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

CS 414 - Spring 2009

CS 414 – Multimedia Systems Design Lecture 20 – TCP Augmentations for Multimedia &Midterm Review Session

Klara Nahrstedt

Spring 2009


Homework 1 deadline – March 6solutions 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


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


TCP Header


Bit offset Bits 0–3 4–7 8–15 16–31

0 Source portDestination port

32 Sequence number64 Acknowledgment number

96 Data offset Reserved CWR ECE URG ACK PSH RST SYN FIN Window

128 Checksum Urgent 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 linearlyCS 414 - 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


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%


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


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


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 231 bytes

In case of 1 Gbps, it takes 17 seconds to send 231 bytes


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


Midterm

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

sheet


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


Material Media Characteristics

Synchronous, Isochronous, AsynchronousRegular, irregularWeakly and strongly periodic streams

Audio CharacteristicsSamples, frequency,Perception, psychoacoustic effects, loudness, pitch,

decibel, intensitySampling rate, quantization


Material

Audio CharacteristicsPCM, DPCM, ADPCM, signal-to-noise ratio

Image CharacteristicsSampling, quantization, pixels Image properties: color, texture, edgesSimple edge detection process


Material

Video technology Color perception: hue, brightness, saturation,Visual representation: horizontal and vertical

resolution , aspect ratio; depth perception, luminance, temporal resolution and motion

Flicker effectColor coding: YUV, YIQ, RGBNTSC vs HDTV formats


Material Basic Coding schemes

Run-length codingStatistical coding

Huffman coding Arithmetic coding

Hybrid codesJPEG: image preparation, DCT

transformation, Quantization, entropy coding, JPEG-2000 characteristics


Material

Hybrid CodingVideo 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


Material

Quality of Service conceptsService 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


Material

Resource Management conceptsQoS and resources, establishment phase and

transmission/enforcement phaseAdmission control of resources, reservation

and allocation of resourcesLBAP arrival model Enforcement of guarantees: rate control, error

control, resource monitoring and adaptation


Material

Multimedia Transport Requirements and constraintsExamples of translation and negotiation protocolsAdmission control for bandwidth and delayReservation protocols, types of reservationsTraffic Shaping, how is a traffic shape expressed


Material

Multimedia Transport Traffic Shaping – Leaky Bucket, (r,T) shaping,

Token Bucket, difference between themRate 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) ,


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


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.


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


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


Documents

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