On Aug 14, 2009, at 6:22 PM, Satyam Sinha wrote:
>
> > 2) Should the remote system apply a sliding window for Detection Time or
> > fixed slotted windows that are not overlapped are acceptable?
> What does the window contain? (I understand you are trying to do
> something similar to TCP). Are you using a mechanism like that for
> echo packets?
From a transmit perspective, if you take into account jitter, one should have the timers as sliding window based. One should schedule the next transmit at last-transmit-time + tx-timer (jittered) instead of expected-last-transmit-time + tx-timer (jittered). The variance in the jitter alongwith slotted window usage between two transmits could cause the tx-time between two packets to be more than the tx-timer.
This doesn't matter as long as the timers aren't severely late. In most cases the jitter subtraction will more than make up for latencies in the timer system, and even if a packet is sent a little late, it doesn't matter, so long as *some* packet arrives within the detection time.
From a receive perspective you could do either. If you used slotted windows, you might see more than one packet in a slot but you are still guaranteed to see atleast one packet every slot.
This is all very implementation-specific, and is identical in character to any hello-based protocol. The only real difference is that in some cases you may run BFD with a much shorter timeout, so all of the system components have to be up to the task, however you do it.
--Dave
