P-TMSI in 2G/3G network

P-TMSI stands for "Packet - Temporary Mobile Subscriber Identity".

It is a temporary identifier that the SGSN assigns to the UE during the attach procedure.

The P-TMSI is used in order to enhance the security of the UE, as the UE stores this P-TMSI locally, and uses it, instead of its IMSI, to identify itself to the network in all subsequent communications with the network.