reach is
used to bypass the metro network and terminate at a core edge
node; this enables the removal of the local exchange or remote
concentrator site. In the U.K., this would require 100 of these
core edge nodes with long reach spans of 100 km and bit rates
of at least 10 Gb/s.
CWDM/OCDMA PONs: Coarse WDM (CWDM) allows
low-cost WDM to be deployed (as device cooling is not re-quired), and CWDM uses a channel spacing of 20 nm, so only
eight or so channels can normally be deployed. Optical code-
division multiple access (OCDMA) has been demonstrated
[28], [29] as a robust complementary technology that could
also be deployed in conjunction with CWDM to increase the
number of users. As with WDM, OCDMA offers the possibility
of translation from one channel to another (code translation),
opening many interesting possibilities.
V. EMERGENCE OF AN ALTERNATIVE NETWORK MODEL
Following the realization that a computer bus speed cannot
match a lambda-based optical network (at 10 Gb/s), it was
suggested that it should be possible to create a tightly integrated
cluster of computational, storage, visualization, and instrumen-
tation resources linked over parallel dedicated optical networks
across campus, metro, national, and international scales to sup-
port scientific tasks, and this concept is now being demonstrated
in network testbeds and NRENs. Scientific and grid applica-
tions have complex workflows, which will make extensive use
of an optical network, for example, to transfer huge amounts of
data between storage and computing or visualization resources.
In many ways, NRENs mirror the possible future requirements
on telecommunication networks and may evolve to use a similarset of optical technologies (e.g., OBS).
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Fig. 4. NRENs.
NRENs have high-speed optical backbones and can already
offer dedicated channels (wavelengths) to individual research
users. Switching within these networks is, at present, generally
achieved through OEO switches, allowing wavelength rout-
ing. NRENs are seen as an important vehicle for advancing
innovation and discovery and as a platform for undertaking
network research. In Europe, GEANT connects 30 such NRENs
(with bit rates up to 10 Gb/s); in Japan, JGN2 provides an
research and development environment (at 10 Gb/s); Abiline in
the United States interconnects 50 states; Canada has CA,net;
and Chinas CERNET2 connects 20 cities (at 10 Gb/s). Global
Lambda Integrated Facility (GLIF) [30] is an international
virtual organisation whose members are NRENs and promotes
lambda networking for international collaboration and research.
In todays NRENs, resources are provided either exclusively
for an application or are shared on a best-effort base. Many
emerging applications demonstrate a dynamic nature and re-
quire connectivity, bandwidth, or QoS that may change with
time and/or user profile. The administrative and technical over-
head to provide such network services and the high associatedcosts currently inhibit a wider commercial adoption of such de-
manding applications. A short- to medium-term solution to the
above requirements is the ability to negotiate flexible service
level agreements between the application and the resource pro-
vided. This is a subject of current research and standardization
within the Global Grid Forum [31].
As a longer-term solution, a new network service model that
allows users or/and applications to adapt the network to their
applications is discussed here. This network model will require
the network topology to migrate from the traditional edge-core
telecom model (Fig. 2) to a more distributed model. In this type
of network, the user may have the ability to control routingin an end-to-end manner and set up and tear-down lightpaths
between routing domains. To facilitate this level of user control,
users or applications will be offered management/control of the
network resources (i.e., bandwidth allocation at the wavelength
and subwavelength level). These resources could be leased and
exchanged between users. Such new topological solutions will
have a direct impact on network management and control as
well as the network infrastructure, including network elements
and user interfaces to enable and support these functionalities.
An important step toward this is the ability to make dynamic
resource reservations immediately when needed or in advance
for a time period in the future. Dynamic optical networking
can satisfy the bandwidth and reconfiguration requirements ofthis model together with software tools and frameworks for
end-to-end on-demand provisioning of network services across
multiple administrative and network technology domains.
Fig. 4 illustrates the global interconnection of a number of
NRENs using interconnecting networks such as GEANT or
GLIF. Within each network, the choice of switching technol-
ogy and transport format is an important consideration that
influences the ability to deliver NG network services. As dis-cussed above, optical switching offers bandwidth manipulation
at the wavelength and subwavelength level (e.g., with optical
circuit/burst/packet switching) as well as the capability to ac-
commodate a wide variety of traffic characteristics and distri-
butions. The transport format determines how signaling and
control messages as well as data are sent from the user/client
to the optical network and depends on the form of switching.
Thus, for 1) circuit switching, signaling is sent in conjunction
with the data or over a dedicated wavelength or SDH/SONET
connection, and for 2) OBS/OPS, signaling is sent using a
signaling packet or control burst; hybrid approaches can also
be used.
The service model proposed here does not depend on
transport technology (i.e., CS, OBS, OPS). Actually, the first
implementation will address wavelength-switched optical in-
frastructures. However, subwavelength granularity will enable
the offering of dynamic network services to a wider range of
users and applications.
The choice of transport format is mainly driven by an un-
derstanding of the traffic characteristics generated by users and
their applications. For example, wavelength switching may be
the preferred solution for moving terabytes of data from A to B
but is inappropriate for video games applications.
The diagram also shows other important elements of this
global network. Each NREN has an associated network re-sources provisioning system (NRPS) currently being devel-
oped and deployed around the world by different international
organizations. These systems are based on the abstraction of
network resources. For instance, the user-controlled lightpath
provisioning system (UCLP) can be thought of as a configu-
ration and partition manager that exposes each lightpath in a
physical network and each network element associated with a
lightpath as an object or service that can be put under the
control of different network users to create their own IP network
topologies. UCLP, as proposed by CANARIE, is an NRPS that
deals with the abstraction of network resources as objects to
allow end users to manage them in order to build reconfigurablediscipline or application-specific networks. More specifically,
UCLP [32] is a set of distributed services that are used to es-
tablish and tear down end-to-end connections across an optical
network.
The service plane mainly involves application-level middle-
ware and Application Programming Interfaces (APIs). The
service middleware in this architecture will provide a unified
application execution environment relying on a high-bandwidth
QoS-enabled network infrastructure of global scale. The mid-
dleware could implement service abstractions exposing net-
work resources (end-to-end QoS management). Hence, it will
be possible for an application to request network constraints
(e.g., guaranteed bandwidth or latency among computationalnodes).
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VI. KEY NETWORK TECHNOLOGIES
Research on advanced switching and networking technolo-
gies is mainly determined by the needs identified in the core
of the network, where large amounts of data with different
characteristics (generated by different services) require efficient
switching in terms of bandwidth utilization, resource manage-
ment, and performance. Following the switching technologyevolution plan presented earlier (Fig. 3), research in the area
of optical networking can be categorized in a) the near termas automatically reconfigurable circuit-switching solutions,
b) near to long term as OBS solutions, and c) long term as OPS
solutions. The feasibility of implementing these solutions is
reflected in the results of research studies and demonstrations;
these are briefly discussed here to understand feasibility.
A. Optical Circuit Switching
The widely deployed circuit-switching technology is cur-
rently moving toward the deployment of fast and automatically
reconfigurable nodes with switching granularity at the wave-length level. This is now represented in standards by the ASON
architecture [4]. To enable dynamic networking, the provi-
sioning of lightpaths is automated. This is achieved with an
advanced control plane, which provides the necessary signaling
capabilities. The user can request, through the UNI, a new
lightpath, and the controllers in the network nodes exchange,
through NNIs, the necessary information for the lightpath setup
(allocation of wavelengths, etc.).
Research in this area is at the level of final product develop-
ment and is carried out by a number of leading companies pre-
senting applicable solutions for a) node design like ROADMs
based on WSSs and for b) control planes for dynamic network-ing, channel provisioning, and management based on IP/MPLS
solutions. Demonstrations of these can both be represented as
that in Fig. 2, where for IP/MPLS the core has an MPLS router
as the SE together with an optical switch (initially OEO, but
with possible upgrading to OOO) at the nodes. For the ASON
network, the SE represents an OXC controller, and lightpaths
are being set up by the control layer.
As currently viewed, the ASON network, which is based on
SDH/SONET, has advantages in terms of QoS, management,
and security, and is able to reduce the load taken from the
IP/MPLS network. However, due to the domination of IP-
centric traffic, future solutions are focusing on bursty net-
working models able to handle dynamic segments instead ofcontinuous data.
B. OBS
Segmented data transmission has been derived by the In-
ternet paradigm in order to mainly offer increased bandwidth
utilization and reduced overhead. One idea is to set-up and tear
down a path dynamically (similar to circuit switching) but for
a much shorter duration, equal only to the duration required
to transmit a complete set of data, a data burst. This is the
fundamental premise of OBS, which is based on the separation
of the control and data planes, and the segregation of func-
tionality within the appropriate domain (electronic or optical).Prior to data burst transmission, a burst control packet (BCP)
is created and sent toward the destination by an OBS ingress
node (edge router). The BCP is typically sent out-of-band over
a separate signaling wavelength and processed at intermediate
OBS routers. It informs each node of the impending data
burst and sets up an optical path for its corresponding data
burst. Data bursts remain in the optical plane end-to-end and
are typically not buffered as they transit the network core.The bursts content, protocol, bit rate, modulation format, and
encoding are completely transparent to the intermediate routers.
The main advantages of the OBS in comparison to the other
optical networking schemes are that unlike optical wavelength-
switched networks, the optical bandwidth is reserved only for
the duration of the burst, and that unlike the OPS network, it can
be bufferless, but it also needs a switch reconfiguration speed in
the order of microseconds.
Due to these implementation issues (easier processing,
bufferless operation, and slow switching requirements), OBS
is seen as a practical solution and is considered as the next
evolution step in future optical networking. The feasibility of
OBS technology can be identified by a number of reportedresults from field trials and testbeds. The most complete demon-
strator was set up in Japan under the OBS network project
and accommodated six nodes with MEMS-based switches,
achieving switching times of 1 ms for bursts with a minimum
size of 100 ms [33]. In China, a collaborative work between two
universities under the TBOBS project resulted in an OBS field
experiment that comprises three edges and one core node [34].
In this demonstrator, switching is achieved in nanosecond times
utilizing a tunable WSS based on semiconductor optical am-
plifiers (SOAs). Additionally, high-speed electronics are used
for the header control mechanism. The fast switching time
allows routing of relatively small packets, 720 s, transmittedat 1.25 Gb/s.
OBS makes an attractive proposition for deployment in
metro/wide area networks. Until now, the only way to build net-
works with more than 10 Gb of bandwidth has required the use
of DWDM technology to create point-to-point circuits for every
path across a network. This has proven to be both expensive and
cumbersome to manage. OBS offers a new alternative by using
burst transponders that can communicate directly with multiple
destinations across a network. This means no circuit needs to
be preprovisioned, and high-speed transponders need not be
dedicated for every single communication path. This frees up
capital, simplifies network design, and enables the creation of
packet metro aggregation networks where bandwidth shifts inreal time to where it is needed in the network.
A new generation of startup companies [35] is appearing and,
for the first time, delivering commercial equipment merging
the best of both worldsthe efficiencies of Ethernet packet
switching with the bandwidth of DWDM optical technology.
OBS has also been identified as a compatible solution for
the physical layer infrastructure in grid computing applications
with possible realization on NRENs [36].
C. OPS
OPS is a purely connectionless networking solution thatis fully compatible with IP-centric data traffic and offers the
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finest network granularity and optimum bandwidth utilization.
In OPS networking, incoming IP packets are assembled at
the network edge to form the payload of an optical packet,
which has a leading optical header. At the switch node, the
header is interrogated and used to configure the associated
optical switch for forwarding of the payload. OPS requires the
use of more demanding subsystems (than OBS) with intrinsicintelligence to realize adequate packet processing and routing
on the fly. The main challenges in OPS are the implementation
of the optical header processing mechanism, the development
of an intelligent switch controller, the realization of ultrafast
switching in nanosecond timescale, and the exploitation of
buffering mechanisms to reduce packet blocking.
In contrast to OBS, complete OPS demonstrators are mainly
restricted to the development of fully functional but small
switching elements that simply show the feasibility of fast
packet switching on the physical layer with some extensions to
the link layer. In the OPSnet project [12], dynamic switching of
asynchronous optical packets at 40 Gb/s has been demonstrated
in a fully controllable set up able to identify and process the
header and route the payload accordingly. In [37], contention
resolution on the wavelength level is also considered on a
10-Gb/s packet switching node. Newly developed schemes [38]
are based on the same concept and use more advanced elec-
tronics for faster clock extraction and processing, while the
integration capabilities with the WSS are investigated. A more
feasible approach toward the implementation of OPS considers
the use of synchronously (slotted) transmitted packets with
fixed lengths, but in this case, the hardware overhead is on
the implementation of the packet synchronizer at the input.
However, slotted solutions are attractive for other applications
like computer interconnects.Despite their feasibility limitations, OPS demonstrators
assisted the development of numerous ultrafast switching and
processing techniques regarding wavelength conversion, header
encoding/decoding and processing, label swapping, fast clock
extraction, regeneration, and optical contention resolution.
Additionally, various switch architectural designs and control
protocols have been proposed, which in combination with the
significant technological advances over the last years indicated
the possible deployment of OPS in the future. However, its
future relies on advances in photonic integration that will enable
cost-effective subsystems to be constructed.
D. OCDMA
OCDMA has been studied as an alternative networking
solution able to increase passively the number of users per
wavelength. The other solution is OTDM, but this requires ac-
tive processing. The advantages of OCDMA have been evident
for some time through its successful use in wireless networks.
For optical networking, its potential for enhanced security,
decentralized control, and flexibility in bandwidth granularity
provides interesting possibilities to solve these well-known
issues in the development of future networks. Additionally, the
feasibility of OCDMA has been assisted by newly developedcomponents able to provide simple ways of coding and decod-
ing signals in a passive manner, which is a particularly attractive
and cost-effective feature.
The principle of OCDMA relies on applying unique or-
thogonal codes to each user while they share the same band-
width (wavelength). User codes are multiplexed on to the fiber
channel and are matched at the receiver against copies of the
codes through an autocorrelation process. The code length ischosen to try and maximize discrimination in the detection
process, where multiple access interference (MAI) is a key
problem. OCDMA must support many users, and hence, the
codes chosen must satisfy certain correlation conditions. Both
the time-shifted autocorrelation function of each code and the
cross-correlation function between codes must be low when
compared to the peak autocorrelation value. The recent devel-
opment of coherent OCDMA en/decoders allowed the efficient
separation of a large number of simultaneously transmitted
users providing a feasible solution for low-cost applications
in multiuser LAN environments. Also, the combination of
OCDMA with CWDM technology can boost the total number
of supported users, showing compatibility with PON architec-
tures for FTTP solutions.
The combination of OCDMA and WDM technology in
a LAN/access environment has been recently demonstrated
in [28]. The paper reported the field trial of a 3-WDM
10-OCDMA 10.71-Gb/s system over a 111-km field trial.
Key aspects of the approach were 1) the use of a multiport
encoder/decoder in the central office, which can give multiple
optical codes in multiple-wavelength bands (this device gives
good correlation properties to suppress MAI and beat noise),
and 2) the use of a super structured fiber Bragg grating (SSFBG)
(or tunable transversal filter) at the optical network unit (ONU).
The use of DPSKOCDMA with balanced detection is seen asa key enabler over conventional ON/OFF-keying OCDMA with
superior noise performance.
In recent times, other interesting possibilities for OCDMA
have been considered. One such is the concept of code trans-
lation, where, analogous to wavelength conversion, codes can
be transformed to match users in other subnets (i.e., provide
routing). Experiments [29] have also shown how a narrowband
spectral-phase-encoded (NB-SPE) OCDMA compatible with
existing WDM networks can be used with passive code transla-
tion to play a role in ring- and star-based network architectures.
Finally, the use of optical codes under a different concept has
shown the feasibility to implement an OPS node [39]. Here, op-tical codes are used as labels in order to distinguish the different
headers of the transmitted packets. After header matching, the
autocorrelation peak triggers an electronic controller that shows
the output port where the packet should be routed.
VII. KEY SUBSYSTEMS AND TECHNOLOGIES
The roadmap in Fig. 3 and the above discussion broadly out-
line a much argued route forward to the future with switching or
transmission aspects relevant to a future global heterogeneous
optical network. Generally, the picture is that transmission
speeds are still predicted to increase as before (e.g., to 160 Gb/s
probably using DPSK), within the context of a more dynamicand granular network, supported by appropriate control plane
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(e.g., GMPLS with extensions). Many of the key functional
subsystems needed for this future flexible network have al-
ready been described with experimental demonstrations (e.g.,
all-optical regeneration at 40 Gb/s has been widely reported
[40], as has wavelength conversion, fast tunable lasers, tunable
dispersion compensators, MEMS-based switch fabrics, etc.).
Others are still gleams in the eye of the network designerwith, as yet, no sure route for realization, for example, optical
memory and multiwavelength optical regeneration.
However, what has become well recognized is that the
future of realizing the full potential of optical networks, at
affordable cost, lies in the ability to perform good levels of
photonic integration. This has not been an easy route to date,
but some interesting examples of future approaches are starting
to appear. Generally, the integration of photonic components
is not straightforward as the substrate technology for various
components differs (e.g., lasers are grown on InP, whereas
filters benefit from silicon technology). Existing photonic in-
tegration approaches are based on hybrid integration, where
individual components are laid down and interconnected on a
suitable substrate (e.g., silicon); hybrid integration offers full
functionality, lower cost, and shorter development times; or
on monolithic integration, where a limited set of functions,
realizable on a common material, is combined.
Recent advances in the integration of MachZehnder inter-
ferometers (MZI) illustrate the potential benefits of integration.
In a typical device, a pump signal is split between two inter-
ferometer arms, and the phase difference between arms is con-
trolled by the optical signal operating on a nonlinear element,
typically an SOA. Integrated MZIs can be used for a variety of
functions needed in future systems and cannot be realized by
assembling discrete components; current commercial devicescan operate at 40 Gb/s and have been extensively used for
wavelength conversion at 10 and 40 Gb/s with regenerative
capabilities [41]. To maximize speed, pushpull configurations
have been suggested where, by applying phase changes in
both arms, performance can be significantly enhanced, with
up to 160-Gb/s operation reported [42]. This configuration has
been used in a number of different signal processing appli-
cations such as regeneration, add-drop multiplexing, time slot
interchange switching [43] format, and wavelength conversion,
and other optical processing functions. 3R regeneration can be
achieved by using the input signal to gate-extracted optical-
clock pulses in a pushpull configuration. The ability to inte-grate many interferometers in one substrate makes the device
very interesting and versatile, for example, to realize logic
functions and bursty receivers [44].
Recently, novel approaches based on silicon photonic inte-
gration (Silicon Photonics) have been reported by Intel [45].
Silicon is a well-understood material and the basis of low-
cost electronics. It is transparent at infrared wavelengths and
so can be used to guide light but cannot emit light. Intel is
pioneering a process whereby a laser chip mounted in a silicon
external cavity forms a tunable laser, which together with
silicon modulators (realized by MZI configurations) and photo-
detectors (with Ge doping) shows promise as a future low-cost
integration strategy. The current performance is at 1 Gb/s, but1040 Gb/s is predicted.
There are a number of key functions necessary, at a link and
network level, to enable efficient operation of the future optical
network. Examples are as follows.
A. Optical Switching
To fully advance to transparent networking, OOO switches
are required at microsecond (for OBS), millisecond (for OXCs),
and nanosecond (for OPS) reconfiguration times. 3-D MEMS
switches (ms reconfiguration) are now available with port
counts to 160 160 [46], and the recent interest in the de-
ployment of ROADMs means that the functionality of OOO
switches is now available. Fast (in nanoseconds) switch fab-
rics (of high dimension) are realized through the combination
of tunable lasers/wavelength converters together with arrayed
waveguides; it is hard to see this situation changing. Neverthe-
less, low-dimension nanosecond switch modules are available
[47]. An example based on the total internal reflection in a
compound semiconductor power line carrier [48] forms the core
of a commercially deployed OPS system.Recent advances in fabrication have made it possible to
fabricate compact microring resonators with radii as small as
2.5 m and quality factors as high as 10 000 by tightly confining
semiconductor waveguides [49]. The large field-enhancement
factors obtained in these microcavities can result in three to four
orders of magnitude reduction in the required switching powers,
while the small dimension of the devices helps reduce the cavity
lifetime, and hence the switching times, down to the picosec-
onds regime. With the microring arranged in either the single-
coupler (all-pass) or double-coupler (adddrop) configuration,
the device can be used to perform efficient switching, pulse
routing, wavelength conversion using four-wave mixing, aswell as logic functions; further research is needed to understand
the potential of this approach.
B. Optical Monitoring
As the network performance increases, it is crucial to un-
derstand the state of the physical layer so that appropriate
routing and remedial actions can be taken. For example, within
a network, a variety of bit rates from 10 to 160 Gb/s may exist,
with some routes more appropriate to one bit rate than another
from the point of view of optical signal-to-noise ratio, residual
dispersion channel power, etc. Information should be available
through optical monitoring to inform routing decisions at net-work nodes; this trend now appears in the area of cross-layer
routing and is an important one for research.
C. Optical Encryption
Security will always be of great importance in networks, and
it proves difficult to perform electronic encryption at speeds
beyond 10 Gb/s. Thus, there is a strong interest in the inves-
tigation of encryption possibilities in the optical medium. Two
main techniques have been investigated based on 1) quantum
cryptography and 2) chaos cryptography. The first is based on
secure key distribution, in which the key can then be used to
transmit information securely by the conventional algorithm-based encryption. Quantum cryptography guarantees secure
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communications by harnessing the quantum nature of photons
sent between users. Any attempt to intercept the photons will
disturb their quantum state, and as this quantum quality is an
integral part of key generation, the disturbance will be detected.
Several experiments have extended the key distribution over an
ordinary 100-km fiber [50]; however, the technique is sensitive
to noise.Chaos-based encryption has the advantage of allowing
very high encryption speeds (> 10 Gb/s). It relies on the
synchronization of chaotic systems, for example, a pair of
unidirectionally coupled single-mode semiconductor lasers
subjected to coherent optical feedback or injection. Synchro-
nization means that the chaotic output of the emitter device
can be reproduced by the receiver. Once the two lasers have
synchronized, the output light of the emitter can be used to en-
code a message. An experiment over a commercially installed
fiber (2.5 Gb/s) showed the possibility of recovering chaotic
transmission after 120 km [51].
D. All-Optical Wavelength Conversion and Regeneration
All-optical wavelength conversion and regeneration are de-
sirable (including from a power and footprint viewpoint) for
networks operating at speeds of> 40 Gb/s. To achieve conver-
sion, the physical properties of a nonlinear element are used
to perform a logic function between the input signal and a
pump. The main nonlinear elements used are SOA, an electro-
absorption modulator (EAM), fiber, a photonic crystal, and
periodically poled LiNbO3 waveguides (PPLNs). SOA-based
devices, especially quantum dot, and EAMs have the added
advantages of compactness and low-energy requirements to
trigger nonlinearities. Fibers have an instantaneous response to
pulses but, on the other hand, have limited nonlinearity, even in
specially designed photonic crystal fibers; hence, long lengths
are required. PPLNs require intermediate lengths, and very fast
conversion (40160 Gb/s) has been demonstrated.
Considerable research has been done in the area of single-
wavelength subsystems. For example, advanced all-optical
regenerative schemes at bit rates beyond 100 Gb/s have been
recently proposed in [52] as well as well reported demonstra-
tions at 40 Gb/s [53]. Multiwavelength all-optical regeneration,
if feasible, will dramatically decrease the cost of DWDM
transmission links. A number of techniques are currently being
considered, for example, 1) through the mechanism of self-phase modulation, which in principle enables operation at
speeds of> 160 Gb/s, and 2) based on the inhomogeneously
broadened gain of self-assembled quantum dots in quantum dot
SOAs [54].
E. Optical Memory
All-optical buffering through fiber delay lines is an approach
that requires complex control, and packets are delayed rather
than stored. Recently, in the framework of LASOR [18], inte-
grated delay lines have been developed as it has been shown
[55] that a small number of low-depth buffers are sufficient foran OPS network.
Nevertheless, recent research has established that it is possi-
ble to exercise control of the velocity of light pulses propagating
through a material. Light propagation with a very low group
velocity (slow light) has been observed in atomic vapors and
solid-state crystal via electromagnetically induced transparency
and coherent population oscillation. Recently, direct time-
domain measurements in SOA quantum wells showed control-lable delay up to 1 ns; this results in a direct measurement
of group velocity of < 200 m/s, giving a slow down factor
of up to 1.5 106 [56]. Various other methods have been
proposed and demonstrated, and the area is still one of strong
research. Critics of this technique have concluded that there is a
delaybandwidth product that inevitably limits the achievement
of reasonable delays at high bit rates.
VIII. FUTURE GLOBAL HETEROGENEOUS
OPTICAL NETWORK
In the above discussions, it has been shown that there are
ever-growing demands on future networks from a number of
directions. The historic telecommunications network is seen as
evolving to a fully pervasive or ubiquitous network supporting
a wide variety of users. Key to this goal is the evolution
to a multiservice platform comprising (eventually) an optical
core with wavelength and subwavelength granularities together
with an advanced control plane such as GMPLS. The core
data plane will support electrical circuit switching (e.g., with
DXCs), electronic packet switching using IP/MPLS routers,
OBS using microsecond optical switches with appropriate edge
interfaces to set incoming data on to specific wavelengths, and
finally, possibly OPS using nanosecond optical switches and
appropriate edge interfaces.The optical transport core will be accessible to the user via
fixed and wireless access networks, providing high bandwidth
availability. Single-channel transmission speeds will increase in
the very near future to 40 Gb/s (matching router interface rates),
and it is likely that development will continue to move to higher
rates such as 160 Gb/s, perhaps using DPSK, and via OTDM.
Continued development in photonic integration will enable
appropriate optical processing subsystems, for example, all-
optical regeneration, to be realized supporting these changes.
From the scientific user direction, it was shown that dedicated
optical networks, for example, NRENs, based on dark fiber and
readily available optical technology are already being put inplace to satisfy the requirements of these users for a dynamic
network with specific requirements on bandwidth, latency, and
availability, to access global processing resources, transfer high
data volumes with QoS, and provide a secure infrastructure
for future high-end services. These networks, with their well-
defined requirements, will likely continue to rely on dynamic
circuit-based switching, but the advantages of OBS for grid
applications make it likely that this technology will move to
these networks as well.
Fig. 5 shows how these separate networks might eventually
coexist to form a global heterogeneous optical network, increas-
ingly supported by advanced optical technology. The figure
shows how a core telecommunications network can providea platform for both residential users through the metro/access
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Fig. 5. Global heterogeneous optical network.
route or for scientific communities through the interconnection
with NRENs.
This solution is one that allows telecom operators to build
a ubiquitous network, which also supports the flexible services
needed by high-end researchers. The future vision here is of op-
erators providing transport services to research users and legacy
ones (i.e., residential/business users), on different sections of
the same network infrastructure or sharing the same infrastruc-
ture, but under a single unified control and management plane.
It is necessary that this common control plane should interwork
with the existing NRPS used by NRENs in order to dynamicallyimplement worldwide optical transport services.
GMPLS has proved to be the most efficient telecom-oriented
solution for the fast and automated provisioning of connections
across multitechnology (IP/MPLS, Ethernet, SDH/SONET,
DWDM, OBS, etc.) and multidomain networks: GMPLS en-
ables advanced network functionalities for traffic engineering,
traffic resilience, automatic resource discovery, and manage-
ment. However, GMPLS is not natively designed to support the
flexible network services described above, and a major tech-
nical challenge rises from the interworking of the application
platforms and of their resource management systems with the
underlying NG optical networks powered with the GMPLScontrol plane.
This network vision needs to ensure a service boundary is
kept between the users and the network service provider but
also enable differentiated and configurable interfacing proce-
dures. According to this approach, the boundary of the network
will be transparent only for power users (i.e., scientific and
high-performance grid) who will
obtain network topology information to be used by re-
source brokering entities (i.e., NRPS);
request specific lightpaths by providing lightpath descrip-
tion;
communicate application layer information (e.g., CPU,storage, etc.) into the GMPLS control plane, which will
allow dissemination of this information within the same
virtual.
The proposed coordination between the telecom network
control plane, the NRPS, and the service plane on top of the
switched physical layer will enable end-to-end dynamic service
provisioning across a global heterogeneous optical network
infrastructure.In this scenario, therefore, it is likely that progress will
continue toward a common or shared optical infrastructure sup-
porting residential, business, and scientific users. All these users
require a more dynamic network with wavelength and subwave-
length access, which will likely eventually be supported, for
example, through OBS or indeed (in the far distance) OPS. The
common core network will continue to move to higher speeds
with an eventual move from OEO to OOO switching. Photonic
integration is seen as a key to enable high-performance optical
networking. For the global heterogeneous optical network,
however, there are many challenges on both physical and
network layers, requiring much cooperation among traditional
electronic engineers, computer scientists, and users.
IX. SUMMARY
This paper presented a story of the evolution of optical
networking from early concepts to its strong progression to
provide the main high-capacity and flexible platform necessary
to support the near and future requirements of a global network
supporting the communication requirements of a growing di-
versity of residential, enterprise, and scientific users. Many of
the switching and subsystem technology solutions necessary
to achieve these aims have already been glimpsed but need
considerable progress in integration techniques to overcomedeployment cost problems. There is also much research to be
done at the software level to ensure interoperability between
networks at a global level. Eventually, hardware and software
evolution may lead to increased levels of transparency in these
future optical networks.
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4696 JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 24, NO. 12, DECEMBER 2006
Michael J. OMahony (M91SM91) received thePh.D. degree in digital transmission systems from theUniversity of Essex, Colchester, U.K., in 1978.
In 1979, he was with the Optical System ResearchDivision, British Telecom, working on research intofiber-optic systems for undersea systems, in partic-ular, experimental and theoretical studies of receiverandtransmitter design. In 1991,he joinedthe Depart-
ment of Electronic Systems Engineering, Universityof Essex, as Professor of communication networksand was Head of the department from 1996 to 1999.
He is the Principal Investigator for grants supported by industry, nationalresearch councils, and the EU. He is the author of over 200 papers relatingto optical communications. His current research is related to the study of futurenetwork infrastructures and technologies.
Dr. OMahony is a member of the Institution of Electrical Engineers (IEE).
Christina Politi (S05) was born in Zografou,Greece, in 1975. She received the degree in physicsfrom the University of Athens, Athens, Greece,in 1998 and the M.Sc. degree in the physics oflaser communications from the University of Essex,Colchester, U.K., in 2000. She is currently workingtoward the Ph.D. degree on ultrafast wavelength con-version and optical processing for optical circuit andpacket-switched networks at the University of Essex.
She has been involved with the EuropeanIST-OPTIMIST and IST-BREAD projects.
Dimitrios Klonidis (M02) received the degree inelectrical and computer engineering from AristotleUniversity, Thessaloniki, Greece, in 1998 and theM.Sc. degree in telecommunication and informationsystems from the University of Essex, Colchester,U.K., in 2001. He is currently working toward thePh.D. degree in high-speed optical packet switchingat the University of Essex.
Since August 2004, he has worked for the EPSRCproject OPSnet. He is currently involved with a
number of research activities within the Universityof Essex. His main research topics are in the area of ultrafast optical communi-cation networks.
Reza Nejabati (M02) received the B.Sc. degree inelectrical engineering from Shahid Beheshti (Melli)University, Tehran, Iran, in 1997 and the M.Sc.degree (with distinction) in telecommunication andinformation systems from the University of Essex,Colchester, U.K., in 2001.
He is a Senior Research Officer with the PhotonicNetwork Research Group, University of Essex. His
main research interests are in the area of opticalsubwavelength switching and grid networking.
Dimitra Simeonidou (M95) received the B.Sc.and M.Sc. degrees from the Physics Department,Aristotle University, Thessaloniki, Greece, in 1987and 1989, respectively, and the Ph.D. degree fromthe University of Essex, Colchester, U.K., in 1994.
She has over ten years of experience in the fieldof optical transmission and optical networks. From1992 to 1994, she was a Senior Research Officerwith the University of Essex in association with theMWTN RACE project. In 1994, she was a PrincipleEngineer with Alcatel Submarine Networks and con-
tributed to the introduction of wavelength-division-multiplexing (WDM) tech-nologies in submerged photonic networks. She participated in standardizationcommittees and was an advising member of the Alcatel Submarine networkspatent committee. She is a currently a Professor with the University of Essex.She is the author over 120 papers and holds 11 patents relating to photonic tech-
nologies and networks. Her main research interests include optical wavelengthand packet-switched networks, network control and management, and GRIDnetworking.
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