Next we have the ssrc related lines. SSRC stands for Synchronization Source and it is an unique identifier of the RTP media stream source. In this we have many sources. Roughly speaking, these lines establish a relationship between the SSRC flow identifier - an older RTP concept – to a WebRTC Media Stream – a newer WebRTC concept.
The cname source attribute associates a media source with its Canonical End-Point Identifier which will remain constant for the RTP media stream. This is the value that the media sender will place in its RTCP SDES packets.