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Designing for applications



Some applications are very sensitive to some wireless features like roaming and latency. If you use your laptop or tablet for some voice over WLAN application, layer 3 roaming can become a problem. With layer 3 roaming, the client receives a new IP address and this will affect voice application or other sensitive applications. The not-correct roaming type can result in delay. Some application cannot deal with high latency. VoIP for example cannot have a round-trip time (RTT) of more than 300 ms or a unidirectional latency of 150 ms or less. This latency doesn’t need to be just on wireless, but also impacts the wired links or processing devices. For example, overloaded routers or encryption. For this, besides roaming mechanism, QoS can be helpful. You should design for latency around 90-100 ms.

Some applications have throughput demanding, like with video and audio codecs. To measure the throughput, you can connect the client and the server on a gigabit switch and monitor the throughput when you do actions in the application. This gives you a good idea, and when you multiply the outcome with the number of clients that will use the application at the same time, you have a good value to design with. It is good to add 10% and round it up to the nearest half Mbps.

In most warehouses are barcode scanners, and oftentimes, these scanners have mainly cheap chipsets that use old technologies, like 802.11b/g. They don’t support the latest features; however, barcode scanners do not demand high throughput.

For medical devices, you need both a good coverage and capacity network. Communication is critical, so when an access point is not working, another access point needs to be able to take over. The devices are nomadic, which means they are portable, but when you use the device, the devices are, at that moment, stationary (for example, x-ray scanners).

Nowadays, there are also ID badges that use wireless. Like with barcode scanners, they are often 802.11b/g only and there are even devices that are WEP only. Thankfully, those are rare, but there are still devices that cannot work with WPA/WPA2-Enterprise, and need per se WPA/WPA2-Personal.

When you are going to use location tracking systems, you need to have three access points. This is because of triangulation to locate the specific device as well as possible.