Wireless communication method and apparatus for supporting reconfiguration of radio link control parameters

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Wireless communication method and apparatus for supporting reconfiguration of radio link control parameters

IntcrDigital Technology Corporation C.196162

[0001] WIRELESS COMMUNICATION METHOD AND APPARATUS FOR SUPPORTING RECONFIGURATION OF RADIO LINK

CONTROL PARAMETERS

[0002] FIELD OF INVENTION

[0003] This application is related to wireless communications.

[0004] BACKGROUND

[0005] Some of the major goals of high speed packet access (HSPA) evolution include higher data rates, higher system capacity and coverage, enhanced support for packet services, reduced latency, reduced operator costs and backward compatibility. Meeting these goals requires evolutions to the radio interface protocol and network architecture. More specifically, meeting these goals has required a set of enhancements and architecture changes to layer 2 (L2), (i.e., radio link control (RLC) and medium access control (MAC)), functionalities.

[0006] Some of the L2 enhancements include flexible size RLC protocol data units (PDUs), (i.e., RLC PDUs having flexible sizes), high speed MAC (MAC-hs) segmentation/concatenation and multiplexing. In universal terrestrial radio access (UTRA) Release 6 (R6), the acknowledge mode (AM) RLC entities can only use fixed size RLC PDUs, (i.e., RLC PDUs having a fixed size). In addition, the MAC-hs sub-layer in the Node-B can only support concatenation of dedicated MAC (MAC-d) PDUs. The L2 enhancements of UTRA Release 7 (R7) result in significant RLC/MAC changes of R6 features.

[0007] Currently, when radio bearers (RBs) are setup or reconfigured via radio resource control (RRC) signaling, the information element (IE) “RB mapping info** is present. The "RB mapping info" contains information about the RLC instance and transport channels corresponding to the RB.

[0008] The MAC-hs configuration has to be the same across all RBs mapped to a high speed-downlink shared channel (HS-DSCH), or else an invalid configuration will result. [0009] In HSPA, the high speed shared channels are monitored by a wireless transmit/receive unit (WTRU) in a single cell, (i.e., the serving HS-DSCH cell). Due to mobility, when the WTRU is moving from one cell to the other, the WTRU needs to perform a serving cell change by switching to a new serving HS-DSCH cell and terminating communication with the old serving HS-DSCH cell. In a Node-B relocation procedure, an inter-Node-B handover occurs from an old Node-B, (i.e., a source Node-B) to a new Node-B, (i.e., a target Node-B).

[0010] At the time of a serving Node-B change, the target Node-B needs to start transmission of data over the new configuration. The handover can occur among evolved HSPA Node-Bs which support the L2 enhancements, or to/from cells with or without L2 enhancements. For both cases, the WTRU must be able to perform a handover, adjust to the new configurations, and minimize data loss. [0011] With the introduction of new L2 enhancements, new procedures need to be defined in order to optimize and minimize data loss during a handover between R7 cells, or between an R7 cell and an R6 cell. Specifically, procedures that deal with resetting of the MAC-hs entity need to be modified in order to account for the new L2 enhancements.

[0012] In addition, it cannot be assumed that all of the R6 Node-Bs will be upgraded at the same time to R7 Node-Bs. Therefore, handovers between R6 and R7 cells may frequently occur. Due to the functional changes of the RLC and MAC, methods to perform handovers with minimal loss of quality and data between these cells must be defined. Specifically, on the WTRU side, the MAC-hs and the RLC must perform functional changes during the handovers.

[0013] SUMMARY

[0014] A variety of wireless communication methods and apparatus for supporting reconfiguration of RLC parameters are disclosed. An RRC reconfiguration message is generated that indicates that an RLC unit in a WTRU or a universal terrestrial radio access network (UTRAN) should be reconfigured from supporting flexible size RLC PDUs to supporting fixed size RLC PDUs or vice versa. If an IE "one sided RLC re-establishment" is present in the RRC reconfiguration message, only a receiving side or a transmitting side subassembly in the RLC unit is re-established. Otherwise, both the receiving side subassembly and a transmitting side subassembly in the RLC unit are reestablished. Flexible size RLC PDUs may be discarded and a message indicating the discarded flexible size RLC PDUs may be transmitted. The flexible size RLC PDUs may be modified such that they correspond to a set of pre-defined sizes.

[0015] BRIEF DESCRIPTION OF THE DRAWINGS

[0016] A more detailed understanding of the invention maybe had from the following description in conjunction with the accompanying drawings wherein: [0017] Figure 1 is an exemplary block diagram of a WTRU that moves between R6 and R7 cells, and is configured to operate with the new RLC and MAC-hs sub-layers when a handover message is received during a serving cell change procedure; and [0018] Figure 2 is an exemplary block diagram of a UTRAN that sends an RRC reconfiguration message to the WTRU of Figure 1.

[0019] DETAILED DESCRIPTION

[0020] When referred to hereafter, the terminology "wireless transmit/receive unit (WTRU)'1 includes but is not limited to a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, a cellular telephone, a personal digital assistant (PDA), a computer, or any other type of user device capable of operating in a wireless environment. When referred to hereafter, the terminology "base station" includes but is not limited to a Node-B, a site controller, an access point (AP), or any other type of interfacing device capable of operating in a wireless environment.

[0021] A variety of wireless communication methods are disclosed herein that optimize handover scenarios, reset procedures, reconfiguration procedures for an RLC entity. Furthermore, a variety of wireless communication methods for handovers between cells in which one or both of the cells support L2 enhancements are disclosed. Both the uplink (UL) and downlink (DL) are applicable to these wireless communication methods.

[0022] The following terms are used throughout the following description and are briefly defined. An enhanced MAC-hs (MAC-ehs) payload unit is a MAC-ehs service data unit (SDU), or a segment of a MAC-ehs SDU contained in a MAC-ehs PDU. A MAC-ehs reordering PDU is a set of MAC-ehs payload units in a MAC-ehs PDU that belongs to the same priority queue. An enhanced cell is a cell that supports L2 enhancements, i.e., flexible size RLC PDUs. A non-enhanced cell is a cell that does not support L2 enhancements, i.e., fixed size RLC PDUs.

[0023] When referred to hereafter, R6 includes but is not limited to a cell, a

Node-B, or a radio network controller (RNC) that does not support flexible size RLC PDUs, (i.e., fixed size RLC PDUs are supported). When referred to hereafter, R7 includes but is not limited to a cell, a Node-B or an RNC that supports flexible size RLC PDUs.

[0024] When referred to hereafter, UTRAN includes but is not limited to a cell, a Node B, an RNC, or a network node.

[0025] Figure 1 is an exemplary block diagram of a WTRU 100 that moves between non-enhanced cells and enhanced cells, and is configured to operate with the new RLC and MAC-ehs sub-layers when a handover message is received during a serving cell change procedure. As shown in Figure 1, the WTRU 100 includes an RRC unit 105, an RLC unit 110, a MAC unit 115 and a physical (PHY) layer 1 (LI) unit 120. The initiation of a serving cell change may occur in response to the receipt of an RRC reconfiguration message 125, such as an RB RRC reconfiguration message, a transport channel RRC reconfiguration message or a physical channel RRC reconfiguration message. The RLC unit 110 includes a transmitting side subassembly 130 and a receiving side subassembly 135. The transmitting side subassembly 130 includes a transmission buffer 140.

[0026] The RRC reconfiguration message 125 may be generated by a UTRAN. Figure 2 is a block diagram that depicts an example of a configuration of a protocol stack in UTRAN 200. The UTRAN 200 may include an RRC unit 205, an RLC unit 210, a MAC unit 115 and PHY LI unit 220. The RLC unit 210 includes a transmitting side subassembly 230 and a receiving side subassembly 235. The transmitting side subassembly 230 includes a transmission buffer 240. The RRC unit 205 generates the RRC reconfiguration message 125 to initiate a serving cell change.

[0027] The UTRAN 200 may also include a target Node-B, a source Node-B, a controlling RNC (CRNC) and a serving RNC (SRNC) (not shown). The RNC may include an RLC unit and an RRC unit (not shown). Alternatively, the RNC functionalities are included in the Node-B and thus no controlling RNC or serving RNC is present.

[0028] RLC instances are not required to have the same RLC configuration for all RBs mapped to an HS-DSCH. For example, a WTRU connected to an enhanced cell may simultaneously support one or more RLC instances configured with fixed size RLC PDUs and/or flexible size RLC PDUs. The enhanced MAC-ehs is capable of supporting reception of both fixed size RLC PDUs and flexible size RLC PDUs.

[0029] However, a WTRU operating in a non-enhanced cell cannot support RLC instances with flexible size RLC PDUs. All RLC entities mapped to a normal HS-DSCH, (i.e., a MAC-hs), have to be configured with fixed size RLC PDU operation. This is due to the fact that the normal MAC-hs configuration does not support the reception and signaling of flexible size RLC PDUs. Accordingly, an RLC supporting fixed size RLC PDUs may refer to an AM RLC instance or an unacknowledged mode (UM) RLC instance.

[0030] To avoid re-establishments, the logical channels corresponding to an RLC instance do not have to change their configuration when moving from a non-enhanced cell to an enhanced cell. For example, when a WTRU moves from a cell with a normal MAC-hs configuration to a cell with an enhanced MAC-ehs configuration, the RLC instances configured for supporting fixed size RLC PDUs do not have to be reconfigured to support flexible size RLC PDUs.

[0031] The RB supporting fixed size RLC PDUs in an enhanced cell may maintain the fixed size RLC PDU configuration, or may be reconfigured to support flexible size RLC PDUs at the time of the handover or at a later time, in which case an RB reconfiguration procedure will be triggered and the RRC will perform the required steps. This allows signaling RBs to maintain their existing RLC configuration and avoid re-establishment of the RLC entity. If handovers between non-enhanced and enhanced cells occur often within a network, this method avoids re-establishment of the non-enhanced RLC AM instances if the WTRU moves frequently between non-enhanced and enhanced cells. This method also allows optimizations for UM RLC instances. If UM RLC instances are not extended to support flexible size RLC PDUs in R7, the UM RLC instances do not have to be re-established or reconfigured when moving from non-enhanced cells to enhanced cells, and vice versa. If flexible size PDUs are introduced for UM RLC instances, then the same methods as described for AM RLC apply. [0032] RLC Behavior Re-establishment Per RB When Moving Between Enhanced Cells and Non-enhanced Cells [0033] When the WTRU changes serving cells during handover which support different releases, (i.e., R6 and R7), the WTRU has the option of maintaining an existing RLC instance without changing its configuration, (i.e., supporting fixed size RLC PDUs over an enhanced MAC configuration), or the existing RLC instance may be reconfigured. However, an RLC instance supporting flexible size RLC PDUs in an enhanced L2 cell cannot maintain its configuration when moving to a non-enhanced L2 cell because the normal MAC-hs cannot support reception of flexible size RLC PDUs. Therefore, an RLC reestablishment is required or a new procedure handling the change of RLC configuration is necessary to minimize data loss. The change of reconfiguration of the RLC unit may also occur due to a SRNS relocation, which involves moving from a SRNC that supports flexible size RLC PDU to a SRNC that does not support flexible size RLC PDUs.

[0034] Methods to perform and evaluate the need of RLC re-establishment are required on a per RB basis. When a WTRU moves between enhanced and non-enhanced L2 cells, or when the RLC changes configuration, no RLC reconfiguration occurs and thus no RLC re-establishment is performed, and/or a change of RLC configuration from fixed size RLC PDUs to flexible size RLC PDUs occurs. In this case, a RLC reconfiguration procedure maybe triggered. A re-establishment of the RLC entity in this case is not always required, but may optionally be performed.

[0035] The reconfiguration procedure only configures the RLC entity to start supporting flexible size RLC PDUs. No loss of data occurs, since the fixed size RLC PDUs can be transmitted and be transparent to the WTRU and the MAC-ehs. The reconfiguration procedure only configures the RLC entity to start supporting flexible size RLC PDUs. No loss of data occurs as the fixed size RLC PDUs may be transmitted to the WTRU and the MAC-ehs. When a change of RLC configuration from flexible size RLC PDUs to fixed size RLC PDUs occurs, an RLC re-establishment is required or, optionally, a new procedure that deals with the change and attempts to minimize data loss may be performed. The WTRU is configured to always remain in R7 RLC and support flexible size RLC PDUs. The UTRAN may change RLC configurations without explicitly indicating to the WTRU a change from R6 to R7, or vice versa, had occurred. [0036] Evaluation Criteria for Performing an RLC Reconfiguration or Re establishment [0037] When the RLC changes its configuration, an RB reconfiguration procedure will be triggered. RRC RB reconfiguration procedures and information elements are used to evaluate and indicate the need of a RLC re-establishment. [0038] The need of a RLC re-establishment for the signaled RB may be determined by the RRC explicit signaling that adds a new field in an existing RB or a signaling RB (SRB) information element (IE) that indicates RLC reestablishment. The RRC explicit signaling may indicate a one sided or full reestablishment. RRC procedures corresponding to the RB reconfiguration procedure may be modified to perform condition checks on the new configuration parameters provided (i.e. size of RLC PDU, flexible or fixed) and the old configuration parameters of the reconfigured RLC entity (i.e. size of RLC PDU, flexible or fixed) and to evaluate the need for a RLC re-establishment. [0039] The evaluation of re-establishment criteria may be performed in the description of generic actions on receipt of the RB mapping info IE, in the description of generic actions on receipt of the "RLC info" IE, and/or by adding a new section that describes generic actions on receipt of the downlink (DL) or uplink (UL) RLC configuration IE.

[0040] The following sections describe the different possibilities of evaluating and performing RLC re-establishment criteria, and is applicable to both RLC DL, RLC UL and optionally to UM entities.

[0041] Option 1 [0042] For this option, the RLC re-establishment evaluation is performed within the actions of the "RB mapping info" IE or in a new section that deals with actions upon receipt of the "RLC configuration" IE. Note that the RLC configuration (i.e. whether RLC choice is fixed or flexible) is provided in the "RB mapping info" IE for this option. However, the "RLC configuration" IE may be provided in other information elements. The "RLC configuration" IE may provide the WTRU with information regarding whether the RLC instance is configured to support fixed size RLC PDUs or flexible size RLC PDUs.

[0043] If the "RLC configuration" IE is set to the value “enhanced" and the previously stored value was set to “normal,” (or if the value is different from the one currently set), an RLC entity (or layer) is reconfigured according to the DL RLC configuration IE. Optionally, if re-establishment is required, the RLC entity is re-established. Otherwise, if the "RLC configuration" IE is set to the value “normal” and the previously stored value was set to “enhanced” (or if the value is different from the one currently set). The RLC entity is re-established by performing one sided or full re-establishment.

[0044] Upon the reception of a RRC message that results in the reconfiguration of the RB, the WTRU performs a set of actions related to RB mapping. For the UL RLC operation, the condition for re-establishment may optionally be performed here. More specifically, if that RB is using AM and the RLC PDU configuration (i.e. choice of RLC PDU size) applicable to the UL logical channel is changed from a configuration that supports flexible size RLC PDUs to fixed size RLC PDUs, and if the IE "one sided RLC re-establishment" is included in that RRC message and it is set to TRUE, then the WTRU re-establishes the transmitting side of the corresponding RLC entity. Otherwise, the WTRU reestablishes the corresponding RLC entity.

[0045] When the a configuration that supports fixed size RLC PDUs is changed to a configuration that supports flexible size RLC PDUs, the RLC reestablishment is optional and may be performed when the length indicator indicated in a length indicator field of the RLC PDUs changes between 7 and 15 bits. As described above, either only the transmitting side subassembly 130 and 230, (if the IE “one sided RLC re-establishment” is included), or the entire RLC unit 110 and 210, (i.e., both the transmitting side subassembly 130 and 230, and the receiving side subassembly 135 and 235), may be re-established.

[0046] Option 2 [0047] The RLC re-establishment criteria is evaluated in the actions upon receipt of the "RLC info" IE. When the actions corresponding to the "RLC info" IE are performed, the procedure needs to be aware of the configuration of the RLC entity, (i.e., flexible size RLC PDU or fixed size RLC PDU). This may be performed by adding a new IE in the "RLC info" IE indicating the RLC configuration. The new IE indicates whether flexible or fixed RLC PDU size may be used. The new IE also indicates whether enhanced or a normal RLC is used. [0048] The DL RLC PDU size IE set of values may be extended to contain a reserved value that implicitly indicates that the RLC supports flexible size RLC PDUs. For example, value 0 or 8 may be used, or “all 1” in binary, and the like. The "RB mapping info" IE and the "DL RLC configuration" IE that specifies the version of the RLC configuration used are examined. Information of the RLC configuration is obtained from any other IE that contains this information. If the new IE is not included in the "RLC info" IE, the re-establishment procedure is then based on information from other elements or the re-establishment procedure occurs in the RB mapping info IE.

[0049] If a new RB supports, (i.e., is configured to start operating with), fixed size RLC PDUs and an old RB supports, (i.e., was configured to operate with flexible size RLC PDUs), then the RLC entity is re-established. The reestablishment may be a one sided re-establishment. For example, for the DL RLC, only the receiving side may be re-established and, for the UL RLC, only the transmitting side may be re-established. To perform a one-sided reestablishment, the existing IE ’’one sided re-establishment" in the "RLC info" IE may be used. Optionally, the RRC procedure specifically indicates to re-establish the receiving entity or transmitting entity without using the IE "one sided reestablishment".

[0050] If a new RB supports flexible size RLC PDUs and an old RB supports fixed size RLC PDUs, and the RLC unit 110 and 210 is reconfigured, then re-establishment may be optional.

[0051] A description of the RRC procedure is described below. The RRC procedure has been modified corresponding to the "RLC info" IE, For the purposes of this description, a new information element “DLRLC size indicator” is added to the "RLC info" IE or the UL, “UL RLC size indicator”, which has a value of fixed or normal RLC. An example of the new IE is shown in Table 1. [0052] The RRC procedure corresponding to the actions performed when the "RLC info" IE is present is modified to account for changes in the RLC instance configuration. The "RLC size indicator" IE is used as an example in the procedure described below. However, in general, the "RLC size indicator" IE represents an indication of the RLC configuration and may be called differently and have a different enumeration such as enhanced/normal or values.

[0053] The modified RRC procedure may be performed as follows:

Upon reception of the IE “RLC info”, the WTRU shall: 1> if the IE “Downlink RLC mode” is present and is set to “AM RLC”: 2> If the IE “DL RLC size indicator” is present and set to the value “fixed”;

3> if the value is different from the one currently set in the RLC entity: 4> if the IE “one sided RLC re-establishment” is set to TRUE:

5> re-establish the receiving side of the corresponding RLC entity. 4> else: 5> re-establish the corresponding RLC entity. 3> configure the corresponding RLC entity according to the new RLC PDU size indicator; 2>else, if the “DL RLC size indicator” is present and set to “flexible”; 3> if the value is different from the one currently set in the RLC; 4> reconfigure the RLC entity (optionally, re-establish RLC if the RRC is configured to re-establish when moving from a non-enhanced cell to an enhanced cell). 2> else; (following the else statement are the procedures that deal with the fixed RLC PDU size instances or with the case where the DL RLC size indicator is not present. The steps following this else statement correspond to steps in R6); 3> if IE “DL RLC PDU size” is not present; 4> determining the downlink RLC PDU size will be handled at RLC level, without any configuration from RRC. NOTE: The case where this mandatory IE is not present is meant to handle the interaction with a network using an earlier release of the specification. 3> else, if the IE “DL RLC PDU size” is present and no downlink RLC PDU size is currently set in the RLC entity: 4> configure the corresponding RLC entity with the downlink RLC PDU size. 3> else, if the IE “DL RLC PDU size” is present and its value is different from the one currently set in the RLC entity: NOTE: The downlink RLC PDU size set in the RLC entity can either be explicitly configured or, in case no explicit configuration is provided, derived by the first received RLC PDU. 4> if the IE “one sided RLC re-establishment” is set to TRUE:

5> re-establish the receiving side of the corresponding RLC entity. 4> else: 5> re-establish the corresponding RLC entity.

4> configure the corresponding RLC entity with the new downlink RLC PDU size.

[0054] The condition check for RLC re-establishment is not restricted to the order specified in the above two options, and thus may be performed in any order. In addition, the name of the new IEs, such as DL RLC configuration IE and DL RLC size indicator IE, are subject to changes. The procedure corresponding to this IE remains the same regardless of the IE names.

[0055] For Option 2, an example of the "RLC info" IE functional definition is provided in Table 1 below.

Table 1. Modified "RLC info" IE

Information Element/Group name Need Multi Type and roforence Semantics description Vorsion CHOICE Uplink RLC mode OP indicates if Acknowledged, Unacknowledged or Transparent mode RLC shall be used. >AM RLC «Transmission RLC discard MP Transmission RLC discard 10.3.4.25 «Transmission window size MP lnteger{1,8,16,3 2,64.128,256.51 2,768,1024,153 6,2047,2560,30 72,3584,4095) Maximum number of RLC PDUs sent without getting them acknowledged. This parameter is needed if acknowledged mode Is used. WTRU shall also assume that the UTRAN receiver window Is equal to this value. «Tlmer_RST MP lnteger{50,100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 700, 800, 900, 1000) Elapsed time in milliseconds. It is used to trigger the retransmission of RESET PDU. »Max_RST MP lnteger(1,4, 6, 8. 1216, 24, 32) «Polling info OP Polling info 10.3.4.4 >UM RLC «Transmission RLC discard OP Transmission RLC discard 10.3.4.25 >TM RLC «Transmission RLC discard OP Transmission RLC discard 10.3.4.25

Information Ele mo nt/Group name Need Multi Typo and reference Semantics description Version »Segmentation indication MP Boolean TRUE indicates that segmentation is performed. CHOICE Downlink RLC mode OP Indicates if Acknowledged, Unacknowledged or Transparent mode RLC shall be used >AM RLC »DL RLC PDU size indicator MP Enumeratedffix ed, flexible) Indicates if flexible of fixed RLC PDU sizes shall be used REL-7 »DL RLC PDU size MP lnteger{16.500 0 by step of 8) Unit is bits REL-5 »ln-ssquence delivery MP Boolean TRUE Indicates that RLC shall preserve the order of higher layer PDUs when these are delivered. FALSE indicates that receiving RLC entity could allow SDUs to be delivered to the higher layer in different order than submitted to RLC sublayer at the transmitting side. »Receiving window size MP lnteger(1,8,16,3 2,64,128,256,51 2,768,1024,153 6,2047,2560,30 72,3584,4095} Maximum number of RLC PDUs allowed to be received. This parameter is needed if acknowledged mode Is used. WTRU shall also assume that the UTRAN transmitter window is equal to this value »Downlink RLC status info MP Downlink RLC status info 10.3.4.1 >UM RLC »DL UM RLC LI size MP Integer(7,15) Size in bits to use for the downlink RLC UM LI. REL-5 »DL Reception Window Size CV-Nof- SIB16O lnteger{32,48, 64,80, 96,112} REL-6 >TM RLC »Segmentation indication MP Boolean TRUE indicates that segmentation is performed. One sided RLC re-establishment MP Boolean TRUE indicates that only one side of the AM RLC entity is reestablished. REL-5 Alternative E-bit interpretation CV-Nof- SIB16o Enumerated (true) The absence of this IE implies: “normal E-bit interpretation". REL-6 [0056] If the RLC re-establishment for different RLC configurations is not evaluated in the "RLC info" IE, then the condition checks for DL RLC PDU size within the "RLC info" IE should only be performed if the AM RLC instance supports fixed RLC PDU sizes. Otherwise, if the condition check is performed and the DL RLC PDU size is present for flexible RLC configurations, unnecessary re-establishments may result.

[0057] Referring to Figures 1 and 2, an alternative method for adjusting the new RLC configuration in the WTRU 100 and the UTRAN 200 will now be disclosed. This alternative method is applicable when the receiving side subassembly 135 and 235 explicitly signals the RLC configuration via the RB RRC reconfiguration messages and is configured to support flexible size RLC PDUs. When the receiving side subassembly 135 and 235 is configured to support flexible size RLC PDUs, the receiving side subassembly 135 and 235 may receive an indication of the RLC PDU size that the transmitting side subassembly 130 and 230 is using, (when configured for supporting fixed size RLC PDUs), from the higher layers. This method is also applicable to the case where the RLC unit 110 and 220 changes the size of the length indicator field of the RLC PDUs between 7 and 15.

[0058] When changing from an RLC configuration that supports flexible size RLC PDU to an RLC configuration that supports fixed RLC PDU sizes, the transmitting side subassembly 130 and 230, and the receiving side subassembly 135 and 235 have to discard flexible size RLC PDUs. More specifically, at a given activation time, the transmitting side subassembly 130 and 230 discards flexible size RLC PDUs, (or RLC PDUs with a size other than the fixed acknowledged mode data (AMD) PDU size), that have been transmitted once and have not been acknowledged yet. An example activation time may be the time when the Node-B starts using the normal MAC-hs in the DL case, or the MAC-i/is in the UL case. The transmitting side subassembly 130 and 230 may discard the RLC PDUs according to one or a combination of any of the following rules. 1) Any RLC PDU with a size different than the length of the fixed RLC PDU, (applies to flexible size RLC PDUs that have been created but have not necessarily been transmitted yet); 2) Any RLC PDU with a size different than the length of fixed RLC PDUs that have already been transmitted at least once, (only applies to the RLC PDUs that have been transmitted or submitted to lower layers, whereby the RLC PDUs that have been created but have not yet been transmitted are not discarded); 3) All RLC PDUs with a sequence number (SN) up to and including the last RLC PDUs with a flexible RLC PDU size (or a size different than the length of the fixed PDU); 4) All RLC PDUs with an SN up to and including the last RLC PDU with a flexible RLC PDU size (or a size different than the length of the fixed PDU) that was transmitted at least once; 5) All RLC SDUs up to the last SDU contained within the last RLC PDU with a flexible PDU size (or a size different than the configured fixed PDU length); 6) All RLC SDUs up to the last SDU contained within the last RLC PDU with a flexible PDU size (or a size different than the configured fixed PDU length); 7) All RLC SDUs for which at least one segment was contained in a PDU of a size different than the configured fixed PDU size that was transmitted at least once; and/or 8) All RLC PDUs in a retransmission buffer that have been transmitted to lower layers and that have an SN assigned.

[0059] If the last RLC PDU discarded contains a segment of an RLC SDU, that RLC SDU may be optionally reconstructed using the new configuration, (i.e., a new fixed RLC PDU size).

[0060] The transmitting side subassembly 130 and 230 does not reinitialize state parameters and sequence numbers. Then, the transmitting side subassembly 130 and 240 proceeds to indicate to the receiving side subassembly 135 and 235 the RLC PDUs or RLC SDUs that have been discarded.

[0061] A move receive window (MRW) control super field (SUFI) may be used to indicate the discarded RLC PDUs or RLC SDUs. If “Send MRW” is not configured, the MRW SUFI is assembled with the discard information. More specifically, it should indicate the last SN of the discarded RLC PDU or RLC SDU, (SN_MRW = last discarded RLC PDU SN + 1)). The receiving side subassembly 135 and 235 then discards all RLC PDUs with SN < SN_MRW and moves the receive window accordingly.

[0062] If “Send MRW” is not configured, then the information of only 15 discarded SDUs can be indicated. This may not be enough to indicate all the RLC SDUs to be discarded, especially if a large number of SDUs are discarded. Therefore, more than one MRW SUFI may have to be sent.

[0063] An N length field can always be set to zero, or it may optionally be set to indicate the length of the last SDU pertaining to the PDU.

[0064] A new MRW SUFI is now introduced that is only used for handover purposes. The new MRW SUFI may include an SN_MRW field to indicate the sequence number of the last PDU or SDU to be discarded. The receive window is updated accordingly and all RLC PDUs with SN up to and including the SN_MRW field are discarded. Optionally, prior to discarding all RLC PDUs, the receiving side subassembly 135 and 235 can assemble all RLC PDUs into RLC SDUs and deliver them to higher layers. The receiving side subassembly 135 and 235 can then discard all RLC PDUs up to and including SN_MRW that cannot be reassembled into RLC SDUs.

[0065] RLC re-establishment can be avoided by using the SDU discard function to discard SDUs that have been created with flexible size RLC PDUs when the serving cell changes to a legacy Node-B, or when a legacy Node-B is added to the enhanced dedicated channel (E-DCH) active set for the UL case. The RLC then uses the MRW SUFI to indicate to the WTRU to move the receive window and discard the same RLC PDUs.

[0066] This method results in the same amount of data loss as RLC reestablishment if the reconfiguration takes place at the activation time. However, data loss can be minimized if the transmitting side subassembly 130 and 230 start generating fixed RLC PDUs when the handover decision is made or when the transmitting side subassembly 130 and 230 is made aware of the handover. At the time the handover takes place, (i.e., at the given activation time), the discard function is initiated. This will allow the RLC unit 110 to try to flush out some RLC PDUs with flexible size until the activation time expires. At the time data is transmitted over the target cell radio link, (i.e., a handover is performed), all non-acknowledged flexible size RLC PDUs in the retransmission buffer 140 and 240 must be discarded using the SDU discard function, since they are not supported by the target Node-B. [0067] This may pose a disadvantage because the transmitting side subassembly 130 and 230 may only update its transmit parameters and state variables after a MRW_ACK is received from the WTRU, which may temporarily stall the transmit window. However, an advantage to this method is that data loss can be minimized.

[0068] The initiation of the procedure can be indicated by one or a combination of the following options: 1) The procedure may be indicated through explicit signaling from higher layers (i.e., initiate SDU discard for handover purposes). 2) The procedure may be internally triggered by the RLC when a change from flexible to fixed RLC PDU size is detected (i.e., when a reconfiguration from flexible to fixed is indicated in the RRC messages). 3) The procedure initiated at a given activation time for handover purposes if a synchronized change is requested.

[0069] SDU discard function for acknowledged, unacknowledged, and transparent mode [0070] Discard for RLC reconfiguration purposes [0071] This alternative is only applicable for RLC acknowledge mode entities. It is triggered when the RLC configuration changes from flexible to fixed RLC PDU size. Optionally, this procedure can also be triggered if the RLC configuration changes from a fixed size RLC PDU configuration to a flexible size RLC PDU configuration, and/or the length indicator size changes.

[0072] If the RLC configuration changes from a flexible size RLC PDU configuration to a fixed size RLC PDU configuration, all SDUs that have segments or “length indicators” indicating the end of the SDUs in the AMD PDUs that have been transmitted to lower layers are discarded, (optionally, up to and including the last AMD PDU), with a size different than the new configured AMD PDU size, and explicit signaling is utilized to inform the receiving side subassembly 135 and 235.

[0073] Transmitter RLC Behavior to Minimize Data Loss [0074] Optionally, the behavior of the transmitting side subassembly 130 and 230 may be modified in order to minimize data loss when switching from flexible PDU sizes to fixed PDU sizes. When the transmitting side subassembly 130 and 230 is made aware of the switch to fixed PDU sizes, the transmitting side subassembly 130 and 230 should start generating fixed size RLC PDUs prior to the activation time specified by higher layers (i.e., when the switch will take place). These fixed size RLC PDUs may include all PDUs already created that have not yet been transmitted, (i.e., they should be regenerated according to the fixed size), and all new PDUs created from newly arrived or buffered SDUs. Alternatively, the transmitting side subassembly 130 ahd 230 can continue generating RLC PDUs with a flexible size, but change the configured maximum RLC PDU size to match the fixed RLC PDU size that is going to be configured when the handover takes place.

[0075] At the activation time, if all PDUs in the transmitting side subassembly 130 and 230, (including PDUs in the retransmission buffer 140 and 240), are of a size equal to the configured fixed size RLC PDUs, the transmitting side subassembly 130 and 230 should continue normal operation with the fixed size RLC PDUs, without discarding any PDUs. Otherwise, the transmitting side subassembly 130 and 230 should only discard RLC PDUs that are not the same size as the configured fixed length, including those RLC PDUs that have already been transmitted.

[0076] When an RLC re-establishment procedure is performed, the procedure should be modified to take into account that not all PDUs are discarded at the activation time. When the transmitting side subassembly 130 and 230 indicates to the receiving side subassembly 135 and 235 to move its receive window (MRW indication), the PDU discard procedure described above may be used to indicate which PDUs have been discarded.

[0077] Optionally, the procedure could be modified such that the MRW indication is sent earlier and the receiving side subassembly 135 and 235 only adjust its receive window at the activation time. The time when the receiving side subassembly 135 and 235 must adjust its receiving window could be explicitly indicated in the MRW indication, or the receiving side subassembly 135 and 235 may adjust its receiving window at the activation time when the transport channel reconfiguration should take place.

[0078] The transmitting side subassembly 130 and 230 should be informed of the switch from flexible to fixed PDU size as soon as possible once the decision is made at higher layers, rather than waiting until the activation time. This allows more time prior to the activation time to successfully transmit the remaining flexible size PDUs and limits the number of flexible size PDUs that will be discarded at the activation time.

[0079] Method of avoiding RLC re-establishment and minimizing data loss [0080] This method may be used alone or in a combination with one of the methods described above.

[0081] In order to minimize data loss, at the time of change from flexible size RLC PDUs to fixed size RLC PDUs, the transmitting side subassembly 130 and 230 does not discard any of the flexible RLC PDUs created and transmitted. However, since the normal MAC-hs or MAC-e/es will only support reception of RLC PDUs with fixed sizes corresponding to one of a size index identifier (SID) for the DL or a data descriptor identifier (DDI) for the UL configured for each priority queue or logical channel, the retransmitted RLC PDUs over the normal MAC-hs or MAC-e/es have to correspond to one of these pre-defined sizes. [0082] Padding can be used to ensure that the RLC PDUs are of a valid size. At the time of the RLC configuration change, at the time the handover decision is made, or at the given activation time, the transmitting side subassembly 130 and 230 can use padding to change the size of all flexible RLC PDUs (i.e., with a size different than fixed) to be retransmitted, such that they match one or a combination of the following sizes: 1) A configured fixed RLC PDU size, if the flexible RLC PDU size is less than the fixed RLC PDU size. 2) The configured flexible maximum RLC PDU size prior to the reconfiguration. The RNC must ensure that the MAC-hs or MAC-e/es is also configured to maximum RLC PDU size. 3) The maximum RLC PDU size present in the retransmission buffer. The RNC must ensure that the MAC-hs or MAC-e/es is also configured to support the receptions of this size, (i.e., one of the SIDs must correspond to this maximum RLC PDU size). 4) For each flexible RLC PDU, match the size to next largest SID or DDI size configured for the MAC-hs queue to which the logical channel (MAC-d flow) corresponds too.

[0083] If the RLC PDU size is larger than any of the sizes to be matched as listed above, padding cannot be used. However, the WTRU may discard them using the SDU discard procedure as described above.

[0084] Alternatively, the RLC PDUs can be re-segmented to match the new fixed RLC PDU size, and if the last remaining segment is less than the fixed RLC PDU size (or less than the configured size to be matched), then padding can be used.

[0085] The change from flexible size to fixed size can be signaled to the receiving side subassembly 135 and 235, or optionally, it can be transparent to the receiving side subassembly 135 and 235, (i.e., the receiving side subassembly 135 and 235 always operates in flexible RLC).

[0086] When adding padding, the length indicator field(s) of the RLC PDU may have to be updated to reflect the changes and indicate where the padding begins.

[0087] Embodiments 1. A wireless communication method of performing a reconfiguration of a radio link control (RLC) unit in a wireless transmit/receive unit (WTRU), the method comprising: receiving a radio resource control (RRC) reconfiguration message indicating that the RLC unit should be reconfigured from receiving flexible size RLC protocol data units (PDUs) via a downlink channel to receiving fixed size RLC PDUs via the downlink channel, wherein the RLC unit comprises a transmitting side subassembly and a receiving side subassembly; and re-establishing at least the receiving side subassembly. 2. The method of embodiment 1 further comprising: if an information element (IE) "one sided RLC re-establishment" is present in the RRC reconfiguration message, re-establishing only the receiving side subassembly; and if an IE "one sided RLC re-establishment" is not present in the RRC reconfiguration message, re-establishing both the receiving side subassembly and the transmitting side subassembly. 3. The method as in any one of embodiments 1 and 2 wherein the receiving side subassembly is reconfigured from receiving flexible size RLC PDUs to receiving fixed size RLC PDUs when the WTRU moves from a first cell that supports enhanced high speed medium access control (MAC-ehs) to a second cell that does not support enhanced MAC-ehs. 4. The method as in any one of embodiments 1-3 wherein the receiving side subassembly is reconfigured from receiving flexible size RLC PDUs to receiving fixed size RLC PDUs when the WTRU moves from a first cell that supports flexible size RLC PDUs to a second cell that does not support flexible size RLC PDUs. 5. The method as in any one of embodiments 1-4 wherein the receiving side subassembly is reconfigured from receiving flexible size RLC PDUs to receiving fixed size RLC PDUs when an RRC connection is relocated from a serving radio network controller (SRNC) that supports flexible size RLC PDUs to an SRNC that does not support flexible size RLC PDUs. 6. The method as in any one of embodiments 1-5 wherein RLC reestablishment criteria is evaluated when an information element (IE) "RLC info" is present in the RRC reconfiguration message. 7. The method of embodiment 6 wherein the RLC re-establishment criteria is evaluated on a per radio bearer (RB) basis. 8. A wireless transmit/receive unit (WTRU) comprising: a radio link control (RLC) unit including a transmitting side subassembly and a receiving side subassembly; and a radio resource control (RRC) unit configured to receive an RRC reconfiguration message indicating that the RLC unit should be reconfigured from receiving flexible size RLC protocol data units (PDUs) via a downlink channel to receiving fixed size RLC PDUs via the downlink channel, wherein at least the receiving side subassembly is re-established. 9. The WTRU of embodiment 8 wherein if an information element (IE) "one sided RLC re-establishment" is present in the RRC reconfiguration message, only the receiving side subassembly is re-established, and if an IE "one sided RLC re-establishment" is not present in the RRC reconfiguration message, both the receiving side subassembly and the transmitting side subassembly are reestablished. 10. The WTRU as in any one of embodiments 8 and 9 wherein the receiving side subassembly is reconfigured from receiving flexible size RLC PDUs to receiving fixed size RLC PDUs when the WTRU moves from a first cell that supports enhanced high speed medium access control (MAC-ehs) to a second cell that does not support enhanced MAC-ehs. 11. The WTRU as in any one of embodiments 8-10 wherein the receiving side subassembly is reconfigured from receiving flexible size RLC PDUs to receiving fixed size RLC PDUs when the WTRU moves from a first cell that supports flexible size RLC PDUs to a second cell that does not support flexible size RLC PDUs. 12. The WTRU as in any one of embodiments 8-11 wherein the receiving side subassembly is reconfigured from receiving flexible size RLC PDUs to receiving fixed size RLC PDUs when an RRC connection is relocated from a serving radio network controller (SRNC) that supports flexible size RLC PDUs to an SRNC that does not support flexible size RLC PDUs. 13. The WTRU as in any one of embodiments 8-12 wherein RLC reestablishment criteria is evaluated when an information element (IE) "RLC info" is present in the RRC reconfiguration message. 14. The WTRU of embodiment 13 wherein the RLC re-establishment criteria is evaluated on a per radio bearer (RB) basis. 15. A wireless communication method of performing a reconfiguration of a radio link control (RLC) unit in a wireless transm.it/receive unit (WTRU), the method comprising: receiving a radio resource control (RRC) reconfiguration message indicating that the RLC unit should be reconfigured from receiving fixed size RLC protocol data units (PDUs) via a downlink channel to receiving flexible size RLC PDUs via the downlink channel, wherein the RLC unit comprises a transmitting side subassembly and a receiving side subassembly; and determining whether a re-establishment of at least the receiving side subassembly is required. 16. The method of embodiment 15 wherein if it is determined that the re-establishment is required, the method further comprises: if an information element (IE) "one sided RLC re-establishment" is present in the RRC reconfiguration message, re-establishing only the receiving side subassembly; and if an IE "one sided RLC re-establishment" is not present in the RRC reconfiguration message, re-establishing both the receiving side subassembly and the transmitting side subassembly. 17. The method as in any one of embodiments 15 and 16 wherein the receiving side subassembly is reconfigured from receiving fixed size RLC PDUs to receiving flexible size RLC PDUs when the WTRU moves from a first cell that does not support enhanced high speed medium access control (MAC-ehs) to a second cell that supports enhanced MAC-ehs. 18. The method as in any one of embodiments 15-17 wherein the receiving side subassembly is reconfigured from receiving fixed size RLC PDUs to receiving flexible size RLC PDUs when the WTRU moves from a first cell that does not support flexible size RLC PDUs to a second cell that supports flexible size RLC PDUs. 19. The method as in any one of embodiments 15-18 wherein the receiving side subassembly is reconfigured from receiving fixed size RLC PDUs to receiving flexible size RLC PDUs when an RRC connection is relocated from a serving radio network controller (SRNC) that does not support flexible size RLC PDUs to an SRNC that supports flexible size RLC PDUs. 20. The method as in any one of embodiments 15-19 wherein RLC reestablishment criteria is evaluated when an information element (IE) "RLC info1' is present in the RRC reconfiguration message. 21. The method of embodiment 20 wherein the RLC re-establishment criteria is evaluated on a per radio bearer (RB) basis. 22. A wireless transmit/receive unit (WTRU) comprising: a radio link control (RLC) unit including a transmitting side subassembly and a receiving side subassembly; and a radio resource control (RRC) unit configured to receive an RRC reconfiguration message indicating that the RLC unit should be reconfigured from receiving fixed size RLC protocol data units (PDUs) via a downlink channel to receiving flexible size RLC PDUs via the downlink channel, wherein a determination is made as to whether a re-establishment of at least the receiving side subassembly is required. 23. The WTRU of embodiment 22 wherein if it is determined that the re-establishment is required, only the receiving side subassembly is reestablished if an information element (IE) "one sided RLC re-establishment" is present in the RRC reconfiguration message, and both the receiving side subassembly and the transmitting side subassembly are re-established if an IE "one sided RLC re-establishment" is not present in the RRC reconfiguration message. 24. The WTRU as in any one of embodiments 22 and 23 wherein the receiving side subassembly is reconfigured from receiving fixed size RLC PDUs to receiving flexible size RLC PDUs when the WTRU moves from a first cell that does not support enhanced high speed medium access control (MAC-ehs) to a second cell that supports enhanced MAC-ehs. 25. The WTRU as in any one of embodiments 22-24 wherein the receiving side subassembly is reconfigured from receiving fixed size RLC PDUs to receiving flexible size RLC PDUs when the WTRU moves from a first cell that does not support flexible size RLC PDUs to a second cell that supports flexible size RLC PDUs. 26. The WTRU as in any one of embodiments 22-25 wherein the receiving side subassembly is reconfigured from receiving fixed size RLC PDUs to receiving flexible size RLC PDUs when an RRC connection is relocated from a serving radio network controller (SRNC) that does not support flexible size RLC PDUs to an SRNC that supports flexible size RLC PDUs. 27. The WTRU as in any one of embodiments 22-26 wherein RLC reestablishment criteria is evaluated when an information element (IE) "RLC info" is present in the RRC reconfiguration message. 28. The WTRU of embodiment 27 wherein the RLC re-establishment criteria is evaluated on a per radio bearer (RB) basis. 29. A wireless comm uni cation method of performing a reconfiguration of a radio link control (RLC) unit in a wireless transmit/receive unit (WTRU), the method comprising: receiving a radio resource control (RRC) reconfiguration message indicating that the RLC unit should be reconfigured from transmitting flexible size RLC protocol data units (PDUs) via an uplink channel to transmitting fixed size RLC PDUs via the uplink channel, wherein the RLC unit comprises a transmitting side subassembly and a receiving side subassembly; and re-establishing at least the transmitting side subassembly. 30. The method of embodiment 29 further comprising: if an information element (IE) "one sided RLC re-establishment" is present in the RRC reconfiguration message, re-establishing only the transmitting side subassembly; and if an IE "one sided RLC re-establishment" is not present in the RRC reconfiguration message, re-establishing both the receiving side subassembly and the transmitting side subassembly. 31. The method as in any one of embodiments 29 and 30 wherein the transmitting side subassembly is reconfigured from transmitting flexible size RLC PDUs to transmitting fixed size RLC PDUs when the WTRU moves from a first cell that supports flexible size RLC PDUs to a second cell that does not support flexible size RLC PDUs. 32. The method as in any one of embodiments 29-31 wherein the transmitting side subassembly is reconfigured from transmitting flexible size RLC PDUs to transmitting fixed size RLC PDUs when adding a new cell that does not support flexible size RLC PDUs to an active set that contains only cells that support flexible size RLC PDUs. 33. The method as in any one of embodiments 29-32 wherein the transmitting side subassembly is reconfigured from transmitting flexible size RLC PDUs to transmitting fixed size RLC PDUs when an RRC connection is relocated from a serving radio network controller (SRNC) that supports flexible size RLC PDUs to an SRNC that does not support flexible size RLC PDUs. 34. The method as in any one of embodiments 29-33 wherein RLC reestablishment criteria is evaluated upon actions related to radio bearer (RB) mapping. 35. The method of embodiment 34 wherein the RLC re-establishment criteria is evaluated on a per radio bearer (RB) basis. 36. A wireless transmit/receive unit (WTRU) comprising: a radio link control (RLC) unit including a transmitting side subassembly and a receiving side subassembly; and a radio resource control (RRC) unit configured to receive an RRC reconfiguration message indicating that the RLC unit should be reconfigured from transmitting flexible size RLC protocol data units (PDUs) via an uplink channel to transmitting fixed size RLC PDUs via the uplink channel, wherein at least the transmitting side subassembly is re-established. 37. The WTRU of embodiment 36 wherein if an information element (IE) "one sided RLC re-establishment" is present in the RRC reconfiguration message, only the transmitting side subassembly is re-established, and if an IE "one sided RLC re-establishment" is not present in the RRC reconfiguration message, both the receiving side subassembly and the transmitting side subassembly are re-established. 38. The WTRU as in any one of embodiments 36-37 wherein the transmitting side subassembly is reconfigured from transmitting flexible size RLC PDUs to transmitting fixed size RLC PDUs when the WTRU moves from a first cell that supports flexible size RLC PDUs to a second cell that does not support flexible size RLC PDUs. 39. The WTRU as in any one of embodiments 36-38 wherein the transmitting side subassembly is reconfigured from transmitting flexible size RLC PDUs to transmitting fixed size RLC PDUs when adding a new cell that does not support flexible size RLC PDUs to an active set that contains only cells that support flexible size RLC PDUs. 40. The WTRU as in any one of embodiments 36-39 wherein the transmitting side subassembly is reconfigured from transmitting flexible size RLC PDUs to transmitting fixed size RLC PDUs when an RRC connection is relocated from a serving radio network controller (SRNC) that supports flexible size RLC PDUs to an SRNC that does not support flexible size RLC PDUs. 41. The WTRU as in any one of embodiments 36-40 wherein RLC reestablishment criteria is evaluated upon actions related to radio bearer (RB) mapping. 42. The WTRU of embodiment 41 wherein the RLC re-establishment criteria is evaluated on a per radio bearer (RB) basis. 43. A wireless communication method of performing a reconfiguration of a radio link control (RLC) unit in a wireless transmit/receive unit (WTRU), the method comprising: receiving a radio resource control (RRC) reconfiguration message indicating that the RLC unit should be reconfigured from transmitting fixed size RLC protocol data units (PDUs) via an uplink channel to transmitting flexible size RLC PDUs via the uplink channel, wherein the RLC unit comprises a transmitting side subassembly and a receiving side subassembly; and . determining whether a re-establishment of at least the transmitting side subassembly is required. 44. The method of embodiment 43 wherein the re-establishment is required if an RLC protocol header format of headers in the RLC PDUs is changed. 45. The method of embodiment 44 wherein the change of the RLC protocol header format corresponds to a change in the size of a length indicator field in the headers. 46. The method as in any one of embodiments 43-45 wherein if it is determined that a re-establishment is required, the method further comprises: if an information element (IE) "one sided RLC re-establishment" is present in the RRC reconfiguration message, re-establishing only the transmitting side subassembly; and if an IE "one sided RLC re-establishment" is not present in the RRC reconfiguration message, re-establishing both the receiving side subassembly and the transmitting side subassembly. 47. The method as in any one of embodiments 43-46 wherein the transmitting side subassembly is reconfigured from transmitting fixed size RLC PDUs to transmitting flexible size RLC PDUs when adding a new cell that supports flexible size RLC PDUs to an active set and removing a cell that does not support flexible RLC PDUs from the active set, wherein the final active set contains only cells that support flexible size RLC PDUs. 48. The method as in any one of embodiments 43-47 wherein the transmitting side subassembly is reconfigured from transmitting fixed size RLC PDUs to transmitting flexible size RLC PDUs when an RRC connection is relocated from a serving radio network controller (SRNC) that does not support flexible size RLC PDUs to an SRNC that supports flexible size RLC PDUs. 49. The method as in any one of embodiments 43-48 wherein the transmitting side subassembly is reconfigured from transmitting fixed size RLC PDUs to transmitting flexible size RLC PDUs when a path over which the RLC PDUs are transmitted changes from including a first cell that does not supports flexible size RLC PDUs to including a second cell that supports flexible size RLC PDUs. 50. The method as in any one of embodiments 43-49 wherein RLC reestablishment criteria is evaluated when an information element (IE) "RLC info" is present in the RRC reconfiguration message. 51. The method of embodiment 50 wherein the RLC re-establishment criteria is evaluated on a per radio bearer (RB) basis. 52. A wireless transmit/receive unit (WTRU) comprising: a radio link control (RLC) unit including a transmitting side subassembly and a receiving side subassembly; and a radio resource control (RRC) unit configured to receive an RRC reconfiguration message indicating that the RLC unit should be reconfigured from transmitting fixed size RLC protocol data units (PDUs) via an uplink channel to transmitting flexible size RLC PDUs via the uplink channel, wherein a determination is made as to whether a re-establishment of at least the transmitting side subassembly is required. 53. The WTRU of embodiment 52 wherein the re-establishment is required if an RLC protocol header format of headers in the RLC PDUs is changed. 54. The WTRU of embodiment 53 wherein the change of the RLC protocol header format corresponds to a change in the size of a length indicator field in the headers. 55. The WTRU as in any one of embodiments 52-54 wherein if it is determined that a re-establishment is required, only the transmitting side subassembly is re-established if an information element (IE) "one sided RLC reestablishment" is present in the RRC reconfiguration message, and both the receiving side subassembly and the transmitting side subassembly are reestablished if an IE "one sided RLC re-establishment" is not present in the RRC reconfiguration message. 56. The WTRU as in any one of embodiments 52-55 wherein the transmitting side subassembly is reconfigured from transmitting fixed size RLC PDUs to transmitting flexible size RLC PDUs when adding a new cell that supports flexible size RLC PDUs to an active set and removing a cell that does not support flexible RLC PDUs from the active set, wherein the final active set contains only cells that support flexible size RLC PDUs. 57. The WTRU as in any one of embodiments 52-56 wherein the transmitting side subassembly is reconfigured from transmitting fixed size RLC PDUs to transmitting flexible size RLC PDUs when an RRC connection is relocated from a serving radio network controller (SRNC) that does not support flexible size RLC PDUs to an SRNC that supports flexible size RLC PDUs. 58. The WTRU as in any one of embodiments 52-57 wherein the transmitting side subassembly is reconfigured from transmitting fixed size RLC PDUs to transmitting flexible size RLC PDUs when a path over which the RLC PDUs are transmitted changes from including a first cell that does not supports flexible size RLC PDUs to including a second cell that supports flexible size RLC PDUs. 59. The WTRU as in any one of embodiments 52-58 wherein RLC reestablishment criteria is evaluated when an information element (IE) "RLC info" is present in the RRC reconfiguration message. 60. The WTRU of embodiment 59 wherein the RLC re-establishment criteria is evaluated on a per radio bearer (RB) basis. 61. A wireless communication method of performing a reconfiguration of a radio link control (RLC) unit in a universal terrestrial radio access network (UTRAN), the method comprising: determining that a reconfiguration of the RLC unit is required; reconfiguring the RLC unit from fixed RLC protocol data unit (PDU) sizes to flexible RLC PDU sizes, wherein the RLC unit comprises a transmitting side subassembly and a receiving side subassembly; and re-establishing at least one of the transmitting side subassembly and the receiving side subassembly. 62. The method of embodiment 61 wherein the transmitting side subassembly is reconfigured from transmitting fixed size RLC PDUs to transmitting flexible size RLC PDUs when a path over which the RLC PDUs are transmitted changes from including a first cell that does not support enhanced high speed medium access control (MAC-ehs) to including a second cell that supports enhanced MAC-ehs. 63. The method as in any one of embodiments 61 and 62 wherein the receiving side subassembly is reconfigured from receiving fixed size RLC PDUs to receiving flexible size RLC PDUs when a path over which the RLC PDUs are received changes from including a first cell that does not support flexible RLC PDUs to a second cell that supports flexible RLC PDUs. 64. The method as in any one of embodiments 61-63 further comprising: transmitting a radio resource control (RRC) reconfiguration message to a wireless transmit/receive unit (WTRU) indicating that the WTRU should be reconfigured from receiving fixed size RLC PDUs to receiving flexible size RLC PDUs. 65. The method of embodiment 64 wherein the RRC reconfiguration message includes an information element (IE) "one sided RLC re-establishment" if it is determined that an RLC re-establishment of the receiving side subassembly is required by the WTRU. 66. The method as in any one of embodiments 61-63 further comprising: transmitting a radio resource control (RRC) reconfiguration message to a wireless transmit/receive unit (WTRU) indicating that the WTRU should be reconfigured from transmitting fixed size RLC PDUs to transmitting flexible size RLC PDUs. 67. The method of embodiment 66 wherein the RRC reconfiguration message includes an information element (IE) "one sided RLC re-establishment" if determined that an RLC re-establishment of the transmitting side subassembly is required by the WTRU. 68. A universal terrestrial radio access network (UTRAN) comprising: a radio link control (RLC) unit including a transmitting side subassembly and a receiving side subassembly; and a radio resource control (RRC) unit configured to determine that a reconfiguration of the RLC unit is required, reconfigure the RLC unit from fixed RLC protocol data unit (PDU) sizes to flexible RLC PDU sizes, and re-establish at least one of the transmitting side subassembly and the receiving side subassembly. 69. The UTRAN of embodiment 68 wherein the transmitting side subassembly is reconfigured from transmitting fixed size RLC PDUs to transmitting flexible size RLC PDUs when a path over which the RLC PDUs are transmitted changes from including a first cell that does not support enhanced high speed medium access control (MAC-ehs) to including a second cell that supports enhanced MAC-ehs. 70. The UTRAN as in any one of embodiments 68 and 69 wherein the receiving side subassembly is reconfigured from receiving fixed size RLC PDUs to receiving flexible size RLC PDUs when a path over which the RLC PDUs are received changes from including a first cell that does not support flexible RLC PDUs to a second cell that supports flexible RLC PDUs. 71. The UTRAN as in any one of embodiments 68-70 further comprising: a transmitter configured to transmit a radio resource control (RRC) reconfiguration message to a wireless transmit/receive unit (WTRU) indicating that the WTRU should be reconfigured from receiving fixed size RLC PDUs to receiving flexible size RLC PDUs. 72. The UTRAN of embodiment 71 wherein the RRC reconfiguration message includes an information element (IE) "one sided RLC re-establishment" if it is determined that an RLC re-establishment of the receiving side subassembly is required by the WTRU. 73. The UTRAN as in any one of embodiments 68-70 further comprising: a transmitter configured to transmit a radio resource control (RRC) reconfiguration message to a wireless transmit/receive unit (WTRU) indicating that the WTRU should be reconfigured from transmitting fixed size RLC PDUs to transmitting flexible size RLC PDUs. 74. The UTRAN of embodiment 73 wherein the RRC reconfiguration message includes an information element (IE) "one sided RLC re-establishment" if determined that an RLC re-establishment of the transmitting side subassembly is required by the WTRU. 75. A wireless communication method of performing a reconfiguration of a radio link control (RLC) unit in a universal terrestrial radio access network (UTRAN), the method comprising: determining that a reconfiguration of the RLC unit is required; reconfiguring the RLC unit from flexible RLC protocol data unit (PDU) sizes to fixed RLC PDU sizes, wherein the RLC unit comprises a transmitting side subassembly and a receiving side subassembly; and re-establishing at least one of the transmitting side subassembly and the receiving side subassembly. 76. The method of embodiment 75 wherein the RLC unit is reconfigured from transmitting flexible size RLC PDUs to transmitting fixed size RLC PDUs when a path over which the RLC PDUs are transmitted changes from including a first cell that supports enhanced high speed medium access control (MAC-ehs) to including a second cell that does not support enhanced MAC-ehs. 77. The method as in any one of embodiments 75 and 76 wherein the RLC unit is reconfigured from flexible size RLC PDUs to fixed size RLC PDUs when the WTRU moves from a first cell that supports flexible size RLC PDUs to a second cell that does not support flexible size RLC PDUs. 78. The method as in any one of embodiments 75-77 wherein the RLC unit is reconfigured from flexible size RLC PDUs to fixed size RLC PDUs when an RRC connection is relocated from a serving radio network controller (SRNC) that supports flexible size RLC PDUs to an SRNC that does not support flexible size RLC PDUs. 79. The method as in any one of embodiments 75-78 further comprising: transmitting a radio resource control (RRC) reconfiguration message to a wireless transmit/receive unit (WTRU) indicating that the WTRU should be reconfigured from receiving flexible size RLC PDUs to receiving fixed size RLC PDUs. 80. The method of embodiment 79 wherein the RRC reconfiguration message includes an information element (IE) "one sided RLC re-establishment". 81. The method as in any one of embodiments 75-78 further comprising: transmitting a radio resource control (RRC) reconfiguration message to a wireless transmit/receive unit (WTRU) indicating that the WTRU should be reconfigured from transmitting flexible size RLC PDUs to transmitting fixed size RLC PDUs. 82. The method of embodiment 81 wherein the RRC reconfiguration message includes an information element (IE) "one sided RLC re-establishment". 83. A universal terrestrial radio access network (UTRAN) comprising: a radio link control (RLC) unit including a transmitting side subassembly and a receiving side subassembly; and a radio resource control (RRC) unit configured to determine that a reconfiguration of the RLC unit is required, reconfigure the RLC unit from flexible RLC protocol data unit (PDU) sizes to fixed RLC PDU sizes, and reestablish at least one of the transmitting side subassembly and the receiving side subassembly. 84. The UTRAN of embodiment 83 wherein the RLC unit is reconfigured from transmitting flexible size RLC PDUs to transmitting fixed size RLC PDUs when a path over which the RLC PDUs are transmitted changes from including a first cell that supports enhanced high speed medium access control (MAC-ehs) to including a second cell that does not support enhanced MAC-ehs. 85. The UTRAN as in any one of embodiments 83 and 84 wherein the RLC unit is reconfigured from flexible size RLC PDUs to fixed size RLC PDUs when the WTRU moves from a first cell that supports flexible size RLC PDUs to a second cell that does not support flexible size RLC PDUs. 86. The UTRAN as in any one of embodiments 83-85 wherein the RLC unit is reconfigured from flexible size RLC PDUs to fixed size RLC PDUs when an RRC connection is relocated from a serving radio network controller (SRNC) that supports flexible size RLC PDUs to an SRNC that does not support flexible size RLC PDUs. 87. The UTRAN as in any one of embodiments 83-86 further comprising: a transmitter configured to transmit a radio resource control (RRC) reconfiguration message to a wireless transmit/receive unit (WTRU) indicating that the WTRU should be reconfigured from receiving flexible size RLC PDUs to receiving fixed size RLC PDUs. 88. The UTRAN of embodiment 87 wherein the RRC reconfiguration message includes an information element (IE) "one sided RLC re-establishment". 89. The UTRAN as in any one of embodiments 83-86 further comprising: a transmitter configured to transmit a radio resource control (RRC) reconfiguration message to a wireless transmit/receive unit (WTRU) indicating that the WTRU should be reconfigured from transmitting flexible size RLC PDUs to transmitting fixed size RLC PDUs. 90. The UTRAN of embodiment 89 wherein the RRC reconfiguration message includes an information element (IE) "one sided RLC re-establishment". 91. A wireless communication method of performing a reconfiguration of a radio link control (RLC) unit in a wireless transmit/receive unit (WTRU), the method comprising: reconfiguring the RLC unit from flexible RLC protocol data unit (PDU) sizes to fixed RLC PDU sizes, wherein the RLC unit comprises a transmitting side subassembly and a receiving side subassembly; and the transmitting side subassembly discarding flexible size RLC PDUs. 92. The method of embodiment 91 further comprising: transmitting a message indicating the discarded flexible size RLC PDUs. 93. The method of embodiment 92 wherein the message further indicates RLC service data units (SDUs) corresponding to the discarded flexible size RLC PDUs. 94. The method as in any one of embodiments 92 and 93 wherein the message includes a move receive window (MRW) control super field (SUFI) to indicate the discarded RLC PDUs. 95. The method of embodiment 94 wherein the MRW SUFI indicates the sequence number (SN) of a last RLC PDU or RLC SDU that is discarded. 96. The method as in any one of embodiments 91-95 wherein any RLC PDU with a size different than the length of the fixed size RLC PDUs is discarded. 97. The method as in any one of embodiments 91-95 wherein any RLC PDU with a size different than the length of fixed size RLC PDUs that have already been transmitted at least once is discarded. 98. The method as in any one of embodiments 91-95 wherein all RLC PDUs with a sequence number (SN) up to and including the last RLC PDU with a flexible RLC PDU size, or an RLC PDU size different than the length of a fixed RLC PDU, are discarded. 99. The method as in any one of embodiments 91-95 wherein all RLC PDUs with a sequence number (SN) up to and including the last RLC PDU with a flexible RLC PDU size, or an RLC PDU size different than the length of a fixed RLC PDU that was transmitted at least once, are discarded. 100. The method as in any one of embodiments 91-95 wherein all RLC service data unit (SDUs) up to the last SDU contained within the last RLC PDU with a flexible RLC PDU size, or an RLC PDU size different than the fixed RLC PDU length, are discarded. 101. The method as in any one of embodiments 91-95 wherein all RLC SDUs for which at least one segment was contained in an RLC PDU of a size different than a fixed size RLC PDU that was transmitted at least once are discarded. 102. The method as in any one of embodiments 91-95 wherein all RLC PDUs in a retransmission buffer that have been transmitted to lower layers and that have an assigned sequence number (SN) assigned are discarded. 103. The method as in any one of embodiments 91-102 wherein data loss is minimized by creating and transmitting fixed size RLC PDUs when a handover decision is made. 104. The method as in any one of embodiments 91-103 wherein the transmitting side subassembly discards flexible size RLC PDUs in response to explicit signaling from higher layers. 105. A wireless communication method of performing a reconfiguration of a radio link control (RLC) unit in a wireless transmit/receive unit (WTRU), the method comprising: receiving a message from higher layers indicating an activation time; and prior to the activation time, reconfiguring the RLC unit from generating flexible size RLC protocol data units (PDUs) to generating fixed size RLC PDUs. 106. The method of embodiment 105 further comprising: regenerating, according to a fixed size, all PDUs that have been created but have not yet been transmitted. 107. The method of embodiment 105 further comprising: regenerating, according to a fixed size, all new PDUs that have been created from newly arrived or buffered service data units (SDUs). 108. The method as in any one of embodiments 105-107 wherein a handover takes place at the activation time. 109. The method of embodiment 106 wherein the remaining flexible size RLC PDUs are discarded. 110. A wireless communication method of performing a reconfiguration of a radio link control (RLC) unit in a wireless transmit/receive unit (WTRU), the method comprising:

the RLC unit generating flexible size RLC protocol data units (PDUs); receiving a message from higher layers indicating an activation time; prior to the activation time, changing a configured maximum RLC PDU size associated with the flexible RLC PDUs to match a fixed RLC PDU size; and at the activation time, reconfiguring the RLC unit from generating flexible size RLC protocol data units (PDUs) to generating fixed size RLC PDUs. 111. The method of embodiment 110 wherein a handover takes place at the activation time. 112. A wireless communication method of performing a reconfiguration of a radio link control (RLC) unit in a wireless transmit/receive unit (WTRU), the method comprising: reconfiguring the RLC unit from transmitting flexible size RLC PDUs to transmitting RLC PDUs having a size selected from a pre-defined set of RLC PDU sizes; and changing the size of the flexible size RLC PDUs to be retransmitted to match a particular size in the pre-defined set of RLC PDU sizes. 113. The method of embodiment 112 wherein padding of the flexible size RLC PDUs is performed to match the particular size. 114. The method of embodiment 113 wherein the flexible RLC PDUs are padded up the next highest available size in the pre-defined set. 115. The method of embodiment 114 wherein a flexible size RLC PDU with a size higher than the maximum size of the RLC PDU sizes in the predefined set are discarded. 116. The method of embodiment 112 wherein all flexible size RLC PDUs that have not been transmitted or submitted to lower layers are regenerated to fit into fixed size RLC PDUs. 117. A wireless communication method of performing a reconfiguration of a radio link control (RLC) unit in a universal terrestrial radio access network (UTRAN), the method comprising: reconfiguring the RLC unit from transmitting flexible size RLC PDUs to transmitting RLC PDUs having a size selected from a pre-defined set of RLC PDU sizes; and changing the size of the flexible size RLC PDUs to be retransmitted to match a particular size in the pre-defined set of RLC PDU sizes. 118. The method of embodiment 117 wherein padding of the flexible size RLC PDUs is performed to match the particular size. 119. The method of embodiment 118 wherein the flexible RLC PDUs are padded up the next highest available size in the pre-defined set. 120. The method of embodiment 119 wherein a flexible size RLC PDU with a size higher than the maximum size of the RLC PDU sizes in the predefined set are discarded. 121. The method of embodiment 117 wherein all flexible size RLC PDUs that have not been transmitted or submitted to lower layers are regenerated to fit into fixed size RLC PDUs.

[0088] Although the features and elements are described in particular combinations, each feature or element can be used alone without the other features and elements or in various combinations with or without other features and elements. The methods or flow charts provided may be implemented in a computer program, software, or firmware tangibly embodied in a computer-readable storage medium for execution by a general purpose computer or a processor. Examples of computer-readable storage mediums include a read only memory (ROM), a random access memory (RAM), a register, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks, and digital versatile disks (DVDs).

[0089] Suitable processors include, by way of example, a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs) circuits, any other type of integrated circuit (IC), and/or a state machine.

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