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摘要:
为满足未来航电系统音视频信息传输的需求,考虑车载嵌入式系统的候选实时多媒体网络AVB在航电环境中的应用,并对AVB与AFDX的传输进行了对比研究。首先构建AVB与AFDX标准对比;其次提出基于网络演算的AVB和AFDX端到端延迟计算方法;然后通过定义不同的消息传输场景,采用理论方法分析消息传输实时性的干扰要素;最后利用仿真方法予以验证。在典型1 000条虚拟链路的组网规模下,结果显示:AFDX高优先级流量的端到端延迟优于AVB,对于低优先级流量端到端延迟,则AVB和AFDX各有优劣;但受突发的流量影响,在增加50条各0.22 Mbit/s带宽的低优先级流量干扰情况下,高优先级流量平均端到端延迟的变化率在AVB中为0.25%,在AFDX中为0.38%;在增加50条各0.22 Mbit/s带宽的高优先级流量干扰情况下,低优先级流量平均端到端延迟的变化率在AVB中为5.17%,在AFDX中为10.25%。结果表明:时间敏感消息在AVB网络中传输实时性的抗干扰能力优于AFDX。
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关键词:
- 航空电子网络 /
- 音视频桥接(AVB)网络 /
- 航空电子全双工交换以太网(AFDX) /
- 实时性 /
- 抗干扰
Abstract:AVB is considered to meet the demands of audio video transmission in future avionics system, which is a real-time multimedia network and has become a candidate for in-vehicle embedded systems. Comparative study on AFDX and AVB is implemented. First, standards of AVB and AFDX are compared. Second, the method for end-to-end delay in AVB and AFDX is discussed by network calculus. Then the elements interfering real-time transmission are analyzed depending on different transmission scenarios. Conclusions are verified by simulation. In typical networking with 1 000 virtual links, the results show that the end-to-end delay of high priority traffic in AFDX is smaller than that in AVB; the advantage and disadvantage of end-to-end delay for low priority traffic exist in both AVB and AFDX. But influenced by the burst 50 low priority streams (each with 0.22 Mbit/s bandwidth), the variation rate of average end-to-end delay for high priority traffic is 0.25% in AVB and 0.38% in AFDX; influenced by the burst 50 high priority streams (each with 0.22 Mbit/s bandwidth), the variation rate of low priority traffic is 5.17% in AVB and 10.25% in AFDX. Real-time anti-jamming transmission of time-sensitive information in AVB is superior to AFDX.
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表 1 SR_A类和SR_B类参数
Table 1. Parameters of SR_A and SR_B
类型 优先级 最大帧长/Byte 发送频率/μs 7跳最大延迟/ms 最大抖动/μs SR_A 高 1 171 125 2 125 SR_B 低 1 500 250 50 1 000 表 2 端到端延迟对比
Table 2. Comparison of end-to-end delay
表 3 配置信息
Table 3. Configuration information
VLi 源节点 目的节点 帧长/Byte AFDX AVB BAG/ms 流量类型 ServiceRate/ms MIF 流量类型 1~50 ① ② 72 2 低优先级 40 20 SR_B 51~150 ① ④ 172 16 高优先级 160 10 SR_A 151~350 ② ⑥ 800 128 低优先级 1 280 10 SR_B 351~450 ③ ⑦ 100 8 高优先级 40 5 SR_A 451~650 ④ ⑧ 200 32 高优先级 320 10 SR_A 651~850 ⑤ ⑦ 372 64 低优先级 320 5 SR_B 851~950 ⑧ ⑥ 72 4 高优先级 40 10 SR_A 951~1 000 ⑨ ⑥ 872 32 高优先级 160 5 SR_A 951~1 000 ⑨ ⑥ 872 32 低优先级 160 5 SR_B 表 4 VL151~350平均端到端延迟对比
Table 4. Comparison of average end-to-end delay for VL151~350
场景 平均端到端延迟/ms AFDX AVB 场景1 19.292 15.053 场景2 21.270 15.831 表 5 VL851~950平均端到端延迟对比
Table 5. Comparison of average end-to-enddelay for VL851~950
场景 平均端到端延迟/ms AFDX AVB 场景1 2.901 3.561 场景2 2.912 3.570 -
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