Patent Publication Number: US-2010122136-A1

Title: Method and apparatus for reduced data block transmission in an automatic repeat request system

Description:
FIELD OF THE DISCLOSURE 
     The present invention relates generally to packet based wireless communications systems employing automatic repeat request (ARQ) mechanisms and more particularly to a method and apparatus for reducing data block transmissions in such wireless packet based communications systems. 
     BACKGROUND 
     Automatic repeat request (ARQ) mechanisms make use of retransmission in packet based wireless communications systems, as well as other communications systems, to increase the probability that data has been transferred from a transmitter to a receiver. Retransmission of data however may reduce a system&#39;s net data throughput which may be of particular significance for various wireless communications systems. 
     In wireless communications systems based on the IEEE 802.16 standard, various timers are defined with respect to the ARQ mechanism. Specifically, a block lifetime timer is assigned to each ARQ block such that the blocks are discarded at the expiry of the timer. However, in general any ARQ block will only be a fraction of a Medium Access Control Layer (MAC) Service Data Unit (MSDU). Therefore if a fraction of an MSDU is discarded due to timer expiry, the entire MSDU becomes obsolete, and it is futile and also wasteful of bandwidth, to transmit and/or retransmit any remaining ARQ blocks associated with the same MSDU. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a data packet structure. 
         FIG. 2  is a block diagram of a wireless network employing automatic repeat request (ARQ). 
         FIG. 3  is a block diagram of a wireless mobile station in accordance with the various embodiments. 
         FIG. 4  is a diagram illustrating a high-level architecture of a mobile station and a base station in accordance with the various embodiments. 
         FIG. 5  is a flow chart illustrating high level operation of a receiver in accordance with various embodiments. 
         FIG. 6  is a flow chart illustrating high level operation of a transmitter in accordance with various embodiments. 
         FIG. 7  is a flow chart illustrating relevant segments of a transmitter state wherein the transmitter is operating in accordance with an embodiment. 
         FIG. 8  is a flow chart illustrating relevant segments of a receiver state wherein the receiver is operating in accordance with an embodiment. 
         FIG. 9  is a message flow diagram illustrating an exemplary message flow of a transmitter and receiver in accordance with an embodiment. 
         FIG. 10  is a block diagram illustrating operation of a sliding receiver window. 
         FIG. 11  is a block diagram illustrating operation of a sliding receiver window in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Methods and apparatuses for reducing data block transmission in systems employing Automatic Repeat Request (ARQ) are provided herein. 
     In a first aspect of the various embodiments, a method of operating a wireless transceiver in an Automatic Repeat Request (ARQ) mode comprises fragmenting a packet of data into a series of sequential data blocks and assigning each of the data blocks a block sequence number; sending at least a first data block from the series of sequential data blocks, and a first block sequence number corresponding to the first data block, to a remote wireless transceiver; setting an acknowledgment timer specifying a time interval in which to receive an acknowledgment message from the remote transceiver, the acknowledgment message corresponding to the first data block; determining that the acknowledgment timer has timed out; and sending a discard message to the remote transceiver specifying at least a second block sequence number corresponding to at least a second data block, and specifying that the second data block is to be discarded. 
     A second aspect of the various embodiments is a method of operating a wireless transceiver in an ARQ mode comprising receiving from a remote transceiver at least a first data block including a first block sequence number, the first data block being from a series of sequential data blocks forming a packet; receiving from the remote transceiver a discard message specifying at least a second block sequence number corresponding to at least a second data block, where the discard message specifies that the second data block is to be discarded; and discarding the second data block. 
     A third aspect is a wireless communication station comprising a transceiver; a processor coupled to the transceiver which has a medium access control layer, and configured to fragment a packet of data into a series of sequential data blocks and assign each of the data blocks a block sequence number; send at least a first data block from the series of sequential data blocks, and a first block sequence number corresponding to the first data block, to a remote wireless transceiver; set an acknowledgment timer specifying a time interval in which to receive an acknowledgment message of the first data block from the remote transceiver; determine that the acknowledgment timer has timed out; and send a discard message to the remote transceiver specifying at least a second block sequence number corresponding to at least a second data block, and specifying that the second data block is to be discarded. 
     Turning now to the drawings wherein like numerals represent like components,  FIG. 1  illustrates the structure of a signal burst  103  from a transmitter to a receiver  101  over an air interface  105 . The signal burst  103  will generally comprise at least one packet of data having the structure of a Medium Access Control (MAC) header  107 , various sub-headers  109 , further fragmentation or packing sub-headers  111 , a data portion  113 , and in some embodiments, a cyclic redundancy check portion  115 . 
     The data  113  may contain a data packet structured by a Medium Access Control Layer (MAC) wherein the data packet may be referred to in some embodiments as a Service Data Unit (SDU), or more specifically a MAC SDU (MSDU). Additionally, such MSDUs may be partitioned or “fragmented” to produce packet fragments, or smaller data blocks. Groups of such MSDU fragments or MSDU data blocks are subsequently transmitted in “Protocol Data Units” (PDUs). Therefore, the payload may be a complete MSDU, or in the case of large MSDUs, may be one of more fragments of an MSDU, which are contained in a PDU. Such fragmentation operation is dictated by Quality of Service (QoS) requirements and by the efficient use of bandwidth as understood by those of ordinary skill. 
     The data  113  may also be “packed” data, that is, the MAC layer of the transmitter may discretionally pack several MSDUs into one PDU. Additionally, the transmitter MAC layer may pack various MSDU fragments into a single PDU. For ARQ systems, the packing and/or fragmentation sub-headers  111  will contain a Block Sequence Number (BSN) which the ARQ system uses to identify missing or otherwise lost fragments so that the fragments may be retransmitted. 
     Generally, when packing is employed, the packing sub-header  111  will also contain fragmentation information for the MSDU or fragment thereof contained within data  113 . However, if packing is not used, then sub-headers  111  will be a fragmentation sub-header and contain the fragmentation information for the corresponding fragment. Therefore, the configuration of the signal  103  payload may be a sequence of sub-headers  111  and corresponding data  113  portions wherein the fragmentation subheader or each packing sub-header contains a BSN and/or fragmentation information for the specific fragment. 
     Further, the signal  103  payload may contain one or more initial PDU transmissions combined with one or more PDU retransmissions. The BSN of a fragment may be an 11-bit field in some embodiments in which 802.16 is employed. Fragmentation information may be a 2-bit field and indicate whether a fragment is a “First Fragment,” “Continuing Fragment,” “Last Fragment,” or “Unfragmented” by the binary values “10,” “11,” “01,” and “00” respectively. 
     Lastly, data  113  may also contain an ARQ feedback message, which may be in combination with other PDU data as discussed above. For example, an ARQ feedback message may be “piggybacked” with other data by using a packing subheader. However, an ARQ feedback message may also be sent as a stand alone MAC management message without a subheader. The data  113  may also employ encryption in some embodiments. 
     Signal  103  may include a Cyclic Redundancy Check (CRC) field  115  in some embodiments which may cover the MAC header  107  as well as data  113 . Further, in some embodiments the MAC header  107  will contain a CRC-8 header checksum and CRC field  115  may contain a CRC-32 checksum to cover the data. If encryption is used as mentioned above, the CRC field will be determined subsequent to encryption operations. Signal  103  may also include padding (not shown). 
     In ARQ systems, an MSDU may be logically segmented into a series of data blocks and subsequently encapsulated into PDUs as discussed briefly above. The BSN, which is contained in the fragmentation or packing sub-headers  111  likewise as discussed above, will correspond to the first data block of the series of data blocks after the sub-header  111 , which are being transmitted together. For retransmission, the transmitter may make a policy decision as to whether retransmitted data blocks are arranged in the same PDUs. 
       FIG. 2  illustrates a communications network  200 , with various base stations  203 , each base station  203  having a corresponding radio coverage area  207 . In general, base station radio coverage areas may overlap and, in general, form an overall network coverage area. A coverage area may comprise a number of base station coverage areas  207 , which may form a contiguous radio coverage area. However, it is not required to have contiguous coverage and therefore the coverage area may alternatively be distributed throughout an overall network coverage area. Furthermore, each base station  203  may communicate with a number of mobile stations such as mobile station  201 , via an air interface  205 . The mobile station  201  may communicate with various base stations via handover operations as the mobile station  201  moves throughout the network  200  radio coverage areas. 
     A number of base stations  203  may be connected to a base station controller  209  via backhaul connections  211 . The overall network may comprise any number of base station controllers, each controlling a number of base stations. Note that the base station controller  209  may alternatively be implemented as a distributed function among the base stations. The base stations  203  may communicate with the mobile station  201  via any number of standard air interfaces such as, but not limited to, UMTS, E-UMTS, CDMA2000, 802.11 or 802.16. 
     The base stations  203  may perform a number of control functions such as, but not limited to, a Radio Link Control (RLC) function and Medium Access Control (MAC) function. Base station controller  209  may provide a centralized Radio Resource Management (RRM) function to synchronize various functions between the base stations  203  such as, but not limited to, scheduling and segmentation and reassembly functions as well as to coordinate the RLC and MAC functions between the various base stations  203 . 
       FIG. 3  is a block diagram illustrating the primary components of a mobile station in accordance with some embodiments. Mobile station  300  comprises user interfaces  301 , at least one processor  303 , and at least one memory  305 . Memory  305  has storage sufficient for the mobile station operating system  307 , applications  309  and general file storage  311 . Mobile station  300  user interfaces  301 , may be a combination of user interfaces including but not limited to a keypad, touch screen, voice activated command input, and gyroscopic cursor controls. Mobile station  300  has a graphical display  313 , which may also have a dedicated processor and/or memory, drivers etc. which are not shown in  FIG. 3 . 
     It is to be understood that  FIG. 3  is for illustrative purposes only and is for illustrating the main components of a mobile station in accordance with the present disclosure, and is not intended to be a complete schematic diagram of the various components and connections there-between required for a mobile station. Therefore, a mobile station may comprise various other components not shown in  FIG. 3  and still be within the scope of the present disclosure. 
     Returning to  FIG. 3 , the mobile station  300  may also comprise a number of transceivers such as transceivers  315  and  317 . Transceivers  315  and  317  may be for communicating with various wireless networks using various standards such as, but not limited to, UMTS, E-UMTS, CDMA2000, 802.11, 802.16, etc. 
     Memory  305  is for illustrative purposes only and may be configured in a variety of ways and still remain within the scope of the various embodiments herein disclosed. For example, memory  305  may be comprised of several elements each coupled to the processor  303 . Further, separate processors and memory elements may be dedicated to specific tasks such as rendering graphical images upon a graphical display. In any case, the memory  305  will have at least the functions of providing storage for an operating system  307 , applications  309  and general file storage  311  for mobile station  300 . In some embodiments, applications  309  may comprise a software stack having a Medium Access Control (MAC) layer that communicates with a stack MAC layer in a base station or base station controller. 
     Turning now to  FIG. 4 , mobile station and base station architectures in accordance with the various embodiments are illustrated. Mobile stations  401  comprises a stack having a Radio Link Controller (RLC)  407 , a Medium Access Controller (MAC)  409 , and a Physical Layer (PHY)  411 . Base station  403  similarly has an RLC  413 , MAC  415  and PHY  417 . 
       FIG. 5  illustrates high level operation of a receiver, operating in an ARQ mode, in accordance with various embodiments. Initial operation begins with notification or a determination that an ARQ data block or blocks has/have been discarded  501 . Next, as shown in block  503 , the receiver determines whether the discarded ARQ block or blocks belongs to an MSDU for which other ARQ blocks have already been received. If so, then all ARQ data blocks corresponding to the failed MSDU are discarded as shown in block  505 . 
     A high level transmitter operation in accordance with various embodiments is illustrated by  FIG. 6 . In step  601 , the transmitter may fragment data packets into a series of data blocks and assign Block Sequence Numbers (BSNs) and/or fragmentation control information. One or more of the data blocks is then sent to a receiver as shown in step  603 . 
     The transmitter will set one or more acknowledgement timers, as shown in step  605 , and wait for an ACK or NACK message from the receiver. This step may include a number of retransmit attempts based on one or more of the step  605  timers timing out. However, after final timeout, the MSDU can be considered to have failed. Therefore, in step  607 , the transmitter will send a discard message to the receiver indicating that other ARQ data blocks that are part of the same MSDU should be discarded. 
     Segments of the transmitter state machine useful for understanding the various embodiments in a transmitting equipment are illustrated by  FIG. 7 . However, it is to be understood that  FIG. 7  is not intended to be a full and complete description of the transmitter state machine, but rather is intended to provide those details necessary for understanding the various embodiments. Therefore, a transmitter state machine may comprise various other steps or procedures not shown by  FIG. 7 , and such transmitters employing the procedures illustrated by  FIG. 7  with other such steps or procedures not shown, remain in accordance with the various embodiments herein disclosed. 
     Therefore, in step  701  the transmitter may segment an MSDU into a number of data blocks and include fragmentation control information in appropriate sub-headers, such as fragmentation or packing sub-headers  111  shown in  FIG. 1  and discussed previously. One or more data blocks may then be sent by the transmitter as shown in step  703 . It is to be understood that step  703  may also represent a retransmission of the ARQ mode such that a signal payload may comprise a number of initial data block transmissions and also retransmissions as was discussed previously with respect to  FIG. 1 . 
     In general as shown in step  705 , the transmitter waits for the data block or blocks to be acknowledged by the receiver by an ACK message. If the data block is acknowledged then the block state will be updated. For example, a data block may be in one of four states; “not-sent,” “outstanding,” “discarded,” and “waiting-for-retransmission.” Therefore, a data block initial state is “not-sent.” 
     After the block is sent it becomes “outstanding” until an ACK is received in  705 , or a “not-acknowledged” (NACK) is received as in  707 , or if ACK timeout occurs as in  709 . Upon receipt of an ACK message in  705 , the block state will be updated to “discarded” by the transmitter. In this case, the block state may be updated to “discarded” in  711 , after which a pointer may be moved to the next Block Sequence Number (BSN) or numbers as in  713 , and the next data block or set of blocks may be sent in  703 . 
     However, if a NACK is received as in  707 , or if ACK timeout occurs as in  709 , then the block state will be changed to “waiting for retransmission” in  715  and the block will be resent in  703 . 
     Upon the initial sending of the data block in  703 , a data block lifetime timer is also set, and the timeout is pending as shown in step  717 . If the data block lifetime timer times out in  717 , a discard message is sent to the receiver in  719 . The discard message may in some embodiments provide an indication to the receiver of every related data block, that is, an indication of every data block BSN pertaining to the same MSDU for which the discarded block occurred. It is to be understood that various implementations are possible for indicating the related data blocks and that such implementations remain in accordance with the various embodiments disclosed herein. Thus, in one exemplary implementation of the various embodiments, the discard message may specify a range of BSNs which are to be discarded, by providing an initial BSN and a final BSN. Further, in some embodiments the receiving side may infer whether certain data blocks belong to a discarded MSDU and therefore in such embodiments only a single BSN may be provided, for example an initial BSN or a final BSN. In other alternative embodiments, the discard message may provide an initial BSN for a new MSDU so that the receiving side may advance its receive window accordingly, in addition to deleting data blocks with BSNs corresponding to the failed MSDU. 
     Returning now to  FIG. 7 , the transmitter then waits for an ACK or NACK message in  721 . The timer sequence for  721  may be identical to the sequence of  705 ,  707  and  709  in some embodiments, such that  721  will have the same time duration as  705 ,  707  and  709 . Returning to  721 , if a NACK is received, or if a timeout occurs, then the discard message will be resent in  719 . Otherwise, after an ACK is received in  721 , the transmitter will discard the data blocks in  723  and will advance a transmission (Tx) window to the next BSN to be sent. 
       FIG. 8  illustrates the operation of a receiver state machine in accordance with the embodiments, and generally corresponding to the transmitter state machine illustrated by  FIG. 7 . Similar to the intent and understanding of  FIG. 7 , it is to be understood that  FIG. 8  is not intended to be a full and complete description of the receiver state machine, but rather is intended to provide those details necessary for understanding the various embodiments. Therefore, a receiver state machine may comprise various other steps or procedures not shown by  FIG. 8 , and such receivers employing the procedures illustrated by  FIG. 8  with other such steps or procedures not shown, remain in accordance with the various embodiments herein disclosed. Also, with respect to both  FIGS. 7 and 8 , it is to be understood that the various embodiments will be a transceiver station, that is, a base station or a mobile station having both transmitting and receiving capability and therefore both base stations and mobile stations may employ the various inventive methods and techniques herein disclosed in both the transmission and reception aspects. 
     Returning now to  FIG. 8 , a receiver receives a data block or data blocks in  801 . For embodiments employing a Cyclic Redundancy Check (CRC) as was discussed with respect to  FIG. 1 , the CRC will be performed as in  803  and if the data passes, it will be unpacked or defragmented as needed in  805 . The BSNs will then be checked in  807  to determine whether the received data block or data blocks is/are within the expected window as in  809 . If not, then the blocks will be discarded in  811 . 
     If the data block was in fact within the appropriate BSN window then the data block may be stored in  813 , and the receive (Rx) window may be advanced to the next expected BSN if the received data block BSN is equal to the current Rx window start pointer value. The receiver will then send an ACK message to the transmitter in  815 . During the normal operation of the receiver in ARQ mode, various blocks will be received such that the process of  801  through  815  will repeat until the successful reception of one or more MSDUs or unless, a discard message is received as in  817 . If a discard message is not received in  817 , the receiver will continue to receive data blocks in  801  that are expected within the Rx window. However, if a discard message is received as in  817 , the receiver will determine whether currently stored data blocks belong to the same MSDU as blocks specified by the discard message. 
     As discussed above with respect to the transmitter states illustrated by  FIG. 7 , the discard message may contain various indications to inform the receiver of which blocks are to be discarded. Therefore, for example, only the first and last BSNs of the discardable data blocks may be specified. Alternatively, the next BSN to which the receiver should advance the Rx window may be specified. In any case, for some embodiments, the receiver may check the fragmentation information for stored blocks as shown in  819 . The fragmentation information may be used by the receiver to infer which stored blocks belong to the discarded MSDU, even if the transmitter discard message did not provide information specific for all MSDU blocks. For example, if a first block BSN was specified, then any blocks having “Continuing Fragment” or “Last Fragment” binary indications belonging to the same MSDU may be discarded prior to advancing the Rx window. For any of the above described embodiments, the receiver determines which additional data blocks if any must be discarded as shown in  821 . 
     Therefore in  823 , all data blocks related to the same MSDU for which any data block was to be discarded, as specified by the transmitter discard message, or as inferred by the receiver, may likewise be discarded. The receiver will then, in  825 , update the block state to “received,” even though the blocks have in fact not been received, and send an ACK message to the transmitter in  827 . The ACK message will inform the transmitter that the blocks were discarded. In  829 , the receiver will advance its Rx window to the next BSN. 
       FIG. 9  is a message flow diagram providing an example of message flows between a transmitter and receiver in accordance with various embodiments. In  FIG. 9 , the base station  903  is assumed to be transmitting data blocks, while the mobile station (MS)  901  is assumed to be receiving data blocks. However, it is to be understood that in the various embodiments, communication of data is bi-directional such that the mobile station  901  may transmit data blocks, while the base station  903  may receive data blocks. 
     Therefore in accordance with the exemplary  FIG. 9  assumption of base station  903  data transmission, an ARQ data block is sent to the MS  901  from base station  903  as signal  905 . The base station will then set the timer “ARQ_BLOCK_LIFETIME TIMER”  907  and also set an “ARQ_RETRY_TIMEOUT TIMER”  909 . On the receiver side, the MS  901  will set an “ARQ_RX_PURGE_TIMEOUT TIMER”  911 . 
     Returning to the base station  903  side, and assuming that an ACK is not received, the timer  909  will timeout and the base station  903  will resend the data block  913 . The resend  913  may also occur if a NACK message is received as was discussed above. In  FIG. 9 , it is assumed that an ACK message, or a NACK message, is never received by the base station  903  such that ARQ_BLOCK_LIFETIME TIMER  915  times out, in which case discard message  917  is sent to the MS  901 . 
     The MS  901  will discard any specified ARQ blocks in  921 , and may also infer other blocks not specified, if such blocks may be related to the same MSDU by using for example, the block fragmentation control information as was discussed above. The MS  901  will then advance the ARQ_RX_WINDOW_START  923  to the next BSN, and will send an ARQ feedback message  925  to the base station  903  indicating that the ARQ blocks have been discarded. The base station  903  likewise discards any ARQ blocks queued for the MSDU in  919 . 
       FIG. 10  illustrates how an ARQ sliding receiver window operates and  FIG. 11  illustrates how the ARQ window operates in accordance with an embodiment. Therefore, in  FIG. 10 , when fragmentation is used on an ARQ connection, only a part of the ARQ blocks for a specific MSDU might be discarded because the MSDU may have been fragmented over several PDUs. As discussed in detail above, ARQ blocks may be discarded for various reasons, one of which is that, after multiple retries the ARQ_RX_PURGE_TIMEOUT TIMER  911  for example, may timeout on the receive side, or a discard message  917  may have been received when the transmitter ARQ_BLOCK_LIFETIME TIMER  915  timeout occurs, for example. 
     Therefore, in  FIG. 10 , in which various ARQ data blocks are represented as consecutive data blocks having BSNs  1  through  12 , data blocks  1 ,  2  and  3  correspond to a first MSDU, while data blocks  4  through  8  correspond to a second MSDU. Block  5  has been received, while block  4  has not been received. If a discard message is received specifying data block  4  is to be discarded, the receiver will advance the window  1001  to BSN  6  as shown by window  1003 . It is to be noted that data blocks  6 ,  7  and  8  also belong to the second MSDU, are still within the pending window  1003 , and have not been discarded, even though theses blocks are no longer of any use. 
     Therefore, the various embodiments employ the technique illustrated by  FIG. 11 . Therefore as shown in  FIG. 11 , the receiver may utilize the fragmentation control (FC) information to deduct related ARQ blocks not yet received, because an FC indication of “First Fragment,” must be ended by an FC set to “Last Fragment.” Before the receiver sends an ARQ feedback message, the receiver may examine if any other ARQ blocks would complete the MSDU and thereby shift the receive window  1101  beyond these additional blocks as well. 
     It is assumed in  FIG. 11  that either a receiver ARQ_RX_PURGE_TIMER timeout occurred for ARQ block  5 , or that a discard message was received for ARQ block  4 . The receiver may read the FC information of received blocks  5  and  7  determining that  5  and  7  are “Continuing Fragments” which can be discarded. The receiver may further note that  6  and  8 , which have not been received, are a “Continuing Fragment” and a “Last Fragment,” respectively. Block  8  is logically inferred to be the “Last Fragment” of the discarded MSDU because received block  9  is a “First Fragment” of a new MSDU. Likewise, the receiver may determine that blocks  9 ,  10  and  11  are the “First Fragment,” and “Continuing Fragments” of a second MSDU and therefore the window may be advanced to window position  1103  which corresponds to BSN  12 . 
     If the receiver is unable to deduct all information needed to discard a complete MSDU, one such case being where consecutive data blocks have not been received, then on reception of new information concerning this MSDU, the receiver may continue to discard the remaining MSDU data blocks. In the event of consecutive data blocks which are not received, and which are part of a discarded MSDU, the receiver will, in the various embodiments, set a discard flag. For example, assuming a discarded MSDU consists of data blocks  4  through  9  wherein all blocks have been received, except for blocks  6  and  7 . In this case the receiver would forward the window to BSN  6  because it cannot determine whether blocks  6  and  7  are “Continuing Fragments,” or whether block  6  is a “Last Fragment” and block  7  is a “First Fragment” of a new MSDU. Therefore the receiver in this case can only safely discard up through “Continuing Fragment” block  5 . However, when the receiver receives block  6  having FC information set to “Continuing Fragment,” it will discard blocks  6  through  9 , and advance the window to BSN  10 . Because block  8 , which is a “Continuing Fragment,” and block  9 , which is a “Last Fragment,” have been received, and because block  6 , subsequently received is then known to be continuing, block  7  logically must likewise be continuing and may be discarded. Thus, the receiver appropriately discards blocks  6  though  9  and advances the receive window to BSN  10 . 
     Additionally, it is to be understood that the transmitter side may also employ the techniques described above and illustrated by  FIG. 11 , in the event of for example an ARQ_BLOCK_LIFETIME TIMER  915  timeout, such that the blocks marked “not received&#39; would be “not acknowledged&#39; with respect to the transmitter side. The transmitter may thus accordingly advance the transmission window thereby saving unnecessary data block transmissions or retransmissions. 
     Returning briefly to  FIG. 9 , further optimizations may be employed by the various embodiments. For example, ARQ_RX_PURGE_TIMEOUT TIMER  911  may be applied to several data blocks simultaneously, if a set of data blocks having consecutive BSNs is received in a single PDU. Otherwise if the timer  911  is set for each individual data block, the timer for that block must be reset if a duplicate data block were received. Therefore, in the various embodiments, only a single purge timer is set for consecutive BSN data blocks received in a single PDU. The timer is then only reset in the event that duplicates of all BSNs within the PDU set have been received. Similarly on the transmitter side, the ARQ_BLOCK_LIFETIME_TIMER  907  may be applied to all ARQ data blocks that are sent in the same PDU. 
     While various embodiments have been illustrated and described, it is to be understood that the invention is not so limited. Numerous modifications, changes, variations, substitutions and equivalents will occur to those skilled in the art without departing from the spirit and scope of the present invention as defined by the appended claims.