KR101969055B1 - Method for Rleasing UE Context on UE initiated Detachment - Google Patents

Abstract

A method for removing a mobile terminal context in a base station when a mobile terminal is released. The method of the present invention can be performed during a procedure of processing a Detach Request initiated by a UE, thereby preventing UE Context deletion delay due to unnecessary retransmission of an RRC message. To this end, in the case where there is no response from the terminal to the RRC message, the base station apparatus of the present invention can quickly terminate the procedure for terminal disconnection by limiting the retransmission of the RRC message and performing a 'transmission completion' process.

Description

[0001] The present invention relates to a method for removing a UE context in a base station when a mobile communication terminal releases a call,

The present invention relates to a method for efficiently deleting a UE context in a base station at the start of a call release procedure initiated at a terminal in a mobile communication network.

1. RLC Retransmission of Base Station RLC

The Acknowledge Mode (AM) mode of the RLC (Radio Link Control) is the most complicated RLC transmission mode that requests ACK (transmission success) or NACK (Not ACK, transmission failure) After the RLC transmission end receives the status report from the RLC receiving end, the RLC transmission end prepares for the retransmission of the received data packet PDU (Protocol Data Unit). A simple rule to initiate retransmissions is to retransmit only Data PDUs that have received a NACK. That is, it is prohibited to arbitrarily retransmit from the transmitting end.

However, the only exception is autonomous retransmission for polling purposes. If there is no opportunity to send a new PDU due to Window Stalling or because the last PDU sent is the last packet in the stream with no retransmission allowed because the status report is not received, the RLC sender will send It is impossible to send polling because there is not. In order to prevent such a deadlock, if there is no transmittable PDU, the RLC sender is allowed to send its own retransmission exceptionally.

In case of independent retransmission, the RLC transmitting end can select one of the data PDUs that did not receive the status report and send it by setting the Polling bit to 1 in the header. Unless it is re-segmented, the data is retransmitted without any change. Proprietary retransmission prevents a significant delay at the end of the data stream or window stalling.

The maximum number of retransmissions of the RLC data PDU is controlled by RRC (Radio Resource Control). When an RLC protocol error occurs, for example, if the State Variable is not synchronized, theoretically retransmission will continue to fail. To recover from such a protocol error, the maximum number of retransmissions of the AM mode RLC Entity is determined. The maximum number of retransmissions affects Quality of Service (QoS) and is set for each radio bearer according to the characteristics of the radio bearer. If the maximum number of retransmissions is exceeded, the AM RLC Entity informs the RRC of the retransmission failure and initiates an 'RRC Connection Re-establishment Procedure'.

2. RLC ARQ

ARQ (Automatic Repeat Request) is performed for lossless transmission in AM RLC. In the basic ARQ operation, when the NACK is received at the receiving end, retransmission is performed. Here, the AM RLC transmitting end can request the receiving end status report (Polling) and re-segmentation of the PDUs to be retransmitted.

3. Polling

Polling is used by the transmitting end to receive status reports from the receiving end. The transmitting end can transmit the PDU only when receiving ACK of the transmission window updated by the status report and the PDU in the window. Therefore, if the status report is delayed, the transmission window will be stalled and the transmission will be stopped. In addition, a PDU that has not yet received an ACK will be in the retransmission buffer until it receives an ACK, and the buffer will soon be full. To avoid this problem, it is necessary for the RLC transmitter to receive the status report on time. For this reason, the RLC transmitter has four trigger functions for triggering the polls as shown below.

(1) poll PDU: When the number of RLC data PDUs is transmitted by a predetermined number without a poll, a poll is triggered. The RLC sender has a PDU counter (Counter) to count the number of newly transmitted PDUs. When a poll is transmitted, the PDU counter is reset to zero.

(2) pollByte: As in the above, it has a byte counter, counts how many bytes are newly transmitted, and is reset when a poll is transmitted. If the PDU is last in the transmit or retransmission buffer, a poll is triggered. Except when an already transmitted RLC data PDU is waiting for ack.

(3) t-PollRetransmit: Waits for a certain response waiting time (t-PollRetransmit) after transmission of PDU. When the response wait time expires, a poll is triggered. If any type of poll is triggered, the timer will start or restart. If ack or nack is received through the status report after the timer has started, it will be interrupted.

The triggered poll is included in the Data PDU to be transmitted. If the polling field of the PDU header is set to 1, it means polling. Since the polling field is always attached to the RLC header, there is no overhead for transmitting a poll.

4. Status Reporting (Status Reporting)

The RLC receiver uses the status report to inform the RLC transmitter of the receipt of data. The status report conveys the ack or nack up to the RLC Data PDU after harq reordering. After the HARQ reordering related to the RLC data PDU is completed, the RLC receiving end triggers the status report if the following conditions are met.

(1) When receiving an RLC data PDU with a polling field of 1

(2) When there is a data PDU in which a loss is detected

It is not efficient for the status report to be sent several times in a short period of time. This is because it is likely to have the same information. In addition, redundant Nacks can cause unnecessary retransmissions and duplicate reception. This prevents status reports from being sent multiple times within a short interval.

For this purpose, the "Status Prohibit" function is applied to the RLC receiving end. The Prohibit Interval is controlled by a "Status Prohibit Timer." This timer is used when the status report is transmitted During the timer operation, the RLC receiver can not send additional status reports, and even if multiple status reports are triggered, only one status report is transmitted after the timer expires if the timer is running .

"Prohibit status report" prevents frequent status report transmissions. However, prohibiting too long transmission may cause the RLC transmission end window to be disabled or stalled. Thus, the prohibition interval should consider the trade-off between radio range efficiency and transmission delay.

 The RLC receiver can trigger if the transmission of the status report is not prohibited. The status report is transmitted via the STATUS PDU and contains the last buffer status information regardless of when the status report was triggered. The status report is controlled by the 'status report prohibit' function, so it is better to include as much information as possible. And the status information up to the last data PDU, which is usually HARQ reordering, is included. However, the size of the RLC resource allowed by the MAC does not always guarantee as much as the status report requires. In this case, the status report can contain only partial information according to the size of the RLC resource.

5. UE Context Release at call release procedure

1 is a diagram showing the structure of System Architecture Evolution (SAE) on the 3GPP LTE standard. An EPC (Evolved Packet Core) 50 is a network to which a terminal (UE) 10 and a base station (e-NodeB) 20 are connected. The EPC 50 includes a Mobility Management Entity (MME) 31, a Serving Gateway 33, and a PDN Gateway 35.

The base station 20 stores the UE Context for the serving terminal 10. The UE Context refers to parameters of the IP bearer service, network internal routing information, and the like, and radio resources in the base station 20 are allocated by the UE Context. When the terminal 10 is detached from the base station 20, the base station 20 deletes the 'UE Context' related to the terminal, thereby preventing unnecessary resource allocation. Hereinafter, a UE Context deletion procedure at the time of call release will be described with reference to FIG.

<Terminal separation request of terminals: S201 to S205>

Referring to FIG. 2, when the user turns off the power of the terminal 10 or enters the airplane mode, the terminal 10 transmits a Non-Access Stratum (NAS) message called 'Detach Request' To the base station (20). At this time, the detach type is set to '1' (EPC detach) and the SwitchOff flag (Flag) is set to '1' (S201). The 'Detach Request' message is transmitted as an NAS message to the MME 31 via the base station 20 (S203, S205).

&Lt; Reception of UE Context deletion request of EPC: S207 >

The MME 31 of the EPC 30 transmits an S1AP (S1 Application Protocol) message of 'ueContextRelease', which is one of the NAS messages, to the base station 20 in order to delete the UE Context for the corresponding terminal 10 To the RRC 29 of FIG.

<RRC connection release procedure of the base station: S209 to S211>

The RRC 29 receiving the 'ueContextRelease' message sends an RRC message 'rrcConnectionRelease' to the terminal 10 to delete the RRC connection procedure between the terminal 10 and the terminal 10 before deleting the internal UE context (S209).

However, since the RF transceiver of the terminal 10 is already turned off, the terminal 10 can not receive the 'RRC connection release' message of the base station 20. The MAC 23 of the base station 20 will retransmit the RRC connection release message in the HARQ operation and the RLC 25 higher in the MAC 23 will not receive any response from the receiver and will not wait for the response waiting time t -PollRetransmit), the RRC connection release message is retransmitted. The retransmission in the RLC 25 operates for the maximum retransmission allowance times set in the maxRetxThreshold of the Signaling Radio Bearer (SRB) 1 (S211).

&Lt; Deletion of UE context due to radio link failure: S213 to S219 >

The RLC 25 of the base station 20 determines that it is a radio link failure (RLF) and notifies the RRC 29 of the RLC 29 (S213). If the RRC The mobile station 29 proceeds to a state for preparing for RRC re-establishment of the terminal 10 (S215).

The RRC 29 deletes the UE context after determining that the wireless link of the corresponding terminal 10 has completely disappeared after a predetermined time (RRC Re-establishment timer) has elapsed (S217) Message to terminate the UE Context Release procedure (S219).

According to the above procedure, the EPC 30 and the base station 20 retain the unnecessary UE context until the final processing of the RRC message is completed in step S 211 after step S 209, 10 attempts to re-attach to the base station.

It is an object of the present invention to provide a method for efficiently deleting a UE context in a base station at the start of a call release procedure initiated at a terminal in a mobile communication network.

In order to achieve the above object, a method of removing a UE context of a base station apparatus in a procedure according to a 'Detach Request' of a mobile communication terminal according to the present invention is characterized in that the RLC of the base station apparatus transmits an RRC connection Determining a retransmission after transmitting a release message and waiting for an ACK or NACK response from the terminal for a predetermined response waiting time; The RLC of the base station apparatus transmits a 'Delivery Indication' message to the RRC of the base station apparatus without retransmitting the RRC disconnect message; And the RRC of the base station apparatus deletes the UE Context according to the delivery completion message and transmits a message 'UE ContextReleaseComplete' to the EPC.

According to an embodiment of the present invention, the removal method of the present invention is characterized in that the RRC receives a UE Context Delete Request (ueContextRelease) corresponding to a 'UE Disconnection Request' of the UE from the EPC and receives an 'RRC Disconnect' And transmitting the 'RRC connection release' message to the RLC that the RRC connection release message is the final message.

In connection with the delivery time of the 'Delivery Indication' message, according to the first embodiment, the step of transmitting the 'Delivery Indication' message may include, after determining the retransmission, Can be performed immediately after the resend message is retransmitted.

According to a second aspect of the present invention, there is provided a method of controlling a radio network controller, comprising: after the step of determining retransmission, the RLC retransmits the RRC connection release message and changes the response wait time to a settable minimum time; And re-transmitting the RRC connection release message after the changed response waiting time elapses after retransmission of the RRC connection release message. Here, the step of transmitting the 'Delivery Indication' message may be performed after the retransmission.

In the second embodiment, the setting change step does not transmit the 'RRC connection reset' message related to the change of the response wait time to the terminal, so that the change of the response wait time is regarded as valid only in the base station apparatus can do.

The present invention controls the retransmission of the RLC message of the RLC terminal by controlling the terminal to minimize the response to the RRC message since the terminal is already in a state of communication incapability in the process according to the detach request of the terminal Thereby preventing resource waste of the additional UE context in the base station due to the radio link failure (RLF) processing occurring when the retransmission is exceeded. As with the EPC, deleting the UE context between the internal configuration of the EPC can be prevented from being delayed upon completion of the immediate deletion of the UE Context.

Further, since this process is performed only in the control of the base station apparatus, it is not required to change the setting of the MME or the terminal, and the processing is very simple.

Fig. 1 is an Eltisan network diagram,
FIG. 2 is a flowchart provided in a description of a UE Context release procedure at the time of call release in the related art,
3 is a protocol hierarchy diagram representing the base station apparatus of the present invention, and
4 is a flowchart provided in the description of the UE Context release procedure according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail with reference to the drawings.

The method of the present invention relates to a UE Context Release procedure in the base station apparatus 300 to which the 3GPP LTE standard is applied. Therefore, the SAE structure of FIG. 1 is applied.

Referring to FIG. 3, a base station to which the present invention is applied is referred to as a base station apparatus 300 by being distinguished from the base station 20 of FIG. The protocol layer structure of the base station 300 includes a physical layer PHY 301, a medium access control (MAC) layer 303, a radio link control (RLC) layer 305 for providing a service data unit (SDU) A Packet Data Convergence Protocol (PDCP) 307 for performing header compression and encryption, and an RRC (Radio Resource Control) 309 for providing a control signal message between the terminal 10 and the terminal 10. Although the PHY 301, the MAC 303, the RLC 305, the PDCP 307 and the RRC 309 are described as functions for forming a protocol layer structure, the individual configurations of the base station apparatus 300 Should be understood. The PHY functional unit 301, the MAC functional unit 303, the RLC functional unit 305, the PDCP functional unit 307, and the RRC functional unit 309 may be referred to as PHY 301, the MAC 303, the RLC 305, the PDCP 307, and the RRC 309.

The base station apparatus 300 also performs the role of the e-NodeB in the SAE structure of FIG. 1 except for the procedure described below.

Hereinafter, the procedure of releasing the UE Context upon release of the call according to the present invention will be described with reference to FIG. Here, the call release means that the terminal 10 is turned on or enters the &quot; airplane mode &quot; and is started by the terminal 10. Here, the airplane mode means that the operation of the wireless interface (mobile communication, wireless LAN, Bluetooth, etc.) of the portable terminal is turned off.

<Initiation of the ueContextRelease procedure of the MME according to the 'terminal separation request' of the terminal: S401 to S407>

Basically, the terminal 10 transmits a NAS (Non-Access Stratum) message of 'Detach Request' to the MME 31, and the MME 31 transmits a message 'ueContextRelease' to the base station apparatus 300 The process is the same as S201 to S207 in Fig.

When the user turns off the power of the terminal (UE) 10 or enters the airplane mode, the terminal 10 sends a NAS message 'Detach Request' to the base station apparatus 300. At this time, the detach type is set to '1' (EPC detach) and the SwitchOff flag (Flag) is set to '1' in the 'Detach Request' message (S401). The 'Detach Request' message is transmitted as an NAS message to the MME 31 via the base station apparatus 300 (S403 and S405).

The MME 31 of the EPC 30 sends an S1AP (S1 Application Protocol) message called 'uContextRelease' to the base station apparatus 300 to request deletion of the UE context for the corresponding terminal 10 (S407).

&Lt; RRC ' RRC disconnection ' message transmission: S409 >

The RRC 309 receiving the 'ueContextRelease' message sends an RRC message 'RRC Connection Release (RRC Connection Release)' to the UE 10 and deletes the RRC connection termination procedure between the UE 10 and the UE 10 .

<Notify RLC that it is the last SRB message: S411>

On the other hand, the RRC 309 of the base station apparatus 300 knows that the cause (NAS Cause) of the S1AP message 'ueContextRelease' transmitted from the MME 31 is the detachment of the terminal 10, and therefore the 'rrcConnectionRelease Quot; message is &quot; the last RRC message (SRB) &quot;. The RRC 309 of the present invention notifies the RLC 305 that the 'rrcConnectionRelease' message is the last SRB message by providing a message 'final RRC message' to the RLC 305.

<Transmission of RRC connection release message to terminal and waiting for response: S413>

The RLC 305 having received the 'rrcConnectionRelease' message from the RRC 309 as the last SRB message first sends the first 'rrcConnectionRelease' message to the terminal 10. Then, the RLC 305 waits for ACK or NACK to be transmitted from the terminal 10. The waiting time at this time is the response waiting time (for example, 20 ms) initialized to t-PollRetransmit. The process of sending an RRC connection release message and waiting for a predetermined response waiting time is the same as the conventional method. Therefore, if ACK or NACK is not received from the terminal 10 during the response waiting time, the RLC 305 must retransmit the RRC message.

&Lt; Minimization of response waiting time: S415 >

When the initial response waiting time (for example, 20 ms) elapses after transmitting the first 'rrcConnectionRelease (RRC connection release)' message to the terminal 10, the RLC 305 transmits an RRC connection release message to the terminal 10 Retransmit.

However, according to the present invention, the RLC 305 sets the response wait time to a settable minimum value (for example, 5 ms) at the same time as the first retransmission of the RRC connection release message. The setting of the response waiting time can be changed by changing the value of t-PollRetransmit of the SRB (Signaling Radio Bearer). However, the t-PollRetransmit change is regarded as valid only in the base station apparatus 300, and the terminal 10 transmits an 'rrcConnectionReconfiguration' message related to a change in the response wait time (t-PollRetransmit) to the terminal 10 Do not transmit.

Since the RF transceiver of the terminal 10 is powered off, the RLC 305 does not receive ACK or NACK during the changed response waiting time (5 ms). Accordingly, the RLC 305 retransmits 'rrcConnectionRelease' message to the terminal 10 when the changed response waiting time elapses from the primary retransmission.

The primary and secondary retransmissions of the RRC message by the RLC 305 are prepared in case the terminal 10 is not turned off. However, the secondary retransmission minimizes the waiting time required for response, thereby minimizing the waiting time consumed unnecessarily can do.

Nevertheless, step S415 is not an essential constitution of the present invention. If the method of performing step S415 corresponds to the first embodiment, the second embodiment does not perform step S415. According to the second embodiment, if the RLC 305 transmits the first 'rrcConnectionRelease' message in step S413 and does not receive the ACK or NACK from the terminal 10 during the initial response waiting time, The procedure may proceed to step S417 to end the retransmission procedure and initiate the deletion of the UE Context.

Delivery of <fake 'Delivery Indication': S417>

Since the RF transceiver of the terminal 10 is turned off, if the primary or secondary retransmission occurs due to the HARQ failure and the response waiting time elapses, the RLC 305 determines the maximum retransmission allowance frequency (maxRetxThreshold) of the SRB, No further retransmission procedures are performed.

Instead, the RLC 305 regards that the transmission of the corresponding SRB message is successful and transmits a 'Delivery Indication' message to the RRC 309 via the PDCP 307. It is a kind of 'Fake Delivery Indication' message. However, the step S417 is limited to the case where the message 'final RRC message' is received from the RRC 309 in step S411, that is, the 'terminal detachment' is the cause of the NAS.

&Lt; Deletion Completion of UE Context: S419, S421 >

The RRC 309 having received the 'Delivery Indication' message deletes the UE context in the base station apparatus 300 based on the transmission success of the corresponding rrcConnectionRelease (S417), and transmits the S1AP message 'ueContextReleaseComplete' to the EPC 30 Thereby notifying that the UE Context has been released and terminating the disconnection of the terminal 10. [

In this way, the base station apparatus 300 of the present invention can efficiently delete the UE context held when the call release procedure is started.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be construed as limiting the scope of the invention as defined by the appended claims. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention.

Claims (5)

delete A method for removing a UE context of a base station apparatus in a procedure according to a 'Detach Request' of a mobile communication terminal,
The RRC of the base station apparatus receives a UE Context Delete Request (ueContextRelease) corresponding to a 'UE Disconnection Request' of the UE from the EPC, and transmits an RRC Disconnect message to the RLC of the RAS, &Lt; / RTI &gt; message to the RLC;
The RLC transmitting the RRC connection release message to the terminal and waiting for an ACK or NACK response from the terminal during a predetermined response waiting time;
If the RLC does not receive the ACK or NACK during the response waiting time, transmitting a 'Delivery Indication' message to the RRC of the base station apparatus without retransmitting the RRC disconnect message; And
Wherein the RRC of the base station apparatus deletes the UE context according to the delivery completion message and transmits a UE ContextReleaseComplete message to the EPC.
A method for removing a UE context of a base station apparatus in a procedure according to a 'Detach Request' of a mobile communication terminal,
The RLC of the base station apparatus transmits an RRC connection release message to the terminal and waits for an ACK or NACK response from the terminal during a predetermined response waiting time;
If the RLC does not receive the ACK or the NACK during the response waiting time, transmitting the RRC connection release message to the MS;
Transmitting, by the RLC, a 'Delivery Indication' message to the RRC of the base station apparatus after the primary retransmission; And
Wherein the RRC deletes the UE Context according to the delivery completion message and transmits a 'UE Context Release Complete' message to the EPC.
A method for removing a UE context of a base station apparatus in a procedure according to a 'Detach Request' of a mobile communication terminal,
The RLC of the base station apparatus transmits an RRC connection release message to the terminal and waits for an ACK or NACK response from the terminal during a predetermined response waiting time;
If the RLC does not receive the ACK or the NACK during the response waiting time, resets the RRC connection release message to the terminal and changes the response wait time to a settable minimum time;
When the changed response waiting time elapses after the first retransmission of the RRC connection release message, the RLC secondly retransmits the RRC connection release message to the MS;
Transmitting the 'Delivery Indication' message to the RRC of the base station apparatus after the secondary retransmission without the RLC retransmitting the RRC disconnect message; And
Wherein the RRC of the base station apparatus deletes the UE context according to the delivery completion message and transmits a message 'UE ContextRelease Completion' to the EPC.
5. The method of claim 4,
Wherein the setting change step does not transmit the 'RRC connection reset' message related to the change of the response wait time to the terminal, thereby processing that the change of the response wait time is valid only in the base station apparatus Of UE Context.

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