As wireless LAN deployments and usage has increased, coupled with the near ubiquity of embedded Wi-Fi in laptops and smart phones, many enterprises are experiencing complaints from their users of slow or even dropped connections.
Virtual Cells: The Only Scalable
Multi-Channel Deployment
As wireless LAN deployments and usage has increased, coupled with the near ubiquity of embedded Wi-Fi in laptops and smart phones, many enterprises are experiencing complaints from their users of slow or even dropped connections. Many times this is due to a high density of users all accessing the wireless LAN (WLAN) simultaneously. Unfortunately, today's wireless LAN solutions are not designed 1to deal with high densities of users that comes along with a pervasive WLAN in a corporation and what was formerly liberating is now frustrating.
While some vendors have created WLAN switch architectures to help large deployments, they focus primarily on security management and central management of access points (APs) configuration parameters. Solving these problems is both important and necessary, but it is not enough. The key challenge is managing contention, interference and Quality of Service (QoS) in a pervasive Wi-Fi deployment with both data and voice clients. This means minimizing the problems of co-channel interference, inter-AP handoff, as well as wireless network fidelity (for reliable communication) even with the limitation of few available channels. Meru Networks has created a Wi-Fi certified system designed from the ground up to account for co-channel interference and allow single channel or Virtual Cell operation creating the only truly scalable deployment architecture available today.
Why Traditional WLANs Fail in High Density Situations
Traditional wireless LANs are analogous to an Ethernet hub. As the 802.11 protocol is a shared medium, all users contend for the same bandwidth delivered by a single Access Point (AP). As higher numbers of users access the wireless LAN, the collision avoidance protocol used by 802.11 to manage contention increases each individual client's time to access the network. As the number of users increases, more and more delay occurs resulting in slower speeds for each user and even application timeout.
To solve these issues, conventional wisdom is to deploy more access points at a closer spacing. The reasoning behind this practice is, in summary, that if one access point provides 54 Mbps of bandwidth (802.11g or 802.11a), then additional APs will increase the capacity. This is true only to 2a limited extent. A number of reasons including only three non-overlapping channels and co-channel interference as more than three APs are deployed limit the effectiveness of this approach. Reducing cell size by reducing the output power of the AP from the default 100mW to somewhere on
1 Pervasive Wi-Fi deployments are defined as deployments whose intent is to provide wireless voice and data access throughout a building or campus 2 802.11b and 802.11g
WP4-0705 1Virtual Cells: The Only Scalable Multi-Channel Deployment
3the order of 30mW (a practice also known as creating "Microcells" ) is often mentioned as a way to mitigate this, but when it comes right down to it, the solution is still inadequate for pervasive deployments. The more APs deployed in close proximity, the more contention there is, resulting in even more problems with throughput and connectivity for high numbers of users. And with a limited number of channels it is impossible to avoid having some APs on the same channel (particularly in a multi-story building).
Figure 2: With only three to five active contenders, the total bandwidth available from a single AP dramatically declines.
With the power reduced on the AP you also artific... [download for more]
