Abstract:
A mobile unit, or UE (User Equipment) includes a Radio Resource Control (RRC) and a plurality of unique states defining the connectivity between the UE and a base station. Once a RRC indicates that it is “Out of Service”, a series of timers are started to limit the duration of attempts by the RRC to re-enter an “In Service” condition before the RRC releases allocated resources and moves to an Idle Mode. In certain circumstances, it is necessary to stop one or more of these timers to prevent inadvertently severing the connection.

Description:
BACKGROUND OF INVENTION 
   1. Field of the Invention 
   The present invention relates to a wireless communications network. In particular, the present invention discloses a method for a mobile unit, often known as a UE (User Equipment), to re-enter a 3GPP service area. 
   2. Description of the Prior Art 
   Please refer to FIG.  1 .  FIG. 1  is a simple block diagram of a wireless communications network  10 , as defined by the 3 rd  Generation Partnership Project (3GPP) specifications 3GPP TS 25.322 V3.10.0 “RLC Protocol Specification”, and 3GPP TS 25.331 V3.10.0 “Radio Resource Control (RRC) Specification”, which are included herein by reference. The wireless communications network  10  comprises a plurality of radio network subsystems (RNSs)  20  in communications with a core network (CN)  30 . The plurality of RNSs  20  is termed a Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network, or UTRAN for short. Each RNS  20  comprises one radio network controller (RNC)  22  that is in communications with a plurality of Node Bs  24 . Each Node B  24  is a transceiver, which is adapted to send and receive wireless signals, and which defines a cell region. A plurality of Node Bs  24  defines a UTRAN Registration Area (URA). The wireless communications network  10  assigns a mobile unit  40  (generally termed a “UE” for User Equipment) to a particular RNS  20 , which is then termed the serving RNS (SRNS)  20   s  of the UE  40 . 
   Data destined for the UE  40  is sent by the CN  30  (or UTRAN  20   u ) to the SRNS  20   s . It is convenient to think of this data as being sent in the form of one or more packets that have a specific data structure, and which travel along one of a plurality of radio bearers (RBs)  28 ,  48 . An RB  28  established on the SRNS  20   s  will have a corresponding RB  48  established on the UE  40 . The RBs  28 ,  48  are numbered consecutively, from RB 0  to RBn. Typically, RB 0  to RB 4  are dedicated signaling RBs (SRBs), which are used for passing protocol signals between the UTRAN  20   u  and the UE  40 . RBs  28 ,  48  greater than four (i.e., RB 5 , RB 6 , etc.) are typically used to carry user data. 
   The RNC  22  utilizes a Node B  24 , which is assigned to the UE  40  by way of a Cell Update procedure, to transmit data to, and receive data from, the UE  40 . The Cell Update procedure is initiated by the UE  40  to change a cell as defined by a Node B  24 , and even to change a URA. Selection of a new cell region will depend, for example, upon the location of the UE  40  within the domain of the SRNS  20   s . The UE  40  broadcasts data to the wireless communications network  10 , which is then picked up by the SRNS  20   s  and forwarded to the CN  30 . Occasionally, the UE  40  may move close to the domain of another RNS  20 , which is termed a drift RNS (DRNS)  20   d . A Node B  24  of the DRNS  20   d  may pick up the signal transmitted by the UE  40 . The RNC  22  of the DRNS  20   d  forwards the received signal to the SRNS  20   s . The SRNS  20   s  uses this forwarded signal from the DRNS  20   d , plus the corresponding signals from its own Node B  24  to generate a combined signal that is then decoded and finally processed into packet data. The SRNS  20   s  then forwards the received data to the CN  30 . Consequently, all communications between the UE  40  and the CN  30  must pass through the SRNS  20   s.    
   Please refer to  FIG. 2  in conjunction with FIG.  1 .  FIG. 2  is a simple block diagram of a UMTS radio interface protocol architecture, as used by the communications network  10 . Communications between the UE  40  and the UTRAN  20   u  is effected through a multi-layered communications protocol that includes a layer  1 , a layer  2  and a layer  3 , which together provide transport for a signaling plane (C-plane)  92  and a user plane (U-plane)  94 . Layer  1  is the physical layer  60 , and in the UTRAN  20   u  is responsible for combining signals received from the DRNS  20   d  and SRNS  20   s . Layer  2  includes a packet data convergence protocol (PDCP) layer  70 , a Radio Link Control (RLC) layer  72 , and a Medium Access Control (MAC) layer  74 . Layer  3  includes a Radio Resource Control (RRC) layer  80 . The U-plane  94  handles user data transport between the UE  40  and the UTRAN  20   u , whereas the C-plane  92  handles transport for signaling data between the UE  40  and the UTRAN  20   u . The RRC  80  sets up and configures all RBs  28 ,  48  between the UTRAN  20   u  and the UE  40 . The PDCP layer  22  provides header compression for Service Data Units (SDUs) received from the U-plane  94 . The RLC layer  72  provides segmentation of PDCP  70  SDUs and RRC  80  SDUs into RLC protocol data units (PDUs), and under acknowledged mode (AM) transfers, can provide upper layers (such as the PDCP layer  70  or the RRC layer  80 ) with a confirmation that RLC PDUs have been successfully transmitted and received between the UTRAN  20   u  and the UE  40 . The MAC layer  74  provides scheduling and multiplexing of RLC PDUs onto the transport channel, interfacing with the physical layer  60 . 
   It is the RRC layer  80  that is responsible for the establishment and configuring of the RBs  28 ,  48 . The RRC layer  80  has various operational states that affect how the RRC layer  80  behaves. Please refer to  FIG. 3  with reference to FIG.  1  and FIG.  2 .  FIG. 3  is a state diagram of the RRC layer  80 . The RRC layer  80  has two primary states: an Idle Mode  81  and a UTRA RRC Connected Mode  86 . While in Idle Mode  81 , the RRC layer  80  has no lines of communication open with its peer RRC layer  80 , except perhaps along RB 0 , which is a common channel. That is, there are no available SRBs  28 ,  48  that enable communications between peer entity RRC layers  80 . 
   Utilizing the UE  40  as an example platform, once the RRC layer  80  of the UE  40  establishes a connection (i.e., an SRB  28 ,  48 ) with its peer RRC layer  80  on the UTRAN  20   u , the RRC layer  80  of the UE  40  switches into the UTRA RRC Connected Mode  86 . This connection is typically initiated along RB 0 , which is a shared channel. Internally, the UTRA RRC Connected Mode  86  has four unique states: CELL_DCH  82 , CELL_FACH  83 , CELL_PCH  84  and URA_PCH  85 . In the CELL_DCH state  82 , a dedicated channel is allocated to the UE  40  for uplink (UE  40  to UTRAN  20   u ) and downlink (UTRAN  20   u  to UE  40 ) communications. In the CELL_FACH state  83 , no dedicated channel is allocated to the UE  40 , but instead the UE  40  is assigned a default common or shared transport channel for uplink and downlink. In the CELL_PCH state  84 , no dedicated physical channel is allocated to the UE  40 , no uplink activity is possible for the UE  40 , and the position of the UE  40  is known by the UTRAN  20   u  on a cell level (i.e., a node B basis  24 ). In the URA_PCH state  85 , no dedicated physical channel is allocated to the UE  40 , no uplink activity is possible for the UE  40 , and the position of the UE  40  is known by the UTRAN  20   u  on a URA basis. 
   A number of reconfiguration procedures are available to the RRC layer  80  to setup and configure RBs  28 ,  48 . These procedures involve the UTRAN  20   u  sending a specific message to the UE  40  along an RB  28 ,  48 , and the UE  40  responding in turn with a corresponding message. Typically, the message is sent along RB 2 , which is an SRB. The messages include Radio Bearer Setup, Radio Bearer Reconfiguration, Radio Bearer Release, Transport Channel Reconfiguration, and Physical Channel Reconfiguration. For each of these reconfiguration messages, the UE  40  has a corresponding “Complete” or “Failure” response message indicating success or failure of the procedure on the UE  40  side, and which may provide the UTRAN  20   u  any necessary information for the UTRAN  20   u  to complete the procedure. The reconfiguration message and the response message may all carry optional information elements (IEs), which are fields of data that hold ancillary information. In addition to these reconfiguration procedures, there also exists a Cell Update procedure, which originates with a Cell Update message from the UE  40  and is responded to by the UTRAN  20   u . The Cell Update procedure is used by the UE  40  to indicate a change of cell location (i.e., Node B  24 ), of URA, or connection state  82 ,  83 ,  84 , and  85 . The UE  40  initiates a Cell Update procedure in a variety of cases; to uplink data transmitted from the UE  40  to the UTRAN  20   u , as a paging response, due to a radio link failure, re-entering a service area, due to an RLC  72  unrecoverable error, for cell reselection, and a periodical cell update. 
   The UE  40  considers itself as having detected an “In Service” condition if a suitable cell (i.e., a node B  24 ) is found allowing normal communication with the UTRAN  20   u  and as having detected an “Out of Service” condition when a suitable cell is not found and normal communication with the UTRAN  20   u  is not possible. A series of timers are used by the UE  40  to regulate how long certain conditions are to be maintained when the UE  40  is “Out of Service”. The duration for each timer is set in an IE “UE Timers and constants in connected mode” and is included in the System Information Block type 1 broadcast by the UTRAN  20   u.    
   When a Cell Update procedure is initiated, the UE  40  sends a CELL UPDATE message to the UTRAN  20   u  stating the reason for the Cell Update and starting a timer T 302 . Then, the UE  40  waits for a CELL UPDATE CONFIRM message from the UTRAN  20   u . If the timer T 302  expires before the response from the UTRAN  20   u  is received by the UE  40 , the UE  40  retransmits the CELL UPDATE message. The maximum number of times of retransmission is determined by N 302 , a value that is also stored in the IE “UE Timers and constants in connected mode”. During the period from when the UE  40  initiates a Cell Update procedure until the Cell Update procedure ends, the UE  40  may transmit additional Cell Update messages to the UTRAN  20   u  citing different causes. 
   When the UE  40  is in the CELL_FACH  83 , URA_PCH  85 , or CELL_PCH  84  state, a periodical Cell Update procedure is performed regularly attempting to find the most suitable cell for service. A periodical Cell Update procedure will be configured if a timer T 305  in the IE “UE Timers and constants in connected mode” is set to any value other than “infinity” and the timer T 305  expires. The timer T 305  regulates the frequency of periodical Cell Updates. If the timer T 305  expires and the UE  40  detects that an “In Service” condition exists, the UE  40  will perform the Cell Update or a URA Update procedure. If the timer T 305  expires and the UE  40  detects that an “Out of Service” condition exists, cell re-selection attempts are made and a timer T 307  is started. The timer T 307  regulates how long the UE  40  should try to select a suitable cell before entering the Idle Mode  81 . If the timer T 307  expires before the UE  40  re-enters an “In Service”, the UE  40  releases all dedicated resources and moves to the Idle Mode  81 . 
   If the UE  40  is in the CELL_FACH state and an “Out of Service” condition is detected, a timer T 317  is started. The timer T 317  also regulates how long the UE  40  should try to select a suitable cell before entering the Idle Mode  81 . If the timer T 317  expires and the “Out of Service” condition still exists, the UE  40  releases all dedicated resources and moves to the Idle Mode  81 . If the UE  40  is in the CELL_PCH or URA_PCH state and an “Out of Service” condition is detected, a timer T 316  is started. The timer T 316  regulates how long the UE  40  should try to select a suitable cell before starting the timer T 317  and entering the CELL_FACH state  83 . If the timer T 316  expires, the UE  40  starts the timer T 317 , moves to the CELL_FACH state  83 , and continues cell re-selection. Again, if the timer T 317  expires and the “Out of Service” condition still exists, the UE  40  releases all dedicated resources and moves to the Idle Mode  81 . 
     FIG. 4  is a flowchart of the above described timers according to prior art. When an “Out of Service” condition is detected and the UE  40  is in the CELL_PCH state  84  or URA_PCH state  85 , the timer T 316  is started and cell reselection continues attempting to re-establish service. If the UE  40  detects an “In Service” condition before the timer T 316  expires, the UE  40  stops the timer T 316  ( FIG. 4 , item  100 ). However, if the UE  40  remains “Out of Service” when the timer T 316  expires, the UE  40  starts the timer T 317  and moves to the CELL_FACH state  83  ( FIG. 4 , item  105 ). 
   A problem with the prior art occurs when the UE  40  detects an “Out of Service” condition and is in the CELL_PCH state  84  or URA_PCH state  85 . If the timer T 305  expires, a periodical Cell Update cannot be completed because the UE  40  cannot contact the UTRAN  20   u . Therefore, the timer T 307  is started ( FIG. 4 , item  110 ). If the UE  40  remains “Out of Service” when the timer T 307  expires, the UE  40  releases all allocated resources and enters the Idle Mode  81  ( FIG. 4 , item  115 ). However, if the UE  40  detects an “In Service” condition before the timer T 307  expires, the UE  40  fails to stop the timer T 307  and the connection is unintentionally broken when the timer T 307  expires ( FIG. 4 , item  120 ). 
   When the UE  40  detects an “Out of Service” condition and is in the CELL_FACH state  83 , the timer T 317  is started and cell reselection continues attempting to re-establish service. If the UE  40  remains “Out of Service” when the timer T 317  expires, the UE  40  releases all allocated resources and enters the Idle Mode  81  ( FIG. 4 , item  125 ). If the UE  40  detects an “In Service” condition and no Cell Update or URA Update procedure is ongoing, the UE  40  stops the timer T 317  ( FIG. 4 , item  130 ). However, if the UE  40  detects an “In Service” condition and a Cell Update or URA Update procedure is ongoing, the UE  40  fails to stop the timer T 317  and the connection is unintentionally broken when the timer T 317  expires ( FIG. 4 , item  135 ). 
   When the UE  40  detects an “Out of Service” condition and is in the CELL_FACH state  83  and the timer T 305  expires, again a periodical Cell Update cannot be completed because the UE  40  cannot contact the UTRAN  20   u . Therefore, the timer T 307  is started. If the UE  40  remains “Out of Service” when the timer T 307  expires, the UE  40  releases all allocated resources and enters the Idle Mode  81  ( FIG. 4 , item  125 ). However, if the UE  40  detects an “In Service” condition before the timer T 307  expires, the UE  40  fails to stop the timer T 307  and the connection is unintentionally broken when the timer T 307  expires ( FIG. 4 , item  140 ). 
   Failing to stop either the timer T 307  or the timer T 317  when the UE  40  detects an “In Service” condition will result in the release of all allocated resources, unintentionally breaking the connection. However, the prior art (sub-clause 8.5.5.2.2 in TS 25.331 V3.10.0) calls for only stopping the timer T 316  when the UE  40  is in the CELL_PCH or URA_PCH state and re-enters the service area ( FIG. 4 , item  100 ). The timer T 307  should be stopped if the timer T 307  is active when service is regained. 
   Additionally, if the timer T 316  expires before re-entering the service area, the UE  40  moves to the CELL_FACH state and starts the timer T 317 . The prior art (sub-clause 8.5.5.2.2 in TS 25.331 V3.10.0) calls for only stopping the timer T 317  if no Cell Update or URA update procedure is ongoing when the UE  40  is in the CELL_FACH state and re-enters the service area ( FIG. 4 , item  130 ). The timer T 317  should be stopped whether a Cell Update or URA procedure is ongoing or not. Similarly, if the timer T 307  is running when the UE  40  re-enters the service area while in the CELL_FACH state  83 , the timer T 307  is not always stopped and will break the connection upon expiry of the timer T 307 . 
   SUMMARY OF INVENTION 
   It is therefore an objective of the claimed invention to provide a method for ensuring that a Radio Resource Control (RRC) supported by a mobile unit of a wireless communications system does not inadvertently release allocated radio bearers and move the mobile unit to an Idle Mode after the RRC switches from indicating an “Out of Service” condition to indicating an “In Service” condition. 
   Briefly summarized, the claimed invention discloses a method for maintaining connectivity between a mobile unit and a base station in a wireless communications system. The RRC is used to establish at least a radio bearer when the mobile unit is within a service area of the base station. The RRC is also capable of releasing allocated radio bearers, and comprises a plurality of internal states, each state defining a connective relationship between the RRC and the wireless communications system. 
   A first situation exists when the RRC detects an out of service condition for a previously established radio bearer and the mobile unit enters a CELL_PCH state where the mobile unit is known to the base station on a cell level or enters a URA_PCH state where the mobile unit is known to the base station on a URA level. The CELL_PCH state and the URA_PCH state both have no dedicated physical channel existing between the mobile unit and the base station and no uplink activity is possible for the mobile unit. If a first timer expires indicating a need for performing a periodical Cell Update procedure, because the RRC indicates that the mobile unit is currently “Out of Service”, a second timer is started to limit the duration of time that the RRC continues attempting to re-establish a radio bearer and normal connectivity with the base station. If the second timer expires, the RRC releases allocated resources and enters an Idle Mode, breaking the connection. If the RRC detects an in service condition before the second timer expires, the claimed invention stops the second timer to avoid releasing the established radio bearer, which would otherwise break the connection. 
   A second situation exists when the mobile unit enters a CELL_FACH state and the RRC detects an out of service condition for a previously established radio bearer. In the CELL_FACH state, the mobile unit is known to the base station on a cell level and no dedicated channel is allocated to the mobile unit, but the mobile unit is assigned a default common or shared transport channel for uplink and downlink. Again, if a first timer expires indicating a need for performing a periodical Cell Update procedure, because the RRC indicates that the mobile unit is currently “Out of Service”, a second timer is started to limit the duration of time that the RRC attempts to detect an in service condition, and thus normal connectivity with the base station. If the second timer expires, the RRC releases the allocated radio bearer and enters an Idle Mode, breaking the connection. If the second timer is active when the RRC detects an in service condition for the radio bearer and no Cell/URA Update procedure is ongoing, the claimed invention stops the second timer to avoid breaking the connection. 
   A third situation exists when the mobile unit enters the CELL_FACH state and the RRC detects an out of service condition. A third timer used for limiting a duration used by the RRC to detect an in service condition for the radio bearer before the RRC releases the radio bearer and enters an Idle Mode. If the RRC detects an in service condition for the radio bearer and a Cell Update procedure or a URA procedure (or both) is ongoing, the claimed invention stops the third timer to avoid breaking the connection. 
   It is an advantage of the claimed invention to always stop the second and third timers when the RRC re-enters an “In Service” condition from an “Out of Service” condition. By stopping the timers, the inadvertent release of allocated radio bearers by the RRC and the severing of connection between the mobile unit and the base station as a result of the release can be avoided. 
   These and other objectives of the claimed invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment, which is illustrated in the various figures and drawings. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a block diagram of a wireless communications system. 
       FIG. 2  is a simple block diagram of a UMTS radio interface protocol architecture of the wireless communications system of FIG.  1 . 
       FIG. 3  is a state diagram of the RRC layer of a UMTS radio interface protocol architecture of FIG.  2 . 
       FIG. 4  is a flow chart showing different timers used when a mobile unit of  FIG. 1  detects “Out of Service”. 
       FIG. 5  is a flow chart showing different timers used when a mobile unit detects “Out of Service” according to the present invention. 
   

   DETAILED DESCRIPTION 
   In the following description, user equipment (UE) may be a mobile telephone, a handheld transceiver, a personal data assistant (PDA), a computer, or any other device that requires a wireless exchange of data. It is assumed that this wireless exchange of data conforms to 3GPP-specified protocols. It should be understood that many means may be used for the physical layer to effect wireless transmissions, and that any such means may be used for the system hereinafter disclosed. 
   Please review  FIGS. 1-4  when referring to FIG.  5 .  FIG. 5  is a flow chart of the handling of the UE  40  re-entering a 3GPP service area. The chart begins when the Radio Resource Control (RRC)  80  supported by the UE  40  detects that an “Out of Service” condition exists and the UE  40  is out of normal radio contact with the base station of the wireless communications network. The RRC  80  comprises a plurality of timers for various timing operations. The duration for each timer is set in the IE “UE Timers and constants in connected mode” and is included in the System Information Block type 1 broadcast by the UTRAN  20   u.    
   A first situation at which the present embodiment is directed occurs when the UE  40  is “Out of Service” while in the CELL_PCH state  84  or the URA_PCH state  85 . The CELL_PCH state  84  indicates that the UE  40  is known to the base station on a cell level and the URA_PCH state  85  indicates that the UE  40  is known to the base station on a URA level. Both the CELL_PCH state  84  and the URA_PCH state  85  have no dedicated physical channel existing between the mobile unit and the base station and no uplink activity is possible for the mobile unit. 
   While in the first situation, a first timer T 305  may expire, indicating a need for performing a periodical Cell Update procedure. The Cell Update procedure is used by the UE  40  to indicate a change of cell location (i.e., Node B  24 ), of URA, or connection state  82 ,  83 ,  84 , and  85 . Because the RRC  80  indicates that the mobile unit is currently “Out of Service”, a second timer T 307  is started to limit the duration of time that the RRC  80  attempts cell reselection and to re-establish normal connectivity with the base station, i.e., to move back into an “In Service” area. If the second timer T 307  expires, the RRC  80  releases allocated resources (such as the previously-established radio bearer) and enters the Idle Mode  81 , breaking the connection, obviously an undesirable result if the RRC  80  has detected that the UE  40  is within an “In Service” area before the second timer T 307  expires. 
   Therefore in the first situation, once the second timer T 307  becomes active, if the RRC  80  detects an in service condition before the second timer T 307  expires, the embodiment stops the second timer T 307  ( FIG. 5 , item  200 ) to avoid mistakenly breaking the connection when the timer T 307  eventually does expire. 
   A second situation at which the present embodiment is directed occurs when the UE  40  is “Out of Service” while in the CELL_FACH state  83 . In the CELL_FACH state  83  no dedicated channel is allocated to the UE  40 , but instead the UE  40  is assigned a default common or shared transport channel for uplink and downlink. 
   While in the second situation, again, a first timer T 305  may expire indicating a need for performing a periodical Cell Update procedure. Because the RRC  80  indicates that the mobile unit is currently “Out of Service”, a second timer T 307  is started to limit the duration of time that the RRC  80  attempts cell reselection. If the second timer T 307  expires, the RRC  80  releases allocated resources (such as the radio bearer) and enters the Idle Mode  81 , breaking the connection, again an obviously undesirable result if the RRC  80  detects an “In Service” condition before the second timer T 307  expires. 
   If the RRC  80  re-enters the “In Service” condition, there remains two possibilities depending on whether a Cell update procedure or a URA update procedure is ongoing. According to the current specification, whenever a cell update procedure or a URA update procedure is initiated, the timer T 305  will be stopped. So the timer T 307  can only be active if there is no cell update procedure or URA update procedure ongoing. However, by the specification, if neither a Cell Update procedure nor a URA Update procedure is ongoing, the second timer T 307  is not stopped and will eventually expire, causing the RRC  80  to release the allocated radio bearer, resulting in an unintentionally severed connection. 
   Therefore in the second situation, once the second timer T 307  becomes active, if the RRC  80  detects an “In Service” condition before the second timer T 307  expires, the embodiment stops the second timer T 307  when no Cell Update procedure or URA Update procedure is ongoing ( FIG. 5 , item  230 ) to avoid inadvertently breaking the connection when the timer T 307  eventually does expire. 
   A third situation at which the present embodiment is directed occurs again when the UE  40  is “Out of Service” while in the CELL_FACH state  83 . While in the third situation, a third timer T 317  is started for limiting the duration of time that the RRC  80  will attempt to find a suitable cell enabling the RRC  80  to re-enter the “In Service” condition before the RRC  80  releases allocated resources and moves to the Idle Mode  81 , severing the connection. 
   If the RRC  80  is again “In Service” before the third timer T 317  expires, the current specification calls for stopping the third timer T 317  only when no Cell Update procedure nor URA Update procedure is ongoing. 
   Therefore in the third situation, once the second timer T 307  becomes active, if the RRC  80  detects an “In Service” condition before the third timer T 317  expires, the embodiment stops the second timer T 307  when a Cell Update procedure or a URA Update procedure (or both) is ongoing ( FIG. 5 , item  250 ) to avoid inadvertently breaking the connection when the timer T 317  eventually does expire. 
   In contrast to the prior art, the present invention provides an improved method of handling the re-entry of a UE into a service area of a base station in a wireless communications system. In the prior art, the second timer T 307  and the third timer T 317 , both able to cause the RRC  80  to break the connection between the UE  40  and the base station, were not always stopped when the RRC  80  re-enters an “In Service” condition from an “Out of Service” condition. The present invention stops the second timer T 307  and the third timer T 317  in these described situations. The inadvertent release of allocated radio bearers by the RRC  80  caused by failure to stop internal timers and the severing of connection between the mobile unit and the base station as a result of the release is avoided in the present invention. 
   Those skilled in the art will readily observe that numerous modifications and alterations of the method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.