1. AN OVERVIEW TO DIGITAL SWITCHING
SYSTEM AND DIGITAL TRANSMISSION
SYSTEM
Prepared by:
Nikhil Kumar
Electronics & Communication Department
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7th Semester
NRI Institute of Research & Technology
Bhopal

2. Contents….
• Introduction.
• Digital System.
• Digital Switching System.
• Telecomm. Switching System and Administration.
• Digital Transmission Technology.
• Telecomm. Transmission System.
• FTTH and DWDM Technology.

3. Introduction…
• Today's telecommunication network is a complex interconnection of variety of heterogeneous switching
system…..Electromechanical and electronic system, direct and common control system, hard wired and
stored program control system.
• Presently two important classes of telecommunication system network ...PSTN and PDN is widely used
using analog switching and it is expected to use the newly emerging technology to be widely used named
ISDN for the complete digitalisation of telecommunication network.
• In the early 1960's the telephone companies began using a new form of transmission called "digital." This
system allowed them to accept standard Analog voice signals and convert them to digital signals for
transmission.
• This service was called T-Carrier in the North America and E-Carrier in Europe.
• With the evolution ,Whether the incoming transmission is voice, data, video or images it will be translated
into common digital format and moved through a common digital network worldwide.

4. Digital System…
• A telecommunication network is required to transmit messages between subscribers using signals that are
either digital or analogue. Channels used to transmit signals, but it does not follow that a digital signal
always requires a digital channel and an analogue signal always requires an analogue channel. A digital
signal may be transmitted over an analogue channel by modulating a carrier wave.
• Digital System or Digital communications System is the physical transfer of Digital Bit stream over point
to point or point to multi point Communication System .
• Basically there are three subsystem followed for the transmission…
– Transmission transport information between end points of a system.
– Switching establish, maintain, and change connectivity between circuits.
– Signalling exchange control information between systems.
The Generation And Transmission of Digital Signal Involves….
Sampling
Quantisation
Encoding

5. Digital Switching System-DSS…
• The Digital Switching System Involves the following Categories in the telecomm. Industry….
– Telecomm Switching Network.
– Electronic exchange & subscriber Administration
– Facility Offered
– Testing, Traffic and Billing Administration
– Trunk Administration and Hierarchy.

6. DSS -Telecomm Switching Network..
• Telecomm. Switching network is widely used in the switching process where message is to be transmitted
between a transmitter to the desired receiving user.
• The telecommunication network which allows us to speak or send faxes or other data is an aggregation of
interconnected networks of different types.
• To overcome the limitations of manual switching, the first electronic exchange employing Space-Division
switching is designed used to switch data between two user. switching network are used to perform switching
functions of an exchange.

7. DSS-Electronic exchange & subscriber
Administration…
• The prime purpose of an exchange is to provide a temporary path for simultaneous bi-directional
transmission of speech between subscriber and exchange and vice versa.
• The most commonly used Exchange is STORED PROGRAMME CONTROLLED EXCHANGE (SPC).
In an SPC exchange, a processor similar to a general purpose computer, is used to control the functions of
the exchange . All the control functions, represented by a series of various instructions, are stored in the
memory.
• BLOCK SCHEMATIC OF SPC EXCHANGE
– Terminal equipment, provides on individual basis for each subscriber line and for interexchange
trunk.
– Switching network, may be space- division or time-division,uni-directional or bi-directional.
– Switching processor, consisting mainly of processors and m/m.
– Switching peripherals (Scanner, Distributor and Marker), are Interface Circuits between control
system terminal equipment and switching network.
– Signalling interfaces depending on type of signalling used.
– Data Processing Peripherals (Tele - typewriters, Printers, etc.) for man- machine dialogue for
operation and maintenance of the exchange.

8. SPC Exchange…

9. Subscriber Administration…
• Administration of a telephone exchange involves such day-to- day operations as putting new
subscriber lines into service, modifying subscriber's entitlements, transfer of a subscriber line and
taking a subscriber line out of service. These operations come under the review of administration of
subscriber lines, trunks and routes. These administration tasks involve dialogues between the
operators and the switching system.
• It includes basically….
– Subscriber line management.
– Creation of subscriber.
– Modification of Subscriber.
– Safe Custody.

10. Facility Offered…
Facilities to Subscriber
Call Charge printout, Malicious
Call Identification
Call Forwarding, Do Not
Disturb, Conference Calls, Call
Waiting, Call Repetition
Priority Subscriber Lines, Toll
(Outgoing Call) Restriction
Facilities to Administration
Reduced Switch Room
Accommodation, Faster
installation and Easy Extension
Economic Consideration,
Automatic test of Subscriber line

11. Digital Transmission Technology…
• Introduction of Digital Transmission Systems which were mainly Digital UHF, Digital Microwave,
Digital Coaxial and Optical Fibre Systems, started during 1990 aimed to improve STD services.
• TYPES OF MULTIPLEXING
– Space-division multiplexing: It implies diff. point-to-point wires for diff. channels. In wireless
comm., space-division multiplexing is achieved by multiple antenna elements forming a phased
array antenna.
– Frequency-division multiplexing (FDM): The spectrum of each input signal is shifted to a
distinct frequency range. FDM is inherently an analog technology. FDM achieves the
combining of several digital signals into one medium by sending sgl in several distinct freq.
ranges over that medium.
– Time-division multiplexing (TDM) involves sequencing groups of a few bits or bytes from
each individual I/O stream, in such a way that they can be associated with the appropriate
receiver.
– Code division multiplexing (CDM) is techniques where several channels simultaneously share
the same frequency spectrum, and this spectral bandwidth is much higher than the bit rate.
CDM techniques are used as an channel access scheme, namely Code Division Multiple Access
(CDMA).

12. DTS- Continues…
• COMPONENTS OF TRANSMISSION NETWORK
– A Digital Distribution Frame (DDF) is the interface when coaxial cable has to be terminated,
organized or cross-connected in long-distant transport networks, or in access networks close to
subscribers.
– Fibre distribution frame (FDF) provides efficient cable connections between outside plant cable
and equipment in the buildings and communication facilities. FDF integrates fibre splicing,
storage, and cable connections together in single unit.
• Devices Used In Digital Transmission System
– Filters, Waveguides & Transmission Lines
– Amplifiers & Antennas
– Source & Detectors

13. Telecomm. Transmission System…
• Synchronous Digital Hierarchy (SDH) is standardized protocols that transfer multiple digital bit
streams over OFC using lasers or LED. At low transmission rates data can also be transferred via an
electrical interface. The method was developed to replace the PDH system for transporting large
amounts of telephone calls and data traffic over the same fibre without synchronization problems. SDH
is not itself a communications protocol, but a transport protocol.
• SDH evolution is possible because of the following factors:
– Fibre Optic Bandwidth: The bandwidth in Optical Fibre can be increased and there is no limit for
it. This gives a great advantage for using SDH.
– Technical Sophistication: Although, SDH circuitry is highly complicated, it is possible to have
such circuitry because of VLSI technique which is also very cost effective.
– Intelligence: The availability of cheaper memory opens new possibilities.
– Customer Service Needs: The requirement of the customer with respect to different bandwidth
requirements could be easily met without much additional equipment.
• ADVANTAGES OF SDH
– High transmission rates up to 40Gbps & SDH interfaces are globally standardized
– Simplified add & drop function & Reliability.
– High availability and capacity matching & Future-proof platform for new services.

14. Telecomm. Transmission System…

15. FTTH and DWDM Technology…
• FTTH: “Fiber to the Home” is defined as a telecommunications architecture in which a
communications path is provided over OFC extending from an Optical Line Terminal (OLT) unit
located in central office (CO) connects to an Optical Network Terminal (ONT) at each premise.
FTTH consists of a single OFC from the base station to the home. The optical/electrical signals are
converted and connection to the user’s PC via an Ethernet card.
• FTTB: “Fiber to the Building” is defined as a telecommunications architecture in which a
communications path is provided over OFC extending from an OLT unit located in CO connects to
an ONU at the boundary of the building enclosing the home or business of the set of subscribers.
FTTB regarded as a transitional stage to FTTH.
• FTTC: It is a method of installing OFC by the curb near the user’s home. An optical communications
system is then used between the ONU installed outside from the installation centre. Finally, copper
cable is used between the ONU and user.

16. Continues…
• DWDM SYSTEM….
– Optical Terminal Multiplexer (OTM)- Optical Transponder unit (OTU),Optical Multiplexer unit
(OMU),Optical De-multiplexing (ODU),Optical Amplifiers (OA,OBA,OPA), Common Control
cards are the main components of DWDM System.
– Optical Line Amplifier (OLA) - EDFA (Erbium Doped Fiber Amplifier) Technology & Raman
Amplifying Technology.
– Optical Add and Drop Multiplexer (OADM) - OADM is an element that allows some
wavelengths to be dropped and added while allowing the remaining wavelengths to pass
through optically without OEO conversion (which is very expensive).
– Optical Cross Connect (OXC) - OXCs are very popular which convert optical data streams into
electronic data, using electronic cross-connection technology, and then converting electronic
data streams into optical. This is known as the hybrid.

17. DWDM SYSTEM

18. References…
• www.en.wikipedia.org/wiki/Pulse-code_modulation
• www.telecombasics.net/
• http://en.wikipedia.org/wiki/Microwave
• https://en.wikipedia.org
• Website of FTTH Council Europe
• http://learntelecom.bsnl.co.in/eetp_reports_module/eetp_material_report1.a
sp.
• http://learntelecom.bsnl.co.in/eetp/home/eetpindex.asp

19. THANKS