WLAN most common terms

In WLAN we use some common terms in explaning any scenarios. Below are the some of the most common terms that will be used in most of the time.

1. Basic Service Set (BSS)
2. Extended Service Set (ESS)
3. Independent Basic Service Set (IBSS)
4. Service Set Identifier(SSID)
5. Infrastructure mode
6. Adhoc Mode
7. Roaming


1. Basic Service Set (BSS)

     When one access point is connected to a wired network and a set of
wireless stations, the network configuration is referred to as a basic
service set (BSS).  A basic service set consists of only one access point
and one or more wireless clients, as shown in Figure .  A basic service
set uses "infrastructure mode" , a mode that requires use of an access point
and in which all of the wireless traffic traverses the access point.  No
direct client-to-client transmissions are allowed

2. Extended Service Set (ESS)

   An extended service set is defined as two or more basic service sets
connected by a common distribution system, as shown in Figure.
The distribution system can be either wired, wireless, LAN, WAN, or any
other method of network connectivity.  An ESS must have at least 2
access points operating in infrastructure mode.  Similar to a BSS, all
packets in an ESS must go through one of the access points.

3.Independent Basic Service Set (IBSS)

   An independent basic service set is also known as an "Ad hocnetwork".  An
IBSS has no access point or any other access to a distribution system, but
covers one single cell and has one SSID, as shown in Figure.  The
clients in an IBSS alternate the responsibility of sending beacons since
there is no access point to perform this task.
 

4. Service Set Identifier(SSID)

   The "Service set identifier" (SSID) is a unique, case sensitive, alphanumeric
value from 2-32 characters long used by wireless LANs as a network
name.  This naming handle is used for segmenting networks and in the process of joining a network.
The SSID value is sent in beacons, probe requests, probe responses, and other types of frames.  A client station must be configured for the correct
SSID in order to join a network.  The administrator configures the SSID
(sometimes called the ESSID) in each access point


5. Infrastructure mode
 
      In  "infrastructure mode" will use  an access point
and in which all of the wireless traffic traverses the access point.  No
direct client-to-client transmissions are allowed.

6. Adhoc Mode

          In this mode there will be no "Accesspoint" in that network. Communication will happen between the clients only directly.
Clients will send beacons between them for syncronization between them .


7. Roaming

   Roaming is the process or ability of a wireless client to move seamlessly
from one cell (or BSS) to another without losing network connectivity.
Access points hand the client off from one to another in a way that is
invisible to the client, ensuring unbroken connectivity.  Figure
illustrates a client roaming from one BSS to another BSS.
When any area in the building is within reception range of more than one
access point, the cells' coverage overlaps.  Overlapping coverage areas
are an important attribute of the wireless LAN setup, because it enables
seamless roaming between overlapping cells.  Roaming allows mobile
users with portable stations to move freely between overlapping cells,
constantly maintaining their network connection