Hi Hinmani,
SR prohibit timer is used to prevent UE being transmits SR again and again. Some application doesn't require to send SR frequently , say some application sends few bytes of data (maybe TCP ACK/NACK ) frequently ,in this case UE will send SR frequently to get few bytes of UL data to send .so they have introduced SR prohibit timer to prevent ue to send SR and it buffers few bytes of data till SR prohibit timer expires and it sends SR to ENB. This is applicable only if the application is delay tolerant.
