Method for handling timers after an RLC re-establishment in a wireless comminications system

A method for handling timers in a wireless communication system includes starting a Timer_Poll_Periodic timer for a Radio Link Control Acknowledged Mode (RLC AM) entity, performing a re-establishment procedure for the RLC AM entity, and not stopping the Timer_Poll_Periodic timer after re-establishment of the RLC AM entity.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for handling timers in a wireless communications system, and more specifically, to a method for handling a Timer_Poll_Periodic timer after an RLC re-establishment in a wireless communications system.

2. Description of the Prior Art

Technological advances have moved hand in hand with more demanding consumer expectations. Devices that but ten years ago were considered cutting edge are today obsolete. These consumer demands in the marketplace spur companies towards innovation. The technological advances that result only serve to further raise consumer expectations. Presently, portable wireless devices, such as cellular telephones, personal digital assistants (PDAs), notebook computers, etc., are a high-growth market. However, the communications protocols used by these wireless devices are quite old. Consumers are demanding faster wireless access with greater throughput and flexibility. This has placed pressure upon industry to develop increasingly sophisticated communications standards. The 3rd Generation Partnership Project (3GPP) is an example of such a new communications protocol.

Please refer toFIG. 1.FIG. 1is a simplified block diagram of the prior art communications model. In a typical wireless environment, a first station10is in wireless communications with one or more second stations20. The first station10is comprised of upper layers12, a radio link control (RLC) entity14, and lower layers16which are below the RLC14. In the following disclosure, all of the RLC entities are assumed to be RLC acknowledged mode (RLC AM) entities. The upper layers12can deliver messages to the RLC14through service data units (SDUs)13. The SDUs13may be of any size, and hold data that the upper layers12wish delivered to the second station20. The RLC14composes the SDUs13into one or more protocol data units (PDUs)15. Each PDU15of the RLC14is of a fixed size, and is delivered to the lower layers16. The lower layers16include the physical layer, which is in charge of transmitting data to the second station20.

The second station20shown has exactly the same basic structure as the first station10. The second station20also includes upper layers22, an RLC24, and lower layers26. Just as with the first station10, the second station20uses the upper layers22to transmit SDUs23to the RLC24, and uses the RLC24to transmit PDUs25to the lower layers26. The data transmitted by the first station10is received by lower layers26of the second station20and reconstructed into one or more PDUs25, which are passed up to the RLC24. The RLC24receives the PDUs25and from them assembles one or more SDUs23, which are then passed up to the upper layers22. The upper layers22, in turn, convert the SDUs23back into messages, which should be identical to the original messages that were generated by the first station10. In communication systems, the terms SDU and PDU have broad meanings. For purposes of the following disclosure, the term “SDU” is used to indicate SDUs passed from the upper layers to the RLC, and the term “PDU” should be understood as PDUs passed from the RLC to lower layers.

The 3rdGeneration Partnership Project (3GPP) specification 3GPP TS 25.322 V3.11.0 “RLC Protocol Specification has defined parameters, variables, timers, control PDUs, etc., for operations of the first station10and the second station20. According to the specification, in some circumstances, the RLC layers14and24must be re-established with an RLC re-establishment function, e.g. when starting a reset procedure. However, the specification does not specify how the timers should be handled during re-establishment. Due to this lack of guidelines, potential problems could develop due to the improper use of the timers.

Firstly, please refer toFIG. 2, which is a phase diagram illustrating a transmission window of an RLC AM entity according to the prior art. During normal operation, the RLC AM entity14(transmitter) transmits acknowledged mode data (AMD) PDUs to the RLC AM entity24(receiver), and each PDU is marked with a sequence number (SN). The SNs have a fixed bit length of n bits. In the preferred embodiment, the bit length n is12. Hence, the SNs have a range of values from zero to 4095 (212−1). The phase diagram for SNs can thus be represented by a circle. For the following example, point30is the sequentially lowest transmitter PDU SN value waiting for acknowledgment from the receiver in the form of a STATUS PDU, which contains information on which PDUs have been acknowledged. In other words, point30marks the beginning of the transmitting window. In this example, assume a window size =X. Point32marks the highest PDU SN value of an AMD PDU that has been sent so far. Therefore, in order to prevent the transmitting window from filling up, the difference of PDU SN values at point32and point30has to be less than X. Otherwise, the transmitting window fills up, and deadlock occurs. Deadlock can occur if AMD PDUs sent from the transmitter to the receiver are not properly acknowledged by the receiver. This would cause point30to remain stationary, and the difference between point32and point30would eventually equal the maximum window size of X.

As mentioned in the specification 3GPP TS 25.322 V3.11.0, a Timer_Poll_Periodic timer is started for the RLC AM entity14of the first station10when the RLC AM entity14is created, and is used by the RLC AM entity14to poll its peer RLC AM entity24to send a STATUS PDU. When the Timer_Poll_Periodic timer of the RLC AM entity14expires, a poll request is send to the RLC AM entity24asking for a STATUS PDU to be sent back to the RLC AM entity14. Since the specification does not specify how the Timer_Poll_Periodic timer should be handled during re-establishment, the Timer_Poll_Periodic timer may be stopped by the RLC entity upon reception of a re-establishment request, and never restarted after the re-establishment procedure. Therefore, the Timer_Poll_Periodic timer does not ever get started again, and cannot trigger a poll to the peer RLC AM entity24upon expiration of the timer. This means that AMD PDUs with lower SN values indicated by point30inFIG. 2will never be acknowledged. Since point30never moves, eventually the difference between point32and point30will equal the transmission window size of X. Thus, because the timer remains stopped, deadlock occurs, and the RLC AM entity14cannot transmit additional PDUs to the peer RLC AM entity24.

Therefore, since the current 3GPP specification does not specify how each of the previously mentioned timers should be handled during re-establishment, deadlock can occur and quality of service may be reduced substantially.

SUMMARY OF THE INVENTION

It is therefore a primary objective of the claimed invention to provide a method for handling timers after an RLC re-establishment in a wireless communications system in order to solve the above-mentioned problems.

According to the claimed invention, a method for handling timers in a wireless communication system includes starting a Timer_Poll_Periodic timer for a Radio Link Control Acknowledged Mode (RLC AM) entity, performing a re-establishment procedure for the RLC AM entity, and not stopping the Timer_Poll_Periodic timer after re-establishment of the RLC AM entity.

DETAILED DESCRIPTION

Please refer toFIGS. 3 and 4.FIGS. 3 and 4are message sequence charts illustrating handling of the Timer_Poll_Periodic timer during a re-establishment function according to the present invention. After the RLC AM entity14is re-established by upper layers, the present invention method includes not stopping the Timer_Poll_Periodic timer. Alternately, as shown inFIG. 4, the present invention method includes restarting the Timer_Poll_Periodic timer.

Thus, for a re-establishment function, the handling of the Timer_Poll_Periodic timer can be summarized as follows: after re-establishment, the Timer_Poll_Periodic timer is not stopped or is restarted. By not stopping or restarting the Timer_Poll_Periodic timer, the RLC AM entity14will continue to be able to poll its peer RLC AM entity24now that the RLC AM entity14has been re-established, and will prevent deadlock from occurring.

Compared to the prior art, the present invention provides steps for handling the Timer_Poll_Periodic timer after re-establishment. Thus, using the method specified in the present invention will prevent RLC AM entities from experiencing deadlock, and will help maintain the quality of service.