ALL I HAVE LEARNT THERE IS HERE

1. BASIC
TELECOMMUNICATION
PLACE:BSNL,HYDERABAD
DURATION : 25-05-2015 TO 06-06-2015
MANIDEEP SRIRANGAM
ID NO-1041310327
ECE 3rd Year(V sem)
INPLANT TRAINING
ON

2. CONTENTS:-
• Overview of Telecommunication Networks
• PCM Principles and Multiplexing of Telecommunication
• Digital switching principles
• Signaling in Telecommunication
• Introduction to latest switches in Telecommunication Industry
• Introduction to Optical fibre communication
• GSM and CDMA Technologies
• Facilities Provided by Electronic Exchanges
• Broadband and DSL technologies

3. OVERVIEW OF TELECOMMUNICATION
NETWORKS:
• The telecommunications industry is a system of switches and lines that interconnect to
provide communication between multiple parties. Today, the telecommunications
industry includes local telephone service, long distance telephone service, wireless
telephone service, paging service, Internet service, Voice over Internet Protocol (VoIP)
and a wide array of other competitive products and services. All of these different
methods of communication operate through networks forming a global
telecommunications industry.
• To overcome the limitations of manual switching; automatic exchanges, having Electro-
mechanical components, were developed. A large number of moving parts in Register,
marker, Translator, etc., were replaced en-block by a single computer.
• This made the exchange smaller in size, volume and weight, faster and reliable, highly
flexible, noise-free, easily manageable with no preventive maintenance etc.
• Further research resulted in development of Time-Division switching (Digital
Switching) which enabled sharing a single path by several calls, thus providing full
availability.

4. PCM PRINCIPLES AND MULTIPLEXING OF
TELECOMMUNICATION:
• Introduction : 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. However, 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 headway consideration and maintenance problems.
Similarly increasing the number of open wire pairs that can be installed on one
alignment due to headway consideration and maintenance problems. Similarly increasing
the number of pairs to the underground cable is uneconomical and leads to
maintenance problems. 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.

5. • Multiplexing Techniques : There are Two types
1. Frequency Division Multiplexing (FDM)
2.Time Division Multiplexing (TDM)
Frequency Division Multiplexing (FDM): Frequency Division Multiplexing Techniques
(FDM) The FDM techniques is the process of translating individual speech circuits (300-
3400 Hz) into pre-assigned frequency slots within the bandwidth of the transmission
medium. The frequency translation is done by amplitude modulation of the audio
frequency with an appropriate carrier frequency. At the output of the modulator a filter
network is connected to select either a lower or an upper side band. Since the
intelligence is carried in either side band, single side band suppressed carrier mode of
AM is used. This results in substantial saving of bandwidth mid also permits the use of
low power amplifiers. An analogue transmission system is one which is used for
transmitting continuously varying signals.
FDM techniques usually find their application in analogue transmission systems. An
analogue transmission system is one which is used for transmitting continuously
varying signals.

6. Time Division Multiplexing (TDM) : Basically, time division multiplexing involves
nothing more than sharing a transmission medium by a number of circuits in time
domain by establishing a sequence of time slots during which individual channels
(circuits) can be transmitted. Thus the entire bandwidth is periodically available to each
channel. Normally all time slots1 are equal in length. Each channel is assigned a time
slot with a specific common repetition period called a frame interval.
Each channel is sampled at a specified rate and transmitted for a fixed duration. All
channels are sampled one by, the cycle is repeated again and again. The channels are
connected to individual gates which are opened one by one in a fixed sequence. At the
receiving end also similar gates are opened in unison with the gates at the transmitting
end.
The signal received at the receiving end will be in the form of discrete samples and these
are combined to reproduce the original signal. Thus, at a given instant of time, only one
channel is transmitted through the medium, and by sequential sampling a number of
channels can be staggered in time as opposed to transmitting all the channel at the same
time as in EDM systems. This staggering of channels in time sequence for transmission
over a common medium is called Time Division Multiplexing (TDM).

7. FDM:FREQUENCY
DIVISION MULTIPLEXING
TDM:TIME DIVISION
MULTIPLEXING

8. DIGITAL SWITCHING PRINCIPLES:
• INTRODUCTION: A Digital switching system, in general, is one in which signals are
switched in digital form. These signals may represent speech or data. The digital
signals of several speech samples are time multiplexed on a common media before
being switched through the system.
To connect any two subscribers, it is necessary to interconnect the time-slots of the two
speech samples which may be on same or different PCM highways. The digitalized
speech samples are switched in two modes, viz., Time Switching and Space Switching.
This Time Division Multiplex Digital Switching System is popularly known as Digital
Switching System.
• Time and Space Switching: Generally, a digital switching system consists of several
time division multiplexed (PCM) samples. These PCM samples are conveyed on PCM
highways (the common path over which many channels can pass with separation
achieved by time division.). Switching of calls in this environment , requires placing
digital samples from one time-slot of a PCM multiplex in the same or different time-
slot of another PAM multiplex.

9. DIGITAL SWITCH

10. SIGNALING IN TELECOMMUNICATION:
• Introduction : A telecommunication network establishes and realizes temporary connections, in
accordance with the instructions and information received from subscriber lines and inter exchange
trunks, in form of various signals. Therefore, it is necessary to interchange information between an
exchange and it external environment i.e. between subscriber lines and exchange, and between
different exchanges. Though these signals may differ widely in their implementation they are
collectively known as telephone signals.
• A signaling system uses a language which enables two switching equipment's to converse for the
purpose of setting up calls. Like any other language. it possesses a vocabulary of varying size and
varying precision, i.e.. a list of signals which may also vary in size and a syntax in the form of a
complex set of rules governing the assembly of these signals. This handout discusses the growth of
signaling and various type of signaling codes used in Indian Telecommunication.
• Telephony started with the invention of magneto telephone which used a magneto to generate the
ringing current, the only signal, sent over a dedicated line between two subscribers. The need for more
signals was felt with the advent of manual switching. Two additional signals were, therefore,
introduced to indicate call request and call release. The range of signals increased further with the
invention of electro-mechanical automatic exchanges and is still growing further at a very fast pace,
after the advent of SPC electronic exchanges.

11. SIGNALING IN
TELECOMMUNICATION

12. INTRODUCTION TO LATEST SWITCHES IN
TELECOMMUNICATION INDUSTRY:
• Main parts of electronic exchange: 1.Terminal equipment
2.Switching equipment
3.Control equipment
4.Input output peripherals
• Computer keeps in its memory the exchange data that is subscribers, the trunks, routing
and charging etc. It also keeps in its memory the programs required for call processing and
hence it is called Stored Program Control (SPC).Electronic exchanges are noise less. •
While the basic principles of the switching have not changed the size, sophistication ,
efficiency and speed are changed. Though there are number of definite advantages of
electronic exchanges over the electromechanical exchanges, there are certain constraints
which should be considered, at the planning stage for deciding between the two systems.
• The constraints include: Traffic handling capacity , Power supply , Total protection from
dust , Temperature and humidity control , Static electricity and electromagnetic
interference , PCB repair , Faster obsolescence

14. INTRODUCTION TO OPTICAL FIBRE
COMMUNICATION:
Introduction to Optical Fiber Communication:
• The period of the 1900s saw a burgeoning demand on communication-network assets
for services such as database queries and updates, home shopping, video-on-demand,
remote education, telemedicine, and video conferencing. This demand was fueled by
the rapid proliferation of personal computers (PCs), coupled with a phenomenal
increase in their storage capacity and processing capabilities, the widespread
availability of the Internet, and an extensive choice of remotely accessible programs
and information databases. To handle the ever increasing demand for high-bandwidth
services from users ranging from home-based PCs to large business and research
organizations, telecommunication companies worldwide are using light waves
travelling within optical fiber as the dominant transmission system. This optical
transmission medium consists of hair thin glass fibers that guide the light signal over
long distances.

15. • The following step-by-step procedure should be followed when designing any system.
• 1. Determine the correct optical transmitter and receiver combination based upon the
signal to be transmitted (Analog, Digital, Audio, Video, RS-232, RS-422, RS485, etc.).
• 2. Determine the operating power available (AC, DC, etc.). 3. Determine the special
modifications (if any) necessary (such as impedances, bandwidths, special connectors,
special fiber size, etc.). 4. Calculate the total optical loss (in dB) in the system by adding
the cable loss, splice loss, and connector loss. These parameters should be available from
the manufacturer of the electronics and fiber. 5. Compare the loss figure obtained with
the allowable optical loss budget of the receiver. Be certain to add a safety margin factor
of at least 3dB to the entire system. Check that the fiber bandwidth is adequate to pass
the signal desired.
• The major elements of fiber optical communication are 1. Transmitter 2. Regenerator 3.
Receiver.

16. FIBRE TYPES :
• The refractive Index profile describes the relation between the indices of the core and cladding. Two main
relationships exist: 1. Step Index 2. Graded Index The step index fiber has
a core with uniform index throughout. The profile shows a sharp step at the junction of the core and
cladding. In contrast, the graded index has a non uniform core. The Index is highest at the center and
gradually decreases until it matches with that of the cladding. There is no sharp break in indices between
the core and the cladding.
• Optical fibre cable systems have the following parameters. 1. Wavelength 2. Frequency 3. Window 4.
Attenuation 5. Dispersion 6. Bandwidth 7. .Numerical Aperture
OVERVIEW OF PDH SYSTEMS:
• With the arrival of digital systems in the 60s, improving the performance of the old analog
communication networks became a real possibility. These networks were based on a frequency
• modulation scheme for transmitting voice channels, but this approach was very rigid and degraded the
channel quality, due to successive analog modulations and demodulations, which introduced noise in the
transmitted signal. The first digital communications system was set up in 1962 by Bell Labs in the USA,
and consisted of a system of 24 digital voice channels running at what is known today as T1, that is, 1544
Kbit/s. This technology was not completely adopted until the mid 70s, however, due to the large amount
of analog systems already in place and the high cost of digital systems, as semiconductors were very
expensive.

17. STEP INDEX MULTIMODE TYPE FIBRE
GRADED INDEX MULTIMODE FIBRE
TYPE

18. GSM And CDMA Technologies:
• Basic concepts of CDMA wireless transmission system Wireless multiple access
communication As we all know, it is a primary issue that must be considered in any
transmission system how to establish channel links among subscribers within the network in
the radio wave coverage area in the environment of wireless communication. In fact, the
essence of this question is a question of multiple address mobile communication. The wireless
multiple access modes currently in use include: FDMA in analog systems, and TDMA and
CDMA in digital systems. The theoretical basis for the realization of multiple access
connections is the signal division technology. That is, suitable signal design is made at the
transmitting end so that the signals sent from different stations are different; the receiving
end has the signal identifying capability, and can choose the corresponding signal from mixed
signals. When multiple access mobile communication is established based on the difference of
carrier frequencies of the transmission functions, the multiple access mode is called
Frequency Division Multiple Access (FDMA); when multiple access mobile communication is
established based on the difference of signal existence time, it is called Time Division
Multiple Access (TDMA) mode; when the multiple access mobile communication is
established based on the difference of transmission signal code forms, it is called Code
Division Multiple Access (CDMA) mode. Fig. 1-2 gives a schematic diagram of the time
domains and frequency domains of FDMA, TDMA and CDMA transmission processes.

20. Facilities provided by Electronic Exchanges:
• Facilities offered by electronic exchanges can be categorized in three arts. (I) Facilities to the Subscribers. (ii)
Facilities to the Administration. (iii) Facilities to the Maintenance Personnel.
Facilities to the Subscribers:
• MFC Push-button Dialing: All subscribers in an electronic exchange can use push-button telephones, which use Dual
Tone Multi- frequency, for sending the dialed digits. Sending of eleven digits per second is possible, thus increasing
the dialing speed.
• Priority Subscriber Lines: Priority Subscribers lines may be provided in electronic exchanges. These subscribers are
attended to, according to their priority level, by the central processor, even during heavy congestion or emergency.
• Toll (Outgoing Call) Restriction: The facility of toll restriction or blocking of subscriber line for specific types of
outgoing traffic, viz., long distance STD calls, can be availed of by all subscribers. This can be easily achieved by
keying-in certain service codes.
• Service Interception: Incoming calls to a subscriber can be automatically forwarded during his absence, to a
customer service position or a recorded announcement. The customer service position answers the calls and forwards
any message meant for the subscriber.
• Abbreviated Dialing: Most subscribers very often call only limited group of telephone numbers. By dialing only prefix
digit followed by two selection digits, subscribers can call up to 100 predetermined subscribers connected to any
automatic exchange. This shortens the process of dialing all the digits.

21. • Call Forwarding: The subscriber having the call forwarding facility can keep his
telephone in the transfer condition in case he wishes his incoming calls to be transferred
to another telephone number during his absence.
• Do Not Disturb: This service enables the subscriber to free himself from attending to his
incoming calls. In such a case, the incoming calls are routed to an operator position or a
talking machine. This position or machine informs the caller that called subscriber is
temporarily inaccessible.
• Conference Calls: Subscribers can set up connections to more than one subscriber and
conduct telephone conferences under the provision of this facility.
• Camp On Busy: Incoming call to a busy subscriber can be “Camped on” until the called
subscriber gets free. This avoids wastage of time in redialing a busy telephone number.
• Call Waiting: The ‘Cal ring his conversation. It is purely his choice either to ignore the
third party or to interrupt the existing connection and have a conversation with the third
party while holding the first party on the line.

22. • Third party Inquiry: This system permits consolation and the transfer of call to other
subscribers. Consolation can be initiated by means of a special signal from the subscriber
telephone and by dialing the directory number of the desired subscriber without
disconnecting the previous connection.
• Priority of calls to Emergency Positions Emergency calls such as ambulance, fire, etc., are
processed in priority to other calls.
• Subscriber charge: Indicator By placing a charge indicator at the subscriber’s premises
the charges of each call made can be ascertained by him
• Malicious Call Identification: Malicious Call Identification is done immediately and the
information is Obtained in the printout from either automatically or by dialing an
identification code.
• Interception or Announcement: In the following conditions, an announcement is
automatically conveyed to calling subscribers. (I) Change of a particular number of
transferred subscriber. (ii) Dialing of an unallocated cods. (ii) Dialing of an unobtainable
number. (iv) Route congested or out of order. (v) Subscriber’s line temporarily out of order.
(vi) Suspension of service due to non-payment.
• Connection Without Dialing: This allows the subscribers to have a specific connection set
up, after lifting the handset, Without dialing. If the subscriber wishes to dial another
number, then he has to start dialing within a specified time period, say 10 seconds, after

23. • Automatic Wake Up: Automatic wake up service or morning alarm is possible, without
any human intervention.
• Hot Line or Private Wire: Hot line service enables the subscriber to talk to a specific
subscriber by only lifting the handset. This service cannot be used. along with normal
dialing facility. The switching starts as soon as the receiver is lifted. 4.2..22 Denied
Incoming Call A Subscriber may desire that no incoming call should come on a particular
line. He can ask for such a facility so that he can use the line for making only outgoing
calls.
• Instrument Locking: A few subscribers may like to have their telephone sets locked up
against any misuse. Dialing of a secret code will extend such a facility to them.
• Collect call: If so desired, the incoming subscriber is billed for all the calls made to him,
instead of the calling subscriber.
Facilities to the Administration
• Reduced Switch Room Accommodation Reduction in switch room accommodation to
about 1/6th to 1/4th as compared to Cross-bar system is possible.

24. • Faster installation and Easy Extension: The reduced volume of equipment, plug-in
assemblies for interconnecting cables, printed cards and automatic testing of exchange
equipment result in faster installation (about six months for a 10,000 line exchange) Due
to modular structure, the expansion is also easier and quicker.
• Economic Consideration: The switching speed being much faster as compared to Cross-
bar system, the use of principle of full availability of trunk circuits and other equipment
makes the system economically superior to electromechanical systems.
• Automatic test of Subscriber line: Routine testing of subscriber lines for Insulation,
capacitance, foreign potential, etc., are automatically carried out during night. The
results of the testing can be obtained in the printout form, the next day.
Maintenance Facilities
• Fault Processing: Automatic fault processing facility is available for checking all
hardware components and complete internal working of the exchange. Changeover from
a faulty sub-system to stand-by sub-system is automatically affected without any human
intervention. Only information is given out so that the maintenance staff is able to
attend to the faulty sub-system.

25. BROADBAND TECHNOLOGY::
• Introduction: Advances in telecommunications and data technology are creating new
opportunities for countries, businesses and individuals—just as the Industrial
Revolution changed fortunes around the globe. The new economy is defining how people
do business, communicate , shop, have fun, learn, and live on a global basis—connecting
everyone to everything. The evolution of Internet has come into existence & Internet
service is expanding rapidly. The demands it has placed upon the public network,
especially the access network, are great. However, technological advances promise big
increases in access speeds, enabling public networks to play a major role in delivering
new and improved telecommunications services and applications to consumers .The
Internet and the network congestion that followed, has led people to focus both on the
first and last mile as well as on creating a different network infrastructure to avoid the
network congestion and access problems. The solution to this is Broadband.

26. What is Broadband?
• A definition to broadband is a must as different service providers defines in their own
terms & context. TRAI (Telecommunication Regulatory Authority of India) defines
broadband as follows: An ‘always-on’ data connection that is able to support interactive
services including Internet access and has the capability of the minimum download
speed of 256 kilo bits per second (kbps) to an individual subscriber from the Point Of
Presence (POP) of the service provider intending to provide Broadband service where
multiple such individual Broadband connections are aggregated and the subscriber is
able to access these interactive services including the Internet through this POP. The
interactive services will exclude any services for which a separate license is specifically
required, for example, real-time voice transmission, except to the extent that it is
presently permitted under ISP license with Internet Telephony.”

27. Broadband Access :Broadband access technology is broadly classified into two categories. They are Wired
Line & Wireless and further classified as detailed in the following diagram.
Broadband Access Technologies
• DSL (Digital Subscriber Line) :- DSL uses the existing twisted-pair telephone lines as the access media.
Over a period of time, a number of technologies (ds) have been introduced to provide faster data speeds
over this medium. The various dsl technologies are given below.
• 1. ADSL (Asymmetric Digital Subscriber Line)
• 2. VDSL (Very High-Speed Digital Subscriber Line)
• 3. RADSL (Rate Adaptive Digital Subscriber Line)
• 4. HDSL (High Data-Rate Digital Subscriber Line)
• 5. SDSL (Symmetric Digital Subscriber Line
• ADSL (Asymmetric Digital Subscriber Line)
• Asymmetric Digital Subscriber Line (ADSL) is a form of DSL, a data communications technology that
enables faster data transmission over copper telephone lines than a conventional modem can
provide.ADSL has the distinguishing characteristic that the data can flow faster in one direction (used for
download streaming) than the other(used for upload streaming) i.e., asymmetrically.

28. Frequency plan for ADSL
• First the POTS channel is splits off from the digital modem by filter, thus guaranteeing
uninterrupted POTS. After the POTS channel are splitted from the digital data transfer
bandwidth, the 26kHz to 1.1mhz data bandwidth could be further separated by using one of
two ways as describe below:
• 1)Frequency Division Multiplexing (FDM) :- FDM assigns one band for upstream data and one
band for downstream data. Time division multiplexing divides the downstream path into one
or more high speed channels and one or more low speed channels. But the upstream path is
only multiplexed into corresponding low speed.
• 2)Echo cancellation :- Echo cancellation assigns the upstream band to over-lap the
downstream. To separate them is by local echo cancellation. This technique is common in V.32
and V.34 modems(Conventional Modems).
• By using either one of the above techniques, ADSL splits off a 4khz region for POTS at the
DC end of the band.
ADSL MODULATION
• ADSL uses two types of Modulation i.e CAP(Carrier less Amplitude Phase Modulation) &
DMT(Discrete Multi Tone) & DMT is the most widely used one.

29. WHY ADSL?
• ADSL is in place due to both technical and marketing reasons. On the technical side, there
is likely to be more crosstalk from other circuits at the DSLAM (Digital Subscriber Line Access
Multiplex) end (where the wires from many local loops are close together) than at the customer
premises. Thus the upload signal is weakest, while the download signal is strongest at the
noisiest part of the local loop. It therefore makes DSLAM transmit at a higher bit rate than
does the modem on the customer end. Since the typical home user in fact does prefer a higher
download speed, thus telecom companies chose to make a virtue out of necessity, hence ADSL
HOW ADSL WORKS ?
• To obtain the asymmetrical data transfer to suit requirement of Internet and LAN access,
ADSL works by firstly splitting the available bandwidth on the twisted copper wire (telephone
wires) into three different channel:
• 1)A high speed downstream channel (ranges from 1.5 to 8 Mbps) 2)A medium speed upstream
channel (ranges from 16 kbps to 1 Mbps) 3)POTS (Plain Old Telephone Service) channel
• ADSL uses two separate frequency bands. With standard ADSL, the band from 25.875 kHz
to 138 kHz is used for upstream communication, while 138 kHz - 1104 kHz is used for
downstream communication.