# PeerConnection and friends The PeerConnection is the C++-level implementation of the Javascript object "RTCPeerConnection" from the [WEBRTC specification](https://w3c.github.io/webrtc-pc/). Like many objects in WebRTC, the PeerConnection is used via a factory and an observer: - PeerConnectionFactory, which is created via a static Create method and takes a PeerConnectionFactoryDependencies structure listing such things as non-default threads and factories for use by all PeerConnections using the same factory. (Using more than one factory should be avoided, since it takes more resources.) - PeerConnection itself, which is created by the method called PeerConnectionFactory::CreatePeerConnectionOrError, and takes a PeerConnectionInterface::RTCConfiguration argument, as well as a PeerConnectionDependencies (even more factories, plus other stuff). - PeerConnectionObserver (a member of PeerConnectionDependencies), which contains the functions that will be called on events in the PeerConnection These types are visible in the API. ## Internal structure of PeerConnection and friends The PeerConnection is, to a large extent, a "God object" - most things that are done in WebRTC require a PeerConnection. Internally, it is divided into several objects, each with its own responsibilities, all of which are owned by the PeerConnection and live as long as the PeerConnection: - SdpOfferAnswerHandler takes care of negotiating configurations with a remote peer, using SDP-formatted descriptions. - RtpTransmissionManager takes care of the lists of RtpSenders, RtpReceivers and RtpTransceivers that form the heart of the transmission service. - DataChannelController takes care of managing the PeerConnection's DataChannels and its SctpTransport. - JsepTransportController takes care of configuring the details of senders and receivers. - Call does management of overall call state. - RtcStatsCollector (and its obsolete sibling, LegacyStatsCollector) collects statistics from all the objects comprising the PeerConnection when requested. There are a number of other smaller objects that are also owned by the PeerConnection, but it would take too much space to describe them all here; please consult the .h files. PeerConnectionFactory owns an object called ConnectionContext, and a reference to this is passed to each PeerConnection. It is referenced via an webrtc::scoped_refptr, which means that it is guaranteed to be alive as long as either the factory or one of the PeerConnections is using it.