Re: Last Call: draft-lawrence-sipforum-user-agent-config (Session Initiation Protocol (SIP) User Agent Configuration) to Informational RFC

[Scott Lawrence <[e-mail]>]

On Wed, 2010-04-07 at 08:59 -0700, Dave CROCKER wrote:
> 
> On 4/6/2010 9:34 AM, Scott Lawrence wrote:
> >> What is the justification that mandates a more complex model than
> >> these use?  It's not usually considered sufficient to simply cite the fact that
> >> some operators somewhere want something different.  There needs to be a
> >> compelling case made.
> >>
> >> It is always possible to invent edge cases that appear to justify a different
> >> paradigm.  The real question is about real need.
> >
> > The configuration data we're discussing here is substantially more
> > complex and more important to the operation of the device than the
> > information provided by either DHCP or DNS.
> 
> The data are more "important" than the device's IP Address?
> 
> As for "complexity", I don't see how the choice of update mechanism is affected 
> by data complexity.

Spenser was correct in complexity analogy, but there's more to it than
that.  In SIP (at least in the phone/communication systems I'm most
familiar with) the functionality of the system as a whole is distributed
- some things are done in a proxy, some are done in various 'feature
servers', and many things are done in the UAs themselves.  For many
changes in 'phone system' behavior to be done correctly, one must change
the behavior of the UAs at the edge.  Pushing intelligence out to the
edge has many nice scaling and evolution qualities, but it has downsides
too; specifically the need to be able to modify configuration data in
many devices at the edge of the network.

Typical SIP phones have hundreds of configuration parameters - the few
that are listed here are not the ones that would need changing
frequently.  Since there is no standard for what those parameters are or
how they are expressed, they are not in scope for this spec (personally,
I'd have left all of section 3 out).