ECE 101 An Introduction to Information Technology Information Transmission - PowerPoint PPT Presentation

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ECE 101 An Introduction to Information Technology Information Transmission


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Title: ECE 101 An Introduction to Information Technology Information Transmission

ECE 101 An Introduction to Information
TechnologyInformation Transmission
Information Path
Source of Information
Information Display
Digital Sensor
Information Receiver and Processor
Information Processor Transmitter
Transmission Medium
Information Transmission
  • Procedures for transmitting digital information
    over a communication channel
  • Data sent over a channel with a limited channel
    capacity but gt data rate
  • Data rate amount of data that a source
    produces in one second
  • One and two-way data transmission
  • Networks permit data transmission between
    remotely located computers
  • networks transmit data in data packets

Data Rate
  • Source produces data that the transmitter
    converts into signal or waveforms to be sent over
    communications channel
  • Twisted-pair (telephone), coaxial (TV), air
    (acoustical) or EM wave through space
  • Binary transmission two distinguishable signals
    (by amplitude, frequency, phase)
  • M-ary transmission more than two signals to
    represent data resulting in faster data

Data Rate Measurment
  • Let R signal transmission rate (signals
    produced every second)
  • 1/R is the time duration of each signal
  • Data Rate D R log2 M

Channel Noise
  • Noise commonly from thermal energy
  • Atomic (charged) particles vibrating randomly
  • Disturbs the data signal
  • Higher temperatures cause greater thermal motion
  • ? Sensitive receivers are placed in low-temp
  • Noise power level ?n2
  • Maximum signal power level produced by
    transmitter ?s2

Channel Transmission
  • To transmit more data per second over a channel,
    the transmitter could increase M, the number of
    distinct signals
  • Noise limits the value of M
  • ?Noise level present in the transmission channel
    dictates the maximum data rate

Decoding M-ary Signals(figure 8.2, Kuc)
Decoding M-ary Signalsin the presence of
Noise(figure 8.3, Kuc)
Channel Capacity
  • Measures the amount of data that can be reliably
    transmitted over a channel
  • Signal passing through a channel is always
    contaminated by noise
  • Channel capacity C with bandwidth B is
  • C B log2 (1 ?s2/ ?n2) bps
  • ?s2/ ?n2 is the signal to noise ratio

Channel Capacity
  • C B log2 (1 ?s2/ ?n2) bps
  • ?s2/ ?n2 is the signal to noise ratio
  • Special cases
  • ?n2 ? 0 C ? ?
  • ( ?s2/ ?n2 ) 1 C ? B log2 (?s2/ ?n2) bps
  • ?n2 ?s2 ? 0 C ? B log2 (1) 0
  • Long distances attenuation occurs so ?s2 is
    decreasing, but ?n2 is increasing

Asynchronous Data Transmission
  • Sends data over a transmission one bit at a time
    or serially
  • channel and receiver are idle much of the time
    waiting for data
  • data are packaged in a format
  • start bit
  • data - one code word at a time (byte sized are
  • parity bit - error detection (even or odd)
  • stop bit(s) - to terminate data
  • all BUT data represent over head to transmit

Asynchronous Data Transmission and Character
Format (figures 8.4 and 8.5, Kuc)
One-Way Data Transmission
  • Typically used to control remotely a device such
    as a TV, projector, VCR, garage door
  • Infrared Remote (IR) Control
  • Encodes the pressed button into a sequence of IR
    light pulses
  • The remote control generates a binary signal that
    consists of a sequence of light pulses modulated
    at 40 kHz for time periods of TB

Infrared Remote Control Signal(figure 8.6, Kuc)
Infrared Remote Control
  • Binary communication, M2
  • Transmits a single bit of information every TB
    seconds, or R 1/TB signals per second
  • Data Rate D R log2 M 1/TB log2 2 1/TB
  • Number of data bits in a code word depends upon
    the number of buttons on the remote
  • n bits will take up to 2n buttons
  • multiple transmission provides error correction
    by repetition the receiver counts votes

Digital Television
  • Standard TV as grid of small squares or picture
    elements (pixels) arranged in 700 columns and 400
    rows per frame
  • assume each pixel is encoded with 8 bits
  • TV transmits 30 frames per second
  • Data rate D 67.2 ? 106 bits/second
  • or D 67.2 Mbps

  • MPEG - Motion Picture Experts Group - reduce the
    number of bits required to transmit video since
    many scenes have static parts. So may only have 2
    to 6 Mbps
  • Freeze Frame video if the data rate is greater
    than the channel capacity, then each frame waits
    till all data received and the result appears as
    a series of still pictures

Two-way Data Transmission With Modems
  • Dialog between two systems
  • Communication over the same channel require
    separation between the signals to distinguish
    transmitted and received signals
  • Modems - transmit and receive data over telephone
    channels - data to audible tones data rates gone
    from 300 bps to over 50kbps

Modem Data Transmission Techniques
  • Use sinusoidal signals that have features that
    can be modified to represent data
  • Amplitude-modulation changes amplitude only of a
    single frequency sinusoid,
  • Frequency-shift keying use different frequencies
  • Phase-shift keying methods change phase of a
    single frequency sinusoid
  • Baud expresses number of signal intervals that
    can be reliably transmitted over a channel per
    second (same as R used earlier).

Frequency Shift Keying (figure 8.8, Kuc)
Frequency Shift Keying
  • Frequency-shift keying uses different frequencies
  • 300 to 3300 Hz bandwidth of the telephone network
  • example, two different frequencies might
    represent 1s 0s
  • Or, more practically, four frequencies, each one
    assigned to a two-bit value Baud rate the same,
    but the data rate doubles with the two bits per
    sample period.

Modem Two Way Communication (figure 8.9, Kuc)
Phase-Shift Keying
  • Changes the phase at a constant frequency and
  • Can make M-ary transmission by having each value
    have a different phase shift relative to the
    immediately preceding sinusoidal signal
  • M4 dibits with dibit varying by 360/4 90o
  • M8 tribits, with tribits varying by 360/845o
  • Phase shift occurs every Tbaud seconds

Phase-Shift Keying (figure 8.11, Kuc)
Phase-Shift Keying
  • Phase shift occurs every Tbaud seconds and if
    M4, every shift encodes 2 bits, so the data rate
    is twice the baud rate.
  • Modem factor 1 bit/cycle 1 bps/Hz
  • If M8, we transmit 3 bits every 2 cycles of the
    waveform for a modem factor of 1.5 bps/Hz

Phase-Shift Keying with Amplitude Modulation
  • Can go to quadbits, shifting the amplitude to two
    different levels and using phase shift of 45o
  • Now transmit 4 bits per 2 cycles of the waveform
    for a modem factor equal to 2 bps/Hz

AM and Phase-Shift Keying (figure 8.14, Kuc)
Establishing Modem Communication
  • No energy for 48 Tbaud
  • after answering the ring, both modems listen to
    channel to determine the noise level and if
    little noise use higher data rate
  • Alternation between 2 known signals for 128 Tbaud
    to synchronize the two modems
  • Pseudo-random alternations between known signals
    for 384 Tbaud
  • compensate for distortions in the telephone line
  • Transmission of known data sequence for 48 Tbaud
    to verify all circuits are ok

Digital Cellular Telephone
  • Uses wide frequency band width radio channel to
    transmit electromagnetic signals
  • Frequency band divided into channels with each
    having a transmit receive frequency
  • Each user uses the first sub-baud pair as a
    control channel to communicate to all users (a
    code determines who can actually receive the
  • Voice channel is assigned to a user when a call
    is made or received

Cellular Telephone Frequency Channels (figure
8.16, Kuc)
Communications(IEEE Web site)
  • Must always be visible to the antenna with which
    it communicates
  • Uses a geosynchronous orbit as the satellite
    remains stationary at 36,000 km (22,300 miles)
    above a point on the earth
  • Signal delay Tt (dt dr)/c, c3?108 m/s
  • Delays can be large fraction of a second hence
    one-way communications better than two

Data Packets
  • Transmission of multiple-byte units over networks
    of interconnected computers
  • Five parts or fields
  • address with routing information about the
    desired destination and address of the source
  • data length indicating the number of bytes in the
    data field (46 to 1500 bytes)
  • tag - a number that indexes the data packet
    (often single byte with numbers 0 to 255)

Data Packets
  • data field contains the information to be
    transmitted - for internet applications the data
    segment is approximately 500 bytes - compromise,
    smaller needs more packets, larger would cause
    delays for access to communication links
  • cyclic redundancy clock (CRC) - error detection -
    often a one byte number simply adding up all the
    1s that are in the data and retaining the
    smallest 8 bits of the sum. This is modulo-256 of
    the sum. Alternative is parity bit

Data Networks
  • Local Area Network (LAN)
  • connects computers and peripheral devices
  • can use various means or protocols to transfer
  • Wide Area Networks (WAN)
  • Connects devices wherever long-distance
    communications exist
  • Most common is international network known as the

Star Architecture for LAN(figure 8.18, Kuc)
Star Architecture
  • All nodes connect to hub computer called a server
  • fast since message only goes to server then its
  • server can store message if it is not delivered
  • all communication stops if the server is down
  • limited number of connections to server

Ring Architecture for LAN(figure 8.18, Kuc)
Ring Architecture
  • Each node connects to two neighboring nodes and
    the data packets flow around the loop in one
  • If the packet address corresponds to the node
    address the message is read if not it is just
    passed on
  • Does not require a separate server but it
    performs properly only when all the nodes are

Bus Architecture
  • Most common LAN
  • all nodes (users) connect to the same bus
  • Each node can transmit and each much recognize
    its address to receive
  • Doesnt require a separate server
  • Additional nodes easily added
  • Highly reliable since it remains operational when
    a node fails or is turned off

Bus Architecture for LAN(figure 8.18, Kuc)
A Wide-AreaNetwork(figure8.19, Kuc)
Data Packets
  • Recall earlier we looked at the transmission of
    data in data packets
  • tag - a number that indexes the data packet
    (often single byte with numbers 0 to 255)
  • data field contains the information to be
    transmitted - for internet applications the data
    segment is approximately 500 bytes - compromise,
    smaller needs more packets, larger would cause
    delays for access to communication links

Wide-Area Network
  • Consists of many switching computers or routers
    between the source and destination
  • Moving packets around the wide-area network is
    packet switching
  • The exact path of a particular packet is random
    otherwise bottlenecks
  • More sophisticated networks offer the fastest
  • Recall that each packet has the destination and a
    tag to help it arrange the packets in order

  • Most common communication channel for
    transmitting data packets
  • Standard has capacity of 10 million bps
  • Fast ethernet 100 Mbps, Gigabit ethernet 1
    billion bps
  • Special data signal using two wires to transmit
    data and two wires to receive data

  • Hence etherner uses dedicated cables to
    interconnect computers directly
  • Computer connects to network through a special
    network interface card (NIC)
  • packages the data bytes from the computer into
    data packets
  • at the receiving end another NIC receives the
    data packets, checks for errors, and delivers the
    data bytes (typically 46 to 1500 bytes)

Data Packets on Ethernet
  • Preamble 7 repetitions of 10101010 to
    synchronize the receiver (7 bytes)
  • Start byte with a value of 10101011 to indicate
    the start of the information fields (1 byte)
  • Destination Address (6 bytes)
  • Source address (6 bytes)

Data Packets on Ethernet
  • Tag/Length field that indicates the packet number
    and length of data (2 bytes)
  • Data varies in length (46 to 1,500 byte)
  • A cyclic redundancy check (CRC) for error
    detection (4 bytes)
  • Total overhead of 26 additional bytes

Asynchronous Transfer Mode (ATM)
  • Ethernet packets have variable length fields.
  • To simplify server design, ATM is used
  • ATM packets are always 53 bytes long (5 for
    routing and 48 for data
  • All ATM packets use the same path to the
    destination, so path designate by just 5 bytes to
    reduce the routing information
  • Error checking done only at the destination

Transmission Protocols on the Internet
  • Data on the internet are transmitted as data
  • Methods of data transfer are protocols such as
  • TCP/IP guarantees that the received data is
    correct hence reliable
  • UDP/IP transmits data quickly but does not
    retransmit erroneous packets hence speed

  • Transmission control protocol/Internet protocol
  • Uses parity bits and check character to ensure
    the integrity of the data.
  • When the data packet is received correctly it
    sends an acknowledgement (ACK) to the transmitter
  • If ACK is not received it sends the message again
    hence the transmission rate is reduced

  • Universal datagram protocol/Internet protocol or
  • Transmits data with minimum delay
  • it finds the quickest available route to send the
    data and does not acknowledge receipt or
    retransmit erroneous packets
  • Music uses this protocol

Internet (Introduction to Internet - S. James)
  • Who runs it?
  • Backbone funded by NSF
  • Internal Advisory Board - helps to set standards
  • Growing exponentially
  • 1980s - 213 hosts on internet
  • 1986 - 2,300 hosts
  • now millions
  • 1991 - business use gt academic use

Internet (Introduction to Internet - S. James)
  • Computers available in late 1950s
  • Immediate need to communicate with one another
  • ARPA Net formed (Advanced Research Projects
    Agency) in 1969
  • developed Transmission Control Protocol/Internet
    Protocol (TCP/IP)

Internet (Introduction to Internet - S. James)
  • Etiquette - prescribed forms and practices of
    correct behavior
  • Netiquette - rules for the internet
  • avoid flame wars
  • update address
  • dont use all caps
  • reply to questions

Internet (Introduction to Internet - S. James)
  • Advantages
  • Access information anytime
  • Blind to race, religion, sex, creed
  • Direct cost minimal, generally your time
  • Communicating by writing - tends to be more
  • Send many messages of nearly any length
    relatively quickly to many people

Internet (Introduction to Internet - S. James)
  • Disadvantages
  • Credibility of information
  • Internet gets crowded - connection time slow
  • Addictive
  • People may write what they wouldnt say
  • Mistakes get amplified
  • Junk mail

Internet (Introduction to Internet - S. James)
  • Hosts
  • computers on internet that provide some service
    (such as e-mail, file transfer, web site, etc.)
  • Hostname
  • all computers that are registered on the internet
    have a unique host name and domain name
  • teal - computer name
  • - domain name
  • edu - extension

Internet (Introduction to Internet - S. James)
  • IP Address
  • all computers on internet must have an Internet
    Protocol IP address
  • handed out by Internet Network Information Center
  • Unix
  • popular operating system for computers
  • runs on PCs and mainframes
  • original TCP/IP computers ran Unix

Internet (Introduction to Internet - S. James)
  • Internet 2
  • universities research organizations joining
    together to create another internet exclusivley
    for their use
  • Internet Service Providers (ISP)
  • computer companies that have the necessary
    hardware/software to allow your computer to dial
    into the ISP and in turn connect you to the
  • some use cable for higher speeds rather than
    phone lines or use satellites

Web (Introduction to Internet - S. James)
  • Origin goes back to need to communicate
  • Hypertext Markup Language (HTML)
  • text stored in electronic form with
    cross-reference links between pages (example -
    our syllabus)
  • In 1993 almost 100 computers were equipped to
    serve up HTML pages - those linked pages were
    called the World Wide Web (WWW).
  • Means for referencing text on the Internet
  • Web Browsers
  • view graphic images were developed like Netscape

Data Networking Laboratory (Room 228, ST 2)
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