This is a video which explains the relationship between
SIP, RTP and RTCP protocol packet exchanges in a VoIP Communication.
The VOIP Data could be for example:
Asterisk VOIP Server (or PBX) to VOIP phones/clients (soft voip-phones and hard voip-phones)
SIP - Session Initiation Protocol
RTP - Real-time Transport Protocol
RTCP - Real-time Transport Control Protocol