Network Design Essentials

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Network Design Essentials
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Contents

• 1. Examining the Basics of a Network Layout
• 2. Understanding Standard Topologies
• 3. Examining Variations of Physical Topologies
• 4. Hubs and Switches
• 5. Constructing a Network Layout

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1. Examining the Basics of a Network Layout

• To implement a network, you must first decide how
  to best situate the components in a topology
• Topology refers to the physical layout of its
  computers, cables, and other resources, and also
  to how those components communicate with each
  other
• The arrangement of cabling is the physical
  topology
• The path that data travels between computers on a
  network is the logical topology
• Topology has a significant effect on the
  networks performance and growth, and equipment
  decisions

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2. Understanding Standard Topologies

• 2.1. Physical Bus Topology
• 2.2. Logical Bus Topology
• 2.3. Physical Ring Topology
• 2.4. Logical Ring Topology
• 2.5. Physical Star Topology
• 2.6. Wireless Topologies

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• Networks are based on three physical topologies
• A bus consists of a series of computers connected
  along a single cable segment
• Computers connected via a central concentration
  point (hub) are arranged in a star topology
• Computers connected to form a loop create a ring
• Physical topologies describe cable arrangement
• How the data travels along those cables might
  represent a different logical topology
• The logical topologies that dominate LANs include
  bus, ring, and switching, all of which are
  usually implemented as a physical star

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2.1. Physical Bus Topology
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2.1.1. Signal Propagation

• Computers communicate by sending information
  across the media as a series of signals
• In a typical (copper wire) physical bus, those
  signals are sent as electrical pulses that travel
  along the length of the cable in all directions
• The signals continue to travel until they weaken
  enough so as not to be detectable or until they
  encounter a device that absorbs them
• This traveling across the medium is called signal
  propagation
• At the end of a cable, the signal bounces back

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2.1.2. Signal Bounce
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2.1.3. Cable Termination
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2.1.4. Cable Failure
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2.2. Logical Bus Topology

• Logical topologies describe the path that data
  travels from computer to computer
• A physical bus topology is almost always
  implemented as a logical bus as well
• Technology has moved past the physical bus, but a
  logical bus topology is still in use on some
  physical topologies, in particular a star
• All computers communicate in the same way
• They address data to one or more computers and
  then transmit that data across the cable in the
  form of electronic signals

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Sending the Signal

• When a computer has data to send, it addresses
  that data, breaks it into manageable chunks, and
  sends it across the network as electronic signals
• All computers on a logical bus receive them
• Only the destination accepts the data
• All users must share the available amount of
  transmission time
• Thus, network performance is reduced
• A bus topology is a passive topology
• In an active topology network, computers and
  other devices regenerate signals and are
  responsible for moving data through the network

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2.3. Physical Ring Topology
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2.4. Logical Ring Topology

• Data in a logical ring topology travels from one
  device, or node, on the network to the next
  device until the data reaches its destination
• Token passing is one method for sending data
  around a ring
• Modern logical ring topologies use smart hubs
  that recognize a computers failure and remove
  the computer from the ring automatically
• An advantage of the ring topology lies in its
  capability to share network resources fairly

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2.5. Physical Star Topology
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2.5.1. A Logical Bus Implemented as a Physical
Star
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2.5.2. A Logical Ring Implemented as a Physical
Star
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2.5.3. Switching Implemented as a Physical Star

• Switching is neither a bus nor a ring logically,
  but is always implemented as a physical star
• A switch takes a signal coming from a device
  connected and builds a circuit on the fly to
  forward the signal to the intended destination
  computer
• Superior to other logical topologies because,
  unlike bus and ring, multiple computers can
  communicate simultaneously without affecting each
  other
• Dominant method used in almost every LAN design

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2.6. Wireless Topologies

• Wireless networking has a logical and physical
  topology
• Ad hoc topology two computers can communicate
  directly with one another sometimes called a
  peer-to-peer topology
• Infrastructure mode Use a central device, called
  an access point (AP), to control communications
• Star physical topology because all the signals
  travel through one central device
• Logical bus topology

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3. Examining Variations of Physical Topologies

• 3.1. Extended Star Topology
• 3.2. Mesh Topology
• 3.3. Combination Star Bus Topology

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• The major physical topologies have three typical
  variations or combinations
• Extended star
• Mesh
• Combination star and bus
• These combinations can be used to get the most
  from any network

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3.1. Extended Star Topology
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3.2. Mesh Topology
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3.3. Combination Star Bus Topology
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4. Hubs and Switches

• 4.1. Hubs
• 4.2. Switches

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• Both hubs and switches can act as the center of a
  star topology
• Basic operation was discussed briefly this
  section expands on them

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4.1. Hubs

• In everyday use, a hub is the center of
  activity
• This definition is appropriate in network usage
  also
• In network usage, there are a number of
  variations on this central theme
• Active hub
• Passive hub
• Repeating hub (just a type of active hub)
• Switching hub

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4.1.1. Active Hubs

• Most common type of hub today
• Regenerate, or repeat, the signals
• Require electrical power to run
• Generally, have many portseight or more
• Also called multiport repeaters or repeating hubs
• Takes a signal coming in on one port
• Cleans the signal (e.g., by filtering out noise)
• Strengthens the signal
• Sends the regenerated signal out to all other
  ports
• Drawback require sharing the cable bandwidth
  among all connected stations

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4.1.2. Passive Hubs
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4.2. Switches

• Central connecting point in a star topology
  network
• Does more than simply regenerate signals
• Looks just like a hub, with several ports for
  connecting workstations in a star topology
• Determines to which port the destination device
  is connected and forwards the message to that
  port
• This capability allows a switch to handle several
  conversations at one time, thereby providing the
  full network bandwidth to each device rather than
  requiring bandwidth sharing

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5. Constructing a Network Layout

• 5.1. Selecting a Topology
• 5.2. Creating the Layout

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• The first step in any network design is to
  evaluate the underlying requirements
• First determine how the network will be used,
  which often decides the topology you use
• Decide the types of devices for interconnecting
  computers and sites
• Finally, the type and usage level of network
  resources dictates how many servers you need and
  where to place servers

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5.1. Selecting a Topology

• Most new network designs come down to only one
  choice How fast should the network be?
• The physical topology will certainly be a star,
  and the logical topology is almost always
  switching
• Ethernet switches are typically used on a LAN,
  but you might consider other logical topologies
  for other reasons
• Use of legacy equipment
• Network size
• Cost restrictions
• Difficulty to run cables

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5.2. Creating the Layout

• Network must be documented
• Useful questions before drawing the diagram
• How many client computers will be attached?
• How many servers will be attached?
• Will there be a connection to the Internet?
• How will the buildings physical architecture
  influence decisions, such as whether to use a
  wired or wireless topology, or both?
• Which topology or topologies will you use?
• Network diagram must be kept up to date

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Summary

• Basic physical topologies bus, star, or ring
• Physical bus easy to install but outdated
• The logical bus topology is still used, but is
  almost always implemented as a physical star
• Physical ring connects devices in such a way
  that the cabling starts and ends with the same
  computer
• Rarely used (except in FDDI)
• Logical ring topology typically uses token
  passing to send data around ring normally
  implemented as a star
• Physical star centralized management and higher
  degree of fault tolerance
• Topology of choice in todays networks

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• For wireless networks ad hoc or infrastructure
  mode
• Variations on major topologies
• Extended star (most widely used)
• Mesh (most fault tolerant)
• Combination star and bus
• Hub central point of concentration for a star
  network
• Can be active (if it regenerates the signals) or
  passive
• Switch provides better performance than a hub
• Device of choice in corporate star topology
  networks
• Network layout should be consistent and
  maintained accurately as the network changes

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• Chapter Summary
• Networks build upon one of three basic topologies
• Bus topology is easy to install but is
  outdatedtopology not used for new installations
• Star topology offers centralized managementand
  higher degree of fault tolerance since
  singlecable or computer failure does not affect
  rest ofnetwork
• Star topology is topology choice for
  todaysnetworks

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• Ring topology offers computers equal time
  onnetwork, but network performance degradeswhen
  more computers are added
• Hub, a central point of concentration for
  starnetwork, passes electronic signals to
  network
• Active hub regenerates signals
• Passive hub simply passes signals along

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• Switch offers greater bandwidth and
  intelligence,providing significant performance
  advantagesover hubs
• Switches have become device of choice
  incorporate star topology networks
• Variations on major topologies allow
  greaterfault tolerance and flexibility
• Mesh is most fault tolerant of all
  networktopologies, allowing every computer
  tocommunicate with every other computer

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• Star bus or star ring combines centralizedmanagem
  ent of star and best of bus andring topologies
• Network layout should be consistent withexisting
  network and accurately maintainedas network
  changes
• Many third-party tools can assist in designand
  maintenance

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