The most used protocols in VoIP infrastructure:
H.323: H.323 is data on the IP standard provided by the International Telecommunications Union Standardization Sector (ITU-T). As you can see, this standardization agency uses some letters to describe the scope based on the many criteria listed here:
H: For audiovisual and multimedia systems
G: For transmission systems and media
Q: For switching and signaling
T: For terminals for telematics services
H.323 is one of the oldest packet-based communication systems protocols. Thus, this protocol is stable. Current version v6. Cisco call manager is used by many vendors in many products such as NetMeeting and RadVision.H.323.
Skinny Client Control Protocol: The Skinny Call Control Protocol (SCCP) developed by Selsius is a Cisco-specific protocol. This dialog uses the following different message types:
RTP / RTCP: Real Time Protocol (RTP) is a transport protocol based on RFC 3550, especially over UDP.
Secure Real Time Transfer Protocol (SRTP): Secure Real Time Transfer Protocol (SRTP) is an application protocol based on RFC3711. SRTP offers advanced security features; Thus, it secures RTP through encryption with a keystream using the XOR process.
H.248 and Media Gateway Control Protocol: Media Gateway Control Protocol (MGCP) is a protocol developed by Cisco.
Session Initiation Protocol (SIP): Session Initiation Protocol (SIP) is a session management protocol based on the RFC 3261 protocol.