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WHAT IS DATA COMMUNICATIONS ?

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Title: WHAT IS DATA COMMUNICATIONS ?


1
WHAT IS DATA COMMUNICATIONS ?
Transmission of data and information between two
or more computers
2
EXAMPLES OF HOW COMMUNICATIONS IS USED
  • Electronic mail (e-mail)
  • Voice mail
  • Facsimile (fax)
  • Telecommuting
  • Videoconferencing
  • Electronic meetings
  • Desktop videoconferencing
  • Electronic data interchange (EDI)
  • Reduced paper flow
  • Lower transaction costs
  • Faster transmission of documents
  • Reduced data entry errors
  • Global positioning systems (GPSs)
  • Determine geographic location
  • Tracking and navigation
  • Measuring distances
  • The Internet
  • Global network of computer networks

3
DATA COMMUNICATION COMPONENTS
SENDING UNIT TRANSMISSION RECEIVING
UNIT CHANNEL Computer
Telephone Line Computer Terminal
Radio Waves Terminal
Microwaves
software Twisted Pair software Co-
axial Cable
Fibre-optic Cable Satellite
4
Data Transmission
  • MODEM (modulator-demodulator)
  • Modulation converting from digital to analog
  • Demodulation converting from analog to digital
  • Enables digital microcomputers to communicate
    across analog telephone lines.
  • The speed of modems measured in bps(bits per
    second)
  • 33.6kbps, 56kbps

5
Communication Software
  • Communications software consists of programs
  • help users establish a connection to another
    computer or network
  • manage the transmission of data, instructions,
    and information
  • provide all interface for users to communicate
    with one another.
  • Examples of application software for
    communications
  • e-mail, FTP, Web browser, newsgroup / message
    boards
  • chat rooms, instant messaging
  • video conferencing, and video telephone calls.
  • Features of communication software
  • keep database of telephone numbers
  • automatic redial
  • act as a terminal
  • easy sending/receiving of files
  • data encryption (software at other end must know
    how to decrypt it).

6
DATA TRANSFER
TWO methods. 1. Asynchronous transmission 2.
Synchronous transmission
7
Asynchronous TRANSMISSION
  • usually used to describe communications in which
    data can be transmitted intermittently rather
    than in a steady stream.
  • Also called start-stop transmission
  • data transmission requiring stop and start bits
  • when a byte is sent
  • -gt send a start bit 0
  • followed by 8 data bits
  • -gt then a stop bit 1
  • Most commonly used for the simplest data link,
    i.e. terminals to computers.

8
SYNCHRONOUS TRANSMISSION
  • Occurring at regular intervals
  • no start and stop bits used
  • no pause between sending characters
  • involves sending large blocks of characters
  • each block has special sync characters which are
    sent at the beginning of these blocks

SYN SYN SYN DATA CS CS

SYN Synchronous chars CS Check Sum
9
Synchronous VS Asynchronous transmission
  • Asychronous
  • Start 1 char stop
  • 1 bit 8 bits 1 bit
  • Send 1000 chars
  • Data 1000 x 8 8000 bits
  • Extra 1000 x 2 2000 bits
  • Total 10,000 bits
  • 2) Send 40 chars
  • Data 40 x 8 320 bits
  • Extra 40 x 2 80 bits
  • Total 400 bits
  • Sychronous
  • SYN CI Data CS
  • 3 bytes 2 bytes 5 bytes
  • Send 1000 chars
  • Data 1000 x 8 8000 bits
  • Extra 10 x 8 80 bits
  • Total 8,080 bits
  • 2) Send 40 chars
  • Data 40 x 8 320 bits
  • Extra 10 x 8 80 bits
  • Total 400 bits

10
Data transmission
  • Serial and parallel transmission
  • Serial data transmission
  • Bits flow in a series or continuous stream
  • Data sent over telephone lines
  • Serial port in microcomputers
  • RS-232 connector
  • Asynchronous communication port
  • Parallel data transmission
  • Bits flow through separate lines simultaneously
  • Limited to communications over short distance
  • System unit to printer

11
PROTOCOLS
A protocol is a set of rules for the exchange of
data between computers.. The TCP/IP
(Transmission Control Protocol/Internet Protocol)
permits any computer to communicate with the
Internet network standard, specifically a
protocol, which defines how messages (data) are
routed from one end of a network to the other,
ensuring the data arrives correctly.
12
DIRECTION OF DATA COMMUNICATIONS
SIMPLEX Is one way flow of data. Eg. Television
HALF-DUPLEX Allows for two-way data
transmission, but only one direction at a time.
Eg. CB radio
Walkie-talkie
FULL DUPLEX Is simultaneous, two-way
transmission. Eg. Telephone
13
Networks
  • A network is a group of two or more computer
    systems linked together via communications
    devices
  • transmission media, allowing computers to share
    resources, such as hardware, software, data, and
    information.

14
NETWORKS OTHER ISSUES
What is a Network?
  • A number of computers or terminals connected
    together make up a NETWORK.
  • Can either be a WAN (Wide area network) or a LAN
    (Local area network)
  • WANs involve using the telephone system,
  • LANs - privately owned cabling.
  • Each computer is known as a NODE.
  • Computers and devices that allocate resources for
    a network are called servers.
  • The shape of the network is its TOPOLOGY.

15
Types of Computer Networks
  • Local-Area Networks (LANs) The computers are
    geographically close together (that is, in the
    same building).
  • Wide-Area Networks (WANs) The computers are
    farther apart and are connected by telephone
    lines or radio waves.
  • Campus-Area Networks (CANs) The computers are
    within a limited geographic area, such as a
    campus or military base.
  • Metropolitan-Area Networks (MANs) A data network
    designed for a town or city.
  • Home-Area Networks (HANs) A network contained
    within a user's home that connects a person's
    digital devices.

16
LOCAL AREA NETWORK (LAN)
  • Consists of
  • hardware - PC additional communications board
    in the computer
  • a software package eg Windows XP
  • cabling joining the computers and other
    peripheral devices together
  • LAN
  • Allows sharing of software, hardware (server,
    printers, modems) and information.
  • Server workstation has large hard disk with
    application programs data others can access.
  • LAN's normally within the same building
  • or complex.
  • Cabling is usually twisted pair or co-axial

17
WIDE AREA NETWORK (WAN)
  • Wide Area Network (WAN)
  • Network that covers a large geographic area (such
    as a city, country or the world)
  • Typically, a WAN consists of two or more LANs.
  • Uses communications channel that combines many
    type of media such as telephone lines, cables and
    radio waves.
  • Computers connected to a wide-area network are
    often connected through public networks, such as
    the telephone system. They can also be connected
    through leased lines or satellites.
  • The Internet is the worlds largest WAN.

18
Network Topologies
  • Network topology is the geometric arrangement of
    a computer system. Common topologies include a
    bus, star, and ring
  • Ring Topology
  • Star Topology
  • Bus Topology

19
TYPICAL TOPOLOGIES
  • Star
  • one or more smaller computers connected to a
    central host (mini or mainframe) eg. banks.
  • Nodes can communicate only via central computer.
    If host goes down, network is inoperable.
  • Ring (Token ring)
  • Used in LAN's
  • electronic (data) token sent from workstation to
    workstation
  • incoming data read from token.
  • outgoing data attached to empty token.
  • Communication is usually one-way around the ring
    no collisions
  • One node going down disables the network.
  • Wiring is twisted pair or coaxial cable
  • Need a Token Ring interface card

20
TYPICAL TOPOLOGIES (CONTD)
  • Bus
  • All nodes are connected to a single line via an
    interface box.
  • Even if one of the nodes fails, the network is
    not affected.
  • Nodes can communicate with each other without
    bypassing the server.

In buses and rings all nodes receive every
signal. Each node determines if the message is
addressed to that node either receiving the
message or passing it on.
21
Network Communications Technologies
  • Ethernet
  • Token Ring
  • TCP/IP
  • 802.11
  • Bluetooth
  • IrDA
  • WAP
  • Intranet
  • Extranet

22
Ethernet
  • Ethernet is a local-area network (LAN)
    architecture developed by Xerox Corporation in
    cooperation with DEC and Intel in 1976.
  • Ethernet uses a bus or star topology and supports
    data transfer rates of 10 Mbps.
  • The Ethernet specification served as the basis
    for the IEEE 802.3 standard, which specifies the
    physical and lower software layers.
  • Ethernet uses the CSMA/CD access method to handle
    simultaneous demands. It is one of the most
    widely implemented LAN standards.

23
Token Ring
  • Token ring is a network standard in which
    computers and devices on the network share or
    pass a special signal, called a token, in a
    unidirectional manner and in a preset order.

24
802.11
  • 802.11 and 802.11x refers to a family of
    specifications developed by the IEEE for wireless
    LAN technology.
  • 802.11 specifies an over-the-air interface
    between a wireless client and a base station or
    between two wireless clients.
  • The IEEE accepted the specification in 1997.

25
Bluetooth
  • Bluetooth is an industrial specification for
    wireless personal area networks (PANs).
  • Bluetooth provides a way to connect and exchange
    information between devices such as mobile
    phones, laptops, PCs, printers, digital cameras,
    and video game consoles over a secure, globally
    unlicensed short-range radio frequency.

26
IrDA
  • Short for Infrared Data Association, a group of
    device manufacturers that developed a standard
    for transmitting data via infrared light waves.
  • Increasingly, computers and other devices (such
    as printers) come with IrDA ports. This enables
    you to transfer data from one device to another
    without any cables.
  • For example, if both your laptop computer and
    printer have IrDA ports, you can simply put your
    computer in front of the printer and output a
    document, without needing to connect the two with
    a cable.
  • IrDA ports support roughly the same transmission
    rates as traditional parallel ports.
  • The only restriction on their use is that the two
    devices must be within a few feet of each other
    and there must be a clear line of sight between
    them.

27
WAP
  • WAP is short for the Wireless Application
    Protocol
  • a secure specification that allows users to
    access information instantly via handheld
    wireless devices such as mobile phones, pagers,
    two-way radios, smartphones and communicators.

28
Intranet
  • An intranet is a network based on TCP/IP
    protocols (an internet) belonging to an
    organization.
  • accessible only by the organization's members,
    employees, or others with authorization.
  • An intranet's Web sites look and act just like
    any other Web sites, but the firewall surrounding
    an intranet fends off unauthorized access.

29
Extranet
  • An extranet is a private network that uses
    Internet protocols, network connectivity, and
    possibly the public telecommunication system to
    securely share part of an organization's
    information or operations with suppliers,
    vendors, partners, customers or other businesses.

30
CONNECTING NETWORKS
A hub is a central point that connects several
devices in a network together
31
CONNECTING NETWORKS
Bridge combination of hardware/software to
connect similar networks eg. two PC networks
Gateway hardware/software to connect different
networks eg. A PC and Macintosh network
Routers Connect several networks together and
transmits data to its correct destination.
32
Network Architecture
  • Client-Server
  • Peer-to-Peer
  • Internet Peer-to-Peer
  • Wireless Network

33
NETWORK ARCHITECTURE
The design of computers, devices and media in a
network .
Client-Server One of more computers act as a
server The other computers on the network request
for services from the server.
Peer-to-Peer A simple inexpensive network that
typically connects less than 10 computers.. Each
computer has equal responsibilities and
capabilities.
34
NETWORK ARCHITECTURE (CONTD)
Internet Peer-to-Peer Called P2P, is an Internet
network on which users connect directly to each
others hard disk and exchange files over the
Internet.
35
Wireless Network
  • no physical wired connection between sender and
    receiver
  • the network is connected by radio waves and/or
    microwaves to maintain communications
  • Wireless networking utilizes specific equipment
    such as NICs, APs (Access Point, ?????) and
    routers in place of wires (copper or optical
    fiber) for connectivity.

36
Wireless Network Architecture
37
Communications Channel
  • A communications channel is the transmission
    media on which data, instructions, or information
    travel, in either analog or digital form,
    depending on the type of communications channel.
  • Two examples of communications channels
  • cable television lines
  • telephone lines

38
Communications Channel
  • Basic Concepts
  • Bandwidth
  • Latency
  • Baseband
  • Broadband
  • Transmission Media

39
Basic Concepts
  • Bandwidth
  • the amount of data that can be transmitted in a
    fixed amount of time.
  • For digital devices, the bandwidth is usually
    expressed in bits per second (bps) or bytes per
    second.
  • For analog devices, the bandwidth is expressed in
    cycles per second, or Hertz (Hz).
  • Latency
  • the amount of time it takes a packet to travel
    from source to destination.
  • latency and bandwidth define the speed and
    capacity of a network.

40
Basic Concepts
  • Baseband
  • Baseband media is the type of media that
    transmits only one signal at a time.
  • Broadband
  • Broadband media is a type of data transmission in
    which a single medium (wire) can carry several
    channels at once. Cable TV, for example, uses
    broadband transmission.
  • Transmission Media
  • materials or substances capable of carrying one
    or more signals in a communications channel.
  • Transmission Media are one of two types physical
    or wireless.

41
Transmission Media
  • Physical Transmission Media
  • Twisted-pair Cable
  • Coaxial Cable
  • Fiber-optic Cable
  • Wireless Transmission Media
  • Infrared
  • Broadcast Radio
  • Cellular Radio
  • Cellular Telephone
  • GSM
  • CDMA
  • Microwaves
  • Communications Satellite

42
Data Processing
  • Use of networks allows an organization to process
    its data in a number of ways.
  • Centralized Data Processing
  • Places everything processing, hardware and
    software - in one central location.
  • Very inefficient system.
  • Data has to be physically transported to the
    computer.
  • Processed material has to be delivered to users.
  • Distributed Data Processing
  • Centralized mainframe computer system is linked
    with minis and micros at external locations.
  • Users have control over processing local data.
  • Central mainframe handles applications involving
    whole company.

43
Exercise and Lab
  • Finish the CHOICE of Revision1Revison4
  • Finish the Calculation questions of
    Revision1Revison4
  • Finish the lab work of Revision1Revison4
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