Hi all. I am a newbie network engineer.
I did a small experiment with iperf3. But I run into a small problem. *(1) My question.* I think TCP flow do not act properly despite of its congestion control. *(2) The experiment environment* - Ubuntu 14.04 - Mininet 2.3.0d5 : [TOPOLOGY] HOST -SWITCH - HOST - Linux tc at kernel version 4.4.0-148-generic : Set all link bandwidth 100Mbps with proper MTC *(3) The contents of experiment* a. server : iperf3 -s -p 1212 -f m -A 7 -i 1 b. client : iperf3 -c 10.0.0.1 -p 1212 -t 10 -f m -b 130M -A 7 -l 63k -w 10M -i 1 Connecting to host 10.0.0.1, port 1212 [ 4] local 10.0.0.2 port 42010 connected to 10.0.0.1 port 1212 [ ID] Interval Transfer Bandwidth Retr Cwnd [ 4] 0.00-1.00 sec 14.0 MBytes 118 Mbits/sec 0 570 KBytes [ 4] 1.00-2.00 sec 15.5 MBytes 130 Mbits/sec 0 1.13 MBytes [ 4] 2.00-3.00 sec 15.5 MBytes 130 Mbits/sec 0 1.69 MBytes [ 4] 3.00-4.00 sec 12.7 MBytes 106 Mbits/sec 0 2.27 MBytes [ 4] 4.00-5.00 sec 11.3 MBytes 95.0 Mbits/sec 0 2.84 MBytes [ 4] 5.00-6.00 sec 11.4 MBytes 95.5 Mbits/sec 0 3.41 MBytes [ 4] 6.00-7.00 sec 11.4 MBytes 95.4 Mbits/sec 0 3.98 MBytes [ 4] 7.00-8.00 sec 11.3 MBytes 95.0 Mbits/sec 0 4.55 MBytes [ 4] 8.00-9.00 sec 11.4 MBytes 95.3 Mbits/sec 0 5.12 MBytes *(4) My question in detail.* - Due to its bandwidth ( 100Mbps ), I think the flow will experience a congestion and decrease its cwnd. - But it didn't. the cwnd of the flow is increasing continuously. - Furthermore, although it didn't decrease its cwnd, it decreased its rate. How can it happen? There is no re-transmission. Could you give me a litte hint for understanding this weird thing? Thank you for reading! Sincerely, ByoungUk Lee.
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