Wireles Networks The Definitive Guide.pdf - Csbdu.in

1001 Announcement traffic indication message (ATIM)
1010 Disassociation
1011 Authentication
1100 Deauthentication
Control frames (type=01) [b]
1010 Power Save (PS)-Poll
1011 RTS
1100 CTS
1101 Acknowledgment (ACK)
1110 Contention-Free (CF)-End
1111 CF-End+CF-Ack
Data frames (type=10) [c]
0000 Data
0001 Data+CF-Ack
0010 Data+CF-Poll
0011 Data+CF-Ack+CF-Poll
0100 Null data (no data transmitted)
0101 CF-Ack (no data transmitted)
0110 CF-Poll (no data transmitted)
0111 Data+CF-Ack+CF-Poll
(Frame type 11 is reserved)
[a] Management subtypes 0110-0111 and 1101-1111 are reserved and not currently used.
[b] Control subtypes 0000-1001 are reserved and not currently used.
[c] Data subtypes 1000-1111 are reserved and not currently used.
ToDS and FromDS bits
These bits indicate whether a frame is destined for the distribution system. All frames on
infrastructure networks will have one of the distribution system's bits set. Table 3-2 shows
how these bits are interpreted. As Chapter 4 will explain, the interpretation of the address
fields depends on the setting of these bits.
Table 3-2. Interpreting the ToDS and FromDS bits
To DS=0
To DS=1
From
DS=0
All management and control frames
Data frames within an IBSS (never
infrastructure data frames)
Data frames transmitted from a wireless station
in an infrastructure network
From Data frames received for a wireless station
Data frames on a "wireless bridge"
DS=1 in an infrastructure network
More fragments bit
This bit functions much like the "more fragments" bit in IP. When a higher-level packet has
been fragmented by the MAC, the initial fragment and any following nonfinal fragments set
this bit to 1. Some management frames may be large enough to require fragmentation; all
other frames set this bit to 0.
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