On Thursday 28 May 2015, Juha Heinanen wrote:
The question has been, what value could I assign to extra_id_pv to uniquely identify the branch. Since $T_branch_idx exists, perhaps a good choice could be $sel(via[1].branch) + $T_branch_idx.
That would work. Just remember to store the value you use somewhere (RR-param or $sht) to be able to tear down the session when a BYE comes in.