Optical Networking is gaining significance due to the ever-increasing
demand for bandwidth and diminishing fiber availability. With
an exponential rise in data traffic, especially for innovative
and sophisticated communication services, service providers
need to deliver services in the right way at the right price.
John C. Collins, Director Asia-Pacific, Optical Internet
Engineering, Nortel Networks, asserts Metro Optical Networking
is the answer to the burgeoning demand for bandwidth, and
says DWDM is the ideal enabling technology. by Minu Sirsalewala
is a metro network and how is it different from a long haul
It is a network running across the city, or it may span a
metropolitan area wherein several cities are connected on
close proximity. In a typical scenario this might be in a
range of 200-400 kilometers.
We are focussed on developing optical networks for high-density
metropolitan areas, which are centers of business and commerce.
The business encompasses a variety of optical networking technologies
that help service providers relieve network congestion, that
is common in metropolitan areas.
A metro network uses sophisticated switching and routing mechanisms
for efficient data transfer. It has the ability to transmit
data in its native protocol. Long haul networks do not use
sophisticated switching and routing technologies and do not
transmit signals in their native protocols.
Where does a metro network fit in better, enterprises or
A metro network is better suited for enterprises. It functions
optimally for industries like banking, finance, airlines,
and medical centers. It is highly recommended in an industry
where operations are spread over geographically displaced
campuses. In a metro, a carrier can provide its service to
another carrier in order to get a better market reach.
Which technology is more suitable for a metro network:
SDH or DWDM?
In the past, SDH (Synchronous Digital Hierarchy) which has
a North American equivalent named SONET (Synchronous Optical
Network) has been the core component in a metro network. The
problem with this technology is that it is highly structured,
has very specific interfaces, offers limited bandwidth, and
does not offer the versatility that's demanded by enterprises.
It is also very difficult and complex to deploy Ethernet over
SDH. It requires high capital expenses and also higher operational
DWDM (Dense Wavelength Division Multiplexing) technology has
emerged as the alternative to SDH in metro networks. A DWDM
environment offers versatility and flexibility and requires
enterprises and carriers to deploy more sophisticated technology.
A DWDM metro network is typically bit-rate protocol independent
and allows you to carry native databases. This lowers capital
expenses and operational expenses, and offers greater sophistication
over SDH-enabled metro networks.
Another important development, which is visible, is the commonality
of Ethernet. We have Ethernet in VoIP (Voice over IP), Ethernet
for videos etc. Instead of relying on a SONET infrastructure,
which is optimized for voice and expensive to deploy, metropolitan
Ethernet providers use a combination of fiber, DWDM and Ethernet
boxes. The combination of DWDM equipment and simple Ethernet
gear is much less expensive than SONET equipment, enabling
metropolitan Ethernet providers to offer cut-rate pricing.
What are the emerging trends in optical networking?
There is a visible and definite move to the DWDM environmentworldwide,
nations are shifting to DWDM. Europe and North America are
already using it. In the Asia-Pacific region we are seeing
penetration in Shanghai, Beijing, and several cities in China.
Companies like SingTel in Singapore, companies in Australia
are all deploying metro networks because it is a multi-services
platform, bit-rate protocol independent, less expensive, and
offers the capability to support new services.
It is difficult to offer new services in an SDH environment.
SDH is a finite building block and does not allow the flexibility
to just plug services as and when required. For instance,
in a DWDM environment, Ethernet can be plugged in and related
services like video conferencing, VoIP etc. are made available.
But to plug services in an SDH environment requires various
manipulations, like lowering the bandwidth for services.
DWDM is going to be the trend and Ethernet is going to play
an important role because of its ubiquity, commonality, and
cost. However, to move over long distances, say over a few
kilometers, it requires that Ethernet is on some kind of signal,
and that signal is the wavelength within the DWDM. Ethernet
is going to be present in 98 percent of interfaces around
the world. Just as an example we can put 160, 10 GB channels
on the same piece of fiber i.e. 1.6 terabytes and still expand
further in the future when need arises.
DWDM is flexible, agile, presents low capital cost, low operational
cost and offers high revenue
What kind of services can hop onto a metro network?
As mentioned earlier it is difficult and expensive to put
Ethernet on SDH, but DWDM opens doors for Ethernet. Systems
like SAN (Storage Area Network) or NAS (Network Attached Storage)
are good examples of the kind of services that can be offered.
To quote statistics from a consulting house, they say "mankind
has created 12 exabytes of data till date, humans will create
another 12 exabytes of data in the next two years." You
need to have the capacity to store such huge data and also
move this data around to put it to use. It is not fruitful
to have the data stored and not put it to use. It is important
to have the capability and the network to move this data around.
There are services like HDTV (high definition television),
and exotic services like holographic imagery. For instance
you could be sitting 1,000 miles away and have a conversation
with me as if we were in the same room. You'll see my 3-D
image and you could be shaking hands with me even though we
are present at locations several miles apart.
Data, voice and video are already on the network, but in the
future we are going to have touch, 3-D images et al. These
services are some years away but are certainly coming in,
being thought about and scientifically pursued. DWDM can enable
all of this and more.
How will metro networks shape up in India?
In India, within the metro areas the population is so great
it is inefficient to use an SDH platform. In SDH today, typically
an STM 16 system gives you 2.5 gigabits and at the same time
its interfaces are very structured. Whereas with DWDM you
can get 32 triple eight G5 interfaces, and can further take
it up to 10 GB. With this capacity you can carry SDH on one
wavelength, ESCON on the other wavelength, Ethernet on another
and also HDTV on another wavelength.
DWDM can be deployed easily, with low cost investment and
in very specific environments too. It can expand as far as
possible and does not have any scalability issues.
From a vendor standpoint, in the next 6 months we expect to
see more implementations of DWDM in a metro network. A metro
network can be deployed very inexpensively, easily and in
a very specific environment. It is possible to expand it as
far as possible. It is scalable, flexible and agile.
DWDM (Dense Wavelength Division Multiplexing) enables data
from different sources to be transmitted on a solitary optical
fiber. Each signal is carried at the same time on its own
separate wavelength. Up to 80 separate wavelengths or channels
of data can be multiplexed into a light stream. Every channel
carries a time division multiplexed (TDM) signal and is also
known as wave division multiplexing (WDM). In a system where
each channel carries 2.5 Gbps, up to 200 billion bits a second
can be delivered by optical fiber.
As each channel gets demultiplexed at the end of the transmission
into the original source, different data formats at different
data rates can be transmitted together.
DWDM technology uses current electronics and fibers, and simply
share fibers by transmitting different channels at different
wavelengths (colors) of light. Systems that already use fiber
optic amplifiers as repeaters do not require upgrading for
most WDM systems. The key benefit of DWDM is that its protocol
and bit-rate independent.
Minu Sirsalewala can be reached at firstname.lastname@example.org