in line
/sal
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.
[MJF] Agreed. This is a decision the package implementor can make as
long as the draft doesn't specify the exact method for when to start
the timer for the next NOTIFY. In event packages that do not allow
overlapping NOTIFYs, the implementor would be free to devise a
mechanism for scheduling the next NOTIFY in a way that both satisfies
the event package rules and produces satisfactory
throttle/average/force behavior. Maybe this calls for adding a warning
that when creating the NOTIFY timer mechanism care should be taken to
remain consistent with the supported event package.
[Sal] but in that case you should implement on the server a specific
timer mechanism different for each event package. It would be better
have a general mechanism that work independently from the specific event
package, it would be also make the implementation easier.
An alternative would be start the timer just after having send out a
Notify, but then, even if the timer fires, wait for the completion of
the transaction before create the new Notify and sending it out.
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