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Mobiprep has created last-minute notes for all topics of Computer networks to help you with the revision of concepts for your university examinations. So let’s get started with the lecture notes on Computer networks.
Our team has curated a list of the most important questions asked in universities such as DU, DTU, VIT, SRM, IP, Pune University, Manipal University, and many more. The questions are created from the previous year's question papers of colleges and universities.
Network Models
Question 1) What is the need of using layered architecture in networking?
Answer) In layered network architecture, several communication functions are combined together to form groups called layers. The layered architecture clearly defines the functionalities of each layer and the interaction between the layers. It helps parallel execution of different parts of an application with minimal dependency. It enables the development of loosely coupled systems. Hence, layered architecture is preferred for computer networks.
Question 2) What is meant by reference model?
Answer) In layered network architecture, several communication functions are combined together to form groups called layers. The layered architecture clearly defines the functionalities of each layer and the interaction between the layers. It helps parallel execution of different parts of an application with minimal dependency. It enables the development of loosely coupled systems. Hence, layered architecture is preferred for computer networks.
Question 3) Define OSI network model. explain it with a diagram.
Answer) OSI – Open System Interconnection
The OSI Model is a conceptual reference framework that has seven different layers. It is the universal standard for computer networking. It provides the standards for communication between the computer systems. The whole process of communication is divided into different tasks (or layers) which are independent of each other.
Question 4) What are the layers in the OSI model? what are their functions?
Answer) The seven different layers in the OSI model are:
1. APPLICATION LAYER
a. The application layer provides user interface.
b. Services provided by application layer:
Network virtual terminal
File transfer, access and management
Mail services
Directory services
c. Example: E-mail
2. PRESENTATION LAYER
a. This layer is concerned with the syntax and semantics of the information exchanged between two segments
b. Responsible for
i. Translation :
Information usually consists of character strings, number and so on.
Information must be changed into bit streams before being transmitted. This is called translation.
ii. Compression
Compression reduces number of bits contained in the information.
iii. Encryption
Encryption is done to ensure privacy.
3. SESSION LAYER
This layer acts as a network dialog controller.
This layer is responsible for dialog control and synchronization.
The session layer is responsible for establishment, maintenance and synchronization of interaction between communication systems.
4. TRANSPORT LAYER
a. The transport layer is responsible for process to process delivery of the entire message.
b. The transport layer ensures that the whole message arrives intact and in order at the receiver.
c. Responsibilities of transport layer:
i. Service-point addressing
ii. Segmentation and reassembly
Message is divided into segments, with each segment containing a sequence number
This sequence number helps in reassembly of messages correctly at the destination
iii. Connection control
iv. Flow control (between source and destination)
v. Error control
5. NETWORK LAYER
a. The network layer is responsible for host to host delivery is responsible for delivery of individual packets from the source host to the destination host.
b. It ensures that each packet gets from the point of origin to its final destination.
c. Responsibilities of network layer:
Logical addressing (IP)
Routing
Fragmentation
6. DATALINK LAYER
The data link layer is responsible for hop to hop delivery
Responsibilities of the data link layer
Hop to hop delivery
Framing
Physical addressing
Flow control
Managing the data rate at sender and receiver at the same pace.
Error control
Detection and retransmission of lost frames is done
It adds reliability of the data to physical layer
Access control :
When two or more devices are connected to the same link, datalink protocols determine which device has control over the link at any point of time
Methods – CSMA-CD, Aloha, Token ring or token bus
7. PHYSICAL LAYER
The physical layer converts the data bits into signals which can be transmitted over the medium
Physical layer is responsible for movements of individual bits from one hop (node) to the next
Data in physical layer consists of stream of bits (0’s and 1’s). These must be encoded into signals –- electrical or optical
Question 5) Mention some protocols that are used in each layer of the OSI model?
Application Layer - HTTPS, HTTPS, SMTP, FTP
Presentation Layer - JPEG, JPG, PNG, GIF, MIME
Session Layer - SQL, NFS, ASP, RPC
Transport Layer - TCP, UDP
Network Layer - IP, ICMP, IGMP
Data link Layer - PPP, HDLC, Ethernet
Physical Layer - RJ45, ST/SC, V Series
Question 6) Explain TCP/IP protocol suite.
Answer) The TCP/IP protocol suite is a set of hierarchical protocols which is used to provide end-to-end communication between the computer systems. It is a concise version of the OSI Model. It is a more practical model when compared to the OSI model. It consists of four layers. They are:
Application layer
Transport layer
Internet layer
Host to network layer
The following diagram shows the comparison between the TCP/IP and the OSI models.
Question 7) What are the layers in the tcp/ip model? what are their functions?
Answer) a. Application layer
It is the top-most layer in the TCP/IP model
This layer is the combination of the application layer, presentation layer and the session layer in the OSI model.
The functions of the application layer are:
Process to process communication and
Provision of user interface
b. Transport layer
The functions of this layer is similar to the transport layer in the OSI model
The functions of the transport layer are:
Message segmentation
Traffic control
Error detection and correction
Session multiplexing and
Message reordering
c. Internet layer
This layer is similar to the network layer in the OSI model
The functions of the internet layer are:
Logical addressing
Traffic control and
Routing
d. Host to network layer
The data link layer and the physical layers are combined to form the host-to-network layer. The functions of the host-to-network layer are:
Frame synchronization
Line coding
Error detection
Bit synchronization
Question 8) What is the difference between OSI model and TCP/IP model?
Answer)
OSI Model | TCP/IP Model |
It is based on Layered functioning. | It is based on Protocols used |
Has 7 layers | Has 4 layers |
It is a theoretical model | It is a practical model |
Vertical approach is followed | Horizontal Approach is followed |
Multiple layers can work in parallel | |
Provides both connection-oriented and connectionless service. | Provides connectionless service only. |
Protocol replacement is not easy | Protocol replacement is easy. |
Has separate Presentation layer and session layer | Does not have separate presentation layer and session layer. |
The transport layer guarantees the delivery of packets | The transport layer does not guarantee the delivery of packets |
Question 9) What is SAP, PDU, and SDU?
Answer) SAP
SAP – Service Access Point
SAP is an identifier to the buffer area in the memory.
It identifies the protocol handler that is used to process the incoming frame.
It is used to define the communication between the layers in the OSI Model.
PDU
PDU – Protocol Data Unit
PDU is the unit of data of a particular layer in OSI model
The OSI model has seven PDUs (for seven Layers)
The following are the PDUs used in each layer of the OSI Model
LAYER | PDU |
Application layer | Data |
Presentation layer | Data |
Session layer | Data |
Transport layer | Segment or datagram |
Network layer | Packet |
Datalink layer | Frame |
Physical layer | Bits |
SDU
SDU – Service Data Unit
SDU is the data unit that has been passed from an OSI layer to the sub-layer (or the layer below it)
The lower layer encapsulates the SDU from its upper layer to form the PDU.
Question 10) What role does interface plays in a networking?
Answer) The interface (Network Interface Card) helps the computer to connect to the network. It provides dedicated network connection to the computer. It enables both intra-network and inter-network communications. It works in the data link layer and the physical layer. Each NIC has a MAC address which is used to uniquely identify the computer system. Hence, the NIC is a very important component for communication in the computer network.
Question 11) What are various connection oriented and connectionless services?
Answer) Connection oriented service
In connection oriented services, the connection is established prior to the beginning of communication session. A dedicated channel is established between the sender and the receiver. The following are the steps followed in connection oriented service:
Connection establishment
Data transfer
Connection termination
The connection oriented service is more reliable and secure than the connectionless service.
Connectionless service
In connectionless service, the connection is not established prior to the beginning of the communication session. The data is routed independently from source to destination. There is no dedicated path between the source and destination. The packets of the same data do not follow the same path. Hence, they are received out of order at the destination.
The connectionless service is unreliable and insecure. But, it is much faster and cheaper than the connection oriented service.
Question 12) How PDU'S are used in TCP/IP model?
Answer) The steps involved in encapsulation of PDUs and SDUs are given below:
The top-most layer (Layer 4) sends the message called ‘segment’ to layer 3. Segment is the PDU of the layer 4.
The segments are SDUs of layer 3. These are encapsulated into Packets at layer 3 (internet layer). Then, the packets are sent to layer 2. (Packets are the PDUs of layer 3).
Layer 2 encapsulates the packets into Ethernet Frames (PDU of layer 2)
Question 13) Explain various types of addresses used in data transfer?
Answer) The different types of addresses used in data transfer are:
IP address
The IP address is a logical address which is used to locate a computer uniquely in a network. It is assigned by the Internet Service Provider. It is a 32-bit (IPv4) or 48-bit (IPv6) address. It contains both network id and host id.
MAC address
The MAC address is the physical address which is used to uniquely identify a hardware device in the network. The MAC address is used in the data link layer. It is assigned by the manufacturer. It is a 48-bit address.
Port address
The port address is the logical address given to each process that uses the network. The port address is assigned by the operating system. It is a 16 bit address.
Question 14) What do you understand by physical address and how it is different from logical address?
Answer) Physical Address
The Physical address is a unique address given to the hardware. It is also called MAC address or hardware address. The MAC address is given to the NIC card of a computer system. The MAC address works at the Data Link Layer.
The MAC address is a 48 bit address which acts as a fingerprint to the hardware device. So, totally 248 devices can be addressed using the MAC address. The address is divided into 2 parts, each of 2 hexadecimal digits. The first three parts represent the manufacturer and the next three parts represent the host.
Physical Address | Logical Address |
It is also called MAC address | It is also called IP address. |
It is a 48-bit address. | It is a 32-bit (IPv4) or 48-bit (IPv6) address |
It is assigned by the manufacturer | It is assigned by the Internet Service Provider |
It is unique for a Hardware Device. | It is not unique for a Hardware device. But it is unique for a network. |
Cannot be changed | Can be changed. |
Used by the datalink layer | Used by the network layer. |
A third party device cannot find the MAC address easily. | A third party device can find the Mac address easily. |
Example: 02-D0-56-F2-A5-12 | Example: 192.168.1.1 |
Question 15) What do you understand by serial and parallel transmission?
Answer) Serial transmission
In serial transmission, only one bit is transmitted at a time. The bits are transmitted one by one. Here, the data flows in a single line. Hence, it is slow.
Serial transmission is less expensive than parallel transmission as it involves only one line for transmission.
Parallel Transmission
In parallel transmission, many bits are transmitted at a time. The bits are transmitted parallel. Here, the data flows in multiple lines. Hence, parallel transmission is much faster than serial communication.
Parallel transmission is more expensive than serial transmission.
