In LTE, when UE wish to establish RRC connection with eNB, it transmits a Random Access Preamble, eNB estimates the transmission timing of the terminal based on this. Now eNB transmits a Random Access Response which consists of timing advance command, based on that UE adjusts the terminal transmit timing.
Now coming to your query when -
After receiving RACH Request, eNB PHY calculates the timing advance which is transmitted to the UE as part of response message.