SEMINAR ON :
Wireless LANs(WLAN)-IEEE 802.11
PRESENTED BY :
ABHISHEK G - 4KV13EC002
CHANDRASHEKAR P R - 4KV14EC402
Basic Service Set (BSS)
Extended Service Set (ESS)
. Wireless LANs-IEEE 802.11
Wireless communication is one of the fastest-growing technologies.
WLAN is a wireless computer network that links two or more devices using a wireless
distribution method within a limited area
Wireless LANs can be found on college campuses, in office buildings, and in many public areas.
IEEE 802.11 wireless LANs, sometimes called wireless Ethernet.
There are three specification in the family : 802.11, 802.11a and 802.11b .All three specification
Use CSMA/CD as the path sharing protocol
• 802.11 LAN is based on a cellular
• The system is divided into cell. Each cell is
control by base station.
• Cell is called as Basic Service Set (BSS)
and base station is Acess Point (AP).
• Set of BSS can be interconnected by a
distribution system to form an Extended
Service Set (ESS).
• Each BSS has an access point.
• An ESS can also provide gateway access
for wireless users into a wired network such
• The standard also defines concept of a
Portal. Portal is a interconnects between an
802.11 and another 802LAN.
TYPES OF 802.11x
Standard Speed Range Range(meter) Frequency
802.11b 11 Mbps 150 Feet 45.72 M 2.4 GHz
802.11g 54 Mbps 50 Feet 15.24 M 2.4 GHz
802.11a* 54 Mbps 50 Feet 15.24 M 5 GHZ
802.11n 300 Mbps
175 Feet 51.85 M 2.4/5 GHZ
Topics discussed in this section:
- Architecture of IEEE 802.11
- MAC Sublayer of IEEE 802.11
- Physical Layer of IEEE 802.11
Architecture of IEEE 802.11
- The standard defines two kinds of services
a. Basic service set (BSS)
b. Extended service set (ESS).
1. Basic Service Set (BSS)
• IEEE 802.11 defines the basic service set (BSS) as the building block of a wireless LAN.
• A BSS defines as a group of stations that co-ordinates their access to the medium under a given instance of
the medium access control.
• A basic service set is made of stationary or mobile wireless stations and an optional
• Each BSS has an Access Point (AP)
• central base station, known as the access point (AP).
Figure 1.25 Basic service sets (BSSs)
NOTE: BSS without an AP is called an ad hoc network
BSS with an AP is called an infrastructure network
2. Extended Service Set (ESS)
• An extended service set (ESS) is made up of two or more BSSs with APs.
• In this case, the BSSs are connected through a distribution system, which is usually a
• wired LAN.
• The distribution system connects the APs in the BSSs.
• IEEE 802.11 does not restrict the distribution system; it can be any IEEE LAN such as
• Note that the extended service set uses two types of stations: mobile and stationary.
• The mobile stations are normal stations inside a BSS. The stationary stations are AP
stations that are part of a wired LAN
Figure 1.26 Extended service sets (ESSs)
IEEE 802.11 defines three types of stations based on their mobility in a wireless LAN.
- No-transition: A station with no-transition mobility is either stationary (not moving) or
moving only inside a BSS
- BSS transition: Station with BSS-transition mobility can move from one BSS to
another, but the movement is confined inside one ESS.
- ESS-transition mobility: A station with ESS-transition mobility can move from one
ESS to another. However, IEEE 802.11 does not guarantee
that communication is continuous during the move.
MY SINCERE THANKS TO
PROFESSOR SURESHA V
Thank you Sir for sharing your
gifts of teaching with us and
Thanking you for your Guidance