Friday, April 2, 2010


There are many different types of wireless networks:PAN - Personal Area Network (Bluetooth, Wireless Mouse, etc.)
LAN - Local Area Network (Home Wireless LANs)
MAN - Metropolitan Area Networks (Point-to-Point Wireless Bridges)
WAN - Cellular, 3G HSDPA

A WAP communicates like a hub. It uses a shared signal and is half-duplex. A WAP uses unlicensed bands of RF. You do not have to apply for a permit because it's unmanaged. But if your area is saturated with wireless networks, you can get serious interference and there's no way you can complain. Wireless is prone to connectivity issues because of interference.

Wireless is a Layer 1 and 2 standard. Instead of CSMA/CD, wireless makes use of CSMA/CA. This however does not change the concepts that apply to Ethernet. You can think of wireless as an Ethernet without wires, the IP addresses and MAC addresses still apply.

Wireless cannot detect collisions. Therefore it must use CSMA/CA. This is because wireless cannot send and receive signals at the same time. Clients have to wait for the access points to allow it to send. This is done by preempting the access point.

There are currently three ranges of unlicensed frequencies. These are:
-900MHz Range: 902MHz to 928MHz
-2.4GHz Range: 2.4GHz to 2.483GHz
-5GHz Range: 5.150GHz to 5.350GHz

The lower the frequency, the further range you can get. However, you'll have to sacrifice bandwidth. Unlicensed frequencies are free to be used as long as you do not deliberately launch DoS attacks on the wireless medium. In Europe, there are more unlicensed bands available for use.

RF waves are absorbed (by walls) or reflected (by metal). Higher frequencies of RF allow higher data rates, but have shorter ranges. As you move further away, data rates will drop.

There are four common wireless standards:
-Official as of September 1999
-Up to 11Mbps (1,2,5.5,11)
-Three "clean" channels

-Official as of June 2003
-Backward compatible with 802.11B
-Up to 54Mbps (12 data rates)
-Three "clean" channels

-Official as of September 1999
-Up to 54Mbps
-Not cross-compatible with 802.11B/G
-12 to 23 "clean" channels

-Official as of October 2009
-Up to 150Mbps
-Backward compatible with 802.11A/B/G
-Uses MIMO (Multiple-In Multiple-Out)

Channels are ranges of frequencies. Below is a graph which shows the clean channels:

In typical setups, the goal is to set up access points so that the channels do not overlap. This is the typical wireless cell pattern:

The ITU-R regulates the RF used for wireless transmission. The IEEE maintains the 802.11 wireless transmission standards. The Wi-Fi Alliance ensures certified interoperability between 802.11 wireless vendors.

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