modul6-Data Link Layer Overview

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Questions and Answers

What is the primary function of the Data Link Layer in the OSI model?

  • Handles networking protocols at the application layer.
  • Encapsulates application data into transport packets.
  • Responsible for end-to-end communication across different networks.
  • Manages NIC-to-NIC communications on the same physical network. (correct)

Which sublayer of the Data Link Layer is defined by IEEE 802.2?

  • Media Access Control (MAC)
  • Logical Link Control (LLC) (correct)
  • Frame Relay Control (FRC)
  • Network Interface Card (NIC)

Which access method is used in legacy shared networks like hubs?

  • Mesh Networking
  • Full-Duplex
  • Point-to-Point
  • Half-Duplex (correct)

What type of addressing is unique to each NIC and used for local delivery?

<p>MAC Addressing (D)</p> Signup and view all the answers

Which of the following describes CSMA/CD?

<p>A contention-based method used to detect collisions in Ethernet hubs. (C)</p> Signup and view all the answers

Which topology is characterized by one central router connected to multiple branches?

<p>Hub-and-Spoke (B)</p> Signup and view all the answers

Which is NOT a typical data link layer protocol?

<p>HTTP (B)</p> Signup and view all the answers

When a frame crosses a router to reach a new network, which addressing is updated?

<p>Layer 2 (MAC) addresses (C)</p> Signup and view all the answers

Flashcards

Data Link Layer

OSI Layer 2, responsible for communication between network interface cards (NICs) on the same physical network, encapsulating Layer 3 packets into frames for transmission.

Encapsulation

The process of wrapping a Layer 3 packet (like an IP packet) inside a frame with additional headers and trailers for transmission over the local network.

Frame Structure

The structure of a data frame in the Data Link Layer, typically including a header with Layer 2 addresses, the data itself, and a trailer for error checking.

LLC (Logical Link Control)

A sublayer of the Data Link Layer defined by IEEE 802.2, responsible for communication with upper-layer protocols (like IP) and identifying the Layer 3 protocol within the frame.

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MAC (Media Access Control)

A sublayer of the Data Link Layer responsible for data link addressing (source & destination MAC addresses), frame delimiting, error detection (FCS), and media access control.

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Half-Duplex

A method of network access where only one device transmits at a time, commonly used in legacy shared networks like those with hubs.

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Full-Duplex

A method of network access where devices can transmit and receive data simultaneously, typical in modern switched Ethernet.

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Contention-Based Access

A method of network access where devices contend for access to the shared medium, using techniques like CSMA/CD or CSMA/CA to prevent collisions.

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Study Notes

  • Layer 2 is responsible for communication between network interface cards (NICs) on the same physical network.
  • Encapsulates Layer 3 packets (IP packets) into frames for transmission.
  • Frame structure typically includes a header (source/destination Layer 2 addresses), data (Layer 3 packet), and a trailer (error detection, e.g., FCS/CRC).

Sublayers: LLC and MAC

  • Logical Link Control (LLC): Defined by IEEE 802.2; communicates with upper-layer protocols (like IP); identifies the Layer 3 protocol within the frame.
  • Media Access Control (MAC): Handles data link addressing (source and destination MAC addresses); manages frame delimiting, error detection (FCS), and media access (how devices share the medium).

Media Access Control Methods

  • Half-Duplex: One device transmits at a time; used in legacy shared networks (hubs); contention-based access (CSMA/CD or CSMA/CA).
  • Full-Duplex: Devices can transmit and receive simultaneously; common in modern switched Ethernet.
  • Contention-Based Access (Shared Media):
    • CSMA/CD (Ethernet hubs): detects collisions.
    • CSMA/CA (Wireless LAN): avoids collisions; uses acknowledgments.

Network Topologies

  • Physical Topology: Physical layout (e.g., star, extended star, point-to-point).
  • Logical Topology: How data flows through the network (often star or bus logically).
  • WAN Topologies:
    • Point-to-point: Simplest, direct link.
    • Hub-and-spoke: Central router to many branches.
    • Mesh: Multiple interconnected routers.
  • LAN Topologies:
    • Star/Extended Star: Most common for Ethernet.
    • Bus and Ring: Legacy.

Layer 2 Addressing (MAC Addresses)

  • MAC addresses are unique physical addresses for each NIC or interface; used for local delivery on the same network.
  • Frames only contain MAC addresses within the same network segment.
  • Routers update MAC addresses when frames cross to new networks.
  • Ethernet (IEEE 802.3)
  • 802.11 Wireless LAN
  • WAN protocols (PPP, HDLC, Frame Relay, etc.) - often replaced by Ethernet in modern WANs.

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