Hi,
see my comments in line
thanks
Sal
Michael Froman wrote:
<snip>
[Sal] that is exactly the point. Throttle/force/average do not break
or modify in any way the retransmission mechanism.
[MJF] Perfect. I think your statement here is far more clear than the
last sentence of the paragraph you quoted above. More on this below.
or that, for example, retransmissions modify the time between
forced NOTIFYs by the time taken for the retransmissions to
successfully complete the transaction? An example is the case when
the NOTIFY gets to the subscriber quickly, but the 200OK is slow to
make it back to the notifier. Start with a force value of 2
seconds. The subscriber thinks the transaction is over and is now
expecting a forced NOTIFY 2 seconds from now. The notifier has not
completed the transaction. The next NOTIFY from the notifier can
happen anytime up to T1 + 2 sec.
I agree that throttle/force/average should not interfere with the
normal retransmission mechanism. However, I don't agree that
waiting for the transaction to complete before starting the
throttle/force/average timer is going to give much benefit (or
always predictable results).
[Sal] While I agree that this behaviour (waiting for the transaction
to complete) can not always give "predictable" results and that is
bad especially if you want use it to track the location of a UA,
However making "throttle/force/average" timers independent (so to
say) from the the retransmission mechanism can lead to situation
where the timer fires and then you should send out a new NOTIFY when
there is still a retrasmission of a previous one. Any thought on how
to solve this situation without break the retransmission mechanism?
[MJF] Sending out a new NOTIFY while there is still a retransmission
of a previous NOTIFY is definitely not an optimal solution, but it
does not break the retransmission mechanism. It might violate a
particular package's rules on overlapping NOTIFYs, but that would be
an implementer's obligation to handle correctly.
My primary objection is that the text in the draft seems to specify
exactly one way to deal with when to schedule the next NOTIFY. Waiting
for the response to the NOTIFY before scheduling the time for the next
NOTIFY is an expensive operation with virtually no benefit under
normal operation. If the network is working well, the NOTIFY/200OK
happens effectively immediately and there is no real value in waiting
to start the throttle/force/average timing until the transaction
closes. The timer can start when the NOTIFY goes out.
[Sal] right, but as usual in the ideal situation you do not have
problems. I do think that your suggestion of starting the timer when the
NOTIFY goes out, it a good idea and would improve the mechanism. However
before to change the text I would like to investigate and discuss deeper
the possible side effects.
If the network isn't working well, both sides are receiving and/or
sending messages they'd rather not deal with. Setting the timer prior
to the transaction completing doesn't make the situation appreciably
worse. Because the server cannot accurately determine the client's
view of when the transaction ends during network misbehavior, this
method is guaranteed to produce results confusing to the user.
[Sal] if the server sends out a new NOTIFY before the previous one is
acknowledged could be worse in some situation, I am thinking of the
cases where a NOTIFY contains a state deltas. In this scenario (that I
think it will be the most common) if a NOTIFY is received out of order
the the Subscriber has to re-subscribe to force a NOTIFY containing a
complete state.
I would suggest the following text replace the last paragraph of 4.2.2
(and similar changes to 5.2.2 and 6.3.2):
Retransmissions of NOTIFY requests are not affected by the throttle,
i.e., the throttle only applies to the generation of new
transactions. In other words, the throttle does not in any way
break or modify the normal retransmission mechanism.
This allows the implementor to decide, possibly based on package
considerations and network traffic, how to schedule the time of the
next NOTIFY.
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