the status report by the receiver. The request of polling includes the following: Timer-based polling: the RLC sender sends polling periodically as decided by a timer. Poll timer: this starts whenever a polling message is sent and stops when a status report is received. This primarily retransmits a poll if it is lost in the link. Last PDU in buffer: a poll should be sent with the last PDU in the RLC sender's transmission buffer. Last PDU in retransmission buffer: the RLC sender always puts the unac- knowledged PDUs into the retransmission buffer to wait for possible retransmission. The last PDU in the retransmission buffer should be sent with a poll, if it is scheduled for retransmission. Poll every N PDU: this triggers the poll for every NPDU sent. Poll every N SDU: this triggers the poll for every NSDU sent. Window-based polling: this sets the polling bit when a certain percentage of the transmission window is sent. Also, a number of triggers for the receiver RLC to send the status report are listed as follows: The "polling bit" in a received AMD (acknowledged mode data) PDU is set to "1." "Missing PDU indicator" is configured and a missing AMD PDU is detected. The missing PDU indicator is optional; this tells the RLC receiver to send a status report whenever a hole in the received PDU sequence is detected. The "timer-based STATUS transfer" is configured and the timer Timer_ Status_Periodic has expired. A status report can be triggered by the MAC, following the MAC-hs (the MAC entity for high-speed downlink packet access [HSDPA]) reset operation. On the other hand, the status report can be prohibited even if any of the pre- ceding situations holds true, except if the status report is triggered by the MAC-hs reset. This is controlled by the timer Timer_Status_Prohibit, which prohibits the status report transfer if it is started. Upon its expiry, a status report is sent if it is © 2009 by Taylor & Francis Group, LLC Long Term Evolution: 3GPP LTE Radio and Cellular Technology triggered and prohibited before. Thus,