udp丢包过程是怎样的（结合iperf的测量结果具体分析）

[wahahahql]

mininet中，拓扑为h1-s1-s2-h2，s1-s2之间的带宽为2M，测量结果如下：
客户端：
root@ubuntu:/home/wang/Desktop# iperf -c 10.0.0.2 -p 40001 -i 1 -t 80000 -u -b
10M
------------------------------------------------------------
Client connecting to 10.0.0.2, UDP port 40001
Sending 1470 byte datagrams
UDP buffer size: 208 KByte (default)
------------------------------------------------------------
[ 15] local 10.0.0.1 port 35105 connected with 10.0.0.2 port 40001
[ ID] Interval Transfer Bandwidth
[ 15] 0.0- 1.0 sec 1.19 MBytes 10.0 Mbits/sec
[ 15] 1.0- 2.0 sec 1.19 MBytes 10.0 Mbits/sec
[ 15] 2.0- 3.0 sec 1.19 MBytes 10.0 Mbits/sec
[ 15] 3.0- 4.0 sec 1.19 MBytes 10.0 Mbits/sec
[ 15] 4.0- 5.0 sec 1.19 MBytes 10.0 Mbits/sec
[ 15] 5.0- 6.0 sec 1.19 MBytes 10.0 Mbits/sec
[ 15] 6.0- 7.0 sec 1.19 MBytes 10.0 Mbits/sec
...（同上）
服务器端：
root@ubuntu:/home/wang/Desktop# iperf -s -u -p 40001 -i 1
------------------------------------------------------------
Server listening on UDP port 40001
Receiving 1470 byte datagrams
UDP buffer size: 208 KByte (default)
------------------------------------------------------------
[ 15] local 10.0.0.2 port 40001 connected with 10.0.0.1 port 35105
[ ID] Interval Transfer Bandwidth Jitter Lost/Total Datagrams
[ 15] 0.0- 1.0 sec 237 KBytes 1.94 Mbits/sec 4.868 ms 0/ 165 (0%)
[ 15] 1.0- 2.0 sec 238 KBytes 1.95 Mbits/sec 4.911 ms 0/ 166 (0%)
[ 15] 2.0- 3.0 sec 237 KBytes 1.94 Mbits/sec 4.903 ms 0/ 165 (0%)
[ 15] 3.0- 4.0 sec 237 KBytes 1.94 Mbits/sec 4.858 ms 0/ 165 (0%)
[ 15] 4.0- 5.0 sec 238 KBytes 1.95 Mbits/sec 4.886 ms 0/ 166 (0%)
[ 15] 5.0- 6.0 sec 237 KBytes 1.94 Mbits/sec 4.898 ms 0/ 165 (0%)
[ 15] 6.0- 7.0 sec 237 KBytes 1.94 Mbits/sec 4.874 ms 0/ 165 (0%)
[ 15] 7.0- 8.0 sec 237 KBytes 1.94 Mbits/sec 1.795 ms 335/ 500 (67%)
[ 15] 8.0- 9.0 sec 238 KBytes 1.95 Mbits/sec 0.348 ms 688/ 854 (81%)
[ 15] 9.0-10.0 sec 237 KBytes 1.94 Mbits/sec 0.333 ms 683/ 848 (81%)
[ 15] 10.0-11.0 sec 238 KBytes 1.95 Mbits/sec 0.375 ms 688/ 854 (81%)
[ 15] 11.0-12.0 sec 237 KBytes 1.94 Mbits/sec 0.351 ms 684/ 849 (81%)
[ 15] 12.0-13.0 sec 237 KBytes 1.94 Mbits/sec 0.286 ms 683/ 848 (81%)
[ 15] 13.0-14.0 sec 238 KBytes 1.95 Mbits/sec 0.516 ms 688/ 854 (81%)
[ 15] 14.0-15.0 sec 237 KBytes 1.94 Mbits/sec 4.890 ms 5164/ 5329 (97%)
[ 15] 14.0-15.0 sec 29 datagrams received out-of-order
[ 15] 15.0-16.0 sec 237 KBytes 1.94 Mbits/sec 4.866 ms 0/ 165 (0%)
[ 15] 16.0-17.0 sec 237 KBytes 1.94 Mbits/sec 4.881 ms 0/ 165 (0%)
[ 15] 17.0-18.0 sec 238 KBytes 1.95 Mbits/sec 4.856 ms 0/ 166 (0%)
[ 15] 18.0-19.0 sec 237 KBytes 1.94 Mbits/sec 4.866 ms 0/ 165 (0%)
[ 15] 19.0-20.0 sec 238 KBytes 1.95 Mbits/sec 4.869 ms 0/ 166 (0%)
[ 15] 20.0-21.0 sec 237 KBytes 1.94 Mbits/sec 4.852 ms 0/ 165 (0%)
[ 15] 21.0-22.0 sec 237 KBytes 1.94 Mbits/sec 0.296 ms 314/ 479 (66%)
[ 15] 22.0-23.0 sec 238 KBytes 1.95 Mbits/sec 0.275 ms 688/ 854 (81%)
[ 15] 23.0-24.0 sec 237 KBytes 1.94 Mbits/sec 0.303 ms 683/ 848 (81%)
[ 15] 24.0-25.0 sec 237 KBytes 1.94 Mbits/sec 0.292 ms 684/ 849 (81%)
[ 15] 25.0-26.0 sec 238 KBytes 1.95 Mbits/sec 0.531 ms 687/ 853 (81%)
[ 15] 26.0-27.0 sec 237 KBytes 1.94 Mbits/sec 0.335 ms 684/ 849 (81%)
[ 15] 27.0-28.0 sec 237 KBytes 1.94 Mbits/sec 0.297 ms 684/ 849 (81%)
[ 15] 28.0-29.0 sec 238 KBytes 1.95 Mbits/sec 0.307 ms 688/ 854 (81%)
[ 15] 29.0-30.0 sec 237 KBytes 1.94 Mbits/sec 0.319 ms 683/ 848 (81%)
[ 15] 30.0-31.0 sec 237 KBytes 1.94 Mbits/sec 0.307 ms 684/ 849 (81%)
[ 15] 31.0-32.0 sec 238 KBytes 1.95 Mbits/sec 0.346 ms 687/ 853 (81%)
[ 15] 32.0-33.0 sec 237 KBytes 1.94 Mbits/sec 0.304 ms 684/ 849 (81%)
[ 15] 33.0-34.0 sec 237 KBytes 1.94 Mbits/sec 0.335 ms 684/ 849 (81%)
[ 15] 34.0-35.0 sec 238 KBytes 1.95 Mbits/sec 0.404 ms 687/ 853 (81%)
[ 15] 35.0-36.0 sec 237 KBytes 1.94 Mbits/sec 0.304 ms 684/ 849 (81%)
[ 15] 36.0-37.0 sec 237 KBytes 1.94 Mbits/sec 0.276 ms 683/ 848 (81%)
[ 15] 37.0-38.0 sec 238 KBytes 1.95 Mbits/sec 0.368 ms 688/ 854 (81%)
[ 15] 38.0-39.0 sec 237 KBytes 1.94 Mbits/sec 0.314 ms 684/ 849 (81%)
[ 15] 39.0-40.0 sec 237 KBytes 1.94 Mbits/sec 0.440 ms 683/ 848 (81%)
[ 15] 40.0-41.0 sec 238 KBytes 1.95 Mbits/sec 0.323 ms 688/ 854 (81%)
[ 15] 41.0-42.0 sec 237 KBytes 1.94 Mbits/sec 0.331 ms 683/ 848 (81%)
[ 15] 42.0-43.0 sec 237 KBytes 1.94 Mbits/sec 0.344 ms 684/ 849 (81%)
[ 15] 43.0-44.0 sec 238 KBytes 1.95 Mbits/sec 0.295 ms 688/ 854 (81%)
[ 15] 44.0-45.0 sec 237 KBytes 1.94 Mbits/sec 0.325 ms 683/ 848 (81%)
[ 15] 45.0-46.0 sec 237 KBytes 1.94 Mbits/sec 0.962 ms 689/ 854 (81%)
[ 15] 46.0-47.0 sec 238 KBytes 1.95 Mbits/sec 0.352 ms 688/ 854 (81%)
[ 15] 47.0-48.0 sec 237 KBytes 1.94 Mbits/sec 0.339 ms 689/ 854 (81%)
[ 15] 48.0-49.0 sec 237 KBytes 1.94 Mbits/sec 0.304 ms 683/ 848 (81%)
[ 15] 49.0-50.0 sec 238 KBytes 1.95 Mbits/sec 0.327 ms 688/ 854 (81%)
[ 15] 50.0-51.0 sec 237 KBytes 1.94 Mbits/sec 0.415 ms 688/ 853 (81%)
[ 15] 51.0-52.0 sec 237 KBytes 1.94 Mbits/sec 0.660 ms 679/ 844 (80%)
[ 15] 52.0-53.0 sec 237 KBytes 1.94 Mbits/sec 0.423 ms 684/ 849 (81%)
[ 15] 53.0-54.0 sec 238 KBytes 1.95 Mbits/sec 0.369 ms 688/ 854 (81%)
[ 15] 54.0-55.0 sec 237 KBytes 1.94 Mbits/sec 0.393 ms 684/ 849 (81%)
[ 15] 55.0-56.0 sec 237 KBytes 1.94 Mbits/sec 0.469 ms 683/ 848 (81%)
[ 15] 56.0-57.0 sec 238 KBytes 1.95 Mbits/sec 0.355 ms 684/ 850 (80%)
[ 15] 57.0-58.0 sec 237 KBytes 1.94 Mbits/sec 0.374 ms 683/ 848 (81%)
[ 15] 58.0-59.0 sec 238 KBytes 1.95 Mbits/sec 0.365 ms 688/ 854 (81%)
[ 15] 59.0-60.0 sec 237 KBytes 1.94 Mbits/sec 0.278 ms 679/ 844 (80%)
[ 15] 60.0-61.0 sec 237 KBytes 1.94 Mbits/sec 0.366 ms 683/ 848 (81%)
[ 15] 61.0-62.0 sec 238 KBytes 1.95 Mbits/sec 0.454 ms 688/ 854 (81%)
[ 15] 62.0-63.0 sec 237 KBytes 1.94 Mbits/sec 0.511 ms 682/ 847 (81%)
[ 15] 63.0-64.0 sec 237 KBytes 1.94 Mbits/sec 0.356 ms 685/ 850 (81%)
[ 15] 64.0-65.0 sec 238 KBytes 1.95 Mbits/sec 0.317 ms 688/ 854 (81%)
[ 15] 65.0-66.0 sec 237 KBytes 1.94 Mbits/sec 0.360 ms 684/ 849 (81%)
[ 15] 66.0-67.0 sec 237 KBytes 1.94 Mbits/sec 0.491 ms 683/ 848 (81%)
[ 15] 67.0-68.0 sec 238 KBytes 1.95 Mbits/sec 0.373 ms 688/ 854 (81%)
[ 15] 68.0-69.0 sec 237 KBytes 1.94 Mbits/sec 0.390 ms 683/ 848 (81%)
[ 15] 69.0-70.0 sec 237 KBytes 1.94 Mbits/sec 16.155 ms 5573/ 5738 (97%)
[ 15] 69.0-70.0 sec 30 datagrams received out-of-order
[ 15] 70.0-71.0 sec 238 KBytes 1.95 Mbits/sec 4.857 ms 0/ 166 (0%)
[ 15] 71.0-72.0 sec 237 KBytes 1.94 Mbits/sec 4.857 ms 0/ 165 (0%)
[ 15] 72.0-73.0 sec 237 KBytes 1.94 Mbits/sec 4.869 ms 0/ 165 (0%)
[ 15] 73.0-74.0 sec 238 KBytes 1.95 Mbits/sec 4.863 ms 0/ 166 (0%)
[ 15] 74.0-75.0 sec 237 KBytes 1.94 Mbits/sec 4.885 ms 0/ 165 (0%)
[ 15] 75.0-76.0 sec 237 KBytes 1.94 Mbits/sec 4.875 ms 0/ 165 (0%)
[ 15] 76.0-77.0 sec 238 KBytes 1.95 Mbits/sec 4.861 ms 0/ 166 (0%)
[ 15] 77.0-78.0 sec 237 KBytes 1.94 Mbits/sec 0.330 ms 593/ 758 (78%)
[ 15] 78.0-79.0 sec 237 KBytes 1.94 Mbits/sec 0.314 ms 684/ 849 (81%)
[ 15] 79.0-80.0 sec 238 KBytes 1.95 Mbits/sec 0.333 ms 687/ 853 (81%)
[ 15] 80.0-81.0 sec 237 KBytes 1.94 Mbits/sec 0.451 ms 684/ 849 (81%)
[ 15] 81.0-82.0 sec 237 KBytes 1.94 Mbits/sec 0.403 ms 683/ 848 (81%)
[ 15] 82.0-83.0 sec 238 KBytes 1.95 Mbits/sec 0.375 ms 688/ 854 (81%)
[ 15] 83.0-84.0 sec 237 KBytes 1.94 Mbits/sec 0.341 ms 684/ 849 (81%)
[ 15] 84.0-85.0 sec 237 KBytes 1.94 Mbits/sec 0.310 ms 683/ 848 (81%)
[ 15] 85.0-86.0 sec 238 KBytes 1.95 Mbits/sec 0.314 ms 688/ 854 (81%)
[ 15] 86.0-87.0 sec 233 KBytes 1.91 Mbits/sec 0.326 ms 671/ 833 (81%)
[ 15] 87.0-88.0 sec 237 KBytes 1.94 Mbits/sec 0.368 ms 684/ 849 (81%)
[ 15] 88.0-89.0 sec 237 KBytes 1.94 Mbits/sec 0.318 ms 688/ 853 (81%)
[ 15] 89.0-90.0 sec 237 KBytes 1.94 Mbits/sec 0.307 ms 684/ 849 (81%)
[ 15] 90.0-91.0 sec 235 KBytes 1.93 Mbits/sec 0.320 ms 679/ 843 (81%)
[ 15] 91.0-92.0 sec 238 KBytes 1.95 Mbits/sec 0.334 ms 688/ 854 (81%)
[ 15] 92.0-93.0 sec 237 KBytes 1.94 Mbits/sec 0.502 ms 701/ 866 (81%)
[ 15] 93.0-94.0 sec 237 KBytes 1.94 Mbits/sec 0.303 ms 683/ 848 (81%)
[ 15] 94.0-95.0 sec 238 KBytes 1.95 Mbits/sec 0.276 ms 684/ 850 (80%)
[ 15] 95.0-96.0 sec 237 KBytes 1.94 Mbits/sec 0.351 ms 684/ 849 (81%)
[ 15] 96.0-97.0 sec 237 KBytes 1.94 Mbits/sec 0.439 ms 691/ 856 (81%)
[ 15] 97.0-98.0 sec 238 KBytes 1.95 Mbits/sec 0.368 ms 687/ 853 (81%)
[ 15] 98.0-99.0 sec 237 KBytes 1.94 Mbits/sec 0.291 ms 694/ 859 (81%)
[ 15] 99.0-100.0 sec 237 KBytes 1.94 Mbits/sec 0.278 ms 684/ 849 (81%)
[ 15] 100.0-101.0 sec 237 KBytes 1.94 Mbits/sec 0.435 ms 683/ 848 (81%)
[ 15] 101.0-102.0 sec 238 KBytes 1.95 Mbits/sec 0.342 ms 688/ 854 (81%)
[ 15] 102.0-103.0 sec 237 KBytes 1.94 Mbits/sec 0.486 ms 684/ 849 (81%)
[ 15] 103.0-104.0 sec 238 KBytes 1.95 Mbits/sec 0.267 ms 687/ 853 (81%)
[ 15] 104.0-105.0 sec 237 KBytes 1.94 Mbits/sec 0.397 ms 680/ 845 (80%)
[ 15] 105.0-106.0 sec 237 KBytes 1.94 Mbits/sec 0.318 ms 689/ 854 (81%)
[ 15] 106.0-107.0 sec 237 KBytes 1.94 Mbits/sec 0.316 ms 684/ 849 (81%)
[ 15] 107.0-108.0 sec 238 KBytes 1.95 Mbits/sec 0.362 ms 688/ 854 (81%)
[ 15] 108.0-109.0 sec 237 KBytes 1.94 Mbits/sec 0.416 ms 683/ 848 (81%)
...
问题：1、为什么最开始的一段时间没有丢包（在第一秒的时候所接收的数据包就已经远远大于接收缓冲区的大小了啊）；
2、为什么每隔一段时间又会从没有丢包开始重复之前的过程呢？
3、当丢包率又从0开始的前一秒，丢包率为什么会发生突变呢？（如：14.0-15.0 sec，69.0-70.0 sec）