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IEEE Std 802.11™‐2020 · 9.3.3.5 Association Request Frame Format

本节描述了 Association Request（关联请求）帧 的结构与组成字段。当无线终端（STA）尝试与接入点（AP）建立连接时，会发送该帧以表明自身能力、支持的速率与安全特性。帧体（Frame Body）包含多个信息元素（Information Elements, IEs），每个元素采用 Type-Length-Value (TLV) 编码格式，其顺序与内容如Table 9-64所示。

This section specifies the format of the Association Request frame. When a STA (station) attempts to associate with an AP, it sends this frame to indicate its capabilities, supported rates, and security features. The frame body consists of several Information Elements (IEs), each encoded as a Type-Length-Value (TLV) field.

管理帧（Management Frame）结构简介

802.11 标准中管理帧（Management Frame）的格式定义在 Figure 9-128。所有管理帧的子类型都包含以下基础字段：
Frame Control、Duration、Address 1、Address 2、Address 3，以及 Sequence Control。

对于 未通过 VHT、S1G PPDU 或 2.4GHz 频段以外的 HE PPDU 发送的 MMPDU，其最大长度由标准中的 Table 9-34 定义。
HT Control 字段是否出现，由 Frame Control 字段中的 +HTC 子字段 决定。

如果 MMPDU 是通过 VHT、S1G 或非 2.4GHz 的 HE PPDU 承载，其最大长度遵循以下规则：

当只有一个接收方时：最大 MPDU 大小 = 接收方支持的最大 MPDU 长度 − 最短的管理帧 MAC Header 与 FCS 长度。
当有多个接收方时：取所有接收方支持的最小 MPDU 长度，再减去最短的管理帧 MAC Header 与 FCS。

Figure 9-128 — Management Frame Format

Association Request Frame Body，Table 9-64

Order	Information Element	Notes
1	Capability Information	See 9.4.1.4 for Capability Information field format.
2	Listen Interval	Specifies how often the STA listens to beacon frames from the AP.
3	SSID	Identifies the service set the station is requesting to join.
4	Supported Rates and BSS Membership Selectors	This element is not present if `dot11DMGOptionImplemented` is true.
5	Extended Supported Rates and BSS Membership Selectors	Present if there are more than eight supported rates (optional otherwise). Not present if `dot11DMGOptionImplemented` is true.
6	Power Capability	Present if `dot11SpectrumManagementRequired` or `dot11RadioMeasurementActivated` is true.
7	Supported Channels	Present if `dot11SpectrumManagementRequired` is true and `dot11ExtendedChannelSwitchActivated` is false.
8	RSN	RSN Information Element (RSNE) is present if `dot11RSNAActivated` is true.
9	QoS Capability	Present if `dot11QosOptionImplemented` is true.
10	RM Enabled Capabilities	Present if `dot11RadioMeasurementActivated` is true.
11	Mobility Domain	Present if `dot11FastBSSTransitionActivated` is true and the AP advertised FT capability in its MDE (Beacon or Probe Response).
12	Supported Operating Classes	Present if `dot11ExtendedChannelSwitchActivated` or `dot11OperatingClassesRequired` is true.
13	HT Capabilities	Present when `dot11HighThroughputOptionImplemented` is true.
14	20/40 BSS Coexistence	Optionally present when `dot112040BSSCoexistenceManagementSupport` is true.
15	Extended Capabilities	Present if any of the fields in this element are nonzero.

Each Information Element (IE) is a Type-Length-Value (TLV) structure defined in Clause 9.4 of the IEEE 802.11 standard. The presence of optional elements depends on specific PHY/MAC features enabled in the station or the AP.

在线体验：802.11 Association Request MAC Header · Encode

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Frame Control — Byte 1（固定字段）

Protocol Version (2 bits) 固定为 0（802.11 标准）

Type (2 bits) 固定为 0（Management frame）

Subtype (4 bits) 固定为 0（Association Request）

ToDS (1 bit)

FromDS (1 bit)

More Frag (1 bit)

Retry (1 bit)

Power Mgmt (1 bit)

More Data (1 bit)

Protected_Frame (1 bit)

+HTC (1 bit)

Duration/ID (2 bytes, 0~65535)

Address 1 (6 bytes, hex with “:”, e.g. 01:02:03:04:05:06)

Address 2 (6 bytes, hex with “:”, e.g. 01:02:03:04:05:06)

Address 3 (6 bytes, hex with “:”, e.g. 01:02:03:04:05:06)

Sequence Control: Sequence Number (12 bits)

Sequence Control: Fragment Number (4 bits)

HT Control (暂不支持)

当前编码器不支持 HT Control，该开关仅为界面预留，不参与编码。

Frame Body · Mandatory

Capability Information（non-DMG STA，16 bits，逐位勾选）

ESS (1 bit)

IBSS (1 bit)

Privacy (1 bit)

Short Preamble (1 bit)

Spectrum Mgmt (1 bit)

QoS (1 bit)

Short Slot (1 bit)

APSD (1 bit)

Radio Meas. (1 bit)

EPD (1 bit)

未列出的 spare 位默认 0。

Listen Interval (2 bytes, 1~65535)

SSID (Optional)

（如果启用，则 SSID 将作为可变长度字符串写入 Frame Body，长度不定。）

SSID 字符串

Supported Rates & BSS Membership Selectors (Optional)

（输入单位为 Mbps，逗号分隔，最多 8 个。每个速率会编码为 1 字节： RateType = 0， RateValue = Mbps × 2（以 500 kbit/s 为单位）。）

HT Capabilities（Optional, 只配置 Octet 1–2 与 26）

（该域有26 octets，这里只配置： HT_Capability_Information（Octets 1–2） 和 ASEL_Capabilities（Octet 26）；其他字段默认为 0。）

HT_Capability_Information（Octets 1–2, 16 bits）

LDPC_Coding_Capability (1 bit: 0~1)

Supported_Channel_Width_Set（40 MHz）(1 bit: 0~1)

SM_Power_Save (2 bit: 0~3)

HT_Greenfield (1 bit: 0~1)

Short_GI_for_20_MHz (1 bit: 0~1)

Short_GI_for_40_MHz (1 bit: 0~1)

Tx_STBC (1 bit: 0~1)

Rx_STBC (2 bit: 0~3)

Maximum_A_MSDU_Length (1 bit: 0~1)

DSSS_CCK_Mode_in_40_MHz (1 bit: 0~1)

Forty_MHz_Intolerant (1 bit: 0~1)

ASEL_Capabilities（Octet 26, 8 bits）

Antenna_Selection_Capable (1 bit: 0~1)

Explicit_CSI_FB_Based_Tx_ASEL_Capable (1 bit: 0~1)

Antenna_Indices_FB_Based_Tx_ASEL_Capable (1 bit: 0~1)

Explicit_CSI_FB_Capable (1 bit: 0~1)

Antenna_Indices_FB_Capable (1 bit: 0~1)

Receive_ASEL_Capable (1 bit: 0~1)

Transmit_Sounding_PPDUs_Capable (1 bit: 0~1)

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