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Basic Telecom Course
CONTEN
Transmission Lines Basic
Analogue and Digital Signal
ISDN Basic
Circuit switch system Vs Packet switchedsystem
GSM Network Overview
ADSL Network
1
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Transmission Lines Basic
Telecommunications means:
The electronic transmission of alltypes of information audio, video,
voice, graphics, pictures, animation
from a location to another over acommunications link.
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Basic Elements of a Telecommunication System
Transmitter
Receiver
TransmitterSource
Destination
Channel
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Telecommunications Channels
Transmission lines - carrier is electrical energy - channelisnormally copper cable
Optical fibers - carrier is electromagnetic energy at lightfrequencies - channel is the optical fiber cable
Radio waves - carrier is electromagnetic energy at radio
frequencies - channel is free space between transmitting Antennaand receiving Antenna.
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Transmission Media
Transmission Medium
Physical path between transmitter and receiver
Guided Media
Waves are guided along a solid medium
E.g., copper twisted pair, copper coaxial cable, optical fiber
Unguided Media
Provides means of transmission but does not guide
electromagnetic signals
Usually referred to as wireless transmission
E.g., atmosphere, outer space
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Copper transmission line
Coaxial cable - this is called an unbalanced line ( has one
conductor grounded or exposed to the outside elements
in greater magnitude than the other conductor.)
Twisted Pair Cable- this is called a balanced line (each
line has equal impedance relative to ground or itssurroundings)
Guided Media
Fiber optic Transmission Line
Unguided MediaElectromagnetic waves, called wir eless transmission
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PSTN Architecture, Lines and Trunks
PBX
PBX
Telephone
Telephone
Individualuserstations,Linens orExt
ResidentialServices
CPE Local Loop Backbone,or CoreNetwork
LocalExchangeTrunks
Subs Line
Subs Line
InterexchangeTrunks
Local
Exchanges
TandemTrunks
International GatewayFor routing calls betweencountries
Toll/Transit Switchfor routing calls to orfrom other cities
Tandem/Junction Excfor routing calls between localExc within the city
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Local Exchange
Main Exchange
Main Exchange
Main Exchange
Subs
SubsSubs
Subs
Cell Tower
Mobile Exchange
International
Exchange
Cell
Phone Box
Telephone
Poles
River
PayphoneBox
Payphone
Fiber Optic
Cables
Local Ex. Is connected to
all the phones in a small
geographical area
Signal leaves your house
to a telephone box outside
From the Local & Mobile
Exs. Calls are routed to
the main Ex.
Cell phone calls travel to
the cell tower & from
there, on to a mobile ex.
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Local Exchane
Main Exchange
Subs
SubsSubs
Subs
Phone Box
Telephone
PolesRiver
International
Exchange
International
Exchange
Undersea
Cable
Satellite
To Other
Countries
The Calls are sent to the other
countries via undersea cables or
satellite systems
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Analog Signals and Digital Signal
A continuously varying electromagnetic wave that may be
propagated over a variety of media, depending on frequency
Examples of media:
Copper wire media (twisted pair and coaxial cable)
Fiber optic cable
Atmosphere or space propagation
Analog signals can propagate analog and digital data
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Analog and Digital Transmission
Analog Transmission
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Digital Signals
A sequence of voltage pulses that may be transmitted over a copper wire medium
Generally cheaper than analog signaling
Less susceptible to noise interference
Suffer more from attenuation
Digital signals can propagate analog and digital data
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ISDN Basic
What is ISDN?
Integrated Service Digital Network,
A system of digital phone connections, which allow
voice and data to be transmitted simultaneously
using end-to-end digital connectivity.
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Integrated Service Digital Networks
ISDN - is a digital telephone service which
provides fast, accurate voice & data transmissionover existing copper telephone wiring.
ISDN based on a number of fundamental building blocks.
First, there are two types of ISDN
"channels" or communication paths:
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Integrated Service Digital Networks
B-channel The Bearer ("B") channel is a 64 kbps channel
This channel can be used for video, data, voice, ormultimedia calls.
D-channel The Delta ("D") channel can be either a 16 kbps or 64
kbps channel
Mainly this channel is used for communications (or
"signaling") between switching equipment in the ISDNnetwork & the ISDN equipment at your location.
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Integrated Service Digital Networks
These channels are delivered to the user in one of two pre-defined
configurations:
Basic Rate Interface (BRI)
BRI is the ISDN service used to connect to the Internet. BRI connectionsupports two channels B and D over a standard phone line. often called"2B+D".
Primary Rate Interface (PRI)
ISDN PRI service is used primarily by large organizations with intensivecommunications needs. This PRI connection supports 30 64kbps
European- (23 64 kbps) American B-channels and one 64 kbps D-channel
(30B+D , 23B+D) over a high speed (T1 or E1) circuit.
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Circuit Switching
Circuit switching Dedicated communications path between two stations
E.g., public telephone network ( Plain Old Telephone System- POTS)Phases of Circuit Switching
Circuit establishment
An end to end circuit is established through switching nodes
Information Transfer ( call progress and transfer)
Information transmitted through the network
Data may be analog voice, digitized voice, or binary data
Circuit disconnect
Circuit is terminated
Each node de-allocates dedicated resources
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Circuit Switched
Telephone
Telephone
Switch 1 Switch 2
Switch 3 Switch 4
Three phases of circuit switched:- Establish,
- Transfer,- Disconnect
To establish aconnection:Must haveswitching Capacity& Channel Capacity
Must haveintelligenceto workoutrouting
SubsLoop Trunk
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Packet Switching
computer2
computer2
D C B A
Packet switching Message is broken into a series of packets Each node determines next leg of transmission for each
packet
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Packet Switching Advantages
Line efficiency is greater
Many packets over time can dynamically share the
same node to node link
Packet-switching networks can carry out data-rate
conversion
Two stations with different data rates can
exchange information
Unlike circuit-switching networks that block callswhen traffic is heavy, packet-switching still accepts
packets, but with increased delivery delay
Priorities can be used
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Disadvantages of Packet Switching
Each packet switching node introduces a delay
Overall packet delay can vary substantially
This is referred to as jitter
Caused by differing packet sizes, routes taken
and varying delay in the switchesEach packet requires overhead information
Includes destination and sequencing
information
Reduces communication capacity
More processing required at each node
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Comparison between packet switching networks and circuit switching networks
Circuit Switching
Dedicated transmission path
Continuous transmission
No storage of data/messages
Same path for duration of
connectionCall setup required
Overload may block call
Busy signal if called busy
Fixed bandwidth transmission
Charging by minute
Packet Switching
No dedicated path
Transmission of packets
Packets may be stored
Each packet may take
different routeNo call setup needed
Overload increases packetdelay
No busy signal
dynamic use of bandwidth
Charging by packet
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Leased Line
Leased Line (Private Line or Dedicated Line)
Point-to-point connection
Always on
Lower cost per minute than dial-up service Must be provisioned (set up)
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GSM GSM stands for
Global System for Mobiletelecommunications.
Cell Structure the coverage area of an operator is divided
into cells
A cell is the area that one or more transmitterscan cover
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Introduction
Types of Cells
Different types of cells are used depending ofthe population density in a country
Macrocells
Microcells Selective or sectorized cells
Umbrella cells
Nano-cells
Pico-cells
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Cell Types
Macrocells
Large cells for remote and separate populated areas
Can be larger than 3 to 35 km
Microcells
Used for densely populated areas by splitting theexisting cell into smaller cells
May be as small as .1 to 1 km
Pico-cells
smaller version of microcells
Covers approximately .01 to 1 km
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Cell Types cont.
Nano-cells
Smaller and smaller segments Covers .01 to .001 km
Umbrella Cells Covers several micro-cells to solve the problem of
overabundance of handovers among the different smallneighboring cells
When the speed ofis too high, the is handed off toumbrella cell
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GSM Architecture
A GSM networks consists of
several functional entities
SIM
Mobile TE Um Abis ABSSNSS
MSC
BSC
BTS
ME
HLR VLR AuC EIRPSTN
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Cellular System Architecture
MSC MSC
HLR
VLR
HLR
VLRTo otherMSCs
PSTNPSTN
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Cellular System Architecture
Each cell is served by a base station (BS)
Each BS is connected to a mobile switchingcenter (MSC) through fixed links
Each MSC is connected to other MSCs andPSTN
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Each MSC is a local switching exchange thathandles switching of mobile user from one basestation to another
Locating the current cell of a mobile user Home Location Register (HLR): database recording
the current location of each mobile that belongs tothe MSC
Visitor Location Register (VLR): database recording
the cell ofvisiting
mobiles
Interfacing with other MSCs and PSTN
Cellular System Architecture
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One channel in each cell is set aside for signalinginformation between BS and mobiles
Mobile-to-BS: location, call setup for outgoing,
response to incoming BS-to-Mobile: cell identity, call setup for
incoming, location updating
Cellular System Architecture
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The Network & Switching Subsystem
The switching system (SS) is responsible for performing call processingand subscriber-related functions. The switching system includes the following
functional units:home location register (HLR)The HLR is a database used for storage andmanagement of subscriptions. it stores permanent data about subscribers, including asubscriber's service profile, location information, and activity status.
buys a subscription from one of the PCS operators, he or she is registered in theHLR of that operator
Mobile Services Switching Center (MSC) - MSC performs the telephonyswitching functions of the system
controls calls to and from other telephone and data systems
also performs such functions as toll ticketing, network interfacing, commonchannel signaling, and others.
Visitor location register (VLR) -VLR is a database that contains temporaryinformation about subscribers that is needed by the MSC in order to service visitingsubscribers.
The VLR is always integrated with the MSC. When a mobile station roams into a new MSCarea, the VLR connected to that MSC will request data about the mobile station from the HLR.Later, if the mobile station makes a call, the VLR will have the information needed for callsetup without having to interrogate the HLR each time.
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Authentication center (AUC) -A unit called the AUC provides
authentication and encryption parameters that verify the user's identity andensure the confidentiality of each call.
The AUC protects network operators from different types of fraudfound in today's cellular world.
Equipment identity register (EIR) - The EIR is a database that containsinformation about the identity of mobile equipment that prevents calls fromstolen, unauthorized, or defective mobile stations
The AUC and EIR are implemented as stand-alone nodes or as acombined AUC/EIR node.
The Network & Switching Subsystem Cont.
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Base Station System (BSS)
All radio-related functions are performed in the BSS, which consists of base station
controllers (BSCs) and the base transceiver stations(BTSs)
BSC - The BSC provides all the control functions and physical links between the MSC
and BTS.
It is a high-capacity switch that provides functions such as handover, cell configuration data,
and control of radio frequency (RF) power levels in base transceiver stations. A number of
BSCs are served by an MSC.
BTS - The BTS handles the radio interface to the mobile station. The BTS is the radio
equipment (transceivers and antennas) needed to service each cell in the network. A
group of BTSs are controlled by a BSC.
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ADSL
Asymmetric Digital Subscriber Line (ADSL)
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Heres What You Will Learn About ADSL!
What is it?
What are the benefits?
How fast is it?
How does it work?
What can I use it for?
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What is ADSL?
ADSL is a latest broadband
communication technology
that creates high-speed
access to the Internet and
remote networks using thephone lines that are already
present in your home.
ADSL is an asymmetr ic comm unicat ion techno logy designed
for resident ia l users; i t is no t suitable for businesses.
Note
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What are the benefits of ADSL?
You can talk on the phone and use the Internet at
the same time on a single phone line
You can connect to the Internet at up to 140 times
faster than analog modems
Your connection to the Internet is always on
Your home has its own dedicated connection
Your connection is highly reliability
Your connection is highly secure
Si lt C ti
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Simultaneous Connections
Talk on the phone and surf the Internet at the same time on the
same phone line!
You do not have to disable call waiting to connect to the Internet.
Even if the power goes out, you will still be able to make phone
calls. Unlike cable modems, your connection speed will not be affected by
how much bandwidth your neighbors use.
ADSL Reliability
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Always On
Because the information is transmitted separately from
the voice/fax calls, your Internet connection can stay on
all the time.
No more logging on and off
No more busy signals
No more waiting
just open your browser and go!
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ADSL Security
The dedicated connection that ADSL uses
provides more security than cable.
Cable modem users share bandwidth with theirneighbors. Information traveling across the
network is easier to snoop.
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ADSL modem
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DSLAM
To interconnect multiple ADSL users a Digital Subscriber Line Access Multiplexer
(DSLAM) is used
DSLAM is used at the telephone central office that separates the data signals
from the telephone line
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What can I use ADSL for?
Faster downloads of anything digital
CD-quality audio
Graphics-rich websites
Faster and better multimedia
High-speed multiplayer games
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Types of DSL
ADSLAsymmetric DSL
R-ADSL Rate Adaptive DSL
HDSL High Bit Rate DSL
SDSL Single Line DSL
VDSL Very High Bit Rate DSL
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ADSL Summary
ADSL provides a new way to use existing phone
lines.
Its faster!
Its always on!
Voice and data on one line at the same time!
ADSL is the bestway to get online!