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## Guide to Networking Essentials

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### 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

1
Guide to Networking Essentials
• Chapter 2
• Network Design Essentials

2
Objectives
• Basics of network layout
• The standard networking topologies
• The variations on standard networking topologies
• Hubs and switches
• Construct a network layout

3
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
other
• Topology has a significant effect on the
networks performance and growth, and equipment
decisions
• Terms topology, layout, diagram, map

4
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

5
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

6
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
backbone
• Why does physical bus
• topology become obsolete?

7
Signal Propagation
• In any network, computers communicate by sending
information across the media as a series of
signals
• 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
them
• This traveling across the medium is called signal
propagation
• At the end of a cable, the signal bounces back

8
Signal Bounce
Is there any problem with signal bouncing?
9
Cable Termination
• A terminator attached to each end of a cable
prevents signals from bouncing.
• Clearing the network for new communications.

10
Cable Failure
What would happen if a cable break occurs?
11
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
reduced
• Lets watch simulation 2-1

12
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.

13
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?

14
Logical Ring Topology
• Data in a logical ring topology travels from one
computer
• to the next computer until the data reaches its
destination
• 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
sender.
• Upon receiving the acknowledge packet, the sender
releases the tokens and sends it around the ring.

15
Logical Ring Topology (2)
• Logical ring on a physical star show how it
works
• 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.
Why?

16
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

17
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.

18
A Logical Ring on Physical Star (star ring)
• The center device in a star ring is usually
called a concentrator.

19
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
computer
• Superior to other logical topologies because
• unlike bus and ring, multiple computers can
communicate simultaneously without affecting each
other
• A dominant logical topology in LAN design

20
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

21
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

22
Extended Star Topology
• Other switches (or hubs) are connected to the
central switchs ports.
• Extended star is also referred to as a
hierarchical star

23
Mesh Topology
• The most fault tolerant and the most expensive
topology.
• n (n -1) / 2 cable segments for a mesh topology
with n computers.
• Mesh topology is used in a WAN. An example

24
(No Transcript)
25
Combination Star Bus Topology
26
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
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 (a type of active hub)
• Switching hub

27
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
ports
• Drawback require sharing the cable bandwidth
among all connected stations

28
Passive Hubs
• The signal passes through the passive hub without
any amplification or regeneration.
• As a junction point and requires no power

29
Switches
• Switch is a 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
• is able to handle several conversations at one
time
• ? providing the full network bandwidth to each
device rather than requiring bandwidth sharing
• Lets watch simulation 2-2 basic operation of
a switch

30
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

31
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 such as token ring
• Network size using hub-based bus topology
• Cost restrictions using hub instead of switch
• Difficulty to run cables go wireless ?

32
Creating the Layout
• Network must be documented, and network diagram
must
• 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?

33
Creating the Layout (cont)
34
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

35
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
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
• Constructing a network layout
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