2 APPENDIX
Glossary
Ad hoc mode
A type of network for wireless LAN communications. In this mode a network is easily built because no access point is required. However, this mode is not available for multiple simultaneous communications due to its poor extensibility; in other words, it is unsuitable for wireless LAN communication connecting many devices.
AP (Access Point)
Stands for Access Point. Access points are required to relay terminals for a communication in the Infrastructure mode, explained later in this section.
Channel
A segment for 2.4 GHz frequency bandwidth for wireless LAN communications. When more than one access point exists in a narrow area in the Infrastructure mode, different channels are required for each in order to avoid radio wave interference. Communications among devices with different channels are not available even if their SSIDs (explained later in this section) are the same.
CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance)
A type of access controlling method for wireless LAN communications. In this method terminals constantly monitor their communication status with each other. When one terminal is communicating, others stop their communications and wait until they confirm that an available access route comes up, in order to avoid the collision of communication signals as much as possible.
DSSS (Direct Sequence Spread Spectrum)
A type of signal transmission system for wireless LAN communications. As one of the characteristics of this system, less noise occurs during communication and thus DSSS communication interferes with other communications less, because signals are spread to a wide spectrum with a small amount of electric power. Also this system uses the Pseudo Noise Code for the modulation and demodulation of signals, so a confidential communication with less risk of being intercepted is available.
IEEE (Institute of Electrical and Electronics Engineers)
An organization that promotes studies for electronic related fields. The major activities of IEEE are holding academic conferences and publishing technical papers. Also its internal committees establish and recommend technical standards. The IEEE802 LAN/MAN Standard Committee of IEEE is in charge of technical standards for wireless LAN communications.
IEEE802.11b / IEEE802.11g
Technical standards established by IEEE for wireless LAN communications with a 2.4 GHz frequency bandwidth.
Infrastructure mode
A type of network for wireless LAN communications. This mode is suitable for a wireless LAN communication connecting more than one device because a simultaneous communication among these devices is available by installing access points. Also interface ports embedded in each access point can extend the range of communication by integrating wireless LAN and wired LAN.
OFDM (Orthogonal Frequency Division Multiplexing)
A type of communication system for wireless LAN communications. This is one of the
PMK (Pairwise Master Key) cache
A function to cache PMKs, base information for encryption keys, to multiple access points. By caching the PMKs, the period of time for authentication is greatly reduced for a terminal which once succeeded its authentication. Therefore in a case in which an access point is switched during communication due to the movement of a terminal, for example, the period for which the communication is paused will be minimized.
PSK
“PSK” is a preset encryption key shared with terminals and “passphrase” is a character string required for PSK authentication. A passphrase consists of a number of words (phrase), while a general password is only a short single word. This means passphrases have a stronger tolerance toward security invasion than passwords.
RADIUS (Remote Authentication Dial In User Service)
A protocol for network service authentication. This protocol originally developed for authentication for
52 Glossary
