RTS and Fragmentation Threshold
Distance and ACK Timeout
Enable Aggregation
Enable Multicast and Extra Reporting
Enable DFS
Sensitivity Threshold
RTS/CTS (Request to Send / Clear to Send) are the mechanism used by the 802.11
wireless networking protocol to reduce frame collisions introduced by the hidden terminal
problem. RTS/CTS packet size threshold is 0-2346 bytes. If the packet size the node wants
to transmit is larger than the threshold, the RTS/CTS handshake gets triggered. If the
packet size is equal to or less than threshold the data frame gets sent immediately.
System uses Request to Send/Clear to Send frames for the handshake that provide collision
reduction for an access point with hidden stations. The stations are sending a RTS frame first while data is sent only after a
handshake with an AP is completed. Stations respond with the CTS frame to the RTS, which provides clear media for the requesting
station to send the data. CTS collision control management has a time interval defined during which all the other stations hold off the
transmission and wait until the requesting station will finish transmission.
Fragmentation Threshold: specifies the maximum size for a packet before data is fragmented into multiple packets. The range is
256-2346 bytes, or word “off”. Setting the Fragmentation Threshold too low may result in poor network performance.
The use of fragmentation can increase the reliability of frame transmissions. Because of sending smaller frames, collisions are much less
likely to occur. However, lower values of the Fragmentation Threshold will result in lower throughput as well. Minor or no modifications of
the Fragmentation Threshold value is recommended while default setting of 2346 is optimum in most of the wireless network use cases.
AirOS v5.3 has a new auto-acknowledgement timeout algorithm, which dynamically optimizes the frame acknowledgement timeout value
without user intervention. This is a critical feature required for stabilizing long-distance 802.11n outdoor links. The user also has the
ability to enter the value manually, but it’s not recommended.
Distance: specify the distance value in miles (or kilometers) using slider or
enter the value manually. The signal strength and throughput falls off with
range. Changing the distance value will change the ACK Timeout to the
appropriate value of the distance.
ACK Timeout: specify the ACK Timeout. Every time the station receives the
data frame it sends an ACK frame to the AP (if transmission errors are absent). If the station receives no ACK frame from the AP within
set timeout it re-sends the frame. The performance drops because of the too many data frames are re-send, thus if the timeout is set too
short or too long, it will result in poor connection and throughput performance.
Changing the ACK Timeout'' value will change the Distance to the appropriate distance value for the ACK Timeout.
Auto Adjust control will enable the ACK Timeout Self-Configuration feature. If enabled, ACK Timeout value will be derived dynamically
using an algorithm similar to the Conservative Rate Algorithm (used in AirOS v3.4). It is very recommended to use Auto Adjust option for
802.11n.
If two or more stations are located at the considerably different distance from the Access Point are associated to, the highest ACK
Timeout for the farthest station should be set at the AP side. AirOS v5.3 includes an improved ACK Timeout algorithm.
Aggregation: A part of the 802.11n standard (or draft-standard). It allows sending
multiple frames per single access to the medium by combining frames together into one
larger frame. It creates the larger frame by combining smaller frames with the same
physical source and destination end points and traffic class (i.e. QoS) into one large frame
with a common MAC header.
Frames – determines the number of frames combined on the new larger frame.
Bytes – determines the size (in Bytes) of the larger frame.
Multicast Data: This option allows all the Multicast packet pass-through functionality. By default this option is disabled.
Enable Extra Reporting: feature will report additional information (i.e. Host Name) in the 802.11
management frames. This information is commonly used for system identification and status
reporting in discovery utilities and Router operating systems.
Enable DFS: DFS is the part of the IEEE 802.11h wireless standard. Enable DFS option allows to
enable/disable DFS support (applicable to M5 series only). DFS may be mandatory in some
regulatory domains and should be tuned according to the regulations of the selected country. Please consult
compliance guide (http://www.ubnt.com/wiki/RF_Compliance) and official regulations authorities for further
explanation of compliance requirements for the country where AirOS v5.3 based device is installed.
Enable Client Isolation: This option allows packets only to be sent from the external
network to the CPE and vice verse (applicable for AP/AP WDS mode only). If the Client
Isolation is enabled wireless stations connected to the same AP will not be able to
interconnect on both layer 2 (MAC) and layer 3 (IP) level. This is effective for the
associated stations and WDS peers also.
Sensitivity Threshold, dBm: defines the minimum client signal level accepted by the AP, for the client to remain associated. Any client
with a signal level lower than that specified will be kicked out. Actually, this feature is helpful to maintain good signal levels within the
stations associated, assuring better overall performance. Unchecking the OFF checkbox disables the feature.
Advanced Ethernet Settings
AirOS 5.3 - Ubiquiti Wiki
http://www.ubnt.com/wiki/AirOS_5.3
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