802.11 Fundamentals

802.11 is a family of specifications adopted by the Institute of Electrical and Electronics Engineers (IEEE) for implementing wireless LANs. 802.11 is similar to the IEEE 802.3 Ethernet standard in that it maps to Layer 2 and Layer 1 protocols and services.¹ With Ethernet CSMA/CD technology, wireless nodes address each other using MAC addresses, which are embedded into the compatible network cards. However, 802.11 does not rely on wires for carrying signals on Layer 1. This means that 802.11-compliant nodes can wirelessly communicate with each other within a range defined by the specifications and supported by their wireless equipment. Because the wireless aspect of communications is limited to the media access and physical layers, higher-level protocols such as IP, TCP, and UDP do not need to be aware that datagrams are transported without wires.

802.11 networks that are most frequently deployed within companies require the use of one or more access points (APs). An AP is a device that facilitates wireless communications between 802.11 nodes and bridges the organization's wireless and wired networks. In this configuration, known as infrastructure mode, wireless nodes must go through the AP when communicating with each other and with nodes on the wired network. Alternatively, wireless networks can be deployed using an ad hoc topology, in which case participating 802.11 nodes communicate directly with each other on a peer-to-peer basis.²

Three main types of 802.11 networks are in use today:

• 802.11b This was the first standard to really catch on for wireless networking. It runs at 11Mbps, uses a wireless frequency of 2.4GHz, and has a range of up to 300 feet. It is also the most common 802.11 network type. A need for transfer speeds greater than 11Mbps created demand for 802.11a equipment.

• 802.11a 802.11a network components run at an improved bandwidth of 56Mbps and use a broadened frequency range of 5GHz, which causes fewer conflicts with typical appliances such as cordless phones and microwaves. The 802.11a specification allows for up to 12 simultaneous communication channels, as opposed to the three channels of the 2.4GHz standards, thus equaling support of a greater number of stations per wireless network. However, because it uses a different frequency range, 802.11a offers no built-in compatibility with already deployed 802.11b equipment. Also, 802.11a equipment is much pricier and has a decreased range over its 2.4GHz counterparts (about 50 feet at the full 54Mbps).

• 802.11g Many people have waited to fulfill their wireless bandwidth requirements with the 802.11g standard. With a speed of 56Mbps and using the 2.4GHz frequency range, 802.11g equipment is backward compatible with the more popular 802.11b standard and offers a similar distance range of up to 300 feet, allowing full 54Mbps speeds at as far as about 100 feet. 802.11g equipment offers the speed of 802.11a, at a more competitive price and with backward compatibility with 802.11b, making for a much easier and inexpensive upgrade path.