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What are control frames and data frames? To solve this problem, today the editor summarizes this article about control frames and data frames, hoping to help more friends who want to solve this problem to find a more simple and easy way.

In the 802.11 frame format, the first two bytes are Frame Control fields, and the first two bits are the protocol version. Because there is currently only one version of the 802.11 protocol suite, these two bits have always been 00, the next two bits are frame type, and there are currently three values: 00 for the management frame, 01 for the control frame, and 10 for the data frame. The management frame is introduced above, and the control frame and data frame are introduced here.

The control frame contains only header information and is transmitted at the lowest base rate to ensure that devices in each network are more adequate to receive the control frame. It has the functions of clearing channel, requesting channel, confirming unicast frame, assisting data frame and managing frame transmission.

Data frames are mainly used for data transmission. Most data frames carry data payloads from layers 3-7, and the data payloads are often encrypted. Some specific data frames that do not contain upper layer data are used for special media access control.

Let's first talk about the subtypes of control frames:

0000-0110 Reserved

Reserved field, which has not been assigned to use

0111 Control wrapper

Introduced in 802.11n to carry other control frames (excluding Control Wrapper frames) and some HT control domains.

1000 Block ack request (BlockAckReq)

802.11e introduces BA mechanism to aggregate multiple acknowledgment frames into one acknowledgment frame, which improves the channel transmission efficiency.

1001 Block ack (BlockAck)

The reply frame of a BAR frame is an aggregate reply to a plurality of unicast frames.

1010 PS-Poll

For power saving mode

1011 RTS

1100 CTS

RTS/CTS is an enhancement to the virtual carrier mechanism. Before sending data, STA will send a RTS request to the other party, and the surrounding devices will re-adjust the value of their NAV when they hear that the STA of RTS. The receiver returns a CTS, and the STA that listens to the CTS adjusts the value of their NAV. This kind of machine system effectively avoids access conflicts between STA that neither can listen for data sent by each other.

1101 ACK

The 802.11 rate transmission is in half-duplex mode, so in order to confirm the success of the data transmission, each unicast data needs an acknowledgement frame, which is 14 bytes long.

1110 CF-End

1111 CF-End and CF-Ack

Contention Free (CF) frames are mainly used to acquire channels, and the frame format is as follows

The subtypes of data frames are as follows:

1. Data frames carrying data:

0000 Data

0001 Data + CF-Ack [PCF only]

0010 Data + CF-Poll [PCF only]

0011 Data + CF-Ack + CF-Poll [PCF only]

1000 QoS Data [HCF]

1001 QoS Data + CF-Ack [HCF]

1010 QoS Data + CF-Poll [HCF]

1011 QoS Data + CF-Ack + CF-Poll [HCF]

Data frames that do not carry any data:

0100 Null (no data)

0101 CF-Ack (no data) [PCF only]

0110 CF-Poll (no data) [PCF only]

0111 CF-Ack + CF-Poll (no data) [PCF only]

1100 QoS Null (no data) [HCF]

1101 Reserved

1110 QoS CF-Poll (no data) [HCF]

1111 QoS CF-Ack + CF-Poll (no data) [HCF]

When it comes to data frames, we have to talk about four issues related to them: data frame address format, fragmentation, aggregation, and transmission rate.

1. Data frame address format: because the back end of AP is the 802.3 network, or DS. So we will see the following four address formats:

two。 Fragmentation: a complete data frame is divided into several frames for transmission in a high interference environment. When the interference is serious, the use of slicing mechanism can reduce the cost of retransmission. However, when the interference is not very serious, the slicing mechanism will increase the transmission overhead and reduce the throughput.

3. Aggregation: as opposed to fragmentation, aggregation refers to the aggregation of several frames into a single data frame for transmission. It is divided into A-MPDU and A-MSDU.

A-MPDU:

A-MSDU:

4. Transmission rate: the basic rate set is defined in the protocol standard, which must be supported by every STA or AP. In addition, some rates other than the base rate set can be supported. As the distance between AP and STA changes, so does the rate at which data is transferred between them. Generally speaking, as the distance between the two increases, the rate decreases gradually. The data frame lowers the transmission rate each time it is retransmitted to ensure the success of the retransmission.

These are the details of the control frame and the data frame. Have you gained anything after reading it? If you want to know more about it, you are welcome to follow the industry information!

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