ETSF10 Internet Protocols Transport Layer Protocols

Transcription

1 ETSF10 Internet Protocols Transport Layer Protocols 2012, Part 2, Lecture 2.2 Kaan Bür, Jens Andersson

2 Transport Layer Protocols 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 ] 2

3 Quality of Service (QoS) Maintaining a functioning network Meeting applications demands Dealing with flow characteristics 3

4 How to improve QoS Admission control Resource reservation Scheduling Traffic shaping Identified during online discussion. Question: Where to implement them? 4

5 Support from routing protocols? Yes! Optimal path Single metric Multiple metrics? Multiple paths Load sharing Load balancing QoS routing Cross-layer approaches OSPF extensions (RFC2676) Well, sort of! Applies to all traffic No differentiation between flow types What about inter-domain? No control over network resources More sophisticated mechanisms needed Multiprotocol Label Switching (MPLS) 5

6 Where to improve QoS? Admission control INTSERV, DIFFSERV Resource reservation RSVP and underlying WAN technologies: ATM Scheduling Traffic shaping ANYWHERE YOU FIND QUEUES! 6

7 Congestion avoidance Congestion = data load > network capacity Arrival rate > processing rate Processing rate > departure rate A simple method Random early discard (RED) APP TCP IP 7

8 Scheduling: FIFO queuing 8

9 Scheduling: Priority queuing 9

10 Scheduling: Weighted fair queuing 10

11 Traffic descriptors 11

12 Traffic profiles 12

13 Traffic shaping: Leaky bucket 13

14 Traffic shaping: Token bucket 14

15 Traffic shaping: Two approaches Leaky bucket Input flow Token bucket Input flow Output flow after LB Output flow after TB 15

16 Real-time interactive audio/video Two-way communication in real time Internet telephony Voice over IP Video conferencing 16

17 Time relationship Just delay? No problem! 17

18 Jitter Undesired variation in delay 18

19 Timestamps Separation of arrival time from playback time 19

20 Playback buffer 20

21 Exercise: Find the buffer size in s. a) At 00:00:17 b) At 00:00:20 c) At 00:00:25 d) At 00:00:30 a) 3 s (12-9) b) 3 s (15-12) c) 3 s (20-17) d) 1 s (23-22) 21

22 See you in 15 :) After the break UDP RTP/RTCP VoIP 22

23 Still not good enough! Packets can be delivered out of order. Packets can be dropped on their way. Timestamps do not detect lost packets. Sequence numbers More support: Multicast? Translation? Mixing? 23

24 Summary and comparison Performance Requirements Sensitive to: Delay Jitter Not so sensitive to: Packet loss Corrupted packets vs. Characteristics of TCP Sensitive to: Lost or corrupted packets Not so sensitive to: Delay No multicasting! So, what about UDP? 24

25 User Datagram Protocol (UDP) Connectionless Independent datagrams No sessions Unreliable No error control No flow control 25

26 UDP header format Checksum optional No numbering No relation between datagrams 26

27 Real-time Transport Protocol 27

28 Real-time Transport Protocol RTP handles real-time traffic No delivery mechanism Uses UDP/IP Contributions Time-stamping Sequencing Mixing 28

29 RTP header format 29

30 Real-time Transport Control Protocol RTP only carries data Sessions initialised by SIP RTCP carries control messages Flow control Service quality Feedback to source 30

31 Sender report Sent by active senders Periodical Statistics Transmission Reception Absolute timestamp Receivers can synch RTP messages Important for audio and video 31

32 Receiver report Sent by listeners Not sending RTP packets Feedback about QoS And others... 32

33 Voice over IP (VoIP) Internet telephony Uses two protocols SIP Session Initiation Protocol IETF standard H.323 Communication (telephone, computer) ITU-T standard 33

34 Session Initiation Protocol (SIP) Application layer protocol Multimedia session management Text-based messages Various address types 34

35 A simple SIP session 35

36 Tracking the callee 36

37 H.323 Communication (telephone, computer) Gateway = 5-layer translation device Gatekeeper = registrar 37

38 H.323 protocols Resource reservation Compression method negotiation Audio exchange & management Connection setup 38

39 H.323 session 39

40 Next Lecture Group in 2 Weeks IPv4, IPv6, transition from IPv4 to IPv6 ICMPv4, ICMPv6, ARP Special Topic: Virtual private networks (VPN) BOOTP, DHCP, NAT, DNS Mobile IP Special Topic: Wireless LAN NOW: Introduction to TCP Lab! 40