Hi Lisa,
-----Original Message-----
From: ext Lisa Dusseault [mailto:lisa at osafoundation.org]
Sent: 21 July, 2006 22:29
To: widex at ietf.org
Subject: [Widex] Review of Requirements document
This review comes from me as an individual. These are
questions and suggestions for improving the document (not
requirements from your advising AD), and it may well be that I
don't understand the problem space well enough yet.
4. Scenarios
I am not sure why the NAT traversal and IPv4/IPv6 stuff is in
this document in so much detail. Does it require this much
explanation and diagrams? What requirements follow from these
scenarios?
The relation might not be so obvious but, as Widex will define both a
framework and a message exchange used for synchronization (e.g. WOs),
implementers needs to be aware of the network environment challenges
when they will choose the service discovery and session setup
mechanism
and the transport protocol that is most appropriate for their
particular
target environment. We might have gone too deep into details in this
document and a better place for those should have been the framework
document but they are quite important to understand the problem.
To a reader like me, a scenario that described an example use
case justifying the "multiple modes of interaction" would be useful.
Would it be enough if we point the reader instead to the W3C's
Multimodal Architecture which is one possible customer of the Widex
framework?
I think your scenarios are designed for a reader that
understands the problem that's being solved but may not
understand the networking challenges, whereas I'm a reader who
understands the networking challenges more than I understand
the problem being solved :)
5. Requirements
5.1:
" o The framework MUST be modular, e.g. multiple session setup
mechanisms may be used."
Flexibility is good; interoperability is even better. How
about adding something like: "There must be ONE
mandatory-to-implement session setup mechanism" (you might
also add desired characteristics for the mandatory mech.)
The Widex framework can be used in different environments and those
can
have characteristics that differentiate them quite a lot and these
characteristics were taken into account by the developers of the
service
discovery and session setup protocols. For example, in an unmanaged
network like those typically found in home networks, an implementer
may
choose between Rendezvous/Bonjour and UPnP. In other environments,
where
SIP infrastructure is available, implementers can use it. Other
alternatives include SLP or SRV records or it might be possible
that in
some close environments there is no need for service discovery and
session setup at all if you have means to manually input the URL of
the
server in the client.
It would be great if a mandatory mechanism will be defined but it
seems
that we don't have any mechanisms that is universally applicable. For
this reason, in order to help interoperability and to provide a
somehow
unified experience regardless of what is the actual service discovery
and session setup mechanism, the framework has some requirements on
what
the mechanism must and should negotiate (they are listed in the
framework draft).
5.2:
" o The service discovery mechanism MUST be able to discover both
Widex Renderers and Widex Servers."
At a minimum, there are Security Considerations implications
from this, particularly w.r.t. privacy of renderers. I would
like to understand better the reasoning behind the requirement
for discoverability of Widex renderers.
A TV set or a smart screen can play very well the role of Widex
renderer
and it might be useful if you could use this as a secondary
display. Of
course, privacy of the renderers is very important and implementers
should balance what capabilities should be revealed and which
should be
kept private. For example, somebody can choose not to reveal anything
about the renderer besides that it is a Widex renderer but that will
have quite negative impact as the server will not be able to
provide the
UI that best suits the renderer capabilities, instead providing the
default UI.
Privacy concerns are valid also for the Widex servers which might host
sensitive applications and you want to allow only specific
users/renderers to interact with. Fortunately, these issues were taken
into account by the designers of service discovery and session setup
mechanisms.
5.3:
" o The WOs MUST contain only information having remote scope."
I just don't understand this requirement.
The meaning of WOs was defined in section 3.3. and specifically refers
to the WOs.Event. Do you think that we need to be more specific about
which WOs this requirement is about? We need to think that while
developing the framework document we detected that we need more WOs
than
initially envisioned in this document (e.g. WO.Selector) and the
requirement should cover also those ones.
5.3:
" o The WOs MAY support multiple modes of interaction, and it
is the
responsibility of the application to synchronise modalities and
not that of the Widex protocol."
I believe this implies that multiple modes would indicate
multiple Widex protocol sessions. Is that correct? It might
be good to state the implication.
Yes, this implication in correct.
Thanks,
Lisa
Thanks,
Vlad
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