1. CS 414 - Spring 2009 CS 414 – Multimedia Systems Design Lecture 20 – TCP Augmentations for Multimedia & Midterm Review Session Klara Nahrstedt Spring 2009

2. CS 414 - Spring 2009 Homework 1  deadline – March 6  solutions will be posted on March 7 Administrative

3. Transport Protocols (Layer 4) Existing Protocols –  TCP – Reliable Transport Protocol  UDP – Unreliable Transport Protocol New Protocols –  RTP – Real-time Transport protocol  RTCP – Real-time Control Protocol CS 414 - Spring 2009

4. TCP- Transmission Control Protocol - Features Serial communication path between processes exchanging a full-duplex stream of bytes Sequential delivery (no reordering required) Reliable delivery  Achieved through retransmission via timeouts and positive acknowledgement on receipt of information Flow and congestion control is based on window technique CS 414 - Spring 2009

5. TCP Header CS 414 - Spring 2009 Bit offsetBits 0–34–78–1516–31 0 Source port Destination port 32 Sequence number 64 Acknowledgment number 96Data offsetReservedCWRECEURGACKPSHRSTSYNFINWindow 128 ChecksumUrgent pointer 160 Options (optional) 160/192 + Data

6. Flow and Congestion Control in TCP Slow-start algorithm – basic flow and congestion control in TCP The algorithm requires sender to keep congestion window which is the estimate of how much traffic the network can actually take (in- network traffic) Congestion window is managed using two-part algorithm:  Sender sends exponentially until TCP segment gets lost  Sender sends exponentially up to half the previous window, then window grows linearly CS 414 - Spring 2009

7. Techniques for Going Faster TCP predictions (1987) that TCP/IP cannot go faster than 10 Mbps Van Jacobson investigated making TCP faster Techniques:  Memory management – reduce copying  Interrupt handling – clocked interrupts CS 414 - Spring 2009

8. Techniques for Going Faster Better lookup techniques  TCP must lookup connection block for each segment received  IP must find a route to be able send IP packet Use caches of frequently used information  Maximize hit rate, minimize search and maintenance Most effective – small caches Packets travel in packet rates  CACHE OF 20 ROUTES SHOWED HIT RATE OF 90% CS 414 - Spring 2009

9. Techniques for Going Faster Lookup algorithm  Hashing using open chaining – head of each hashed link list keeps a cache of the last accessed control block Prediction  TCP behavior is highly predictable and one can take advantage by optimizing the frequent path through TCP code at sender/receiver  Header prediction CS 414 - Spring 2009

10. Sequence Numbers High delay-bandwidth product has implication on TCP window size and sequence space;  Delay-bandwidth product means how many bytes (represented via packets) are currently in-flight (i.e., inside the network)  Example: If EED is 1 second and network bandwidth (inside network) is 10 Mbps, then delay-bandwidth product is equal to 10 Mbits (1second * 10 Mbps) and this means that one can have 10 Mbits worth of data inside the network before seeing it at the receiver TCP window size is 64 KB – we need possibility to negotiate the window size CS 414 - Spring 2009

11. Sequence Numbers Sequencing uses wrap-around counters to put in sequence numbers  Sequence number space is too small Examples:  In case of 10 Mbps, the IP packet lifetime was designed with 120 seconds and sequence space of 32 bits – takes about 1700 seconds to send 2 31 bytes  In case of 1 Gbps, it takes 17 seconds to send 2 31 bytes CS 414 - Spring 2009

12. Conclusion TCP has been augmented and can achieve high performance suitable for multimedia, but one must optimize TCP for performance  Especially for large video streams CS 414 - Spring 2009

13. Midterm March 9 (Monday), 11-11:50am, 1302 SC Closed Book, Closed Notes You can bring calculator and 1 page cheat sheet CS 414 - Spring 2009

14. Covered Material Class Notes (Lectures 1-17) Book Chapters to read/study:  Media Coding and Content processing book Chapter 2, Chapter 3.1-3.2, 3.8, Chapter 4.1-4.2.2.1, Chapter 4.3 ( as discussed in lecture ) Chapter 5, chapter 7.1-7.5, 7.7  Multimedia Systems book Chapter 2, ( not 2.4.4 – we have not covered QoS routing ), Chapter 5.1 CS 414 - Spring 2009

15. Material Media Characteristics  Synchronous, Isochronous, Asynchronous  Regular, irregular  Weakly and strongly periodic streams Audio Characteristics  Samples, frequency,  Perception, psychoacoustic effects, loudness, pitch, decibel, intensity  Sampling rate, quantization CS 414 - Spring 2009

16. Material Audio Characteristics  PCM, DPCM, ADPCM, signal-to-noise ratio Image Characteristics  Sampling, quantization, pixels  Image properties: color, texture, edges  Simple edge detection process CS 414 - Spring 2009

17. Material Video technology  Color perception: hue, brightness, saturation,  Visual representation: horizontal and vertical resolution, aspect ratio; depth perception, luminance, temporal resolution and motion  Flicker effect  Color coding: YUV, YIQ, RGB  NTSC vs HDTV formats CS 414 - Spring 2009

18. Material Basic Coding schemes  Run-length coding  Statistical coding Huffman coding Arithmetic coding Hybrid codes  JPEG: image preparation, DCT transformation, Quantization, entropy coding, JPEG-2000 characteristics CS 414 - Spring 2009

19. Material Hybrid Coding  Video MPEG: image preparation, I, P, B frames characteristics, quantization, display vs processing/transmission order of frames  Audio MPEG: role of psychoacoustic effect, masking, steps of audio compression  MPEG-4: differences to MPEG-2/MPEG-1 Audio-visual objects, layering CS 414 - Spring 2009

20. Material Quality of Service concepts  Service classes, QoS specification – deterministic, predictive, best effort, QoS classification – application, system, network QoS, relation between QoS and resources  QoS operations: translation, negotiation of QoS parameters CS 414 - Spring 2009

21. Material Resource Management concepts  QoS and resources, establishment phase and transmission/enforcement phase  Admission control of resources, reservation and allocation of resources  LBAP arrival model  Enforcement of guarantees: rate control, error control, resource monitoring and adaptation CS 414 - Spring 2009

22. Material Multimedia Transport  Requirements and constraints  Examples of translation and negotiation protocols  Admission control for bandwidth and delay  Reservation protocols, types of reservations  Traffic Shaping, how is a traffic shape expressed  CS 414 - Spring 2009

23. Material Multimedia Transport  Traffic Shaping – Leaky Bucket, (r,T) shaping, Token Bucket, difference between them  Rate control – fair queuing, delay earliest deadline first, stop-and-go scheme, jitter- earliest deadline first scheme  Error control – go-back-N retransmission, selective retransmission, difference to FEC (forward error correction), CS 414 - Spring 2009

24. Sample Problems Consider the following alphabet {C,S,4,1}, with probabilities: P(C) = 0.3, P(S) = 0.2, P(4)= 0.25, P(1) = 0.25. Encode the word CS414 using  Huffman coding and arithmetic coding  Compare which encoding requires less bits CS 414 - Spring 2009

25. Sample Problems Describe briefly each step in MPEG-1 audio encoding. Specify the functionality, which is performed in each step. You don’t have to provide equations, only a clear explanation of the functionality that is performed inside each step. CS 414 - Spring 2009

26. Sample Problems What is flicker effect and how to remove it? Explain difference between synchronous and isochronous transmission stream modes Provide five differences between MPEG-4 video encoding standard and the previous MPEG video encoding standards CS 414 - Spring 2009

27. Sample Problems Consider voice application (like Skype). If you could redesign the underlying protocol (think about a session layer algorithms/services/protocols) under the voice application, what multimedia- sensitive algorithms would you deploy to achieve appropriate multimedia protocol? Specify clear design of order of algorithms/protocols to be used CS 414 - Spring 2009