Wireless LAN and Bluetooth
IEEE 802.11
• IEEE has defined the specifications for a wireless LAN, called IEEE 802.11, which covers the physical and data link layers.
• The standard defines two kinds of services:
– Basic Service Set
– Extended Service Set
2
Basic Service Set
Basic Service Set
• Building block of Wireless Lan.
– Stationary or mobile wireless station.
– Access Point (AP)
• Ad hoc Architecture
– Stand alone network.
– No AP required
• Infrastructure Network
4
Extended Service Set
Station Types
• No transition
• BSS transition
• ESS Transition Mobility
6
MAC Sublayer
Distributed Coordination Function
• Uses CSMA/CA for Access Method
• Can’t use CSMA/CD for three reason:
– Costly equipments – Hidden Station
– Signal Fading - distance
8
Distributed Coordination Function
Check the energy level
Waits for a period of time - Distributed interframe space and sends a control
frame request to send.
Waits for a Short interframe space time and the destination sends a control
frame clear to send.
Distributed Coordination Function
10
Network Allocation Vector
• A station sends a RTS frame to occupy a channel.
– Includes the duration of transmission
• Other station creates a timer -- Known as NAV
• Collision still occur –
– How ?
• Two or more stations can send the RTS frame at the same time.
– There is no such mechanism for collision detection, they assume that CTS not received and employ the back off strategy.
– Retransmission occurs.
Fragmentation
Frame type
Control frame NAV Four address field Sequence # Type and subtype
of FC field CRC
12
Subfields in FC
Frame Types
• Management Frames
– initial communication
• Control Frames
– channel access and acknowledgement
• Data Frame
14
Frame Types
Values of subfields in control frames
Addressing mechanism
14.16
Table 14.3 Addresses
16
Addressing mechanism
Hidden Station Problem
14.18 18
Hidden Station Solution
Bluetooth
20
Bluetooth
Bluetooth is a wireless LAN technology designed to connect devices of different functions such as telephones, notebooks,
computers, cameras, printers, coffee makers, and so on. A Bluetooth LAN is an ad hoc
network, which means that the network is formed spontaneously.
Bluetooth
• Application
– Peripheral devices – Home Security
– Monitoring Devices
• Developed from a project of Ericsson Company.
• IEEE 802.15
– Wireless Personal Area Network
• Architecture
– Piconet – Scatternet
22
Bluetooth
Scatternet
24
Bluetooth Layers
Bluetooth
• TDD-TDMA
– Half duplex communication system where sender and receiver cannot send at the same time.
• Single Secondary communication
– Time slot of 625 Micro Second
26
Baseband Layers
Baseband Layers
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