Computer Network – Performance

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Bandwidth (Throughput)

  • 一段特定时间内网络能传输的比特数
  • Unit: bps (bits per second), kbps(10^3), Mbps(10^6), Gbps(10^9)

Latency (Delay)

  • 消息从网络一端传到另一端的时间
  • Latency is normally measure in Round-Trip Time (RTT), 往返时间而非单程时间

Formula

  • Latency = Propagation Delay + Transmit Delay + Queue Delay
    • Transmit Delay = TransferSize / Bandwidth
    • Propagation Delay = Distance / SpeedofSignal
    • 传输文件较大时,宽带对延迟影响明显
    • 信号速度越快,占用频谱越宽

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  • Throughput (Effective Bandwidth) = TransferSize / (RTT + Transmit Delay)

Demos

  • Troughput measurement: iperf -c bouygues.iperf.fr -p 5200 -i 1 -t 10
    • -c 指定连接的server
    • -p 指定端口
    • -i 时间间隔
    • -t 持续时间
    • More servers: https://iperf.fr/iperf-servers.php
    • The output is below. ( I’m in education WLAN

  • Latency measurement: ping www.shanghaitech.edu.cn

  • 路由追踪: traceroute www.zhouzean.cn
    • * means there is no package replied.

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