OSI Model

OSI Models Basics and Multiple choice Questions-Answers

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What is the OSI Model?

The OSI Model (Open Systems Interconnection Model) is a conceptual framework used to describe the functions of a networking system. The OSI model characterizes computing functions into a universal set of rules and requirements in order to support interoperability between different products and software. In the OSI reference model, the communications between a computing system are split into seven different abstraction layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application.

Created at a time when network computing was in its infancy, the OSI was published in 1984 by the International Organization for Standardization (ISO). Though it does not always map directly to specific systems, the OSI Model is still used today as a means to describe Network Architecture.

The 7 Layers of the OSI Model

Physical Layer

The lowest layer of the OSI Model is concerned with electrically or optically transmitting raw unstructured data bits across the network from the physical layer of the sending device to the physical layer of the receiving device. It can include specifications such as voltages, pin layout, cabling, and radio frequencies. At the physical layer, one might find “physical” resources such as network hubs, cabling, repeaters, network adapters or modems.

Data Link Layer

At the data link layer, directly connected nodes are used to perform node-to-node data transfer where data is packaged into frames. The data link layer also corrects errors that may have occurred at the physical layer.

The data link layer encompasses two sub-layers of its own. The first, media access control (MAC), provides flow control and multiplexing for device transmissions over a network. The second, the logical link control (LLC), provides flow and error control over the physical medium as well as identifies line protocols.

Network Layer

The network layer is responsible for receiving frames from the data link layer, and delivering them to their intended destinations among based on the addresses contained inside the frame. The network layer finds the destination by using logical addresses, such as IP (internet protocol). At this layer, routers are a crucial component used to quite literally route information where it needs to go between networks.

Transport Layer

The transport layer manages the delivery and error checking of data packets. It regulates the size, sequencing, and ultimately the transfer of data between systems and hosts. One of the most common examples of the transport layer is TCP or the Transmission Control Protocol.

Session Layer

The session layer controls the conversations between different computers. A session or connection between machines is set up, managed, and termined at layer 5. Session layer services also include authentication and reconnections.

Presentation Layer

The presentation layer formats or translates data for the application layer based on the syntax or semantics that the application accepts. Because of this, it at times also called the syntax layer. This layer can also handle the encryption and decryption required by the application layer.

Application Layer

At this layer, both the end user and the application layer interact directly with the software application. This layer sees network services provided to end-user applications such as a web browser or Office 365. The application layer identifies communication partners, resource availability, and synchronizes communication.

Physical Layer (OSI Model) Interview/Exam Question-Answer

Q.1 The physical layer is concerned with ___________.

       A. bit-by-bit delivery

       B. process to process delivery

       C. application to application delivery

       D. port to port delivery

Ans : bit-by-bit delivery

Q.2 Which transmission media provides the highest transmission speed in a network?

       A. coaxial cable

       B. twisted pair cable

       C. optical fiber

       D. electrical cable

Ans : optical fiber

Q.3 Bits can be sent over guided and unguided media as analog signal by ___________.

       A. Digital Modulation

       B. Amplitude Modulation

       C. Frequency Modulation

       D. Phase Modulation

Ans : Digital Modulation

Q.4 The portion of physical layer that interfaces with the media access control sublayer is called ___________.

       A. physical signalling sublayer

       B. physical data sublayer

       C. physical address sublayer

       D. physical transport sublayer

Ans : physical signalling sublayer

Q.5 The physical layer provides __________.

       A. mechanical specifications of electrical connectors and cables

       B. electrical specification of transmission line signal level

C. specification for IR over optical fiber

       D. All of the above

Ans : All of the above

Q.6 In asynchronous serial communication the physical layer provides ___________.

       A. start and stop signalling

       B. flow control

       C. both start & stop signalling and flow control

       D. only start signalling

Ans : both start & stop signalling and flow control

Q.7 The physical layer is responsible for __________.

       A. line coding

       B. channel coding

       C. modulation

       D. All of the above

Ans : All of the above

Q.8 The physical layer translates logical communication requests from the ______ into hardware specific operations.

       A. data link layer

       B. network layer

       C. trasnport layer

       D. application layer

Ans : data link layer

Q.9 A single channel is shared by multiple signals by ____________.

       A. analog modulation

       B. digital modulation

       C. multiplexing

       D. phase modulation

Ans : multiplexing

Q.10 Wireless transmission of signals can be done via ___________.

  A. radio waves

       B. microwaves

       C. infrared

       D. all of the above

Ans : all of the above

Data Link Layer (OSI Model) Interview/Exam Question-Answer

Q.1 The data link layer takes the packets from _________ and encapsulates them into frames for transmission.

. network layer

       B. physical layer

       C. transport layer

       D. application layer

Ans : network layer

Q.2 Which of the following tasks is not done by data link layer?

       A. framing

       B. error control

       C. flow control

       D. channel coding

Ans : channel coding

Q.3 Which sublayer of the data link layer performs data link functions that depend upon the type of medium?

       A. logical link control sublayer

       B. media access control sublayer

       C. network interface control sublayer

       D. error control sublayer

Ans : media access control sublayer

Q.4 Header of a frame generally contains ______________.

       A. synchronization bytes

       B. addresses

       C. frame identifier

       D. all of the above

Ans : all of the above

Q.5 Automatic repeat request error management mechanism is provided by ________.

       A. logical link control sublayer

       B. media access control sublayer

C. network interface control sublayer

       D. application access control sublayer

Ans : logical link control sublayer

Q.6 When 2 or more bits in a data unit has been changed during the transmission, the error is called ____________.

       A. random error

       B. inverted error

       C. double error

       D. burst error

Ans : burst error

Q.7 CRC stands for __________.

       A. cyclic redundancy check

       B. code repeat check

       C. code redundancy check

       D. cyclic repeat check

Ans : cyclic redundancy check

Q.8 Which of the following is a data link protocol?

       A. ethernet

       B. point to point protocol

       C. hdlc

       D. all of the above

Ans : all of the above

Q.9 Which of the following is the multiple access protocol for channel access control?

       A. CSMA/CD

       B. CSMA/CA

       C. Both CSMA/CD & CSMA/CA

       D. HDLC

Ans : Both CSMA/CD & CSMA/CA

Q.10 The technique of temporarily delaying outgoing acknowledgements so that they can be hooked onto the next outgoing data frame is called ____________.

A. piggybacking

       B. cyclic redundancy check

       C. parity check

       D. fletcher’s checksum

Ans : piggybacking

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