Date post: | 20-Jun-2015 |
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Technology |
Upload: | parnal-vast |
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Wi-Fi
IEEE 802.11
ARCHITECTURE
Network Components
Wireless Stations Access Point
Types of Architectures
Basic Service Set
Stationary or Mobile wireless stations
Optional Central Base Station
Extended Service Set
Distributed System
Uses LAN to connect Central Stations form Basic Service Sets
BASIC SERVICE SET [BSS]
AD HOC NETWORK INFRASTRUCTURE NETWORK
EXTENDED SERVICE SET [ESS]
DISTRIBUTION SYSTEM
BSS BSS BSS
TYPES OF STATIONS
NO Transition
BSS Transition
ESS Transition
802.11 Protocol Stack
802.11 FRAME FORMAT
802.11 define 3 classes of frames :
MANAGEMENT
CONTROL
DATA
802.11 FRAME FORMAT
FRAME CONTROL
0 : current version
PROTOCOL VERISION
00 : Management frame01 : Control frame10 : Data frame11 : Unspecified
Control (01)- RTS (1011) CTS (1100)
ACK (1101)
ToDS- 1: frame is addressed to AP for forwarding it to DS
0: other frames
FromDS- 1: frame coming from DS 0 : other frames
1 : When there are more fragments
0 : Sent fragment is last
1 : Frame is retransmitted
0 : Frame is transmitted for the first time
1 : Station in in sleep mode
0 : active mode
1 : indicates that the sender has additional frames
1 : frame body is encrypted
0 : not encrypted
1 : frames transmitted in order
0 : not transmitted in order
Data, Management frame : defines duration of transmission
Control frame : defines ID of frame
Address1 : next device
Address2 : Previous device
Address3 : final destination if not defined by addr1
Address4: original source if not defined by addr2
CASE 1:
ToDS : 0FromDS :0
CASE 2:
ToDS : 0FromDS :1
CASE 3:
ToDS : 1FromDS :0
CASE 4:
ToDS : 1FromDS : 1
Sequence field (16 bits) has 2 subfields:
1. Fragment no.(4 bits)
2. Sequence no.(12 bits)
It can transmit frame with max payload of 2312 bytes
Its is 32bits field containing 32 bits CRC
MANAGEMENT FRAME
RTS FRAME
CTS FRAME
ACK FRAME
CONTOL FRAMES
THANK YOU