[SIP] Comment ondraft-moyer-sip-appliances-framework-00.txt

[Jonathan Rosenberg]

Henning Schulzrinne wrote:
> 
> > Of course it does. You are not displaying them to a user for the purpose
> > of messaging and communications. If you are including content that has
> > semantic meaning to some upper layer system, its not a MESSAGE. Its
> > something else. MESSAGE does not just mean "deliver this to higher layer
> > protocol stack". It means a very specific thing - render this content to
> > the user, where this rendering is some kind of communication which might
> > be responded to.
> 
> While I'm no fan of overloading names, I don't think it's quite as clear
> cut as we'd like. Some considerations:
> 
> - It's bad if the same type of device (or the same name) gets two types
> of messages with very different meaning. This doesn't seem likely in
> this case.

What about a TV which acts as a message center? When a MESSAGE arrives,
is it a message to be displayed to the person watching, or a control for
the device itself?


> 
> - We already have different content for INVITE, distinguished by
> Content-Disposition. It's a bit a matter of taste whether to use a
> different Content-Disposition or a different message.  Thus, you
> definitely need a different Content-Disposition, other than render.

True, but in no case does the content of the message alter the
underlying semantics of the method or response code. It always provides
additional information that qualifies it. Here, its fundamentally
altering what happens to it.

> 
> - Having the same message makes sense if filtering, for example, would
> likely be the same for both.

These things serve much different functions. I think its likely you
would have very different policies for filtering them.

> In summary, I think either a new message type or MESSAGE can be made to
> work as long as the type of content is labeled clearly, not just in
> terms of syntax but also semantics.

This introduces yet another place an implementation needs to look at to
figure out what the purpose of the message is. Method is for that
purpose. 


-Jonathan R.

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