[e2e] How could I know one RTT estimation techniques better than the other?

[Craig Partridge]

I don't think anyone's ever studied in great detail what the standards
for an RTT estimation algorithm should be.  However, what people have
typically used in the path is something like this.

First, remember that the key issue is the RTO algorithm -- the RTT
estimator is used to set a timeout function using the RTO value -- and
what you really care about is when a timeout goes off.

Given you are evaluating when timeouts occur, there are two goals:

    1. Few or no spurious timeouts.  That is, if the timeout goes off,
      the packet is, with very high probability, lost.  Furthermore, this
      is with very high probability over just about any network path
      you can imagine (including flapping network lines, wireless, etc).

    2. Timeouts that occur soon in cases where a packet is really lost.

In short, the perfect RTO algorithm would never timeout when a packet isn't
lost, and timeout the moment a packet is lost.

The goals are ordered -- if you've got lots of spurious timeouts, your
algorithm is no good.   If timeouts take a little while when packets are
lost, that's OK.

Thanks!

Craig


In message <1085755247.40b74f6f9f261 at www.e-web.uum.edu.my>, "Osman Ghazali (FTM
)" writes:

>Hi,
>I have two layered multicast protocols (LMPs). The protocols use different
>RTT eatimation techniques. I created another LMP exactly the same
>as the first LMP but with the second LMP's RTT estimation technique.The
>problem I have now is how could I know which RTT estimation is more
>appropriate/accurate/better for layered multicast. Is there any metric
>for RTT or any way we can evaluate RTT estimation techniques.
>
>Thank you.
>Osman