This is my class note for my class. This notes on Data communication.

1. CITY UNIVERSITY
Department of Computer Science and Engineering
Class note
Course Title: Data Communication
Course Code: CSE 313
Submitted to:
PRANAB BANDHU NATH
Senior Lecturer
Dept. Of CSE
City University
Submitted By:
M. M. Shakhawat Ahammed
ID: 1834902106
Dept.: CSE
Submission Date:

2. Notes on Class 3.
 The OSI Model
OSI Model: The OSI model is a layered framework for the design of network systems that allows
communication between all types of computer systems. It consists of seven separate but related layers, each
of which defines a part of the process of moving information across a network.
Seven layers of OSI model:
Physical Layer
• It coordinates the functions required to transmit a bit stream over physical medium.
• It deals with the mechanical and electrical specifications of interface and transmission medium.
• It defines the procedures and functions that physical devices and interfaces have to perform for
transmission to occur.

3. Data Link layer
• It transform the physical layer,a raw transmission facility. To a reliable link and is responsible for
node to node delivery.
• It makes the physical layer appear error free to the upper layer.
Network Layer
• It is responsible for source to destination delivery of a packet possibly across multiple networks.
• If the two systems are connected to the same link, there is usually no need for a network layer.
• If the two systems are attached to different links with connecting devices between networks, there is
often a need for a network layer.
• If the two systems are attached to different links with connecting devices between networks, there is
often a need of the network layer to accomplish source to destination delivery.
TRANSPORT LAYER
• It is responsible for source to destination delivery of the entire message.
• It ensures that the whole message arrives intact and in order.
SESSION LAYER
• It is the network dialog controller.
• It establishes, maintains and synchronizes the interaction between communicating systems.
• It plays an important role in keeping applications data separate.
PRESENTATION LAYER
• It is responsible for how an application formats data to be sent out onto the network.
• It basically allows an application to read (to understand) the message.

4. Data and Analog Signals.
Analog Signal: An analog signal has infinitely many levels of intensity over a period of time. As the wave
moves from value A to value B, it passes through and includes an infinite number of values along its path.
Digital Signal: A digital signal is a signal that represents data as a sequence of discrete values. A digital signal
can only take on one value from a finite set of possible values at a given time. With digital signals, the physical
quantity representing the information can be many things: Variable electric current or voltage.

5. Frequency: Frequency is the rate of change with respect to time. Change in a short span of time means high
frequency. Change over a long span of time means low frequency.
Phase
The term phase describes the position of the waveform relative to time O. If we think of the wave as something
that can be shifted backward or forward along the time axis, phase describes the amount of that shift. It
indicates the status of the first cycle.
Wavelength
Wavelength is another characteristic of a signal traveling through a transmission medium. Wavelength binds
the period or the frequency of a simple sine wave to the propagation speed of the medium.

6. Bit Rate
Most digital signals are nonperiodic, and thus period and frequency are not appropriate characteristics.
Another term-bit rate is used to describe digital signals. The bit rate is the number of bits sent in Is, expressed
in bits per second (bps).
Bit Length
We discussed the concept of the wavelength for an analog signal: the distance one cycle occupies on the
transmission medium. We can define something similar for a digital signal: the bit length. The bit length is
the distance one bit occupies on the transmission medium.
Bit length =propagation speed x bit duration
Reference:
Book: Data Communication and Networking By Behrouz A.Forouzan
Pictures From:
https://www.slideshare.net/SimranKaur116/osi-model
https://www.imperva.com/learn/application-security/osi-model/
https://www.studytonight.com/post/analog-vs-digital-
signalhttps://www.monolithicpower.com/en/analog-vs-digital-signal
https://circuitglobe.com/difference-between-frequency-and-wavelength.html
https://www.britannica.com/science/wavelength