This document summarizes information about Bharat Sanchar Nigam Limited (BSNL), the seventh largest telecommunications company in the world. It provides an overview of BSNL's services and sections within telephone exchanges, including the main distribution frame room, power room, PCM room, switch room, optical fiber cable section, broadband section, and mobile section. It also describes technologies used like DWDM, signaling, PDH and SDH multiplexing hierarchies, and defines key terms like STM.

1. TELECOMMUNICATIONS
BY
VIPUL VERMA
11002966

2. COMPANY INFO.
 ESTABLISHED in October 2000, with the vision of
becoming the largest telecom service provider in Asia.
 Bharat Sanchar Nigam Limited is the world’s seventh
largest telecommunications company.
 It provides a comprehensive range of services in India,
which include wired connections, CDMA (code division
multiple access) mobile, GSM (global system for mobile
communications) lines, Internet, broadband, MPLS-VPN
(multi protocol label switching-virtual private network),
VoIP (voice over Internet protocol).
 Within this short span of time, it has also become one of
the largest public sector companies in India.

3. EXCHANGE LAYOUT
Main Distribution Frame (MDF) Room
Power Room
PCM ROOM
Switch Room
OFC Section
Broadband Section
Mobile Section

4. LOCAL CABLE CONTACT AT MDF .
IT IS A LARGE IRON FRAME, DIVIDED INTO TWO SIDES I.E.
EXCHANGE SIDE AND LINE SIDE.
THE PRIMARY FUNCTION OF MDF IS TO REMOVE FAULT. IT IS
ALSO KNOWN AS FAULT REMOVE SECTION.
THE TELEPHONE NUMBERS ARE ALSO DISCONNECTED IN
THE MDF BECAUSE OF SOME SPECIFIC REASON.
MAIN DISTRIBUTION FRAME(MDF)

5. MDF LAYOUT
 Vertical side
 Horizontal Side
Vertical side:-
 Rack:- On the rack, the tags are situated. One rack is having
eight tags. The counting is done from up (0) to down (7).
 Tags:- Each rack consists of eight tags
1 tag = 4 core
1 core = 4 bunch
1 bunch = 2 line
 N.E:-The word NE stands for the ‘NUMBER OF EQUIPMENT’. It
is used for testing number.
 Wedge:- Wedge is used as a device for checking the ring.
Wedge is placed in jack strips, which is connected to
telephone for checking.

6. Horizontal side:-
 The horizontal side connected to the
underground cable.
 This cable is having 100 pairs. These pair is distributed
when we allot the telephone number to the subscriber.
 Horizontal side is again subdivided in two
parts:
>One part is connected with the vertical side.
> Another with the subscriber line by using 100
pair underground cable.

7. • This is one of the important sections of the exchange
under whose control the whole exchange runs.
• Here the rectifiers convert 48 amp. AC to 48 amp. DC
current which is suitable and desired by most of the
equipments in the exchange.
• Input Voltage to exchange is 440 Volts.
• In this room the batteries are ever ready for taking
the loads when there is a power failure. They are 2
volts cell each. Each battery can give 400 amp. per
hour.
POWER ROOM

8. PCM ROOM
• A long distance or local telephone conversation between two
persons could be provided by using a pair of open wire lines or
underground cable as early as early as mid of 19th century.
• Due to fast industrial development and increased
telephone awareness, demand for trunk and local traffic went
on increasing at a rapid rate.
• To cater to the increased demand of traffic between two
stations or between two subscribers at the same station we
resorted to the use of an increased number of pairs on either
the open wire alignment, or in underground cable.
• This could solve the problem for some time only as there is a
limit to the number of open wire pairs that can be installed on
one alignment due to maintenance problems.

9.  It, therefore, became imperative to think of new technical
innovations which could exploit the available bandwidth of
transmission media such as open wire lines or
underground cables to provide more number of circuits on
one pair.
 The technique used to provide a number of circuits using a
single transmission link is called Multiplexing.
 This technique is applied in the PCM and OFC Room of
the exchange where firstly the analog signal is converted
into digital form by Pulse Code Modulation Technique and
then the multiplexing is done on the combination of signals
in a pre-defined hierarchy so as to cater the demands of
myriad number of users in the country. And then this
multiplexed signal is send to its destination.

10. The advantages of PCM are:-
• Noise Interference is almost completely eliminated when the
pulse signals exceed noise levels by a value of 20 dB or more.
• The signal may be received and retransmitted as many times as
may be desired without introducing distortion in the signal.
Pulse-code modulation (PCM) is a method used to
digitally represent sampled analog signals.
. In a PCM stream, the amplitude of the analog signal is sampled
regularly at uniform intervals, and each sample is quantized to the
nearest value within a range of digital steps.

11. SWITCH ROOM
 EWSD (Electronic Digital Switching System/Electronic World
Switch Digital) is one of the most widely installed telephone
switching systems in the world.
 The software of EWSD is called APS (Automatic Program
System). The APS is on a hard drive and includes the operating
system, developed by Siemens in cooperation with Bosch.
 It is predominantly written in the CHILL language.
 Its Main subsystems are:
CP (Central Processor), MB (Message Buffer), CCNC
(Common Channel Network Control), LINE (Analog Line
Group), LTG (Line Trunk Group), DLU (Digital Line Unit), SN
(Switching Network), PA (ISDN Primary Access)

12. The transmission of a call takes place as:-
CALLER
|
D.P.
|
PILLAR
|
MDF
|
EXCHANGE
|
TAX
|
EXCHANGE
|
MDF
|
PILLAR
|
D.P.
|
RECEIVER

13. BROADBAND SECTION
 The need of hour is large bandwidth and its
optimum utilization at reasonable cost.
 Any data access rate more than 2 Mbps is
considered as broadband access.
 As per the recent broadband policy of govt. of india,
access rate of over 256 kbps will come under the
category of broadband access.
 The term broadband refers to the
wide bandwidth characteristics of a transmission
medium and its ability to transport multiple signals
and traffic types simultaneously.

14.  This section comprises of many different
components and equipments which are as follows:-
DSLAM, Tier I / Tier II Router, OCLAN,
BNG(Broadband Network Gateway), MPLS(Multi
Protocol Label Switching), Edge Router, Core
Router.
 All the data packets and voice call from the
customers end is splitted in the MDF and then the
data packets from there comes to this section
where they are first fed to the DSLAM(Digital
Subscriber Line Access Multiplexer).
 It multiplexes them and forwards it to the Tier II
router to Tier I router which actually routes the
packets from one n/w to another.
 After that MPLS forwards those packets to Core
Router and then to the Internet Cloud.

15. MOBILE SECTION
 The mobile section comprises of different
subsections like- BTS, BSC, MSC etc.
 BTS (Base Transciever Station) is basically
composed of mobile tower and its ground station
which is responsible for transmitting and receiving
signals
 BSC(Base Station Controller) is connected to the
MSC on one side and to the BTS on the other.
 MSC’s(Mobile Switching Center) function of the
MSC is to coordinate the set up of calls between
GSM mobile and PSTN users.

16. TECHNOLOGIES & CONCEPTS
 DWDM(DENSE WAVELENGTH DIVISION MULTIPLEXING):-
 In fiber-optic communications, wavelength-division
multiplexing (WDM) is a technology which multiplexes a number
of optical carrier signals onto a single optical fiber by using
different wavelengths (i.e. colors) of laser light.
 The term wavelength-division multiplexing is commonly applied
to an optical carrier (which is typically described by its
wavelength), whereas frequency-division multiplexing typically
applies to a radio carrier (which is more often described
by frequency).
 Since wavelength and frequency are tied together through a
simple directly inverse relationship, the two terms actually
describe the same concept.

17. SIGNALLING
 The term signaling, when used in telephony, refers to
the exchange of control information associated with the
establishment of a telephone call on a
telecommunications circuit.
 . An example of this control information is the digits
dialed by the caller, the caller's billing number, and other
call-related information.
 When the signaling is performed on the same circuit that
will ultimately carry the conversation of the call, it is
termed Channel Associated Signaling (CAS).
 In contrast, SS7 signaling is termed Common Channel
Signaling (CCS) in that the path and facility used by the
signaling is separate and distinct from the
telecommunications channels that will ultimately carry
the telephone conversation.

18. PDH & SDH (MULTIPLEXING HIERARCHIES)
 To cope with the demand for ever higher bit rates, a multiplex
hierarchy called the plesiochronous digital hierarchy (PDH)
evolved.
 The bit rates start with the basic multiplex rate of 2 Mbit/s with
further stages of 8, 34 and 140 Mbit/s.
 In North America and Japan, the primary rate is 1.5 Mbit/s.
 The analog telephone signal is sampled at a bandwidth of 3.1
kHz, quantized and encoded and then transmitted at a bit rate
of 64 kbit/s.
 A transmission rate of 2048 kbit/s results when 30 such coded
channels are collected together into a frame along with the
necessary signaling information.
 This so-called primary rate is used throughout the world.

19.  . To recover a 64 kbit/s channel from a 140 Mbit/s PDH
signal, it’s necessary to demultiplex the signal all the way
down to the 2 Mbit/s level before the location of the 64
kbit/s channel can be identified.
 PDH requires “steps” (140-34, 34-8, 8-2 demultiplex; 2-8,
8-34, 34-140 multiplex) to drop out or add an individual
speech or data channel.
The main problems of PDH systems are:
 There are different hierarchies in use around the world.
Specialized interface equipment is required to interwork
the two hierarchies.
 To extract a single voice call -> demultiplex all steps
down.
 Add-drop-multiplexers are hard to build.

20. SDH(Synchronous Digital Hierarchy):-
SDH is a synchronous digital transport system, aim to provide
a simple, economical and flexible telecom infrastructure.
Features:-
 High transmission rates of up to 40 Gbit/s can be achieved in
modern SDH systems.
 Compared with the older PDH system, it is much easier to
extract and insert low-bit rate channels from or into the high-
speed bit streams in SDH.
 Modern SDH networks include various automatic back-up and
repair mechanisms to cope with system faults. Failure of a link
or a network element does not lead to failure of the entire
network which could be a financial disaster for the network
provider.
 The SDH interfaces are globally standardized, making it
possible to combine network elements from different
manufacturers into a network.

21.  The data is usually transmitted in this format, which
comprises of a byte matrix of 9 rows and 270 columns.
 Transmission is row by row, starting with the byte in the
upper left corner and ending with the byte in the lower
right corner.
 The frame repetition rate is 125
ms., each byte in the Payload
represents a 64 kbit/s channel.
 The first 9 bytes in each of the
9 rows are called the overhead,
which consists of supervisory bits.
STM(Synchronous Transport Module)

22. Thank You !!!