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Analysis of latency costs of acknowledge-repeat-request (ARQ) protocols and FEC in wired and wireless environments. Latency over the wired internet ...

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    Slide 1:Paper review on A progressively reliable transport protocol for interactive wireless multimedia

    Review Done By Madhukar Kavuri Instructor: Professor John Buford By Richard Han and David Messerschmitt A progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David Messerschmitt A progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David Messerschmitt

    Slide 2:Introduction

    Current wireless access to multimedia networks Berkeleys InfoPad Xerox PARCs Mpad Web-cognizant PDAs A progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David MesserschmittA progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David Messerschmitt

    Slide 3:General system Architecture supporting wireless media on internet

    Coding/Com-pression Transport Protocol (sender) Lower layers Lower layers Transport Protocol (receiver) Decoding/De-compression Web-enabled laptop or PDA Multimedia data flow Web or video conferencing server Wired Internet backbone Wireless Access link Base station A progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David MesserschmittA progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David Messerschmitt

    Slide 4:Problems posed by Interactive video conferencing

    How to provide rapid packetized image delivery? Reliability Communication over a Noisy Network A progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David MesserschmittA progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David Messerschmitt

    Slide 5:Whats discussed in the paper ?

    Latency costs of error protection Schemes like retransmissions- based protocols and forward error correction(FEC) over wired and wireless links. Calculating a minimum-delay bound over a wireless access link. Impact of FEC on transmission delay. Propose an end-to-end progressively reliable packet delivery system Implementation of the property of successive refinement within a progressively reliable transport protocol A progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David MesserschmittA progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David Messerschmitt

    Slide 6:Analysis of latency costs of acknowledge-repeat-request (ARQ) protocols and FEC in wired and wireless environments.

    Latency over the wired internet ARQ protocols such as TCP incurs significant delay Costs due to large round trip times Costs due to packet loss over multi-hop internet connections What do we prefer for delay-sensitive applications? Its better to have unreliable packet delivery compared to reliable packet delivery since time is a critical factor A progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David MesserschmittA progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David Messerschmitt

    Slide 7:Analysis on wireless network: a minimum-delay bound

    Some facts used for analysis Analysis of lower bound on latency over all protocols to make analysis simple. Using ideal SRP for the analysis as it is the best single-copy ARQ protocol. Ideal SRP assumes transmitter buffers and receiver buffers have infinite length. Also assumes that the senders window size is larger than the roundtrip time causing continued transmission at the sender A progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David MesserschmittA progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David Messerschmitt

    Slide 8:Analysis(contd.)

    The expectation of Npacket i.e., the average number of trials until the first good packet is received is given by E[Npacket] = 1/Pg = 1/(1- BER)K where Pg is probability of transmitting one K-bit packet through the wireless link without any errors and BER is the bit error ratio. If the packets are fragmented then expected number of for each fragments is given by E[Npacket] = 1/Pg = 1/(1- BER)(1/F+H). where F is the number of fragments and H is the number of header bits per fragment. A progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David MesserschmittA progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David Messerschmitt

    Slide 9:Analysis(contd.)

    Then we define Timage as the time needed to reliably transmit a packetized image via ideal SRP, then the average overall time for reliable image transmission is given by E[T image ] ? F . E[N fragment ] . PTT fragment = (1/ (1 BER)(1/F +H) ). (I + F . H)/ BW where PTT fragment is the packet transmission time per fragment and BW is the wireless bandwidth BW increases. This lower bound on the image transfer delay is found to be a separable function of BER and BW. This minimum delay increases exponentially as the BER increases, and decreases inversely linearly as the wireless bandwidth BW increases. A progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David MesserschmittA progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David Messerschmitt

    Slide 10:Analysis(contd.)

    Finally when we do a log-log plot, we can predict the intermediate packet size or optimal fragmentation factor that produces the minimum delay which is given by: F opt = I / 2 . In(1 BER). (-1 root(1 (4/H. In(1- BER)))) A progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David MesserschmittA progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David Messerschmitt

    Slide 11:Analysis of latency costs of forward error correction

    Some facts about FEC It is implemented as a block code and or convolution code, and is often used in link-layer protocols Error protection is achieved by adding redundancy to the sources data. Using FEC, the largest amount of image data is Imax that could be transmitted within the delay bound D is given by Imax = (BW/2) * (D RTT) where minimum factor of two is assumed for FEC overhead factors When Interleaving is considered, the roundtrip delay increases hence increasing PTT. A progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David MesserschmittA progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David Messerschmitt

    Slide 12:Low-latency solution;error-tolerant compression and delivery of corrupt packets.

    Compressing image and decoding of images results in lower end to end distortion than aggressive FEC. It is better to to leave redundancy in the image via error-tolerant compression than to strip out this image redundancy via aggressive compression. Robust compression reduces bandwidth, while tolerating errors by employing fixed-length lossy quantization of images or their transforms. Only the header has to be error free, not the entire payload A detailed delay budget analysis is required to choose between error-tolerant compression or aggressive compression A progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David MesserschmittA progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David Messerschmitt

    Slide 13:Application-transport interface for progressive reliable packet delivery

    Features of Progressively reliable packet delivery -allows reliable delivery of corrupt packets to the receiving application in increasingly reliable fashion; achieving a gain in capacity by traffic smoothing. -out-of-date re-transmissions can be cancelled. -allows the application to specify multiple flows, that are serviced by the underlying protocols packet scheduler. Other basic properties Application data units Receiving application extracts ADU boundaries from the receivers socket buffer by reading the length field in each ADU -ReadMessage() and WriteMessage() primitives. A progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David MesserschmittA progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David Messerschmitt

    Slide 14: Properties(contd.)

    Separate ADUs arriving out of order , must be redefined by the transport service by redefining for a multi copy context. For a bursty Web-image browsing, it is subjectively tolerant to delay retransmission-based redundancy needed to clean up a noisy image; provided we already have a noise version at the receiver for immediate interaction. The properties for all the four properties are shown in Figure2, Figure 3, figure 4. A progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David MesserschmittA progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David Messerschmitt

    Slide 15:Figure-2 End-to-end progressively reliable packet delivery exhibits four basic properties as seen through the socket interface.

    Progressively Reliable Protocol:Sender Sending Application Original ADU ATI Receiving Application Progressively Reliable Protocol: Receiver Internet: Wired and Wireless links Multiple noisy yet increasingly Reliable versions of original ADU A progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David MesserschmittA progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David Messerschmitt

    Slide 16:Figure 3 Traffic shaping of retransmissions

    Traffic Time Retransmit image 1 Image 2 Image 1 Traffic Time Traffic Time Traffic Delayed initial transmissions Delayed Retransmissions Delayed Retransmissions Time (a) (d) (c) (b) Original image arrivals Retransmissions of image 1 prevent Immediate transmission of image 2 Delayed retransmissions of image 1 expedite transmissions of image 2 Retransmissions of image 1 are delayed due to subjective user tolerances A progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David MesserschmittA progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David Messerschmitt

    Slide 17:Figure 4:Retransmissions of out-of-date ADUs are cancelled using ADU labels

    X Y Z Retransmit ADU X Retransmit ADU Y Retransmit ADU X State machine 2 Z New ADU 1 NETWORK ATI Transport Protocol Buffer of ADUs at the sender ADU Label Application (1)The transport protocol receives the new ADU with label Z (2) Retransmission of the previously cached ADU Z is stopped and its old data and state are purged A progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David MesserschmittA progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David Messerschmitt

    Slide 18:Flow-based scheduling of packets and their retransmissions

    Transmission of first flow consists of delay-sensitive original application data, and the second flow consists of delay- tolerant retransmitted packets. The above is analogous to implementing packet scheduling of two flows. This two flow model can be naturally extended to a general number of application-defined flows that are jointly scheduled by the protocol for transmission. The scheduler chooses which packet to transmit next from the pool of eligible packets. Figure 5 shows the protocol scheduling policy. A progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David MesserschmittA progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David Messerschmitt

    Slide 19:Figure 5: The protocols scheduling policy distinguishing between the varying delay sensitive di of retransmissions and initial packet transmissions within a flow, as well as variations across multiple application-defined flows. RSM=retransmission state machine.

    RSM Sending application RSM X Multiple data flows Flow 1 Flow 2 Send flow 2 by d3 Retransmit by d4 Multi-flow scheduler To Network Send flow 1 by time d1 Retransmit by d2 A progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David MesserschmittA progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David Messerschmitt

    Slide 20:Selected implementation issues for leaky ARQ

    Leaky ARQ term is used to denote the leaking of corrupt packets at the receiver application. Caching dirty versions of decoded packets at the receiver maintains history and also enables us to exploit standard packet-combining ARQ techniques to achieve progressively improving reliability. Fig. 6 identifies the major modifications to a standard ARQ protocol architecture that are needed to fully realize All the features proposed for progressive reliability. A progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David MesserschmittA progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David Messerschmitt

    Slide 21:Figure:6 Leaky ARQ

    ARQ Sender 4 2 3 2 1 SR ACK/NAK Noisy ADUs ARQ Receiver Queue At the sender Flow2 Flow 1 1)At the receiver, noisy yet successively refined(SR) packets are delivered to the receiving application.At the sender, 2)retransmissions are delayed. 3)multiple flows are scheduled with different delay objectives, and 4)out-of-date retransmissions are cancelled. A progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David MesserschmittA progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David Messerschmitt

    Slide 22:Successive refinement via packet combining

    Packet combining is a technique that uses history of corrupt retransmissions for a given packet to obtain a better estimate for decoding that packet than the memory less estimate provided by a single isolated retransmission. Various packet combining techniques are Majority-logic decoding Time diversity combining. Code combining(ex. Type-II hybrid). Maximum-likelihood code combining. A progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David MesserschmittA progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David Messerschmitt

    Slide 23:Separating header and payload error detection

    Separation of error detection mechanisms for header and payload. Checksum is applied on header first and if the header is error-free then the TPDU payload is successively refined via packet combining. The successfully refined TPDU is forwarded to the receiving application even if there are errors in the payload after packet combining. A progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David MesserschmittA progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David Messerschmitt

    Slide 24:Leaky ARQ as an application-level protocol

    Few of the approaches for this implementation; Sending first version of image using UDP and a subsequent reliable version via TCP. Decreased efficiency due to conflicting transmissions by TCP and UDP. Another approach is building progressive reliability over UDP UDP checksums are calculated over the IP pseudo-header causing the application-level protocol to receive UDP data- grams with corrupt UDP headers and/or corrupt IP psuedo- headers. Solution would be to partition the error detection responsibility A progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David MesserschmittA progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David Messerschmitt

    Slide 25:Summary

    Traditional ARQ protocols incur exponential delay over low bandwidth high-BER links,and FEC introduce delay due to overhead and interleaving violate interactive delay bounds. Error-tolerant compression provides with a lower distortion solution compared to aggressive compression using FEC. In this context, leaky ARQ was defined to be a progressive reliable packet delivery solution for interactive video conferencing or Web browsing over wired wireless links. This is an effective system as it improves upon the traditional systems and provides with a faster reach to the images for videoconferencing on a wireless network. A progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David MesserschmittA progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David Messerschmitt

    Slide 26:References

    A progressively reliable transport protocol for interactive wireless multimedia. By Richard Han and David Messerschmitt Asymptotically Reliable Transport of Multimedia/Graphics Over Wireless Channels. By Richard Han and David Messerschmitt Tanenbaum A. Computer Networks, 2nd edition, Prentice-Hall, Englewood Cliffs, N.J. A progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David MesserschmittA progressively reliable transport protocol for interactive wireless multimedia By Richard Han and David Messerschmitt

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