Connectivity is like a relay race, if any one runner drops the baton, the race is lost. The runners in our team are:
- the wired network
- the wireless network
- the internet connection
- the devices
- the network applications
Often installed in the days when the teachers had laptops and the students had pens and paper, the wired network is probably not fit for the purpose of supporting a mobile learning scheme.
The primary tasks of the wired network are:
- to provide a gigabit Ethernet connection and power over Ethernet to each wireless access point
- to link the wireless network to the internet connection and to on-site servers and wired services (printers, AV etc)
Schools should evaluate whether they need new switches and perhaps new cabling. Make sure that the switches can supply enough power for all the APs connected and can supply power at the right power level.
Make sure there are no bottle necks in line that will reduce performance. Each AP needs all of its 1Gb/s link right back to the core. Ensure there is no “daisy chaining” of switches – sharing this bandwidth.
Some older cabling will not support gigabit Ethernet.
Teaching and learning with mobile devices is teaching and learning over wi-fi. Focus on getting fast reliable wi-fi that supports high densities of mobile devices, rather than wi-fi that provides a great looking dashboard!
You will probably need one access point per class + 10%. Perhaps less in a primary school. The network should be planned for performance, coverage and mobility:
For a conservative design, you will need one “good” access point for every 30 – 50 concurrently connected devices. This often means one per classroom. One per classroom will be a definite requirement if the walls are “thick”, reducing the wi-fi signal. Access points are not all the same – their ability to support a class full of devices varies hugely.
Once you have decided where the access points need to be to get performance in the high density areas then the network needs to be designed with coverage and interference in mind. Access points can interfere with each other compromising reliability and performance.
Agree a specification for coverage which includes:
- A minimum signal strength e.g -55dBm (allows the highest speed 802.11ac network) or -65dBm (enables the highest speed 802.11n network)
- A maximum signal to noise ratio ie 25 ( this defines the maximum interference that is allowed)
These two measurements are difficult to achieve simultaneously so choose a system that offers single channel operation to eliminate interference, or insist on seeing a pre-order heatmap and post installation survey which show that both signal strength and interference criteria are met. Make the specification part of the contract.
There is a big change in wi-fi requirement if you move from class/trolley based devices to 1:1 or BYOD. With these schemes, students take the devices with them between lessons, so mobility becomes an issue. Make sure that your wi-fi system has features which ensure that your devices always connect to the right access point. Devices must “roam” to a new AP when they reach the minimum signal strength defined above as acceptable, otherwise they stay connected to an AP which is offering poor signal, slow connection and poor reliability.
As more resources move to the cloud it is important to recognize that “the cloud” is at the far end of your internet connection, so the internet connection is critical.
When choosing a service ask what the guaranteed uplink speed and guaranteed downlink speed are. Leased line services usually guarantee a speed and uplink and downlink are the same. Broadband services give a maximum connection speed – uplink is slower than downlink, and you may get nothing like the advertised speed.
You need “enough” bandwidth. How much “enough” is difficult to say. A good rule of thumb for 1:1 schemes using cloud storage is 150Mb/s per 1000 students. However much you have it may not be enough. So..
1. Get a good internet gateway product that enables you to:
- Measure how much bandwidth is being used
- Reserve bandwidth for people, sites, or applications
- Prioritise teachers over pupils
- Restrict or deny access for people, sites or applications
- Prioritise educational traffic
2. Use less internet
Obvious, but how do we do it without defeating the object!
- Deploy local cloud storage
Netbooks used local Microsoft servers for their storage. Tablets use cloud storage such as Google Drive, Office 365 and DropBox. This means that every time students open or save work, the data goes through the internet pipe. When this activity is co-ordinated by a school timetable and teachers issuing the instruction “save your work now” the internet connection can be swamped by all the devices opening or saving work at the same time.Solutions exist which enable the Microsoft servers already owned by schools to be deployed as local cloud storage. Tablets get access to shares on local servers so opening and saving files does not involve the internet connection. They can even cache work on the device enabling home working without internet connection.
- Cache apps for deployment
If you are deploying (or upgrading) one app to one hundred devices that app is downloaded 100 times. If it were for example MS Powerpoint that is 205MB x 100. With dedicated use of a 10Mb/s line this would take more than 6 hours.Apple’s Mavericks server with Caching Server 2 enables anything from the App Store, iTunes Store, iTunes U and iBooks Store to be cached locally before deployment.
If you have control get good network devices.
- Best – 802.11ac
This is the latest and fastest standard. Wi-fi enables only one device to transmit per AP at the same time. The faster they transmit the more time there is to support other devices.
- Good – 802.11n dual band, dual stream
Dual band means it works in 5GHz frequency band as well as in 2.4GHz. 5GHz tends to be more reliable. Dual stream doubles the speed. Higher speed = higher device density
Network applications & IP design
Even if you have all of the above “physical network” right there are still some gotchas.
Make sure you speak with someone to ensure the logical design of your network is correct. You need enough IP addresses available for every device, your network may need to be divided into subnets, and you need to be able to communicate between subnets.
Subnets are used for security and to prevent broadcasts (automatic chatter between devices) from flooding the network. Some network applications, like Apple Airplay and AirPrint are very chatty, but also struggle when there are subnets in place. If you are a big Apple user and want Apple TV in every classroom, make sure your wi-fi has service control.
This is one of three blog posts which will help you make the right decisions on infrastructure:
- Infrastructure: you get what you ask for
- Safety and security without compromising convenience (coming soon)
Written by Rob Leggett, founder of and business development director at Siracom, distributor for our sponsor Meru Networks. Following their recent acquisition by Fortinet, Meru’s sponsorship will continue under the Fortinet brand.