This blog provides a follow up to questions I received about the Cisco Live 2011 high density wireless LAN deployment that I referenced in my blog Look Inside the Cisco Live 2011 NOC to See Amazing Network Management Results . Blog readers wanted to know more about the best practice guidelines and ratio of clients to access points (APs) that was used for the Cisco Live high density WLAN deployment. Given the scope of the answer, I thought it made sense to post this follow up blog.
I talked with Jim Florwick and Mir Alami, Cisco wireless Technical Marketing Engineers, who helped design and deploy the WLAN at Cisco Live 2011 as well as Joe Clarke, a Cisco Distinguished Services Engineer who was on the team managing the Cisco Live Network Operations Center (NOC). We discussed the challenges associated with setting up wireless for high density client usage at Cisco Live and for other large events.
“A conference is a very different environment than most enterprise deployments,” said Jim. “First, the average client to access point ratio assumes a 20% duty cycle for the clients because not all clients will use the AP radio at the same time. This is especially true at conferences where activity is typically focused on light browsing and checking email.”
“Also at a conference, there is often a limit on how many APs can be deployed in a given space,” said Jim. “At Cisco Live with 1,000,000 square feet to cover we used 190 access points with an average of 5250 square feet of coverage per access point. However, not all areas were covered at the same density. Areas where users concentrated like session rooms and hot spots had higher coverage. Locations with transient users such as hallways had lower density coverage across more square footage.”
At Cisco Live during peak activity on the WLAN, there were 6000 users associated. This was about 37% of the 16,000 total attendees. Over the course of the entire week, 28,000 unique Wi-Fi devices were seen on the WLAN. Activity on the WLAN followed predictable cycles. For instance, between sessions and after keynotes, the WLAN saw peak usage with minimal to moderate usage in between these times. The 290 clients per 802.11n access point statistic that I stated in my Cisco Live Network Management blog was in reference to the number of associated clients in some areas during a few peak times – not the number of active clients using bandwidth simultaneously.
“There is a big difference between associated clients and active clients,” said Jim. “For a large conference it’s not unusual to see a high associated client count, as people are moving from room to room through transitional areas. This goes beyond what you would consider best practices for an enterprise WLAN because many of these associations last for only a few minutes often with minimal activity. For a conference, you should design and build the client to access point ratio based on the expected activity, bandwidth usage, client density, and duty cycle. It comes down to how many bits per second are required to support the aggregate demand of the clients.”
“For Cisco Live, we followed our high density best practices guidelines and deployed more access points at lower power levels,” said Mir. “We adjusted the radio resource management (RRM) so that the power did not go lower than 4. The lowest data rate available on any of the Cisco Aironet 3500 Series CleanAir access points was 12 Mbps at 2.4 GHz and 18 Mbps for 5 GHz. For the APs, we used stubby antennas (AIR-ANT5135SDW-R= and AIR-ANT2422SDW-R=).”
The team maximized the AP power settings for throughput instead of range and only allowed clients to associate at 12 Mbps and higher. The goal of this design was to keep clients from associating to distant access points. The team did a thorough site survey before the set up to find optimal locations for each access point.
“We actively managed the WLAN using Cisco Prime Network Control System (NCS) because it gave us converged wired, wireless, and security policy management in a single solution,” said Joe. “We used Cisco Catalyst 3560E Series Switches. The most APs we had on a switch were four, with an average of about two APs per switch. We did not allow 802.11b clients due to the minimum speed requirements. The types/ratio of associated clients was 802.11g, then 802.11a, and then 802.11n.”
“Designing a high density WLAN is complex,” said Jim. “The best practices you use for this type of deployment are different than designing a WLAN for an office or campus environment. It’s important to thoroughly understand and manage all of the variables including activity, bandwidth, density, and duty cycle.”
To learn how to design a high density WLAN, read Jim’s slides from his Cisco Live session: BRKEWN-2019: Managing the Mobile Device Wave: Best Practices or listen to his session replay on the Cisco Live portal http://www.ciscolivevirtual.com/.
Best practice guidelines that are applicable for a variety of high density wireless LAN deployment situations are provided in the Wireless LAN Design Guide for High Density Client Environments.