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 Conclusion

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.

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

Specification 6-byte header

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

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

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.

For (Time-interval = T i ) 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

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.

Delay Results for 2%, 10%, 20% dropping rate

AOTP behavior under various dropping rates and full error recovery

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

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.