The Extricom WLAN System User Guide
17
Frame Aggregation
Definition:
With MAC-layer aggregation, a station with a number of frames to send can combine
them into an aggregate frame (MAC MPDU). The resulting frame contains fewer headers in
overhead than would be the case without aggregating, and because fewer, larger frames are sent, the
contention time on the wireless medium is reduced.
Extricom 802.11n:
Extricom supports frame aggregation.
Block Acknowledgment
Definition:
Block Acknowledgment works in conjunction with frame aggregation, allowing the
transmitter to request a block ACK for a multiple frame improving overall performance.
Extricom 802.11n:
Extricom supports block acknowledgment.
Operating Modes
Definition:
802.11n defines three modes of operation for 802.11n devices:
1.
Legacy mode – In this mode, the 802.11n radio works in legacy 802.11a/b/g mode only.
2.
Mixed mode – In this mode the 802.11n radio can work with both 802.11n & 802.11a/b/g
clients
3.
Greenfield mode – In this mode the 802.11n radio works only with 802.11n clients.
Extricom 802.11n:
Extricom products support both Legacy and Mixed modes. Currently there is no
support for Greenfield mode. With this release, however, Extricom is introducing a unique feature,
the "
HT Only
" blanket in which a specific Channel Blanket can be configured so that only 802.11n
clients (working in mixed mode) can associate to it. This enables a deployment to support co-
existence of ‘n’ and ‘b/g’ clients, from the same set of APs, but separated on different channels, so
there is no mixed-mode throughput degradation occurs.
Coexistence
Definition:
802.11n is designed to operate with backward compatibility for 802.11b/g/a devices—
the method of operation known as mixed mode that was previously described. 802.11b/g/a, on the
other hand, does not have forward compatibility with 802.11n. Therefore 802.11n must protect
802.11b/g/a stations from 802.11n transmissions that may be interpreted as interference
Extricom 802.11n:
Extricom supports PHY layer protection (L_SIG protection) for OFDM
transmissions (802.11a/g clients). MAC layer protection is supported (Dual CTS protection) for
non-OFDM (802.11b) clients.
MCS
Definition:
The complexity of 802.11n rate adaptation has given birth to the concept of Modulation
Coding Scheme (MCS). MCS includes variables such as the number of spatial streams, modulation,
and the data rate on each stream.
Extricom 802.11n:
Extricom supports two data streams; therefore MCS 0 to 15 can be configured.
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