[Sip] Review of draft-ietf-sip-subnot-etags-01

Several comments:

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A possible security issue with the following scenario:
a) Subscriber subscribes with Suppress-Body-If-Match header with
etag of e1.
b) The document has changed but what was changed is suppressed from
that subscriber due to privacy.
c) The subscriber will get notify with new tag but with the same
document.

If the subscriber wants to it can compare to the previous value and
understand that something is being suppressed from it.

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Section 5.2 - second paragraph
"the first notification after the SUBSCRIBE" sounds as the first new
notification due to state change after the SUBSCRIBE. Maybe it is better
to write "the immediate notification following the SUBSCRIBE".
Note that there are other occurrences of the usage of "first" if you
decide to change.

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Section 5.2 - Last paragraph before the examples
typo - "simply copies"  should be  "simply copied"

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Section 5.2 - last example

Maybe there should be some explanation of why * is needed earlier
in the document. Liveliness use case is described below but maybe
better to explain earlier in the doc

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Figure 4
          ... poll interval elapses

Should probably be  "... poll interval elapses immediately"
Since it is zero initially.

Section 5.6
Should not this be the first use case described? From bandwidth pov
it is the most important.

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Section 6.1

"
...The notifier MUST remember the entity-tag of an entity as long
   as the version of the entity is current.  The notifier MAY remember
   the entity-tag longer than this, e.g., for implementing journaled
   state differentials (Section 6.4).
"

I understood from the text that the etag can be deleted by the notifier
when there is no current value to the entity. Consider the case when
a subscriber subscribed and got entity e1. Meanwhile the resource has 
become
stale (all previous publishes expired).
After e.g. two days the subscriber tries to subscribe with e1 for
the suppressing condition. What will the notifier selecting e1 as the
current entity tag again? If it does so the subscriber will not get
a notify (or body of notify) while it should have gotten one.
I hope that this is only my misunderstanding.

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Comment from Ofira Tal (IBM)

Should we consider the change of the entity tag as a reason to
send a notify with the entity tag only even though there is no
need to send an actual notify to the subscriber since the change
affects filtered information due to privacy or just filtering.
This will enable avoiding redundant NOTIFY in subsequent
subscribes since the latest entity tag will be used.

--Avshalom