Research of Preemption Mechanism for Efficient Data Transmission in TSN

Abstract

IEEE 802.1 AVB 표준은 차량 내 통신에서 사용되는 다양한 traffic의 요구사항을 충족시키기 위해 제정되었다. 최근 AVB traffic에 대해 더 낮은 latency를 보장하고 시간에 민감한 control data의 요구사항을 충족시키기 위해 IEEE 802.1 AVB Gen2 표준을 제정하고 있다. AVB Gen2 표준의 가장 큰 특징은 네트워크의 모든 노드가 시간에 따라 동기화 되는 TSN (Time Sensitive Network)이다. TSN 환경에서 시간에 민감한 control data의 전송 요구사항을 충족시키기 위해 scheduled traffic 개념이 추가되었다. scheduled traffic은 Time Division Multiplexing Access (TDMA) 방식으로 정해진 시간에 마다 control data를 전송하는 것이다. IEEE 802.1 AVB Gen2 표준 중 하나인 IEEE 802.1 Qbu는 scheduled traffic의 전송을 보장하기 위해 preemption 메커니즘과 guard band의 사용에 대해 명시하고 있다. preemption은 정해진 시간에 scheduled traffic을 전송해야 할 때, 전송 중이던 AVB traffic이나 best-effort traffic의 전송을 중단하고 scheduled traffic을 우선적으로 전송한다. 전송이 중단된 AVB traffic이나 best-effort traffic은 scheduled traffic이 모두 전송 된 이후에 다시 전송된다. preemption을 사용하면 scheduled traffic의 전송을 보장할 수는 있으나 AVB traffic과 best-effort traffic의 전송 지연이 발생한다. 따라서, 본 논문에서는 위에서 설명한 문제를 해결하기 위해 preemption에서 사용하는 guard band의 크기를 조절할 것이다. 또한, guard band의 크기에 맞춰 AVB traffic 의 frame size를 줄여 preemption의 발생 횟수를 낮추는 것을 제안한다. 대역폭의 낭비를 최소화하는 guard band의 크기를 구하고 end-to-end delay를 최소화 하는 frame size를 확인할 것이다. 그 결과, AVB frame의 frame size를 512 byte로 전송할 경우, end-to-end delay가 최대 frame size로 전송할 때보다 12.2% 감소하였다 그리고 scheduled traffic의 전송 주기가 4ms라고 설정하였을 때, guard band의 크기를 AVB frame 크기와 동일한 512 byte로 증가시키면 기존의 guard band가 차지하는 시간의 비율 보다 0.76% 증가한다. 따라서, 논문에서 제시한 방법을 통해 preemption 기능을 적용하면 preemption의 발생 횟수를 줄여 AVB traffic의 end-to-end delay를 감소시킬 수 있다. scheduled traffic 뿐만 아니라 AVB traffic의 전송을 보장하고 전체적으로 네트워크의 대역폭을 효율적으로 사용할 수 있다.|The IEEE 802.1 AVB (Audio Video Bridging) standard was established to meet the various requirements of the traffic that will be used in the vehicle communication. And recently the IEEE 802.1 AVB Gen2 standard was established to ensure a lower latency for the AVB traffic and to meet the requirements of the time-sensitive control data. The AVB Gen2 standard of the most important feature was the TSN (Time Sensitive Network) that was time synchronized all nodes of the network. The scheduled traffic has been added in order to meet the delivery requirements of the time sensitive control data in the TSN environment. The scheduled traffic was to transmit the control data per the fixed time period by the Time Division Multiplexing Access (TDMA) scheme. The IEEE 802.1 Qbu was one of the IEEE 802.1 AVB Gen2 standard has been specified for the use of preemption mechanisms and guard band to ensure the transmission of scheduled traffic. When it was to transmit the scheduled traffic at the specific time, the preemption stopped the transmission of the AVB traffic and preferentially sent the scheduled traffic. The AVB traffic that was interrupted the transmission was re-sent after all scheduled traffic was sent. If using the preemption, it could guarantee the transmission of the scheduled traffic, but the transmission delay of AVB traffic happened. Therefore, in this paper, it would be adjusted the size of the guard band used in the preemption to solve the problem described above. In addition, reducing the frame size of the AVB traffic was proposed to lower the number of occurrences of preemption. It would obtain the size of the guard band to minimize the waste of bandwidth and it would determine the frame size to minimize the end-to-end delay. As a result, when transferring the frame size of AVB frame as 512 byte, the end-to-end delay decreased 12.2% compared to transmission with the maximum frame size. And when the transmission period of scheduled traffic was set as 4ms, if increasing the size of the guard band as 512 byte the same with AVB frame, it increased the 0.76% in the proportion of time than traditional guard band occupied. Therefore, when applying the preemption function, through the method proposed in papers, by reducing the occurrence of preemption, it could reduce the end-to-end delay of the AVB traffic.; The IEEE 802.1 AVB (Audio Video Bridging) standard was established to meet the various requirements of the traffic that will be used in the vehicle communication. And recently the IEEE 802.1 AVB Gen2 standard was established to ensure a lower latency for the AVB traffic and to meet the requirements of the time-sensitive control data. The AVB Gen2 standard of the most important feature was the TSN (Time Sensitive Network) that was time synchronized all nodes of the network. The scheduled traffic has been added in order to meet the delivery requirements of the time sensitive control data in the TSN environment. The scheduled traffic was to transmit the control data per the fixed time period by the Time Division Multiplexing Access (TDMA) scheme. The IEEE 802.1 Qbu was one of the IEEE 802.1 AVB Gen2 standard has been specified for the use of preemption mechanisms and guard band to ensure the transmission of scheduled traffic. When it was to transmit the scheduled traffic at the specific time, the preemption stopped the transmission of the AVB traffic and preferentially sent the scheduled traffic. The AVB traffic that was interrupted the transmission was re-sent after all scheduled traffic was sent. If using the preemption, it could guarantee the transmission of the scheduled traffic, but the transmission delay of AVB traffic happened. Therefore, in this paper, it would be adjusted the size of the guard band used in the preemption to solve the problem described above. In addition, reducing the frame size of the AVB traffic was proposed to lower the number of occurrences of preemption. It would obtain the size of the guard band to minimize the waste of bandwidth and it would determine the frame size to minimize the end-to-end delay. As a result, when transferring the frame size of AVB frame as 512 byte, the end-to-end delay decreased 12.2% compared to transmission with the maximum frame size. And when the transmission period of scheduled traffic was set as 4ms, if increasing the size of the guard band as 512 byte the same with AVB frame, it increased the 0.76% in the proportion of time than traditional guard band occupied. Therefore, when applying the preemption function, through the method proposed in papers, by reducing the occurrence of preemption, it could reduce the end-to-end delay of the AVB traffic.