OPTICAL SWITCHING: Mirror Mirror, Who Is the Fastest?

Over

two decades ago, when I was doing my Masters project at IIT in fibre-optics, no

one could imagine the true potential this technology held for the telecom. And

also, that one day, many players, including myself, would move from electronics

to a business mostly dependent on optics. The paradigm shift due to bandwidth

explosion is putting pressure on the network switching technologies too.

New Dawn in Switching Technologies

Every advancement in switch performance encourages carriers

to push out even more bandwidth, and that puts more pressure on the installed

switches, which eventually is feared to be unable to keep pace. The speed is

all-important with every new technology trying to bring down another bottleneck.

State-of-the-art telecom networks use light travelling through fibre-optic

cables, instead of electrical signals travelling over wires, to carry voice and

data. Optical fibre has seen dramatic increase in its traffic carrying capacity

due to Dense Wave Division Multiplexing (DWDM) technology*.

This technology has been pushing up the number of channels

that can be carved out of a single beam of white light, increasing rapidly from

20 to 40 to 80 and now to 128. There seems to be no upper limit. Each of those

channels of light needs to be routed, switched, and multiplexed. The networking

equipment slows down the traffic on a fibre network as virtually all the

switching on fibre-optic networks till date is being done electronically. The

"photons" of light that carry the information have to be turned into

"electrons" or electrical signals so they can be read by the existing

generation of network equipment. And after the switch has decided where a

message is headed, the signal has to be converted back to light signal and put

back on the fibre for the next stage of its journey. This conversion-and-reconversion

process takes time, and that limits the performance. Therefore, the carrying

capacity of such a network is determined not only by the size of the pipes it

employs, but also by the speed of these switches. While light is dramatically

faster than electricity, it is only as good as the switches that direct it.

The preferred approach would be switching without converting

the signal from optical to electrical and back to optical again. This is

important because, while electronics' capabilities continue to improve according

to Moore’s Law (doubling every 18 months), optical systems have the potential

for far more rapid evolution and improvement, and even greater capabilities*.

A new dawn in switches–and, in turn, network performance–is

coming in the form of "optical" or "photonic" switching to

forge ahead in its goal of driving more bandwidth onto backbones. Optical

switches are expected to be in operation by the carriers before the

ever-increasing rush of bandwidth overwhelms the existing generation of switches

in the next three to five years.

All-optical Switching

The optical or photonic switch/router can intelligently

switch/route wavelengths without any opto-electronic conversions. Optical

switches would not reduce that bottleneck as these traffic routers would not

need to turn photons into electrons and back into photons to manage the flow of

messages. Instead, they would be able to find the routing directions for each

message in the light itself, and would route light through optical

cross-connects without electronics. That would speed up the flow, thus

increasing the capacity of a fibre network. Besides the immediate cost savings

that would result from that boost, it now looks possible that optical switching

will simplify network architectures and cut down on the amount of network

routing equipment that each fibre needs. The cost savings are projected around

50 percent for a network that has been reconfigured to take advantage of

optical-switching architectures. The cost advantage for a newly built

state-of-the-art system over an older system, that cannot be substantially

reconfigured, is likely to be even larger.

Optical switching systems offer carriers dynamic management

of their optical-layer network, rapid optical service provisioning and reduced

operations costs. Carriers would be able to manage their multi-wavelength

networks much more efficiently than is possible using the existing optical

network gear. Thus, optical switching promises to be the "next big

thing."

Carriers are embracing optical switching because it could

give them and their customers a marketable advantage.

Technology Tornado

It is like being in the middle of a technological tornado.

The fastest growing telecom business is the optical market, last year doing over

$5 billion. Another reflection of it is the catapultic rise of valuation of the

optical networking companies like Sycamore founded by Desh Deshpande, Cerent of

Vinod Khosla (who later sold it to Cisco) …putting Indians in the forefront of

the technology of the new millennium. And that includes Arun Netravali, head of

Bell Labs, Pradeep Sindhu of Juniper, and Krish Prabhu, Alcatel, US.

Mirror Mirror...

Optical switches might use a chemical process or non-moving

parts versus an electromechanical switch. Micro-Electro-Mechanical Systems (MEMS)

technology is used for this, which etches "micro-mirrors" onto silicon

substrate to provide an optical cross-connect. The mirrors are steered

electronically to reflect laser beams in different directions.

One such router, Lucent’s WaveStar LambdaRouter, promises

awesome capabilities: 256 ports–the capacity of 256 separate optical fibres,

each carrying a single wavelength–each starting at 40 Gbps–pushing a total

capacity of 10 Terabits. WDM allows each fibre to carry more than one

wavelength.

The LambdaRouter uses "micro-mirrors" to switch

lightwaves by reflection on a very miniature scale. The wavelengths tell the

mirror how much to bend to route the light appropriately by using a

"digital wrapper"–the optical equivalent of a packet header. In

addition to switching the lightwaves, the wrapper contains information on

restoration and the type of traffic being carried.

Another technology uses "inkjet printing

technologies" to steer wavelengths. The basic chip is a matrix of 32x32

waveguides which are simply grooves in glass, filled with a liquid that allows

light to pass easily. At each intersection of the waveguides, a bubble can be

inserted. If the bubble is there, the wave cannot continue down the groove and

is reflected off to one side or the other, switching the wavelengths.

*Technology of the Future & O-commerce

The impact of optical switching could be as dramatic as DWDM*,

which transformed core network transport almost overnight. Deshpande of Sycamore

has predicted that technology was advancing fast enough and within 18 months,

there will be enough bandwidth for the whole Internet business model to change.

A US study claims that spending on optical switching systems

will run to more than $31 billion in Europe and North America over the next five

years. The principal driver will be the rapid adoption of DWDM technology among

new and established



network operators.

Optical switching is the technology of the future, but really

how far is the future. Undoubtedly, optical switching promises immense

technological and cost advantages. However, it is not possible to throw out an

existing network worth billions of dollars. Optical switches are already in the

market, but to improve their performance and scalability involves a host of

challenges, including deciding on the core technology involved. Therefore, the

transition for established carriers may be slow and may be spread over five

years. During that time, companies will try to add as much optical switching–with

some electronics still being there–to their networks as they can, while

preserving as much of their existing investment as possible. However, for the

new players the attraction of being able to offer "customer controllable

bandwidth"–with pricing based on use, network viewing and management

capabilities–and becoming optical switched service provider will drive

embracing of such networks rapidly.

Some say, the days of o-commerce (optical-commerce) are

ahead!

* For more information on DWDM and optical networks

evolution, read, "The Business of Telecommunication" by Niraj K Gupta,

published by Tata McGraw-Hill.