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							 Chapter 2: Basic                       Concepts
•   Line Configuration
•   Topology
•   Transmission Mode
•   Categories of Networks
•   Internetworks



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                 Line Configuration
Line configuration defines the attachment of
communication devices to a link

                  Line Configuration



Point-to-point                                         Multi-point
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               Point-to-Point Line
                 Configuration
• Provides a dedicated link between two
  devices
• The entire capacity of the channel is
  reserved for transmission




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               Point-to-Point Line
                 Configuration




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               Point-to-Point Line
                 Configuration




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        Multipoint or Multi-Drop
          Line Configuration
• More than two devices share a single link
• The capacity of the channel is shared either
  spatially or temporally
     – Spatial sharing: devices can use the link
       simultaneously
     – Temporal (time) sharing: devices take turns



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 Multipoint Line Configuration




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               Network Topology
• Network Topology: defines the physical or
  logical arrangement of links in a network
• The relative status of devices to be linked
  determines a topology. Two relationships
  are available:
     – Peer-to-Peer transmission: devices share the link
       equally
     – Primary-Secondary: one device controls traffic and
       the others must transmit through it

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                             Topology




Mesh            Star             Tree                    Bus   Ring




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               Mesh Topology
• Every device has a dedicated point-to-Point
  link to every other device.
• Fully connected mesh has n(n-1)/2 physical
  channels to link n devices.
• Every device must have n-1 I/O ports.


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               Mesh Topology




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                   Advantages
•   Each connection can carry its data load
•   Robust
•   Privacy or Security
•   Simple fault identification and isolation




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                   Disadvantages
•    Huge amount of cabling and I/O ports
•    Difficult to install and reconfigure
•    Space problem
•    The hardware required for connectors is
     expensive



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               Star Topology
• Each device has a dedicated point-to-point
  link only to a central controller (Hub)




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               Advantages
• Each device needs only one link and one
  I/O port
• Easy to install and reconfigure
• Small amount of cabling
• Robust
• Easy fault identification and isolation

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               Disadvantages
• The hub is the bottleneck
• The hub is a single-point-of-failure




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               Tree Topology




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                      Hubs
• Active hub: contains a device that
  regenerates the received bit patterns before
  sending them out (Repeater)
• Passive hub: Provides a simple physical
  connection between the attached devices



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               Hubs (Cont’d)
• Repeating strengthens transmission and
  increases the distance a signal can travel
  between sender and receiver

• The central hub in the tree is an active hub



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                  Advantages
• Tree Topology has the same advantages as
  those of a star.
• Moreover,
     – More devices can be attached to a single central
       hub using secondary hubs
     – It increases the distance a signal can travel
       between devices
     – It provides a mechanism to prioritize and
       isolate communications
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               Bus Topology
• All devices are attached to one long cable
  (backbone)
• Nodes are connected to the bus by drop
  lines and taps
• Drop line: a cable running from the device
  to the bus


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               Bus Topology (Cont’d)
• Tap: a connector that either splices into the
  cable or punctures the sheathing of a cable
  to create a contact with the metallic core

• There is a limit on the number of taps a bus
  can support and on the distance between
  those taps

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               Bus Topology




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               Advantages
• Ease of installation
• Less cabling than mesh, star, or tree




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               Disadvantages
• Difficult reconfiguration and fault isolation
• Signal reflection at the taps can cause
  degradation
• The bus is a single point-of-failure




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               Ring Topology
• Each device has a dedicated point-to-point
  line configuration only with the two devices
  on either side of it

• Unidirectional traffic

• Each device incorporates a repeater
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               Ring Topology (Cont’d)




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               Advantages
• Easy to install and reconfigure
• Simple fault isolation




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               Disadvantages
• Unidirectional traffic
• The ring is a single point-of-failure




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               Hybrid Topology




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