Cisco Cisco Aironet 1140 Access Point 디자인 가이드
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Cisco 1140 Series Access Point Deployment Guide
OL-18384-01
So, What Exactly Is 11n?
MIMO radios are referenced using the formula TxR:S. The 'T' stands for transmit antennas, the 'R' for
receive antennas and the 'S' for the number of spatial streams. The number of spatial streams is the most
important variable as it defines the maximum data rate of the radio. For radios supporting one spatial
stream, the maximum data rate is 150Mbps, and a radio supporting two spatial streams tops out at a
maximum data rate of 300Mbps (assuming a 40MHz-wide channel).
receive antennas and the 'S' for the number of spatial streams. The number of spatial streams is the most
important variable as it defines the maximum data rate of the radio. For radios supporting one spatial
stream, the maximum data rate is 150Mbps, and a radio supporting two spatial streams tops out at a
maximum data rate of 300Mbps (assuming a 40MHz-wide channel).
The Cisco Aironet 1140-series utilizes two 2x3:2 MIMO radios, with one operating in the 2.4GHz band,
and the other in the 5GHz band. This means each radio has two transmit antennas, three receive antennas
and it supports a maximum of two spatial streams. Similarly, a 3x3:2 radio would utilize three transmit
antennas, three receive antennas and support a maximum of two spatial streams. In terms of
performance, radio configurations of 2x3:2 and 3x3:2 will be equivalent as their maximum speeds are
capped at 300Mbps given the number of spatial steams are identical.
and the other in the 5GHz band. This means each radio has two transmit antennas, three receive antennas
and it supports a maximum of two spatial streams. Similarly, a 3x3:2 radio would utilize three transmit
antennas, three receive antennas and support a maximum of two spatial streams. In terms of
performance, radio configurations of 2x3:2 and 3x3:2 will be equivalent as their maximum speeds are
capped at 300Mbps given the number of spatial steams are identical.
MAC Enhancements
Up the stack, 11n's MAC enhancements allow bandwidth-hungry applications to make more efficient use
of available transmission time, further increasing effective throughput.
of available transmission time, further increasing effective throughput.
The MAC layer enhancements to 802.11n are deceptively simple in concept, when compared to the
substantial decrease in overhead they offer. Both aggregation and support for block acknowledgments
help reduce the protocol overhead typical of legacy Wi-Fi networks, thereby boosting speeds.
Aggregation allows data frames to be concatenated so that time wasted for medium contention and
interframe spacing gaps may be greatly reduced.
substantial decrease in overhead they offer. Both aggregation and support for block acknowledgments
help reduce the protocol overhead typical of legacy Wi-Fi networks, thereby boosting speeds.
Aggregation allows data frames to be concatenated so that time wasted for medium contention and
interframe spacing gaps may be greatly reduced.
Note
Aggregation will only occur with unicast traffic; broadcast and multicast traffic cannot be aggregated.
Block acknowledgments (ACKs) further reduce protocol overhead by allowing a group, or block of
frames, to be acknowledged with a single ACK frame. Legacy Wi-Fi networks have always required
individual acknowledgment of unicast management and data frames.
frames, to be acknowledged with a single ACK frame. Legacy Wi-Fi networks have always required
individual acknowledgment of unicast management and data frames.
Other Incremental Improvements
There are some additional augmentations to existing 802.11 standards that have been designed into 11n
and which are geared toward differentiated media access services and power savings. 802.11n requires
that clients support the WMM/11e quality of service (QoS) protocol. This establishes a foundation for
administrators to properly enforce QoS policies, and WMM (Wi-Fi Multimedia) serves as the basis for
a portion of 802.11n’s packet aggregation capabilities using Block ACK. 11n also supplements 11e's
power save method, not just requiring that devices support the more intelligent, trigger-based Automatic
Power Save Delivery (U-APSD), but also giving end client devices the abilities to disable transmitters
and receivers as traffic patterns allow, thereby drastically reducing the power drain associated with
operating 11n's many radios.
and which are geared toward differentiated media access services and power savings. 802.11n requires
that clients support the WMM/11e quality of service (QoS) protocol. This establishes a foundation for
administrators to properly enforce QoS policies, and WMM (Wi-Fi Multimedia) serves as the basis for
a portion of 802.11n’s packet aggregation capabilities using Block ACK. 11n also supplements 11e's
power save method, not just requiring that devices support the more intelligent, trigger-based Automatic
Power Save Delivery (U-APSD), but also giving end client devices the abilities to disable transmitters
and receivers as traffic patterns allow, thereby drastically reducing the power drain associated with
operating 11n's many radios.
Understanding the parts of 802.11n and how they converge to provide enhanced performance, reliability,
and predictability will prove imperative when it comes time to design an 11n-ready Cisco Unified
Wireless Network.
and predictability will prove imperative when it comes time to design an 11n-ready Cisco Unified
Wireless Network.
Note
For more detailed technical information on 802.11n, please see the “802.11n: The Next Generation of
Wireless Performance” whitepaper at this URL:
Wireless Performance” whitepaper at this URL: