What is role of TMSI during SRVCC?

Hi Experts,
Please let me know what is role of TMSI during SRVCC?

During call Transfer, the MSC Server performs other TMSI reallocation towards the UE.
And it also performs a MAP Update Location to the HSS/HLR.
Now all steps are closed & Voice is flowing on new Path Similarly, for Data Part, Handover completion & Bearer Updation is done between SGSN & PGW. so that user can start Internet Session in 3G radio Now.