Chromecast in 95 Rooms
In a media driven age, providing a reliable and effective method of presenting content within the classroom is a huge factor in the success of our students.
The reliability of presenting to a TV or Projector is an important part of every teacher’s day. If a teacher encounters an issue during a presentation, it creates a disruption of learning for those in the classroom, greatly reducing the effectiveness of the lesson.
What’s wrong with plain old cables?
We currently have 95 projectors installed at our campus. Each projector is used at least once every school day at an absolute minimum-sometimes up to six times.
As you can imagine, such high usage results in a significant amount of cable failures, costing the school both time and money to replace. To put this in to perspective, we tend to a classroom for a cable failure once a day on average and the school spent $25,000 on replacements throughout 2016 alone.
So, how do we ditch the cables?
We needed a solution for wireless presentation — one which was reliable and did not require endless tinkering to implement. We needed something as close to a turnkey solution as possible and most importantly we needed to remove the need for cables.
Whatever we implemented, it had to be compatible with multiple operating systems, including Windows, MacOS and ChromeOS, which ruled a large number of products out immediately. After researching almost every solution available, including those aimed at education, we found ourselves coming back to Google’s Chromecast. It was the only multi-platform option which offered simplicity in both its operation and installation — not to mention it was the cheapest of them all.
We also found that iOS or ChromeOS updates would often break third party solutions, whereas Chromecast is supported end-to-end. Additionally, Chromecast allows the user to cast a single Tab to the room while multitasking and working in other Tabs. This is a huge convenience for teachers, particularly when marking the roll or dealing with sensitive information.
Is it that easy?
At a glance, Chromecast seems like a miracle solution, but making a non-enterprise product perform in an enterprise environment is quite a challenge. The way Chromecast is designed assumes that there is a limited number of users connected to the network. It operates on a protocol called mDNS and broadcasts its visibility to anyone and everyone on the network. Any user connected to the same network as the Chromecast is able to control it.
A good example of the type of issues this design can cause is the network-wide Android notification recently implemented by Google. If you are not aware of this notification, it is generated by Google Play Services on every Android device whenever a Cast session is seen as active on the same network, allowing the user full control. The user assumes it is their phone Casting, or they just want that pesky notification to go away, so instead of dismissing the notification, they hit the “X”, which ends the Casting session.
The same notification is also generated on ChromeOS in the system tray.
To solve this problem, we created a separate VLAN for the Chromecast devices, implemented a Virtual Machine running Ubuntu and a service called Avahi. Avahi “reflects” all mDNS traffic between the Chromecast VLAN and the Staff VLAN, making mDNS discovery possible for clients of the Staff VLAN.
In addition, we blocked access from our Student VLAN’s to the Chromecast VLAN via an Access Control List (ACL) on the core switch. ACL’s allowed us to prevent any IP communication from the Chromecast VLAN making it across to the Student VLAN’s, as in our setup, it was still possible for Chromecast to be discovered via mDNS — blocking IP access was the only method which prevented discovery. Learn more on ACL’s in Matthew’s article on the topic.
Blocking student access certainly wasn’t our aim. However, it was necessary at this stage in the project. Having around 1000 Android devices and 2000 Chromebook’s in the school meant that Casting sessions would be stopped constantly if this was left open.
It is a priority that we revisit students ability to Cast in the near future — however, at this stage we are relying on Google to remove the notification from Android devices as well as ChromeOS.
The results so far
Providing an alternative to VGA or HDMI output immediately reduced the frequency of disruptions in the classroom. We found that the few teachers who were reluctant to the shift in technology would turn to Chromecast when the cables failed, preventing any ongoing disruptions and encouraging them to ditch the cables for good.
A quick stroll through the school shows that most teachers have abandoned cables. Word of mouth appears to be spreading and feedback around the staff room is largely positive.
Thanks for reading and stay tuned for updates on how this progresses.
