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,1. What are the components of the data link layer?
The data-link layer is the second layer from the bottom in the OSI network architecture model. It is responsible for
node-to-node delivery of data. Its major role is to ensure error-free transmission of information. DLL is also
responsible for encoding, decoding, and organizing outgoing and incoming data. This is considered the most complex
layer of the OSI model as it hides all underlying complexities of hardware from other layers.
Sub-layers of Data Link Layer:
The data link layer is further divided into two sub-layers, which are as follows:
Logical Link Control (LLC):
This sublayer of data link layer deals with multiplexing, and flow of data among applications and other services, and
LLC is responsible for providing error messages and acknowledgments as well.
Media Access Control (MAC):
MAC sublayer manages the device's interaction, responsible for addressing frames, and also controls physical media
access.
2. What is the OSI model? List its layers and Explain their responsibilities in short.
OSI stands for Open Systems Interconnection. It was developed by 150-"International Organization for
Standardization', in the year 1984. It is a 7-layer architecture with each layer having specific functionality to perform.
All these 7 layers work collaboratively to transmit data from one person to another across the globe.
Physical Layer (Layer 1):
The lowest layer of the OSI reference model is the physical layer. It is responsible for the actual physical connection
between devices. The physical layer contains Information in the form of bits. It is responsible for transmitting
individual bits from one node to the next. When receiving data, this layer will get the signal received convert it into
0’s and 1’s, and send them to the Data Link layer, which will put the frame back together.
Data Link Layer (DLL) (Layer 2):
The data link layer is responsible for the node-to-node delivery of messages. The main function of this layer is to make
sure data transfer is error-free from one node to another, over the physical layer. When a packet arrives in the
network, it is the responsibility of the DLL to transmit it to the Host using its MAC address.
Data Link Layer is divided into two sublayers:
1. Logical Link Control (LLC)
2. Media Access Control (MAC)
Network Layer (Layer 3):
The network layer works for the transmission of data from one host to another located in different networks. It also
takes care of packet routing Le, the selection of the shortest path to transmit the packet, from several routes available.
The sender & receiver's IP addresses are placed in the header by the network layer.
Transport Layer (Layer 4):
The transport layer provides services to the application layer and takes services from the network layer. Data in the
transport layer is referred to as Segments. It is responsible for End to end-to-end delivery of complete messages. The
transport layer also provides acknowledgment of successful data transmission and re-transmits data if an error is
found.
Session Layer (Layer 5):
This layer is responsible for the establishment of connection, maintenance of sessions, and authentication, and also
ensures security.
Presentation Layer (Layer 6):
The presentation layer is also called the Translation layer. Data from the application layer is extracted here and
manipulated as per the required format to transmit over the network.
Application Layer (Layer 7):
At the very top of the OSI Reference Model stack of layers, we find the Application layer which is implemented by
network applications. These applications produce data, which has to be transferred over the network. This layer also
serves as a window for application services to access the network and for displaying received information to the user.
, 3. Explain types of transmission impairment.
Noise:
Noise is a major factor for transmission distortion as any unwanted signal gets added to the transmitted signal by
which the resulting transmitted signal gets modified and at the receiver side it is difficult to remove unwanted noise
signal. These noises are various kinds like shot noise, impulse noise, thermal noise, etc.
Distortion:
This kind of distortion mainly appears in the case of composite signals in which composite signal has various frequency
components and each frequency component has some time constraint which makes a complete signal. But while
transmitting this composite signal, if a certain delay happens between frequency components, then there may be a
chance that the frequency component will reach the receiver end with a different delay constraint from its original
which leads to a change in the shape of the signal. The delay happens due to environmental parameters or from the
distance between the transmitter and receiver etc.
Attenuation:
Attenuation is generally decreased in signal strength, by which received signal will be difficult to receive at the
receiver end. This attenuation happens due to the majority factor by environment as the environment imposes a lot
of resistance and signal strength decreases as it tries to overcome the resistance imposed
4. Explain serial transmission along with its types.
When data is sent or received using serial data transmission, data bits are organized in specific order, since they can
only be sent one after another. The order of data bits is important as it dictates how transmission is organized when
it is received. It is viewed as a reliable data transmission method because the data bit is only sent if the previous data
bit has already been received. Serial transmission has two classifications:
Asynchronous Serial Transmission:
Data bits can be sent at any point in time. Stop bits and start bits are used between data bytes to synchronize
transmitter and receiver and to ensure that data is transmitted correctly.
Synchronous Serial Transmission:
Data bits are transmitted as a continuous stream in time with the master clock.
5. Define modulation with its types.
The process by which data/information is converted into electrical/digital signals for transferring that signal over
medium is called modulation. It increases strength for maximum reach of signals. Types of modulation:
1. Amplitude modulation:
It is a type of modulation in which only the amplitude of the carrier signal is varied to represent data being added
to signals whereas the phase and frequency of the signal are kept unchanged.
2. Frequency modulation:
It is a type of modulation in which only the frequency of the carrier signal is varied to represent the frequency of
data whereas the phase and amplitude of signals are kept unchanged.
3. Phase modulation:
It is a type of modulation in which the phase of the carrier signal is varied to represent data being added to the
signal. Different information values are represented by different phases.
6. Explain Parallel transmission and Serial transmission.
Parallel transmission:
Parallel transmission defines a transmission structure that shares multiple data bits at similar times over separate
media. In general, parallel transmission can be used with a wired channel that uses multiple, separate wires. First, in
addition to parallel wires that each hold data, parallel interfaces generally include other wires that enable the sender
and receiver to coordinate. Second, to create installation and troubleshooting simply, wires for parallel transmission
systems are located in a single physical cable. Thus, one expects to view a single, large cable connecting the sender
and receiver rather than a set of independent physical wires.
Serial Transmission:
When data is sent or received using serial data transmission, data bits are organized in specific order, since they can
only be sent one after another. The order of data bits is important as it dictates how transmission is organized when
it is received. It is viewed as a reliable data transmission method because the data bit is only sent if the previous data
bit has already been received. It has two classifications: Asynchronous Serial Transmission & Synchronous Serial
Transmission
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