Help calculate tcp retransmission rate from json result, end. sum.sent

[megaxm]

Hi.
Could you please explain if it is possible to calculate the tcp retransmission rate.
Given the following json result, end. sum.sent
"sum_sent": { "start": 0, "end": 60.000091, "seconds": 60.000091, "bytes": 2942828544, "bits_per_second": 392376544.0955748, "retransmits": 291, "sender": true }
My understanding is that the field "retransmits" is in segments, so I would calculate the retransmission rate using
retransmits / total_segments_sent, but I only have the bytes_sent field, is there anyway to convert the number on the field bytes_sent into segments, or the filed retransmits into bytes for that matter, so that I can apply the same unit to get the rate?
Thanks so much in advance.

[davidBar-On]

Hi, pack length is fixed size and is set by the -l parameter (default is usually 128KB = 131,072 bytes). Therefore dividing bytes by the packet size should work. E.g, in the example data you gave and assuming the default packet length was used, 22,452 packets were sent.

[megaxm]

Thanks so much.

[megaxm]

Sorry David, one more thing.
I have the "blksize": 131072, in the result as you pointed out, but also the "tcp_mss" is set to 1514,
Should I still use blksize or tcp_mss? to get the the counts of packets Eg. packets=bytes/blksize or packets=bytes/tcp_mss.
then rate=retransmits/packets ?
Could you please let me know.
Thanks.

[davidBar-On]

Hi, the "tcp_mss" is the socket's TCP_MAXSEG value, which is the segment size used by the TCP/IP stack for sending the data to the other side. However, it is not related to the packet size used by iperf3.

To make sure, you can use the -k option to set the number of packets transmitted. E.g. set -k 10, and if the packets=bytes/blksize is correct test results should show "bytes": 1310720.

[megaxm]

Excellent thanks again for your time.