ETSF10 Internet Protocols Transport Layer Protocols

Transcription

1 ETSF10 Internet Protocols Transport Layer Protocols 2012, Part 2, Lecture 2.1 Kaan Bür, Jens Andersson

2 Transport Layer Protocols Process-to-process delivery [ed.4 ch.23.1] [ed.5 ch.24.1] Transmission Control Protocol (TCP) [ed.4 ch.23.3] [ed.5 ch ] Special Topic: Network performance [ed.4 ch.3.6] [ed.5 ch.3.6] Congestion control [ed.4 ch ] [ed.5 ch ] 2

3 Transport Layer Communication between applications Process-to-process delivery Client/server concept Local host Remote host 3

4 Process-to-Process Delivery Same host, multiple applications 4

5 Addressing in TCP/IP 5

6 Logical and port addresses 6

7 Addressing the processes Port numbers Organised by a central authority (IANA) 7

8 IP addresses and port numbers 8

9 Socket addresses Combination of IP address & port number Unique for each process on the host 9

10 Transmission Control Protocol (TCP) Connection-oriented Sessions Byte stream service Reliable Flow control Error control Retransmissions Congestion control 10

11 TCP header format 11

12 Exercise: Fill in the header FF... 0x0532 0x0017 0x x x5 0x002 0x07FF 12

13 Sending and receiving buffers 13

14 ... turned into Segments Sequence numbers 14

15 TCP operation Connection establishment Three-way handshake Data transfer Flow control ( congestion control) Error control Connection termination Three-way handshake Half-close 15

16 Connection establishment 16

17 Data transfer 17

18 Connection termination 18

19 Half-close 19

20 Error control Reliable transport layer service Provided by TCP 20

21 Error control in TCP Checksum Acknowledgement ACK recieved data Retransmission After time-out RTO = f(rtt) After 3 duplicate ACK Fast retransmission 21

22 Normal operation 22

23 Lost segment 23

24 Fast retransmission 24

25 See you in 15 :) After the break Network performance Congestion control 25

26 Network performance Bandwidth Bits per second (capacity) Throughput Efficiency, always less than capacity (<1) Latency (Delay) Transmission, propagation, processing, queueing Jitter real-time data! 26

27 Exercise: Find the delays. Given: Packet size 1 MB Bandwidth 200 Kbps Propagation speed 2x10 8 m/s Link length km Transmission delay? Propagation delay? = = = / = / 27

28 Bandwidth-delay product How much data can fill the link Important for congestion avoidance Delay = Round Trip Time (RTT) Burst = 2 * bandwidth * delay 28

29 Bandwidth-delay product bandwidth: 5 bps, delay: 5s bandwidth x delay = 25 bits 29

30 Delay and throughput Related to network load Normal operation vs. congestion 30

31 Congestion control Avoiding and eliminating congestion Open-loop = proactive Closed-loop = reactive 31

32 Closed-loop congestion control (1) Backpressure 32

33 Closed-loop congestion control (2) Choke packet 33

34 Congestion Control in TCP Congestion window Sliding window (byte-oriented) Variable size Hybrid impl. (Go-back-N & Selective repeat) Slow start (state) Congestion avoidance (state) Congestion detection (event to act upon) 34

35 Congestion window 35

36 Slow start: Exponential increase 36

37 Congestion avoidance: Additive increase 37

38 Reaction to congestion detection Detection by time-out Probably both channels congested New slow start phase Detection by three ACK Probably sending channel congested only New congestion avoidance phase 38

39 TCP congestion policy: Summary 39

40 TCP congestion policy: Example 40

41 Coming Up Special Topic: Quality of Service (QoS) [ed.4 ch ] [ed.5 ch ] Real-time interactive audio/video [ed.4 ch.29.5] [ed.5 ch ] RTP/RTCP, UDP [ed.4 ch ] [ed.5 ch ] Special Topic: Voice over IP (VoIP) [ed.4 ch.29.8] [ed.5 ch ] 41