[SR-Users] A parameter with a life span of the entire dialog

Dear All, I'm trying to set a few parameters for an "INVITE", and access their values in the failure routine if the call fails. $var() doesn't seem suitable for my purpose as it only lasts for one process. I think if I set a $var() in "INVITE", it will be gone when I receive the failure response. $sht() seems able to last long but it will be accessed by all processes which might include ones not belonging to the same dialog. I wonder if somebody would give me some suggestions here to handle such situations.  Does Kamailio provide a mechanism to set up a parameter with a life span of the entire dialog? Thanks. Regards,Jay