Details for the data transfer over the logical interface are set on the 'Transmission' tab.
LANconfig: Wireless LAN / General / Logical WLAN settings / Transmission
WEBconfig: LCOS menu tree / Setup / Interfaces / WLAN / Transmission
- Packet size Smaller data packets cause fewer transmission errors than larger packets, although the proportion of header information in the traffic increases, leading to a drop in the effective network load. Increase the factory value only if your wireless network is largely free from interference and very few transmission errors occur. Reduce the value to reduce the occurrence of transmission errors.
- Minimum and maximum transmit rate The access point normally negotiates the data transmission speeds with the connected WLAN clients continuously and dynamically. The access point adjusts the transmission speeds to the reception conditions. As an alternative, you can set fixed values for the minimum and maximum transmission speeds if you wish to prevent the dynamic speed adjustment.
- Modulation Coding Scheme (MCS)
A specific MCS number denotes a unique combination from the modulation
of the individual carriers (BPSK, QPSK, 16QAM, 64QAM), coding rate (i. e.
proportion of error correction bits in the raw data and number of spatial
streams. 802.11n uses this term instead of the term "data rate" used
in older wireless LAN standards because data rate is no longer an unequivocal
description.
The MCS selection therefore indicates the type and minimum or maximum number of modulation parameters that should be used for one or two spatial data streams. Within these limits, the appropriate MCS is selected when the connection is established depending on the current conditions and may be adapted during the connection if required. This also defines the maximum attainable data throughput, indicated in the last column of the table (here for the short guard interval GI = 0.4 µs using the 40 MHz channel).
MCS index Data streams Modulation Coding rate Data throughput (GI=0.4 µs, 40 MHz) 0 1 BPSK 1/2 15 1 1 QPSK 1/2 30 2 1 QPSK 3/4 45 3 1 16QAM 1/2 60 4 1 16QAM 3/4 90 5 1 64QAM 1/2 120 6 1 64QAM 3/4 135 7 1 64QAM 5/6 150 8 2 BPSK 1/2 30 9 2 QPSK 1/2 60 10 2 QPSK 3/4 90 11 2 16QAM 1/2 120 12 2 16QAM 3/4 180 13 2 64QAM 1/2 240 14 2 64QAM 3/4 270 15 2 64QAM 5/6 300 - Broadcast rate The defined broadcast rate should allow the slowest clients to connect to the WLAN even under poor reception conditions. A higher value should only be set here if all clients are able to connect "faster".
- Number of spatial streams
The spatial multiplexing function allows several separate data streams
to be transmitted over separate antennas in order to increase data throughput.
The use of this function is only recommended when the remote device can
process the data streams with corresponding antennas.
Note: With the 'Auto' setting all spatial streams that are supported by the wireless LAN module in question are used.
- RTS threshold
The RTS threshold prevents the occurrence of the "hidden station“
phenomenon.
Here, the three access points , , and are positioned such that no direct wireless connection between the two outer devices is possible. If sends a packet to , is not aware of this as it is outside of 's coverage area. may also try, during the transmission from , to send a packet to as well, because has no knowledge of the medium (in this case the wireless connection) being blocked. A collision results and neither of the transmissions from nor to will be successful. The RTS/CTS protocol is used to prevent collisions.To this end, precedes the actual transmission by sending an RTS packet to , that answers with a CTS. The CTS sent by is now within "listening distance" of , so that can wait with its packet for . The RTS and CTS signals each contain information about the time required for the transmission that follows. A collision between the very short RTS packets is improbable, although the use of RTS/CTS leads to an increase in overhead. The use of this procedure is only worthwhile where long data packets are being used and the risk of collision is higher. The RTS threshold is used to define the minimum packet length for the use of RTS/CTS. The best value can be found using trial and error tests on location.Note: The RTS/CTS threshold value also has to be set in the WLAN client, as far as the driver and/or operating system allow this.
- Long preamble for 802.11b Normally, the clients in 802.11b mode negotiate the length of the preamble with the access point. "Long preamble" should only be set when the clients require this setting to be fixed.
- Short guard interval This option is used to reduce the transmission pause between two signals from 0.8 µs (default) to 0.4 µs (short guard interval). This increases the effective time available for data transmission and thus the data throughput. However, the wireless LAN system becomes more liable to disruption that can be caused by interference between two consecutive signals. The short guard interval is activated in automatic mode, provided that the remote station supports this. Alternatively the short guard mode can be switched off.
- Frame aggregation Frame aggregation is used to combine several data packets (frames) into one large packet and transmit them together. This method serves to reduce the packet overhead, and the data throughput increases. Frame aggregation is not suitable when working with mobile receivers or time-critical data transmissions such as voice over IP.
- Hard retries This value defines the number of times that the hardware should attempt to send packets before a Tx error message is issued. Smaller values mean that a packet which cannot be sent blocks the sender for less time.
- Soft retries If the hardware was unable to send a packet, the number of soft retries defines how often the system repeats the attempt to transmit. The total number of attempts is thus (soft retries + 1) * hard retries. The advantage of using soft retries at the expense of hard retries is that the rate-adaption algorithm immediately begins the next series of hard retries with a lower datarate.