AirConnect devices use radio signals to transmit and receive data without wires. You can communicate with the network by establishing radio links between wireless clients and APs.
AirConnect uses Quadative Phase Shift layered modulation (QPSK) to transmit digital data from one device to another. Using QPSK, a radio signal begins with a carrier signal that provides the base or center frequency. The digital data signal is superimposed on the carrier signal in process called "modulation." The radio signal then travels through the air as electromagnetic waves. A receiving antenna in the path of the waves absorbs them as electrical signals. The receiving device "demodulates" the signal by removing the carrier signal. This demodulation results in the original digital data.
AirConnect uses its environment (the air and certain other objects) as the transmission medium. AirConnect radio devices transmit in the 2.4-2.5 GHz frequency range, a license-free range throughout most of the world. The actual range your AirConnect network operates at is country-dependent.
AirConnect devices, like other Ethernet devices, have unique, hardware-encoded Media Access Control (MAC), or IEEE, addresses. MAC addresses determine the device sending or receiving data. A MAC address is a 48-bit number written as six hexadecimal bytes separated by colons. A typical MAC address might be:
The AP MAC address is printed on the bottom of the unit, as shown below.
The AP establishes an average communication range with wireless clients called a Home Service Area (HSA), or cell. When a wireless client is in a particular cell, the wireless client associates and communicates with the AP in that cell. Each cell has a Home Service Area Identifier (HSA_ID). Under the 802.11 standard, the MAC address of an AP represents its HSA_ID. The wireless client recognizes the AP it associates with using the HSA_ID. Adding APs to a LAN establishes more cells in an environment, creating a wireless network using the same NET_ID. This type of network is called a Wireless LAN Service Area (WSA), as shown below.
APs with the same WLAN service area define a coverage area. The wireless client searches for APs with a matching wireless LAN service area and synchronizes with an AP to establish communications. This allows wireless clients within the coverage area to roam between AP cells. As you roam from cell to cell, your wireless client switches APs. The switch occurs when the wireless client analyzes the reception quality at a particular location and selects an AP to communicate with, based on such factors as signal strength and wireless client load.
When the wireless client begins to lose the signal as it moves away from an associated AP, it performs a scan to find another AP. As wireless clients switch APs, the AP updates the association table. Roaming is invisible to the user.
The network administrator assigns the wireless LAN system area for the APs in a WSA. A valid wireless LAN system area is an alphanumeric, case-sensitive identifier of up to 32 characters. All nodes within one LAN use the same wireless LAN system area to communicate on the LAN. Multiple wireless LANs can coexist in a single environment by assigning different wireless LAN system areas for the corresponding APs.
This protocol creates a loop-free topography with exactly one path between every LAN. This is the shortest path from the Root AP to each AP and LAN. If an AP or LAN fails, a new route is calculated and added to the tree. All packet forwarding follows the spanning tree. APs have to choose one AP as the Root AP. The same holds true for WLAPs associating with the root AP or another AP connected to the Ethernet LAN to prevent forming loops.
For optimal performance, place wireless clients and APs away from transformers, heavy-duty motors, fluorescent lights, microwave ovens, refrigerators and other industrial equipment.
Signal loss can occur when metal, concrete, brick, walls or floors block transmission. Locate antennas in open areas or add additional APs as needed to improve coverage.
A site survey analyzes the installation environment and provides users with recommendations for the number and placement of APs. 3Com recommends that a site survey be conducted at any new site prior to installing AirConnect equipment.
To improve AP management and performance, users need to understand basic AP functionality and configuration options. The AP includes features for different interface connections and network management.
The AP provides MAC layer bridging between its interfaces. The AP monitors traffic from its interfaces and, based on frame address, forwards the frames to the proper destination. The AP tracks the frames sources and destinations to provide intelligent bridging as wireless clients roam or network topologies change. The AP also handles broadcast and multicast message initiations and responds to wireless client association requests.