 an aggregate of grants in response to per connection requests from the MS. Transport connections, once established, may require active maintenance, with requirements which may vary depending on the type of service. In the following sections, the IEEE MAC CPS functions are classified and described according to their location on the data-plane using a systematic approach. 7.1 Automatic repeat request 7.1 AUTOMATIC REPEAT REQUEST 7.1.1 ARQ Principles Automatic Repeat Request (ARQ) is an error-control mechanism for data transmission which uses acknowledgements (or negative acknowledgements) and timeouts to achieve reliable data transmission over an unreliable communication link. In an ARQ scheme, the receiver uses an error detection code, typically a Cyclic Redundancy Check (CRC), to detect whether the received packet is in error. If no error is detected in the received data, the transmitter is notified by sending a positive acknowledge- ment. If an error is detected, the receiver discards the packet and sends a negative acknowledgement to the transmitter, and requests a re-transmission. An Acknowledgement (ACK) or Negative Acknowl- edgement (NACK) is a short message sent by the receiver to the transmitter to indicate whether it has correctly or incorrectly received a data packet, respectively. Timeout is a predetermined time interval after the sender sends the packet; if the sender does not receive an acknowledgement before the timeout, it usually re-transmits the packet until it receives an acknowledgement or exceeds a pre- defined number of re-transmissions. There are three types of ARQ protocol including [4]: Stop-and-Wait ARQ is the basic form of ARQ protocol where the sender sends one packet at a time and then waits for an ACK or NACK signal from the receiver before sending the same or a new packet. The receiver sends an ACK signal following receipt of a good packet. If the ACK does not reach the sender before the timeout, the sender re-sends the same packet. Go-Back-NARO is a form of ARQ protocol in which the