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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


1
ECE 101 An Introduction to Information
TechnologyInformation Transmission
2
Information Path
Source of Information
Information Display
Digital Sensor
Information Receiver and Processor
Information Processor Transmitter
Transmission Medium
3
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

4
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
    transmission

5
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

6
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
    environments
  • Noise power level ?n2
  • Maximum signal power level produced by
    transmitter ?s2

7
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

8
Decoding M-ary Signals(figure 8.2, Kuc)
9
Decoding M-ary Signalsin the presence of
Noise(figure 8.3, Kuc)
10
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

11
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

12
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
    common)
  • parity bit - error detection (even or odd)
  • stop bit(s) - to terminate data
  • all BUT data represent over head to transmit
    serially

13
Asynchronous Data Transmission and Character
Format (figures 8.4 and 8.5, Kuc)
14
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

15
Infrared Remote Control Signal(figure 8.6, Kuc)
16
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

17
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

18
MPEG
  • 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

19
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

20
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).

21
Frequency Shift Keying (figure 8.8, Kuc)
22
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.

23
Modem Two Way Communication (figure 8.9, Kuc)
24
Phase-Shift Keying
  • Changes the phase at a constant frequency and
    amplitude
  • 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

25
Phase-Shift Keying (figure 8.11, Kuc)
26
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

27
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

28
AM and Phase-Shift Keying (figure 8.14, Kuc)
29
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

30
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
    message)
  • Voice channel is assigned to a user when a call
    is made or received

31
Cellular Telephone Frequency Channels (figure
8.16, Kuc)
f
32
Communications(IEEE Web site)
33
Satellites
  • 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

34
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)

35
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

36
Data Networks
  • Local Area Network (LAN)
  • connects computers and peripheral devices
  • can use various means or protocols to transfer
    data
  • Wide Area Networks (WAN)
  • Connects devices wherever long-distance
    communications exist
  • Most common is international network known as the
    Internet

37
Star Architecture for LAN(figure 8.18, Kuc)
38
Star Architecture
  • All nodes connect to hub computer called a server
  • fast since message only goes to server then its
    destination
  • server can store message if it is not delivered
  • all communication stops if the server is down
  • limited number of connections to server

39
Ring Architecture for LAN(figure 8.18, Kuc)
40
Ring Architecture
  • Each node connects to two neighboring nodes and
    the data packets flow around the loop in one
    direction.
  • 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
    operational

41
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

42
Bus Architecture for LAN(figure 8.18, Kuc)
43
A Wide-AreaNetwork(figure8.19, Kuc)
44
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

45
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
    paths
  • Recall that each packet has the destination and a
    tag to help it arrange the packets in order

46
Ethernet
  • 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

47
Ethernet
  • 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)

48
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)

49
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

50
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

51
Transmission Protocols on the Internet
  • Data on the internet are transmitted as data
    packets
  • 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

52
TCP/IP
  • Transmission control protocol/Internet protocol
    (TCP/IP)
  • 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

53
UDP/IP
  • Universal datagram protocol/Internet protocol or
    UDP/IP
  • 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

54
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

55
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)

56
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

57
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
    organized
  • Send many messages of nearly any length
    relatively quickly to many people

58
Internet (Introduction to Internet - S. James)
  • Disadvantages
  • Credibility of information
  • Internet gets crowded - connection time slow
  • Addictive
  • People may write what they wouldnt say
    face-to-face
  • Mistakes get amplified
  • Junk mail

59
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.gmu.edu
  • teal - computer name
  • gmu.edu - domain name
  • edu - extension

60
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

61
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
    internet
  • some use cable for higher speeds rather than
    phone lines or use satellites

62
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
    Navigator

63
Data Networking Laboratory (Room 228, ST 2)
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