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I am dealing with a Private caller case where the Privacy header is only passed in the initial INVITE but not in the subsequent mid-dialog requests (e.g. CANCEL).

When the Privacy header is present, my downstream expects me to send them another header.

For the most part, I was able to deal with this by using dlg module to keep track of state within dialog so that the mid-dialog requests will know about the Privacy header's presence in initial INVITE.

However, a problem i have is that just for the CANCEL request, I am unable to add any headers to the SIP request relayed to downstream.

I've read in other posts (dated years back) that an option would be to use stateless CANCELs downstream. Another potential option would be to start a new transaction at my level.

I am wondering if there are other alterantives to this. I would've recommended my downstream to use $avp but it seems like even though initial INVITE and the CANCEL are supposed to be in same transaction, the $avp value stored in initial INVITE is not accessible by the CANCEL.

There are other tricks that can work. Such as using the Record-Route as a data store (that can be security issue) or asking downstream to use dlg module, which can be a big performance cost to the,.

I am wonder if any of you have solved this problem already.

user1836155
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Instead of dialog module , i prefer that using htable to store transaction until get ACK. It is faster than it . After getting ACK , stored transaction can be removed.

In addition , You can look at TM module and TMX module that has features about Cancel.

Yasin Caner
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