Ieee 802.11R - Siemens SIMATIC NET System Manual

Frame aggregation
With IEEE 802.11n/ac, it is possible to bundle together individual frames to form one larger
frame, a process referred to as frame aggregation. There are two types of frame
aggregation:
● Aggregated MAC Service Data Unit (A-MSDU)
Multiple MSDU frames with the same destination address are bundled and sent as one A-
MSDU. This reduces the network load. Due to their shorter maximum length, A-MSDUs
are mainly suitable for bundling several shorter frames.
● Aggregated MAC Protocol Data Unit (A-MPDU)
Multiple MPDU frames with the same destination address are bundled and sent as one
large A-MPDU. This allows the total throughput to be increased.
The SCALANCE W devices support both types of frame aggregation. You make the settings
on the WBM page "AP 802.11n/ac".
Maximum ratio combining (MRC)
In a multiple antenna system, the wireless signals are received by the individual antennas
and combined to form one signal. The MRC method is used to combine the wireless signals.
The MRC method weights the wireless signals according to their signal-to-noise ratio and
combines the wireless signals to form one signal. The signal-to-noise ratio is improved, and
the error rate is reduced.
1.5.6

IEEE 802.11r

During roaming, the WLAN client roams from one access point to the next. A delay time of
several 100 ms can come about at the connection transition.
The following steps can be executed during this time:
● Client searches for a new access point (scanning)
● Logon at a new access point (authentication and association)
● Allow a data connection via the new access point
Shorter delay times are required for time-critical applications, for example, Voice over IP.
The standard IEEE 802.11r contains amendments which optimize roaming and therefore is
also referred to as Fast BSS Transition (FT).
With FT, the WLAN client must not authenticate every time the access point changes. For
this purpose, the access points are grouped into a mobility domain. The WLAN client
receives the mobility domain ID from the first access point to which it logs on. The log-on
information is buffered within the mobility domain. This logon is valid for all members of the
mobility domain.
Based on the ID, the WLAN client recognizes whether the access point is a member of the
same mobility domain and can therefore log on without delay. Only WLAN clients with IEEE
802.11r support can use the improved roaming or handover functions.
Industrial Ethernet
System Manual, 09/2019, C79000-G8976-C242-10
Basics of communication with Industrial Ethernet
1.5 Wireless LAN
57