Determine Best Network Topology

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Unit of Competence
Determine Best-Fit Topology

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Determine Best-Fit Topology
Unit Descriptor
 This unit defines the competence required to determine the
most appropriate way of networking computers to meet user
needs and business requirements.

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Learning Outcomes
L01 Identify key information source
L02 Determine user needs
L03 Develop best topology

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L01: Identify key information source
Introduction to Network Topologies
 The term topology, or more specifically, network topology,
refers to the arrangement or physical layout of nodes (computers,
cables, and other) components on the network.
 A network topology is the pattern in which nodes (i.e.,
computers, printers, routers or other devices) are connected to a
local area network (LAN) or other network via links (e.g., twisted
pair copper wire cable or optical fiber cable).
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What is a (computer) network?
 A computer network is an interconnection of various
computer systems located at different places.
 In computer network two or more computers are linked
together with a medium and data communication devices
for the purpose of communicating data and sharing
resources

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Types of Network Topology
Physical Topology: of a network
refers to the configuration of cables,
computers, and other peripherals
Logical Topology:- is the method
used to pass information between
workstations.

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Factors that affect the choice of one topology over another:
◦ Type of equipment the network needs.
◦ Capabilities of the equipment.
◦ Growth of the network.
◦ Method the network is managed.

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Data communication components
There are five basic components in data communication system:
Message: it is the information that is to be communicated.
Sender (source): the sender is the device that sends the message.
Medium: the transmission medium is the physical path that
communicates the message from sender to receiver.
Receiver (sink): the receiver is the device that receives the message.
Protocol: Protocol refers to a set of rules that coordinates the exchange
of information.
Both the sender and the receiver should follow the same protocol to
communicate data.

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Introduction to Network Topology
There are Six types of Physical topologies, based on
topological structure such as
 Bus
Star
Ring
Mesh
Hybrid
Tree Topology
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Bus Topology
 It is often referred to as a ―linear bus‖ because all nodes
are connected in a single communication channel
The bus permits only one pair of nodes to establish
communication at a time
 In a bus topology, all computers are connected to a shared
communication line, called a trunk or a backbone. The
computers are connected to the backbone using T-
connectors. Both ends of the backbone use terminators in
order to prevent reflection of signals or bounced signal.

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Cont.……
 If the terminator is missing or is purposely removed, the
data transmissions are disrupted. There is no central device
or any special configuration. A bus topology is normally
implemented with coaxial cable.

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Communication on the Bus
 Computers on a bus topology network communicate by addressing data
to a particular computer and sending out that data on the cable as
electronic signals.
 Only one computer can ‗talk‘ on a network at a time.
A media access method (protocol) called CSMA/CD is used to handle
the collisions that occur when two signals are placed on the wire at the
same time.
 The bus topology is passive topology. In other words, the computers on
the bus simply ‗listen‘ for a signal; they are not responsible for moving
the signal along.
 Signals are broadcast to all stations

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Passive topology
When the computers on the network simply listen and receive the
signal, they are referred to as passive because they don‘t amplify
the signal in any way. Example for passive topology - linear bus.
Features:-
◦ Two nodes in a hardware cluster
◦ A virtual hostname and IP address
◦ A shared storage, to be shared between the two nodes

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Cont.…..
 To understand how computers communicate on a bus, you
need to be familiar with three concepts:
1. Sending the signal
2. Signal bounce
3. Terminator

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Sending the Signal
 Network data in the form of electronic signals is sent to all the
computers on the network. Only the computer whose address
matches the address encoded in the original signal accepts the
information. All other computers reject the data.
 Only one computer at a time can send messages. Because only
one computer at a time can send data on a bus network, the
number of computers attached to the bus will affect network
performance.

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Signal Bounce
 The data, or electronic signal, is sent to the entire
network, it travels from one end of the cable to the other.
 If the signal is allowed to continue continuous, it will
keep bouncing back and out along the cable and prevent
other computers from sending signals. Therefore, the
signal must be stopped after it has had a chance to reach
the proper destination address.

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Terminator
 To stop the signal from bouncing, a component called a
terminator is placed at each end of the cable to absorb free
signals.
 Absorbing the signal clears the cable so that other computers can
send data.
 A break in the cable will bounce signal and all network activity
will stop. The network will not work because it has unterminated
cables

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Network Expansion in bus topology
As the physical size of the site grows, the network will need to grow as
well. Cable in the bus topology can be extended by one of the two
following methods
A component called a barrel connector can connect two pieces of
cable together to make a longer piece of cable. However, connectors
weaken the signal and should be used carefully.
One continuous cable is better to connecting several smaller ones with
connectors. Using too many connectors can prevent the signal from
being correctly received.
BNC (Bayonet Neill–Concelman)

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Cont.……
A device called a repeater can be used to connect two cables.
A repeater actually boost the signal before it sends the signal on its way.
The following figure shows a repeater boosting a weakened signal. A
repeater is better than a connector or a longer piece of cable because it
allows a signal to travel farther and still be correctly received.

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Advantages of Bus Topology
 It is ability to connect any number of nodes without extensive hardware.
 Nodes can also removed from the bus easily.
 Use of cable is economical.
 Media is inexpensive and easy to work with.
 System is simple to maintain and reliable.
 Bus is easy to extend.
Disadvantages of Bus Topology
 Network can slow down in heavy traffic.
 Cable break can affect many users.
 Increasing the number of computer will slow down the performance of the
network
 Less fault tolerant
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Star Topology
 In the star topology, cable segments from each computer are connected to a
centralized component called a hub.
 The HUB offers a common connection for all stations on the network.
Each station has its own direct cable connection to the hub. In most cases,
this means more cable is required than for a bus topology. However, this
makes adding or moving computers a relatively easy task; simply plug them
into a cable outlet on the wall.
 If a cable is cut, it only affects the computer that was attached to it. This
eliminates the single point of failure problem associated with the bus
topology. (Unless, of course, the hub itself goes down.)
 Star topologies are normally implemented using twisted pair cable,
specifically unshielded twisted pair (UTP). The star topology is probably the
most common form of network topology currently in use.

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Cont.…..
In a star network, each node (file server, workstations, and peripherals)
is connected to a central device called a hub.
The hub takes a signal that comes from any node and passes it along to
all the other nodes in the network.
The hub, switch manages and controls all functions of the network.
The star topology reduces the chance of network failure by connecting
all of the systems to a central node.

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Advantages of a Star Topology
Easy to install and wire (implementation).
No disruptions to the network when connecting or removing devices.
Easy to detect faults and to remove parts.
Easy to manage and centralized control
Simple access protocols.
Easy to locate problems (cable/workstations)
Easier to expand than a bus or ring topology.
Easy to detect faults and to remove parts

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Disadvantages of a Star Topology
Requires more cable length than a Bus topology.
If the hub, switch fails, nodes attached are disabled.
More expensive than linear bus topologies because of the cost of the
hubs, etc.

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Ring Topology
 The ring topology connected in the form of closed loop. A single
communication channel is often implemented to provide the connectivity.
Data from the sending node circulate around the ring until it reaches the
destination.
 Unlike the bus topology, there are no terminated ends; the signal travels a
unidirectional or bi-directional. In a unidirectional ring, data moves in one
direction only. In a bi-directional ring, data moves in both directions, but in
one direction at a time.
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Ring Topology
 Single node failure may paralyze the transmission of data to a set of nodes in
a unidirectional ring. But messages can be sent to nodes in either side of the
affected node
 The signals travel around the loop in one direction and pass through each
computer, which can act as a repeater to boost the signal and send it on to the
next computer. This made ring topology to be called active topology.
Note that while this topology functions logically as ring, it is physically wired as a star.
The central connector is not called a hub but a Multi station Access Unit or MAU.
Rings are normally implemented using twisted pair or fiber-optic cable.
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Communication on the Ring Topology
Under the ring concept, a signal is transferred sequentially via a "token" from one
station to the next.
When a station wants to transmit, it "grabs" the token, attaches data and an
address to it, and then sends it around the ring. The token travels along the ring
until it reaches the destination address.
The receiving computer acknowledges receipt with a return message to the sender.
The sender then releases the token for use by another computer.
Each station on the ring has equal access but only one station can talk at a time.
This type of network topology is very organized. Each node gets to send the data
when it receives an empty token. This helps to reduces chances of collision. Also
in ring topology all the traffic flows in only one direction at very high speed.
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Advantages of Ring Topology
Growth of system has minimal impact on performance or Extra
computers can be added easily with little effect on performance
All stations have equal access.
Additional components do not affect the performance of network.
Transmission of data is fairly simple as it only travels in one direction
No data collisions
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Disadvantages of Ring Topology
If one workstation or port goes down, the entire network gets affected.
MAU‘s and network cards are expensive as compared to Ethernet cards and hubs.
If a single machine is switched off, the network doesn't work
If a cable breaks, the network doesn't work
Data must pass through every computer until it reaches its destination. This can make it
slower than other network layouts.
If there are any problems with the network, they can be difficult to identify the cause.
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Mesh Topology
 A mesh topology network offers superior redundancy and reliability.
 In a mesh topology, each computer is connected to every other computer by separate cabling.
 Internet is Mesh Topology.
 This configuration provides redundant paths throughout the network so that if one cable fails,
another will take over the traffic.
 While ease of troubleshooting and increased reliability are definite advantages, these networks
are expensive to install because they use a lot of cabling.
 You can calculate the number of cables used in mesh topology using the following
formula:
◦ No of Cable= n (n-1)/2, where n is no of computer used in mesh topology.
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Example
Calculate the number of cables used for 6 computers in
mesh topology?
=n(n-1)/2 =6(6-1)/2 =6*5/2 =15
Calculate the number of cables used for 10 computers in
mesh topology?
= 45

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Advantages of Mesh topology
 Data can be transmitted from different devices at the same time.
 This topology can with stand high traffic.
 Even if one of the components fails there is always an alternative present.
So data transfer doesn‘t get affected.
 Expansion and modification in topology can be done without disrupting
other nodes.
 Most Fault Tolerant
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Disadvantages of Mesh topology
Overall cost of this network is way too high as compared to
other network topologies.
 Set-up and maintenance of this topology is very difficult.
Even administration of the network is very complex.
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Hybrid Topology
 It is combination of any two or more
network topologies.
 These examples can occur where two
basic network topologies, when connected
together, can still remember the basic
network character, and therefore not be a
hybrid network.
◦ Star-Bus
◦ Star-Ring
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Hybrid Topology
Star Bus
 The star bus The topology is combined with
the linear bus in large networks. In such cases
the linear bus provides a backbone that
connects multiple stars
 In a star-bus topology, several star topology
networks are linked together with linear bus
trunks.
 If one computer goes down, it will not affect the
rest of the network. The other computers can
continue to communicate. If a hub goes down, all
computers on that hub are unable to
communicate. If a hub is linked to other hubs,
those connections will be broken as well.
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Hybrid Topology
Star Ring
The star ring (sometimes called a star-
wired ring) appears similar to the star bus.
Both the star ring and the star bus are
centered in a hub that contains the actual
ring or bus.
Linear-bus trunks connect the hubs in a star
bus, while the hubs in a star ring are
connected in a star pattern by the main hub.
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Advantages of a Hybrid Topology
 It is extremely flexible.
 It is very reliable.
Scalable
Effective
Disadvantages of a Hybrid Topology
 Expensive (costly of hub)
Complexity of design
Costly infrastructure

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Tree Topology
 A tree topology (hierarchical topology) can be viewed as a collection of
star networks arranged in a hierarchy.
 This tree has individual peripheral nodes which are required to transmit
to and receive from one other only and are not required to act as repeaters
or regenerators.
 The tree topology arranges links and nodes into distinct hierarchies in
order to allow greater control and easier troubleshooting.
 This is particularly helpful for colleges, universities and schools so that
each of the connect to the big network in some way.

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Advantages of a Tree Topology
 Point-to-point wiring for individual segments.
 Supported by several hardware and software vendors.
 All the computers have access to the larger and their immediate networks.
Disadvantages of a Tree Topology
 Overall length of each segment is limited by the type of cabling used.
 If the backbone line breaks, the entire segment goes down.
 More difficult to configure and wire than other topologies.

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Summary on Network Topologies
The physical layout of computers on a network is called a topology.
There are four primary topologies: star, bus, ring, and mesh.
Topologies can be physical (actual wiring) or logical (the way they work).
In a bus topology, the computers are connected in a linear fashion on a single
cable.
Bus topologies require a terminator on each end of the cable.
In a star topology, the computers are connected to a centralized hub.
Mesh topologies connect all computers in a network to one another with separate
cables.
In a token-ring topology, the computers are connected physically in a star shape,
but logically in a ring or circle. The data is passed from one computer to another
around the circle.
Hubs are used to centralize the data traffic and localize failures. If one cable
breaks, it will not shut down the entire network.

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Topology Advantages Disadvantages
Bus Use of cable is economical.
Media is inexpensive and easy to work
with.
System is simple and reliable.
Bus is easy to extend.
Network can slow down in heavy
traffic. Problems are difficult to
isolate.
Cable break can affect many users.
Ring System provides equal access for all
computers. Performance is even despite
many users.
Failure of one computer can
impact the rest of the network.
Problems are hard to isolate.
Network reconfiguration disrupts
operation.
Star Modifying system and adding new
computers is easy. Centralized monitoring
and management are possible.
Failure of one computer does not affect
the rest of the network.
If the centralized point fails, the
network fails.
Mesh System provides increased redundancy
and reliability as well as ease of
troubleshooting.
System is expensive to install
because it uses a lot of cabling.
Selecting a topology

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Self check Questions on network topology
Exercise 1.1: Case Study Problem
A small, independent, business/home/life insurance company consisting
of an owner, a business manager, an administrator, and four agents
decides to implement a network. The company occupies half of a small
building in an office park. Their volume of business had been stable for
the past three years, but recently it has been increasing. To handle the
increased business volume, two new agents will be hired.
The Following Figure illustrates the current arrangement.

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Self check Questions on network topology
Everyone in the company has a computer, but the business manager has the
only printer. These computers are not connected by any form of networking.
When agents need to print a document, they must first copy the file to a
flash disk, then carry it to the business manager's computer, where they are
finally able to print it. Similarly, when staff members want to share data, the
only means available is to copy the data on one computer to a flash disk and
insert the disk in another computer.
Recently, problems have arisen. The business manager is spending too
much time printing other people's documents; and it is frequently unclear
which copy of a given document is the current and authoritative version.
Your task is to design a network for this company. To clarify the task of
choosing a solution, you ask some questions. Circle the most appropriate
answers to the following questions:
Which network topology would be most appropriate in this situation?
Bus
Ring
Star
Mesh
Star bus
 Star ring

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Internetwork
 Any interconnection among or between public, private,
commercial, industrial, or governmental networks is defined as an
internetwork (or simply internet). There are at least three variants
of internetwork, depending on who administers and who
participates in them:
◦ Intranet
◦ Extranet
◦ Internet

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Intranet
 An intranet is a set of networks that is under the control of
a single administrative entity. That administrative entity
closes the intranet to all but specific, authorized users.
 Most commonly, an intranet is the internal network of
an organization. A large intranet will typically have at least
one web server to provide users with organizational
information. Example a network of Mary Help College

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An Extranet is a network or internetwork that is limited in scope to a
single organization or entity but which also has limited connections to
the networks of one or more other usually, but not necessarily,
trusted organizations or entities (e.g. a company's customers may be
given access to some part of its intranet creating in this way an extranet).
The Internet is a specific internetwork. It consists of a
worldwide interconnection of governmental, academic, public, and
private networks based upon the networking technologies of the
Internet Protocol Suite.
Extranet and Internet

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Network Hardware Components
 All networks are made up of basic hardware building blocks to
interconnect network nodes, such as Network Interface Cards (NICs),
Bridges, Hubs, Switches, and Routers.
 In addition, some method of connecting these building blocks is
required, usually in the form of galvanic cable (most commonly
Category 5 cable). Less common are microwave links (as in IEEE
802.12) or optical cable ("optical fiber").

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Cont.….
 Transmission media is the way in which information is transmitted
from one location to another.
 It is sometimes referred to as communication media as well.
 In computer communications there are two basic types of
transmission media.
1. These are bounded, or guided, media and
2. unbounded, or unguided, media.
 Bounded media are the physical links to transmit information such as
coaxial or fiber optic cable.
 Unbounded media would be transmission through the air such as via
Wi-Fi or cell phone signals and towers.

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Twisted Pair Cable

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Cont.…
 In its simplest form, twisted-pair cable consists of two insulated strands
of copper wire twisted around each other.
 The two types of twisted-pair cable
1. Unshielded twisted-pair (UTP) and
2. Shielded twisted-pair (STP) cable

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1. Unshielded twisted-pair (UTP)
 UTP, using the 10BaseT specification, is the most popular type of twisted-pair
cable and is fast becoming the most popular LAN cabling.
 The maximum cable length segment is 100 meters, about 328 feet
These standards include five categories of UTP:
Category 1
This refers to traditional UTP telephone cable that can carry voice but not data
transmissions. Most telephone cable prior to 1983 was Category 1 cable.
Category 2
This category certifies UTP cable for data transmissions up to 4 megabits per
second (Mbps). It consists of four twisted pairs of copper wire.

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Cont.…..
Category 3
This category certifies UTP cable for data transmissions up to 16 Mbps. It
consists of four twisted pairs of copper wire with three twists per foot.
Category 4
consists of four twisted pairs of copper wire.
Category 5
consists of four twisted pairs of copper wire.

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Type Use
Category 1 Voice Only (Telephone Wire)
Category 2 Data to 4 Mbps (LocalTalk)
Category 3 Data to 10 Mbps (Ethernet)
Category 4 Data to 20 Mbps (16 Mbps Token Ring)
Category 5 Data to 100 Mbps (Fast Ethernet)

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CAT Cable Bandwidth Data
# Type (MHz) Rate
CAT1 UTP Analog voice
CAT2 UTP Digital voice
CAT3 UTP//STP 16 MHz 4 Mbps
CAT4 UTP//STP 20 MHz 16 Mbps
CAT5 UTP/STP 100 MHz 1 Gbps
CAT5e UTP/STP 100 MHz 1 Gbps
CAT6 UTP/STP 250 MHz 10 Gbps/55 m
CAT6a UTP/STP 500 MHz 10 Gbps/100 m
CAT7 STP 600 MHz 10 Gbps/100 m

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2. Shielded Twisted-Pair (STP) Cable
 STP cable uses a merged copper-braid jacket that is more
protective and of a higher quality than the jacket used by UTP.
 STP also uses a foil covering around each of the wire pairs.
 This gives STP excellent shielding to protect the transmitted data
from outside interference, which in turn allows it to support higher
transmission rates over longer distances than UTP.

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Connectors of Twisted-Pair Cable
 Connection hardware Twisted-pair cabling uses RJ-45 connectors to
connect to a computer. These are similar to RJ-11 telephone connectors.
 The RJ-45 connector is slightly larger and will not fit into the RJ-11
telephone jack. The RJ-45 connector houses eight cable connections,
while the RJ-11 houses only four.

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Twisted-Pair Cabling Considerations
Use twisted-pair cable if:
◦ Your LAN is under budget limits.
◦ You want a relatively easy installation in which computer connections are simple.
Do not use twisted-pair cable if:
◦ Your LAN requires a high level of security and you must be absolutely sure of
data integrity.
◦ You must transmit data over long distances at high speeds.

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Coaxial Cable
 At one time, coaxial cable was the most widely used network cabling.
There were a couple of reasons for coaxial cable's wide usage:
 it was relatively inexpensive, and it was light, flexible, and easy to work
with.
 In its simplest form, coaxial cable consists of a core of copper wire
surrounded by insulation, a braided metal shielding, and an outer cover.
 The term shielding refers to the woven or stranded metal mesh (or other
material) that surrounds some types of cabling.

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Cont.….
 Coaxial cable is more resistant to interference and
attenuation than twisted-pair cabling, attenuation is the
loss of signal strength that begins to occur as the signal
travels farther along a copper cable.
Types of Coaxial Cable
There are two types of coaxial cable:
◦ Thin (thinnet) cable
◦ Thick (thicknet) cable

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1. Thinnet cable
 Thinnet cable is a flexible coaxial cable about 0.64
centimeters (0.25 inches) thick. Because this type of coaxial
cable is flexible and easy to work with it can be used in
almost any type of network installation.
 Thinnet coaxial cable can carry a signal for a distance of
up to approximately 185 meters (about 607 feet) before
the signal starts to suffer from attenuation.

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2. Thicknet Cable
 Thicknet cable is a relatively rigid coaxial cable about 1.27 centimeters
(0.5 inches) in diameter.
 Thicknet cable is sometimes referred to as Standard Ethernet because it
was the first type of cable used with the popular network architecture
Ethernet.
 Thicknet cable's copper core is thicker than a thinnet cable core.

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Cont.…
 The thicker the copper core, the farther the cable can carry signals.
 This means that thicknet can carry signals farther than thinnet cable.
 Thicknet cable can carry a signal for 500 meters (about 1640 feet).
Therefore, because of thicket's ability to support data transfer over longer
distances, it is sometimes used as a backbone to connect several smaller
thinnet-based networks.

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Coaxial-Cable Connection Hardware
 Both thinnet and thicknet cable use a connection component, known as a
BNC connector, to make the connections between the cable and the
computers

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BNC T connector
This connector joins the network interface card (NIC) in the computer to
the network cable.

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The BNC barrel connector
 This connector is used to join two lengths of thinnet cable to make one
longer length.

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The BNC terminator
A BNC terminator closes each end of the bus cable to absorb stray
signals. Otherwise, the signal will bounce and all network activity will
stop.

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Coaxial-Cabling Considerations
Use coaxial cable if you need a medium that can:
 Transmit voice, video, and data.
 Transmit data for greater distances than is possible with less expensive
cabling.

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Fiber-Optic Cable
 In fiber-optic cable, optical fibers carry digital data signals in the form
of modulated pulses of light.
 This is a relatively safe way to send data because, unlike copper-based
cables that carry data in the form of electronic signals, no electrical
impulses are carried over the fiber-optic cable.
 Fiber-optic cable is good for very high-speed, high-capacity data
transmission because of the purity of the signal and lack of signal
attenuation.

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Cont.…
 An optical fiber consists of an extremely thin cylinder of glass, called
the core, surrounded by a concentric layer of glass, known as the
cladding.
 The fibers are sometimes made of plastic.
 Plastic is easier to install, but cannot carry the light pulses for as long a
distance as glass

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Cont.…
 Fiber-optic cable transmissions are not subject to electrical
interference and are extremely fast, currently transmitting
about 100 Mbps with demonstrated rates of up to 1 gigabit
per second (Gbps).

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Fiber-Optic Cabling Considerations
Use fiber-optic cable if you:
◦ Need to transmit data at very high speeds over long distances in very
secure media.
Do not use fiber-optic cable if you:
◦ Are under a tight budget.
◦ Do not have the expertise available to properly install it and connect
devices to it.

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Connector of Fiber optic
cable(MT-RJ)

SetByITDept.
Wireless Transmission Media
Broadcast Radio
◦ Distribute signals through the air over long distance
◦ Uses an antenna
◦ Typically for stationary locations
◦ Can be short range
Cellular Radio
◦ A form of broadcast radio used for mobile
communication
◦ High frequency radio waves to transmit voice or data
◦ Utilizes frequency-reuse

SetByITDept.
Wireless Transmission Media
Microwaves
◦ Radio waves providing high speed
transmission
◦ They are point-to-point (can‘t be obstructed)
◦ Used for satellite communication
Infrared (IR)
◦ Wireless transmission media that sends
signals using infrared light- waves

SetByITDept.
Signal Transmission
Two techniques can be used to transmit the encoded
signals over cable:
1. Baseband and
2. Broadband transmission.

SetByITDept.
Cont.….
 Baseband systems use digital signaling over a single channel. Signals
flow in the form of discrete pulses of electricity or light.
 With baseband transmission, the entire communication channel capacity is
used to transmit a single data signal.
 The digital signal uses the complete bandwidth of the cable, which
constitutes a single channel.
 The term bandwidth refers to the data transfer capacity, or speed of
transmission, of a digital communications system as measured in bits per
second (bps).

SetByITDept.
Cont.…
 As the signal travels along the network cable, it gradually decreases in
strength and can become distorted.
 If the cable length is too long, the received signal can be
unrecognizable or misinterpreted.
 As a safeguard, baseband systems sometimes use repeaters to receive
incoming signals and retransmit them at their original strength and
definition. This increases the practical length of a cable.

SetByITDept.
Cont.…..
Broadband systems use analog signaling and a range of frequencies.
With analog transmission, the signals are continuous and non discrete.
Signals flow across the physical medium in the form of electromagnetic or
optical waves.
With broadband transmission, signal flow is unidirectional.
If sufficient total bandwidth is available, multiple analog transmission
systems, such as cable television and network transmissions, can be
supported simultaneously on the same cable.

SetByITDept.
Cont.….
 While base band systems use repeaters, broadband systems use
amplifiers to regenerate analog signals at their original strength.
 In broadband transmission, signals flow in one direction only, so
there must be two paths for data flow in order for a signal to reach all
devices.

SetByITDept.
Understanding Network Architecture
Access Methods
 The set of rules that defines how a computer puts data
onto the network cable and takes data from the cable is
called an access method.
 Once data is moving on the network, access methods help
to control the flow of network traffic.

SetByITDept.
MajorAccess Methods
The three methods designed to prevent simultaneous use of
the network media include:
1. Carrier-sense multiple access methods with collision detection or
with collision avoidance)
2. Carrier-sense multiple access methods with collision avoidance
3. Token-passing methods that allow only a single opportunity to
send data.

SetByITDept.
Carrier-Sense MultipleAccess with Collision
Detection (CSMA/CD) Access Method
Carrier sense—each station continuously listens for traffic on the
medium to determine when gap between frame transmissions occur.
Multiple access—Stations may begin transmitting any time they
detect that the network is quiet (there is no traffic).
Collision detect—If two or more stations in the same CSMA/CD
network (collision domain) begin transmitting at approximately the
same time, the bit streams from the transmitting stations will
interfere (collide) with each other, and both transmissions will be
unreadable. If that happens, each transmitting station must be
capable of detecting that a collision has occurred before it has
finished sending its frame.

SetByITDept.
Cont.…
 Only when a computer "senses" that the cable is free and that there is
no traffic on the cable can it send data.
 Once the computer has transmitted data on the cable, no other
computer can transmit data until the original data has reached its
destination and the cable is free again.
 Remember, if two or more computers happen to send data at exactly
the same time, there will be a data collision. When that happens, the two
computers involved stop transmitting for a random period of time and
then attempt to retransmit.
 Each computer determines its own waiting period; this reduces the
chance that the computers will once again transmit simultaneously.

SetByITDept.
Carrier-Sense MultipleAccess with Collision
Avoidance (CSMA/CA) Access Method
Carrier-sense multiple access with collision avoidance (CSMA/CA) is
the least popular of the three major access methods.
In CSMA/CA, each computer signals its intent to transmit before it
actually transmits data. In this way, computers sense when a collision
might occur; this allows them to avoid transmission collisions.
Unfortunately, broadcasting the intent to transmit data increases the
amount of traffic on the cable and slows down network performance.

SetByITDept.
Token-Passing Access Method
 In the access method known as token passing, a special type of packet,
called a token, circulates around a cable ring from computer to
computer. When any computer on the ring needs to send data across the
network, it must wait for a free token. When a free token is detected, the
computer will take control of it if the computer has data to send
 The computer can now transmit data.
 Data is transmitted in frames, and additional information, such as
addressing, is attached to the frame in the form of headers and trailers.

SetByITDept.
Mode of Data Transmission
Types of transmission mode
1. Simplex
2. Half-Duplex
3. Full-Duplex

SetByITDept.
Simplex
 The most basic form of data or information transmission is called
simplex. This means that data is sent in one direction(Unidirectional
transmission) only, from sender to receiver.
the source doesn‘t need response
Ex- TV broadcast

SetByITDept.
Half-duplex transmission
 Data is sent in both directions, but in only one direction at a time. With
half-duplex transmission, you can incorporate error detection and request
that any bad data be resent.
 Surfing the World Wide Web is a form of half-duplex data
transmission.
 You send a request for a Web page and then wait while it is being sent
back to you. Most modem connections use half-duplex data
transmission.

SetByITDept.
Cont.…
Ex- Wacky talkies, Fax machine, ATM machine

SetByITDept.
Full-duplex transmission
 The most efficient method of transmitting data is to use a full-duplex
transmission, in which data can be transmitted and received at the same
time.
 A telephone is a full-duplex device because it allows both parties to
talk at the same time.
Ex- Cellular phone

SetByITDept.
1. Circuit switching
 Once a dedicated
circuit has established
the whole file will be
sent & the other
parties should wait
until they get the path
free.
2.Packet switching
 1st the data is divided
into small chunks called
packets.
 Each packet has
addressed & sequence
number attached to it
& they can be sent at
different time.
Transmission methods
Two methods

Determine Best Network Topology

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