Special Coverage Series

Network Computing

Special Coverage Series

Commentary

Lee H. Badman
Lee H. Badman Network Computing Blogger

802.11ac: 10Gig Uplinks Are Overkill

There's talk that 802.11ac requires 10Gig uplinks to support maximum throughput. But you may not even need 2Gig uplinks. Here's why.

In my most recent blog on 11ac, I outlined the work required to upgrade WLAN infrastructures to get the full benefit of the pending wireless standard. While that work is significant, it may not require a 10-Gbps backhaul on the wired side as some observers have suggested.

The 802.11ac standard will be phased in in two waves. Wave 1 promises throughput of about 1.3G bps and uses 80-Mhz channels. Several vendors are shipping Wave 1 products. Wave 2, scheduled for 2014, promises maximum throughput of 3.5 Gbps.

More Insights

Webcasts

More >>

White Papers

More >>

Reports

More >>

The two-phase rollout means IT has several choices: Upgrade to 11ac Wave 1 now to get improved performance over 11n, wait until next year to go all in on Wave 2, or expend capital on two rounds of upgrades. If your environment has new switches and is easy to cable, two rounds of upgrades to adopt 11ac now and then get to its top end in the next couple of years may not be a big deal. Bigger environments (my own WLAN is pushing 4,000 access points) with cabling challenges and a mix of switch technologies have more to ponder.

Back to the numbers. As mentioned in my last piece, emerging industry guidance recommends two data cables per 11ac access point. Access points are already shipping with two Ethernet ports (like Aruba's new 220 series and Motorola's 8200s), though there are variations. Some early APs, like the 220, use an Etherchannel for bandwidth, while others use the second port for power or module-based feature capability. Nothing is simple with 11ac.

Another issue of contention is whether you need a 10-Gig uplink to support the max throughput of 802.11ac. 10 Gig sounds like a good idea for a standard that promises dual-band connectivity and data rates of 3.5 Gbps in the 5-GHz band, and in some cases simultaneous 600 Mbps in the 2.4-GHz band.

But maybe not. Wireless is a shared-medium, half-duplex technology with lots of overhead. As a rule of thumb, you can take any stated wireless data rate and cut it roughly in half to get a sense of what real throughput--the part that makes it to the wired uplink--will be.

This is why a single Gigabit uplink is sufficient for the expected 1.3 Gbps rates of Wave 1. Even when paired with throughput on the 2.4-GHz side of a dual-band AP, first-wave 11ac in 5 GHz won't fill the 1-Gbps uplink. So far, so good, right?

Remember, 11ac promises rates "up to" 3.5 Gbps in Wave 2, just as 11n promised rates up to 600 Mbps. In practice, 11n peters out at 450 Mbps. It's not unreasonable to think that most environments won't see 11ac's maximum rate, either, but there is just no way to know yet. (The 11ac standard also promises 6.9-Gbps maximum throughput at some point, but that's beyond the first two waves.)

If you do the "cut it in half" math on that number, Wave 2's best throughput is still under 2 Gbps, which means a 10-Gbps uplink isn't necessary.

For a better description on the nuances of the 11ac rates, see my colleague Matthew Gast's excellent blog, but be warned: I challenge whether even 2-Gbps backhaul will be needed for many 11ac cells.

One reason is that the explosive growth in mobile devices works against the ability to fully exercise 11ac's high rates because most smartphones operate at what amounts to fast 11n rates. To date, there have been no public hints that faster mobile silicon is on the horizon. Tablets don't fare much better, and laptops (which have the best chances of being equipped with the most robust 11ac adapters) are statistically in decline.

Also, regardless of the advertised top rate, clients need to be very close to the AP to achieve it. Even in dense deployments, only a fraction of clients will be close enough to get the max rates, and that only happens if they are on a laptop that supports the high rate.

We also have to consider that 11ac works exclusively in 5 GHz, and that as the new standard gets as popular as it should, 11ac's wide channels may eventually make the 5-GHz spectrum almost as cluttered as 2.4 GHz is now. This also puts up speed bumps against the fastest rates as RF works against itself. And where my 11ac network bumps up against yours, built-in courtesy mechanisms will slow us both down.

In most cases, I think WLANs will do well with 1G bps to each 11ac access point, unless you have a room full of 11ac laptops all doing HD video.

The bottom line is that 11ac is complicated. It's easy for the WLAN industry to simply tell us all to run new Etherchannels for each new AP, but that puts a lot of cost and burden on the customer for promises that have yet to be proved.



Related Reading



Network Computing encourages readers to engage in spirited, healthy debate, including taking us to task. However, Network Computing moderates all comments posted to our site, and reserves the right to modify or remove any content that it determines to be derogatory, offensive, inflammatory, vulgar, irrelevant/off-topic, racist or obvious marketing/SPAM. Network Computing further reserves the right to disable the profile of any commenter participating in said activities.

 
Disqus Tips To upload an avatar photo, first complete your Disqus profile. | Please read our commenting policy.
 

Editor's Choice

Research: 2014 State of Server Technology

Research: 2014 State of Server Technology

Buying power and influence are rapidly shifting to service providers. Where does that leave enterprise IT? Not at the cutting edge, thatís for sure: Only 19% are increasing both the number and capability of servers, budgets are level or down for 60% and just 12% are using new micro technology.
Get full survey results now! »

Vendor Turf Wars

Vendor Turf Wars

The enterprise tech market used to be an orderly place, where vendors had clearly defined markets. No more. Driven both by increasing complexity and Wall Street demands for growth, big vendors are duking it out for primacy -- and refusing to work together for IT's benefit. Must we now pick a side, or is neutrality an option?
Get the Digital Issue »

WEBCAST: Software Defined Networking (SDN) First Steps

WEBCAST: Software Defined Networking (SDN) First Steps


Software defined networking encompasses several emerging technologies that bring programmable interfaces to data center networks and promise to make networks more observable and automated, as well as better suited to the specific needs of large virtualized data centers. Attend this webcast to learn the overall concept of SDN and its benefits, describe the different conceptual approaches to SDN, and examine the various technologies, both proprietary and open source, that are emerging.
Register Today »

Related Content

From Our Sponsor

How Data Center Infrastructure Management Software Improves Planning and Cuts Operational Cost

How Data Center Infrastructure Management Software Improves Planning and Cuts Operational Cost

Business executives are challenging their IT staffs to convert data centers from cost centers into producers of business value. Data centers can make a significant impact to the bottom line by enabling the business to respond more quickly to market demands. This paper demonstrates, through a series of examples, how data center infrastructure management software tools can simplify operational processes, cut costs, and speed up information delivery.

Impact of Hot and Cold Aisle Containment on Data Center Temperature and Efficiency

Impact of Hot and Cold Aisle Containment on Data Center Temperature and Efficiency

Both hot-air and cold-air containment can improve the predictability and efficiency of traditional data center cooling systems. While both approaches minimize the mixing of hot and cold air, there are practical differences in implementation and operation that have significant consequences on work environment conditions, PUE, and economizer mode hours. The choice of hot-aisle containment over cold-aisle containment can save 43% in annual cooling system energy cost, corresponding to a 15% reduction in annualized PUE. This paper examines both methodologies and highlights the reasons why hot-aisle containment emerges as the preferred best practice for new data centers.

Monitoring Physical Threats in the Data Center

Monitoring Physical Threats in the Data Center

Traditional methodologies for monitoring the data center environment are no longer sufficient. With technologies such as blade servers driving up cooling demands and regulations such as Sarbanes-Oxley driving up data security requirements, the physical environment in the data center must be watched more closely. While well understood protocols exist for monitoring physical devices such as UPS systems, computer room air conditioners, and fire suppression systems, there is a class of distributed monitoring points that is often ignored. This paper describes this class of threats, suggests approaches to deploying monitoring devices, and provides best practices in leveraging the collected data to reduce downtime.

Cooling Strategies for Ultra-High Density Racks and Blade Servers

Cooling Strategies for Ultra-High Density Racks and Blade Servers

Rack power of 10 kW per rack or more can result from the deployment of high density information technology equipment such as blade servers. This creates difficult cooling challenges in a data center environment where the industry average rack power consumption is under 2 kW. Five strategies for deploying ultra-high power racks are described, covering practical solutions for both new and existing data centers.

Power and Cooling Capacity Management for Data Centers

Power and Cooling Capacity Management for Data Centers

High density IT equipment stresses the power density capability of modern data centers. Installation and unmanaged proliferation of this equipment can lead to unexpected problems with power and cooling infrastructure including overheating, overloads, and loss of redundancy. The ability to measure and predict power and cooling capability at the rack enclosure level is required to ensure predictable performance and optimize use of the physical infrastructure resource. This paper describes the principles for achieving power and cooling capacity management.