XPost: alt.comp.os.windows-11   
   From: daniel47@somewhere.someplaceelse   
      
   On 8/09/2025 11:43 pm, Lew Pitcher wrote:   
   > On Mon, 08 Sep 2025 23:24:12 +1000, Daniel70 wrote:   
   >   
   >> On 8/09/2025 10:21 pm, Dan Purgert wrote:   
   >>> On 2025-09-08, Daniel70 wrote:   
   >>>> [...]   
   >>>> Which got me thinking ..... How do "they" Speed-test Internet Links?? ..   
   >>>> particularly How do 'they' distinguish the Up-link TIME from the   
   >>>> Down-link TIME?? e.g. my current speeds, using Speedtest [...]   
   >>>   
   >>> For the most part, a speedtest works by you downloading a file of known   
   >>> size (say 100 MiB), and then sending it back.  Exact file size will vary   
   >>> by testing provider, but essentially it's just this:   
   >>>   
   >>> Download start = 0.00   
   >>> Download end = [TIME]   
   >>>   
   >>> File size / TIME = X Mbit / sec   
   >>   
   >> But how does the distant end know when I have received the entire file   
   >> (i.e. Download end time)??   
   >>>   
   >>> Upload Start = 0.00   
   >>> Upload end = [TIME]   
   >>>   
   >>> File size / TIME = Y Mbit / Sec   
   >>>   
   >> Similarly, how does the distant end know when my computer started the   
   >> Upload (Upload start time)??   
   >   
   > The transfers typically use TCP, and that protocol includes feedback   
   > from the receiving end as to whether or not it has received the data   
   > sent. Typically, this feedback is in small enough packets that transmission   
   > latency doesn't affect the overall throughput measurement enough to   
   > matter.   
   >   
   > In theory, only one end has to make the timing measurements; It can   
   > be the sending end, or the receiving end.   
   >   
   > For sending-end measurement, the sender   
   > - starts the clock   
   > - sends a known amount of data to the receiver, obeying the receiver's   
   >    TCP flow-control requests   
   > - stops the clock at the TCP FIN/FIN-ACK end-of-data acknowledged   
   > - computes elapsed time   
   > - computes upload transfer rate (known amount of data / computed elapsed   
   time)   
      
   O.K., so my computer sends my Start time, then a certain amount of Data   
   (1kB, maybe), and then sends my computers End Time. So including the   
   clock times, totaling, maybe, 1.1kB.   
      
   The Distant computer determines how long it took for my computer to send   
   those three Datas (1.1kB) ..... but is it really able to determine how   
   long it took to get that 1.1kB across the Wire/Cable/Satellite/Whatever   
   connecting medium or just how long it took my Computer to send the data??   
      
   > For receiving-end measurement, the receiver   
   > - waits for the TCP connection   
   > - starts the clock   
   > - receives the data, counting the volume as it goes   
   > - stops the clock at the TCP FIN/FIN-ACK end-of-data received signal   
   > - computes elapsed time   
      
   So the elapsed time (i.e. the time for my computer to actually send the   
   1.1kB), as measured by the receiving-end device should be the same time   
   as measured by my Sending Device .... but still doesn't know how long   
   the data transfer from Me to YOU to happen.   
      
   > - computes download transfer rate (counted amount of data / computed elapsed   
   time)   
   >   
   > With those web-page throughput estimators (https://www.speedtest.net, for   
   example),   
   > the throughput computation usually occurs at the web server, with the   
   webpage providing   
   > javascript (or other code that will execute on the client system) to either   
   > sink the TCP connection and data being sent (from the web server to the   
   client system   
   > for the upload test, or source the TCP connection and data (from the client   
   system to   
   > the web server) being sent for the download test.   
   >   
   >   
   > HTH   
   >   
   I don't know if I've done a good enough job of explaining my situation   
   .... just goes to show how confused I am.   
   --   
   Daniel70   
      
   --- SoupGate-Win32 v1.05   
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