Network Throughput Calculator- how to calculate RTT

[Loc Nguyen]

Hi,

I am using this link below to do Network Throughput Calculator

https://wintelguy.com/wanperf.pl

One of the parameter  is RTT.  Could someone advise where do I get RTT?

As I remember, it is the time between 1st packet and 2nd packet when we start capture a TCP Connection. Is it correct?

In my case, if you look at the picture below. RTT= 76ms. Is it correct?

 

It is urgent and i appreciate it if you can respond quick

Thanks

Loc

[Reza Sharifi]

Hi,

RTT (Round Trip Time) between 2 points.

https://www.wireshark.org/lists/wireshark-users/200707/msg00163.html

HTH

[Loc Nguyen]

Thanks. do you know where we can get an average RTT? 

I see people talk about it in the link you sent but I did not see where to get it.

[Wassim Aouadi]

I guess you want to calculate the TCP RTT, right? As far as I know, one way to define the TCP RTT is as follows: the time between one TCP packet sent and the reception of its ACK.

Select any TCP packet in the capture. Then go in the packet details pane. Expand the [SEQ/ACK Analysis] menu. The information you are looking for is The RTT to ACK the segment was...

Note though, that the TCP RTT varies in time, that is why you will find different values in the capture.

You can also display all TCP RTT values in the TCP communication, Right click on the TCP ACK RTT analysis and select Apply as a column. It will be displayed as a column:

[Loc Nguyen]

Thanks, do you know where we can get an average RTT ?

[Wassim Aouadi]

One way is to use the display filter "tcp.analysis.ack_rtt" (without the quotes). Then go to File -> Export Packet Dissections -> As CSV. Select "All packets". Once you saved your CSV file, you need some Excel skills to extract only the RTT column from the CSV and put it in a column. Then you apply the average function in Excel and you get what you were looking for.

[Loc Nguyen]

Thanks Wassim

[Joseph W. Doherty]

Can you successfully ping between the two hosts?  If so, that too will provide you RTT.

[Loc Nguyen]

Joe, Is the RTT from ping's result different from the RTT when we have a TCP connection?

[Joseph W. Doherty]

They can vary from each other, usually not by much, due to a couple of factors, such as overall network traffic (adding latency) and/or how quickly the host processes the traffic (which can vary per application).  It's also possible, the network, using QoS, might provide different treatment levels.

That noted, generally both likely will show RTTs in the same ballpark with both skipping about a bit in their shown values.

For the calculation you're doing, you'll want to use the minimal value, if you're looking to calculate the maximum possible bandwidth throughput (also this RTT would be used if calculating TCP RWIN size to support the BDP - which your referenced calculator also provides).