802.11ac FAQs | NETSCOUT

Transition to 802.11ac FAQs



AirMagnet Solution

 Should I transition to 802.11ac or does 802.11n provide sufficient coverage and performance?

The key benefit of 802.11ac is user capacity increases, and with the proliferation of Wi-Fi devices, capacity upgrades are needed, especially if you have an 802.11a/b/g network. Considering the costs of an upgrade, going to 802.11ac now may make sense even if 802.11n provides the needed rates and capacity, looking out for the next 2 years. If you have an 802.11n network, consider that a 1:1 swap of AP’s to 802.11ac can increase your user capacity. Also consider that a brand new 802.11ac AP may provide performance improvements even for 802.11a/n clients, considering the latest electronics that come with it.

AirMagnet Survey PRO can accurately calculate the performance delivered on your current network (signal strength, measured physical layer (PHY) data rates, iPerf throughput, etc.) and whether it meets your current and future WLAN design/application requirements.

If I must move to 802.11ac, should I do a complete "rip and replace" or a slow transition?

Consider these factors:

  • Immediate expectations and needs of the users, especially with regard to user capacity (many users now have 3 WLAN devices). 802.11ac will improve user capacity.
  • Client population among 802.11a/b/g/n/ac. If you have few 802.11ac clients, then a transition may make more sense.
  • If you phase in 802.11ac alongside 802.11a/n in a roaming zone, 802.11ac clients may roam from an 80MHz channel to a 20MHz channel and experience notable performance disruptions.

If upgrading from 802.11n, you may benefit from upgrading an area or floor at a time. If upgrading from 802.11a/b/g, you may benefit from upgrading an entire building at a time. Having a greenfield deployment of 802.11ac only for a newly covered area is a great way to start and learn.

AirMagnet Wi-Fi Analyzer PRO will characterize your current 802.11a/b/g/n WLAN environment in terms of client type and utilization of the network, as well as throughput performance, and help determine if a complete upgrade or a phased transition is needed. During a transition, AirMagnet Survey PRO will help optimize your 802.11ac network to ensure performance for all clients.

Will I need more 802.11ac APs as compared to 802.11n?

802.11ac will support more users per AP radio, and hence a 1:1 swap will provide an upgrade in capacity. However, many environments are seeing an exponential increase in WLAN devices. A denser WLAN environment calls for smaller cells and sometimes a dual-channel 5GHz network. You need to plan and deploy according to your client base requirements, including client density, technology type, and bit rate needs. But in many cases an increase in APs is justified.

AirMagnet Survey PRO provides a single-click assessment to determine if user capacity requirements are met. It also provides specific visualizations of key performance factors like channel width, channel overlap, and MCS, to guide you in adjusting channel assignments and AP placement for maximum performance.


Channel selection FAQs



AirMagnet Solution

What channel setting should I use for my 802.11ac APs?

Channel assignments are one of the most critical aspects of an 802.11ac deployment. Although the simplest method is to let APs automatically set their own channels, optimal performance can be achieved by developing a channel allocation plan and assigning channels to APs per this plan. To maximize network performance, this plan should enable use of wider channels while minimizing primary channel overlap.

A pre-deployment AirMagnet survey will reveal where interference affects channel availability. A post-deployment AirMagnet survey will validate channel assignment by revealing any co-channel interference and AP coverage issues. It will also specifically indicate where primary and secondary channels overlap on wider channels.

Will I have to change my channel settings on 802.11n as I transition in 802.11ac with wider channel widths?

802.11ac is backward compatible with 802.11n and 11a, and operates in a mixed mode supporting 802.11a/n/ac clients in the 5GHz band. So your 802.11ac APs can transmit to 802.11ac clients on 80MHz channels, 802.11n clients on 20/40MHz channels, and 802.11a clients on 20MHz channels. However, falling back to 20/40MHz channels will impact performance for 802.11ac clients, so it is important to assign channels in your environment to balance performance among your specific client base.

AirMagnet Survey PRO will validate your channel assignment plan and help you optimize it with graphic visualizations of where different channel widths are supported, and where channels overlap. It will also validate whether your deployment meets the ultimate requirement – user performance – with a throughput survey.

Should I use Dynamic Frequency Selection (DFS) Channels?

Consider first if your client base can support DFS channels. If so, does your environment allow you to reliably keep a DFS channel? If you are near an airport, for example, this may be problematic. The best way to determine this is with spectrum analysis.

AirMagnet provides the only survey solution with integrated spectrum analysis. While performing a site survey, you can detect and measure any RF signal on each channel, and determine if DFS channels are available or occupied.

What services should I offer on 2.4GHz, as 802.11ac is a 5GHz only standard? How can I separate out my network between these 2 bands?

Both bands provide valuable spectrum that can be used to maximize capacity of a WLAN network. One can offer high bit rate / high QoS services like video on 5GHz and best effort services like web browsing on 2.4GHz. Another model is to reserve 2.4GHz for legacy 802.11b/g clients, and serve 802.11n/ac clients at 5GHz. Most APs will support both bands simultaneously.

AirMagnet Survey PRO enables a single walk-through survey to collect all relevant data in both bands. The results will determine if coverage and performance in each band meets your design requirements.

AirMagnet Wi-Fi Analyzer PRO shows you how much the current 802.11a/b/g/n network in each band is utilized, to help you determine the best way to allocate clients and services to each band.


Performance FAQs



AirMagnet Solution

Does 802.11ac improve my coverage (with and without beamforming)?

802.11ac can improve your coverage by providing higher bit rates and capacity at the same distance, vs legacy technologies. Even without beamforming, the signal level and signal-to-noise ratio (SNR) may be the same, but wider channels and higher rate modulation coding scheme (MCS) will improve performance. Beamforming is standardized in 802.11ac, though optional, and we can expect to see it become more prevalent, improving coverage and performance. However, a more important need now is capacity, and having more APs with smaller cells to handle higher user density will likely ensure RF coverage is more than adequate.

AirMagnet Survey PRO will show you where you have sufficient and insufficient coverage for 802.11ac and legacy APs. It also provides a quick single-click assessment against user density requirements to ensure your network is meeting coverage and capacity requirements.

What performance improvement will I get with 802.11ac as compared to 802.11n?

Performance improvements will depend on a number of factors. These include how many legacy 802.11a/n clients are to be supported, what their transmission utilization will be, distance from the AP and the MCS available. In general, 2-3 times better performance over 802.11n can be expected by using 80MHz channels with the same number of spatial streams (MIMO) with no interference. This may be impacted by 802.11a/n client transmissions. Future improvements will come with 160MHz channels, multi-user MIMO, and > 3 spatial streams.

AirMagnet Survey PRO will show actual user throughput maps with iperf surveys, for both 802.11ac and 802.11a/n environments. This enables users to quickly determine areas where performance improvements have been achieved.

Will the new 802.11ac deployment increase interference in my network?

The use of wider channels in 802.11ac increases the likelihood of co-channel interference. 802.11ac has mechanisms that allow adjacent APs with overlapping secondary channels to fallback from 80MHz to 40MHz or 20MHz to transmit simultaneously while avoiding interference. Channel assignment is a critical component to planning an 802.11ac network to make this work.

AirMagnet Survey PRO will show you where primary and secondary channels interfere with each other, and hence where performance may be impacted. Armed with this info, you can adjust channel allocations and AP location to maximize performance for all clients and thus minimize user complaints.

Will 802.11ac increase the signal strength in my network?

802.11ac APs will not have a higher max power level. But even with the same signal strength, performance will improve with higher rates provided by 802.11ac. You will want 30-35 dB of SNR to provide the higher rates available. So you will want smaller cells that can provide this SNR with the same transmit power to realize the benefits of 802.11ac.

AirMagnet Survey PRO will not only show you the signal strength on your floor map, but will also show the resultant MCS and PHY rate coverage. This, along with seeing interference, will validate your design. Then Survey PRO provides the ultimate validation of your deployment with a user throughput survey.

How do I increase the throughput of the 802.11ac network?

There are several ways to improve throughput, each with trade-offs. Use of 80MHz channels is the most direct way, but this may be compromised with support of 802.11a and 802.11n clients. A separate network of APs for 80MHz channels serving 802.11ac clients only may be deployed as an overlay to an 802.11n network, but you need to ensure enough non-overlapping channels in your coverage area. More spatial streams provide nearly linear improvements (2x2 about 2x that of 1x1), but this is limited to client availability. Higher MCS (256 QAM) is available with 802.11ac but only at short distances with high SNR. Beamforming (if available with the AP and clients) will improve SNR and help with this. In the future, 160MHz channels and more spatial streams will further improve this.

AirMagnet Survey PRO will measure and validate user throughputs on both the uplink and downlink by associating with an AP to test the real quality of the connection. It will also show the contributing factors like MCS, PHY rates, and channel widths, to determine why rates may not match objectives.

Why am I not getting the expected throughput from the AP for my existing client?

This may be due to any of a number of factors. Legacy 802.11a or 802.11n clients on the same channel can reduce throughput by taking up airtime with slower transmissions. Further distance from an AP reduces SNR which causes a fallback in MCS which reduces transmission rates. Likewise, noise and interference on the channel also reduces SNR. Your client may only support 1x1 or 2x2 MIMO, limiting the rates available with a 3x3 AP. Even with 2x2 and 3x3 clients, MIMO may not be 100% effective due to the physical environment if not all spatial streams are completely received. If DFS channels are used for bonded channels, a non-Wi-Fi transmission on these channels will force the AP for fallback to another lower bandwidth channel.

AirMagnet Survey PRO will measure and validate user throughputs on both the uplink and downlink associating with an AP to test the real quality of the connection. It will also indicate contributing factors like MCS, PHY rates, and channel widths, to determine why rates may not match objectives.

What throughput change can I expect as I deploy new APs or clients in the environment?

If 802.11ac APs are phased in alongside 802.11n APs, and 802.11ac clients are mixed with 802.11a/n clients, throughput will improve incrementally for 802.11ac clients, moving up to the maximum improvement as all APs and clients become 802.11ac. In an all or mostly 802.11ac environment using 80MHz channels, general improvements of 2-3 times over 802.11n using the same number of spatial streams can be expected. But even 802.11a and 802.11n clients may see small improvements when connecting to a new 802.11ac AP at 802.11a and 802.11n rates, due to the newest chipsets and hardware used in new 802.11ac APs.

AirMagnet Survey PRO will measure and validate user throughputs on both the uplink and downlink associating with an AP to test the real quality of the connection. It will also indicate contributing factors like MCS, PHY rates, and channel widths, to determine why rates may not match objectives.