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Initial version of the interoperability document
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# Assess interoperability of Presentation API implementations | ||
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This document discusses the interoperability of potential Presentation API implementations in particular interoperability | ||
between user agents in case of [2-UA implementations][2ua] and between user agents and presentation displays in case of [1-UA implementations][1ua]. | ||
For this, state of the art technologies and standards that may be useful to implement the Presentation API will be considered. | ||
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## Interoperability between user agents (2-UA) | ||
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The following diagram shows an overview of the main components for the 2-UA implementation. Each of the user agents implements | ||
part of the Presentation API (for controlling browsing context or presenting browsing context). To ensure interoperability | ||
between user agents running on controller devices and user agents running on presentation devices the following aspects should be considered: | ||
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* **Discovery**: to discover presentation devices, the controlling user agent should use the same technology as the presenting | ||
user agent uses to advertise itself. **Potential technologies**: SSDP, mDNS or BLE (BLE Beacon) | ||
* **Launch**: after discovery, the controlling user agent should know how to launch a new presentation or join an existing one. | ||
Common message formats should be also used. **Potential technologies**: DIAL (uses SSDP for discovery), Google Cast (part of it). | ||
* **Communication**: also for communication both user agents should use same technologies/protocols to ensure interoperability. | ||
**Potential technologies**: WebSockets, WebRTC, Raw Socket, Google Cast (part of it) | ||
* **Signaling**: common language and message formats (e.g. using JSON or XML) should be used to exchange signaling information between the two user agents. | ||
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![2-UA implementation][2ua-img] | ||
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## Interoperability between user agents and presentation displays (1-UA) | ||
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The following diagram shows an overview of the main components for the 1-UA Implementation. There are less requirements | ||
as in the 2-UA case to ensure interoperability between controlling user agents and presentation displays. | ||
The controlling user agent implements the Presentation API for both controlling and presenting browsing contexts and the presentation | ||
page is rendered in silent mode (not visible for the user). The user agent captures the UI output of the presentation page rendered | ||
in silent mode and sends the frames to a presentation device like a projector or wireless display. This means the user agent and the | ||
presentation device should use a common streaming technology to ensure interoperability. More than likely, the user agent will use System APIs | ||
offered by the OS to show content on the presentation device. But other technologies not offered directly by the OS are also possible, for example | ||
Google Cast extension for chrome supports Tab cast to Chromecast using WebRTC. **Potentials Technologies**: HDMI, Intel WiDi, Miracast, Airplay, MHL. | ||
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![1-UA implementation][1ua-img] | ||
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[1ua]: http://w3c.github.io/presentation-api/#1-ua | ||
[2ua]: http://w3c.github.io/presentation-api/#2-ua | ||
[1ua-img]: ./images/interoperability-1ua.png | ||
[2ua-img]: ./images/interoperability-2ua.png |