CISY 332/BBIT 446
NETWORK HARDWARE AND
CONFIGURATION
LECTURE 2:
Network Topologies
January 2021: Lecture 2
DEFINITION:
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Network Topology is the layout of the
interconnection of devices in a network.
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It’s the outlook of the network connection.
Network topology may be viewed in two ways
Logical topology
 Physical topology
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Physical topology – outlook of the interconnected
devices. The external data flow diagram.
 Logical topology – movement of data across the
network. The logical DFD
 Traditional network design focused on physical
topology.
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Modern network design focus on logical topology.
CISY 332 Network Hardware and
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January 2021: Lecture 2
WHY TOPOLOGY
Topology help in determination of the
appropriate configuration for a given network.
 Topology influences the choice of technology for a
network.
 Topology determines the segment size for a
network.
 Cabling is dependent on the chosen topology
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January 2021: Lecture 2
NETWORK TOPOLOGY TYPES:
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Network topologies may be categorized into:
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These are the common types of network topology.
 NB: Some topology are applicable in some
network types and not others
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CISY 332 Network Hardware and
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Bus topology
Ring topology
Star topology
Mesh topology
Hybrid topology
Tree topology
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January 2021: Lecture 2
NETWORK TOPOLOGY: BUS
Network hosts are connected to a common
medium called a bus.
 Traditionally, the bus was a high speed cable,
terminated on both ends.
 Modern bus systems use an active device called a
bus switch.
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CISY 332 Network Hardware and
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The devices are connected directly to this switch,
forming a star outlook – physical star.
 Inside the device, a bus cable interconnects the
devices – logical bus
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January 2021: Lecture 2
NETWORK TOPOLOGY: BUS
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January 2021: Lecture 2
BUS TOPOLOGY:
Used in local area networks .
 Each node is connected to a single cable, called a
bus.
 A signal from the source travels in both
directions to all machines connected on the bus
cable until it finds the intended recipient.
 If the machine address does not match the
intended address for the data, the machine
ignores the data.
 Alternatively, if the data does match the machine
address, the data is accepted.
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January 2021: Lecture 2
BUS TOPOLOGY - ADVANTAGES
Easy to implement and extend.
 Easy to install.
 Well-suited for temporary or small networks not
requiring high speeds (quick setup), resulting in
faster networks.
 Cheaper than other topologies (But in recent
years has become less important due to devices
like a [[switch,])
 Cost effective; only a single cable is used.
 Easy identification of cable faults.
 Reduced weight due to fewer wires.
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January 2021: Lecture 2
BUS TOPOLOGY – DISADVANTAGES…
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CISY 332 Network Hardware and
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Limited cable length and number of stations.
If there is a problem with the cable, the entire
network breaks down.
Maintenance costs may be higher in the long run.
Performance degrades as additional computers are
added or on heavy traffic (shared bandwidth).
Proper termination is required (loop must be in closed
path).
Significant Capacitive Load (each bus transaction
must be able to stretch to most distant link).
It works best with limited number of nodes.
Commonly has a slower data transfer rate than other
topologies.
Only one packet can remain on the bus during one
clock pulse
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The host removes its packet from the network
If two devices try to send at the same time,
collision is detected.
 The devices use contention to decide who uses the
network (bus) to send data.
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CISY 332 Network Hardware and
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How a bus topology network operates
 At any given time, only one device may be
transmitting data/packets through the bus.
 Each packet makes a 360 degree run across the
bus, back to the sending host
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January 2021: Lecture 2
NETWORK TOPOLOGY: BUS
No centralized control
CSMA/CD
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CISY 332 Network Hardware and
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A network topology that is set up in a circular
fashion in which data travels around the ring in
one direction and each device on the right acts as
a repeater to keep the signal strong as it travels.
 Each device incorporates a receiver for the
incoming signal and a transmitter to send the
data on to the next device in the ring.
 The network is dependent on the ability of the
signal to travel around the ring.
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January 2021: Lecture 2
RING TOPOLOGY:
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Each host samples the packet and either picks a copy
or just forwards.
 The sending host removes message from hosts.
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A form of contention is used in sharing the
medium.
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CISY 332 Network Hardware and
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Devices are connected together in a manner to
form a ring.
 Communication is achieved by each device
forwarding the message to the next host, until it
gets back to the original host.
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January 2021: Lecture 2
NETWORK TOPOLOGY: RING
Token or slot
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January 2021: Lecture 2
NETWORK TOPOLOGY: RING
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CISY 332 Network Hardware and
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Very orderly network where every device has
access to the token and the opportunity to
transmit
 Performs better than a bus topology under heavy
network load
 Does not require network server to manage the
connectivity between the computers
 No need to switch on all the computers to work
with the network
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January 2021: Lecture 2
RING TOPOLOGY – ADVANTAGES…
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CISY 332 Network Hardware and
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One malfunctioning workstation or bad port in
the MAU can create problems for the entire
network.
 Moves, adds and changes of devices can affect the
network.
 Network adapter cards and MAU's are much
more expensive than Ethernet cards and hubs.
 Much slower than an Ethernet network under
normal load.
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January 2021: Lecture 2
RING TOPOLOGY – DISADVANTAGES…
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Technologies for ring network
CISY 332 Network Hardware and
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Token ring technology
 Slotted ring technology
 FDDI
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January 2021: Lecture 2
NETWORK TOPOLOGY: RING
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CISY 332 Network Hardware and
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Star networks are one of the most common computer
network topologies.
In its simplest form, a star network consists of one central
switch , hub or computer, which acts as a conduit to
transmit messages.
This consists of a central node, to which all other nodes are
connected; this central node provides a common connection
point for all nodes through a hub.
Thus, the hub and leaf nodes, and the transmission lines
between them, form a graph with the topology of a star .
If the central node is passive, the originating node must be
able to tolerate the reception of an echo of its own
transmission, delayed by the two-way transmission time
(i.e. to and from the central node) plus any delay generated
in the central node.
An active star network has an active central node that
usually has the means to prevent echo-related problems.
January 2021: Lecture 2
STAR TOPOLOGY:
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January 2021: Lecture 2
NETWORK TOPOLOGY: STAR
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CISY 332 Network Hardware and
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The star topology reduces the chance of network
failure by connecting all of the systems to a central
node.
All peripheral nodes communicate with all others by
transmitting to, and receiving from, the central node
only.
The failure of a transmission line linking any
peripheral node to the central node will result in the
isolation of that peripheral node from all others, but
the rest of the systems will be unaffected.
It is also designed with each node (file servers,
workstations, and peripherals) connected directly to a
central network hub, switch, or concentrator.
January 2021: Lecture 2
STAR TOPOLOGY…
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CISY 332 Network Hardware and
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Better performance: star topology prevents the passing of
data packets through an excessive number of nodes. At most, 3
devices and 2 links are involved in any communication
between any two devices.
Isolation of devices: Each device is inherently isolated by
the link that connects it to the hub. This makes the isolation
of individual devices straightforward and amounts to
disconnecting each device from the others. This isolation also
prevents any non-centralized failure from affecting the
network.
Benefits from centralization: As the central hub is the
bottleneck, increasing its capacity, or connecting additional
devices to it, increases the size of the network very easily.
Centralization also allows the inspection of traffic through the
network. This facilitates analysis of the traffic and detection of
suspicious behavior.
Easy to detect faults and to remove parts.
No disruptions to the network when connecting or removing
devices.
January 2021: Lecture 2
STAR TOPOLOGY – ADVANTAGES…
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CISY 332 Network Hardware and
Configuration
High dependence of the system on the
functioning of the central hub
 Failure of the central hub renders the network
inoperable
 The performance and scalability of the network
depends on the capabilities of the hub
 Network size is limited by the number of
connections that can be made to the hub
 Other nodes may see a performance drop if traffic
to another node occupies a significant portion of
the central node's processing capability or
throughput.
 Wiring up of the system can be very expensive.
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January 2021: Lecture 2
STAR TOPOLOGY - DISADVANTAGES…
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Point-to-point
CISY 332 Network Hardware and
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The simplest topology is a permanent link between
two endpoints.
 A physical link runs between the two devices.
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January 2021: Lecture 2
NETWORK TOPOLOGIES…
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CISY 332 Network Hardware and
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The type of network topology in which a central
'root' node (the top level of the hierarchy) is
connected to one or more other nodes that are one
level lower in the hierarchy (i.e., the second
level).
 Each node in the network has a specific fixed
number of nodes (called the 'branching factor')
connected to it at the next lower level in the
hierarchy.
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TREE TOPOLOGY:
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Each node has a point-to-point connection with
each other node in the network.
January 2021: Lecture 2
MESH TOPOLOGY:
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CISY 332 Network Hardware and
Configuration
This combines two or more topologies in different
parts of a network.
 A star topology can be used to join several bus
networks.
 Seeks to maximize the advantages of the
topologies used.
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January 2021: Lecture 2
HYBRID TOPOLOGY:
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Transmission Media
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