KR100486033B1 - Applicable pdu range test and calculation for window-based polling - Google Patents

Abstract

The transmitter may send protocol data units (PDUs). Each PDU has an n-bit sequence number. A polling decision method is provided for determining whether polling should be performed according to parameter S, which is an n-bit sequence number. If the PDU to be transmitted next is not a re-transmitted PDU and the polling determination method indicates that polling should be triggered according to the sequence number of the PDU, polling is triggered. The polling determination method uses the following equation to determine if polling should be triggered. Where S is the sequence number of the next PDU. t = ((2 ⁿ + 1 + S- VT (A)) mod 2 ⁿ ) / VT (WS)

Description

APPLICABLE PDU RANGE TEST AND CALCULATION FOR WINDOW-BASED POLLING}

The present invention relates to a wireless communication protocol. More specifically, the present invention discloses a method and system in which a transmitter correctly triggers a polling operation requiring a receiving status of a receiver.

Many communication protocols typically use a three-layered approach to communication. See FIG. 1. 1 is a block diagram of three layers in the communication protocol. In a typical wireless environment, first station 10 is in wireless communication with one or more second stations 20. Application 13 on the first station 10 composes message 11 and forwards the message 11 to layer 3 interface 12 for delivery to the second station 20. The layer 3 interface 12 may also generate layer 3 signaling messages for the purpose of controlling layer 3 operations between the first station 10 and the second station 20. An example of the layer 3 signaling message is a request to cipher key changes, the key changes being the respective layer 3 interfaces 12 and 22 of both the first station 10 and the second station 20. Is caused by. The layer 3 interface 12 delivers either message 11 or layer 3 signaling message 12a to layer 2 interface 16 in the form of layer 2 service data units SDUs 14. Layer 2 SDUs 14 can be any length. Layer 2 interface 16 creates the SDUs 14 into one or more Layer 2 protocol data units (PDUs) 18. Each Layer 2 PDU 18 is of fixed length and conveyed to Layer 1 interface 19. The layer 1 interface 19 is a physical layer and transmits data to the second station 20. The transmitted data is received by layer 1 interface 29 of the second station 20 and reconstructed into one or more PDUs 28 and forwarded to the layer 2 interface 26. The Layer 2 interface 26 receives the PDUs 28 and assembles one or more Layer 2 SDUs 24 from them. The layer 2 SDUs 24 are carried up to the layer 3 interface 22. And this time, on the contrary, the layer 3 interface 22 may cause the layer 2 SDUs 24 to be identical to the original message 11 generated by the application 13 on the first station 10 or the original message generated by the layer 3 interface 12. It must be identical to the signaling message 12a and converted to one of the two Layer 3 signaling messages 22a handled by the Layer 3 interface 22. The received message 21 is delivered to application 23 on the second station 20.

Of particular interest is the layer 2 interface, which acts as a buffer between the relatively high-end data transmission and reception requests of applications and the low-level requests of the physical transmission and reception process. do. In the following, the term "PDU" is used to refer to Layer 2 PDUs, and the term "SDU" is used to refer to Layer 2 SDUs. See FIG. 2. 2 is a diagram of a transmit / receive process from a layer 2 perspective. Layer 2 interface 32 of transmitter 30, which may be either a base station or a mobile station, receives a string of SDUs 34 from layer 3 interface 33. SDUs 34 are arranged sequentially from 1 to 5 and are of unequal lengths. The layer 2 interface 32 converts the string of SDUs 34 into the string of PDUs 36. The layer 2 PDUs 36 are sequentially arranged from 1 to 4, all of the same length. The string of PDUs 36 is then sent to Layer 1 interface 31 for transmission. The reverse process occurs at receiver end 40. The receiver has a receiver layer 2 interface 42 that assembles the received strings of layer 2 PDUs 46 into the received strings of layer 2 SDUs 44 and may also be either a base station or a mobile station. Under special transport modes, the multi-layer protocol asserts that receiver layer 2 interface 42 will in turn assign SDUs 44 to layer 3 interface 43. That is, the layer 2 interface 42 should assign the SDUs 44 to the layer 3 interface 43 in the sequential order of the SDUs 44 starting with SDU 1 and ending with SDU 5. The order of SDUs 44 will not be confused and mixed up, and subsequent SDUs will not be delivered to Layer 3 until all previous SDUs have been delivered.

For line transmissions, this requirement is relatively easy to achieve. However, in the noisy environment of wireless transmissions, receiver 40, which may be a base station or a mobile station, often loses data. Thus any layer 2 PDUs in the received string of PDUs 46 will be lost. So, ensuring that Layer 2 SDUs 44 are in turn faced a significant challenge. Wireless protocols are carefully designed to focus on such issues. Generally speaking, there are two wide modes for sending and receiving data. Ie, AM transport (acknowledged mode transport) and UM transport (unacknowledged mode transport). For AM data, receiver 40 sends a special layer 2 acknowledgment signal to transmitter 30 to indicate successfully received layer 2 PDUs 46. No such signaling is performed for UM data. For the purposes of the present invention, only AM data is considered. See FIG. 3 with reference to FIG. 1. 3 is a simplified block diagram of AM data PDU 50 as defined in the 3GPP ^™ TS 25.322 specification incorporated herein by reference. In general, there are two types of PDUs. That is, it is a control PDU or data PDU. Control PDUs are used by layer 2 interfaces 16 and 26 to control data transmission and reception protocols, such as the layer 2 grant signal mentioned above used to acknowledge received data. This is somewhat similar to the exchange of Layer 3 interfaces 2 and 22 signaling messages 12a and 22a. However, layer 2 interfaces 16 and 26 do not interpret or recognize layer 3 signaling messages 12a and 22a. On the other hand, layer 2 interfaces 16 and 26 recognize layer 2 control PDUs and do not carry layer 2 control PDUs up to layer 3 interfaces 12 and 22. Data PDUs are used to transmit AM data. AM data is reassembled and given to Layer 3. Example PDU 50 is a data PDU and is divided into several fields, as defined by the Layer 2 protocol.

The first field 51 is a single bit indicating that the PDU 50 is either a data or control PDU. When data / control bit 51 is set (ie equal to 1), PDU 50 is indicated as an AM data PDU. The second field 52 is a sequence number field 52 and is 12 bits long. Consecutive PDUs 18, 28 subsequently have higher sequence numbers 52, and in this way the second station 20 can correctly reassemble Layer 2 PDUs 28 to form Layer 2 SDUs 24. For example, if the first PDU 18 is sent with a sequence number 52 such as 536, then the next PDU 18 will be sent with a sequence number 52 such as 537, and so on. By assembling the received data PDUs 50 in their correct subsequent order according to their respective sequence numbers 52, correct reconstruction of the SDU data is ensured. Sequence number 52 may allow retransmitted PDUs 50 to be inserted into their correct subsequent positions relative to other received PDUs 50. In this way, retransmission of data is supported. The single polling bit 53 follows the sequence number field 52, and when set, indicates that the receiver (i.e., the second station 20) must respond with an acknowledgment status PDU, which is a kind of control PDU. Pointing, this will be introduced later. The first station 10 sets the polling bit 53 to 1 to request the second station 20 to send an admission status control PDU. Bit 54 is retained and cleared to zero. The next bit 55a is an extension bit and, when set, indicates the presence of the following length indicator (LI). LI can be either 7 bits long or 15 bits long and is used to indicate the ending position of a layer 2 SDU within a layer 2 PDU 50. If a single SDU fills data area 58 of PDU 50 completely, bit 55a will be zero, thereby indicating that no LI exists. However, in the example PDU 50 there are two Layer 2 SDUs ending at the Layer 2 PDU 50. That is, SDU_1 57a and SDU_2 57b. Therefore, there should be two LIs pointing to the respective ends of SDU_1 57a and SDU_2 57b. The PDU following the PDU 50 (ie subsequently as indicated later by sequence number 52) will retain the LI for SDU_3 57c. The first LI and LI1 are in the field 56a following the extended bit field 55a and indicate the end of SDU_1 57a. LI1 56a has a set extension bit 55b indicating the presence of another LI, LI2 in field 56b. LI2 56b indicates the ending position of SDU_2 57b. And has a cleared extension bit 55c which means there are no more LIs, so that data area 58 is starting. Data area 58 is used to hold actual SDU data.

See FIG. 4 with reference to FIG. 3. 4 is a simplified block diagram of receiver 64 and transmitter 65 in a wireless communication system 60. Both receiver 64 and transmitter 65 have windows within which they expect to receive PDUs 50 and transmit PDUs 50, respectively. Receiver 64 has a receive window 61 bounded by two state variables VR (R) 62 and VR (MR) 63. VR (R) 62 marks the start of the receive window 61 and VR (MR) 63 marks the end of the receive window 61. Receiver 64 will only accept PDUs 50 with sequence numbers 52 that are sequentially on or after VR (R) 62 and sequentially before VR (MR) 63. The sequence number value held in VR (MR) 63 is not considered to be within the receive window 61. Similarly, transmitter 65 has a transmission window 66 bounded by two state variables VT (A) 67 and VT (MS) 68. VT (A) 67 marks the beginning of the transmission window 66 and VT (MS) 68 marks the end of the transmission window 66. Transmitter 65 will only transmit PDUs 50 with sequence numbers 52 that are within the range of transmission window 66, that is, sequentially or after VT (A) 67 and sequentially before VT (MS) 68.

Receive window 61 has a fixed receive window size. The receive window size is simply the number of sequence number values bounded by state variables VR (R) 62 and VR (MR) 63. In other words, VR (MR) 63 is always kept away from VR (R) 62 by a fixed sequence number value distance, which is expressed mathematically as follows. :

VR (MR) = VR (R) + Receive Window Size (1)

Since sequence number 52 is a 12-bit number, equation (1) is a true 12-bit addition, and thus may experience a rollover on overflow. In conclusion, VR (MR) 63 does not always contain numerically larger values than VR (R) 62. Similarly, transmission window 66 has a transmission window size state variable VT (WS) 66a indicating the number of sequence number values delimited by state variables VT (A) 67 and VT (MS) 68. The state variable VT (WS) 66a has an initial value set to the configured transmission window size supplied by layer 3. As above, this is represented mathematically as: :

VT (MS) = VT (A) + VT (WS) (2)

And again, the result from equation (2) may be subject to rollover by overflow. Receiver 64 may explicitly require transmitter 65 to change the value of VT (WS) 66a. However, the value of the required VT (WS) 66a cannot be larger than the transmission window size that was originally configured, i.e. the size indicated by layer 3 of the transmitter.

Since receiver 64 receives PDUs 50 from transmitter 65, receiver 64 will update the value of state variable VR (R) to reflect the sequential earliest sequence number 52 in which all preceding PDUs 50 were successfully received. In other words, VR (R) 62 always retains the sequence number 52 of the earliest PDU 50 in sequence that receiver 64 is waiting to receive. As soon as there is a successful reception of the PDU 50, the receiver 64 advances the state variable VR (R) 62 to the sequence number value 52 of the next PDU 50 that needs to be received, and the state variable VR (MR) 63 accordingly becomes Is updated using 1). In this way, receive window 61 is advanced by receiver 64 as PDUs 50 are streamed from transmitter 65. It should also be appreciated that transmitter 65 may explicitly require receiver 64 to advance the receive window 61 with a layer 2 signaling PDU. However, this is not related to the present invention.

Transmit window 66 is advanced when transmitter 65 receives a Layer 2 acknowledge status PDU from receiver 64. The Layer 2 grant status PDU holds the most recent value of state variable VR (R) 62 and is sent by receiver 64 at regular intervals or in response to an explicit request from transmitter 65. The acknowledgment status PDUs are known to be missing (because, for example, subsequent PDUs have already been received in sequence) and will eventually point to PDUs in the receive window 61 that must be retransmitted. Transmitter 65 will then set the state variable VT (A) 67 equal to the value held in the grant status PDU, which effectively sets VT (A) 67 equal to VR (R) 62. Transmitter 65 accordingly updates state variable VT (MS) 68 using equation (2). In this way, the transmit window 66 tends to lag just one bit behind the receive window 61, and the transmit window 66 and the receive window 61 move forward with each other in a lock step.

Transmitter 65 has an additional state variable VT (S) 69. Transmitter 65 begins transmitting PDUs 50 that lie within transmission window 66. Transmitter 65 starts with PDU 50 with sequence number 52 given by state variable VT (A) 67 and works forward sequentially until it reaches PDU 50 with sequence number 52 immediately preceding VT (MS) 68. . That is, transmitter 65 transmits PDUs 50 sequentially, starting at VT (A) and ending at VT (MS) -1. The state variable VT (S) 69 holds the sequence number 52 of the next PDU 50 to be transmitted. Thus, PDUs 50 having sequence numbers 52 on VT (A) 67 or sequentially after VT (A) 67 and on VT (S) -1 or before VT (S) -1 have been transmitted at least once, They are stored in retransmission buffer 66b until they are approved by receiver 64 via the grant status PDU. If PDU 50 with the same sequence number 52 as VT (A) 67 is approved, then VT (A) 67 is updated with the next sequentially earliest sequence number value in retransmission buffer 66b. PDUs 50 with sequence numbers above or after VT (S) 69 have not yet been sent by transmitter 65.

To ensure that transmission window 66 advances, transmitter 65 must sometimes require receiver 64 to send an acknowledgment status PDU. This is called polling and is implemented through polling bit 53. If transmitter 65 determines it is time to poll the receiver, transmitter 65 has the polling bit 53 set to 1 to the next outgoing PDU 50, i.e., PDU 50 indicated by status variable VT (S) 69, or retransmission buffer 66b. Will send the PDU 50. Upon receiving any PDU 50 with the set polling bit 53, receiver 64 responds by sending an acknowledgment status PDU. The acknowledge status PDU will contain the most recent value of state variable VR (R) 62 and transmitter 65 will use it sequentially for state variable VT (A) 67 to advance the transmission window 66. Various methods may be used by transmitter 65 to determine when to poll receiver 64. For example, transmitter 65 may use polling based on a timer. In timer based polling, polling is performed at regular, regular intervals. Alternatively, transmitter 65 may use window based polling, and transmitter 65 polls receiver 64 when a certain percentage of the transmission window 66 is transmitted in window based polling.

For window based polling, a polling function using VT (S) 69 is used to obtain the polling test value “t”. :

t = PollingFunction (VT (S)) (3)

The polling value is given, which is a simple percentage of the transmission window 66 sent at least once. For example, you can set the polling value to 60%, which indicates that polling should be performed if 60% or more of the transmission window 66 has been sent at least once. If "t" from Eq. (3) exceeds the polling value, polling is triggered. If polling is triggered because of "t", polling bit 53 is set for the next outgoing PDU 50. Since polling bit 53 is always transmitted no matter whether it is set or cleared, triggering polling by setting polling bit 53 does not constrain any propagation resources. However, responding to polling bit 53 via the grant status PDU constrains propagation resources. So the polling bit 53 should not be set to change easily.

However, for cases where VT (S) reaches a sufficiently advanced value for VT (A) 67 and so after polling is triggered, VT (A) 67 is not advanced, state variables VT (S) 69 and Since VT (WS) 66a does not change, any retransmitted PDU in retransmission buffer 66b will trigger a poll. Triggering of this kind of polling can lead to a degradation of the efficient use of propagation resources (with subsequent grant status PDUs in response to the set polling bit 53) and is therefore undesirable. In addition, the exact timing of the update of the state variable VT (S) 69 may be somewhat ambiguous. For some implementations, the VT (S) 69 is updated (ie increased) when the associated PDU 50 is configured. In other implementations, VT (S) 69 is not updated until the associated PDU 50 is sent or sent to the layer 1 interface. This can lead to difficulties in conformance testing.

It is therefore a primary object of the present invention to provide a method for determining triggering of a polling request in a wireless communication protocol for a transmitter that avoids unnecessary polls. And this is consistent across all implementations.

In brief summary, a preferred embodiment of the present invention discloses a method for determining triggering of a polling request in a wireless communication protocol for a transmitter. The transmitter may send protocol data units (PDUs). Each PDU has an n-bit sequence number. A polling determination method is provided for determining whether polling should be performed according to parameter S which is an n-bit sequence number. Polling is triggered if the next PDU to be transmitted is not a retransmitted PDU and the polling determination method indicates that polling should be triggered according to the sequence number of the PDU. The polling determination method uses the following equation to determine if polling should be triggered. t = ((2 ⁿ + 1 + S-VT (A)) mod 2 ⁿ ) / VT (WS) where S is the sequence number of the next exiting PDU.

Various objects of the present invention will no doubt become apparent to those skilled in the art after reading the following detailed description of the preferred embodiment illustrated in the various figures.

In the description that follows, the communication protocol disclosed in the 3GPP ^™ specification TS 25.322 is used as an example. However, it should be apparent to those skilled in the art that a wireless communication protocol requiring polling to acknowledge receipt of transmitted data may utilize the poll-triggering method of the present invention. It should further be appreciated that the transmitters and receivers in the detailed description that follow may include cellular telephones, personal data assistants (PDAs), personal computers (PCs), or other devices using a wireless communication protocol.

By using the following equation, it is the method of the present invention to determine the triggering of the polling request for the transmitter for only PDUs that are not retransmitted. :

t = {(2 ⁿ + 1 + S-VT (A)) mod 2 ⁿ } / VT (WS) (4)

Retransmitted PDUs may be sent with their associated polling bits 53 set to 1 by other polling triggers, such as the “last PDU in retransmission buffer” event. However, retransmitted PDUs do not trigger the polling operation according to the present invention. "S" in equation (4) is the sequence number of the PDU whose polling bit 53 is set or cleared based on "t". "n" is the bit-size of the sequence number "S". In a preferred embodiment, the sequence number "S" is a 12-bit value, so "n" is 12.

To better understand equation (4), see FIG. 5 is a simplified block diagram of a wireless communication system 70 using the method of the present invention. The wireless communication system 70 includes a receiver 80 and a transmitter 90. Both transmitter 90 and receiver 80 use a three-layer communication protocol. At transmitter 90, layer 3 interface 93 delivers layer 2 service data units (PDUs) 93a to layer 2 interface 92 for transmission. Layer 2 interface 92 writes SDUs 93a into Layer 2 protocol data units (PDUs) 92a that are delivered to layer 1 interface 91 for transmission. PDUs 92a have the same format as discussed in the description of the prior art, and therefore do not need to be detailed any more here. In particular, each PDU 92a has an n-bit sequence number 52 that identifies the contiguous order of PDU 92a in the stream of transmitted PDUs 92a. For the preferred embodiment, n is 12, so the sequence numbers for PDUs 92a have a recursive range from 0 to 4095. Each PDU 92a also has a polling bit 53 that can be set by transmitter 90 to poll the receiver 80. As discussed in the prior art, the receiver 80 responds to the polling bit 53 set with the grant status PDU for the transmitter 90 to advance its transmission window 94.

The transmission window 94 is defined by state variables VT (A) 95, VT (WS) 96 and VT (MS) 97. Transmitter 90 will only transmit PDUs 92a with sequence numbers 52 that are within transmission window 94. State variable VT (A) 95 indicates the start value of the transfer window 94. State variable VT (WS) 96 indicates the size of transmission window 94, which is simply the number of sequence number values 52 delimited by transmission window 94. The state variable VT (MS) 97 marks the end of the transfer window 94, so it is only the sum of VT (A) 95 and VT (WS) 96. Because of the overflow, the value held in VT (MS) 97 need not be greater than the value held in VT (A) 95. Finally, the state variable VT (S) 98 holds sequence number 52 of the next PDU 92a in the line to be transmitted. VT (S) 98 will always be sequentially after VT (A) 95 or after VT (A) and sequentially before VT (MS) 97 or before VT (MS). The state variables VT (A) 95, VT (WS) 96, VT (MS) 97 and VT (S) 98 are functionally the same as discussed in the description of the prior art.

The transmitter 90 also includes a calculating unit 99 used to calculate the test value t 99a. The value of t 99a is compared against the polling value 93b supplied by layer 3 interface 93 to determine whether transmitter 90 will poll receiver 80. If polling should be performed, polling bit 53 is set in PDU 98p, which is generated and transmitted sequentially. The test value t 99a is used for window based polling, and the calculation unit generates the state variable VT (A) 95, VT (WS) 96, sequence number S 98s, held in PDU 98p, to generate a value for t 99a. And equation (4). Polling value 93b indicates the transmission percentage of transmission window 94. That is, polling value 93b indicates the percentage of PDUs 92a in transmission window 94 sent by transmitter 90. If the value of t 99a exceeds or equals the polling value 93b, the polling request is triggered by setting polling bit 53 of PDU 98p to one. That is as follows. :

1) If PDU 98p is a retransmitted PDU 92a, the polling bit 53 for PDU 98p is not required to be set to 1 by the present invention. If PDU 98p is being transmitted for the first time, polling bit 53 is set according to test value t 99a and polling value 93b.

2) If required, the test value t 99a is generated using equation (4) above. The parameters of equation (4) are obtained from state variables VT (A) 95, VT (WS) 96, sequence number S 98s of PDU 98p under consideration, and bit size n of sequence number S 98s.

3) If test value t 99a is equal to or exceeds polling value 93b and PDU 98p is not a retransmitted PDU 92a, polling bit 53 for PDU 98p will be set to 1 to trigger polling.

See FIG. 6 with reference to FIG. 5. 6 is a flowchart of the method of the present invention, which is implemented by calculation unit 99 to determine if polling should be triggered by transmitter 90. The steps are described below. :

100: Obtain PDU 98p, where polling bit 53 is set or cleared.

110: If the PDU 98p obtained in step 100 is a retransmitted PDU 98p, go to step 180. Otherwise, go to Step 120.

120: Obtain current values for transmission window 94, current values for transmission window 94 include values from state variables VT (A) 95 and VT (WS) 96, and additionally, PDU 98p obtained from step 100. Extract sequence number S 98s from.

130: The first value x is calculated. The value x is the difference between the sequence number S 98s and the state variable VT (A) 95 plus (2 ⁿ + 1). The n value is the bit size of the sequence number S 98s, so 12 in the preferred embodiment. In conclusion, 4097 is added to (S-VT (A)).

140: The second value y is calculated. The value of y is a modulus of the first value x and 2 ⁿ . So the second value y is x mod 4096.

150: The test value t 99a is obtained by dividing the second value y by the state variable VT (WS) 96. Test value t 99a indicates the current transmission percentage of transmission window 94 in fractional form for PDU 98p.

160: Compare the test value t 99a with the polling value 93b. Since the polling value is stored as a percentage in the form of 0 to 100, the value of t 99a is multiplied by 100 to perform the comparison.

170: If the transmission percentage is greater than or equal to the polling value 93b as indicated by t 99a, polling is triggered for transmitter 90. Polling bit 53 for PDU 98p is set to one.

180: If the transmission percentage is less than the polling value 93b as indicated by t 99a or if PDU 98p is a retransmitted PDU 98p, no polling is required.

190: End of polling method. For the next PDU 98p, the process is repeated from step 100.

In contrast to the prior art, the present invention uses a calculation unit to calculate the test value t according to the following equation. :

t = {(2 ⁿ + 1 + S-VT (A)) mod 2 ⁿ } / VT (WS)

The formula accurately calculates the transmission percentage of the transmitter's transmission window for the PDU under consideration. So the transmitter will trigger the polling request correctly. However, if the PDU under consideration in the above equations is not a retransmitted PDU, polling will only be performed. Polling is not triggered with retransmitted PDUs. In this way, unnecessary use of propagation resources is avoided. This ensures a more efficient wireless transmission system. By using the actual sequence number S 98s inserted into the PDU 98p rather than the current value of the state variable VT (S) 98, implementation ambiguities of the value of VT (S) 98 are avoided. Conformance testing is made easier as a result.

It is an advantage of the present invention that the test value returns exactly the percentage of the transmitted window sent and causes the polling bit of the PDU to be set correctly regardless of how the VT (S) varies from implementation to implementation. In addition, by ensuring that the polling bit is set only for the first transmitted PDUs, unnecessary polling and response procedures are eliminated. This ensures more efficient use of propagation resources.

Those skilled in the art will readily appreciate that numerous modifications and variations of the device may be made while retaining the teachings of the present invention. Accordingly, the above disclosure should be treated as limited only by the scope and scope of the appended claims.

1 is a block diagram of a three-layer communication protocol,

2 is a simplified diagram of a transmit / receive process from a layer 2 perspective,

3 is a block diagram of an acknowledged mode data (AMD) protocol data unit (PDU),

4 is a simplified block diagram of a receiver and a transmitter in a wireless communication system,

5 is a simplified block diagram of a wireless communication system in accordance with the present invention, and

6 is a flowchart of the method of the present invention.

* Explanation of symbols for main parts of the drawing

PDU: 50

Polling bit: 53

Receiver: 80

Transmitter: 90

Claims (4)

A method of determining triggering of a polling request in a wireless communication protocol for a transmitter, wherein the transmitter can send protocol data units (PDUs), each PDU comprising an n-bit sequence number. In the above method of determining, Providing a polling determination method for determining whether polling should be performed; And If the PDU to be transmitted is not a retransmitted PDU, and the polling determination method indicates that polling should be triggered, causing the polling to be triggered. According to claim 1, The polling determination method, Providing a polling value that must be exceeded for polling to be triggered; Obtaining a base sequence number VT (A), wherein the base sequence number VT (A) indicates a base sequence number VT (A) indicating a starting sequence number of a transmission window of the transmitter; Obtaining a first value obtained by adding (2 ⁿ + 1) to the difference between the parameter S and the base sequence number VT (A); Obtaining a second value that is modulus by 2 ⁿ of the first value; And Obtaining a test value obtained by dividing the second value by the size of the transmission window; If the test value is greater than the polling value, polling is triggered and the parameter S is the n-bit sequence number of the PDU to be transmitted. The method of claim 2, If the test value is equal to the polling value, polling is triggered. The method of claim 2, Wherein the polling value indicates a percentage of PDUs in the transmission window sent by the transmitter.