This document discusses the physical layer in computer networks. The physical layer is responsible for getting bits across a physical medium and its key challenge is representing digital bits as analog signals. Common data transmission media include cables like coaxial cable, twisted pair, and optical cable as well as wireless technologies that use radio waves or infrared radiation. The physical layer must also deal with characteristics of the communication channel like bandwidth, delay, and errors. Common physical layer devices include hubs, switches, repeaters, bridges, and modems.

1. Physical Layer

2. COMPUTER NETWORKS
Physical layer
Teacher: Nazirova Assem Bakdauletovna, PhD, senior lecturer of «IT-engineering»
department
E-mail: a.nazirova@aues.kz
Lecture 5
Physical Layer

3. Plan
• Functions of Physical layer
• Key challenge
• Data transmission media
• Communication channel model
Physical Layer

4. PHYSICAL LAYER
• Function:
• Get bits across a physical medium
• Key challenge:
• How to represent bits in analog
• Ideally, want high-bit rate
• But, must avoid desynchronization
Application
Presentation
Session
Transport
Network
Data Link
Physical
Physical Layer

5. PHYSICAL LAYER
Physical Layer 5
• It deals with the mechanical and electrical
specifications (Devices)
• Physical characteristics of interfaces and
medium.
• To move data in the form of electromagnetic
signals across a transmission medium
• The physical layer data consists of a stream of
bits (sequence of Os or 1s)
• Bits are encoded into signals

6. KEY CHALLENGE
•Digital computers
• 0s and 1s
• Analog world
• Amplitudes and frequencies
Physical Layer

7. PHYSICAL LEVEL TASK
• How to represent bits of information in the form of signals
transmitted through the medium
Physical Layer

8. PHYSICAL LAYER
Physical Layer 8

9. SIGNALS
Physical Layer 9
A signal is an electric current
or electromagnetic field used to convey data
from one place to another.
A Transmitter encodes a message into a
signal, which is carried to a receiver by the
communications channel.
Signals can be interpreted as either Analog or
Digital

10. DIGITAL SIGNALS
Physical Layer
• Digital signals are non-continuous, discrete

11. Analog Signals
Physical Layer
• Analog signals are continuous, non-discrete

12. Communication channel model
Physical Layer
 Characteristics of the communication channel
• Bandwidth (bit/s)
• Delay
• Number of errors
 Types of communication channels
• Simplex,
• Duplex,
• Half Duplex
Sender Recipient
Communica
tion channel
Message

13. DATA TRANSMISSION MEDIA
•Cable
• Telephone cable (“noodles")
• Coaxial cable
• Twisted pair
• Optical cable
• 220V power supply wires
•Wireless technologies
• Radio waves
• Infrared radiation
• Satellite channels
• Wireless optics (lasers)
Physical Layer

14. COAXIAL CABLE
Physical Layer
Coaxial cable is used in:
• computer and television networks,
• video surveillance systems,
• alarm and automation systems,
• radio communications.
All models contain four layers. So, they
consist of:
• An internal conductor
• Insulation
• Protective shield
• The outer shell

15. TWISTED PAIR
Physical Layer
Twisted pair is one of the components of
modern structured cabling systems. It is
used in telecommunications and computer
networks as a physical signal transmission
medium in many technologies, such as
Ethernet, Arcnet, Token ring, USB.
Currently, due to its cheapness and ease
of installation, it is the most common
solution for building wired (cable) local
area networks. The cable is connected to
network devices using the 8P8C connector
(which is mistakenly called RJ45).

16. OPTICAL CABLE
• Fiber-optic cable (also fiber-optic or
fiber—optic cable) is a cable based
on fiber light guides designed to
transmit optical signals in
communication lines, in the form of
photons (light). The transmission
speed is less than the speed of
light due to the non-straightness of
movement.
• Fiber-optic cable is actively used to
build telecommunication highways.
It is used by almost all Internet
providers. Fiber-optic cable is used
when creating networks between
different objects of the same
company or organization.
Physical Layer

17. RADIO WAVES
Features of the wireless environment
• The signal is transmitted in several directions
• There may be many receivers of information
• Several signal sources distort each other
andrequire coordination of work
Cellular communication
• GSM – 900 MHz
• Licensing requiredWi-Fi2.4GHz and 5 GHz
• No licensing required
• Other devices also operate at this frequency
Physical Layer

18. ERRORS IN COMMUNICATION
CHANNELS
Data transmission medium Error rate
Optical cables Very rarely
Copper cables Rarely
Radio waves Often
Physical Layer

19. DEVICES
Physical Layer
Some of the common devices are:
Hub
Switch
Repeater
Bridge
Modem
PC, Mobile phone, Telephone or Cables etc are
also devices use for data communication.

20. HUB
• Centralize device that connects many
devices to share data
• Less secure
Physical Layer

21. SWITCH
Physical Layer
•Device that connects many other devices
together to make a network
• More intelligent then Hub
• More secure

22. BRIDGE
Physical Layer
• Creates a single aggregate network from
multiple communication networks

23. MODEM
• The word Modem comes from Modulator- Demodulator
• Modulation: Digital signals to analog
• Demodulation: Analog signals back to Digital
Physical Layer

24. PHYSICAL
TOPOLOGIES
Physical Layer
How the devices are connected to make a
network ?
Mesh topology
Star topology
Bus topology
Ring topology
Hybrid topology

25. Physical Layer

26. Physical Layer

27. Physical Layer

28. Physical Layer

29. Physical Layer

30. Transmission Medium
Physical Layer
• Anything that can carry information from a
source to a destination.
• Uses cables or electromagnetic signals
to transmit data.
Types of Transmission Media
• 1. Wired or Guided Media or Bound Transmission
Media
• 2. Wireless or Unguided Media or Unbound
Transmission Media

31. Physical Layer

32. CONSLUSION
• Physical layer is the lowest, so…
• We tend not to worry about where to place
functionality
• There aren’t other layers that could interfere
• We tend to care about it only when things go wrong
• http://blog.level3.com/level-3-network/the-10-
most-bizarre-and-annoying-causes-of-fiber-cuts/
• Physical layer characteristics are still fundamentally
important to building reliable Internet systems
• Insulated media vs wireless
• Packet vs. circuit switched media
Physical Layer

33. CONSLUSION
•Physical layer
• Transmission of a bit stream over a data
transmission medium
•Data transmission medium
• Copper cables
• Optical cables
• Radio waves
•Characteristics of communication channels
• Bandwidth
• Delay
• Number of errors
Physical Layer

34. THANKS
Physical Layer