Discover the SIP (Session Initiation Protocol) Basic Peculiarities

Discover the SIP (Session Initiation Protocol) Basic Peculiarities

What is SIP or Session Initiation Protocol?

SIP is a signaling protocol intended for organizing, modifying and terminating communication sessions. SIP is independent of transport technologies, but it is preferable to use UDP when establishing a connection. To transfer the voice and video information, it is recommended to use RTP, but the possibility of using other protocols is not ruled out.

The SIP defines two types of signaling messages – a request and a response. There are also six procedures:

  • INVITE (invitation) – invites the user to participate in the VoIP communication session (serves to establish a new connection, can contain parameters for negotiation);
  • BYE (disconnection) – ends the connection between two users;
  • OPTIONS (options) – used to transmit information about supported characteristics (this transfer can be done directly between two user agents or via a SIP server);
  • ASK (confirmation) – used to confirm receipt of the message or for a positive response to the INVITE command;
  • CANCEL (cancel) – stops searching for the user;

REGISTER – transfers information about the user’s location to the SIP server, which can broadcast it to the address server (Location Server).

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