Reducing the density of wireless access points for voice services

It is widely accepted that if an enterprise wants to run the voice application VoWLAN on a wireless LAN, more access points must be deployed than the pure data transmission network. Of course, the higher the density of the deployed access point, the more helpful it is to fill the gaps in the coverage, and these gaps are the main cause of real-time call loss. However, the University of Arizona found that too high access point density also produces a series of problems.

When the university initially installed 5000 Cisco light access points in 65 buildings, data and voice applications were fully taken into account. Justin Miller, a network system analyst at the University of Arizona, said: "school employees do not need to use their own mobile phones at their desks ." This university aims to enable users to use Wi-Fi phones and avoid the cost of local mobile calls.

It is reported that the University of Arizona runs a number of Cisco Aironet 1130 802.11a/B/g access points, covering 3/4 of the accommodation area of middle school students, and uses four Cisco 802.11n 1250 Access Points outdoors. In terms of speech, university staff can use Cisco, Nokia, and T-Mobile phones with Wi-Fi functions. In terms of Cisco's 7921 Wi-Fi Phone, we recommend that you set the minimum planned signal level critical value to-67dBm and the signal-to-noise ratio to 25dB to ensure a good user voice experience.

According to the advice of a third-party project manager, the university uses a 25 dB SNR measurement scheme to determine the number and location of access points required for voice calls. However, this plan does not take into account the received signal strength indicators (bsns) level. This university originally used a third-party planning tool, but it cannot implement blank spaces between active channels and thus cannot reduce interference between channels.

What are the results? "We found that the amount of over-built infrastructure reached 20% to 50%," Miller said ." He explained that this will cause a large number of client-access points to reconnect and the general speech session is unstable. The deployment density of the Access Point is too high, which means that the Wi-Fi phone will be repeatedly connected between the access points and cause call loss.

Therefore, the university switched to the AirMagnet WLAN Planner tool in its 802.11a/B/G network. "After using this tool, we found that the original planning technology was flawed," Miller said ." To ensure the strength of the-68dBm signal, He redesigned the Access Point layout so that the current network can run perfectly.

The University of Arizona's experience can be expanded to more high-density Wireless LAN applications. More users, more traffic, and more multimedia will overload the enterprise's wireless LAN, beyond the original plan design. Obviously, the higher the density of wireless access points, the better the wireless network transmission effect.

If the early Wireless LAN focused on increasing the number of access points covering a specific area. Today, many wireless administrators are focusing on capacity expansion. They often face new expansion challenges. They need to support more users and provide services for more demanding applications while continuing to expand their scale.

Pay attention to deploying high-density WLAN

Clearly understand what access points can and cannot do

Fully test the performance of wireless networks under load

Configure access points by capacity

Make sure that the DHCP server can handle high traffic bursts.

Plan, monitor, and manage IP addresses to avoid address depletion

End-to-End capacity planning is required even if high-throughput 802.11n is used

1. True: Jointly hosted data security and voice services with Cisco
2. Huawei 3Com Quidway XE7000 Series IP voice server