Re-transmissions in Iperf3 test between 2 stations

[bhatramya]

Hi,

I was testing performance of a custom wireless network using Iperf3 and found a lot of retransmissions. Hence I checked Iperf3 for an example network (with 2 stations and 1 access point using the command sudo mn --wifi). Even here, I could see a lot of retransmissions (attached image). Am I missing something here?

Thanks and regrads, Ramya

[ramonfontes]

When a packet is not acknowledged it will be retransmitted and I'm pretty sure that it doesn't occur only when T = 6 and 7. I suggest you check on how Iperf3 calculates TCP Re-transmissions.

[bhatramya]

The above image is the result of Iperf3 for the network generated by sudo mn --wifi command. I am wondering whether you get the similar output for Iperf3. Could you please let me know whether you see any retransmissions?

Thanks and regards, Ramya

[ramonfontes]

Yes, I get similar result.

[  7] local 10.0.0.2 port 34052 connected to 10.0.0.1 port 5201
[ ID] Interval           Transfer     Bitrate         Retr  Cwnd
[  7]   0.00-1.00   sec  7.62 MBytes  63.9 Mbits/sec    0    324 KBytes       
[  7]   1.00-2.00   sec  7.52 MBytes  63.1 Mbits/sec    0    622 KBytes       
[  7]   2.00-3.00   sec  6.25 MBytes  52.4 Mbits/sec    0    923 KBytes       
[  7]   3.00-4.00   sec  7.50 MBytes  62.9 Mbits/sec    0   1.16 MBytes       
[  7]   4.00-5.00   sec  6.25 MBytes  52.4 Mbits/sec    0   1.43 MBytes       
[  7]   5.00-6.00   sec  7.50 MBytes  62.9 Mbits/sec    0   1.67 MBytes       
[  7]   6.00-7.00   sec  6.25 MBytes  52.4 Mbits/sec   29   1.56 MBytes       
[  7]   7.00-8.00   sec  6.25 MBytes  52.4 Mbits/sec  254    987 KBytes       
[  7]   8.00-9.00   sec  6.25 MBytes  52.4 Mbits/sec    0   1.03 MBytes       
[  7]   9.00-10.00  sec  6.25 MBytes  52.4 Mbits/sec    0   1.07 MBytes       
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Retr
[  7]   0.00-10.00  sec  67.6 MBytes  56.7 Mbits/sec  283             sender
[  7]   0.00-10.09  sec  60.4 MBytes  50.2 Mbits/sec                  receiver

However, you can have a different result if you decrease the htb rate (default is 54Mbit for AP and Stations) as you can see below:

mininet-wifi> sta1 tc qdisc del dev sta1-wlan0 root
mininet-wifi> sta2 tc qdisc del dev sta2-wlan0 root
mininet-wifi> sta1 tc qdisc add dev sta1-wlan0 root handle 5:0 htb default 1
mininet-wifi> sta2 tc qdisc add dev sta2-wlan0 root handle 5:0 htb default 1
mininet-wifi> sta1 tc class add dev sta1-wlan0 parent 5:0 classid 5:1 htb rate 40.000000Mbit burst 15k
mininet-wifi> sta2 tc class add dev sta2-wlan0 parent 5:0 classid 5:1 htb rate 40.000000Mbit burst 15k

[  7] local 10.0.0.2 port 34082 connected to 10.0.0.1 port 5201
[ ID] Interval           Transfer     Bitrate         Retr  Cwnd
[  7]   0.00-1.00   sec  5.64 MBytes  47.3 Mbits/sec    0    233 KBytes       
[  7]   1.00-2.00   sec  4.47 MBytes  37.5 Mbits/sec    0    257 KBytes       
[  7]   2.00-3.00   sec  5.03 MBytes  42.2 Mbits/sec    0    257 KBytes       
[  7]   3.00-4.00   sec  4.47 MBytes  37.5 Mbits/sec    0    257 KBytes       
[  7]   4.00-5.00   sec  4.47 MBytes  37.5 Mbits/sec    0    257 KBytes       
[  7]   5.00-6.00   sec  4.47 MBytes  37.5 Mbits/sec    0    257 KBytes       
[  7]   6.00-7.00   sec  4.47 MBytes  37.5 Mbits/sec    0    257 KBytes       
[  7]   7.00-8.00   sec  4.47 MBytes  37.5 Mbits/sec    0    257 KBytes       
[  7]   8.00-9.00   sec  4.47 MBytes  37.5 Mbits/sec    0    257 KBytes       
[  7]   9.00-10.00  sec  4.47 MBytes  37.5 Mbits/sec    0    257 KBytes       
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Retr
[  7]   0.00-10.00  sec  46.5 MBytes  39.0 Mbits/sec    0             sender
[  7]   0.00-10.03  sec  45.5 MBytes  38.1 Mbits/sec                  receiver

[bhatramya]

Thanks for the input. This worked. I will try something similar in my network as well.

T&R, Ramya