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 !
It’s send by the BSC whenever the allocation of a TSL to a new PS call results into a change in the current resource being allocated to an already existing PS call in the opposite direction, in that case the BSC may decide and sends a packet time slot reconfiguration to the MS. For example, if a DL PS call is required to be established on the PACCH of an existing Uplink TBF or a a UL PS call establishment is required using Packet Downlink Ack/Nack msg and the BSC decides that TSL re-allocation is needed, in that case the BSC will send a PTR message to the MS.