Telecommunication Network

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TelecommunicationNetwork

• Course Details
• Semester 1, 2006

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Prof. Madya Dr Mahamod Ismail

• Lecturer in UKM since 1987.
• Diploma - UTM (Electrical Communication), 1981
• BSc. Univ of Strathclyde (Electronics
  Electrical) ,UK, 1985
• MSc UMIST, Manchester (Communication Eng.
  Digital Electronics), 1987
• PhD Univ of Bradford, Mobile Communication,
  1996
• Research Area Mobile Communication Wireless
  Networking
• Team Engineer, Tiungsat, 1997-98, Uni. of Surrey,
  U.K.
• Guest Professor, University Duisburg Essen,
  Germany , 2002
• Currently Coordinator UKM Mercator Office, Fac.
  of Eng. UKM
• Email mahamod_at_eng.ukm.my, dr_mbi_at_yahoo.com
• Telephone [phone]

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Syllabus Program Booklet
KT6123 TELECOMMUNICATION NETWORK Switching
system engineering Types of public switched
network. Switching system circuit, store and
forward, packet. Numbering, routing system and
charging. Subscriber function. Telephone system
basic requirement. Telephone equipment
characteristics. Local circuit and hybrid
transformation. Dialing system decadic and DTMF.
Subscriber and group switching. Analog and
digital switching. Switching Strowger, cross-bar
and time and space. Digital analysis. Controlling
sections. Stored Programmable Controlled
exchange. Signaling subscriber, line and
register. Transmission system FDM and PCM 30/32
channel. CCITT, CCIR function in switching
planning. Digital Network ISDN, SDH. Teletraffic
Engineering telephone traffic performance.
Teletraffic and queuing theory. Delay and loss
system, Grade of service. Erlang and Bernoulli
distribution. Broadband network ATM and B-ISDN.
Intelligent network.
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Course Outline

• Introduction
• Transmission
• Multiplexing and Hierarchy
• Switching
• Telecommunication Traffics
• Switching Network
• Signaling
• Services

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References
1. J.E.Flood, Telecommunications Switching,
Traffic and Networks, Prentice Hall, 1994 2. E.H.
Jolley, Introduction to Telephony and Teleplay,
Pittman Publication. 3. Schwartz, M.,
Telecommunication Networks Protocols, Modelling
Analysis, Addison-Wesley 4. Clarke, M.P., Network
Telecommunications Design Operation, Wiley
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Evaluation

• 2 Assignments 30
• Midterm exam 20
• Quiz 10
• Final exam 40

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Assignment 1

• Report
• Format 1
• Content 5
• Discussion/Conclusion 2
• References 2
• Presentation 5

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TelecommunicationNetwork

• Introduction
• Semester 1, 2006

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Introduction

• Tele/communications
• The process of transmitting a message between two
  remote locations.
• Message - could be Voice, Music, Textual,
  Pictorial (graph, diagram, image, etc.) or moving
  image (video).
• Recently we have a better proportion of data
  communications links and speech is being
  converted into digital forms as well as data
  will eventually be conveyed more naturally in
  these digital forms.
• The purpose of telecommunications is to convey
  information from one location to another.
• Data Precise communication
• Voice More convenient to convey information,
  thats why voice communication has predominated
  for over a century
• The telephone network, until the last decade, was
  almost entirely analog

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Introduction
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Introduction

• Broadband
• is a technique where the data to be transmitted
  is sent using a carrier signal, such as a
  sinusoidal wave. Many different frequency
  carrier signal can be transmitted simultaneously,
  more than one signal can be sent on the same
  wire.
• Baseband
• a single data signal is transmitted directly on a
  wire. The data is transmitted directly on the
  wire using positive and negative voltages.
  RS-232 interface is an example of baseband
  transmission.
• A baseband signal
• is an information signal that has not undergone
  the modulation process.
• represents voice, data, or video information
  signal.
• must be band-limited before being used to
  modulate a carrier signal.

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Introduction

• When data (or any other signal) is to be conveyed
  outside ones place, this involves the modulation
  of the broadband signal onto a carrier frequency,
  either by
• Amplitude Shift Keying (ASK)
• Frequency Shift Keying (FSK)
• Phase Shift Keying (PSK)
• or Combination of the ASK and PSK (QPSK, ?/4-PSK,
  DQPSK)
• In baseband signal recently, speech is being
  conveyed by Pulse Code Modulation (PCM)
• The standard digital voice channel that available
  in today has a capacity of 64 Kbps, or a
  multiplexed of 1.544Mbps T1, 2.048Mbps E1

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Telecommunication System
Input Transducer Encoder Modulator Amplifier
Air, Free Space Copper Cable Optical Fiber
Output Transducer Decoder Demodulator Amplifier
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Telecommunication System
Information signal output
Information signal input
Encoder
Decoder
Modulator/ Transmitter
Demodulator/ Receiver
Transmission Channel
Free-space loss Reflection Refraction scattering M
ultipath Diffraction Shadowing Noise Interference
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Telecommunication System

• Transducer transform one form of Energy into
  another
• eg. Sound Electrical
• Transmitter amplifies and processes the
  electrical replica of message for transmission
• Receiver amplifies and processes the received
  elctrical signal in reverse manner to recover the
  original message
• Transmission Channel a path connecting
  Transmitter Tx to Receiver Rx, which is
  characterized by attenuation
• Factors involve in a communication system
• Type of information (data, text, graphic, voice,
  music, multimedia, etc.)
• Information format (analog, discrete, digital,
  random, deterministic, periodic etc.)
• Transmission speed (low, medium, high, etc.)
• Transmission medium (wired, wireless)
• Transmission distance (short, medium, long)
• Modulation techniques (AM, PM, ASK, PSK, GMSK,
  PCM, OFDM, etc.)
• Error control (BCD, Gray, Morse, ASCII, FEC,
  cyclic, etc.)

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Telecommunication System
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Transmission Mode

• Simplex transmission
• Only one way communication
• Half duplex transmission
• Two ways communication, but one at a time not
  simultaneously
• Full duplex transmission
• Simultaneously in both directions
• Unicast, Multicast, Anycast, Broadcast

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Half Duplex versus Full-Duplex
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Modes of transmission

• Asynchronous
• Each character is considered a unit of
  information
• All timing and error checking is included within
  it
• Synchronous
• Information is sent as a block of data
• Control and error checking information is added
  to each block

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Asynchronous versus Synchronous
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Asynchronous Transmission

• Each character is sent independent of the next
  (or previous character sent)
• Before each character is a START bit
• Time between each character is not constant
• Requires control bits for each character sent
  (for error checking)
• At the end of each character is a STOP bit
• At least 3 of 9 bits (for a 7 bit code) sent are
  not information but overhead. Hence this is
  inefficient

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Synchronous Transmission

• Information is transmitted in a block of bits
• Each block is preceded by a sequence of bits
  called a preamble
• Each block ends with a sequence of bits called a
  postamble
• Control bits are added to allow error checking
• The data plus preamble plus postamble plus
  control information is called a Frame.
• Much more efficient as compared to Asynchronous
  transmission
• More complex and expensive to implement than
  Asynchronous

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Serial versus Parallel Transmission

• Serial mode
• Message is sent one bit at a time
• Parallel mode
• Each character is sent over
• a different wire, simultaneously
• The size of messages depends on its context
• Credit card authorization 1000 bits
• One page typed memo 15000 bits
• One second of digital voice 56000 bits
• One second of Full motion video 100 million bits

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Transmission Topology
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Transmission Topology
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Transmission Topology
As the area covered by a star network and the
number of stations served by it grow, line costs
increase and it then economic to divide the
network into several smaller network served by
its own exchange
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PSTN Topology
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PSTN

• Transmission links/nodes
• Customer nodes
• Switching nodes
• Transmission nodes
• Service nodes
• Subsystem
• Transmission systems
• Switching systems
• Signalling system

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Telecommunication Standard
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Telecommunication Network

• Bearer Service
• provides a "transport system" for
  exchanging information
• Tele-services
• complete
• includes functions for connection, and a
  uniform "language" for communication and for
  shaping the messages conveyed
• Example two telephones talk to each
• other via telephone
  network
• Also, Voice/Data/Text/Image etc

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Typical Network Services

• PSTN(Public Switched Telephone Network)
• PLMN(Public Land Mobile Network)
• PSPDN(Packet Switched Public Data Network)
• ISDN(Integrated Services Digital Network)
• Frame Relay
• Signaling Network(CAS/CCS)
• Internet
• IN(Intelligence Network)

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Network Services
Teleservices depend on particular terminal
apparatus e.g. telephone, teleprinter Bearer
Services transmission capacity that can be used
for any desired function e.g. private circuit
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Network Services
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More About WANs

• Virtual private networks (VPNs)
• A private network configured within a public
  network
• Can be built on top of the Internet
• Service offered by the telephone companies and
  ISPs

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• Value added networks (VANs)
• Public data networks that add value by
  transmitting data and by providing access to
  commercial databases and software
• Use packet switching
• Subscription based
• Often used in electronic data interchange (EDI)
  systems

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• Public switched data network technologies (PSDN)
• Data flows through a public network managed by a
  telecommunications carrier
• Most common technologies
• ISDN (integrated service digital network)
• X.25
• Frame relay
• Asynchronous transfer mode (ATM)

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(example of Frequency Modulation)
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ASK/FSK/PSK
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Sending Multiple Bits Simultaneously

• Each of the three modulation techniques can be
  refined to send more than one bit at a time. It
  is possible to send two bits on one wave by
  defining four different amplitudes.
• This technique could be further refined to send
  three bits at the same time by defining 8
  different amplitude levels or four bits by
  defining 16, etc. The same approach can be used
  for frequency and phase modulation.

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Sending Multiple Bits Simultaneously
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Hybrid Amplitude and Phase modulation

• QAM Quadrature Amplitude Modulation
• represents 4 bits per baud (I.e. V 16)

90o
8 phase changes 2 different amplitude
levels Therefore V 16
135o
45o
0o
180o
315o
225o
Used in ITU V.32 modems
270o
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Digital Encoding of Analog Signals (PCM)

• Concept
• Take samples of analog signal. To each sample -
  assign a code. Then transmit that code (digital
  signal).
• If we sample at the rate of twice the bandwidth
  of the channel then the resulting digital signal
  contains all the information in the original
  analog signal - Nyquists theorem (1924)

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PCM - Pulse Code Modulation
Samples
time
Each is assigned a n bit binary code
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PCM

• Transmitting an analog signal over a digital
  network (eg. Voice on telephone n/w)
• Each signal is sampled 8000 times per second
• Each sample is converted to a 7 bit code
• 1 bit is added for control information
• there are 128 different such codes (27)
• The digital signal is then transmitted at 64,000
  64 Kbps 88000

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Differential PCM

• Voice signals do not change extremely rapidly
• Changes of more than /- 16 levels between
  samples is very rare
• Hence use just 5 bits instead of 7 to represent
  each sample
• If signal jumps very widely then several samples
  are needed to catch up

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Delta Modulation

• Voice signals do not change very rapidly
• Transmit only one bit at each sample (indicating
  a 1 or -1) to indicate whether the signal is
  increasing or decreasing.
• Amplitude of next sample differs from previous
  one by 1 unit (either 1 or -1).
• If very rapid changes take place then the coding
  takes a while to catch up

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Problems (Delta Modulation)
Samples cannot keep up with rapidly changing
signal
time
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Predictive Encoding

• Both sender and receiver extrapolate from the
  last few values received to predict what the next
  value would be.
• The transmitter sends a value only if it were
  different from what is predicted

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Data transfer in the presence of noise

• Shannons Law
• C B log2 (1 S/N) where
• C achievable channel capacity
• B Bandwidth of line (in Hz)
• S Average signal power
• N Average Noise power
• S/N Signal to Noise Ratio
• this is usually measured in decibels (dB)
• where dB 10 log10 (S/N)

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Telephone Channel Capacity
Voice Channel 0-4,000 Hz
Voice Bandwidth 300-3,300 Hz
Voltage
Guard Band
Guard Band
0
300
3,300
4,000
Frequency (Hertz)
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• Example Channel capacity of a telephone line
  (voice grade)
• typical signal to noise ratio of a voice grade
  line
• 30 decibels
• i.e. 30 10 log10(S/N) gt S/N 1000
• Bandwidth 3000 Hz
• Thus C 3000 log2 (11000)
• C 30, 894 bits per second 30 Kbps (approx)
• This is the extreme limit though, hardly ever
  reached since ideal conditions are not present.

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Converting Voice (analog) to digital

• Use PCM
• Sample 8000 times in each second
• Time between each sample 1/8000 125 micro
  seconds (not perceptible to the human ear)
• Voice signals lie between 300 - 3300 Hz hence we
  are sampling at twice the frequency
• What does Nyquists theorem imply ?

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Data Encoding

• Data needs to be encoded in a format that
  computers can understand
• ASCII (8 bits), 128 characters, 1 bit used for
  error detection
• EBCDIC (8 bits), 256 characters
• Baudot (5 bits)

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Digital Signal Encoding
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Transmitting Data

• In order for data to be transmitted and received
  in a legible form
• The receiver must know where
• a character starts
• a character ends
• in the stream of bits that is received from a
  transmitter

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• Flow Control
• Hardware flow control RTS/CTS
• Software flow control XON/XOFF

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Flow Control

• Necessary when data is being sent faster than it
  can be processed by receiver
• Computer to printer is typical setting
• Can also be from computer to computer, when a
  processing program is limited in capacity

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Stop-and-Wait Flow Control

• Simplest form
• Source may not send new frame until receiver
  acknowledges the frame already sent
• Very inefficient, especially when a single
  message is broken into separate frames

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Stop-and-Wait Flow Control
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Basic data communications H/W

• Modem - MOdulator/DEModulator
• used to convert digital signals from a computer
  to analog signals via modulation so as to
  transmit over telephone networks

Old modem (voice-graded telephone line) - ASK
Modern modem FSKSophisticated modem - PSK
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Modem Standards

• V.22bis
• transmission rate 2400 bps
• baud rate 600 bauds
• data compression V.42bis
• Error correction V.42
• Modulation method 4QAM and TCM

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Modem Standards

• V.32
• transmission rate 9.6 Kbps
• Baud rate 2400 bauds
• Data compression/error correction same
• Modulation method 4QAM and TCM
• V.32bis
• same as above except uses 6QAM and TCM