[NW] 2nd : Data Link Layer

struraoΒ·2023λ…„ 3μ›” 25일
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Introduction


μ–΄λ–»κ²Œ μΆ©λŒμ„ ν”Όν•΄μ„œ λ‚΄ μ•žμ˜ λΌμš°ν„°κΉŒμ§€ 전달될 것인가?
MAC : Medium Access Control/Mutiple Access Protocol


Mac protocol

three broad classes:

βœ”οΈ Channel Partitioning

  • 이동톡신 (LTE) κ°€ μ‚¬μš©ν•˜λŠ” 방식
  • μ‚¬λžŒμ΄ λ§Žμ„ λ•Œ 효율적
  • share channel efficiently and fairly at high load
  • inefficient at low load: delay in channel access, I/N bandwidth allocated even if only I active node!
  • TDMA (Time Division Multiple Access)
  • FDMA (Frequency Division Multiple Access)

βœ”οΈ Random Access

  • 이더넷, μ™€μ΄νŒŒμ΄κ°€ μ‚¬μš©ν•˜λŠ” 방식
  • μ‚¬λžŒμ΄ 적을 λ•Œ 효율적
  • channel not divided, allow collisions
  • how to detect, recover from collisions
  • CSMA (Carrier Sense Multiple Access)
    • listen before transmit
    • 물리적 이유둜 좩돌이 λΆˆκ°€ν”Όν•˜λ‹€
    • κ·Έλ ‡λ‹€λ©΄ 좩돌의 damage λ₯Ό μ΅œμ†Œν™”ν•΄μ•Ό ν•œλ‹€
    • κ·Έλž˜μ„œ λ‚˜μ˜¨ 것이 CSMA/CD (collision detection)
      • frame 전솑 쀑, collision detection 좩돌 λ°œμƒ μ‹œ 전솑을 μ€‘λ‹¨ν•œλ‹€
      • random time ν›„ frame 을 μž¬μ „μ†‘ν•΄μ•Ό ν•œλ‹€ (random range κ°€ μ§§μ„μˆ˜λ‘ μ’‹λ‹€)
    • μΌμƒμƒν™œμ—μ„œ μš°λ¦¬κ°€ λŒ€ν™”ν•˜λŠ” 것과 λΉ„μŠ·ν•˜λ‹€
  • efficient at low load: single node can fully utilize channel
  • high load: collision overhead

βœ”οΈ Taking Turns

  • ν˜„μ‹€μ μœΌλ‘œ 많이 쓰이진 μ•ŠλŠ”λ‹€: single point of failure
  • look for best of both worlds!

Ethernet

frame structure

data 에 ip packet 이 λ“€μ–΄κ°„λ‹€
48 bit MAC address κ°€ λ“€μ–΄κ°„λ‹€


Wifi

frame structure


πŸ”— Reference

  • OSI 7계측
  • OSI 7계측 κ·Έλ¦Ό
  • [KOCW] 이석볡 κ΅μˆ˜λ‹˜μ˜ μ»΄ν“¨ν„°λ„€νŠΈμ›Œν¬ κ°•μ˜λ₯Ό μˆ˜κ°•ν•˜κ³  μ •λ¦¬ν•œ λ‚΄μš©μž…λ‹ˆλ‹€.

잘λͺ»λœ λ‚΄μš©μ΄ μžˆλ‹€λ©΄ λŒ“κΈ€λ‘œ μ•Œλ €μ£Όμ‹œλ©΄ κ°μ‚¬ν•˜κ² μŠ΅λ‹ˆλ‹€ 😊

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