OSI Model By W. Graham

1.

Put the upper layers of the OSI model are, in correct order

A.

Session, application, presentation
B.

Application, presentation, session, transport
C.

Session, presentation, application
D.

Session, application, presentation, physical
E.

None of the above

Correct Answer
C. Session, presentation, application

Explanation
Session Layer: The session layer manages communication sessions between devices. It establishes, maintains, and terminates connections, as well as manages synchronization and checkpointing.
Presentation Layer: The presentation layer is responsible for data translation, encryption, and compression. It ensures that data exchanged between applications is formatted correctly and can be understood by the receiving system.
Application Layer: The application layer provides network services directly to end-users and applications. It includes protocols for tasks such as file transfer, email, web browsing, and remote access.

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2.

Routers operate at which layer of the OSI model?

A.

Physical
B.

Transport
C.

Network
D.

MAC sublayer of the data link layer
E.

Session

Correct Answer
C. Network

Explanation
Routers operate at the network layer of the OSI model. The network layer is responsible for routing packets across different networks. Routers use routing tables to determine the best path for forwarding packets to their destination. They examine the network layer header of incoming packets and make routing decisions based on the destination IP address. Routers also perform functions such as packet filtering, network address translation (NAT), and network congestion control.

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3.

Bits are packaged into frames at which layer of the OSI model?

A.

Data link
B.

Transport
C.

Physical
D.

Presentation
E.

Application

Correct Answer
A. Data link

Explanation
Frames are a unit of data that are used to transmit information over a network. The process of packaging bits into frames occurs at the data link layer of the OSI model. This layer is responsible for establishing and maintaining reliable communication between adjacent nodes on a network. It takes the raw stream of bits from the physical layer and organizes them into frames, adding necessary control information for error detection and correction. Therefore, the correct answer is data link.

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4.

Which of the following are benefits of using a layered network model (Tick all that apply)

A.

It specifies how changes to one layer must be propagated through the other layers
B.

It facilitates troubleshooting
C.

It focuses on details rather than general functions of networking
D.

It breaks the complex process of networking into more manageable chunks
E.

It allows layers developed by different vendors to interoperate.

Correct Answer(s)
B. It facilitates troubleshooting
D. It breaks the complex process of networking into more manageable chunks
E. It allows layers developed by different vendors to interoperate.

Explanation
The benefits of using a layered network model include facilitating troubleshooting by isolating and identifying issues within specific layers, breaking the complex process of networking into more manageable chunks, and allowing layers developed by different vendors to interoperate. This model helps in identifying and resolving network problems more efficiently, simplifies the understanding and implementation of networking protocols, and promotes compatibility and interoperability between different networking technologies and products.

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5.

The layers of the OSI model, from the 1 to 7 are:

A.

Application, presentation, session, transport, network, data link, physical
B.

Physical, data link, network, transport, session, presentation, application
C.

Session, presentation, data transport, MAC, network, physical
D.

Presentation, application, session, network, transport, data link, physical
E.

Application, encryption, network, transport, logical link control, physical

Correct Answer
B. pHysical, data link, network, transport, session, presentation, application

Explanation
The layers of the OSI model are organized in a specific order to ensure effective communication between network devices. The physical layer is responsible for transmitting raw data over the physical medium. The data link layer provides error-free transmission of data frames between adjacent nodes. The network layer handles routing and logical addressing to enable communication between different networks. The transport layer ensures reliable delivery of data between end systems. The session layer establishes, manages, and terminates sessions between applications. The presentation layer is responsible for data formatting and encryption. Finally, the application layer provides services directly to the end-user applications.

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6.

Which of the following operate at the presentation layer?

A.

MIDI
B.

FTP
C.

SMTP
D.

TFTP
E.

JPEG

Correct Answer(s)
A. MIDI
E. JPEG

Explanation
MIDI and JPEG operate at the presentation layer. MIDI is a protocol used for communicating musical information between devices, and it is responsible for converting musical data into a format that can be understood by different devices. JPEG is a file format used for compressing and storing digital images, and it is responsible for encoding and decoding image data. The presentation layer is responsible for formatting and presenting data in a way that can be understood by the receiving device, and both MIDI and JPEG perform this function. FTP, SMTP, and TFTP operate at the application layer.

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7.

Which of the following are transport layer protocols?

A.

FTAM
B.

IP and TFTP
C.

TFTP
D.

TCP and UDP
E.

IP

Correct Answer
D. TCP and UDP

Explanation
TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) are both transport layer protocols. The transport layer is responsible for the reliable delivery of data between hosts on a network. TCP provides a connection-oriented and reliable data transfer mechanism, ensuring that all packets are received in the correct order. UDP, on the other hand, is a connectionless and unreliable protocol that allows for faster transmission of data but does not guarantee delivery or order. Both TCP and UDP are widely used in networking applications to facilitate communication between devices.

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8.

Flow control takes place at which layer?

A.

Physical
B.

Transport
C.

Network
D.

MAC sublayer of the data link layer
E.

Session

Correct Answer
B. Transport

Explanation
Flow control takes place at the transport layer. This layer is responsible for ensuring the reliable delivery of data between two endpoints. Flow control mechanisms are used to manage the rate of data transmission, preventing the sender from overwhelming the receiver. By regulating the flow of data, the transport layer ensures that the receiver can handle the incoming data at a pace it can handle, thus preventing congestion and data loss.

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9.

Encryption takes place at which layer?

A.

Application
B.

Presentation
C.

Session
D.

Transport
E.

Data link

Correct Answer
B. Presentation

Explanation
Encryption takes place at the presentation layer of the OSI model. This layer is responsible for the formatting and encryption of data to be transmitted across a network. It ensures that the data is in a format that can be understood by the receiving system and also provides security measures such as encryption to protect the data during transmission.

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10.

True or False: The network layer uses physical addresses to route data to destination hosts.

A.

True
B.

False

Correct Answer
B. False

Explanation
The network layer does not use physical addresses to route data to destination hosts. Instead, it uses logical addresses, such as IP addresses, to identify and route data packets to their intended destinations. Physical addresses, also known as MAC addresses, are used at the data link layer to identify devices within a local network.

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