you have no choice but to use it…
PTR is used when the timeslots used for the packet transfer of a MS should be changed :
(not exhaustive list)
– transfer changes bias (ie. download becomes upload)
– a tch preempted one of your pdch
– a timeslot is now available for pdch -> you can get it if you increase the nb of pdch for your tbf
so it is very necessary, and usually not modifiable by the operators !