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What Affects 802.11ac Capacity?

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What Affects 802.11ac Capacity?

By: Michael McNamee December 12, 2013 3 Category: Strategy, Design, Performance
large crowded stadium with open roof

In a previous blog, I discussed what the capacity of an 802.11n access point. In another blog I also discussed how many users could connect to an 802.11n access point. With 802.11ac technology we have the opportunity for even greater capacity but the variables and factors deciding this capacity are still in play.

An access point’s capacity is still a factor of the following things and will vary from installation to installation and from environment to environment.

Factor 1 – dual radio or single radio (2.4GHz & 5Ghz or just one frequency – more is better!)

Factor 2 – two stream (2x2) or three stream (3x3) MIMO (more is better applies here too!)

Factor 3 – consumer grade or enterprise grade (Netgear or Linksys vs. Cisco or Aruba)

Factor 4 – wired uplink and switching infrastructure

Factor 5 – RF environment

Factor 6 – client device capability and mix

1. Dual Radio or Single Radio

Let’s discuss factor number 1 first. Having both frequencies functional on an access point today is a must. This is especially applicable in environments like schools, universities, hospitals, and office buildings where the 2.4 GHz spectrum is crowded and congested. Having 5 GHz also available opens an option for higher bandwidth delivery and less congested spectrum.

The higher bandwidth will move us towards hosting more clients on an access point and less congested spectrum provides an optimal environment for the wireless clients to operate in.

Not only does this provide an optimal wireless experience but the two radios also gives us two frequencies to load clients onto which equates to more capacity for clients.

2. Two Stream or Three Stream MIMO

Our 2nd factor affecting access point capacity is the number of transmit and receive (TX & RX) spatial streams that the access point can deliver. A two spatial stream access point will not deliver the bandwidth that a three stream (3x3) access point can deliver.

Think of it like this; if you put three straws in your drink cup you are going to be able to draw a lot more liquid than with two straws. The same goes for wireless; with three streams sending and receiving at the same time you are going to download your data much quicker.

This makes an access point capacity much greater because it is able to address client needs much faster.

3. Consumer Grade or Enterprise Grade 

Factor number 3 is like comparing a Fiero (remember those??) to a Ferrari. The Fiero was a sports car from Pontiac with some innovative features, for its, time designed to get you around in style (debatable) at an affordable cost.

A Ferrari however is a totally different animal in price and performance. They are two totally different cars and two totally different applications.

The same goes for consumer grade access points. Consumer grade access points are made for homes and small offices with 10-15 users/devices connecting to them.

Any more than that and you are likely to lock the unit up requiring a reboot to fix it. Enterprise grade access points on the other hand are built with the intent that many clients will be connecting to them.

The hardware in an enterprise grade access point is going to be more robust, able to handle more processing, and is going to have built in features like:

  • spectrum analysis
  • cellular network interference rejection
  • intrusion detection and prevention
  • failover
  • client load balancing
  • AP to AP roaming (handoff) assistance
  • and adaptive power and channel adjustments
These are things you will not find in SOHO/consumer grade equipment. *like the 80’s theme? 

hall and oats with a fiero as example of consumer networking gear vs enterprise gearmagnum pi with a ferrari as an example of enterprise networking equipment vs consumer gear

4. Weird Uplink and Switching Infrastructure 

In regards to factor 4, as much as we would like the world to be all wireless there is, at least for the near future, always going to be a reliance on wired network infrastructure. This infrastructure can play a large part in the effective capacity of an access point. With 802.11n wireless we highly recommended Gigabit switch connectivity to the AP but with 802.11ac Gigabit switching is a must.

The requirement is due to the bandwidth an 802.11ac access point can deliver. 1.3Gbps is the current high bar for 802.11ac technology and if the access point is connected to a 100Mbps network port the wired connection becomes a bottleneck in the process.

We are also advising being ready for 10Gbps uplink from the edge switch to the core if you are considering deploying 802.11ac. If you have multiple APs each providing 1.3Gbps connected to the same switch and it is using a single Gigabit connection to uplink to your core switch the connection is most likely going to become oversubscribed.

gigabit connection illustration

5. RF Environment

Factor 5 is the RF environment as a variable in the capacity equation. A sub-optimal RF domain 

is going to cause challenges in achieving full utilization of the access point’s capacity. Interference, having too many SSID’s, high channel utilization, and too many APs amongst other things can result in the RF environment becoming an obstacle in achieving optimal capacity.

2.4 GHz utilization example

A little crowded wouldn’t you say??

6. Client Device Capability and Mix

Finally client device capability as factor number 6 is significant in deciding the effectiveness of access point capacity. Devices today are sold with an array of different configurations, different standards supported and different capabilities. These all play into the efficiency of performing on the wireless network.

For example, twenty devices connecting to an 802.11ac access point that are only capable of 802.11g data rates will not realize the full potential of the access point.

However, twenty devices that are 802.11ac capable and are 3x3 MIMO will realize much more of the potential of the access point than the 802.11n clients will. Understanding the devices, their capabilities and their numbers on your network are essential to planning an optimally performing wireless network. 

When designing a WLAN to meet our customer’s requirements we factor in all of these things to come up with a design that matches or exceeds what they have asked for.

Let us know if we can be a resource to you in looking forward to an 802.11ac deployment or a phased in implementation with your existing 802.11n network.

We are always happy to help. Just contact us here.

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