IEEE 802.11 SYSTEM AND PROTOCOL ARCHIECTURE

1. IEEE 802.11

2. IEEE 802.11 – SYSTEM ARCHITECTURE
 Station (STA)
 terminal with access mechanisms to the
wireless medium and radio contact to the
access point
 Basic Service Set (BSS)
 group of stations using the same radio
frequency
 Access Point
 station integrated into the wireless LAN and the
distribution system
 Portal
 bridge to other (wired) networks
 Distribution System
 interconnection network to form one logical
network (EES: Extended Service Set) based
on several BSS
Fig: Architecture of infrastructure based IEEE 802.11

3. 802.11 - ARCHITECTURE OFAN AD-HOC NETWORK
Direct communication within a
limited range
 Station (STA):
terminal with access mechanisms to the
wireless medium
 Independent Basic Service Set (IBSS):
group of stations using the same radio
frequency

4. IEEE 802.11 – PROTOCOLARCHITECTURE
Fig : IEEE 802.11 Protocol Architecture and Bridging
DATA LINK
LAYER

5. IEEE 802.11 –LAYERS AND FUNCTIONS
Fig : Detailed IEEE 802.11 protocol architecture
and management
MAC
 access mechanisms, fragmentation,
encryption
MAC Management
 synchronization, roaming, MIB, power
management
PLCP Physical Layer Convergence Protocol
 clear channel assessment (CCA) signal
(carrier sense)
PMD Physical Medium Dependent
 modulation, coding
PHY Management
 channel selection, MIB
Station Management
 coordination of all management functions

6. PLCP Protocol Data Unit
 When the PLCP receives the PSDU, it then prepares the
PSDU to be transmitted and creates the PLCP Protocol
Data Unit (PPDU).
 The PLCP adds a preamble and PHY header to the PSDU.
 The preamble is used for synchronization between
transmitting and receiving 802.11 radios.
 When the PPDU is created, the PMD sublayer takes the
PPDU and modulates the data bits and begins
transmitting.
PLCP Service Data Unit
 The PLCP Service Data Unit (PSDU) is a view of the MPDU from the
Physical layer.
 The MAC layer refers to the frame as the MPDU, while the Physical layer
refers to this same frame as the PSDU.
 The only difference is from which layer of the OSI model you are looking at
the frame.

7. PLCP Protocol Data Unit (PPDU)
 When the PLCP layer receives the PSDU from the MAC layer, the
appropriate PLCP Preamble & PLCP Header are added to the PSDU to
create PPDU. When transmitting data, the Tx STA alerts the Rx STA of
transmission by sending PLCP Preamble at the beginning of transmission.
 IEEE 8021.11- define 3 different preambles
The PPDU consist of 3 parts.
1. PLCP Preamble
2. PLCP Header
3. PSDU
1. Long PLCP Preamble
2. Short PLCP Preamble
3. OFDM PLCP Preamble