WHAT IS DATA COMMUNICATIONS ?

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WHAT IS DATA COMMUNICATIONS ?
Transmission of data and information between two
or more computers
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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

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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
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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

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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).

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DATA TRANSFER
TWO methods. 1. Asynchronous transmission 2.
Synchronous transmission
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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.

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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
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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

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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

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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.
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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
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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.

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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.

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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.

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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

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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.

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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

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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

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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.
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Network Communications Technologies

• Ethernet
• Token Ring
• TCP/IP
• 802.11
• Bluetooth
• IrDA
• WAP
• Intranet
• Extranet

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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CONNECTING NETWORKS
A hub is a central point that connects several
devices in a network together
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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.
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Network Architecture

• Client-Server
• Peer-to-Peer
• Internet Peer-to-Peer
• Wireless Network

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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.
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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.
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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.

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Wireless Network Architecture
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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

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Communications Channel

• Basic Concepts
• Bandwidth
• Latency
• Baseband
• Broadband
• Transmission Media

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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.

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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.

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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

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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.

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Exercise and Lab

• Finish the CHOICE of Revision1Revison4
• Finish the Calculation questions of
  Revision1Revison4
• Finish the lab work of Revision1Revison4