February 12, 2015
As we all know, wireless has freed us from the burden of cords and cables giving us unprecedented mobility. Because mobility is so convenient, wireless access has become the primary path with which corporate users connect to the network. For instance, I can’t recall the last time I physically plugged into the network to get access. Along with this shift to a new network access medium, corporate users now have the expectation that they will get the same performance that they had on the wired network on the wireless network. Additionally, we now hear things like video will be the majority of IP traffic on networks. Video traffic and today’s application traffic in general can be a huge burden on the wireless network. Here are some examples:
802.11n was fast, but unfortunately just not fast enough for today’s demands. We needed something faster or we’d be back to the wired world, and the subsequent loss of freedom from a mobility standpoint. This is where 802.11ac comes into play.
802.11ac is a new IEEE standard referred to as VHT or very high throughput and high density wireless
Let’s make sure we understand the fundamental differences between 802.11ac and 802.11n, as well as the fact that 802.11ac doesn’t replace 802.11n, but rather builds on all the advancements of ‘n’ with a few key tweaks.
- 802.11ac was designed based on the experiences and capabilities/limitations with the 802.11n IEEE standard.
- The main design objective with 802.11ac was the ability to support high-density wireless.
- As more and more users connect only via wireless, and also bring a second device (BYOD) onto the network, density becomes a major area to address in wireless technology. One of the biggest differences is that 802.11ac is only available in the 5GHz spectrum. There are a number of reasons for that but the majority has to do with spectrum. The manner in which 802.11ac gains its speed is by having an increased amount of spectrum available for individual transmissions because the 2.4Ghz band is just too narrow.
Here is a detailed chart that breaks down the key protocol feature enhancements that comes with 802.11ac over 802.11n:
On the left hand side, we have the specific 802.11ac protocol feature that has a direct effect on the performance increase gains over the 802.11n standard, and on the right hand side we have the multiplier for just how much faster that feature makes 802.11ac.
Advantages of 802.11ac
Wider Channels of 80MHz/160MHz
As you can see, going from 802.11n’s 40MHz channel width to 802.11ac’s 80MHz channel width immediately doubles the speed of the wireless network. Then, subsequently going from 802.11ac’s WAVE 1 channel width of 80MHz to 802.11ac’s WAVE 2 channel width of 160MHz again doubles the speed and results in four times the speed of 802.11n. This is all based on the IEEE standards that are available today (i.e. – WAVE 1/WAVE 2). It’s also interesting to note that 802.11ac actually has 8 total spatial streams available, but we are still years away from taking advantage of that fact. The first WAVE of 802.11ac leverages three spatial streams, while the second WAVE utilizes four spatial streams.
256 Quadrature Amplitude Modulation (QAM)
When we talk about the quadrature amplitude modulation (QAM), we are essentially talking about the representation of 1s and 0s in wave form. The fact that 802.11ac is 256 QAM rather than the 64 QAM that comes with 802.11n results in a performance increase of approximately another 33% percent. This higher level of modulation is simply the ability to send more 1s and 0s per wave form, more specifically about four times more 1s and 0s per wave form than 802.11n or 8 bits per wave form with 802.11ac versus 2 bits per wave form with 802.11n.
Multi User – Multi Input Multi Output (MU-MIMO) Protocol Features
MU-MIMO allows you to have up to four users/devices transmitting at the same time. Historically, we’ve only been able to have one user per access point transmitting. This result is a four-fold increased capability in terms of capacity. For example, instead of 1 frame for 1 receiver you can send multiple simultaneous frames to multiple receivers, which is a lot like a switch. MU-MIMO is a switch-like technology, while 802.11n is more a single-user, hub-like technology.
When preparing for 802.11ac, 3 things that need to be done from a network perspective
1. Run at least two network cables to the access point
If possible run at least two network cables to whatever location the access point will physically reside. This is the due to the fact that 802.11ac WAVE 1 and especially WAVE 2 will support multi-gigabit throughput. Since the access points obviously will need to tie into a physical wire to connect to the backbone network infrastructure, having multiple gigabit ports on your network switches per access point will eventually become a requirement. So bottom line, your organization needs to plan for two physical cables to each drop, which is a big change from any network design with previous wireless standards.
2. Provide power to the actual access points
Another area that we need to account for when planning the network for 802.11ac is providing power to the actual access points. Since it’s unlikely that there will be a physical AC power outlet at each location where an access point will reside, we will need to ensure that the proper power is provided via the network switches.
3. Obtain compatible network switches
Corporations will need to have network switches that support Full IEEE PoE+/802.3at which have the capabilities of power up to 30 W on all ports in order to have all radios and antennas operational. 802.11ac can operate on 802.3af POE switches, but the caveat is that they will operate at a level that is less than the access points capabilities. For instance, a Cisco 3702i access point connected to a POE+ network switch port will operate with the full access point functionality of 4X4 multiple-input multiple-output (MIMO) technology with three spatial streams, while an access point connected to a 802.af POE network switch port will only operate with 3×3 MIMO technology. Also, please make sure that your organizations understands that unless your switch is a full POE+ switch, you will only be able to power your access points across about 2/3’s of the ports because of the overall available power budget available to that switch. In other words, don’t expect that you will be able to power an access point across every switch port concurrently.
The table below shows the power draw requirements of Cisco’s 3702I AC access points and Meraki’s MR34 access points
The bottom line is, 802.11ac is here to stay. It brings some significant advantages over the previously wireless standard 802.11n:
- wider channels of 80MHz/160MHz
- 256 QAM modulation
- multiple user – multiple input multiple output (MU-MIMO) protocol features
As a Cisco Gold partner, it’s nice to know that Cisco played a huge part in the definition/creation of the IEEE 802.11ac WAVE 1 and WAVE 2 standards.
Contact Mindsight to discuss whether your network is ready for the new extremely fast, extremely high density 802.11ac protocol standard.
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