Configuring networks for iPad deployments
If you use iPad in class, each student uses bandwidth from your Wi-Fi network, so your Wi-Fi network must be configured properly to support iPad.
802.11 is a shared medium and is limited by other devices connected to your wireless network. Therefore it’s important to look at aggregate throughput.
Device throughput to the Internet depends on the following:
Device connection rate to the access points
Bandwidth you have from your Internet service provider (ISP)
Number of devices using the same channel
Interference (radio, physical, electrical) and the distance from client device to the AP are two major factors that affect observed maximum throughput. The half-duplex nature of wireless, combined with other TCP/IP overhead, also means the actual aggregate throughput is typically 65 percent or less of the data rate.
This chapter provides guidelines for a Wi-Fi network deployment and a way to calculate expected usage based on a way to calculate the maximum number of devices that can be used simultaneously in a classroom.
Considerations
Factors to consider when preparing your network for iPad:
Physical dimensions of the classroom area
Number of students per class
Number of access points (APs) per classroom area
AP mode and antenna directions
Channel and co-channel interference
Network security method
Backbone speed from your school to the Internet
App throughput requirements
Classroom wall material (informs how well RF propagates and reflects/refracts will have appreciable impact on Wi-Fi signal)
RF emitting items in and around the classroom (sources of destructive interference could have a large impact on the quality and consistency of Wi-Fi signal in a given classroom)
Initial network assumptions
The following are initial network assumptions. Your network will have different values.
Assumption | Value |
|---|---|
MAC efficiency (802.11a/b/g/n - no aggregation) | 0.45 |
MAC efficiency (802.11n/ac aggregation) | 0.65 |
Maximum clients per access point | 50 |
Available channel capacity (percent) | 80 A typical available channel capacity is about 80%. |
ISP/WAN speed (Mbps) | 100 |
App usage values
The following are typical throughput values from three main categories; browsing, streaming, and backup of audio-visual data from a Shared iPad to the cloud.
App usage per device | Minimum throughput requirement (Mbps) |
|---|---|
Browsing For example, browsing the Internet | 1 |
Streaming For example, streaming a video | 4 |
A/V backup (~2 GB in 5 minutes) For example, copying a large Keynote or GarageBand file to iCloud Drive | 6 |
Usage calculations
Below is a sample iPad guideline calculation. This isn’t a replacement for an actual Wi-Fi site survey to deploy the network properly. The browsing, streaming, and A/V backup columns show the maximum simultaneous devices.
This formula calculates the maximum number of clients per AP for three categories of Wi-Fi applications: browsing, streaming and backups. The basic calculation is the total available throughput divided by the minimum throughput requirement for each application. Total available throughput is limited either by the data rate of the Wi-Fi being used or by the ISP/WAN speed, whichever is slowest. Depending on the application, the maximum number of clients per access point, as entered in the assumptions, could be achieved.
Important: Performance may vary due to network configuration and RF environment.
Wi-Fi AP configuration | Maximum physical rate (Mbps) | Aggregate data rate (Mbps) | Browsing | Streaming | A/V Backup |
|---|---|---|---|---|---|
802.11a/g | 54 | 19 | 19 | 4 | 3 |
802.11n 1 spatial stream 20 MHz | 72 | 25 | 25 | 6 | 4 |
802.11n 1 spatial stream 40 MHz | 150 | 54 | 50 | 19 | 13 |
802.11n 2 spatial streams 20 MHz | 144 | 51 | 50 | 18 | 12 |
802.11n 2 spatial streams 40 MHz | 300 | 108 | 50 | 25 | 16 |
802.11ac 1 spatial stream 40 MHz | 200 | 72 | 50 | 25 | 16 |
802.11ac 2 spatial streams 40 MHz | 400 | 144 | 50 | 25 | 16 |
802.11ac 1 spatial stream 80 MHz | 433 | 155 | 50 | 25 | 16 |
802.11ac 2 spatial streams 80 MHz | 867 | 312 | 50 | 25 | 16 |