How Cisco IT Plans Capacity for Wireless LAN Access

 

Brett Belding

The capacity requirements for Cisco WLANs have held steady over the last decade—until now. The big change is more devices and more video use: 

• Mobile device explosion: Cisco IT introduced BYOD in 2010. Today it’s not unusual for one person to bring 3-5 devices to work (Figure 1). When these devices are in wireless range, they connect. Therefore, the WLAN needs to support many more connections at the same time. We need to make sure we have enough bandwidth, and enough IP addresses.

Figure 1: Growth in Mobile Devices at Cisco Since July 2013

• More wireless video: Cisco teams often turn on video when they use WebEx or Jabber. They don’t want to change this habit just because they’re using a wireless instead of a wired connection. A WebEx session with video uses about 384 Kbps, and Cisco employees join about 33,000 sessions each day. Jabber sessions with video use 384-2000 Kbps, depending on how much bandwidth is available.

• The Internet of Things: It’s no longer just smartphones, tablets, and laptops that connect to the WLAN. We’ve also got wireless IP phones, video surveillance cameras, and sensors.

For Cisco IT, the goal is to add capacity before users start noticing degraded quality. Here are some of ways we stay ahead.

1 – Tracking Mobile Application Use
We analyze NetFlow data to see which mobile applications that employees are using. If we discover that video traffic is increasing, we know we need to start thinking about adding wireless capacity. Click here for a short article on network data as Big Data.

We use internal tools to monitor IP address allocation and DHCP usage. This helps us understand how many IP addresses the DHCP server needs to provide at the same time. When peak load increases, we reconfigure the server. We’ve noticed peak load increasing in buildings with large conference rooms, because more people are bringing multiple wireless devices—say, a laptop, tablet, and smartphone.

2 – Monitoring Congestion
For wireless voice and video, we need to know about congestion right away. Even a few seconds of pixilation is a problem, so finding out about congestion after the fact is not acceptable.

To see where WLAN congestion is occurring in real-time, we use the medianet features in Cisco switches and routers. During a live broadcast of a company meeting, for example, we can use mediatrace to see the flow from end to end, and pinpoint the source of any congestion.

3 – Moving to Unified Access for Wireless and Wired Connections
Unified access is the single most effective approach to scaling wireless access. We use the Cisco Catalyst 3850 Switch for unified access. This switch has an embedded wireless controller, so it can treat wired and wireless traffic in exactly the same way. The Catalyst 3850 doesn’t slow down wireless traffic, because it provides 40 Gbps of wireless throughput and 480 Gbps of wired throughput. The switch helps us provide the same user experience whether the connection is wired or wireless, even for video. It also reduces management overhead. That’s because instead of separately managing our wired and wireless networks, we now have one policy, one management interface, and one network.

4 – Moving to 802.11ac
We increased bandwidth from 54 Mbps to 300 Mbps when we migrated to the 802.11n standard. The 802.11ac Wave 2 standard will increase bandwidth to 1.3 Gbps. At that time, we’ll upgrade our existing Aironet access points by adding a module. The modular upgrade will cost much less than replacing the access points.

5 – Planning access point placement
When planning new offices, we create coverage maps using Cisco Prime Infrastructure. We can try out different placement of access points, to see interference and overlap. We also use Prime for troubleshooting wired and wireless network connections, and for periodic audits of buildings to make sure coverage is still good.

Here are some of our access point-to-user ratios in different types of spaces:

• Floors with <100 users: 15:1
• Floors with >100 users: 20:1
• Conference centers: 30:1, with 802.11a radios
• Labs: 2500 square feet:1 access point

Next Up: Planning Capacity for Accessing Cloud Services
A growing percentage of traffic on our WLAN is for accessing cloud services, such as WebEx, Box, and Microsoft Office365. In a future blog, I’ll summarize how we plan capacity on links used to access external cloud services.

For More Information

• How Cisco IT implemented Unified Access 
• How Cisco IT introduced BYOD
• How Cisco IT manages BYOD