Introduction

There are many features that manufacturers can choose to implement or support to increase the performance of their devices. Some features improve performance more significantly than others, detailed below.

What you will learn:

  • What are spatial streams and how do they affect performance
  • What are frequency and channels
  • How to squeeze extra performance out of your wireless system

Spatial Streams

Spatial Streams (SS) are one of the key Wi-Fi performance enhancers as a result of MIMO. A radio with multiple transmitters and receivers can split a data transmission into multiple signals (spatial streams) for increased performance and redundancy.

  • Notation - 3x3:2 means the AP has 3 transmitters, 3 receivers, and 2 spatial streams
  • 2 spatial streams - Requires both AP and client to have at least 2 transmitters and 2 receivers.
  • 3 spatial streams - Requires both AP and client to have at least 3 transmitters and 3 receivers.
  • 4 spatial streams - Wave 2 introduced a 4th spatial stream & 80 MHz channel operations, but only a 30% data rate increase over Wave 1.
Channel Bandwidth1 SS2 SS3 SS4 SS
20 MHz 802.11n (2.4 GHz)72.2 Mbps144.4 Mbps216.7 Mbps288.9 Mbps
40 MHz 802.11n (2.4/5 GHz)150 Mbps300 Mbps450 Mbps600 Mbps
80 MHz 802.11ac (5 GHz)433 Mbps867 Mbps1300 Mbps1733 Mbps
160 MHz 802.11ac (5 GHz)867 Mbps1733 Mbps2600 Mbps3467 Mbps
* The data rates may vary depending on client availability

Key Decision: Do You Need 3 or 4 Spatial Streams?
Overview

Most 802.11ac Wave 1 APs on the market today support at least three SS so the two versus three SS decision only comes into play when purchasing 802.11n APs. Wave 2 APs support up to 4 spatial streams.

Considerations

Choosing an AP with three versus four SS is typically a cost versus performance decision. The additional hardware and intelligence for the SS increases the price of the AP, but also increases the performance.

You should also consider the type of client devices that will be on the wireless network. Smartphones typically only support one SS, tablets support one or two SS, and laptops two or three SS.

Recommendations

If purchasing an 802.11ac Wave 1 network, three SS is the norm. Wave 2 APs can support four spatial streams. While there are many clients in use today that only support two SS, the cost versus performance tradeoff is usually not large enough to warrant a four SS network. However, if the majority of the devices are two SS devices, with newer devices supporting a third SS, prioritizing a fourth SS should not be as high a priority if you have a tight budget.

Supported Channels

2.4 GHz Channels - Standard supported channels are 1 - 13, though the only non-overlapping channels are 1, 6, and 11. It is not a requirement to set your APs to channels 1, 6, or 11, but it is best practice to use only these three channels. Bonded channels (40 MHz wide channels) should never be used in the 2.4 GHz band because this frequency space generally has too much interference for bonded channels to operate efficiently.

5 GHz Channels - Standard supported channels are in the U-NII-1 (Channels 36, 40, 44, 48) and U-NII-3 bands (Channels 149, 153, 157, 161). U-NII-2 and U-NII-2 Extended channels require DFS (Dynamic Frequency Selection) functionality and, therefore, special FCC compliance certification. These UNII-2 channels significantly increase the useable frequency of an AP and. Without this extra frequency space, enabling 80 MHz wide channels in 802.11ac Wave 1 is not advisable because only two channels are available. If you are purchasing 802.11ac Wave 1 APs and require the 1.3 Gbps data rates, be sure to check that the AP you are purchasing supports these UNII-2 channels or that the manufacturer has submitted an application to the FCC to enable the channels with approval pending. Wave 2 support channels up to 160 MHz wide. Wave 2 introduced 80+80 channel bonding for non-adjacent channels of 80 MHz channels using 4 SS which has lead to additional hardware costs. Some chipset manufacturers are dividing up processing resources to implement the 80+80 method using 2 SS, but without increasing throughput. Be aware of the variance in channel bonding approaches with Wave 2 APs.

Client Hardware Impact on Performance

The type of client hardware (laptops, tablets, phones) that is on your network has a big impact on performance, so you should consider your client types and make AP choices accordingly. The data rate that is negotiated between the AP and client is what determines the "speed" of any communications between them. Whichever end has the less advanced hardware, whether it is the AP or client, is the end that determines the maximum data rate. So, if an 802.11ac client associates with an 802.11n AP, 802.11n data rates will be used even though the client is capable of a higher data rate. If an 802.11a client associates with an 802.11ac AP, the two will communicate using 802.11a data rates. It is important to be aware that, since the air is a shared medium, the entire network becomes considerably slower when you have many legacy devices. Legacy clients end up taking more than their fair share of airtime and the AP has to reduce its data rate for long periods of time. A few active 802.11b clients can dramatically impact the performance of the network.

Consider the types of clients on your network before deciding which APs to buy. If you have predominantly 802.11n two SS clients with no device refresh plans in the next few years, then purchasing 802.11ac APs may not initially appear worth the investment. A definite consideration is future device replacement plans over the next 3-5 years and understanding if newer devices will be able to support the new functions offered by 802.11ac APs. Some manufacturers' solutions tend to handle certain types of clients better than others. You should do some research to ensure that the solution you are considering has not had any problems supporting your predominant device type. For example, if your school rolled out a 1:1 initiative using Chromebooks, you will want find out if the solution you are considering has any reported issues with your specific Chromebook.

Band Steering

The 2.4 GHz spectrum is becoming increasingly congested and any client that has the capability of operating in the 5 GHz band should be steered away from the 2.4 GHz band to improve overall system performance. Most manufacturers have the capability to steer clients toward the least congested band.

Manufacturer Terminology: Client Band Steering
AerohiveRapid Resource Management (RRM)
Aruba (HP)Clientmatch
CiscoBand Select
ExtremeBand Steering
HPBand Steering
Cisco MerakiBand Steering
Meru (Fortinet)Band Steering
Zebra (Motorola)Band Steering
Ruckus (Brocade)Band Steering
UbiquitiBand Steering
XirrusAutomatic Station Load Balancing

Beamforming

Beamforming is essentially the AP's ability to "point" a signal toward the client by slightly altering the timing of its transmissions from each transmitter. The primary benefit of beamforming is increasing signal strength for long range or hidden clients.

  • 802.11n - Although beamforming is optional in the 802.11n standard, several manufacturers chose to implement it in their 802.11n APs.
  • 802.11ac Wave 1 - Beamforming is still optional in Wave 1
  • 802.11ac Wave 2 - Mu-MIMO functionality relies upon beamforming capabilities.

Number of SSIDs

Any viable wireless solution needs to have the ability to support more than one Service Set Identifier (SSID) which is a unique identifier of a wireless LAN. Allowing users to connect to one of many SSIDs according to their user group enhances the security and manageability of the network. A great example of the use for multiple SSIDs is creating a guest SSID which separates guest traffic from local user traffic.

Many manufacturers market the fact that their products are capable of broadcasting a large number of SSIDs simultaneously. For each SSID broadcast by an AP, overhead increases (performance decreases). Unless there is a very specific reason to use more than 10 SSIDs, this feature should not be a priority.

Number of Clients

Considering that the air is a shared medium, as the number of clients on an AP increase, throughput per client decreases. If there are too many clients on an AP, overall network performance will decrease. Unless the AP has multiple radios per band (for example, Xirrus arrays), supporting more than 50 concurrent clients per AP should not be a priority. For very high user count environments, your priority should be installing APs more densely instead of forcing more users per AP.

Client/AP Balancing

Since wireless (the air) is a shared medium, as the number of clients on a radio increases, the throughput for those clients decreases. For best performance in high density environments, a good wireless solution is able to determine which clients can be moved from a heavily loaded AP, onto a neighboring AP with fewer clients as long as the client still has acceptable signal strength on the neighboring AP.

High density has a different definition depending on which type AP is being used. 802.11n APs tend to handle 30+ clients well, while 802.11ac radios can handle 40+ clients depending on how heavily each of those clients is using the network. This means that in the typical school environment, depending on the Bring Your Own Device (BYOD) policy and how heavily the students are using their personal device, one AP per classroom is approximately the right density of APs to handle all of the student devices without clients constantly being balanced to the AP in the next classroom. You want to design the wireless network such that, based on your density of users, you know how heavily loaded each AP will be, but you still want to have the ability to balance the load as users move around dynamically.

Manufacturer Terminology: Client/AP Balancing
AerohiveRadio Resource Management (RRM)
Aruba (HP)ClientMatch
ExtremeLoad balancing
CiscoAggressive load balancing
HPWi-Fi Clear Connect
Cisco Meraki--
Meru (Fortinet)Channel Layering with Load Balancing
Zebra (Motorola)Client load balancing
Ruckus (Brocade)Client load balancing
UbiquitiLoad balancing
XirrusClient load balancing

QoS/WMM

WMM stands for Wi-Fi Multimedia and provides Quality of Service (QoS) to 802.11 networks. Enabling QoS in any network makes network performance more predictable and bandwidth utilization more effective. QoS allows the network to identify and prioritize certain categories of traffic. WMM prioritizes based on 4 categories.

  • Voice
  • Video
  • Best Effort
  • Background

If you will be running latency sensitive traffic like voice or video over your wireless network, it is advised to enable WMM so that a student downloading a large file will not disrupt a voice call in another classroom. The effectiveness of the QoS implementation depends on how well QoS has been configured from end to end. Some wireless systems have WMM enabled by default and others require more advanced configuration. In almost every case, however, you will need to make sure that the category marking and prioritization are consistent across your wireless and wired networks.

2.4 GHz Band Data Rate Enhancements

There are APs being designed and marketed with data rate enhancements in the 2.4 GHz band. Though the theoretical throughput on these "enhanced" devices seems higher than their competitors, they are unlikely to perform better in a real environment so one should not spend extra for these features.

  • Channel Bonding - In the 2.4 GHz band, channel bonding is possible but never advised because of the limited available frequency and interference levels typically present.
  • Advanced Modulation - In the 2.4 GHz band, advanced modulation is possible but will almost never be practical because of the interference levels typically present.

Guard Interval

The guard interval is the amount of time a transmitter waits between transmissions to ensure the receiver receives distinct transmissions. A short guard interval (400 ns vs 800 ns) can marginally improve the performance on a wireless network. However, this guard interval is only effective in small cell sizes (small coverage area) with low interference, and the performance gain is usually not enough to merit paying extra for this feature. Rural schools or schools with very dense building materials, which block wireless signals, may see a benefit from a short guard interval, however, the majority of districts will not have a clean enough RF environment for the feature to be useable.


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