OSI models

Q: What is the primary role of the Physical Layer?

A: To transmit raw bits over a physical medium as signals.

Q: What are some transmission modes defined at this layer?

A: Simplex, Half-duplex, Full-duplex.

Q: Name devices that operate at the Physical Layer.

A: Hubs, Repeaters, NICs, Cables.

Q: Give examples of physical media used at this layer.

A: Fiber optics, Ethernet cables, radio waves.

Q: Does the Physical Layer understand data or meaning?

A: No, it only transmits electrical/optical signals, not content.

Q: What is the main function of the Data Link Layer?

A: MAC and LLC.

Q: What does the MAC sublayer handle?

A: Access to the medium and MAC addressing.

Q: Which devices operate at Layer 2?

A: Switches, Bridges, NICs.

Q: What addressing system does this layer use?

A: MAC address (physical hardware address).

Q: What type of data unit is used at Layer 2?

A: Frame.

Q: What is the main function of the Network Layer?

A: Routing and logical addressing using IP.

Q: What data unit is used in this layer?

A: Packet.

Q: Which devices operate at this layer?

A: Routers, Layer 3 switches.

Q: Name 3 common protocols in Layer 3.

A: IPv4/IPv6, ICMP, ARP.

Q: What is fragmentation and why does it happen?

A: Splitting large packets into smaller ones due to size limits (MTU).

Q: Does MAC addressing happen at Layer 3?

A: No, MAC is at Layer 2 — this layer uses IP addresses.

Q: What is the primary function of the Transport Layer?

A: End-to-end data delivery, segmentation, and port management.

Q: What are the two main Layer 4 protocols?

A: TCP and UDP.

Q: Which protocol is reliable and uses acknowledgments?

A: TCP.

Q: What does the Transport Layer use to identify applications?

A: Port numbers.

Q: Which layer is responsible for segmenting data?

A: Layer 4 – Transport Layer.

Q: What's the data unit at this layer?

A: Segment (TCP) or Datagram (UDP).

Q: What does the Session Layer do?

A: Establishes, manages, and terminates communication sessions.

Q: Give a real-world example of session layer in action.

A: Zoom call, FTP login session, large file download resuming.

Q: What is dialog control?

A: Manages which party can send/receive data at a time (e.g., turn-taking in communication).

Q: What is checkpointing?

A: A mechanism to save session state so it can resume after failure.

Q: What’s the data unit at this layer?

A: Still considered "Data" — session doesn't define a new unit.

Q: What is the main role of the Presentation Layer?

A: To format, encrypt, and compress data for the application/user.

Q: What kind of encryption is handled here?

A: TLS/SSL for HTTPS and secure communication.

Q: Give examples of data formatting at this layer.

A: JPEG ↔ Bitmap, ASCII ↔ Unicode.

Q: What is data compression used for?

A: To reduce file size for faster transfer (e.g., ZIP, MP3).

Q: Does this layer understand content meaning?

A: No — it only prepares data for the Application Layer.

Q: What is the function of the Application Layer?

A: To provide network services to end-user applications.

Q: Is Layer 7 the same as your software app (e.g., Chrome)?

A: No — it’s the interface between the app and network protocols.

Q: Give examples of Application Layer protocols.

A: HTTP, FTP, SMTP, DNS, Telnet.

Q: What are common services at this layer?

A: Web access, email, file transfer, name resolution.

Q: Why is this layer important?

A: It enables users and applications to use the network.