Investigating Whether The 802.11E Wlan Qos Standard Provides Optimal Performance In Converged Networks
Basic Service Set (BSS): A set of stations (STAs) that have successfully synchronized using the JOIN service primitives11 and one STA that has used the START primitive. Membership in a BSS does not imply that wireless communication with all other members of the BSS is possible. Coordination Function: The logical function that determines when a station (STA) operating within a basic service set (BSS) is permitted to transmit protocol data units (PDUs) via the wireless medium (WM). The coordination function within a BSS may have one hybrid coordination function (HCF), or it may have one HCF and one point coordination function (PCF) and will have one distributed coordination function (DCF). A quality of service (QoS) BSS will have one DCF and one HCF. Enhanced Distributed Channel Access (EDCA): The prioritized carrier sense multiple access with collision avoidance (CSMA/CA) access mechanism used by quality of service (QoS) stations (STAs) in a QoS basic service set (BSS). This access mechanism is also used by the QoS access point (AP) and operates concurrently with hybrid coordination function (HCF) controlled channel access (HCCA). HCF controlled channel access (HCCA): The channel access mechanism utilized by the hybrid coordinator (HC) to coordinate contention-free media use by quality of service (QoS) stations (STAs) for downlink unicast, uplink, and direct-link transmissions. Hybrid Coordination Function (HCF): A coordination function that combines and enhances aspects of the contention-based and contention-free access methods to provide quality of service (QoS) stations (STAs) with prioritized and parameterized QoS access to the wireless medium (WM), while continuing to support non- QoS STAs for best-effort transfer. The HCF includes the functionality provided by both enhanced distributed channel access (EDCA) and HCF controlled channel access (HCCA). The HCF is compatible with the distributed coordination function (DCF) and the point coordination function (PCF). It supports a uniform set of frame formats and exchange sequences that STAs may use during both the contention period (CP) and the contention-free period (CFP). MAC protocol data unit (MPDU): The unit of data exchanged between two peer MAC entities using the services of the physical layer (PHY). Point Coordination Function (PCF): A class of possible coordination functions in which the coordination function logic is active in only one station (STA) in a basic service set (BSS) at any given time that the network is in operation. Transmission Opportunity (TXOP): An interval of time when a particular quality station (STA) has the right to initiate frame exchange sequences onto the wireless medium is defined by a starting time and a maximum duration. The TXOP is either obtained successfully contending for the channel or assigned by the hybrid coordinator (HC). Quality of Service (QoS): The provisioning of service in which the medium access control (MAC) protocol data units (MPDUs) with higher priority are given a preferential treatment over MPDUs with a lower priority. Prioritized QoS is provided through the enhanced distributed channel access (EDCA) mechanism.
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