802.11n LAN design best practices

Now anyone deploying and designing a wireless LAN should use 802.11n wireless access points. This is not only because the price can be comparable to that of 11a/g, but also because of the availability and range of 11n, less wireless access points are required for indoor space. Although some battery-powered devices have not been sold out, most new customers still choose 11n products. In short, unless it is necessary for commercial purposes, you must buy 11n products.

When you want to design an 802.11n Wireless LAN, the best practices are elusive:

◆ Channel structure: almost all products use multi-channel to create micro-cells, but at least two vendors use a single channel to create a large RF layer. It is obvious that when a user moves, the latter will reduce the roaming time, but there is still a heated dispute over the trade-offs.

◆ Distribution Control: 802.11n in a centralized Wireless LAN shows inefficiency and bottlenecks. It is difficult for a small controller to cope with high throughput. Opening all tunnels to a controller will lead to latency and it will be difficult to extend end-to-end Qos. For the best results, centralized management and visibility are required when real-time Qos and security control tasks are assigned to the AP.

◆ Return capability: a fully-used 11n AP may generate more traffic than 11a/g. When more throughput is required, you can detect the 10/100 Ethernet switch and the return link to upgrade the Ethernet.

Regardless of how the IP packet flows over the network, when they arrive at an AP, they will be packaged into 11n frames for radio transmission. Here, RF networks need to be designed to meet wireless coverage, throughput, and program requirements.

◆ Band selection: if possible, the GHz band is used only for the 11g client; the 5 GHz band is for the 11a client and the new 11n client. This operation can reduce interference and carry a larger throughput including 40 MHz bound to the channel), but you must purchase a dual-band 11n client.

◆ Channel deployment: allocate a 5 GHz channel to meet the needs of different programs. For example, assign a static 20 MHz UNII-1 channel to the voice and give the phone a reliable scan list. Assign UNII-2/2e channels only to data and file transfer programs that can allow dynamic frequency selection. Bind a 5 GHz channel to programs that require high throughput, such as HD videos. Do not bind a 2-4 GHz channel.

◆ AP placement: Early APs are often placed based on experience, but the multi-path leads to a gap in the 11n cells and changes over time. Let Wireless LAN planners estimate the number of 11n APs and how to place them to meet the design goal. For the best results, consider the impact of buildings on RF. To keep your plan up to date, use a 5 GHz dual-band AP to replace the 2-4 GHz honeycomb. You can consider targeting antennas to effectively fill the coverage gaps such as long corridor or stair wells.

◆ Design goal: ensure that the AP solution meets the application perception goal all the time. For example, it is generally recommended that the minimum signal strength from 10% to 20% cells overlap-67 dBm for speech. When selecting a cell size, consider that the larger cell can minimize roaming-suitable for latency-sensitive programs, but small cells are suitable for highly intensive areas such as classrooms. Even if you use the automatically configured AP transmit power, select the maximum to match the transmit power of the client.

Although experts have discussed the benefits of 11n on-site surveys, measurement advocates suggest measuring their compatibility with 802.11n design best practices later in deployment. Combined with downlink and uplink, the effective measurement technology can also be used on 11n. Finally, the performance of applications on real client devices must be measured. Because 802.11n clients are widely used, the signal strength may not always be trustworthy based on user experience.