Alvarion BreezeNET PRO.11 Guía de usuario descargar pdf (Pagina 198)

Appendix

User’s Guide 9-42 BreezeNET PRO.11 Series

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This field has two meanings depending on the frame type:

• In Power-Save Poll messages this is the Station ID

• In all other frames this is the duration value used for the NAV Calculation.

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A frame may contain up to 4 Addresses depending on the ToDS and FromDS bits

defined in the Control Field, as follows:

• Address-1 is always the Recipient Address (i.e. the BSS station that is the

immediate recipient of the packet). If ToDS is set, this is the AP Address; if

ToDS is not set, then this is the address of the end-station.

• Address-2 is always the Transmitter Address (i.e. the station which is

physically transmitting the packet). If FromDS is set, this is the AP address; if

it is not set, then it is the Station address.

• Address-3 is in most cases the remaining, missing address. On a frame with

FromDS set to 1, Address-3 is the original Source Address; if the frame has the

ToDS set, then Address 3 is the destination Address.

• Address-4 is used in special cases where a Wireless Distribution System is

used, and the frame is being transmitted from one Access Point to another. In

such cases, both the ToDS and FromDS bits are set, so both the original

Destination and the original Source Addresses are missing.

The following Table summarizes the usage of the different Addresses according to

ToDS and FromDS bits setting:

To DS From DS Address 1 Address 2 Address 3 Address 4

0 0 DA SA BSSID N/A

0 1 DA BSSID SA N/A

1 0 BSSID SA DA N/A

1 1 RA TA DA SA

1 2 ... 193 194 195 196 197 198 199 200 201 202 203 ... 208 209

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Alvarion BreezeNET PRO.11 Guía de usuario Pagina 198