Concepts

Endpoints

An “endpoint” is a single client, usually referring to a client which is in an RTC pool.

Pools

Pools are collections of RTC connections. They are actually managed by the signalling channels, so even if no RTC connections have actually been negotiated, individual endpoints are made aware of their peers and know who to send offers to when appropriate. A single pool might be a video chat room, for instance.

Descriptions

RTCPool implements a system whereby connections can be associated with descriptions - arbitrary JSON objects which can be used to provide further information about the endpoint. Descriptions are meant to be considered trustworthy, so setting descriptions is something that can only be done from the back-end. You can get an endpoint’s description with Pool.get_description().

Signalling

A signalling channel is simply an object that sends and receives RTC negotiation messages. How it sends them is unimportant, but they are sent via a send(message_type, message_data) method. Likewise, how it receives them is unimportant. A signalling class should be a subclass of EventTarget, and when it receives an event from the server, it dispatches an event to itself. The event names are mapped accordingly:

Received From Server	Type of event dispatched
rtc:joined	join
rtc:describe	describe
rtc:request_offers	request
rtc:offer	offer
rtc:answer	answer
rtc:close	close
rtc:candidate	candidate
rtc:stop	stop

RTCPool has built in support for raw WebSocket signalling and socket.io signalling, but you can build your own signalling class by creating a class which functions as described above.

To simplify things, the signalling() automatically handles the event mapping. All you must do is extend transceiver(), and then you can create a signalling instance with something like the below:

const signalling = new rtcpool.signalling(new MyTransceiver());

Perfect Negotiation

RTCPool uses perfect negotiation to be sure that all negotiations result in a successful connections. The details of how perfect negotiation works are out of the scope of this document; however, the fact that this has been implemented can let you rest assured that all your connections will not fail to be established (of course, assuming that you have a functional TURN/STUN configuration and signalling channel to boot!).

Note

While versions before 1.4.0 claimed to implement perfect negotiation, rigorous tests later showed otherwise. Now, those rigorous tests have been shown to pass flawlessly, and as long as the TURN/STUN configuration are valid and the signalling channel is reliable, negotiation and re-negotiation should be managed properly 100% of the time for versions 1.4.0+.