CLID -- Caller ID
DID -- Direct Inward Dial
- Also known as your phone number. For example, your DID may be +1-650-444-5555.
SIP -- Session Initiation Protocol
- SIP is the protocol used to initiate, terminate, and control phone calls. It doesn't not transmit any voice data.
RTP -- Real-time Transfer Protocol
- The protocol used to transfer the voice (audible) portion of any VoIP call.