Which is the correct order of OSI layers from bottom (1) to top (7)?

Physical, Data link, Network, Transport, Session, Presentation, Application

Physical, Network, Data link, Transport, Session, Presentation, Application

Physical, Data link, Network, Transport, Presentation, Session, Application

Data link, Physical, Network, Transport, Session, Presentation, Application

Which set of functions belongs to the presentation layer?

Translation, encryption/decryption and compression

What happens to data as it passes down the layers on the sending side?

Each layer adds its own header, and the receiver removes them in the same order going up

Only the physical layer adds a header

Headers are added only at the application layer

Asked 2/11
2070 Asar · 8 marks
2074 Chaitra · 5 marks
Year not given

Explain OSI model and its layers

Short answer

OSI has seven layers: physical transmits bits, data link frames with MAC and error control, network does IP addressing and routing, transport provides process-to-process delivery, session controls dialog and sync, presentation handles translation and encryption, and application gives user services. Data is encapsulated down and decapsulated up.

Explain the layers of the OSI reference model with an appropriate figure.

The OSI (Open Systems Interconnection) model by ISO divides network communication into seven layers. Each layer uses the services of the layer below and gives services to the layer above. Peer layers on two machines talk through protocols.

 Sender                         Receiver
+----------------+           +----------------+
| 7 Application  |<--------->| 7 Application  |
| 6 Presentation |<--------->| 6 Presentation |
| 5 Session      |<--------->| 5 Session      |
| 4 Transport    |<--------->| 4 Transport    |
| 3 Network      |<--------->| 3 Network      |
| 2 Data link    |<--------->| 2 Data link    |
| 1 Physical     |<--------->| 1 Physical     |
+----------------+           +----------------+
        \_______ transmission medium _______/

1. Physical layer

Transmits raw bits over the medium. It defines voltage levels, bit timing (data rate), synchronization, connectors, topology and transmission mode (simplex, half duplex, full duplex).

2. Data link layer

Moves frames node to node. Functions: framing, physical (MAC) addressing, flow control, error detection and correction (CRC), and media access control.

3. Network layer

Delivers packets from source host to destination host across networks. Functions: logical (IP) addressing, routing, fragmentation and congestion control.

4. Transport layer

Process-to-process (end-to-end) delivery. Functions: port (service-point) addressing, segmentation and reassembly, connection control, end-to-end flow control and error control (TCP, UDP).

5. Session layer

Establishes, manages and terminates sessions. Functions: dialog control (who transmits when) and synchronization using checkpoints for recovery.

6. Presentation layer

Deals with syntax and semantics of the data. Functions: translation between character codes, encryption and decryption, and compression.

7. Application layer

Gives the user (or application) access to the network. Services: file transfer (FTP), mail (SMTP), web (HTTP), remote login (Telnet), directory services.

Data is wrapped with a header at each layer on the sending side (encapsulation) and removed in the reverse order, layer by layer, at the receiver (decapsulation).

✓ Answer checked by Claude Opus 5.5 (high effort)

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