Abstract:
A method for validating radio resource control (RRC) messages includes determining whether an RRC message received by a wireless transmit-receive unit (WTRU) is valid based on: an RRC state for which the WTRU is configured, whether or not the WTRU needs a new transport format combination set, and whether or not the RRC message will configure the WTRU for a CELL_DCH state. A WTRU includes a rule application device configured to implement the method.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 11/312,006, filed Dec. 20, 2005, which claims the benefit of U.S. Provisional Patent Application Ser. No. 60/667,449 filed on Apr. 1, 2005, which are incorporated by reference as if fully set forth. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention generally relates to wireless communication systems, and more particularly, to a method and apparatus for validating radio resource control messages. 
       BACKGROUND 
       [0003]    The 3GPP standard 25.331 specifies the radio resource control (RRC) protocol for the radio interface between a wireless transmit/receive unit (WTRU) and a UMTS terrestrial radio access network (UTRAN). Section 8.6 of standard 25.331 describes the rules that the WTRU must follow for validating downlink peer messages received from the UTRAN. Included in this section are rules regarding transport channel information elements (IEs). 
         [0004]    Specifically, the standard states in Section 8.6.5.2 that if the IE “Transport format combination set” is not included and either (1) if no transport format combination set is stored in the WTRU; or (2) if transport channels are added or removed in the message; or (3) if any transport channel is reconfigured in the message such that the size of the transport format set is changed, then the WTRU shall set the variable INVALID CONFIGURATION to TRUE. 
         [0005]    This means that if the any of the above conditions are met, the WTRU should reject the peer message. The rule does not take additional information into account, such as the type of transport channel being modified, the configured RRC state of the WTRU, etc. 
         [0006]    The two basic operational modes of a WTRU are “Idle” and “Connected” modes. The Connected mode is further divided into several RRC states (i.e., a CELL_DCH state, a CELL_FACH state, a CELL_PCH state, and a URA_PCH state), which define the kind of channels that the WTRU is using. In the CELL_DCH state, dedicated channels are allocated to the WTRU. In the CELL_FACH state, no dedicated channel is allocated for the WTRU but the WTRU uses common channels which are shared by all WTRUs. While in the CELL_FACH state, the WTRU may receive (and must retain) certain information regarding dedicated channels. This information may then be used by the WTRU if the WTRU is directed by UTRAN to transition into the CELL_DCH state. 
         [0007]    During an interoperability test session, a WTRU under test failed several connection attempts. Analysis showed that the WTRU was rejecting the network&#39;s RRC connection setup message because it broke the validation rule. Specifically, the message was directing the WTRU to the CELL_FACH state and was adding a dedicated transport channel, but was not including a transport format combination set (TFCS). The problem was that the validation rule was indeed broken as written. Based on this test result, the implementation of the validation rule could benefit from being more flexible. 
         [0008]    Network operators may be tempted to read this rule liberally, thinking that the rule should only apply to transport channel elements that the WTRU will use in its immediately configured RRC state. The temptation (and perhaps confusion) is reinforced by the current ASN.1 message syntax which requires networks to add dedicated transport channels to all WTRUs upon RRC connection setup, even those being configured for the CELL_FACH state. However, simply delaying an application of the rule until such time as the channels will be used (i.e., when the WTRU is configured for CELL_DCH) will not suffice since the rule is transaction-based. By applying the rule as it is written, the WTRU may reject an operable configuration (such as in the case described above). But by delaying the application of the rule, as the following example shows, the WTRU may accept an inoperable configuration, which is arguably worse. 
         [0009]    For example, consider a WTRU that is operating in a CELL_DCH state. A UTRAN sends a message to the WTRU directing it to a CELL_FACH state and removing a transport channel, but not including a new TFCS. The WTRU accepts this message because the transport channels will not be used in the CELL_FACH state. A UTRAN sends a message to the WTRU directing it to a CELL_DCH state, including neither new transport channel information nor a new TFCS. The WTRU accepts this message because it does not break the validation rule. However, the WTRU will not be able to operate in the CELL_DCH state because it lacks the appropriate transport channel information or TFCS. 
       SUMMARY 
       [0010]    A method for validating radio resource control (RRC) messages includes determining whether an RRC message received by a wireless transmit-receive unit (WTRU) is valid based on: an RRC state for which the WTRU is configured, whether or not the WTRU needs a new transport format combination set, and whether or not the RRC message will configure the WTRU for a CELL_DCH state. 
         [0011]    A WTRU includes a rule application device configured to implement the method. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0012]    A more detailed understanding of the invention may be had from the following description of a preferred embodiment, given by way of example, and to be understood in conjunction with the accompanying drawings, wherein: 
           [0013]      FIG. 1  is a flowchart of a method for applying a validation rule to an incoming RRC message; and 
           [0014]      FIG. 2  is a block diagram of a device configured to apply a validation rule to an incoming RRC message. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]    Hereafter, the term “wireless transmit/receive unit” (WTRU) includes, but is not limited to, a user equipment, a mobile station, a fixed or mobile subscriber unit, a pager, or any other type of device capable of operating in a wireless environment. When referred to hereafter, the term “base station” includes, but is not limited to, a Node B, a site controller, an access point, or any other type of interfacing device in a wireless environment. 
         [0016]    If a WTRU wants to allow for a liberal interpretation of the validation rule as defined in the standard (and therefore operate in the most networks possible) and still protect itself against invalid configurations, the WTRU must perform transport channel validation in a manner not described in the standard. 
         [0017]      FIG. 1  is a flowchart of a method  100  for applying the standard validation rule to an incoming message. The method  100  begins by receiving a peer message at a WTRU (step  102 ). The WTRU applies the validation rule to the received message (step  104 ). A determination is made whether the WTRU needs a new TFCS based on the received peer message (step  106 ). If the WTRU needs a new TFCS, then a TFCS indicator (e.g., a TFCS_NEEDED flag) is set to true (step  108 ). The TFCS indicator is maintained in the WTRU. If the WTRU does not need a new TFCS, then the TFCS indicator is left unchanged. 
         [0018]    Next, a determination is made whether the WTRU received a new TFCS in the received peer message (step  110 ). If the WTRU received a new TFCS, then the TFCS indicator (e.g., the TFCS_NEEDED flag) is set to false (step  112 ). If the WTRU did not receive a new TFCS, then the TFCS indicator is left unchanged. 
         [0019]    A determination is then made whether the WTRU is configuring itself for the CELL_DCH state based on the received peer message (step  114 ). If the WTRU is not configuring itself for the CELL_DCH state, then the message is accepted (step  116 ) and the method terminates (step  118 ). If the WTRU is configuring itself for the CELL_DCH state (step  114 ), then the TFCS indicator is evaluated to determine if it is set to true or false (step  120 ). If the TFCS indicator is set to true, then the WTRU rejects the message (step  122 ) and the method terminates (step  118 ). Since the WTRU needs a new TFCS and the network has not supplied the new TFCS during configuration for the CELL_DCH state, the message is properly rejected. If the TFCS indicator is set to false, then the message is accepted (step  116 ) and the method terminates (step  118 ). Since the network has supplied the WTRU with a new TFCS prior to or during configuration into the CELL_DCH state, the WTRU correctly accepts the message. In all cases, the WTRU continues operating error-free in the data plane. 
         [0020]    The present invention allows the WTRU to operate on networks that interpret the validation rule liberally. The present invention also allows the WTRU to still protect itself against invalid configurations and, therefore, continue operating without self-induced errors in the data plane (leading to less retry and/or fallback handling, and ultimately fewer dropped calls). 
         [0021]    Alternatively, the WTRU may not apply the TFCS validation rule, but the WTRU risks accepting invalid configurations or dropping calls. Another alternative is that the WTRU may delay applying the cited TFCS validation rule until the WTRU is configured for the CELL_DCH state. In this case, the WTRU also risks accepting invalid configurations or dropping calls. 
         [0022]      FIG. 2  is a block diagram of a device  200  configured to apply a validation rule to an incoming RRC message. In a preferred embodiment, the device  200  is a WTRU. The device  200  includes a receiver  202 , a rule application device  204  in communication with the receiver  202 , a message accepting device  206  in communication with the rule application device  204 , and a message rejecting device  208  in communication with the rule application device  204 . In operation, the receiver  202  receives an incoming RRC message for the device  200 . The rule application device  204  applies a message validation rule to the received message and checks the configured state of the WTRU. If the message passes the validation rule or is not configured for the CELL_DCH state, then the message accepting device  206  takes the message and processes it accordingly. If the message fails the validation rule and is configured for the CELL_DCH state, then the message is passed to the message rejecting device  208  and is discarded. 
         [0023]    Although the features and elements of the present invention are described in the preferred embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the preferred embodiments or in various combinations with or without other features and elements of the present invention.