CN109769268B

CN109769268B - Frame aggregation algorithm

Info

Publication number: CN109769268B
Application number: CN201910208112.9A
Authority: CN
Inventors: 杨永鹏
Original assignee: Nanjing Vocational College Of Information Technology
Current assignee: Nanjing Vocational College Of Information Technology
Priority date: 2019-03-19
Filing date: 2019-03-19
Publication date: 2022-05-31
Anticipated expiration: 2039-03-19
Also published as: CN109769268A

Abstract

The invention discloses a frame aggregation algorithm in the field of network communication, which aims to improve the transmission rate of a wireless local area network and comprises the following steps: carrying out AMSDU polymerization on the received MSDU frame, and ending the AMSDU polymerization when reaching the maximum polymerizable AMSDU length to generate an AMSDU frame; carrying out AMPDU polymerization on the AMSDU frame, and ending the AMPDU polymerization when the maximum length of the AMPDU polymerizable calculated according to the maximum bandwidth is reached to generate an AMPDU frame; dividing the AMPDU frame into a plurality of sub AMPDU frames, and transmitting the sub AMPDU frames according to the current bandwidth; wherein the length of the sub-AMPDU frame is the maximum polymerizable length of the AMPDU calculated according to the current bandwidth. The algorithm can improve the throughput rate of data frame sending, and can reduce the packet loss rate under the condition of bandwidth reduction and increase the robustness of data sending.

Description

Frame aggregation algorithm

Technical Field

The invention relates to a frame aggregation algorithm, and belongs to the technical field of wireless network communication.

Background

With the rapid development of wireless network technology, the requirements on the performance of wireless network devices are higher and higher, in order to improve the performance of wireless network devices, the IEEE 802.11 standard has been subjected to standards such as IEEE 802.11A, B, G, N, AC, and with the continuous modification of the standards, many new PHY functions are continuously introduced to improve the performance of wireless network devices, but with the continuous increase of the data rate of PHY layers, the increase of the throughput rate has become unobvious, which is caused by the frame interval of the MAC layer and the overhead caused by the preamble, and if the wireless network devices need to obtain further improvement of the throughput rate, the efficiency of the MAC layer must be improved, so that from the IEEE 802.11N protocol standard, an aggregation mechanism of AMSDU and AMPDU is introduced.

The IEEE 802.11AC standard does not specify how to design the aggregation mechanism of AMSDU and AMPDU, and a new aggregation algorithm is proposed herein mainly for AMSDU and AMPDU in the IEEE 802.11AC protocol standard, which specifies a length calculation method for AMSDU aggregation based on dynamic rate selection, specifies processing under the condition of bandwidth reduction due to environmental factors, and proposes a complete frame aggregation implementation algorithm. Experimental results show that the mechanism can improve the throughput rate of data by improving the efficiency of an MAC layer, and can ensure the correctness and the robustness of the data under the condition of reducing bandwidth.

Disclosure of Invention

The invention aims to provide a frame aggregation algorithm to solve the problem that the data throughput rate of wireless network equipment is not high in the prior art; the AMSDU frame aggregation efficiency is low; and in the case of bandwidth reduction, the data transmission has the defects of low correctness and robustness.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows: a frame aggregation algorithm comprising the steps of: carrying out AMSDU polymerization on the received MSDU frame, and finishing AMSDU polymerization when reaching maximum polymerizable AMSDU length to generate an AMSDU frame; carrying out AMPDU polymerization on the AMSDU frame, and ending the AMPDU polymerization when the maximum length of the AMPDU polymerizable calculated according to the maximum bandwidth is reached to generate an AMPDU frame; dividing the AMPDU frame into a plurality of sub AMPDU frames, and transmitting the sub AMPDU frames according to the current bandwidth; wherein the length of the sub-AMPDU frame is the maximum polymerizable length of the AMPDU calculated according to the current bandwidth.

The method for polymerizing AMSDU comprises the following steps: if the AMSDU frame which is being aggregated exists at the current moment, aggregating the received MSDU frame at the last position of the AMSDU frame; and if the AMSDU frame is not aggregated at the current time, aggregating the received MSDU frame at the first position of the AMSDU frame.

And calculating the maximum polymerizable length of AMSDU by adopting a self-adaptive dynamic rate feedback algorithm, wherein the calculation formula is as follows:

wherein l_amsduMaximum length can be aggregated for AMSDU, and MCS is modulation coding scheme, i.e. rate selected for frame transmission, N_ssFor the number of spatial streams, i.e. the number of spatial streams selected for frame transmission, 1550bytes is the maximum transmission unit of the ethernet.

Before carrying out the AMPDU aggregation, the following judgment is carried out: if (T) is satisfied_i-T_i-1)＜T_durationCarrying out AMPDU polymerization; otherwise, not carrying out AMPDU aggregation; wherein: t is a unit of_iFor the time of starting aggregation of the ith AMSDU frame, T_i-1For the time of starting aggregation of the i-1 st AMSDU frame, T_durationIs a preset standard time difference of polymerization.

Polymerization standard time difference T_durationNot more than 500 milliseconds.

The maximum polymerizable length of the AMPDU is obtained by calculation according to the following formula:

l_ampdu＝f(BW,GI,NSS)*TXOP

wherein l_ampduMaximum length can be aggregated for AMPDUs, TXOP is bounded time period for a particular communication class, f (BW, GI, NSS) is PHY layer rate of IEEE 802.11AC standard calculated by BW, GI, NSS; BW is bandwidth, GI is guard interval, NSS is number of spatial streams.

When AMPDU polymerization is carried out, the method also comprises the following steps: and marking the AMPDU frame according to the maximum polymerizable length of the AMPDU corresponding to different bandwidths, and splitting the AMPDU frame according to the mark to obtain sub AMPDU frames under the corresponding bandwidths.

The rules for AMSDU aggregation include: the sending end, the receiving end and the service category are the same.

Compared with the prior art, the invention has the following beneficial effects:

(1) the frame aggregation algorithm can improve the throughput rate of data by improving the efficiency of an MAC layer;

(2) the frame aggregation algorithm can ensure the correctness and the robustness of data under the condition of reducing bandwidth;

(3) the frame aggregation algorithm can improve the data transmission rate of the wireless local area network.

Drawings

Fig. 1 is a flowchart of an AMSDU aggregation algorithm according to an embodiment of the present invention;

fig. 2 is a flowchart of a frame aggregation algorithm suitable for wireless network data transmission according to an embodiment of the present invention.

Detailed Description

The invention is further described below with reference to the accompanying drawings. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present invention is not limited thereby.

As shown in fig. 1 and fig. 2, a frame aggregation algorithm includes the following steps: and carrying out AMSDU aggregation on the received MSDU frame according to whether the transmitting end, the receiving end and the service class are the same or not, wherein the aggregation length is determined by the rate selected by the dynamic rate selection.

In the algorithm of AMSDU aggregation, two cases are handled. One case is that there is currently an AMSDU frame being aggregated, and in this case, an MSDU frame newly delivered by a protocol stack needs to be aggregated at the tail of the AMSDU frame; another situation is that there is no currently aggregated AMSDU frame, in which case a new AMSDU frame needs to be created and the MSDU frame newly delivered by the protocol stack is placed in the first position of the AMSDU. The end condition for both cases is to reach the maximum length that AMSDUs can be aggregated. The theoretical basis is that under the condition of selecting a larger sending rate, the data throughput rate is larger, and the capability of the length capable of supporting the aggregation of the AMSDUs is correspondingly improved, so that the maximum length capable of being aggregated by the AMSDUs is strongly related to the sending rate of the data, and the data throughput rate can be improved by improving the efficiency of an MAC layer. The maximum length that can be aggregated by the AMSDU obtained in this embodiment is calculated based on the Rate selected by the dynamic Rate selection algorithm, where the dynamic Rate selection algorithm selected in this embodiment is an Adaptive Auto Rate Feedback (AARF [11,12]) algorithm. The maximum length that AMSDU can aggregate is calculated as follows:

wherein l_amsduIs the maximum length that the AMSDU can be aggregated; the MCS is a Modulation and Coding Scheme (MCS), i.e., a rate selected by frame transmission; n is a radical of_ssThe Number of Spatial Streams (NSS), i.e., the number of spatial streams selected for frame transmission; 1550bytes is the MTU value of Ethernet, i.e. the maximum transmission unit.

And after the AMSDU frame aggregation is completed, carrying out AMPDU aggregation. In order to guarantee the integrity of the AMPDU data frames, it is necessary to ensure that the AMPDU frames cannot be transmitted before the aggregation is not finished. In this case, if the time interval between the transmitted frames is long, it is inevitable to waste the channel bandwidth due to waiting for aggregation. For the problem, the present embodiment introduces a frame aggregation timer, that is, when the two frame transmission time intervals satisfy a certain time difference, the two frames are aggregated; otherwise, no polymerization is performed. The method comprises the following specific steps:

a. the ith AMSDU frame enters an AMPDU aggregation module, and the current time T is recorded_i；

b. If (T)_i-T_i-1)＜T_durationIf the time difference condition of the two frames of aggregation is met, the two frames of aggregation can be aggregated; otherwise, not satisfied and not polymerized;

wherein, T_iThe time for the ith frame AMSDU to enter an AMPDU aggregation module; t is_i-1The time for the i-1 th frame AMSDU to enter the AMPDU aggregation module; t is a unit of_durationTo meet the time difference criterion for the polymerization, 500 milliseconds is used in this example.

The length of the AMPDU aggregation frame is calculated from the Number of Spatial Streams (NSS), Bandwidth (BW), Guard Interval (GI), and bounded time period (TXOP) of a specific communication class. The calculation formula is as follows:

l_ampdu＝f(BW,GI,NSS)*TXOP

wherein l_ampduFor the maximum length of AMPDU aggregation, TXOP is the bounded time period of a particular traffic class, and f (BW, GI, NSS) is the PHY layer rate of IEEE 802.11AC standard, i.e. port physical layer rate, calculated from BW, GI, NSS.

The AMPDU enters a data sending stage after the aggregation is finished, if the bandwidth is reduced in the sending process due to the instability of a wireless network environment, for example, the bandwidth is reduced to 80M or even 20M from the original 160M bandwidth, and in this case, packet loss occurs when data is sent continuously according to the calculated maximum length. The basic steps of the algorithm are as follows:

a. calculating the rates under the bandwidths of 20M,40M,80M and 160M according to the formula of f (BW, GI, NSS), and storing the rates by using a one-dimensional array;

b. when the AMPDU is aggregated, the AMPDU is aggregated according to the length calculated by the maximum bandwidth, and the frames with the lengths corresponding to the 20M,40M,80M and 160M bandwidths are marked in a unified way;

c. when the system has bandwidth reduction, recording the current bandwidth, splitting the AMPDU aggregated according to the maximum bandwidth into sub AMPDU blocks with the length corresponding to the current used bandwidth, and retransmitting data.

Dividing the AMPDU frame into a plurality of sub AMPDU frames, and transmitting the sub AMPDU frames according to the current bandwidth; wherein the length of the sub-AMPDU frame is the maximum polymerizable length of the AMPDU calculated according to the current bandwidth. The data correctness and robustness are ensured, and the data transmission rate of the wireless local area network is further improved.

The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, it is possible to make various improvements and modifications without departing from the technical principle of the present invention, and those improvements and modifications should be considered as the protection scope of the present invention.

Claims

1. A method of frame aggregation, the method comprising the steps of:

carrying out AMSDU polymerization on the received MSDU frame, and finishing AMSDU polymerization when reaching maximum polymerizable AMSDU length to generate an AMSDU frame;

carrying out AMPDU polymerization on the AMSDU frame, and ending the AMPDU polymerization when the maximum length of the AMPDU polymerizable calculated according to the maximum bandwidth is reached to generate an AMPDU frame;

dividing the AMPDU frame into a plurality of sub AMPDU frames, and transmitting the sub AMPDU frames according to the current bandwidth;

wherein the length of the AMPDU frame is the maximum polymerizable length of the AMPDU calculated according to the current bandwidth;

wherein l_amsduFor maximum length aggregation of AMSDUs, MCS is modulation coding scheme, i.e. frameSending the selected rate, N_SS1550bytes, which is the maximum transmission unit of the ethernet, is the number of spatial streams, i.e., the number of spatial streams selected for frame transmission;

l_ampdu＝f(BW,GI,N_SS)*TXOP

wherein l_ampduMaximum length can be aggregated for AMPDUs, TXOP is a bounded period of time for a particular communication class, f (BW, GI, N)_SS) Is prepared from BW, GI, N_SSThe calculated PHY layer rate of the IEEE 802.11AC standard; BW is bandwidth, GI is guard interval, N_SSIs the number of spatial streams;

the method also comprises the following judgment before carrying out AMPDU aggregation:

if (T) is satisfied_i-T_i-1)＜T_durationCarrying out AMPDU polymerization; otherwise, the AMPDU polymerization is not carried out; wherein: t is_iFor the time of starting aggregation of the ith AMSDU frame, T_i-1For the time of starting aggregation of the i-1 st AMSDU frame, T_durationIs a preset standard time difference of polymerization.

2. The frame aggregation method according to claim 1, wherein the method for aggregating AMSDUs comprises:

if the AMSDU frame which is being aggregated exists at the current moment, aggregating the received MSDU frame at the last position of the AMSDU frame;

and if the AMSDU frame which is being aggregated does not exist at the current time, aggregating the received MSDU frame at the first position of the AMSDU frame.

3. Frame aggregation method in accordance with claim 1, characterized in that the standard time difference T is aggregated_durationNot more than 500 milliseconds.

4. The frame aggregation method according to claim 1, wherein the AMPDU aggregation is performed, and further includes:

and marking the AMPDU frame according to the polymerizable maximum length of the AMPDU corresponding to different bandwidths, and splitting the AMPDU frame according to the marking so as to obtain the sub-AMPDU frame under the corresponding bandwidth.

5. The frame aggregation method according to claim 1, wherein the rule for AMSDU aggregation comprises: the sending end, the receiving end and the service category are the same.