D-Link DWL-2200AP Инструкция по эксплуатации онлайн [100/192] 41488

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Each frame includes a source and destination MAC address, a control field with protocol
version, frame type, frame sequence number, frame body (with the actual information to
be transmitted) and frame check sequence for error detection.
The 802.11 standard defines various frame types for management and control of the
wireless infrastructure, and for data transmission. 802.11 frame types are (1) management
frames, (2) control frames, and (3) data frames. Management and control frames (which
manage and control the availability of the wireless infrastructure) automatically have
higher priority for transmission.
802.11e uses interframe spaces to regulate which frames get access to available channels
and to coordinate wait times for transmission of different types of data.
Management and control frames wait a minimum amount of time for transmission; they
wait a short interframe space (SIF). These wait times are built-in to 802.11 as infrastructure
support and are not configurable.
The D-Link DWL-2210AP supports the Distribution Coordination Function (DCF) as defined
by the 802.11e standard. DCF, which is based on CSMA/CA protocol, defines the
interframe space (IFS) between data frames. Data frames wait for an amount of time
defined as the DCF interframe space (DIF) before transmitting.
This parameter is configurable.
(Note that sending data frames in DIFs allows higher priority management and control
frames to be sent in SIFs first.)
The DCF ensures that multiple access points do not try sending data at the same time
but instead wait until a channel is free.
Random Backoff and Minimum / Maximum Contention Windows
If an access point detects that the medium is in use (busy), it uses the DCF random
backoff timer to determine the amount of time to wait before attempting to access a
given channel again. Each access point waits some random period of time between
retries. The wait time (initially a random value within a range specified as the Minimum
Contention Window) increases exponentially up to a specified limit (Maximum Contention
Window). The random delay avoids most of the collisions that would occur if multiple
APs got access to the medium at the same time and tried to transmit data simultaneously.
The more active users you have on a network, the more significant the performance
gains of the backoff timer will be in reducing the number of collisions and retransmissions.
Configuring Queues for Qualty of Service (QoS)

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