Industrial, Scientific, and Medical (ISM) Bands :-
The ISM bands are defined by the ITU Telecommunication Standardization Sector (ITU-T). The IEEE 802.11 standard and the subsequent 802.11b and 802.11g amendments all define communications in the frequency range between 2.4 GHz and 2.4835 GHz. This frequency range is one of three frequency ranges called as the Industrial, Scientific, and Medical (ISM) bands. The ISM bands are as follows:
*902–928 MHz (26 MHz wide)
*2.4000–2.4835 GHz (83.5 MHz wide)
*5.725–5.875 GHz (150 MHz wide)
The 900 MHz band is known as the Industrial band, the 2.4 GHz band is known as the Scientific band, and the 5.8 GHz band is known as the Medical band. All three of these bands are license-free bands and there are no restrictions on what types of equipment can be used in any of them. For example, a radio card used in medical equipment can be used in the 900 MHz Industrial band.
900 MHz ISM Band :-
The 900 MHz ISM band is 26 MHz wide and spans from 902 MHz to 928 MHz. 900 MHz frequency range has already been allocated to the Global System for Mobile Communications (GSM) cellular phones.
Although the 900 MHz ISM band is rarely used for networking, many products such as baby monitors, wireless home telephones, and wireless headphones make use of this frequency range.802.11 radio cards do not operate in the 900 MHz ISM band, but many older legacy deployments of wireless networking did operate in the 900 MHz ISM band.
2.4 GHz ISM Band :-
The 2.4 GHz ISM band is currently the most common band used for wireless networking
communications. The 2.4 GHz ISM band is 83.5 MHz wide and spans from 2.4000 GHz to
2.4835 GHZ. Use of the 2.4 GHz ISM is defined under the original 802.11 standard as well
as two of the three major 802.11 networking amendments: 802.11 , 802.11b , 802.11g.
The 2.4 GHz ISM band is also used by microwave ovens, cordless home telephones, baby monitors, and wireless video cameras. The 2.4 GHz ISM band currently is heavily used and one of the big disadvantages of using 802.11b/g radios is the potential for interference.
5.8 GHz ISM Band :-
The 5.8 GHz ISM band is 150 MHz wide and spans from 5.725 GHz to 5.875 GHz. As with
the other ISM bands, the 5.8 GHz ISM band is used by many of the same types of consumer products: baby monitors, cordless telephones, and cameras. The IEEE 802.11a amendment actually defines the use of the 5 GHz Unlicensed National Information Infrastructure (UNII) Bands. Due to the different FCC power requirements, the 5.8 GHz ISM band is a preferred spectrum for long distance wireless bridging.
Unlicensed National Information Infrastructure Bands (UNII) :-
The IEEE 802.11a amendment assigns data transmissions within the frequency space
of the 5 GHz UNII bands. The 802.11a amendment uses three groupings, or bands, of
UNII frequencies, often called as the lower, middle, and upper UNII bands. These three
bands are designated as UNII-1 (lower), UNII-2 (middle), and UNII-3 (upper). All three bands are 100 MHz wide.
The commonly used UNII bands are as follows:
*UNII-1 Lower 5.15–5.25 GHz
*UNII-2 Middle 5.25–5.35 GHz
*UNII-3 Upper 5.725–5.825 GHz