IEEE 802.11 IEEE 802.11

Architecture

Physical Layer

MAC Layer

Addressing Mechanism

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Figure 15.1 BSSs

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Figure 15.2 ESS

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Figure 15.3 Physical layer specifications

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Figure 15.6 MAC layers in IEEE 802.11 standard

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Figure 15.8 CSMA/CA and NAV

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Figure 15.9 Frame format

Table 15.1 Subfields in FC field Table 15.1 Subfields in FC field

Explanation Field

The current version is 0. The current version is 0. Version Version

Type of information: management (00), control (01), or data (10). Type of information: management (00), control (01), or data (10). TypeType

Defines the subtype of each type (see ). Defines the subtype of each type (see ). Subtype Subtype

Defined later. Defined later. To DS To DS

Defined later. Defined later. From DS From DS

When set to 1, means more fragments. When set to 1, means more fragments. More flag More flag

When set to 1, means retransmitted frame. When set to 1, means retransmitted frame. RetryRetry

When set to 1, means station is in power management mode. When set to 1, means station is in power management mode. Pwr mgt Pwr mgt

More data More data When set to 1, means station has more data to send. When set to 1, means station has more data to send.

WEPWEP Wired equivalent privacy. When set to 1, means encryption Wired equivalent privacy. When set to 1, means encryption implemented. implemented.

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Reserved. Reserved. RsvdRsvd

Control Frame

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Control frames

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Table 14.2 Values of subfields in control frames Table 14.2 Values of subfields in control frames

Meaning Subtype

1011 Request to send (RTS) Request to send (RTS)

1100 Clear to send (CTS) Clear to send (CTS)

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1101 Acknowledgment (ACK) Acknowledgment (ACK)

Management Frame

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Data Frame

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Table 15.1 Subfields in FC field Table 15.1 Subfields in FC field

ToTo DSDS FromFrom DSDS Address Address 11 Address Address 22 Address Address 33 Address Address 44

00 00 BSS ID BSS ID N/AN/A Destination Destination station station Source Source station station

00 11 N/AN/A Destination Destination station station Sending Sending APAP Source Source station station

11 00 N/AN/A Receiving Receiving APAP Source Source station station Destination Destination station station

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11 11 Receiving Receiving APAP Sending Sending APAP Destination Destination station station Source Source station station

Figure 15.11 Addressing mechanism: case 1

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To DS =0, From DS = 0

Figure 15.12 Addressing mechanism: case 2

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To DS =0, From DS = 1

Figure 15.13 Addressing mechanism: case 3

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To DS =1, From DS = 0

Figure 15.14 Addressing mechanism: case 4

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To DS =1, From DS = 0