CN100407698C - Data transmission method of radio link control layer - Google Patents

Abstract

The invention discloses a data transmission method of a wireless link control layer, comprising the following steps: A. the wireless link control layer receives the service data unit sent by the upper layer of the local end; B. the wireless link control layer judges the received service Whether the data unit bears the confirmation information TCP ACK; C. The radio link control layer preferentially sends the protocol data unit corresponding to the service data unit bearing the confirmation information TCP ACK. The invention provides an RLC data transmission scheme on the basis of not changing the receiving end and sending TCP parameters. In this scheme, when there are both TCP ACK and data segment information or other control information packets to be sent in the RLC sending buffer, the TCP ACK is sent first, so that when the uplink and downlink transmission channels transmit data at the same time, the TCP transmission rate of the uplink and downlink transmission channels Both are close to the transmission rate of single uplink or single downlink data transmission, and reduce the TCP loopback delay and improve the end-to-end QoS performance.

Description

Data transmission method of radio link control layer

technical field

The invention relates to a data transmission method in the field of wireless communication, in particular to a data transmission method of a wireless link control layer.

Background technique

With the development of communication technology, especially the development of third-generation mobile communication technology, data services have become one of the important services of mobile communication systems. Among them, the wireless data service provides end users with a seamless connection to the Internet network, allowing end users to obtain more convenient Internet information through the wireless system.

Since the existing Internet network mainly uses TCP (Transmit Control Protocol, Transmission Control Protocol)/IP (Internet Protocol, Internet Protocol) to carry out networking and complete data transmission, therefore, the use of wireless data services provides end users with access to the Internet When connecting seamlessly with the Internet, the TCP/IP protocol is also required to realize data transmission. Through simulation and testing, it is shown that TCP-based data transmission is performed simultaneously in the uplink and downlink. For example, when FTP (File Transfer Protocol, file transfer protocol) uploads and downloads files at the same time, if a TCP ACK sent by the upper When there are multiple TCP data segments waiting to be sent, the sending of the TCP ACK is delayed. Whether the transmission rate of uplink or downlink transmission data is close to the transmission rate of single uplink or single downlink data transmission, is related to the TCP receiving buffer size (TcpRxBufferSize, also known as TCP receiving window size) and UE (User Equipment, user equipment) on the network side If the TcpRxBufferSize at both ends is improperly set or the ratio is improper, it may cause congestion on the transmission link. The specific performance is that the transmission rate in one direction is relatively normal while the transmission rate in the other direction is very low or The transfer rate drops in both directions.

In the prior art, congestion control methods mainly include: slow start, congestion avoidance and fast retransmission. The implementation method of the slow start is as follows: Firstly, two parameters are added to each TCP connection state. Congestion window (cwnd) and slow start threshold (ssthresh), the congestion window is the above TCP receiving window. Wherein, the congestion window is a TCP state parameter, represents the maximum amount of data that a TCP allows to send, and is a sending threshold of the maximum amount of data that can be transmitted to the network before the sender receives an acknowledgment (TCPACK); the congestion window includes this Peer congestion window and peer congestion window. The slow start threshold (ssthresh) is used to select whether to use slow start or congestion avoidance algorithm to control data transmission. For example, the TCP sending end starts a congestion window (cwnd) with a length of 1, which is the congestion window of the opposite end. For each TCP ACK received, the TCP sending end increases the size of the congestion window of the opposite end exponentially until equal to Slow start threshold (ssthresh). Then enter the congestion avoidance stage, continue to linearly increase its peer congestion window cwnd, so that the amount of data sent increases linearly, and every time a TCP ACK is received, a new segment is sent to reach a steady state (slow start duration very short and can be considered transient). Then, TCP continues to measure the round-trip delay RTT (Round Trip Time, round-trip time), which is used to calculate the time required for round-trip communication between the sender and the receiver, that is, after sending a data packet, to the receiver The time it took to get a TCP ACK message for this packet.

By comparing the measured loopback delay with the set loopback delay, determine whether the packet is lost. When a packet loss is detected, TCP activates the fast retransmission algorithm, which assumes that the lost packet starts with a duplicate ACK sequence number, and forwards it. At the same time, TCP sets ssthresh to half of the existing window to reduce the amount of data; or resets the size of its congestion window to 1. Therefore, using the active slow-start algorithm can limit the rate at which the congestion window becomes to the previous level.

However, this method needs to modify the TCP parameters (change the size of the TCP receiving window). In actual wireless network applications, the hosts of each service node on the Internet are uncontrollable. On the other hand, in a real commercial system, another An IP terminal is a mobile phone, so it is unrealistic for ordinary users to modify TCP parameters.

There is another solution in the prior art. In a wireless communication system, according to the protocol specification of 3GPP, the wireless interface protocol layer is divided into three layers. The lowest layer is the physical layer, and the protocol layers above the physical layer (L1) are called the data link layer (L2) and the network layer (L3). In the UTRA FDD radio interface, the data link layer is divided into several sublayers. On the control plane, the data link layer (L2) consists of two sublayers - MAC (Medium Access Control, Media Access Control) and RLC (Radio Link Control, Radio Link Control); on the user plane, remove MAC and RLC In addition, there are two protocols related to specific services: PDCP (Packet Data Convergence Protocol, Packet Data Convergence Protocol) and BMC (Broadcast/Multicast Control Protocol).

In the implementation of PDCP layer, the processing of dividing the priority of data is added, and then data packets of different priorities are mapped to logical channels of different priorities in the RLC layer, and MAC prioritizes scheduling of high-priority logical channels, so that control data Packets with high priority can be sent from the air interface to the peer in time. However, since the PDCP parses the TCP/IP packet and breaks the interlayer structure, the implementation is relatively complicated and may affect the processing of header compression.

Contents of the invention

The problem solved by the present invention is to provide a data transmission method of the wireless link control layer, to solve the need in the prior art by modifying the TCP parameters or parsing the TCP/IP packets in PDCP, breaking the interlayer structure, to realize the improvement of TCP Defects in transmission performance.

In order to solve the above problems, the present invention discloses a data transmission method of a radio link control layer, the method comprising the following steps:

A. The radio link control layer receives the service data unit sent by the upper layer of the local end;

B. The radio link control layer compares the size of the received service data unit with a set parameter, and judges whether the received service data unit carries confirmation information TCPACK according to the comparison result;

C. The radio link control layer preferentially sends the protocol data unit corresponding to the service data unit carrying the acknowledgment information TCP ACK.

Including between steps B and C, storing the service data unit carrying the confirmation information TCP ACK into the first queue, and storing the service data unit carrying the data segment information into the second queue, and the first queue has more transmission capacity than the second queue. priority.

The first queue with sending priority sends the stored information according to the principle of first in first out.

The radio link control layer is the radio link control layer of the sending end or the radio link control layer of the receiving end.

The sending end is a network side device, a server or a user equipment.

The receiving end is a network side device, a server or a user equipment.

The upper layer is the network layer or the transport layer.

The confirmation information TCP ACK is sent after the local end receives a data segment information sent by the opposite end.

Compared with the prior art, the present invention has the following advantages:

The invention provides an RLC data transmission scheme from the perspective of changing the RLC data transmission mechanism without changing the receiving end and sending TCP parameters. In this scheme, when there are both TCP ACK (TCP acknowledgment information) and data segment information or other control information packets to be sent in the RLC sending buffer, the TCP ACK is sent first, so that when the uplink and downlink transmission channels perform data transmission at the same time, the uplink and downlink transmission The TCP transmission rate of the channel is close to the transmission rate of single uplink or single downlink data transmission, and reduces the TCP loopback delay and improves the end-to-end QoS (Quality of Service, quality of service) performance.

Description of drawings

Fig. 1 is the flow chart of the basic principle of the data transmission method of the wireless link control layer of the present invention;

FIG. 2 is a structural diagram of the application of the data transmission method of the wireless link control layer in the wireless communication system according to the present invention.

Detailed ways

Basic principle of the present invention is as shown in Figure 1, comprises:

Step s101, the radio link control layer receives the service data unit sent by the upper layer of the local end;

Step s102, the radio link control layer judges whether the received service data unit carries confirmation information TCPACK;

Step s103, the radio link control layer preferentially sends the protocol data unit corresponding to the service data unit carrying the acknowledgment information TCP ACK.

The present invention reduces the loopback delay by reducing the TCP ACK transmission delay, so that the data transmission rate is increased and the congestion time is reduced. Since the TCP loopback delay is composed of two parts: the transmission delay of the data segment and the transmission delay of the corresponding TCP ACK. The transmission delay of the data segment is related to the TcpRxBufferSize of the opposite end. The larger the TcpRxBufferSize, the more the segments to be sent stay in the local RLC sending queue, and the greater the transmission delay of the data segment; and the corresponding TCP The transmission delay of the ACK is related to the TcpRxBufferSize of the local end. In the case of simultaneous data transmission in the uplink and downlink, because at this time the peer RLC layer also has several SDUs carrying TCP datagrams waiting to be sent, therefore, the larger the TcpRxBufferSize of the local end, the TCP ACK The longer the stay in the RLC layer at the opposite end, the greater the transmission delay of TCP ACK. Since the TCP performance is determined by the data transmission delay and the TCP ACK transmission delay of the data confirmation information, reducing the TCP ACK transmission delay can reduce the loopback delay, increase the data transmission rate, and achieve the purpose of optimizing TCP performance.

The wireless communication system structure that the present invention is applied is as shown in Figure 2, comprises receiving terminal (UE side or network side) 201, transmitting terminal (network side or UE side) 202, and transmitting terminal comprises physical layer 205, wireless link layer 204 and the upper layer 203 (the upper layer includes: the network layer, the transport layer, etc.), the receiving end includes the physical layer 208, the wireless link layer 207 and the upper layer 206 (the upper layer includes: the network layer, the transport layer, etc.). The RLC204 (Radio Link Control, radio link control layer) at the sending end receives the SDU (Service Data Unit, service data unit) sent by the upper layer 203, puts the SDU into the sending queue, and the RLC204 only passes through the physical layer 205 successively according to the arrival time of the SDU. To send the corresponding PDU (Protocol Data Unit, protocol data unit) of SDU to the physical layer 208 of the receiving end, the opposite end RLC202 sends the SDU to the upper layer 206, and after the upper layer 206 receives the SDU, sends the TCP ACK information to the sending end in the same way, indicating Data message has been received.

Concrete realization scheme of the present invention is:

First, RLC classifies the SDUs sent by the upper layer. According to the TCP/IP protocol, the size of the message packet carrying the TCP ACK is fixed at 40Byte. Therefore, if the PDCP does not enable the header compression algorithm, the TCP ACK message packet is 40Byte when it reaches the RLC; if the PDCP enables the header compression algorithm, the TCPACK message packet reaches the RLC. is also a fixed value. The header compression algorithm is a method used by PDCP to improve channel utilization. Each PDCP entity uses one or more header compression algorithms, or no header compression algorithm. Several PDCP entities may use the same header compression algorithm. The type and parameters of the algorithm are negotiated by RRC and indicated to PDCP through PDCP Control Service Access Point (PDCP-SAP). Therefore, we can set a parameter TcpAckRefSize, and RLC can identify whether it is an SDU carrying TCP ACK by comparing whether the SDU size is equal to this parameter.

Then, the TCP ACK of the upper layer is preferentially sent downward at the SLC, because what is encapsulated in the SDU sent by the upper layer may be a TCP data segment or a TCP control message (receipt confirmation information), and the key point of the present invention is to transmit as soon as possible TCP receives acknowledgment information. Therefore, RLC treats arriving SDUs differently, and sends upper-layer TCP ACKs first, reducing the transmission delay of TCP ACKs.

The specific way to realize the priority sending of upper-layer TCP ACKs is as follows: logically, divide the RLC sending queue into two, put the SDUs carrying TCP ACKs into one sending queue A separately, and put the SDUs carrying data information or other control information into into another queue B. Every time RLC sends a new AMD PDU, it will give priority to sending the data PDU in queue A (when there are multiple data units to be sent in queue A, first-in-first-out, first-in-last-out or preset sending principles can be used, etc.) . In this way, the delay of TCP ACK in the RLC layer is very small. In this case, the TCP RTT on the UE side and the Server (or network) side is basically not affected by the local TcpRxBufferSize. Therefore, like unidirectional data transmission, it avoids the interaction between uplink and downlink and improves TCP performance. . Because the purpose of the present invention is exactly in order to transmit the TCP ACK data segment as soon as possible, as long as a simple comparison with the prior art, the advantages of the present invention can be embodied.

For example, there are already 1, 2, 3, 4, 5, 6, and 7 pieces of data segment information to be sent in the sending buffer of the prior art solution, and since the sending buffer is scheduled according to the order of first-in-first-out, therefore If two TCP ACK data of 8 and 9 arrive, 8 and 9 need to wait for 1 to 7 pieces of information to be sent to be sent before proceeding. Assuming that each data transmission takes Td time, then, 8 and 9 TCP ACK data needs to wait for an additional 7*Td time, resulting in a time delay. If the technology of the present invention is adopted, the data segment information to be sent and the TCP ACK information area are stored in different sending buffers respectively, when the TCP ACK data of 8 and 9 arrive, they will be placed into the A sending buffer, and Data segment information or other control information is placed in the B sending buffer. And the priority of sending buffer A is higher than that of sending buffer B, that is, as long as there is data in sending buffer A, the data in A is sent, and when there is no data in A, the data in B is sent. Therefore, the data in the sending buffer of A can be sent out quickly, without waiting for the time of 7*Td as in the original technology.

In addition, when uploading or downloading independently, the TCP performance is not affected by this solution. In addition, when the upper layer adopts non-TCP bearer, such as UDP (User Datagram Protocol, User Datagram Protocol), the data transmission performance is not affected by the solution of the present invention.

The above is only a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications should also be It is regarded as the protection scope of the present invention.

Claims (8)

1. the data transmission method of a wireless chain control layer is characterized in that, may further comprise the steps:

A, wireless chain control layer receive the service data unit that the local terminal upper strata sends;

B, described wireless chain control layer compare the size of the service data unit of described reception and the parameter of setting, and judge according to comparative result whether the service data unit of described reception carries confirmation TCPACK;

C, the preferential service data unit corresponding protocols data cell that sends described carrying confirmation TCP ACK of described wireless chain control layer.

2. the data transmission method of wireless chain control layer according to claim 1, it is characterized in that, comprise between step B and the C, deposit the service data unit of carrying confirmation TCPACK in first formation, deposit the service data unit of carrying data segment information in second formation, second formation of described first platoon ratio has the transmission priority.

3. as the data transmission method of wireless chain control layer as described in the claim 2, it is characterized in that described have first formation that sends priority and send the information of depositing according to first in first out.

4. the data transmission method of wireless chain control layer according to claim 1 is characterized in that described wireless chain control layer is transmitting terminal wireless chain control layer or receiving terminal wireless chain control layer.

5. as the data transmission method of wireless chain control layer as described in the claim 4, it is characterized in that described transmitting terminal is network equipment, server or subscriber equipment.

6. as the data transmission method of wireless chain control layer as described in the claim 4, it is characterized in that described receiving terminal is network equipment, server or subscriber equipment.

7. the data transmission method of wireless chain control layer according to claim 1 is characterized in that described upper strata is network layer or transport layer.

8. the data transmission method of wireless chain control layer according to claim 1 is characterized in that, described confirmation TCP ACK sends after local terminal receives the data segment information that an opposite end sends.

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