Wireless Standard Facts

Wireless Standard Facts

The original 802.11 specification operated in the 2.4 GHz range and provided up to 2 Mbps. Additional IEEE subcommittees have further refined wireless networking. Three of the most common standards as well as a new standard in draft stage are listed in the following table:

Specification	Standard
	802.11a	802.11b	802.11g	802.11n
Frequency	5 GHz (U-NII)	2.4  GHz (ISM)	2.4 GHz (ISM)	2.4 GHz (ISM) or 5 GHz (U-NII)
Maximum speed	54 Mbps	11 Mbps	54 Mbps	600 Mbps
Maximum range	150 Ft.	300 Ft.	300 Ft.	1200 Ft.
Channels (non-overlapped)	23 (12)	11 (3)	11 (3)	2.4 GHz--23 (12 or 6) 5 GHz--11 (3 or 1)
Modulation technique	OFDM	DSSS, CCK, DQPSK, DBPSK	DSSS (and others) at lower data rates At higher data rates, OFDM, QPSK, BPSK	OFDM and others, depending on implementation
Backwards-compatibility	N/A	No	With 802.11b	With 802.11a/b/g, depending on implementation

Be aware of the following regarding the wireless network implementation:

• The actual speed depends on several factors including distance, obstructions (such as walls), and interference.
• The actual maximum distance depends on several factors including obstructions, antenna strength, and interference. For example, for communications in a typical environment (with one or two walls), the actual distance would be roughly half of the maximums.
• The speed of data transmission decreases as the distance between the transmitter and receiver increases. In other words, in practice, you can get the maximum distance or the maximum speed, but not both.
• Some newer 802.11a or 802.11g devices provide up to 108 Mbps using 802.11n pre-draft technologies (MIMO and channel bonding).
• The ability of newer devices to communicate with older devices depends on the capabilities of the transmit radios in the access point. For example:
  • Some 802.11n devices can transmit at either 2.4 GHz or 5 GHz. This means that the radio is capable of transmitting at either frequency. However, a single radio cannot transmit at both frequencies at the same time.
  • Most 802.11g devices can transmit using DSSS, CCK, DQPSK, and DBPSK for backwards compatibility with 802.11b devices. However, the radio cannot transmit using both DSSS and OFDM at the same time.

This means that when you connect a legacy device to the wireless network, all devices on the network operate at the legacy speed. For example, connecting an 802.11b device to an 802.11n or 802.11g access point slows down the network to 802.11b speeds.

• A dual band access point can use one radio to transmit at one frequency, and a different radio to transmit at a different frequency. For example, you can configure many 802.11n devices to use one radio to communicate at 5 GHz with 802.11a devices, and the remaining radios to use 2.4 GHz to communicate with 802.11n devices. Dual band 802.11a and 802.11g devices are also available.

 

Credit: Testout 640-802 CCNA Notes