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QoS Management at Transport Layer

QoS Management at Transport Layer. V. Tsaoussidis and S. Wei Information Technology: Coding and Computing,2000. Proceedings. International Conference on , 2000. Outline. Introduction Application Oriented Transport Protocol Specification Implementation Results and Discussion

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QoS Management at Transport Layer

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  1. QoS Management at Transport Layer V. Tsaoussidis and S. Wei Information Technology: Coding and Computing,2000. Proceedings. International Conference on , 2000

  2. Outline • Introduction • Application Oriented Transport Protocol • Specification • Implementation • Results and Discussion • Conclusion

  3. Introduction • Today’s Internet experiences a major weakness in quality. • Quality of Service Management becomes an application-specific process. • We aspire to application QoS considering the tradeoffs developed at the error recovery mechanisms of transport layer.

  4. Application Oriented Transport Protocol (AOTP) • AOTP is an experimental protocol above IP. • Provides end-to-end transport service with functionality to trade off Reliability, Throughput, Jitter in order to support the Application Layer with the required QoS. • Receiver-based retransmission mechanism

  5. Specification • 6-byte header

  6. Specification(cont.) There are 4 types • DATA • S_ACK (Selective Acknowledgment) • Report frames that need not retransmission • NACK • Report missing frames • ACK • acknowledge the receipt of missing segment

  7. Partially Reliable Service • Best Effort Partially Reliable Service • Receiver-based packet loss recovery mechanism • RP (Receiving Percentage) • DP (Desired Percentage) If RP < DP then send NACKs else reassemble and send SACKs

  8. Partially Reliable Service(cont.) • Partially Reliable Service with Priority Control • RR • Receiving Rate • ER • Expected Rate • AR • Accepted Rate described by the receiver • NR • New rate calculated after the retransmission of NACKed frames.

  9. For (Time-interval = Ti) If (RR < ER) send NACK with I,P,B frames to satisfy: NR >=AR; where NR=RR+retransmitted (I+P+B) frames; if (RR>ER) NACK only missing I-Frames; else deliver to higher layers

  10. Results and Discussion • AOTP is implemented on the x-kernel platform simulating a fairly low bandwidth environment with variable error characteristics • VDROP: virtual protocol that drops packets • VDELAY: virtual protocol that delays the packet • We have tested the mechanisms using a Video Transmission application.

  11. Delay Results for2%, 10%, 20%dropping rate

  12. AOTP behavior under various dropping rates and full error recovery

  13. Jitter measurements with and w/o priority control • Jitter is delay variation • Packet video is jitter-intolerant • The jitter buffer adds to overall delay • The jitter buffer Size is dynamically adjusted • Guarantee the ‘I’ frame is received

  14. Conclusion • The main concern of AOTP is to achieve maximum throughput and offer the required level of reliability. • Partially reliable service • Priority-based error recovery strategy • Dynamic playback management • AOTP can be qualified as a transport protocol of choice for several multimedia applications.

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