NEXT GENERATION OPTICAL NETWORKS
K.V.S.S.S.S.SAIRAM, Dr. T. JANARDHANA RAO AND Dr. P.V.D SOMASEKHAR RAO
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 , 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 . 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 , 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)  and the generalized MPLS
need for advances in the long-haul network. UNI  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 , .
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 . 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  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  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  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.  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.  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  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.
. B. Zhu et al., “High spectral density long- (email@example.com) 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
 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
 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
 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
REVIEWER and EDITORIAL MEMBER for
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.