BSNLBSNLTRANSMISSION TRANSMISSION

TROUGH OPTICAL FIBRETROUGH OPTICAL FIBRE

AN OVERVIEW OF AN OVERVIEW OF BSNLBSNL

BSNLBSNL is the 3is the 3rdrd largest cellular largest cellular service provider with over 66.88 service provider with over 66.88 million customers as of June 2010 & million customers as of June 2010 & largest landline telephone provider in largest landline telephone provider in India. Govt further included certain India. Govt further included certain features like:features like:

PCO/STD/ISD Services.PCO/STD/ISD Services. 3 Party Conference.3 Party Conference. Value added services.Value added services.

DESCRIPTION OF ACTUALDESCRIPTION OF ACTUALTELEPHONIC COMMUNICATIONTELEPHONIC COMMUNICATION

First of all, when a subscriber picks up his First of all, when a subscriber picks up his receiver, receiver, dial tonedial tone is provided to him by his is provided to him by his local exchange to which he is subscribed. local exchange to which he is subscribed.

Then when he dials a number, it is sent to the Then when he dials a number, it is sent to the exchange & the local exchange checks the exchange & the local exchange checks the number. number.

At this stage two cases arise : At this stage two cases arise : Local call or Local call or STD/ISDSTD/ISD

1. Local Call:-1. Local Call:- If it is a local call, then the local exchange If it is a local call, then the local exchange

connects the subscriber to local OFC, where the connects the subscriber to local OFC, where the actual switching takes place. actual switching takes place.

CONTDCONTD.... The local OFC checks the exchange code of The local OFC checks the exchange code of

the number dialed & accordingly routes the the number dialed & accordingly routes the subscriber to that exchange. subscriber to that exchange.

This exchange then connects the dialed This exchange then connects the dialed number to the dialing number.number to the dialing number.

2. STD Call :- 2. STD Call :- If local exchange of the dialing number If local exchange of the dialing number

finds a finds a 00 as first digit of the dialed number as first digit of the dialed number i.e. if it is not a local call, then i.e. if it is not a local call, then it connects it connects the dialing number to the tax exchange. the dialing number to the tax exchange.

The tax exchange then checks the dialed The tax exchange then checks the dialed number for the code of the city to which number for the code of the city to which call has been made. call has been made.

This OFC then connects the dialing number This OFC then connects the dialing number to the OFC of the city of the dialed number. to the OFC of the city of the dialed number.

Then, this OFC routes the calling number to Then, this OFC routes the calling number to the tax exchange & then to the local the tax exchange & then to the local exchange of the called number. exchange of the called number.

And at the end, the local exchange makes a And at the end, the local exchange makes a connection between the calling number & connection between the calling number & the called number.the called number.

3. ISD Call :-3. ISD Call :- If there is a 0 at second digit i.e. an ISD If there is a 0 at second digit i.e. an ISD

call, then tax exchange routes the dialing call, then tax exchange routes the dialing number to number to VSNL.VSNL.

TELEPHONIC COMMUNICATIONTELEPHONIC COMMUNICATION

STD/ISD

OPTICAL FIBER TECHNOLOGYOPTICAL FIBER TECHNOLOGY Fiber-optic communicationsFiber-optic communications is based on is based on

the principle that light in a glass medium the principle that light in a glass medium can carry more information over longer can carry more information over longer distances than electrical signals can carry distances than electrical signals can carry in a copper or coaxial medium or radio in a copper or coaxial medium or radio frequencies through a wireless medium. frequencies through a wireless medium.

The purity of today’s glass fiber, The purity of today’s glass fiber, combined with improved system combined with improved system electronics ,enables fiber to transmit electronics ,enables fiber to transmit digitized light signals hundreds of digitized light signals hundreds of kilometers without amplification.kilometers without amplification.

With few transmission losses, low With few transmission losses, low interference, and high bandwidth interference, and high bandwidth potential, optical fiber is an almost ideal potential, optical fiber is an almost ideal transmission mediumtransmission medium..

COMPARISON WITH THE COMPARISON WITH THE ELECTRICAL TRANSMISSIONELECTRICAL TRANSMISSION

Lower material costLower material cost, where large , where large quantities are not required. quantities are not required.

Lower cost Lower cost of transmitters and of transmitters and receivers. receivers.

Capability to carry electrical power as Capability to carry electrical power as well as signals. well as signals.

CONTD..CONTD..

In certain situations fiber may be used even In certain situations fiber may be used even for short distance or low bandwidth for short distance or low bandwidth applications, due to other important features.applications, due to other important features.

Immunity to electromagnetic interferenceImmunity to electromagnetic interference, , including nuclear electromagnetic pulses including nuclear electromagnetic pulses (although fiber can be damaged by alpha and (although fiber can be damaged by alpha and beta radiation). beta radiation).

High electrical resistanceHigh electrical resistance making it safe to making it safe to use near high-voltage equipment or between use near high-voltage equipment or between areas with different earth potentials. areas with different earth potentials.

CONTD..CONTD..

Lighter weightLighter weight of an Optical Fiber as of an Optical Fiber as compared to a coaxial cable. compared to a coaxial cable.

No sparks, important in flammable or No sparks, important in flammable or explosive gas environments. explosive gas environments.

Not electromagnetically radiating, and Not electromagnetically radiating, and difficult to tap without disrupting the signal, difficult to tap without disrupting the signal, important in high-security environments. important in high-security environments.

Much smaller cable sizeMuch smaller cable size - important where - important where pathway is limited.pathway is limited.

OPTICAL FIBEROPTICAL FIBER An Optical Fiber (or Fiber) Optical Fiber (or Fiber) is a glass or plastic fiber designed to guide light along its length by Total Internal Reflection. Fiber opticsFiber optics is the branch of Applied Science and Engineering concerned with such optical fibers. Optical fibers are widely used in Fiber Optic Communication, which permits digital data transmission over longer distances and at higher data rates than electronic communication.

PRINCIPLE OF OPERATION OF AN PRINCIPLE OF OPERATION OF AN OPTICAL FIBEROPTICAL FIBER

The operation of an optical fiber is based on The operation of an optical fiber is based on the principle of the principle of Total Internal Reflection Total Internal Reflection ..

Light reflects (bounces back) or refracts Light reflects (bounces back) or refracts (alters its direction while penetrating a (alters its direction while penetrating a different medium), depending on the angle at different medium), depending on the angle at which it strikes a surface. which it strikes a surface.

Light waves are guided through the core of the Light waves are guided through the core of the optical fiber in much the same way that radio optical fiber in much the same way that radio frequency (RF) signals are guided through frequency (RF) signals are guided through coaxial cable. coaxial cable.

The light waves are guided to the other end of The light waves are guided to the other end of the fiber by being reflected within the core.the fiber by being reflected within the core.

CONTD..CONTD..

The composition of the cladding glass The composition of the cladding glass relative to the core glass determines the relative to the core glass determines the fiber’s ability to reflect light. fiber’s ability to reflect light.

That reflection is usually caused by creating That reflection is usually caused by creating a higher refractive index in the core of the a higher refractive index in the core of the glass than in the surrounding cladding glass than in the surrounding cladding glass, creating a “waveguide”.glass, creating a “waveguide”.

The refractive index of the core is increased The refractive index of the core is increased by slightly modifying the composition of the by slightly modifying the composition of the core glass, generally by adding small core glass, generally by adding small amounts of a amounts of a dopant.dopant.

Alternatively, the waveguide can be created Alternatively, the waveguide can be created by reducing the refractive index of the by reducing the refractive index of the cladding using different dopants.cladding using different dopants.

MODES OF AN OPTICAL MODES OF AN OPTICAL FIBERFIBER

There are basically 2 modes of fiber that There are basically 2 modes of fiber that are used in the operation of Optical are used in the operation of Optical Fiber Communication, namely:-Fiber Communication, namely:-

Single Mode Fiber.Single Mode Fiber. Multi Mode Fiber.Multi Mode Fiber.

These modes are explained in the These modes are explained in the following slides.following slides.

The most common type of Single-mode fiberSingle-mode fiber has a core diameter of 8 to 10 μm and is designed for use in the near infrared.

It uses a single strand of fibre made of glass.

Light travels down one single path along the single strand of glass fibre.

SINGLE MODE FIBERSINGLE MODE FIBER

MULTI MODE FIBERMULTI MODE FIBER

Fiber with large (50-100 microns) core diameter and transmit multiple modes at the same time can be called as multimode.

It uses 2 or more strands of glass fibre.

In this the the light signals can travel multiple paths allowing for higher bandwidth.

Basic Components OfBasic Components OfOptical Fiber Communication Optical Fiber Communication

SystemsSystems

RESOLVING THE CAPACITY RESOLVING THE CAPACITY CRISISCRISIS

There are 3 ways by which Capacity Crisis can There are 3 ways by which Capacity Crisis can be resolved, namely:-be resolved, namely:-

Laying more new fibers-Laying more new fibers- But this is not an But this is not an economical technique.economical technique.

Increasing the bit rate using Time Division Increasing the bit rate using Time Division Multiplexing, by using the following 2 Multiplexing, by using the following 2 techniques:techniques:

1)1) PDH Multiplexing Technique.PDH Multiplexing Technique.2)2) SDH Multiplexing Technique.SDH Multiplexing Technique.

DWDMDWDM Technique.Technique.

PDHPDH MULTIPLEXING MULTIPLEXING TECHNIQUETECHNIQUE

Fig. : PDH ArchitectureFig. : PDH Architecture

It can provide data rate from 8 Mbps It can provide data rate from 8 Mbps to 140 Mbps on existing fiber.to 140 Mbps on existing fiber.

SDHSDH MULTIPLEXING MULTIPLEXING TECHNIQUETECHNIQUE

Fig. : SDH ArchitectureFig. : SDH Architecture

It can provide data rate from 155 Mbps It can provide data rate from 155 Mbps to 2.5 Gbps on existing fiber.to 2.5 Gbps on existing fiber.

DWDMDWDM MULTPLEXING MULTPLEXING TECHNIQUETECHNIQUE

The third choice for service is The third choice for service is DWDMDWDM , which , which increasesincreases the the capacity of embedded fibercapacity of embedded fiber by first assigning incoming by first assigning incoming optical signals to specific frequency( wavelength) within a optical signals to specific frequency( wavelength) within a designated frequency band and then multiplexing the result designated frequency band and then multiplexing the result signal out onto one fiber.signal out onto one fiber.

DWDM can provide data rate from 2.5 Gbps to 80 Gbps on DWDM can provide data rate from 2.5 Gbps to 80 Gbps on existing fiber.existing fiber.

LimitationsLimitationsJoining Cables: Joining Cables:

The best way of joining cables is to use fusion The best way of joining cables is to use fusion splicing. splicing.

This is where fiber ends are fused to one another This is where fiber ends are fused to one another by melting the glass. by melting the glass.

Making such splices in a way that will ensure Making such splices in a way that will ensure minimal loss of signal is a skilled task that requires minimal loss of signal is a skilled task that requires precision equipment. precision equipment.

It is particularly difficult to do outdoors in very It is particularly difficult to do outdoors in very extreme temperatures. extreme temperatures.

In the early days of fiber optical systems (the early In the early days of fiber optical systems (the early 1980s) connectors which allowed cables to be 1980s) connectors which allowed cables to be plugged and unplugged were unreliable and caused plugged and unplugged were unreliable and caused a large amount of signal loss (as much as 3 dB per a large amount of signal loss (as much as 3 dB per connector).connector).

Bending Cables :Bending Cables :

As light travels along the fiber, it is reflected As light travels along the fiber, it is reflected from the interface between the core and from the interface between the core and cladding whenever it strays from the path cladding whenever it strays from the path straight down the center. straight down the center.

When the fiber is bent, the light only stays in the When the fiber is bent, the light only stays in the fiber because of this reflection. But the reflection fiber because of this reflection. But the reflection only works if the angle of incidence is relatively only works if the angle of incidence is relatively low.low.

If you bend the fiber too much the light escapes. If you bend the fiber too much the light escapes. The mount of allowable bending is specific to The mount of allowable bending is specific to particular cables because it depends on the particular cables because it depends on the difference in refractive index, between core and difference in refractive index, between core and cladding. cladding.

Thus the more the bending occurs, the more are Thus the more the bending occurs, the more are the losses in light rays.the losses in light rays.