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. RTCPool has built-in support for socket.io and raw WebSockets as signalling channels, but you may implement your own by extending transceiver() and ensuring the following:

• Implement a send method that accepts a message type and data as a JSON object.

• Implement code that passively listens for data from the signalling channel, and when an event is available, dispatches the event to this (since transceiver() extends EventTarget)

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

All versions pre-3.0.0 have some negotiation failure cases. Each successive version improved upon the shortcomings of the previous one, but true perfect negotiation was not achieved until version 3.0.0 with a complete rewrite of the internal negotiation process.

Managed Connections

The primary purpose of RTCPool is to simplify the use of the WebRTC API. As such, negotiation is completely abstracted away and handled internally. The ManagedConnection() class provides all the functionalities of a WebRTC peer connection that you’d want - media tracks and data channels galore. Instances of this class are exposed in events and by Pool.connections, and are what you will always be using unless you are accessing Pool._raw_connections (DON’T DO THIS - you should have no need to). Additionally, the only events exposed to ManagedConnection() are track and datachannel.

To some, this may seem restrictive, but again, all negotiations are handled internally for maximal success, and trying to get your hands in that process is only likely to cause frustration. If you feel you need to get your hands on the raw SDP to add custom information, save yourself the headache and use Descriptions instead. This is the reason they were implemented!