Data Communications and Networking: Basic Definitions.

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Data Communications and Networking Basic
Definitions.

• Data Communication is the exchange of data (in
  the form of 0s and 1s) between two devices via
  some form of transmission medium (such a cable)
• Data Communication Local or Remote
• A data communication is considered local if the
  communicating devices are in the same building or
  in similarly restricted geographical area.

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• A data communication is considered remote if the
  devices are farther apart.
• A communication system is a set of devices
  (hardware and software) whose purpose is sharing
  data.
• The fundamental characteristics of a
  communication system are
• Delivery The system must deliver data to the
  correct destination. Data must be received by
  the intended device or user and only by that
  device or user.

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• Accuracy The system must deliver data
  accurately. Data that have been altered in
  transmission and left uncorrected are unusable.
• Timeliness The system must deliver data in a
  timely manner. Data delivered late are useless.
• In the case of video, audio, voice data, timely
  delivery means delivering data as they are
  produced, in the same order that they are
  produced, and without significant delay. This
  kind of delivery is called real-time
  transmission.
• The following figure shows a basic model of a
  communication system

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Data communication system components
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• Components of a Communication System
• Message The message is the information (or data)
  to be transmitted. For example, text, numbers,
  pictures, sound, video, or any combination of
  these.
• Sender The sender is the device that sends the
  data message.It can be a computer, telephone,
  video camera, and so on.
• Receiver The receiver is the device that
  receives the message.
• Medium (Channel) The transmission medium is the
  physical path by which a message travels from the
  sender to receiver. For example twisted pair
  wire, coaxial cable, fiber-optic cable, radio
  waves (terrestrial or satellite microwaves).

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• The medium defines the speed (the data rate) at
  which data can travel through a connection. For
  example 100 megabits per second.
• Protocol A protocol is a set of rules that
  govern data communication. It represents an
  agreement between the communicating devices.
• Network A network is a set of devices (often
  referred to as nodes) connected by links.
• A node can be a computer, printer, or any other
  device capable of sending and/or receiving data
  generated by other nodes on the network.

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Line Configuration

• Line configuration refers to the way two or more
  communication devices attach to a link.
• A link is the physical communication pathway that
  transfers data from one device to another.
• There are two line configurations
• Point-to-Point
• Multipoint
• A point-to-point line configuration provides a
  dedicated link between two devices. The entire
  capacity of the channel is reserved for
  transmission between those two devices.

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Point-point connection
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• A multipoint line configuration is one in which
  more than two specific devices share a single
  link. In a multipoint environment, the capacity
  of the channel is shared, either spatially or
  temporally.
• If several devices can use the link
  simultaneously, it is a spatially shared line
  configuration.
• If users must take turns, it is a time-shared
  line configuration.
• Topology
• The topology of a network is the geometric
  representation of the relationship of all links
  and linking devices to one other.
• Two or more devices connect to a link two or
  more links form a topology.

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Multipoint line configuration
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• There are five basic topologies
• Mesh
• Star
• Tree
• Bus
• Ring
• Note A consideration when choosing a topology is
  the relative status of the devices to be linked.
  Two relations are possible peer-to-peer, where
  the devices share the link equally, and
  primary-secondary, where one device controls
  traffic and the others must transmit through it.

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Mesh Topology In a mesh topology, every device
has a dedicated point-to-point link to every
other device. The term dedicated means that the
link carries traffic only between the two devices
it connects.
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Mesh topology
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• Advantages
• The use of a dedicated links guarantees that each
  connection can carry its own load, thus
  eliminating the traffic problems that can occur
  when links must be shared by multiple devices.
• A mesh topology is robust. If one link becomes
  unusable, it does not incapacitate the entire
  system.
• Privacy. When every message sent travels along a
  dedicated link, only the intended recipient sees
  it. Physical boundaries prevent other users from
  gaining access to messages.
• Point-to Point links make fault identification
  and fault isolation easy.

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• Disadvantages
• A big amount of cabling and a big number of I/O
  ports required, i.e, the hardware required can
  be very expensive.
• Because every device must be connected to every
  other device, installation and reconfiguration
  are difficult.
• For these reasons a mesh topology is usually
  implemented in a limited fashion.
• For example, as a backbone connecting the main
  computers to a hybrid network that can include
  several other topologies.

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• Star Topology
• In a star topology, each device has a dedicated
  point-to-point link only to a central controller,
  usually called a hub.
• A star topology does not allow direct traffic
  between devices. If one device wants to send data
  to another, it sends the data to the controller,
  which then relays the data to the other
  connected device.
• Advantages
• It is easy to install and reconfigure
• The star topology is robust. If one link fails,
  only that link is affected. This factor also
  lends itself to easy fault identification and
  fault isolation.

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Star topology
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• Disadvantages
• A big amount of cabling and a big number of I/O
  ports required, i.e, the hardware required can
  be very expensive.
• Note Star topology requires far less cable than
  Mesh topology.
• Tree Topology
• A tree topology is a variation of a star. As in
  the star, nodes in a tree topology are linked to
  a central hub that controls the traffic to the
  network.
• The majority of devices connect to a secondary
  hub that in turn is connected to a central hub.

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• The central hub in a tree is an active hub. An
  active hub contains a repeater, which is a
  hardware device that regenerates the received bit
  patterns before sending out.
• Repeating improves the transmission quality, and
  increases distance that a signal can travel.

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• The advantages and disadvantages of a tree
  topology are generally the same as those of a
  star.
• A good example of tree topology can be seen in
  cable TV technology where the main cable from the
  main office is divided into main branches and
  each branch is divided into smaller branches and
  so on. The hubs are used when a cable is divided.
• Bus Topology
• In a bus topology one long cable acts as a
  backbone to link all the devices in the network.
• Nodes are connected to the bus cable by drop
  lines and taps.
• A drop line is a connection running between the
  device and the main cable.

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• A tap is a connector that either splices into the
  main cable or punctures the sheathing of a cable
  to create a contact with the metallic core.
• When a signal travels along the backbone, some of
  its energy is transformed into heat.Therefore, it
  becomes weaker and weaker the farther it has to
  travel. For this reason there is a limit on the
  number of taps a bus can support and on the
  distance between those taps.
• Advantages
• Easy to install
• Bus topology uses less cabling than mesh, star,
  or tree topologies.

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Bus topology
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• Disadvantages
• Difficult reconfiguration and fault isolation.
• A bus is usually designed to be optimally
  efficient at installation. It can therefore be
  difficult to add a new devices.
• A fault or break in the bus cable stops all
  transmission, even between devices on the same
  side of the problem. The damaged area reflects
  signals back in the direction of origin, creating
  noise in both directions.
• Ring Topology
• In a ring topology, each device has a dedicated
  point-to-point line configuration only with the
  two devices on either side of it.

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• Advantages
• Easy to install and reconfigure. To add or delete
  a device require only two connections.
• Easy fault isolation
• Disadvantages
• A break in the ring (such as a disabled station)
  can disable the entire network.

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• Hybrid Topologies
• Often a network combines several topologies as
  sub networks linked together in a larger
  topology.

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Transmission Mode

• The term transmission mode is used to define the
  direction of signal flow between two linked
  devices.
• There three types of transmission modes simplex,
  half-duplex and full-duplex
• SimplexIn simplex mode, the communication is
  unidirectional, as one-way street.

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• Examples keyboards and traditional monitors are
  both examples of simplex devices.
• Half-Duplex In half-duplex mode, each station
  can both transmit and receive, but not at the
  same time. When one device is sending, the other
  can only receive, and vice versa.
• Examples Walkie-talkies and CB (citizens band)
  radios are both half-duplex systems.

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• Full-Duplex In a full-duplex mode (also called
  duplex), both stations can transmit and receive
  simultaneously.
• Examples the telephone network

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Categories of Networks
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LANs

• A local area network (LAN) is usually privately
  owned and links the devices in a single office,
  building or campus. Currently, LAN size is
  limited to a few kilometers.
• LANs are designed to allow resources be shared
  between personal computers or workstations. The
  resources to be shared can include hardware (e.g.
  a printer), software (e.g. an application
  program), or data.

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• In general, LANs use only one type of
  transmission medium.
• The most common LAN topologies are bus, ring and
  star.
• LANs have data rates in the 4 to 16Mbs range.
  Today, however, speeds are increasing and can
  reach 100Mbps with gigabit systems in
  development.
• Metropolitan Area Networks
• A metropolitan area network (MAN) is designed to
  extend over an entire city.
• A MAN may be wholly owned and operated by a
  private company, or it may be a service provided
  by a public company, such as a local telephone
  company.

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MAN
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Wide Area Network

• A Wide Area Network (WAN) provides long-distance
  transmission of data, voice, image, and video
  information over large geographical areas that
  may comprise a country, a continent, or even the
  whole world.