Eight Keys For A Successful Migration To 802.11n

By  Luc Roy, VP Enterprise Mobility, Siemens Communications, Inc. — September 19, 2008

In millions of businesses around the world, WiFi users expect wireless capability and availability as much as they do a dial-tone and even electricity itself. According to a study from Aberdeen Group, the top two drivers of WiFi deployment strategies in the enterprise are the need to respond to customers faster and the need to increase employee productivity.1

Of course, for users, those drivers translate into unwired convenience and mobile access to information, applications and each other. As multimedia enriches those channels with video, sound and animation, another driver is sure to appear: the need for ever more bandwidth.

Current over-the-air 54 Mbps throughputs for 802.11a/b/g modes cannot handle increasingly data-intensive video, multimedia, music, gaming download, streaming and data backup requirements. Those need more bandwidth, like the theoretical maximum 300 Mbps promised by 802.11n.

Step Right Up
From a technical, interoperability and cost-effective perspective, 802.11n is ready to go today. Although 802.11n can deliver up to twice the range of 802.11a/b/g WiFi networks, there is an inverse relation between range and throughput. The deployment of 802.11n is essentially about gaining higher performance and lower latency at existing range. Both of these benefits are what will help 802.11n become the dominant LAN technology, moving it beyond being just the leader in the world of WLAN.(Need a snapshot of the two new technology enhancements at the heart of 802.11n?)

To ensure a successful 802.11n deployment, enterprises need to be aware of two key issues facing the technology today:

Power over Ethernet (PoE): PoE is defined by the IEEE 802.3af specification and allows the electrical current necessary for the operation of a remote device to be carried over Ethernet LAN cables rather than by power cords. PoE reduces network cost and complexity by reducing the number of wires that must be pulled to install a network.

Still, a great majority of the current crop of Draft 2.0 certified 802.11n APs require a proprietary PoE solution for their power-hungry needs. If they use the 12.95 watts standard for PoE, most have to reduce their abilities and thus their power consumption, which will affect performance and range effectively negating the advantages of moving to 802.11n in the first place.

While advanced PoE requirements are addressed in the new and yet to be ratified 802.3at PoE spec (also referred to as PoE+), the implementation of the spec will require expensive upgrades to network switches or the use of power injectors -- again significantly impacting the viability of early 11n deployments.

There are, however, a limited number of solutions available now that do provide full 802.11n over PoE -- making 802.11n easy to deploy and at significant cost savings. In fact, a 10 percent cost savings at minimum can be achieved with up to 90 percent savings if switches don't have to be replaced. This clearly shows that it's worth the extra time to search out those solutions that put PoE as a top priority.

Traffic Forwarding (Centralized, Distributed, Intelligent)
When planning for 802.11n, consider how much traffic your wireless network will generate on your WLAN. Many enterprise WLAN architectures require access points (APs) to backhaul all traffic to a centralized controller, which then routes it across the wired network. Multiple 802.11n APs can produce a much higher load on your LAN than legacy 802.11a/b/g APs; 802.11n performance is up to six times more than 802.11a or 802.11g. This depends on the size of the WLAN deployment and on how much application data is forwarded to the controller. Therefore distributing traffic at the access point should be seriously considered instead of tunneling all traffic centrally.

As open communications architectures lead to more and more high-bandwidth applications integrated into business processes, 802.11n WLANs will become baseline enterprise requirements. One possible example is wireless video communications in a dispatch application; another is real-time medical consultations while surgery is underway; and a third is multimedia-enabled, multi-party video conferencing.

Planning Recommendations
802.11n technology is a realistic consideration for enterprise deployment now, and the benefits are tangible today. It's important to properly develop the right architectural approach and select the right components from the outset. Doing so now will allow you to get the most out of your existing WLAN while building a future WLAN foundation on 802.11n to serve you for years to come.

Here are some important recommendations to keep in mind:

1. The time is now. You should seriously consider deploying 802.11n now if you are in the process of evaluating and deploying a WLAN for the first time, upgrading to a controller-based system from a fat AP solution, or significantly expanding your WLAN coverage area to support VoWLAN deployments. You should also consider deploying 802.11n if you have reliability issues with your existing WLAN or your current or near future applications require more bandwidth.

Many have expressed concerns about 802.11n's designation of Draft 2.0. This designation is somewhat misleading because the WiFi Alliance has adopted Draft 2.0 as the basis for 802.11n certification. The IEEE will continue to enhance 802.11n with features such as beam forming and packet aggregation, but the bulk of the technology for increased performance and more has already been delivered. If and when the newer 802.11n technology comes out, the current 802.11n Draft 2.0 standard will be backward compatible.

2. Dual-radios are best. Concurrent 2.4 GHz and 5 GHz 802.11n APs should be deployed that support both frequencies simultaneously. Why? Chances are that you won't upgrade all of your enterprise wireless clients to 802.11n at the same time. Most likely your WLAN will need to support both legacy (802.11a/b/g) and 802.11n clients for both 2.4 GHz and 5 GHz. For 802.11n client purchases, it is best to purchase dual mode clients (2.4 and 5 GHz). Ensure that your legacy clients and your client purchasing strategy are aligned with a complete migration plan.

3. Plan AP placements carefully. Another key benefit of 802.11n is its extended range. However, when doing a site survey it is important not to rely on this extended range to cut corners and decrease AP density. Doing so can cause oversubscription and degraded performance for all connected clients, especially legacy ones. Generally it's better to focus on the improved capacity and performance instead of increased range.

For existing 802.11a/b/g networks, you should add 802.11n APs as required to replace legacy 802.11a/b/g APs. Configure both bands for 802.11n support to achieve ideal performance and reliability, while providing backward compatibility to legacy 802.11a/b/g clients; use channel bonding only at 5 GHz so channel overlapping is not a problem at 2.4 GHz. For greenfield deployments, a dual mode 802.11n AP (2.4 GHz and 5 GHz) is highly recommended. Make sure that the client strategy also supports this approach -- 802.11n clients only - because protection mode (support of legacy clients using 802.11a/b/g) could reduce performance gains.

4. Provide adequate network infrastructure: backhaul, power, cabling. 802.11n can lead to more traffic on your wired network, both at the APs and at the core, eventually needing Gigabit Ethernet to support traffic loads in excess of 100 Mbps; upgrade your wiring closet switch from Fast Ethernet to Gigabit Ethernet only when needed because the average WLAN is less than 10 percent utilized.

Some new 802.11n APs require more than 12.95 watts, which exceeds the limits on regular PoE. Other APs may need two Ethernet cables (and ports) to support them. Well-engineered APs use only a single 802.3af port, and require minimal upgrades to the infrastructure. The new 802.3at standard is on the horizon, but has not been approved yet. Also, cabling should be Cat5e or better, such as Cat6.

5. Focus on flexible, feature-rich wireless controllers. Your WLAN controllers are the kingpins of your WLAN architecture. Most controller architectures require all traffic, including security enforcement, to go through the controller. That means many existing controllers may not be capable of meeting the needs of 802.11n throughputs. The ideal is a distributed intelligent controller architecture that can allow traffic to be either tunneled or locally bridged on a per SSID basis. The advantages of each controller architecture are:

  • Centralized forwarding enables all traffic to be routed through the WLAN controller, keeping traffic near central resources. This is best for applications with low bandwidth, for applications that require real-time multi-subnet roaming such as VoWLAN, and for traffic that requires deep filtering such as guest access.
  • Distributed forwarding enables WLAN management traffic to be routed to the WLAN controller but all data traffic is locally bridged at the AP. This is best for networks characterized by high bandwidth, remote branches, and applications that only require portability such as email software and web browsers. It sends traffic immediately to the Ethernet so the network core isn't taxed with double traffic. Employee traffic can be locally bridged since their policies are the same whether wireless or wired. Video is another application that should be locally bridged.
  • Adaptive forwarding represents the best of both worlds, enabling traffic to be routed through the controller or locally bridged at the APs on a per application basis. The APs always perform encryption and Quality of Service (QoS). This hybrid approach minimizes strain on central resources and infrastructure while optimizing performance. Its flexibility also provides for easier network integration and for change management.
7. Intrusion detection and prevention. Wireless Intrusion Detection and Prevention Systems (WIDS/WIPS) require an immediate solution to detect rogue 802.11n APs. Certain vendors already have equipment that can detect unauthorized 802.11n APs with the current 802.11a/b/g sensors. These solutions will detect and locate rogue 802.11n APs. Upgrade to 802.11n sensors only when required.

8. Select the right clients
. A wide variety of 802.11n clients are available today with more on the way as manufacturers standardize on chipsets supporting 802.11n. Today the biggest client considerations are performance and battery life. Although 802.11n consumes more power, the greater bandwidth can mean that client devices must engage the network for shorter periods, limiting the power drain. Going forward, you would be best served by selecting client devices that support 5 GHz, as the 5 GHz 802.11n radios provide channel bonding where the 2.4 GHz spectrum is not practical for channel bonding. Finally, only purchase WiFi certified devices to ensure interoperability and highest performance.

Pervasive 802.11n WLANs promise many enterprise benefits, especially ubiquitous and seemingly unlimited bandwidth for media-rich applications along with low latencies. Over time, new standards, technology developments and evolving network engineering models will help make 802.11n not just the WLAN technology of choice but the choice for all LANs as well. In the meantime, network designers and administrators will serve their enterprises best to plan for a migration to 802.11n well in advance and look for flexible platforms to give them the most options for when they do begin their migrations.

1 "Enterprise Mobile Adoption: A Corporate Conundrum" by Philippe Winthrop and Stephen Walker, The Aberdeen Group. October 2006. 


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