WIFI

1. Wi – Fi ( 802.11)

2. Why we go for Wi - Fi
 Data Transfer rate is about 250-600 Mbps
 Coverage Distance is about 100m.
 Here More number of devices can be connected
( Depending upon the Router ) whereas in
Bluetooth only 7 devices are supported for
transmission

3. Definition of Wi - Fi
 It is a Wireless Technology that uses “ Radio
Waves” to provide high speed Internet Access.
 It has no physical cables like Coaxial, UTP, STP
etc.

4. Built In Wireless Transmitter
 The Pc’s and Laptops which are available
today all have Built In Wireless Transmitter.
(i.e. It is very easy to connect to a Wi – Fi ).
 If the Pc’s and Laptops does not have a Built
In Wireless Transmitter, the Wi-Fi can be
accessed by using Wi- Fi Dongle which should
be connected in any USB ports.

5. d

6. Hotspot
The area or location where a Wi – Fi access is
available is called a Hotspot.

7. SSID
 An SSID is the name of a wireless local area
network (WLAN).
 All wireless devices on a WLAN must employ
the same SSID in order to communicate with
each other.
 SSID is a 32 alphanumeric character unique
identifier.

8. Types of 802.11
a) 802.11 a -> It can support upto a data rate of
54 Mbps.
b) 802.11 b -> It is the low speed version of Wi-
Fi. It supports upto a speed of 11 Mbps.

9. Types of 802.11
c) 802.11 n -> It can support upto a data rate of
110 Mbps. It is a Backward Compatible and
Forward Compatible one.
Backward Compatible is defined as suppose if
the Wi – Fi Dongle is designed for Windows 8
OS, the same Dongle must also supports
Windows 7, Windows XP, Linux, Fedora OS.

10. Types of 802.11
d) 802.11 AC
-> It was introduced in the year 2013.
-> It can support upto a data rate of 450
Mbps.
-> It is also a Backward Compatible one.

11. Access Point
 It is a device that allows Wireless devices to
connect to wired network.
 It is also called as a Base Station because it
transmit and receive signal from it.
 It also provides Security Mechanisms so that
only Authenticated users can able to access
the Network.

12. Access Point
-> The data rate of Access Point depends upon
the number of users using the network (i.e.
Data rate is shared amongst all the users)
( Ex) If the data rate speed of Access Point is 10
Mbps, suppose if there are 5 users are there
each will get 2 Mbps data rate.

13. Access Point
-> A single Access Point can support upto a
maximum of 20-25 users ( or) clients at a time.
-> If the number of users are increasing the data
rate is going to be greatly reduced.

14. Hidden Station Problem

15. Explanation
 B is called the Access Point ( otherwise called a
Base Station).
A, C and D are within the range of Access Point.
 Suppose if A wants to access the channel and at
the same time C wants to access the same
channel, A doesn’t knows C and C doesn’t knows
A.
B can provide channel to any one either A or C.

16. How to resolve the Hidden Station
Problem

17. RTS, CTS and NAV
 RTS -> Request to Send ( I capture the
channel)
 CTS -> Clear to Send ( I don’t hear any other
requests you can use my channel).
 NAV -> Negative Allocation Vector ( Keeps
other Station Quiet).

18. Exposed Station Problem

19. Exposed Station Problem

20. Architecture of Wi-Fi

21. Architecture of Wi - Fi
 Each computer, mobile, portable or fixed, is
referred to as a station in 802.11
 When two or more stations come together to
communicate with each other, they form a
Basic Service Set (BSS).

22. Architecture of Wi - Fi
 A BSS that stands alone and is not connected
to a base station ( or ) Access Point is called
an Independent Basic Service Set (IBSS).
 Two or more BSS's are interconnected using a
Distribution System or DS. Entry to the DS is
accomplished with the use of Access Points
(AP).

23. Architecture of Wi - Fi
 A Portal is the logical integration between
wired LANs and 802.11.
 All data going to an 802.11 LAN from an 802.X
LAN must pass through a portal.

24. Security Measures in Wi - Fi
1) Media Access Control Address Filtering
 It never asks any password to authendicate to
wi – fi access, instead all the Machine Address
are registered first, so that only registered
users can access the network others not.

25. Security Measures in Wi - Fi
2) Wired Equivalent Privacy ( WEP)
The goal of WEP is to make Wireless network a
more secure one.
Types of WEP
a) OFF -> No security Mechanisms is provided
here. (i.e.) Everyone can access the Wi-Fi
network without any Authentication
mechanism.

26. Security Measures in Wi - Fi
b) 128 Bit
 Client sends an Authentication request to
Access Point (i.e. Username and Password )
If the Client request matches it sends a
positive reply to your device to you to access
to the network.

27. Pros of Wi - Fi
 The Internet access can be accessed
anywhere where the wi fi signalexists.
 Low cost when compared to wired network.
 Wi – Fi is compatible with all OS.
 Simple Setup.

28. Cons of Wi - Fi
 Security is the greatest disadvantage in
Wireless network.
 Scalability is the main problem ( i.e.) The
number of users are limited here to use the
Wi- Fi.
 Coverage distance of an Access Point is very
low here.