CSS Prepare

optional · CSS study notes

Physical & Data Link Layer

  • Error Detection & Control: parity bits, checksums, CRC (Cyclic Redundancy Check) for detecting transmission errors
  • ARQ (Automatic Repeat reQuest): error-control method that requests retransmission of corrupted/lost frames
  • Link layer addressing: MAC addresses — unique hardware identifiers, unlike IP addresses which are logical/assignable
  • LAN technologies: Ethernet (wired standard), Wi-Fi (wireless standard)
  • Bridges connect/filter traffic between LAN segments at the data link layer; Hubs simply repeat/broadcast signals to all ports at the physical layer (no intelligence)
  • Multiple Access protocols: CSMA/CD (Collision Detection, used in classic wired Ethernet) and CSMA/CA (Collision Avoidance, used in Wi-Fi)

MCQ Trap

  • Hubs operate at the Physical layer (no filtering); Bridges/Switches operate at the Data Link layer (filter by MAC address).