1. Basic of Wireless
Introduction:
Wireless networks use radio waves to connect devices such as laptops to the Internet, the
business network and applications. When laptops are connected to Wi-Fi hot spots in public
places, the connection is established to that business’s wireless network.
Types of wireless networks
1. WLAN (Wireless Local Area Networks)
2. WMAN (Wireless Personal Area Networks)
3. WWAN (Wireless Wide Area Networks)
4. WPAN (Wireless Personal Area Networks)
2. Introduction to 802.11 Standards
802.11 and 802.11x refers to a family of specifications
developed by the IEEE for wireless LAN (WLAN) technology. 802.11
specifies an over-the-air interface between a wireless client and a
base station or between two wireless clients. The IEEE accepted the
specification in 1997.
The IEEE Standards protocols are as follows:-
I. 802.11-1997(802.11 legacy)
II. 802.11a(OFDM waveform)
III. 802.11b
IV. 802.11g
V. 802.11n
VI. 802.11ac
VII. 802.11ad
VIII. 802.11af
IX. More….
3. IEEE Standards Frequency Range (Max) Year Devices/Hardware
802.11 / 802.11a
2.4GHz
5GHz
1 to 2Mbps
54Mbps
1999
Generic boards,
Routers, Wi-fi
receivers
802.11b 2.4GHz 11Mbps 1999
Microwave ovens,
Bluetooth devices,
Cordless telephones
802.11g 2.4GHz
54Mbps 2003 Broadband Routers
802.11n
2.4GHz
5GHz
248Mbps 2009 ----------------
802.11ac 5GHz 1Gbps 2013
Dual Band Wireless
routers, Laptop,
Tablets, Digital TV
802.11ad 71GHz
8Gbps/ 50 times
faster than 802.11n
2012 Fibre Optic Cables
IEEE 802.11 Standards Table
4. Methods of transmitting Radio Signals
1. Frequency Hopping Spread Spectrum in the 2.4GHz Band (FHSS).
2. Direct Sequence Spread Spectrum in the 2.4 Band (DSSS).
3. Infrared (IR).
5. The Mac Layer
IEEE 802.11 is part of the IEEE 802 set of LAN protocols, and specifies
the set of media access control (MAC) and physical layer (PHY) protocols for
implementing wireless local area network (WLAN) Wi-Fi computer
communication in various frequencies, including but not limited to 2.4, 5,
and 60 GHz frequency bands.
IEEE 802.11 defines two MAC sub-layers :-
1. Distributed Coordination Function (DCF)
2. Point Coordination Function (PCF)
6. The Basic Access Methods: CSMA/CA
The basic access mechanism, called Distributed Coordination Function, is
basically a Carrier Sense Multiple Access with Collision Avoidance mechanism
(usually known as CSMA/CA). CSMA protocols are well known in the industry,
where the most popular is the Ethernet which is a CSMA/CD protocol (CD
standing for collision Detection).
A CSMA protocol works as follows
A station desiring to transmit senses the medium, if the medium is busy
(i.e. some other station is transmitting) then the station will defer its
transmission to a later time, if the medium is sensed free then the station is
allowed to transmit.
7. Virtual Carrier Sense
The network allocation vector(NAV) is a virtual carrier –sensing
mechanism used with wireless networks protocols such as IEEE 802.11
(Wi-Fi) and IEEE 802.16 (Wi-Max).
This mechanism reduces the portability of a collision on the
receiver area by a station that is “hidden” from the transmitter, to the
short duration of the RTS (Request to Send)
8. 802.11 ARCHITECTURE
The 802.11 architecture defines two types of services .
1. Basic Service Set (BSS)
2. Extended Service Set (ESS)
Before describing these services we will explain some basic concepts
about wireless terminology.
9. Stations :- In IEEE 802.11 (Wi-Fi) terminology, a station (abbreviated
as STA) is a device that has the capability to use the 802.11 protocol. For
example, a station may be a laptop, a desktop PC, PDA, access point or Wi-Fi
phone.
10. Access Point:- It is a device that contain IEEE 802.11 conformant MAC
and PHY interface to the wireless medium, and provides access to a
distribution system for associated stations.
11. 1. Basic Service Set (BSS)
The basic service set (BSS) is a set of all stations that can communicate
with each other at PHY layer. Every BSS has an identification (ID) called the
BSSID, which is the MAC address of the access point servicing the BSS.
There are two types of BSS: Independent BSS (also referred to as IBSS), and
infrastructure BSS. An independent BSS (IBSS) is an ad hoc network that
contains no access points, which means they cannot connect to any other
basic service set.
12. There are two types of BSS modes in a wireless LAN
1. Independent BSS :- An independent BSS is an ad hoc network that
contain no access points. In ad hoc network mode, each node
communicates directly with others nodes so no access point
control is needed.
13. 2. Infrastructure BSS :- In infrastructure mode, the communication occurs
only between the wireless nodes and access points(AP), but not directly
between wireless nodes.
14. 2. Extended Basic Service Set (ESS)
Extended Service Set(ESS) is a set of one or more Basic Service
Set interconnected by a Distribution System (DS). In this traffic always
flow via Access-Point.
15.
16. 1. WMANS: Wireless Metropolitan Area Networks:- This technology allows
the connection of multiple networks in a metropolitan area such as
different buildings in a city, which can be an alternative or backup to laying
copper or fiber cabling.
17. Types of WMAN
1. Point to Point System :- A point to point solution uses RF or infrared
signals that utilize either semi directional or highly directional antenna to
extend rang across metropolitan areas, such as college campus and cities,
Range can be as high as 30 miles for RF system using highly directional
antenna.
18. 2. Point to-Multipoint System:- A typical point-to-multipoint link utilizes a
centralized omnidirectional antenna that provides a signal transceiver
point for trying together multiple remote stations.
19. 3. Packet Radio System :- A packet radio system utilizes special wireless
routers that forward data contained within packets to the destination. Each
user has a packet radio NIC that transmit data to the nearest wireless router.
This router then retransmits the data to the next router. This hopping from
router to router occurs until the packet reaches the destination.
20. 2. WLANS: Wireless Local Area Networks:- WLANS allow users in a local area,
such as a university campus or library, to form a network or gain access to
the internet. A temporary network can be formed by a small number of
users without the need of an access point; given that they do not need
access to network resources.
21. Types of WLAN
1. Peer-to-Peer Wireless LAN:-
A peer-to-peer network allows wireless devices to directly communicate
with each other. Wireless devices within range of each other can discover
and communicate directly without involving central access points. This
method is typically used by two computers so that they can connect to each
other to form a network
22. 2. Access Point Wireless LAN:- A wireless access point (WAP) is a hardware
device or configured node on a local area network (LAN) that allows
wireless capable devices and wired networks to connect through a wireless
standard, including Wi-Fi or Bluetooth. WAPs feature radio transmitters
and antennae, which facilitate connectivity between devices and the
Internet or a network
23. 3. Wireless Distribution System:- A wireless distribution system (WDS) is
a method of interconnecting access points in a wireless local area
network (WLAN), whether or not they are connected through a
backbone wired network. According to the IEEE 802.11 standard, a
distribution system is an infrastructure that connects access points
(AP). Distributed WLAN means that the access points are configured
with the same service set identifier.
24. 4. Monitoring Station:- Network monitoring is the use of a system that
constantly monitors a computer network for slow or failing components
and that notifies the network administrator (via email, SMS or other
alarms) in case of outages or other trouble. Network monitoring is part
of network management.
25. 3. WPANS: Wireless Personal Area Networks:- The two current technologies
for wireless personal area networks are Infra Red (IR) and Bluetooth (IEEE
802.15). These will allow the connectivity of personal devices within an area
of about 30 feet. However, IR requires a direct line of site and the range is
less.
26. 4. WWANS: Wireless Wide Area Networks:- These types of networks can be
maintained over large areas, such as cities or countries, via multiple satellite
systems or antenna sites looked after by an ISP. These types of systems are
referred to as 2G (2nd Generation) systems.
