An example for a SIP call session between two phones


Figure 1 - SIP call session between two phones

A SIP call session between two phones can be built in the following way:

  1. The caller device sends an INVITE
  2. The called phone answers with a 100 Trying
  3. When the called phone starts to ring, it sends a 180 Ringing
  4. When the caller picks up the phone, the callee acknowledges it with a 200 OK
  5. The caller confirms it with an ACK
  6. The real conversation is executed with RTP (Real-time Transport Protocol)
  7. When one of the parties hangs up the call, sends a BYE request
  8. The other participant responds with a 200 OK

It is really simple! The SIP is logical and easy to understand.

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