Cisco Aironet 2702i AIR-CAP2702I-E-K9 Folheto

 

 

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Also, IT administrators typically upgrade their APs on a three-, four-, or five-year schedule. These IT administrators 

should continue to upgrade their APs on schedule, since 

the capability of today’s APs significantly exceeds the 

capabilities of previous generations of APs. Until 802.11ac APs become available, we do recommend that modular 

802.11n APs be installed, so as to provide an upgrade path to 802.11ac. 

802.11a/n deployments not upgraded to 802.11ac still have to consider the effect of 802.11ac introduced by 

neighbors in the normal way and the additional exploits available to attackers. 

802.11ac affects RRM, since overlapped devices can now transmit over 80 or even 160 MHz. With a software 

upgrade, it is possible for existing RRM systems to detect the presence of 802.11ac APs from the new 802.11ac 

fields in beacon frames and extract the affected bandwidth. With this knowledge, the RRM system can mitigate the 

effect from nearby 802.11ac APs. The RRM system has to work harder since (1) a single overlapped 802.11ac AP 

affects a wider bandwidth, and (2) the effect on any 20-MHz subchannel depends on whether or not the primary 

20-MHz subchannels of the in-network and overlapped APs are aligned (see 

). 

Users should verify that their APs are capable of using all the available channels, even those subject to radar 

detection (dynamic frequency selection, or DFS) requirements. (Many consumer-grade and some enterprise-grade 

APs are not certified by regulators to operate on DFS channels. This is unfortunate, since in the United States, for 

example, 63 percent of 20-MHz channels are DFS channels.) 

In general, the wireless intrusion protection system (WIPS) of an 802.11a/n deployment can detect and mitigate 

many attacks by 802.11ac devices, particularly when conducted by naïve attackers. This is because the 802.11ac 

device communicates using 802.11a/n format packets when communicating with 802.11a/n devices, and 802.11ac 

devices invariably continue to transmit beacons, probe requests, and probe responses at 802.11a rates. However, 

packets sent using 802.11ac format cannot be decoded by 802.11a/n devices. The recommended countermeasure 

against such attacks is to provide a sprinkling of 802.11ac APs operating full-time WIPS (for example, one 

802.11ac WIPS AP for five or six serving 802.11a/n APs) or a full upgrade of all APs. 

5. Summary 

The new 802.11ac standard is an improved version of 802.11n, offering higher speeds over wider bandwidths. It is 

worth having when it is available, especially when the client mix converges to being dominated by 802.11ac 

devices. In the meantime, 802.11n offers many of the same technologies, albeit at lower speeds, and is available 

today. IT administrators looking to invest in wireless LANs in the near term should strongly consider 802.11n APs 

that are field-upgradable to 802.11ac. 

Appendix: What Is 802.11n? 

802.11n was a major advance over 802.11a. 802.11n introduced several major advances in the MAC sublayer and 

physical (PHY) layer, namely: 

● 

Multiple input, multiple output (MIMO). MIMO brings with it a host of benefits: 

◦ 

Greater speed without an increase in spectrum consumption using spatial multiplexing (SM). SM splits up 

the data into pieces and sends each piece along parallel “spatial” channels in a fraction of the time that it 

would take to send the same data serially. Without SM, 802.11n maxes out at 150 Mbps. With SM, 300 

and 450 Mbps are available as long as both transmitter and receiver have at least two and three 

antennas (and RF chains), respectively.