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Computer Network Class/Exam2006_2


1. ๋ฌธ œ  „ฒด  •ด„

๋ณด•ˆ ๊ธฐ๋ฒ•—„œ •Œ๊ณ ๋ฆฌฆ˜๊ณผ ž„•œ ๊ตฌ˜„๋ฒ•— ๋Œ€•œ ๋‚ดšฉ€ ๊ตˆ˜๋‹˜ด ง€–‘•˜‹ ๋“ฏ. (๋‚œด๋„ ๋‚ฎถ”๋ ค๊ณ  •œ๋“ฏ•จ)
๊ฐœ๋ณ„ ธ ๊ธฐˆ ˜ ƒ„ธ ๋‚ดšฉ„ ๋ฌป๊ธฐ๋ณด๋‹ค๋Š”  „ฒด ๊ธฐˆ — ๋Œ€•œ ๋น„๊ต๊ณผ ฐจด — ๋Œ€•œ ด•ด๋ฅผ ค‘‹ฌœผ๋กœ ถœ œ.
(•œ๋งˆ๋””๋กœ ๋„“๊ฒŒ ๊ณต๋ถ€•ด•ผ ๊ฒฐ๊ณผ ข‹„๋“ฏ•จ.)

ธ„ฐ๋„ท ๋ณด•ˆ ๊ด€๋ จ๋œ ๋ฌธ œ—„œ ๋ฌธ œ๋กœ ถœ œ ๋  ๋งŒ•˜๋‹ค๊ณ  ƒ๊ฐ–ˆ๋˜ ๋ถ€๋ถ„ธ Authencation Protocol (3-way-handshake, keberos, using RSA)— ๋Œ€•œ ๋‚ดšฉ—ญ‹œ ๋ฏธถœ œ๋˜—ˆŒ. ๋•๋ถ„— ‹œ—˜ ๋‚œด๋„๋Š” ๋‚ฎ•„กŒง€๋งŒ, PEM ˜ ๊ตฌกฐ— ๋Œ€•œ „ค๋ช…ด ๋“ค–ด๊ฐ”๊ธฐ ๋•Œ๋ฌธ— ๋”ฐ๋กœ ๊ด€‹ฌ„ ๊ฐ€ง€๊ณ  ๊ณต๋ถ€•œ ‚ฌ๋žŒด •„๋‹ˆ๋ฉด •ฝ๊ฐ„ –ด๋ ค› „ง€๋„ ๋ชจ๋ฅด๊ฒ Œ.

TCP˜ ๋ฆ„ œ–ด ๋ถ€๋ถ„€ ›Œ๋‚™— ค‘š”•˜๋‹ค๊ณ  „ค๋ช…–ˆ๊ธฐ ๋•Œ๋ฌธ— SLOWSTART, FAST RETRANSMIT, VEGAS — ๋Œ€•œ ด•ด๋ฅผ •ด•ผ–ˆ„๋“ฏ.

2. ๋ฌธ œ

1. ๋ณด•ˆ˜ ข…๋ฅ˜, นจž…๋ฐฉ๋ฒ•, ๊ทธ—๋”ฐ๋ฅธ ๋ณด•ˆ ๊ธฐ๋ฒ• ˜ˆ, ๊ฐ„๋‹จ•œ „ค๋ช…
secrecy(interception -> DES, RSA)
authenticate(fabrication -> 3-way handshake, keberos, using RSA)
integrigy(modification -> keyed MD5)
availability(interruption, DoS, Jamming -> Firewall, Proxy-base Network System)— ๋Œ€•œ „ค๋ช…๊ณผ ˆ˜—…๋•Œ ๋ฐฐšด ๋ณด•ˆ๊ธฐˆ ๋“ค„ ๋ถ„๋ฅ˜•˜๊ณ  „ค๋ช…•˜๋Š” ๋ฌธ œž„.

2. ๋ฉ€‹ฐ๋ฏธ๋””–ด ŠคŠธ๋ฆฌ๋ฐ „œ๋น„Šค— ๊ด€๋ จ๋œ ๋ฌธ œ ถœ œ. (RTP, ๋ฒ„ผ๋ง, QoS ๋“˜ ๋ฌธ œ๋ฅผ ๋ณต•ฉ‹œผฐŒ)
2.1 playback time — ๋Œ€•œ …—  œ‹œ๋œ ๊ทธ๋ž˜”„๋ฅผ ๊ทธ๋ฆฌ๊ณ  ๊ทธ „ค๋ช…„ •˜๋Š” ๋ฌธ œ. (2.1 ๋ฌธ œ—„œ๋Š” MPEG ๊ณผ ๊ฐ™€ ••ถ• ๊ธฐ๋ฒ•ด ดšฉ๋˜ง€ •Š๋Š”๋‹ค๊ณ  ๊ฐ€ •)
2.2 MPEG „ ‚ฌšฉ•˜๋ฉด ๊ทธ๋ž˜”„๊ฐ€ –ด๋–ป๊ฒŒ ๋ณ€• ๊นŒ?
2.3 RTP —ค๋”— ฌ•จ๋˜๋Š” 3๊ฐœ๋ฅผ ๋“ค–ด„œ „ค๋ช…
SSRC, CSRC, Contribution Count, timestamp, sequence number, Version etc —๋Œ€•œ ๋‚ดšฉ„  ๊ณ  •ด„
2.4 play back € ๋ฌด—‡ด๊ณ  –ธ œ –ด๋–ป๊ฒŒ ‚ฌšฉ๋˜๋‚˜

  playback point, playback time — ๋Œ€•œ ด•ด๋ฅผ ๋ฌป๋Š” ๋ฌธ œž„. adaptive playback —๋Œ€•œ ๋ฌธ œ๋„ ถœ œ๋˜—ˆŒ.
2.5 ๋ฉ€‹ฐ๋ฏธ๋””–ด „œ๋น„Šค—„œ TCP๋Š” ™œ ž˜ ‚ฌšฉ •ˆ๋ ๊นŒ

  ๋ฉ€‹ฐ๋ฏธ๋””–ด ŠคŠธ๋ฆฌ๋ฐ „œ๋น„Šค™€ TCP˜ ๊ถ•ฉด ž˜ ๋งžง€•Š๋Š” ดœ ๋ฅผ ๊ธฐˆ •˜๋ผ๋Š” ๋ฌธ œ. ˆ˜—…‹œ๊ฐ„— ๋ช‡๋ฒˆ ๋ง–ˆ๊ธฐ ๋•Œ๋ฌธ— ๋‚œด๋„ ‰ด. (UDP œ„— RTP ๋ฅผ ˜ฌ๋ฆฌ๊ฒŒ ๋œ ดœ ™€ ผ๋งฅƒ†ต•จ)

3. PEM œผ๋กœ ด๋ฉ”ผ ๋ณด๋‚ผ๊ฒฝšฐ, ๋ณด๋‚ดง€๋Š” ๋‚ดšฉ๋“ค ๊ตฌกฐ™€ •จ๊ป˜ „ค๋ช…. ๊ฐ™ด ๋ณด๋‚ดง€๋Š” ฒจ๋ถ€ ŒŒผ€ a.jpg
 ผ๋ฐ˜ ธ ๋ฉ”ผ  „†ก ”„๋กœ† ฝœ˜ ด•ด™€ MIME ”„๋กœ† ฝœ— ๋Œ€•œ ๊ฐ„๋‹จ•œ ด•ด. ๊ทธ๋ฆฌ๊ณ  E(MD(5), PrivateKeyOfSnd) ˜ •ด„ ๋ฐฉ๋ฒ•๊ณผ ๊ณ„ธต  ธฆ— ๋Œ€•œ ด•ด๋ฅผ ๋ฌป๋Š” ๋ฌธ œ˜€Œ.
 ๋ฌธ œ˜ ๋‚ดšฉ— ๋ฉ”ผ˜ —ค๋”™€ ๊ตฌกฐ๋ฅผ ๋‚˜ƒ€๋‚ด๋ผ๋Š” ๋งด žˆ๊ธฐ 떄๋ฌธ— …„ ฐธกฐ•˜๊ฐ๋‚˜ ผ๋ฐ˜ œผ๋กœ ๋ฐ›๋Š” ด๋ฉ”ผ˜ ๊ตฌกฐ๋ฅผ •œ๋ฒˆ ๋ณธ๋’ค ‹œ—˜„ ๋ณด๋ฉด ข‹Œ.
 („๋„ ๋‚˜๊ฐ€๊ธฐ  „ ˆ˜—…๋•Œ ๋ฉ”ผ ๊ตฌกฐ ๋ณด๊ณ  ˜ค๋ผ๊ณ –ˆ๋Š”๋ฐ •„๋ฌด๋„ •ˆ๋ณด๊ณ  ™€„œ ๋‚ธ๋“ฏ•จ. ใ…ก.ใ…ก)

4. slow start ๋‚˜˜ค๋Š” ๊ทธ๋ž˜”„
4.1 slow start ‘œ‹œ, ๋ฌด—‡ธง€ „ค๋ช…

  SLOWSTART ‚ฌšฉ‹œ๊ธฐ™€ •ด๋‹น ๊ธฐ๋ฒ•˜ ‚ฌšฉดœ — ๋Œ€•œ •ด„
4.2 fast restrasntmit — ๋Œ€•œ „ค๋ช…๊ณผ ๊ทธ๋ ‡๊ฒŒ –ˆ„๋•Œ ๊ทธ๋ž˜”„๊ฐ€ –ด๋–ป๊ฒŒ ๋ณ€•˜๋‚˜?

  FRดšฉ‹œ ๊ทธ๋ž˜”„˜ ๋ณ€™” ถ”ด™€ ๊ทธ ดœ ๋ฅผ „ค๋ช…. ค‘๋ณต ACK  „†ก— ๋Œ€•œ ด•ผ๊ธฐ™€ VEGAS—„œ ดš”•˜๋Š” faster retransmit „ค๋ช…–ˆŒ.

5. †ต•ฉ „œ๋น„Šค™€, ฐจ๋ณ„ „œ๋น„Šค˜  ‘๊ทผ๋ฒ•˜ ฐจด๋ฅผ “ฐ๊ณ  (Qos— ๋”ฐ๋ฅธ „œ๋น„Šค๋ฅผ  œ๊ณต•ดฃผ๋Š” ๋Œ€‘œ ธ ๊ธฐ๋ฒ•) ๊ฐ „œ๋น„Šค—„œ WFQ๋ฅผ –ด๋–ป๊ฒŒ ๊ตฌ˜„–ˆ๋Š”ง€
 Integrated Service(flow-based), Differentiated Service(service-based) —๋Œ€•œ  „๋ฐ˜ ธ ด•ด๋ฅผ •˜๋Š” ๋ฌธ œ. •ด๋‹น ๊ธฐ๋ฒ•— WFQ๋ฅผ  šฉ•˜๋Š” ๋ฐฉ๋ฒ•— ๋Œ€•œ ด•ด๋ฅผ ๋ฌป๋Š” ๋ฌธ œ๋กœ •ฝ๊ฐ„ ‘šฉ•ด„œ  œผ๋ž€ ๊ฒƒœผ๋กœ ๋ณดž„. …— DS— ๋Œ€•œ „ค๋ช…€ WRED, RIO— ๋Œ€•œ „ค๋ช…๋งŒ ๋˜–ดžˆ—ˆ๊ณ , ด ๋ฐฉ‹€ Queuing — ˜•œ WFQ˜ ‚ฌ›„ ฒ˜๋ฆฌ๊ฐ€ •„๋‹Œ ‚ฌ „ ฒด๋ฆฌ— ๊ด€๋ จ๋œ ๋‚ดšฉด—ˆŒ. †”งžˆ WFQ ™œ ๋ƒˆ๋Š”ง€ ๋ชจ๋ฅด๊ฒ Œ. -_-;;
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