1. IEEE 802.11 Wireless LAN Standard
Chapter 14

2. IEEE 802 Protocol Layers

3. Protocol Architecture
Functions of physical layer:
Encoding/decoding of signals
Preamble generation/removal (for synchronization)
Bit transmission/reception
Includes specification of the transmission medium

4. Protocol Architecture
Functions of medium access control (MAC) layer:
On transmission, assemble data into a frame with address and error detection fields
On reception, disassemble frame and perform address recognition and error detection
Govern access to the LAN transmission medium
Functions of logical link control (LLC) Layer:
Provide an interface to higher layers and perform flow and error control

5. Separation of LLC and MAC
The logic required to manage access to a shared-access medium not found in traditional layer 2 data link control
For the same LLC, several MAC options may be provided

6. IEEE Services

7. MAC Frame Format MAC control Destination MAC address
Contains Mac protocol information, e.g. priority level
Destination MAC address
Destination physical attachment point
Source MAC address
Source physical attachment point
Data
The body of the MAC frame (LLC PDU)
CRC
Cyclic redundancy check

8. LLC Services Unacknowledged connectionless service
No flow- and error-control mechanisms
Data delivery not guaranteed
Connection-mode service
Logical connection set up between two users
Flow- and error-control provided
Acknowledged connectionless service
Cross between previous two
Datagrams acknowledged
No prior logical setup

9. IEEE
IEEE is a set of standards for implementing WLAN computer communications in 2.4, 3.7, and 5 GHz frequency band.
The first standard was IEEE b
The Wi-Fi Alliance
Industry consortium formed in 1999.
Wi-Fi is concerned whether products from different venders will successfully interoperate (Certification process).

10. Data rate per stream (Mbit/s)
IEEE
protocol
Release
Freq. (GHz)
Bandwidth (MHz)
Data rate per stream (Mbit/s)
Modulation
Range
(m)
Jun 1997
2.4 20
1, 2
DSSS, FHSS
100 a
Sep 1999 5
6, 9, 12, 18, 24, 36, 48, 54
OFDM 35
120
3.7 —
5,000 b
5.5, 11
DSSS
140 g
Jun 2003
OFDM, DSSS 38 n
Oct 2009
2.4/5
7.2, 14.4, 21.7, 28.9, 43.3, 57.8, 65, 72.2 70
250 40
15, 30, 45, 60, 90, 120, 135, 150
ac (DRAFT)
Nov. 2011 80
433, 867
160
867, 1.73 Gbit/s, 3.47 Gbit/s, 6.93 Gbit/s

11. IEEE 802.11 Architecture Distribution system (DS) Access point (AP)
Basic service set (BSS)
Stations competing for access to shared wireless medium
Isolated or connected to backbone DS through AP
Extended service set (ESS)
Two or more basic service sets interconnected by DS

12. IEEE 802.11 WLAN topologies Infrastructure mode
Wireless hosts communicate with an Access Point
Basic Service Set (BSS) (cell) contains:
1 access point (AP): base station
Several wireless hosts
Access point realizes the control functionality
Medium access, mobility management, authentication
Wireless stations only need a minimum of functionality

13. IEEE 802.11 WLAN topologies Ad-Hoc mode No AP
Wireless hosts communicate with each other
Transferring packet from wireless host A to B may need to route through other wireless hosts.
Independent Basic Service Set (IBSS)
When all stations in the BSS are mobile stations with no connection to other BSSs.
Applications:
“Laptop” meeting in conference room / interconnection of “personal” devices / battlefield

14. IEEE 802.11 WLAN Terminologies
Access Point – perform the wireless to wired bridging function between networks
Wireless medium – means of moving frames from station to station
Station – computing devices with wireless network interfaces (phones, laptops, desktops, PDAs, play-stations)
Distribution System – backbone network used to relay frames between access points
e.g. Wired Ethernet 14

15. Distribution of Messages Within a DS
Distribution service
Used to exchange MAC frames from station in one BSS to station in another BSS
Integration service
Transfer of data between station on IEEE LAN and station on integrated IEEE 802.x LAN

16. Transition Types Based On Mobility
No transition
Stationary or moves only within BSS
BSS transition
Station moving from one BSS to another BSS in same ESS
ESS transition
Station moving from BSS in one ESS to BSS within another ESS

17. Access and Privacy Services
Authentication
Establishes identity of stations to each other
Deauthentication
Invoked when existing authentication is terminated
Privacy
Prevents message contents from being read by unintended recipient

18. Association-Related Services
Establishes initial association between station and AP
Reassociation
Enables transfer of association from one AP to another, allowing station to move from one BSS to another
Disassociation
Association termination notice from station or AP

19. Station Connecting to a WLAN
When a station moves into the coverage area of a WLAN, the following procedures take place:
1- Scanning: the station searches for a suitable channel over which subsequent communication takes place.
2 - Association: the station associates with an AP
3 - IP address allocation: the station gets an IP address, for instance from a DHCP server
4 - Authentication: only if this security option is required

20. Handover to another AP
When a station has noticed that the radio connection to another AP is a better than the existing connection:
1- Reassociation: the station associates with another AP.
2 - No new IP address is needed; however, the WLAN must be able to route downlink traffic via the new AP.
3 - Authentication: this security option, if required, will result in a substantially increased handover delay (complete procedure sequence: deauthentication, disassociation, reassociation, authentication).