3. Introduction
Created and maintained by IEEE
Set of media control(MAC) and physical layer
Used to implement wireless local area
network(WLAN)
In the frequency band 2.4,3.6,5 and 60 GHz
Wi-fi refers to the IEEE 802.11 communication for
WLAN
The Linksys WRT54G contains a router with an
802.11b/g radio and two antennas
4. Introduction cntd.
Adopted in 1997
Family of 802
Origins in a 1985 ruling by the U.S. Federal
Communications commission
Consist of series of half duplex over the air
modulation
Uses same basic protocols
It uses two spread spectrum technology
Frequency Hopping Spread Spectrum (FHSS)
Direct Sequence Spread Spectrum (DSSS)
5. 802.11 Physical Layer (PHY)
The 802.11 physical layer (PHY) is the interface
between the MAC and the wireless media where
frames are transmitted and received.
The PHY provides three functions.
First, the PHY provides an interface to exchange
frames with the upper MAC layer for transmission and
reception of data.
Secondly, the PHY uses signal carrier and spread
spectrum modulation to transmit data frames over
the media.
Thirdly, the PHY provides a carrier sense indication
back to the MAC to verify activity on the media.
6. Architectures
Station (STA) Architecture:
It contains IEEE 802.11
conformant MAC and PHY
interface to the wireless
medium, but does not
provide access to a
distribution system
Access-Point Architecture:
Device that contains
IEEE802.11 conformant
MAC and PHY interface to
the wireless medium, and
provide access to a
distribution system for
associated stations
Implemented in infra-
structure products that
connect to wired backbones
7. General terminologies
BSS (basic service set):
Group of stations that communicate each other
IBSS(independent basic service set):
It is a BSS without access point
Extended Service Set (ESS):
A set of one or more Basic Service Sets inter
connected by a distribution System (DS)
9. General terminologies cntd
Service Set Identifier (SSID):
It is network name similar to domain id
One network (ESS or IBSS) has one SSID
Basic Service Set Identifier (BSSID)
It is cell identifier and is 6 octets long
Similar to NW ID in pre-IEEE Wave LAN systems
10. Frame format
Bytes 2 22 6 6
6
66 2 6 0-
2312
4
Frame control Durati
on ID
A1 A2 A3 seq.ctr
l
A4 Frame
body
CRC
802.11 MAC header
Bits :2
2 2 4 1 1 1 1 1 1 1
Protocol
version
type Sub
type
To DS From
DS
More
flag
Retry Pwr
Mgt
More
data
wep rsvd
Frame control Field
11. protocols
802.11 legacy
Release in Jun 1997
Original version of 802.11
Specifies two net bit rate 1or 2 mbits per sec
It has forward error correction code
Three alternatives physical layer
Diffuse infrared
Frequency hopping spread spectrum
Direct sequence spread spectrum
12. 802.11a(ofdm waveform)
Release in sep 1999
Data rates 1.5 to 54 mbit/s
First widely accepted 802 family
Operates at 5GHz frequency band
Less range
13. 802.11b
Release on the market in 2000
Maximum raw data rate of 11mbit/s
High throughput
Low cost
Interference problem
14. 802.11g
Release on june 2003
Operates in the 2.4 GHz band
Uses OFDM based transmission scheme
Operates at the average bit rate of 22 Mbit/s or
maximum 54 Mbit/s
Its hardware are full back compatible with
802.11b hardware
15. 802.11n
Release on October 2009
It is the improvement over previous 802.11
standard
It has MIMO antennas
Operates at the 2.4 GHz or less than 5GHz
bands
Data rates from 54 Mbit/s to 600 Mbit/s
16. 802.11ac
Release in December 2013
It is an amendment to IEEE 802.11
It has wider channels(80 or 160 MHz)
Operates at 5GHz band
It supports multi-user MIMO
Data rates up to 1300 Mbit/s
17. 802.11ad
Release in Dec 2012
It defines new physical layer for 802.11 n/w
Operates in the 60GHz millimeter wave
spectrum
Product implementing this standard are being
brought under the name of wigig brand
Peak transmission rate 7 Gbit/s
18. Other Protocols
802.11 AH
Estimated to release 2016
Bandwidth 900MHz
802.11 AJ
Estimated to release 2016
Bandwidth 24/60
802.11 AX
Estimated to release 2019
Bandwidth 2.4/5
19. 802.11 Media Access Control
The 802.11 MAC layer provides functionality to allow reliable data
delivery for the upper layers over the wireless PHY media.
The data delivery itself is based on an asynchronous, best-effort,
connectionless delivery of MAC layer data.
There is no guarantee that the frames will be delivered successfully.
The 802.11 MAC provides a controlled access method to the shared
wireless media called Carrier-Sense Multiple Access with Collision
Avoidance (CSMA/CA).
CSMA/CA is similar to the collision detection access method
deployed by 802.3 Ethernet LANs.
20. 802.11 Media Access Control cntd
Another function of the 802.11 MAC is to
protect the data being delivered by providing
security and privacy services.
Security is provided by the authentication
services and by Wireless Equivalent Privacy
(WEP), which is an encryption service for data
delivered on the WLAN.
21. Security
For security 802.11 specifies two
Authentication modes:
OSA(Opens Systems Authentication)
• Device that request to access the network is granted
without any security check
Shared Key Authentication
• Device that request to access the network is granted
with security check
• WEP: wired equivalent privacy
ESSID offers casual separation of traffic