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System and Method of Filtering MRWs, ACKs and NACKs after RLC Re-Establishment

IP.com Disclosure Number: IPCOM000130514D
Publication Date: 2005-Oct-25
Document File: 2 page(s) / 30K

Publishing Venue

The IP.com Prior Art Database

Abstract

In a wireless communication systems such as UMTS, radio-bearer characteristics sometimes changes during the course of a connection. When certain radio-bearer parameter changes a reestablishment of the RLC entity is required. The RLC re-establishment is made in such a way that there should be a minimum of data loss between the RLC peers. The UTRAN can order the UE to perform re-establishment immediately or later at a specified time. During a RLC re-establishment, the RLC sequence numbers for receiver and transmitter part are reset to zero. A possible scenario for immediate re-establishment is as follows: 1. UTRAN stops all downlink transmission. 2. UTRAN signals to the UE to perform re-establishment. 3. The UE performs the re-establishment. 4. The UE signals to UTRAN that the re-establishment is complete. 5. UTRAN re-establishes the RB. 6. UTRAN starts the downlink transmission. A possible scenario for delayed re-establishment is as follows: 1. UTRAN signals to the UE to perform re-establishment with delay. 2. The UE signals to UTRAN that the re-establishment will be made. 3. At activation time both UE and UTRAN re-establishes the RB. When the RLC entity is re-established, all Data PDUs and Control PDUs are discarded. The problem occurs in UTRAN RLC in the case where the UE RLC has transmitted either one of the following messages immediately prior to reestablishment (as data PDUs and Control PDUs that was already given to MAC/L1 for transmission will not be discarded): 1. STATUS PDU with Acknowledgement (ACK). 2. STATUS PDU with Negative Acknowledgement (NACK). 3. STATUS PDU with Move Receiver Window (MRW). If either of those messages are received immediately after UTRAN RLC has performed the re-establishment, the following events can happen: 1. UTRAN RLC triggers the RLC reset procedure as the sequence number does not match the expected sequence numbers after re-establishment (for case 1 and 2. See 25.322 10.1). This will lead to additional RLC signalling and possible loss of user data. 2. UTRAN RLC updates its receiver variables (VR(R) for example) believing that the UE RLC has discarded data. This will lead to UTRAN RLC discarding all subsequent PDUs that have a sequence number lower than the last sequence number indicated in the MRW. This will lead to loss of user data. The likelihood of triggering the problem in UTRAN RLC is greater for the delayed re-establishment and when radio bearer with different TTIs are used as the transfer time for PDUs on different RBs will be different. The problem is also triggered in the UE RLC in the case of delayed re-establishment and the UTRAN RLC has sent any of the above mentioned messages and they arrive after the UE has performed the re-establishment. The UE will trigger the same events as mentioned for RLC UTRAN above. For re-establishment without delay the proposed solution is for UTRAN to stop the radio bearer while the UE re-establishment is ongoing. Any STATUS PDUs with ACKs, NACKs, or MRW received while the UE is re-establishing are discarded, as are data PDUs. When UTRAN receives the confirmation that the UE has completed the re-establishment, UTRAN continues the radio bearer and starts a timer. While the timer is running, the RLC UTRAN should discard any STATUS PDUs with ACKs, NACKs, or MRWs. Normal protocol handling should resume when the timer expires. For re-establishment with delay, the proposed solution is for UTRAN and UE to start a timer after re-establishing the radio bearer. While the timer is running, the RLC should discard any STATUS PDUs with ACKs, NACKs, or MRWs. Normal protocol handling should resume when the timer expires. By discarding these PDUs, the problem with triggering RLC reset procedure and setting the receiver part variables will not occur. The filter time X should be configurable from UTRAN. A value no longer than 1/2 round trip time for a PDU should be sufficient.

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DATA FILTERING TECHNIQUE

System and Method of Filtering MRWs, ACKs and NACKs after RLC
Re-Establishment

Disclosed Anonymously

In a wireless communication systems such as UMTS, radio-bearer characteristics sometimes changes during the course of a connection. When certain radio-bearer parameter changes a reestablishment of the RLC entity is required. The RLC re-establishment is made in such a way that there should be a minimum of data loss between the RLC peers.

The UTRAN can order the UE to perform re-establishment immediately or later at a specified time. During a RLC re-establishment, the RLC sequence numbers for receiver and transmitter part are reset to zero.

A possible scenario for immediate re-establishment is as follows:

1. UTRAN stops all downlink transmission.

2. UTRAN signals to the UE to perform re-establishment.

3. The UE performs the re-establishment.

4. The UE signals to UTRAN that the re-establishment is complete.

5. UTRAN re-establishes the RB.

6. UTRAN starts the downlink transmission.

A possible scenario for delayed re-establishment is as follows:

1. UTRAN signals to the UE to perform re-establishment with delay.

2. The UE signals to UTRAN that the re-establishment will be made.

3. At activation time both UE and UTRAN re-establishes the RB.

When the RLC entity is re-established, all Data PDUs and Control PDUs are discarded.

The problem occurs in UTRAN RLC in the case where the UE RLC has transmitted either one of the following messages immediately prior to reestablishment (as data PDUs and Control PDUs that was already given to MAC/L1 for transmission will not be discarded):

1. STATUS PDU with Acknowledgement (ACK).

2. STATUS PDU with Negative Acknowledgement (NACK).

3. STATUS PDU with Move Receiver Window (MRW).

If either of those messages are received immediately after UTRAN RLC has performed the re-establishment, the following events can happen:

1. UTRAN RLC triggers the RLC reset procedure as the sequence number does not match the expected sequence numbers after re-establishment (for case 1 and 2. See 25.322 10.1). This will lead to additional RLC signalling and possible loss of user dat...