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

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

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 Spring 2009

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 Spring 2009

TCP Header CS 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

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 Spring 2009

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 Spring 2009

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 Spring 2009

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 Spring 2009

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 Spring 2009

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 Spring 2009

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 Spring 2009

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

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

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 Spring 2009

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 Spring 2009

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 Spring 2009

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 Spring 2009

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 Spring 2009

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 Spring 2009

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 Spring 2009

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 Spring 2009

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 Spring 2009

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) = Encode the word CS414 using  Huffman coding and arithmetic coding  Compare which encoding requires less bits CS Spring 2009

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 Spring 2009

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 Spring 2009

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 Spring 2009