Standards

The original 802.11-1997 standard assumed data transmission rates of up to 2 Mbps. Since then, several versions of the standard have come into practical use:

• 802.11a, at up to 54 Mbps at frequencies in the 5 GHz range

• 802.11b, at up to 11 Mbps at frequencies in the 2.4 GHz range

• 802.11g, at up to 54 Mbps at frequencies in the 2.4 GHz range

• 802.11n draft standard, at up to five times the performance and up to twice the range compared to the earlier Apple 802.11g standard implementation

802.11a provides for transmission rates up to 54 Mbps, and the 5 GHz range offers more bandwidth and less congestion than the 2.4 GHz range. One serious drawback of the 5 GHz range is that its use is restricted in several countries, often to military purposes. Signal propagation at higher frequencies can also be problematic; signals do not travel as far, they drop off rapidly, and they are less able to penetrate walls. Although the restricted market made devices more expensive, the transmission speed made 802.11a attractive to enterprise markets.

802.11b uses the popular 2.4 GHz frequency band. Frequencies within this band (with minor variations in certain countries) are available for wireless networking worldwide. With a worldwide market, conformant devices soon became affordable, spurring rapid adoption of 802.11b. One drawback, however, is that other devices such as cordless phones and microwaves can cause interference and congestion in this band.

802.11g is rapidly growing in popularity. It is backward-compatible with 802.11b, uses the same 2.4 GHz range, but provides for transmission rates up to 54 Mbps.

802.11n is based on the current draft standard specification. It adds technology called multiple-input multiple-output (MIMO), a signal processing and smart antenna technique for transmitting multiple data streams through multiple antennas. For additional information, refer to Apple's 802.11 site.

Topology

The nature of wireless networks presents numerous challenges not common to wired networks. Computers using the WLAN may be portable (typically used at one physical location while within the coverage area of a network access point) or even mobile (moving in and out of the coverage area or even between coverage areas of different network access points. The size and boundaries of the WLAN can be indeterminate and mutable due to environmental factors. Foreign radio signals can interfere with reception. And non-authorized devices can receive network traffic without a physical connection.

The 802.11 standard is designed to fit within the IEEE’s 802 family of LAN standards, particularly to allow efficient integration of WLANs and wired LANs. To this end, it defines the services that Wi-Fi equipment must provide to implement the physical and data link layers of the Open Systems Interconnect (OSI) network model so that they accommodate the special requirements of wireless networking. A network device that implements both the medium access control (MAC) and the physical interface (PHY) layers in conformance with 802.11 is known as a station. A station that connects other stations via distribution services is known as an access point. A device that provides a WLAN interface to a non-802.11 LAN is known as a portal; it is said to integrate the WLAN and the wired LAN. A single device can serve as both an access point and a portal.

Data Security

AirPort Extreme has several features designed to maintain the security of the user's data:

• In 802.11b mode, the system uses direct-sequence spread-spectrum (DSSS) technology that uses a multibit spreading code that effectively scrambles the data for any receiver that lacks the corresponding code.

• The system can use an Access Control List of authentic network client ID values (wireless and MAC addresses) to verify each client’s identity before granting access to the network.

• When communicating with a base station, AirPort Extreme uses 64-bit and 128-bit Wired Equivalent Privacy (WEP) encryption and Wi-Fi Protected Access (WPA) personal and enterprise modes to encode data while it is in transit. Additional security features may be available via software or firmware upgrades as 802.11 enhancements are ratified by IEEE.

• The AirPort Extreme Base Station can be configured to use NAT (Network Address Translation), protecting data from Internet hackers.

• The AirPort Extreme Base Station can authenticate users by their unique Ethernet IDs, preventing unauthorized computers from logging into your network. Network administrators can take advantage of RADIUS compatibility, used for authenticating users over a remote server. Smaller networks can offer the same security using a local look-up table located within the base station.

As an additional data security measure, Virtual Private Network (VPN) can be used in conjunction with the AirPort Extreme data security.

AirPort Extreme Hardware

AirPort Extreme provides a media access controller (MAC), a digital signal processor (DSP), and a radio-frequency (RF) section in a fully-integrated, wireless LAN module compliant with the IEEE 802.11g standard using both OFDM (orthogonal frequency-division multiplexing) and DSSS technologies. Using DSSS, AirPort Extreme is interoperable with PC-compatible wireless LANs that conform to the 802.11b standard at speeds of 11 Mbps, 5.5 Mbps, 2 Mbps, and 1 Mbps. Using OFDM, AirPort Extreme is compatible with all 802.11g standard speeds. Current implementation of AirPort Extreme is based on an IEEE 802.11n draft specification and is compatible with IEEE 802.11a, IEEE 802.11b, and IEEE 802.11g.

AirPort Extreme Software

The following software is provided to set up and use AirPort Extreme:

• AirPort Setup Assistant, an easy-to-use program that guides users through the steps necessary to set up AirPort Extreme or set up an AirPort Extreme Base Station.

• AirPort status menu, which users can use to switch between wireless networks and to create and join peer-to-peer networks.

• AirPort Admin Utility, a utility for advanced users and system administrators. With it the user can edit the administrative and advanced settings needed for some advanced configurations.

• AirPort Extreme enabler software, enables 802.11n draft standard in supported products.