Attended Call Forward


I don’t think this is a FreePBX issue but I was hoping that someone may be able to explain to me or help out on my issue below

Server is FreePBX 2.11

I have numerous Polycom IP500 wired handsets and they can forward between each other without any issues however I also have a number of Unidata WPU-7800 wifi handsets. I have recently found that if someone does an attended transfer from an IP500 to a wifi handset and hangs up (therefore sending the call through) before the wifi user has answered then the call will fail after 20-30seconds (they do initially get the person and can hold a conversation but not for long). If an IP500 user does an attended transfer to a wifi handset and waits until the wifi user answers then the call will transfer correctly. Blind transfers work fine.

Can someone explain what’s going on with the attended transfer?

I do see a critical packet error within asterisk when the call drops so obviously an issue with the wireless phone but i’m not sure what.


It’s worth a look. Please enable SIP debug for a test call reproducing this issue and post the log to

Hi there

I’ve been doing a bit of digging today and found the cause of the issue above however it raises another question regarding Session Expire timers whcih I hope someone can explain.

By default the wifi handsets have a session expire timer of 600 seconds. This is not a problem with internal calls however when they dial outside numbers which passes through A2Billing the call cuts off with a ‘Time Out’ message on the handset - This is the session expire timer. I can set it to a maximum of 3600 however people can therefore only hold an outside call for an hour before being cut off. If I disable the timer calls work fine however I then get my original issue of the call transfers failing. I have set the timer to 3600 and all is well however they will now get cut off after an hour.

If I bypass A2billing it all works perfectly.


I should add that this is only a problem with the wifi handsets. THe IP500 corded handsets have no problem whatsoever with calls being cut off after any length of time.