asterisk users - Nov 2009 - Restricting transfers between SIP phones

Hello,

We are in the process of splitting our phone system into two separate
logical systems for our two departments.  One of the goals of this
switch is to restrict members of one department from transferring calls
to the other, but not restrict them from calling that department
themselves.  So what I need to know is how to detect whether a call
from a member of that department is a transfer or an original call.

I've looked at the TRANSFER_CONTEXT setting, but that's only for
transfers with # and the T and t flags to Dial().  But we use SIP
hardphones (Linksys SPA942 & Grandstream GXP2020), which have built-in
transfer functions, and we would like to continue using those for
transfers, rather than building it into features.conf or dialplan...
Because we prefer attended transfers, and the user experience seems
more modern.

So, does anyone know of a way to detect whether a call from a SIP phone
is the first step of an attended transfer or an original call?  

Thanks!

-- 

C. Chad Wallace, B.Sc.
The Lodging Company
http://www.skihills.com/
OpenPGP Public Key ID: 0x262208A0

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"C. Chad Wallace" <cwallace at lodgingcompany.com> writes:
> So, does anyone know of a way to detect whether a call from a SIP phone
> is the first step of an attended transfer or an original call?  
This is impossible. At that point the phone has done this:

1) Put the original caller on hold
2) Made a new outgoing call

At some future point the phone might drop the second outgoing call and
go back to the first, or it might bridge the two in a transfer. You
can't know in advance.

The only way to achieve what you want is to never allow a call to a
different department when the same phone already has a call on hold.
This will however stop the (in some places quite common) practice of
calling the other department to ask a quick question, then returning to
the original caller.

It could be somewhat tricky to implement as well, but it should be
doable with call-groups.


/Benny

Hi!
> > So, does anyone know of a way to detect whether a call from a SIP
phone
> > is the first step of an attended transfer or an original call?  
It could probably work if you put a SIP proxy in between (ref. Kamilio).
> The only way to achieve what you want is to never allow a call to a
> different department when the same phone already has a call on hold.
> This will however stop the (in some places quite common) practice of
> calling the other department to ask a quick question, then returning to
> the original caller.
Workaround: Have a second SIP account on the phone which must be used if 
you call the other appartment.
> It could be somewhat tricky to implement as well, but it should be
> doable with call-groups.
With SNOM phones you could use an "Action URL" to catch phone-based 
attended or blind transfer actions. The called URL can then trigger 
anything you like on your server.

Philipp