The document discusses network packets and TCP/IP protocols. It introduces key concepts like packet structure, IP headers, TCP segments, round-trip time (RTT), retransmission timeout (RTO), and TCP retransmission algorithms like Karn's algorithm and Jacobson's algorithm. It explains TCP terminology such as slow start, congestion avoidance, time out, and exponential weighted moving average. The document also discusses packet vs. segment, ports, checksum, TTL, smoothed RTT, RTT variation, and algorithms for calculating RTO values and performing timer back-off for retransmissions.

1. Packet
Packet부터 시작하는 네트워크

2. What Packet?

3. Why Packet?
Packet Network
VS
Circular Network

4. IP Packet
PDU in Network Layer
related with
Data Structure, Algorithm
set of Data

5. IP Packet
IP Header

6. IP Packet Analysis - Wireshark Example
IP Header

7. TCP Segment Analysis - Wireshark Example
TCP Header

8. Packet vs Segment
Sender Port /
Destination Port
CheckSum
Sender Address /
Destination Address,
TTL

9. TCP Terminology
1. rwnd : receiver window
2. cwnd : congestion window

10. TCP Terminology
1. SS : Slow Start
2. CA : Congestion Avoidance
3. TO : Time out

11. TTL(Time to Live)
the upper bound on how long
this internet datagram may exist

12. TTL(Time to Live)
TTL value = 3 TTL value = 2
TTL value = 1
TTL value = 0
IPv6 : TTL field => hop limit

13. Terminology
SRTT (Smoothed round-trip time)
RTTVAR (round-trip time variation)
G (Clock Granularity)
타이머가 측정할 수 있는
최소 시간의 단위

14. RTO(Retransmission Timeout)
Duration of Timer
Retransmission Timer = Ensure Data Delivery

15. RTT(Round-Trip Time)

16. LET`S CHECK ALGORITHM
RTO 너는 무엇이냐?

17. Basic Algorithm

18. Basic Algorithm

19. Basic Algorithm
RTO < 1초 => RTO round(1)
RTO가 최소 60초면 최대값 지정 가능

20. TCP Retransmission Algorithm
1. Karn`s Algorithm 2. Jacobson Algorithm

21. TCP Retransmission Algorithm
1. Karn`s Algorithm
첫 번째 전송으로 받은 ACK와
Retransmission으로 받은
ACK 구별 가능?

22. TCP Retransmission Algorithm
1. Karn`s Algorithm
Retransmission Segment
ignore!
(When update RTT)
So Simple!

23. TCP Retransmission Algorithm
만약 지연이 급격히 증가한 후,
TCP가 Segment를 보낸다면?
Karn Algorithm에 따라,
Up된 Delay에 조정 X =>
모든 Segment를 계속
retransmission

24. TCP Retransmission Algorithm
Solution : RTT + Timer Back-Off Strategy
Timer Back-Off : initial timeout
Timer가 만료되어 재전송 => TCP는 RTT를 2배로 늘림
(성능, 효율성의 균형 유지 효과적)

25. TCP Retransmission Algorithm
2. Jacobson`s Algorithm
exponential weighted
moving average method
(EWMA)

26. What is EWMA?
EWMA = Exponentially Weighted Moving Average
지수적으로 감소하는 가중치 적용
오래된 데이터
=> 기하급수적 감소

27. 참고
https://brunch.co.kr/@alden/15
http://ktword.co.kr/test/view/view.php?m_temp1=1687
https://ko.wikipedia.org/wiki/%ED%94%84%EB%A1%9C%ED%86%A0%EC%BD%9C_%EB%8D%B0%EC%9D%B4%ED%84%B
0_%EB%8B%A8%EC%9C%84
https://ko.wikipedia.org/wiki/%EC%9D%B4%EB%8F%99%ED%8F%89%EA%B7%A0
https://en.wikipedia.org/wiki/Van_Jacobson
https://moleman.tistory.com/279
https://en.wikipedia.org/wiki/Karn%27s_algorithm
http://ktword.co.kr/test/view/view.php?m_temp1=1687
https://ko.wikipedia.org/wiki/%ED%8C%A8%ED%82%B7_%EA%B5%90%ED%99%98
https://www.sfu.ca/~ljilja/cnl/presentations/wan/wireless_TCP/sld012.htm
https://parknom.tistory.com/entry/tcp-%EC%95%8C%EA%B3%A0%EB%A6%AC%EC%A6%98
https://ko.wikipedia.org/wiki/Time_to_live

28. 알고리즘, 자료구조 열심히 공부합시다
39ghwjd@naver.com