SIP

Session Initiation Protocol

SIP is typically used for VoIP: SIP-phones
SIP is a signaling protocol
SIP has many similarities with HTTP and SMTP, like
- it's text-based
- Requests have methods (REGISTER, INVITE, ACK, BYE, ...) similar to HTTP-methods (GET, POST, ...)
- Responses have status codes (1xx, 200: success, 3xx: redirection, 5xx: server errors, ...)
SIP can use UDP, TCP or SCTP as transport protocols
- TCP/UDP port numbers:
  - 5060: non-encrypted
  - 5061: encrypted with TLS
SIP UA's: Each UA (User Agent) is both client and server
- UAC: User Agent Client
- UAS: User Agent Server
- UAC- and UAS-roles only last for duration of a SIP transaction
SIP Registrar: location service

Sources:

SDP

Session Description Protocol

SDP is used as the payload of some SIP-messages
SDP can be used by 2 endpoints to negotiate network metrics, media types, ... (the session profile)

= Real-time Transport Protocol

Also SRTP: Secure RTP (with TLS)

for transmission of multimedia formats
has different profiles or payload formats, like
- for Audio and video conferences
- for H.265-encoded video
- !!! for MIDI !!!
- ...

Golang:

= RTP Control Protocol

helps RTP-sessions (provides out-of-band statistics and control information)
mainly for QoS (Quality of Service)
statistics:
- packet counts
- packet loss
- packet delay variation (jitter)
- round-trip delay time (RTT / ping-time)

sources: