[Freeswitch-users] att_xfer and loopback

Alex Lake alex at digitalmail.com
Thu Jun 7 17:56:15 MSD 2012

(Reconnecting to Mailing List)

Hi guys - so I go for a break to celebrate 60 years of the queen and 
look what's here now!

Some really useful bits here. Thanks to Avi for answering in my place. 
The reasons he cites for desiring to use loopback are correct. However, 
because our scripts are auto-generated (from a base spec in our own XML 
format), it is viable (if somwhat undesirable) to spew out a 
superficially long and complex lua script as an alternative.

One of the (seemingly radical) things we're trying to do is to offer 
SIP-grade functionality to mixed SIP & PSTN endpoints. This is best 
illustrated with an example:

User Fred is a mobile kind of guy - although he will generally take 
calls on the SIP handset on his desk, he is often out and about, and so 
will also take calls on his mobile. His company has one of our hosted 
pbx services and he's extension 305. He's set things up so that the 
calls ring first on his SIP handset and, after a delay of 5s, on his 
mobile. Because mobiles have voicemail systems that can get in the way, 
he has the "voicemail defeat" option, whereby on answering the call (and 
hearing the whisper) he has to press 1 to show it's really him accepting 
the call.

A colleague, Bill, on extension 301 is in a very similar situation.

When Bill and Fred are both in the office, things are easy: If Bill gets 
a call that he wishes to handover to Fred (with a briefing), he can do a 
simple attended transfer SIP to SIP.

When they're both out of the office, things are a little more complex:

Firstly, Bill takes the call on his mobile (which doesn't have a 
transfer button) - he uses the * * key sequence to access a mid-call 
menu, selects the "attended transfer" facility and keys in Fred's 
extension number (305). The attended transfer script must do just what a 
normal call to Fred's DDI would do - i.e. Call the SIP handset then, 5s 
later, start trying to find him on his mobile (with the "push 1 to 
accept" feature).

Hopefully that gives an idea of how what we're doing is a bit complicated.

I will definitely try Antony's runes and see how that works.

I'm also up for trying to "improve" the wiki from the point of view of 
FreeSwitch beginners. The main thing I would suggest is much more use of 
examples (and fully contextualised examples, not just free-floating 

Anyway, thanks all (and hope this email gets through to the list)

Join us at ClueCon 2011 Aug 9-11, 2011
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