asterisk users - Jun 2015 - Can Asterisk help me with some requeriments, of my current project?

> 1 - My SIP server (Asterisk) will have some SIP clients registered in its
SIP registrar. Let's say 6 SIP clients. In my project I have to implement a
way of a SIP client making a call to a number and all others 5 SIP clients ring.
That is, the others 5 SIP clients must receive the SIP INVITE. Can Asterisk help
me with such functionality?
The Dial() application lets you specify two or more destinations,
separated by "&" characters.  When you execute an application call
of
this sort in your dialplan, Asterisk dials all of the destinations in
parallel.  If they're SIP clients, each will receive an INVITE at the
same time.

http://lists.digium.com/pipermail/asterisk-users/2005-April/094621.html
> 2 - When several SIP client ring, if one answer the call first, the others
will have to stop ringing immediately. Can Asterisk help me with this
requirement?
If you use the "dial in parallel" technique I just described, when one
client answers the call, Asterisk sends out a "cancel invite" to each
of
the other clients it had dialed.

This *should* result in each of those other clients stopping their ring
promptly... but that's up to the client.
> 3 - How to avoid one of the SIP clients receiving SIP INVITES? That is, one
of the SIP clients is forbidden to receive calls. Is there a way to program it
in Asterisk, maybe via dial plan?
The question of which clients are called in response to a Dial() in your
dial-plan, depends entirely on which clients are named in that Dial().
If you have five clients, and only include three of them in a particular
Dial(), only those three will ring.

If you have a client which is never named in a Dial() anywhere in your
dialplan, Asterisk will never call it.  It will be an "outbound calls
only" client.

> 4- Let's suppose that I have a data base (let's say SQLite) in my
SIP server (Asterisk) and I need implement a way of SIP Clients executing
queries in such database. Could such queries be done/sent via SIP messages to
Asterisk? Is there a way of accessing a database by meas of Asterisk, during a
call, for example to collect information about others SIP Clients?  Here I'm
intending to create a software to be a kind of interface between Asterisk and
the database, if necessary.
In principle, a client could "dial" a URI which includes parameters
for
a SIP query.  Asterisk's dialplan would recognize this URI (for example,
it might start with *888* or some other such string), parse it, and feed
the bits to an SQL query.

With this approach (or any approach which accepts an SQL query or
parameters from a client) you must be *EXTREMELY* careful to avoid "SQL
injection" attacks.

The story of little Bobby Tables is what I'm talking about here:
https://xkcd.com/327/
> 5 - If I need to send SIP messages all encrypted, using SSL or TLS , to the
Asterisk, will this SIP server be able to interpret all messages correctly? Is
there a way of let Asterisk talk with SIP clients in a secure way, using SSL,
for example? Can Asterisk help me with this?
https://wiki.asterisk.org/wiki/display/AST/Secure+Calling+Tutorial