Chapter 15' Wireless LANs

1
Chapter 15. Wireless LANs

• IEEE 802.11
• Bluetooth

2
Basic Service Set (BSS)

• BSS
• The building block of a wireless LAN
• BSS with an AP
• Access Point (AP) central base station
• BSS without an AP
• Stand-alone network
• Cannot send data to other BSSs
• Ad hoc architecture

3
BSS
4
Extended Service Set (ESS)

• BSSs are connected through a distribution system
  infrastructure network

5
802.11 PHY

• 802.11 2.4 GHz 1 or 2 Mbps
• 802.11a 5 GHz 54 Mbps
• 802.11b 2.4 GHz 11 Mbps
• 802.11g 2.4 GHz 54 Mbps

6
FHSS

• Frequency-Hopping Spread Spectrum
• Dwell time the amount of time spent at each
  subband
• This is not a case of multiple access

7
DSSS

• Direct Sequence Spread Spectrum
• Each bit is replaced by a chip code
• DSSS is implemented at the PHY it is not a
  multiple access method

8
CSMA/CA
9
CSMA/CA and NAV
10
Frame Format
11
Addressing To DS 0 and From DS 0
12
Addressing To DS 0 and From DS 1
13
Addressing To DS 1 and From DS 0
14
Addressing To DS 1 and From DS 1
15
Blueooth Piconet
16
Bluetooth Scatternet
17
Bluetooth Layers

• Radio layer
• 2.4 GHz ISM band
• FHSS
• Bluetooth hops 1600 times per second
• Dwell time is 625 µsec ( 1/1600 sec)
• Baseband layer
• TDD-TDMA
• L2CAP layer
• For asynchronous data exchange

18
Single-Slave Communication
19
Multiple-Slave Communication
20
Frame Types

• 259 µsec is needed for hopping and control