Top 10 Interview Questions & Answers | OSI Model

OSI model is an important concept if you want to understand networking. Remember, the OSI model is not a network architecture as it is not specified services and protocols at each layer. OSI model is helpful in giving an idea related to the functionality of each layer and what are the inflows and outflows from different layers. Today we will discuss the most asked interview questions on the OSI model.

Q1. Define OSI layers.

Ans: OSI stands for Open System Interconnection. There are 7 layers in the OSI model and each layer has a different capability. OSI model helps networking professionals in understanding information flow from one source to destination. Although the OSI model does not perform any function in the networking process.

Remember, all devices and software applications use the OSI model to explain data flow between source and destination.

OSI Model Information Flow

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Q2. Are there any alternative models to the OSI model? If yes, define it.

Ans: TCP/IP is the alternate model that also explains the information flow in the network. It is a simpler representation compared to the OSI model but contains fewer details of protocols than the OSI model.

Q3. What is the difference between TCP and UDP?

Ans: TCP and UDP: Comparison between Two Transport Protocols

 TCPUDP
AcronymTransmission Control ProtocolUser Datagram Protocol
ConnectionConnection Oriented ProtocolConnection Less Protocol
FunctionMessage transfer from source to destination in an ordered and error-checked stream.Message transfer from one point to another without checking any order and any error in the stream.
UsageHigh reliability
More transmission time
Low reliability
Less transmission time
ReliabilityGuarantee Data transfer and arrives in the same order in which it was sent.No guarantee that the messages or all packets sent would reach from source to destination.
Other protocolsHTTP, HTTPs, FTP, SMTP, TelnetDNS, DHCP, TFTP, SNMP, RIP, VOIP
Header sizeTCP header size is 20 bytesUDP header size is 8 bytes
HeadersFields in TCP Header
1. Sequence Number,
2. AcK number,
3. Data offset,
4. Reserved,
5. Control bit,
6. Window,
7. Urgent Pointer
8. Options,
9. Padding,
10. CheckSum,
11. Source port,
12. Destination port
Fields in UDP Header
1.Length,
2.Source port,
3.Destination port,
4.CheckSum
HandshakeThree-way handshakeNo handshake
Data Flow ControlIt controls the flow of dataDoes not have an option for flow control of data

Q4. What is the importance of the Physical Layer in the OSI model?

Ans: Physical layer is the first layer that connects systems physically and resembles the actual transfer of information from source to destination in the form of bitstream - electrical impulse, light, or radio signal. In simple words, it accepts a frame from the data link layer and converts it into bits. It also accepts bits from the physical medium and converts them into the frame. It helps in managing the Network Interface Card's (NIC) hardware interface such as cabling, voltage levels, etc.
Standard protocols for this layer are EIA/TIA-232, EIA/TIA-449, X.21, HSSI, V.24, V.35, and SONET.

Q5. Which layers perform error detection and flow control?

Ans:  On receiving and while transmission of information, Layer 2 - Data Link layer decoded and encoded data into bits. This layer is the firmware layer of NIC. It converts datagrams into frames and also adds start and stop flags to each frame.

The data link layer is further divided into two sublayers: The Media Access Control (MAC) layer and the Logical Link Control (LLC) layer. This layer also performs error checking and flow control.

Q6. How does the network administrator detect the problem?

Ans: Network administrators may use the OSI model to understand the information flow and try to find problems by further understanding each layer's protocols. Experience in networking reduces the time to find problems and resolve them. Network problems may be a loose physical connection, configuration issues, etc.

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Q7. What is the difference between flow control and error control?

Ans: As the name suggests, flow control controls the rate of information transmitted to ensure the receiver's efficient delivery of data. While error controls check and correct errors in the data bits and packets.

Q8. What is Data encapsulation?

Ans: Data encapsulation is a process of adding extra information at each layer of the OSI model while information flow from one host to another host. Information such as source and destination address, protocol information, type of data, etc.

Q9. What are the differences between the MAC sublayer and LLC sublayer?

Ans: MAC sublayer stands for Media Access Control layer.  MAC address works on Layer 2- Data Link Layer. This layer controls the permission of data to transmit.

LLC sublayer stands for Logical Link Control layer. This layer controls frame synchronization, flow control, and error checking.

Q10. What is the difference between half-duplex and full-duplex?

Ans: In a half-duplex, information can flow in both directions but not simultaneously. While in full-duplex, information can flow in both directions simultaneously.

Miscellaneous Questions

Q. Explain the role of the presentation layer.

Ans: The presentation layer is number 6 in the OSI model. On the sending system, It will receive data from the application layer, transform and encrypt in a legible format and pass it to the session layer. On the receiving system, simply converts the incoming data from the session layer so that data is readable at the application layer.

Q. Explain the role of the Transport layer.

Ans: The presentation layer is number 4 in the OSI model. I am listing different roles of the transport layer as mentioned below:

  1. to check the reliability of data
  2. flow control of data
  3. to check the order of data
  4. ensure the reliability of data
  5. to prevent congestion

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Disclaimer: This tutorial is for educational purpose only. Individual is solely responsible for any illegal act.

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1 Response

  1. Brendan Jendras says:

    Way cool! Some extremely valid points! I appreciate you writing this post plus the rest of the website is very good.

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