Record time duration for fax in vxml

Question

I am going to get the time duration used for fax sending in vxml:
<transfer name="mycall" destexpr="'fax://' + phone_num" bridge="false" connecttimeout="120s" maxtime="180s" cisco-longpound="true" cisco-mailtoaddress="'xxxx'" >
<catch event="telephone.disconnect.transfer">
<assign name="mydur" expr="mycall$.duration"/>
<goto next="#timeCount"/>
</catch>
</transfer>
<var name="startTime" expr="new Date();"/>
<var name="endTime"/>
<form id="timeCount">
<block>
<assign name="document.startTime" expr="startTime.getTime();"/>
<assign name="document.startTime" expr="Number(startTime);"/>
<assign name="document.endTime" expr="new Date();"/>
<assign name="document.endTime" expr="endTime.getTime();"/>
<assign name="document.endTime" expr="Number(endTime);"/>
<assign name="mydur" expr="document.endTime - document.startTime;"/>
</block>
</form>
But mycall$.duration is 0 after transferring fax.
And even if I use codes to count time duration, the duration, mydur, is about the same regardless of the number of pages sent.
Is it possible to use vxml to record time duration of fax?
Thank you!

Answer 1

Paste the following Config:
sh ver
sh run
debug of one call demonstrating the problem :
debug voip ivr all
debug vxml all