A keypunch or key punch is a device used for precisely punching holes in specific locations on a stiff card. It was used in conjunction with early punched card computers. The punched card served as the program instruction for the computer. The locations of the punches were determined by the keys being struck by a human operator, much like typing...
802.11e is an amendment to 802.11 standards, which defines a set of quality of service (QoS) for wireless LAN applications through alterations to the media access control layer. It also provides essential services for delay sensitive applications, such as streaming video and Voice over Internet Protocol (VoIP). It corresponds to the Wi-Fi multimedia certification of the Wi-Fi Alliance.
802.11e offers subscribers high speed internet access with VoIP, full motion video and high quality audio. Networks using 802.11e operate at radio frequencies ranging between 2.4 GHz and 2.4835 GHz or between 5.75 GHz and 5.850 GHz. This higher frequency ranges accounts for advantages such as more channels, fast data transfer speeds and less chances of interference.
802.11e is an enhancement to 802.11q and 802.11b wireless LAN specifications. It provides QoS features prioritizing video transmissions, data and voice. It also enhances the MAC layer with coordinated time division multiple access construct and add up error correcting mechanisms for delay sensitive applications. This standard also provides interoperability between home, business and public environments
The 802.11e standard has backward compatibility with distributed coordination function and point coordination function, which are supported by hybrid coordination function (HCF) and enhanced distribution coordination function (EDCF). Stations operating under 802.11e are called enhanced stations, which work optionally as a centralized controller for other stations and are referred to as a hybrid coordinators.
The hybrid coordination function provides a policing and deterministic channel access by controlling channels through the hybrid coordinator. The HCF model provides guaranteed services with much higher probability. Its uses signaling protocol to facilitate admission control and specifies the service rate requirement.
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