This document discusses various network topologies including physical and logical topologies. It describes the key characteristics of bus, star, ring, point-to-point and mesh topologies. It also covers token ring networks and how data travels on different physical topologies like bus, star and ring. Logical topologies like bus and ring are described along with baseband and broadband signaling.

2. Network Topologies
Chapter: 03
Computer Networks
By Prof: M. Naeem Akhtar

3. Simple Physical Topologies
Physical Topology: physical layout of nodes on a network
The arrangements of cabling and how cables connect one drive
to another in a network are considered the network’s physical
topology
Five fundamental shapes:
 Bus
 Star
 Ring
 Point to Point / Peer to Peer / P2P
 Mesh
May create hybrid topologies
Topology integral to type of network, cabling infrastructure, and
transmission media used

4. Bus Topology
Single cable connects all network nodes without intervening
connectivity devices
Devices share responsibility for getting data from one point to
another
Terminators stop signals after reaching end of wire
 Prevent signal bounce
Inexpensive, not very scalable
Difficult to troubleshoot, not fault-tolerant
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5. Bus Topology (continued)
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6. Advantages of Bus Topology
Works well for small networks
Relatively inexpensive to implement
Easy to add to it – strength of bus’s topology
Weaknesses of strength:
There’s limit of 30 computers per cable segment
Maximum total length of cabling is 185 meters
Both ends of the bus must be terminated
Any break in the bus brings down the entire network
Adding or removing a machine brings down the entire network temporarily
Technologies of this topology limited to 10 Mbps half duplex communication
because of using coaxial cabling
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7. How Data Travels in a Physical Bus
Information travels across the media as a series of signals as
electrical pulses
These signals continue travelling along the cable through devices
until they weaken enough to detect signal propagation
To avoid the reflection or bouncing back, you should install
terminators at the end of the medium.
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8. Disadvantages of Bus Topology
Management costs can be high
Potential for congestion with network traffic
Limitation of 30 computers per cable segment
 30 computers can be daisy chain together
Limitation of total cabling length is 185 meters
Max bandwidth 10 Mbps with coaxial cable
Max bandwidth 100 Mbps with twisted pair cables 26
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9. Physical Star Topologies
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10. Star Topologies
Star Topology uses a central device such as a hub or switch, to
interconnect computers in a LAN
Every node on the network is connected through a central device
Each computer has a single length of cable going from its NIC to the
central device
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11. Star Topology (continued)
Any single cable connects only two devices
 Cabling problems affect two nodes at most
Requires more cabling than ring or bus networks
 More fault-tolerant
Easily moved, isolated, or interconnected with other networks
 Scalable
Supports max of 1024 addressable nodes on logical network
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12. Physical Start Topology
Advantages of Star Topology
Much faster than bus topology
Centralized monitoring and management of network traffic is
possible – Easy to manage
Good option for modern networks
Low startup costs
Offers opportunities for expansion
Network upgrades are easier
Most popular topology in use; wide variety of equipment available
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13. Physical Star Topology
How Data Travels in a Physical Star
Data travelling in the network depends on the type of central devices
Data transmission starts from the computer along the medium until
it reaches the central device .
Transmission paths differs through Hubs, switches etc.
Transmission paths also differs due to logical topology such as
Ethernet and Token ring.
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14. Physical Star Topology
Extended Star Topology
Star topology is a good option for modern networks as it offers
opportunities for expansion of networks instead of computers
A central device, Hub/Switch, sits at the middle forming additional
stars referred to hierarchical star
This topology is most effective when the center of the star is running
at a much faster (1000 Mbps) than other devices (100 Mbps).
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15. Physical Star Topology
Disadvantages of Star Topology
Hub is a single point of failure
Requires more cable than the bus
Contrary to daisy chain
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16. Physical Ring Topology
• In Ring topology devices are attached (like bus topology) in daisy
chain.
• But instead terminating each end, the cabling is brought around the
last device back to the first device to form a ring.
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17. Physical Ring Topology
Also has reliability issues as data had to transmit from one station to
the next – as in bus data is forward to all directions and terminated at
both ends
A ring doesn't have any beginning or end.
Each station produce data and pass to the next station until it reaches
the destination
Ring topology used FDDI technology (Fiber Distributed data Interface)
to expand LANs and as well to avoid the dual ring
However FDDI technology is costly.
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18. Physical Ring Topology
Advantages:
 Easier to manage; easier to locate a defective node or cable problem
 Well-suited for transmitting signals over long distances on a LAN
 Handles high-volume network traffic
 Enables reliable communication
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19. Physical Ring Topology
Disadvantages
 Expensive
 Requires more cable and network equipment at the start
 Not used as widely as bus topology
Fewer equipment options
Fewer options for expansion to high-speed communication
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20. Point to Point Topology
In point to point topology there is a direct link between two
computers/devices
Often used in WAN – as business's network has a dedicated link to
a communication provider.
Data travels in dedicated link and did not share its bandwidth –
advantage
This topology tends to expensive when used as a WAN link to a
distant branch office – disadvantage
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21. Physical Mesh Topology
A Mesh topology connects each device to every other devices in a
network.
In mesh topology multiple point to point connections for the
purpose of redundancy and fault tolerance
If each computer or switch is connected with each other then is
called “mesh topology” otherwise called “partial mesh”.
Provides fast and collision free communication.
Difficult to install and manage a lot of cables
Initial cost is mush high – expensive topology
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22. Logical Topologies
Logical topology: how data is transmitted between nodes
May not match physical topology
Bus logical topology: signals travel from one network device to
all other devices on network
Required by bus, star, star-wired physical topologies
Ring logical topology: signals follow circular path between
sender and receiver
Required by ring, star-wired ring topologies
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23. Baseband and Broadband Signals
Baseband Signals
• A transmission method which sends digital signal of each bit
represented by a pulse of electricity (on copper media) or light pulse
(on fiber-optic).
• These signals are sent at a single fixed frequency, using the
medium’s entire bandwidth.
• As these signals occupies the entire bandwidth so no other frames
can be sent along with it.
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24. Baseband and Broadband Signals
Broadband Signals:
• Broadband systems use analog techniques to encode binary 1s and
0s across a continuous range of values.
• These signals move across the medium in the form of continuous
electromagnetic or optical waves rather than discrete pulses.
• On broadband systems signals flow at a particular frequency and
each frequency represents a channel of data
• different frequencies represents different channels.
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25. Token Ring Networks
(developed by IBM in 1980s)
 This technology provides albeit slow by today’s standards, transport
of data
 Based on IEEE 802.5 standard, token ring networks are cabled in a
physical star topology but function as a logical ring
 Token ring originally operates at 4 Mbps but now increased to 16
Mbps and later to 100 Mbps in 2001.
 Most token ring networks used Cat-4 or higher UTP.
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26. Token Ring Networks
Token Ring Media Access
 Token Ring uses the token passing media access method, in which
a special frame called the “token” passes from one computer to the
next
 Only the computer having the token can send data
 One computer can hold the token for a specific amount of time, if it
has not to sent data it passes the token to the next computer.
 No collision in token ring because of token and there’s possibility
of collisions in CSMA/CD as every computer is sensing the media.
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27. Token Ring Networks
Token Ring Media Access Disadvantages
1.
 Computer have to wait for the token.
 In case of large amount of data after first transmission there
might be wait time for second transmission because a circuit
should have to complete.
2.
 Complicated process of creating and passing tokens
 More expensive equipment than what’s used in CSMA/CD.
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28. Thanks for giving your attention