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With high-bandwidth and on-demand applications continuing to emerge, next-generation core optical
networks will require significant improvements in capacity, configurability, and resiliency. In addition to
probing issues related to increased capacity, configurability is also examined, mainly in the context of
switching architectures. Advanced network protection is discussed as well, at a high level. A central theme
is how to harness the trend of optics scaling better than electronics. Throughout this paper, potential
advancements in architecture and technology are enumerated to serve as a foundation for the research
needed to attain the goals of next-generation core networks.

Keywords—All-optical regeneration, all-optical switch, backbone networks, configurability, core networks,
grooming, long-haul networks, shared mesh restoration, wavebands.

   In long-haul1 network technology over the              format transparency, the bulk of the applications
past ten years, most notably in fiber capacity,           will not.
optical switching, and optical reach [1], have
shifted the bandwidth and operational                         For example, the higher the transport rate of
bottlenecks from the core network to metro and            an individual wavelength, the fewer the number
access networks. However, as advances in                  of wavelengths that need to be switched, but the
wavelength-division     multiplexing      (WDM)           more grooming needed to pack the wavelengths
technology propagate closer to the network edge,          efficiently. Various solutions in these three areas
thereby enabling the proliferation of applications        are proposed and analyzed from the point of
with very high bandwidth and/or stringent                 view of overall network technological feasibility.
performance requirements, core networks
eventually will become strained in both capacity              The requirement of rapid reconfigurability
and flexibility.                                          poses challenges especially in the area of
                                                          switching architecture. We discuss several core
   Thus, while the capabilities of today’s                optical switch architectures, along with their
applications become more tied to the transfer of          performance tradeoffs. We also consider
large amounts of data, the ability to survive             simplification of the switch technology through
multiple concurrent failures will become                  the use of more flexible transmit/receive cards.
essential. It is important that all of these goals be     The ability to rapidly reconfigure a network
met in a scalable fashion with respect to network         typically requires the predeployment of some
cost, equipment size, and power requirements. It          amount of networking equipment that is utilized
is desirable that solutions that are suitable for a       on an as-needed basis (e.g., in response to a shift
range of commercially deployed networks as                in demands).
well as government owned networks be found in
order to achieve economies of scale.                         We propose architectures that can minimize
Furthermore, note that the requirements of the            the impact of predeployed equipment while
network will be very heterogeneous. For                   maintaining a high degree of flexibility. In
example, while some applications may require              looking at the challenges of providing very high
capacity and configurability, the trend of optics      it is expected that a large number of video
to scale better than electronics suggests that         “narrow casters” will spring up, offering a
optics should play a greater role as networks          variety of specialized content over the Internet.
evolve. For example, optical aggregation of
subrate traffic at the edge of the network may             To     complement       access     infrastructure
prove to be a more scalable means of packing           deployments, advanced protocols are being
wavelengths as compared to conventional                developed to provide higher quality high
electronic multiplexing or grooming.                   bandwidth services. For example, to provide an
                                                       enterprise Ethernet local area network (LAN)-
   Furthermore, all-optical regeneration may           like environment over a backbone network, the
become more cost effective and consume less            virtual private LAN service (VPLS) standard has
power than its electronic counterpart when the         been proposed [4]. It combines Ethernet access
line rate increases beyond a certain threshold.        with multiprotocol label switching (MPLS) core
The role of optics will be discussed more in-          technology to deliver end-to-end quality of
depth throughout this paper. Advances in               service. Virtual all-to-all private networks can be
optoelectronic and Photonic integration [3],           established much more easily than is currently
though also important, will not be discussed in        possible, which will encourage carriers to expand
detail. To gain insight into the requirements of       their markets and businesses to subscribe to
next-generation core networks, the next section        more advanced services.
examines various types of applications that can
be expected to evolve over the next several                Furthermore, 100-Gb/s Ethernet is likely to
years.                                                 emerge in the next five to ten years as both a
                                                       bandwidth driver at the network edge as well as a
II APPLICATIONS                                        transport mechanism in the core. Protocols that
                                                       depend on the optical layer being reconfigurable
    The applications that are currently emerging       are also being developed. For example, the
and that will continue to mature over the next         Optical Internetworking Forum user–network
several years are the driving force behind the         interface (UNI) [5] and the generalized MPLS
need for advances in the long-haul network.            UNI [6] provide a means for higher layer
Clearly, it would be impossible to predict the full    “clients,” e.g., the Internet protocol (IP) layer, to
range of future applications. Rather, the goal of      request via the control plane the establishment
this section is to enumerate a number of these         and tear-down of connections
applications, both commercial and military,            in the optical layer.
that have very diverse requirements.
                                                          These protocols are designed to enable more
   Growth in capacity requirements will come           optimal resource utilization, greater network
from both a surge in the number of users with          resiliency, and advanced services such as end-
high-speed access and a proliferation of               user-initiated provisioning through automated
bandwidth-intensive applications. Assuming that        network configuration. Another growing
service providers follow through with their plans      application is grid computing, which is used as a
to deploy optical fiber directly to homes or           means of sharing distributed processing and data
neighborhoods, in the next few years, access           resources that are not under centralized control in
speeds of up to 100 Mb/s will be available to          order to achieve very high performance. There
tens of millions of users. Some carriers are even      are already dozens of grid networks in existence,
planning for up to 1-Gb/s access speeds. This is       some with requirements of petabyte data sets and
substantially faster than current digital subscriber   tens of teraflops of computational power [7], [8].
line (DSL) and cable modem speeds, which are
typically less than 10 Mb/s.                               To support these massive requirements, large
                                                       pipes are required to connect the major sites,
    The growth of “triple-play services,” i.e., the    essentially forming a national-scale optical
convergence of high-speed data, video, and             backplane. For example, the TeraGrid network,
telephony over a single pipe, will significantly       which is supported by the National Science
increase network capacity demands, especially          Foundation for scientific research, has a 40-Gb/s
due to video traffic. On-demand video is already       bit rate between its major sites [9]. While grid
a rapidly growing application. In addition,            computing for the most part has been limited to
                                                       the academic arena, there has been growing
interest from the commercial sector to take          to the electronic domain, regardless of whether
advantage of the synergies that can be               or not the traffic is destined for that node. The
attained.                                            line rate of these legacy networks is generally 2.5
                                                     Gb/s, or in some cases, 10 Gb/s, with a total
    As this application expands to businesses, it    capacity per fiber of 50–200 Gb/s. The
will be accompanied by a surge in demand for         transponders are fixed; i.e., a given transponder
high-bandwidth pipes. The demands of grid            transmits and receives one particular wavelength.
computing in supporting research in “e-science”
areas such as high-energy physics, genomics,             (A     transponder      is      a     combination
and astrophysics are expected to grow to terabyte    transmitter/receiver card that has a short reach
data sets and petaflop computation over the next     interface on the client side and a WDM
decade, requiring terabit link capacity. For         compatible signal on the network side.) Almost
example, in some high-energy physics                 all of the traffic is subrate, i.e., the traffic rate is
experiments, multiterabyte data files need to        lower than the line rate, and synchronous optical
be disseminated to multiple locations in a           network/synchronous digital hierarchy
very short period of time. Such applications         (SONET/SDH)-based             O–E–O          grooming
require on the order of terabit per second           switches are used to pack the wavelengths.
capacity, but for relatively short periods of time
(minutes to hours).                                     The grooming switch may also be used as a
                                                     core switch operating on all wavelengths
    Two critical components of the “network-         entering the node and thus may be very large. A
centric warfare” concept are the “sensor grid”       typical legacy network node is depicted in Fig.
and the “global information grid” (GIG). The         1(a), with an IP router used as the grooming
sensor grid comprises both active and passive        switch.
sensors that are deployed in the air, undersea,
and on the ground to provide battlespace                The network deployments of the past few
awareness. For example, sensors will be used to      years represent a major departure from this
monitor troop position, the environment, etc.        legacy architecture. The most significant
Sensor data are collected and securely               development is the advent of optical bypass,
transmitted by the GIG, which is a collection of     where traffic transiting a node can remain in the
wireless, satellite, and wired networks that span    optical domain as opposed to undergoing costly
the globe.                                           O–E–O conversion. Optical bypass is enabled by
                                                     the combination of long (or ultralong) optical
    The GIG must be capable of rapidly               reach and all-optical switching nodes.
delivering large amounts of data to generate an
integrated view of the battlespace through real-         Optical reach is the distance that an optical
time data fusion, synchronization, and               signal can travel before the signal quality
visualization. An important goal of the GIG is to    degrades to a level that necessitates regeneration.
provide war fighters and planners with on-           In recently deployed backbone networks, the
demand access to this information from any           optical reach is on the order of 1500–4000 km,
perating point in the world.                         which has been achieved through the use of
                                                     Raman Amplification, advanced modulation
3. NETWORK ARCHITECTURES                             techniques, and powerful forward error
                                                     correcting codes. (Legacy networks use only
   While there is no single canonical core           erbium-doped fiber amplifier (EDFA)-based
network architecture, the deployments of several     amplification and have an optical reach of about
new commercial and government long-haul              500 km.)
networks over the past few years have several
common aspects. Before describing the                CONCLUSION
architecture of these networks, we briefly
summarize the architecture of legacy networks,          This paper has examined numerous aspects
as a point of comparison.                            related to the requirements of next-generation
                                                     core optical networks. The network modeled.
    Legacy backbone networks are typically           Modeling a core optical network with 100-Tb/s
optical– electrical–optical (O–E–O) based, with      aggregate demand, which is an order of
all traffic routed through a node being converted    magnitude increase over today’s networks,
highlighted several areas where research is
needed. First, the capacity requirements on a link   [5] S. Sengupta et al., “Switched optical
will be on the order of 16 Tb/s.                     backbone for cost-effective scalable core IP
                                                     networks,” IEEE Commun. Mag., vol. 41, no. 6,
   To reach this goal on a single fiber-pair, the    pp. 60–70, Jun. 2003.
spectral efficiency will need to increase by a
factor of 10 over today’s networks; this needs to    [6] R. Lingampalli and P. Vengalam, “Effect of
be achieved while maintaining an optical reach       wavelength and waveband grooming on all-
of 1500–2000 km. These targets are significantly     optical networks with single layer Photonic
beyond even current experimental results and         switching,” in Proc. OFC, Anaheim, CA, Mar.
will require the development of advanced             17–22, 2002, pp. 501–502, Paper ThP4.
multilevel modulation formats and detection          [7] X. Cao et al., “Waveband switching in
schemes. This affects the development of other       optical networks,” IEEE Commun.Mag., vol. 41,
technologies.     For     example,     all-optical   no. 4, pp. 105–112, Apr. 2003. [50] P. Bullock et
regeneration is a technology that will possibly      al., “Optimizing wavelength grouping
improve the scalability of future networks;          granularity for optical add–drop network
however, most current work in this area is           architectures,” presented at the Optical Fiber
compatible with only relatively simple binary        Communication Conf. (OFC), Atlanta, GA, Mar.
modulation schemes that are capable of carrying      23–28, 2003, Paper WH2.
an analog signal all-optically end to- end in the
network.                                             [8] V. Kaman et al., “A cyclic MUX–DMUX
                                                     Photonic cross-connect architecture for
   By selecting portions of the spectrum with        transparent waveband optical networks,” Photon.
minimal impairments, increasing the wavelength       Technol. Lett.,vol. 16, no. 2, pp. 638–640, Feb.
spacing in these spectral regions, and giving        2004.
preferential signal-to-noise-ratio treatment to
these Wavelengths within the optical amplifiers      [9] D. Blumenthal, “Optical packet switching,”
and switches, true end-to-end transparency may       in Proc. LEOS Annu.Meeting, Rio Grande,
be attainable. However, more research is needed      Puerto Rico, Nov. 7–11, 2004, pp. 910–912.
to determine the feasibility of this approach.
                                                     AUTHORS BIOGRAPHY
[1]. B. Zhu et al., “High spectral density long-     ( is working as
haul 40-Gb/s transmission using CSRZ-DPSK            Senior Associate Professor, ECE Department,
format,” J. Lightw. Technol., vol. 22, no. 1, pp.    Bharat Institute of Engineering & Technology,
208–214,                                             Mangalpally,      Ibrahimpatnam,     Hyderabad,
Jan. 2004.                                           Andhra Pradesh State, IDIA. He was previously
                                                     worked as Lecturer and Assistant Professor in
[2] Z. Xu, K. Rottwitt, and P. Jeppesen,             Dr. M.G.R. Deemed University, Chennai. He is
“Evaluation of modulation formats for160 Gb/s        pursuing his Ph.D (Optical Communications)
transmission systems using Raman amplifiers,”        under the guidance of Dr. P.V.D Somasekhar
in Proc. LEOS Annu. Meeting, Rio Grande,             Rao and Dr. T. Janardhana Rao, UGC-ASC
Puerto Rico, Nov. 7–11, 2004, pp. 613–614.           Director,      J.N.T.University,     Kukatpally,
                                                     Hyderabad – 72 & Professor &HOD of the ECE
[3] S. Hardy, “A long road ahead for 40G             Department, Sridevi Women’s Engineering
pioneers,” Light wave, vol. 22, no. 3,p. 39, Mar.    College, V.N.Pally, Gandipet, Hyderabad- 75.
2005.                                                He got his Bachelors Degree in ECE from
                                                     Karnataka University, Dharwad in 1996 and
[4] K. Grobe, L. Friedrich, and V. Lempert,          Masters Degree from Mysore University,
“Assessment of 40 Gb/s techniques for                Mysore in 1998.His research interests are Optical
metro/regional Applications,” presented at the       Communication, Networking, Switching and
Optical Fiber Communication Conf. Expo.              Routing and Wireless Communication. He was
(OFC)/National Fiber Optic Engineers                 published 30 PAPERS in IEEE Communication
Conf.(NFOEC), Anaheim, CA, Mar. 5–10, 2006,          Magazine, IEEE Potentials, International and
Paper NThA1.                                         National Conferences. He is an IEEE
Optical Society of America, Journal on
Photonics and IEEE Journal on Quantum
Electronics and IASTED.

    Dr. P.V.D. Somasekhar Rao B.E. (SVU),
M.Tech.(IIT, Kharagpur), Ph.D. (IIT, Kharagpur.
Professor and Head of the Department & UGC-
ASC Director Specialized in Microwave and
Radar Engineering. His research interests include
Analysis and design of Microwave circuits,
Antennas, Electro Magnetics, Numerical
Techniques. He published 20 research papers in
National and international Journals and
Conferences. He is presently guiding two Ph.D.
students. He prepared the source material for
School of Continuing and Distance Education,
JNTU, in the subjects such as computer
programming & Numerical Techniques, Radar
Engineering, Antennas and Propagation and
Microwave Engineering. He has more than 20
years of teaching and research experience, which
include R&D works at Radar Centre, IIT
Kharagpur and at Radio Astronomy centre and
TIFR. He is a Senior Member of IEEE, Fellow
of IETE. He delivered a number of invited
lectures. He is a reviewer for the Indian Journal
of Radio & Space Physics from 1991. He is the
recipient of the IEEE -USA outstanding Branch
Counselor/Advisor award for the year 1993-94.
He had completed a number of projects aided by
AICTE. He has been a visiting faculty at
Assumption University, Bangkok, during 1997-

   Dr. T. Janardhana Rao is working as
Professor and Head of the Department in Sridevi
women’s Engg College, V.N.Pally, Gandipet,
Hyderabad, and Andhra Pradesh State, INDIA.
His research interests include Optical Networks,
Digital Electronics, Bio-Medical Engg.,&Power
Electronics. He published 15 International and
National Journal Conferences. Professor Rao
was a former a member of faculty of
S.V.University with a teaching experience about
45 years. He is a life member of ISI and ISTE.

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Description: UBICC, the Ubiquitous Computing and Communication Journal [ISSN 1992-8424], is an international scientific and educational organization dedicated to advancing the arts, sciences, and applications of information technology. With a world-wide membership, UBICC is a leading resource for computing professionals and students working in the various fields of Information Technology, and for interpreting the impact of information technology on society.
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About UBICC, the Ubiquitous Computing and Communication Journal [ISSN 1992-8424], is an international scientific and educational organization dedicated to advancing the arts, sciences, and applications of information technology. With a world-wide membership, UBICC is a leading resource for computing professionals and students working in the various fields of Information Technology, and for interpreting the impact of information technology on society.