[NW] 2nd : Data Link Layer

seunghyunยท2023๋…„ 3์›” 25์ผ
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๐Ÿ’ป

๋ชฉ๋ก ๋ณด๊ธฐ
12/16

Introduction


์–ด๋–ป๊ฒŒ ์ถฉ๋Œ์„ ํ”ผํ•ด์„œ ๋‚ด ์•ž์˜ ๋ผ์šฐํ„ฐ๊นŒ์ง€ ์ „๋‹ฌ๋  ๊ฒƒ์ธ๊ฐ€?
MAC : Medium Access Control/Mutiple Access Protocol


Mac protocol

three broad classes:

โœ”๏ธ Channel Partitioning

  • ์ด๋™ํ†ต์‹  (LTE) ๊ฐ€ ์‚ฌ์šฉํ•˜๋Š” ๋ฐฉ์‹
  • ์‚ฌ๋žŒ์ด ๋งŽ์„ ๋•Œ ํšจ์œจ์ 
  • 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)

โœ”๏ธ Random Access

  • ์ด๋”๋„ท, ์™€์ดํŒŒ์ด๊ฐ€ ์‚ฌ์šฉํ•˜๋Š” ๋ฐฉ์‹
  • ์‚ฌ๋žŒ์ด ์ ์„ ๋•Œ ํšจ์œจ์ 
  • channel not divided, allow collisions
  • how to detect, recover from collisions
  • CSMA (Carrier Sense Multiple Access)
    • listen before transmit
    • ๋ฌผ๋ฆฌ์  ์ด์œ ๋กœ ์ถฉ๋Œ์ด ๋ถˆ๊ฐ€ํ”ผํ•˜๋‹ค
    • ๊ทธ๋ ‡๋‹ค๋ฉด ์ถฉ๋Œ์˜ damage ๋ฅผ ์ตœ์†Œํ™”ํ•ด์•ผ ํ•œ๋‹ค
    • ๊ทธ๋ž˜์„œ ๋‚˜์˜จ ๊ฒƒ์ด CSMA/CD (collision detection)
      • frame ์ „์†ก ์ค‘, collision detection ์ถฉ๋Œ ๋ฐœ์ƒ ์‹œ ์ „์†ก์„ ์ค‘๋‹จํ•œ๋‹ค
      • random time ํ›„ frame ์„ ์žฌ์ „์†กํ•ด์•ผ ํ•œ๋‹ค (random range ๊ฐ€ ์งง์„์ˆ˜๋ก ์ข‹๋‹ค)
    • ์ผ์ƒ์ƒํ™œ์—์„œ ์šฐ๋ฆฌ๊ฐ€ ๋Œ€ํ™”ํ•˜๋Š” ๊ฒƒ๊ณผ ๋น„์Šทํ•˜๋‹ค
  • efficient at low load: single node can fully utilize channel
  • high load: collision overhead

โœ”๏ธ Taking Turns

  • ํ˜„์‹ค์ ์œผ๋กœ ๋งŽ์ด ์“ฐ์ด์ง„ ์•Š๋Š”๋‹ค: single point of failure
  • look for best of both worlds!

Ethernet

frame structure

data ์— ip packet ์ด ๋“ค์–ด๊ฐ„๋‹ค
48 bit MAC address ๊ฐ€ ๋“ค์–ด๊ฐ„๋‹ค


Wifi

frame structure


๐Ÿ”— Reference

์ž˜๋ชป๋œ ๋‚ด์šฉ์ด ์žˆ๋‹ค๋ฉด ๋Œ“๊ธ€๋กœ ์•Œ๋ ค์ฃผ์‹œ๋ฉด ๊ฐ์‚ฌํ•˜๊ฒ ์Šต๋‹ˆ๋‹ค ๐Ÿ˜Š

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