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Guide to Networking Essentials


As a junction point and requires no power Switches Switch is a central connecting point in a star topology network Does more than simply regenerate signals Looks ... – PowerPoint PPT presentation

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Title: Guide to Networking Essentials

Guide to Networking Essentials
  • Chapter 2
  • Network Design Essentials

  • Basics of network layout
  • The standard networking topologies
  • The variations on standard networking topologies
  • Hubs and switches
  • Construct a network layout

Basics of Network Layout
  • The basics of good network design
  • Analyzing network requirements
  • Selecting a network topology
  • Selecting the equipments to fit that topology
  • Topology refers to the physical layout of its
    computers, cables, and other resources, and also
    to how those components communicate with each
  • Topology has a significant effect on the
    networks performance and growth, and equipment
  • Terms topology, layout, diagram, map

Physical Topology vs. Logic Topology
  • Physical topology the arrangement of cabling
  • Three physical topologies bus, ring, star
  • Logical topology the path that data travels
    between computers on a network
  • Three logic topologies bus, ring, switching
  • What are the differences of physical topology
    and logic topology?
  • The logical topologies (bus, ring, and switching)
    are usually implemented as a physical star.
  • Lets see an example

Physical Topology
  • Three physical topologies
  • A bus consists of a series of computers
    connected along a single cable segment
  • A ring computers connected to form a loop
  • A star computers connected via a central
    concentration point

Physical Bus Topology
  • Physical bus topology is the simplest, and once
    the most common method for connecting computers
  • All computers are connected via a single cable
  • Why does physical bus
  • topology become obsolete?

Signal Propagation
  • In any network, computers communicate by sending
    information across the media as a series of
  • In a physical bus topology, the signals 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
  • This traveling across the medium is called signal
  • At the end of a cable, the signal bounces back

Signal Bounce
Is there any problem with signal bouncing?
Cable Termination
  • A terminator attached to each end of a cable
    prevents signals from bouncing.
  • Clearing the network for new communications.

Cable Failure
What would happen if a cable break occurs?
Logical Bus Topology
  • A physical bus topology is almost always
    implemented as a logical bus
  • Although physical bus is obsolete, logical bus
    topology is still in use (usually on physical
    star topology)
  • 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 computer accepts the data
  • All users must share the available amount of
    transmission time, ? network performance is
  • Lets watch simulation 2-1

Passive Topology vs. Active Topology
  • In an active topology network, computers and
    other devices regenerate signals and are
    responsible for moving data through the network
  • In a passive topology network, computers only
    listen for data being sent they are not
    responsible for moving data from one computer to
    the next.
  • A logic bus topology belongs to a(n) (active /
    passive) topology network.

Physical Ring Topology
  • Each computer connects directly to the next
    computer in a line
  • A circle of cable forms a physical ring
  • Every computer in a ring is responsible for
    retransmitting the data
  • ?
  • so it is a(n) active / passive topology.
  • Is there any problem with the
  • physical ring topology?

Logical Ring Topology
  • Data in a logical ring topology travels from one
  • to the next computer until the data reaches its
  • Token passing is one method for sending data
    around a ring
  • Token is a small packet, passes around the ring
    to each computer in turn.
  • If a computer (sender) has packets to send, it
    modifies the token, adds address and data, and
    sends it around the ring.
  • The receiver returns an acknowledge packet to the
  • Upon receiving the acknowledge packet, the sender
    releases the tokens and sends it around the ring.

Logical Ring Topology (2)
  • Logical ring on a physical star show how it
  • 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.

Physical Star Topology
  • Computers connected by cable segments to a
    central device.
  • Pros
  • Inherent centralization of resources ? easy for
    administration and trouble shooting
  • Robust network still works even any computer or
    cable segment fails
  • Cons
  • Single point for failure
  • Requires more cable installation

A Logical Bus on Physical Star (star bus)
  • The center device is a hub.
  • Once the hub receives signals, it retransmits
    them down every other cable segment to all other
    computers attached to the hub.

A Logical Ring on Physical Star (star ring)
  • The center device in a star ring is usually
    called a concentrator.

Switching on 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
  • Superior to other logical topologies because
  • unlike bus and ring, multiple computers can
    communicate simultaneously without affecting each
  • A dominant logical topology in LAN design

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

Variations of Physical Topologies
  • Three typical variations or combinations of
    physical topologies
  • Extended star
  • Mesh
  • Combination star and bus
  • These combinations can be used to get the most
    from any network

Extended Star Topology
  • Other switches (or hubs) are connected to the
    central switchs ports.
  • Extended star is also referred to as a
    hierarchical star

Mesh Topology
  • The most fault tolerant and the most expensive
  • n (n -1) / 2 cable segments for a mesh topology
    with n computers.
  • Mesh topology is used in a WAN. An example

(No Transcript)
Combination Star Bus Topology
Hubs and Switches
  • Both hubs and switches can act as the center of a
    star topology
  • In everyday use, a hub is the center of
  • This definition is appropriate in network usage
  • In network usage, there are a number of
    variations on this central theme
  • Active hub
  • Passive hub
  • Repeating hub (a type of active hub)
  • Switching hub

Active Hubs
  • Active hub is the most common type of hub today
  • Regenerate, or repeat, the signals
  • Require electrical power to run
  • have eight or more ports
  • 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
  • Drawback require sharing the cable bandwidth
    among all connected stations

Passive Hubs
  • The signal passes through the passive hub without
    any amplification or regeneration.
  • As a junction point and requires no power

  • Switch is a central connecting point in a star
  • 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
  • is able to handle several conversations at one
  • ? providing the full network bandwidth to each
    device rather than requiring bandwidth sharing
  • Lets watch simulation 2-2 basic operation of
    a switch

Construct a network layout
  • Steps to evaluate the underlying requirements
  • Determine how the network will be used
  • which often decides the topology you use
  • Decide the types of devices for interconnecting
    computers and sites
  • The type and usage level of network resources
    dictates how many servers you need and where to
    place servers

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
  • Ethernet switches are typically used on a LAN,
    but you might consider other logical topologies
    for other reasons
  • Use of legacy equipment such as token ring
  • Network size using hub-based bus topology
  • Cost restrictions using hub instead of switch
  • Difficulty to run cables go wireless ?

Creating the Layout
  • Network must be documented, and network diagram
  • be kept up to date.
  • Some useful questions to be answered 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?

Creating the Layout (cont)
  • 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
  • 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

Summary (cont)
  • 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
  • Can be active (if it regenerates the signals) or
  • Switch provides better performance than a hub
  • Device of choice in corporate star topology
  • Constructing a network layout