Tethered caching is a major new system from Apple to speed up device provisioning, app installs and app updates. It’s most helpful in places where many iPhones and iPads are clustered together, such as healthcare, retail, and hospitality. But it only works if you have updated iPhones and Macs (yes, Macs).
Tethered caching provides two separate but related features: tethered networking & app caching.
- Tethered Networking: When active, all network traffic from the iOS device will be routed through the USB connection and out the Mac’s Ethernet connection. This includes web pages, MDM instructions, and push notifications.
- App Caching: App Caching dramatically speeds up app installs if you are doing repetitive provisioning. As your tethered devices download apps, the Mac inserts itself as middleman, and will save copies of each installed app. Subsequent installs of the same apps (on the same or other tethered devices) are much quicker, since the apps load from the Mac’s hard drive instead of the Internet.
The two features work together, as illustrated by the following diagram:
Does GroundControl work with tethered caching?
GroundControl and tethered caching works really, REALLY well together, with our Launchpad software running side-by-side with tethered caching. It runs as a background service on your Macs, while our Launchpad app runs in the foreground.
GroundControl already locally cached some content, such as device backups, iOS updates, and enterprise apps. But we never cached iTunes apps. Apple’s new service takes care of that.
Are you using temporary provisioning networks in your workflows? You may not need those any more. Tethered devices no longer require WiFi to enroll into MDM, making enterprise WiFi deployments much simpler.
Requirements for tethered caching
Apple details requirements and setup here: https://support.apple.com/en-us/HT207523
- It’s Mac only, with no Windows version today (and likely not ever)
- Macs must be upgraded to macOS 10.12.4
- iTunes must be upgraded to version 12.6
- Devices must be upgraded to iOS 10.3
- The Mac must be on an Ethernet connection, and WiFi should be turned off
- The Mac will not sleep while tethered caching is active
- Apple’s macOS Server app can not be installed on the same Mac
To function, devices must pair with the Mac. This is no problem if the devices start out as erased, or if an “erase” is part of your workflow (e.g. patient engagement). But already-provisioned devices may need extra work before they can use these services.
Details and tips
Tethered caching as it exists today — April 2017 — is a bit unpolished for an Apple tool. It is not even an app, it’s a shell script!
Apple has not documented how to make it launch at startup (but we figured it out: Launching tethered-caching at startup). There are also no tools yet for monitoring or tuning the service, but we think those are good opportunities for GroundControl to help.
You can think of tethered networking like “Personal Hotspot,” but in reverse. Instead of the Mac using the iPhone’s networking, the iPhone uses the Mac’s networking. In fact, devices show up in the Mac’s Internet Sharing preference pane.
The tethered caching service creates a private IP subnet to assign your devices IP addresses. It tries to find an unused subnet (192.168.x.x), but the system may have trouble in complex enterprise networks. The page man tethered-caching provides options for specifying the subnet range.
- While tethered, the device’s WiFi indicator disappears (we hope Apple adds a tethering icon), but Settings confusingly shows a connected WiFi network
- The assigned IP address does not appear in Settings, but you can see it on the Mac using ifconfig
- Even in Airplane Mode, a tethered device can browse the web — a nifty party trick!
- Many devices may be tethered simultaneously using a USB hub
- App caching works well with and without MDM, with and without VPP, basically everything works, except…
- App caching does NOT cache enterprise (aka “in house”) apps, but GroundControl handles enterprise apps, so this should be no big deal for GroundControl customers
Should you switch your Launchpads to Mac?
We think our hospital customers can benefit the most from tethered caching. These customers sometimes install 10-30 apps on a patient-facing iPad, and apps are installed daily. Many already use WiFi caching servers, but tethered caching should be significantly quicker.
If you are only installing one or two apps from the App Store, and on a handful of devices, then the switch may or may not be worth it. If you are installing several apps, or if your network bandwidth is constrained, or you have a whole lot of iOS devices to set up, then using Mac may be the best choice you can make.