It just works...except when it shouldn't.
Fling enables one device to "fling" a URL to a TV (or other media device) for playback. It feels like Airplay and Chromecast, but it does what they don't do.
It just works...
Even if the mobile device and the network device are on different networks.
Even if the mobile device is an Android phone or an Apple phone purchased in the dark ages.
Even if the mobile device is any phone that at least provides web browsing capabilities with a web browser that is reasonably compatible with modern browsers, or provides a sufficiently similar app development environment.
Even if the user "flinging" has no account or prior affiliation with the receiving media device.
For flinging from a web page, it works even if the user has not installed any application that is fling-enabled. Fling only requires javascript.
Further, it doesn't require the user to enter a short code or scan a QR code. And it doesn't realy on access to microphones or cameras.
...except when it shouldn't
Bob's neighbor cannot fling porn to Bob's 5 year old daughter watching TV.
Bob's college frenemy down the hall in their dorm cannot fling porn to Bob's TV even though they are both in the same building using the same wifi network.
More specifically, Fling won't work if the mobile device is not in physical proximity to the media device.
Fling won't work if the mobile device is in a different room such that there is an intervening wall.
Unless... the media device's owner has allowed policy exceptions to the above requirements.
From Joe User's perspective. Joe walks into Bob's house. Joe's old iPhone 8 is not on Bob's wifi network and is using only cellular data. Joe opens a youtube page in the phone's Safari browser. A button appears beneath the video, perhaps alongside the button for casting or airplaying. Joe pushes this button and it opens an iframe, frame, or web page showing the video to be flung, a list of detected media devices if more than one is nearby or the name of the device if there is only one, and lastly a "fling" button. Joe pushes "fling" and the video starts playing on Bob's TV.
Joe User didn't have to join Bob's wifi network. Joe User didn't have to join any wifi network. Joe User didn't have to upgrade his phone. Joe User didn't enter any usernames, passwords, QR codes, or short codes.
Clearly some "magic" is going on. How did Joe's iPhone 8 communicate with the TV when Joe isn't even on Bob's wifi network? Before answering the question, let's talk about Sandbox Reachable Services.
Fling is an example of Sandbox-Reachable Services (SRS). SRS is a system that allows a sandboxed application like a web page or mobile app to communicate with nearby network devices.
SRS has been around since 2008, when it was first deployed in Vizio televisions, under the name Web Videos. Web Videos only implemented fling. Or should I say, "it only implemented Fling 1." Fling 1 and more generally SRS 1 required the mobile device and the media device to be on the same network. Fling 1 provided little benefit over Airplay or Chromecast.
Fling 1 made it onto all Vizio TVs, because AirPlay and Chromecast did not exist when Fling was first introduced.
David Harrison holds several patents for sandbox reachable services.
SRS 2 and by extension Fling 2 changes the problem. We want to fling even when the mobile device and the media device are NOT on the same network, but when the mobile device and the media device are in proximity to each other or in the same room.
Consider the Joe and Bob example:
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Joe's iPhone is emitting electromagnetic radiation.
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Bob's TV is equipped with a wifi antenna (maybe two) and possible other hardware (although hopefully this isn't required)
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Joe is in proximity to Bob's TV.
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Bob's TV is doing signal processing to pick up the presence of Bob's iPhone based on upper harmonics from Joe's cell antenna.
Even devices using different technology may introduce noise on nearby antennas. This "noise" may be low energy and only suitable for low bitrate communications. However, it could be used to communicate a token.
Joe's cell phone has cell data enabling moderately high bitrate Internet access.
Bob's TV has wifi enabling high bitrate Internet access.
All Joe's cell phone needs to do is to tell Bob who to talk to on the Internet to relay information across their respective modertely high and high bitrate channels to the Internet. The token can do that.
The token could be a short code that is communciated to a centralized server or a Distributed Hash Table (DHT) node. The server or DHT node could act as the relay for further communications between Joe's cell phone and Bob's TV. Once communications is established via the relay, Joe's can communicate at higher bitrate to Bob's TV in order to make API calls such as "play this URL."
SRS is promiscuous. Fling is a double entendre in the same mode.
SRS is promiscuous in that makes services available with zero prior affiliation the service and the requstor and it does so without requiring any exchange of any form of identification. This does not make sense for many types of services, but it does not have to. Do not use promiscuous services if they are inappropriate. Promiscuous services may be promiscuous, but this does not imply lack of consent. The device offering the service does so intentionally. The device communicating with the service does so intentionally.
This does not mean that the two parties consent without information. Promiscuous services may still make decisions based on policy. Policy decisions may be made based on policy inputs that are inferred rather than explicitly provided by the user. Such policy inputs may include inferring proximity between the two parties, or inferring relative location or inferring the presence of intervening walls.
The proxies require some means for inferring said proxies. We could use a camera or microphone to enable proximity detection, but cameras and microphones are often deemed as too intrusive. For Sandbox Reachable Services we rely on EM emissions that are normally generated by mobile devices in order to enable communications without requiring the mobile device to join the same network as the media device.
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Sandbox Reachable Service: a network service designed to be discovered by and to communicate with sandboxed applications.
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Sandbox Reachable Services 1: system that enables communications between a sandboxed application and nodes on the same network.
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Sandbox Reachable Services 2: system that enables communications between a sandboxed application and nodes running sandbox reachable services in physical proximity to the node running the sandboxed application. The device running the sandboxed application and the media device do not have to be on the same network, but they must communicate using electromagnetic emissions that are sufficiently similar as to induce oscillations in the antenna(s) on the
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Sandboxed Application: a web page or mobile app that run in a web or web-like security sandbox.
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Sandboxed Initiator Beacon (a.k.a., beacon): a piece of javascript (or app code) that operates within a sandboxed application to make its presence known to nearby unsandboxed beacon detectors. Because beacon is sandboxed, it can only perform operations that available to sandboxed applications. At the very least, a sandboxed application can force DNS queries, download small files, open connections to a variety of IP addresses. The operations performed by the beacon establish a low bitrate covert channel that can be detected by unsandboxed beacon detectors.
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Unsandboxed Beacon Detector (a.k.a., beacon detector): a beacon detector runs as part of sandbox-reachable services on the device offering one or more services to sandboxed applications. As implied by the title, the beacon detector is not subject to the limitations of a web or web-like security sandbox. In fact, an unsandboxed beacon detector has low level (device-driver level) access to the antenna(s) on the media device. We can upgrade the media device running the unsandboxed beacon detector to increase the range of devices it can detect, though the idea is to try to enable beacon detection using only software, machine learning, and a wifi-antenna.