Catholic University College of Ghana Fiapre-Sunyani

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Catholic University College of GhanaFiapre-Sunyan
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Data Communications and Networks Internet

• INFORMATION TECHNOLOGY II

Audrey Asante, Faculty of ICST
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• Computer communication is the transmission of
  data and information over a communications
  channel between two computers, which can be
  several different things.
• Communications between computers can be as simple
  as cabling two computers to the same printer. It
  can be as complex as a computer at NASA sending
  messages through an elaborate system of relays
  and satellites to tell a computer on Mars how to
  drive around without hitting the rocks.

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• Depending on the context, for computer
  communications you might use the terms
• Data Communications for transmission of data and
  information over a communications channel  
  Telecommunications for any long-distance
  communications, especially television  
  Teleprocessing for accessing computer files
  located elsewhere

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Communications Channel

• A communications channel, also called a
  communications line or link, is the path that the
  data follows as it is transmitted from one
  computer to another.

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COMPUTER NETWORK

• A network is a system of interconnected
  computers, telephones, other communications
  devices that can communicate with one another and
  share applications and data

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NETWORK MODEL

• OSI (Open Systems Interconnect ) Reference Model
• TCP/IP Reference Model

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OSI MODEL
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LAYERS FUNCTIONS

• Application (Layer 7)
• This layer supports application and end-user
  processes.
• Communication partners are identified, quality of
  service is identified, user authentication and
  privacy are considered, and any constraints on
  data syntax are identified.
• Everything at this layer is application-specific.
  
• This layer provides application services for file
  transfers, e-mail, and other network software
  services.

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LAYERS FUNCTIONS

• Presentation (Layer 6)
• This layer provides independence from
  differences in data representation (e.g.,
  encryption) by translating from application to
  network format, and vice versa.
• The presentation layer works to transform data
  into the form that the application layer can
  accept.
• This layer formats and encrypts data to be sent
  across a network, providing freedom from
  compatibility problems. It is sometimes called
  the syntax layer.

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LAYERS FUNCTIONS

• Session (Layer 5)
• This layer establishes, manages and terminates
  connections between applications.
• The session layer sets up, coordinates, and
  terminates conversations, exchanges, and
  dialogues between the applications at each end.
• It deals with session and connection coordination.

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LAYERS FUNCTIONS

• Transport (Layer 4)
• This layer provides transparent transfer of data
  between end systems, or hosts
• The layer is responsible for end-to-end error
  recovery and flow control.
• It ensures complete data transfer.

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LAYERS FUNCTIONS

• Network (Layer 3)
• The layer provides switching and routing
  technologies
• Creates logical paths, known as virtual circuits,
  for transmitting data from node to node
• Provides routing and forwarding functions
• Transforms the Logical Names into Physical
  Addresses
• Provides internetworking, error handling,
  congestion control and packet sequencing.

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LAYERS FUNCTIONS

• Physical (Layer 1)
• This layer conveys the bit stream - electrical
  impulse, light or radio signal -- through the
  network at the electrical and mechanical level
• It defines the electrical characteristics of the
  signals
• It provides the hardware means of sending and
  receiving data on a carrier
• It defines Network Interface Cards (NIC), cables,
  and connectors

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TYPES OF NETWORKS

• Local network
• It is a privately owned communications network
  that serves users within a confined geographical
  area. The range is usually within a mile-an
  office, a building, a campus. There are two
  types-private branch exchanges (PBXs) and Local
  area networks
• Metropolitan area network
• It is a communications network covering a
  geographic area the size of a city or suburb. The
  purpose is often to bypass local telephone
  companies when accessing long-distance services.

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• Wide area network
• It is a communications network that covers a wide
  geograhical area, such as a state or a country.
  The internet links together hundreds of computer
  WANs. Most telephone systems are WANs.
• Global area network
• It is a communications network that covers the
  world. An examples is the internet.

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Advantages

• Sharing of peripheral devices
• Sharing of programs and data
• Better communications
• Security of information
• Access to databases

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DISADVANTAGES

• More complexity adds new problems to handle.  
  Less customization is possible for shared
  programs and folders. Everyone will have to
  follow the same conventions for storing and
  naming files so others can find the right files.
    Sharing is hard for some people

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LAN

• They are local networks consisting of a
  communications link, network operating system,
  microcomputers or workstations, servers, and
  other shared hardware.

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TYPES OF LAN

• Client/Server LAN
• Peer-to-peer they dont rely on a server.

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TOPOLOGY OF LANs

• Topology is the logical layout or shape of a
  network. The five basic topologies are star,
  ring, bus, hybrid, FDDI, Mesh

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STAR TOPOLOGY

• All microcomputers and other communication
  devices are connected to a central server. If the
  server goes down, the entire network will go off
  because it handles the flow of information. The
  maximum number of network devices is 1,024 . This
  configuration is good for businesses that have
  large amounts of rapidly changing data, like
  banks and airline reservation . Standard
  twisted-pair Ethernet uses a star topology

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ADVANTAGES OF STAR TOPOLOGY

• The server prevents collisions between messages.
• If a connection is broken between any
  communications device and the server, the rest of
  the devices on the network will continue
  operating.
• It's easy to add and remove nodes.

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DISADVATANGES OF STAR TOPOLOGY

• They require more cabling than other topologies

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RING TOPOLOGY

• All microcomputers and other communication
  devices are connected in a continuous loop. Each
  device is connected directly to two other
  devices, one on either side of it. There is no
  central server. Electronic messages are passed
  around the ring until they reach the right
  destination. Messages travel around the ring,
  with each node reading those messages addressed
  to it.

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Ring Topology

• The most common type of cabling used for token
  ring networks is twisted pair. Transmission rates
  are at either 4 or 16 megabits per second

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ADVANTAGES OF THE RING TOPOLOGY

• Messages flow in only one direction.
• There is no collisions
• Requires less cabling.
• They offer high bandwidth and can span large
  distances

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DISADVANTAGES OF RING TOPOLOGY

• If the connection is broken, the entire network
  stops working.
• Ring topologies are relatively expensive and
  difficult to install
• Moves, adds and changes of devices can affect the
  network
• Much slower than an Ethernet network under normal
  load

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BUS TOPOLOGY

• All communications devices are connected to a
  common channel called the bus or backbone. There
  is no central server. Each communications device
  transmits electronic messages to other devices.
  If some of those messages collide, the device
  waits and tries to retransmit. Ethernet 10Base-2
  and 10Base-5 networks are bus networks.

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Disadvantages

• If a connection in the bus is broken, the entire
  network may stop working.
• Extra circuitry and software are needed to avoid
  collisions between data
• Can't connect a large number of computers this
  way. It's physically difficult to run the one
  communications line over a whole building, for
  example.

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ADVANTAGES OF BUS NETWORK

• It may be organized as a client/server or
  peer-to-peer network
• Any one computer or device being down does not
  affect the others.
• Bus networks are relatively inexpensive and easy
  to install for small networks.

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MIXED/HYBRID TOPOLOGIES

• The purpose of such topologies is to avoid some
  of the inconveniencies of the simple topologies
  and to use more effectively their advantages.
• In such topologies, there at least one station,
  which belongs to the both topologies. Its role is
  to transform the signals and the protocols of the
  both networks.

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RING BUS TOPOLOGY

• An interesting example is the mixed topology,
  based on token ring (optical cable) and star
  topology is very often used.
• The optical ring can cover more long distances
  (between different buildings), and within each
  building the topology can be either star or bus.

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RING BUS TOPOLOGY

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FDDI

• Fiber distributed data interface uses fiber-optic
  cable with an adaptation of ring topology using
  not one but two token rings. It is costly and
  fragility because fiber-optic cables are fragile.
  It overcomes the vulnerability by sending data on
  a clockwise and a counterclockwise ring

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• in the event of a break data is wrapped back onto
  the complementary ring before it reaches the end
  of the cable, maintaining a path to every node
  along the resulting "C-Ring
• In addition to covering large geographical areas,
  FDDI local area networks can support thousands of
  users.

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ADVANTAGES OF FDDI

• High speed
• Because of the adaptation of two token rings, if
  one should fail, the network can continue
  operating with the second ring.

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MESH TOPOLOGY

• This is a network topology in which devices are
  connected with many redundant interconnections
  between network nodes.
• There are two types of mesh topologies
• full mesh
• partial mesh.

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FULL MESH TOPOLOGY

• Every node has a circuit connecting it to every
  other node in a network.
• Very expensive to implement but yields the
  greatest amount of redundancy
• If one of those nodes fails, network traffic can
  be directed to any of the other nodes.
• Full mesh is usually reserved for backbone
  networks

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PARTIAL MESH TOPOLOGY

• Less expensive to implement and yields less
  redundancy than full mesh topology.
• With partial mesh, some nodes are organized in a
  full mesh scheme but others are only connected to
  one or two in the network.
• Partial mesh topology is commonly found in
  peripheral networks connected to a full meshed
  backbone.

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COMPONENTS OF LAN

• Connection or cabling system Cabling or
  connection system is either wired or wireless.
  Wired connections may be done by twisted-pair,
  coaxial or fiber-optic cables. Wireless
  connections may be infrared or radio-wave
  transmission. Wireless are essential if computers
  are portable.

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• Transmission media just means the physical
  materials that are used to transmit data between
  computers.

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Twisted wire(phone line)

• AdvantageEasy to string Cheap DisadvantageSubjec
  t to interference static and garble.
• attenuation

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Fiber optic line (glass fibers)

• Advantage Smaller Lighter Faster (speed of
  light!) No interference
• Disadvantage Expensive Harder to install and
  modify

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Wireless(infrared, light, radio)

• Advantage Flexible Portable
• DisadvantageSlower data transfer than hard-wired
  methodsSubject to interference

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Microwave

• AdvantageSpeed of light Uses a few sites
• Disadvantage Line-of-sight only

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Satellite

• Advantage Always in sight
• Disadvantage Expensive uplink and downlink
  facilities

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Signals

• Two types of signals are used for data
  transmission           Digital and Analog.  

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• A digital signal is a stream of 0's and 1's. So
  this type is particularly appropriate for
  computers to use. An analog signal uses
  variations (modulations) in a signal to convey
  information. It is particularly useful for wave
  data like sound waves. Analog signals are what
  your normal phone line and sound speakers use.

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Coaxial cable(round insulated wire)

• AdvantageNot susceptible to interference
  Transmits faster
• DisadvantageHeavy bulky Needs booster over
  distance
• Cross talk

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COMPONENTS OF LAN cotn

• Microcomputers with network interface cards. For
  communication to go on between two or more
  computers, they should have network interface
  cards
• Network Operating System NOS manages the
  activities of the network. Example Windows Server
  2003
• Other shared devices printers, fax, scanners,
  peripherals

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COMPONENTS OF LAN cotn

• Bridges, routers, and gateways LANs can be stand
  alone but to connect to other networks you can
  make use of other types of hardware and software
  devices as an interface to make these
  connections.
• A bridge is a hardware and software combination
  used to connect the same types of networks
• A router is a special computer that directs
  communicating messages when several networks are
  connected together.
• A gateway is an interface that enables dissimilar
  networks to communicate, such as a LAN with a WAN
  or two LANs based on different topologies or
  network operating systems.

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NETWORK SERVERS

• File Server it is a computer that stores the
  programs and data files shared by users on a LAN.
• It provides global disk space for users which
  have certain access and directories
• It organize access rights and allocate resources
  to the users

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Database Server

• It is a computer in a LAN that stores data.
  Unlike a file server, it does not store programs.

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PRINT SERVER

• It is a computer in a LAN that controls one or
  more printers. It stores the print-image output
  to the printer or printers one document at a
  time.
• Printer is shared on the network
• They are for cost efficiency since not every
  station needs its own printer

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COMMUNICATION SERVER

• It handles data exchange with the outside world
  as well as internal data exchange
• They usually provide
• Sending and reception of email
• Sending and reception of fax messages
• Connection to the internet
• Connection to other networks

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FAX AND MAIL SERVERS

• Fax servers are dedicated to managing fax
  transmissions
• Mail servers manage email

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BACK UP SERVER

• It is important to backup workstation or server
  data.
• They are mainly performed in the nights

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INTERNET

• What is Internet
• Connecting to the Internet
• Internet Addresses
• Features of the Internet

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INTERNET

• It is the global interconnection of networks.
• TCP/IP is the standardized set of computer
  guidelines (protocols) that allow different
  computers on different networks to communicate
  with each other efficiently.

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Connecting to the Internet

• Through school or work
• Online information services
• Internet service providers

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INTERNET ADDRESS

• dasoul_at_cug.edu.gh
• Dasouluserid
• _at_separator
• Cug.edu.gh domain

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TOP LEVEL DOMAINS

• .com commercial organizations
• .edu educational and research organizations
• .firm
• .gov
• .info
• .org
• .int
• .mil
• .net

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SERVICES OF THE INTERNET

• Email
• Telnet
• File Transfer
• Gopher
• Chat
• World Wide Web (WWW)