RTT calculations

[Eddie Kohler]

> The later part of my click config file looks like this:
> 
> Myelement -> EtherEncap() -> ToDevice();

If this is really the later part of your config -- no Queue or anything --
and you are using a polling driver, then the packet will probably get sent
very soon after MyElement emits it. By "sent", I mean "handed to the device
for sending", but that latency is usually pretty predictable.

On the other hand, if there is a Queue, then there's queueing delay; and if
you are using an interrupting driver (FromDevice/ToDevice, instead of
PollDevice/ToDevice), then Click sends the packet via Linux queues, whcih
may introduce another delay.

I'm surprised your RTT is so variable, but people have been reporting
things like that on the list recently.

So are you using PollDEvice or FromDevice? Which interface card? Is the RTT
variable with Linux alone?

Eddie