How it works...

  1. When a UA desires to establish a multimedia session, it sends an INVITE method to the remote UA. In the following diagram, you can see an example of a basic call flow:
An end device in SIP is called UA. A user agent can initiate or receive a call. A UA can be an IP phone, video camera, software client, or any device or software that participates in an SIP session.
  1. After INVITE, you should see Trying, Session Progress, Ringing, or a combination of them coming from the other side
  1. We can see here how the session progress between the initiator on 172.18.110.200 and the responder on 172.18.110.203:
    • The INVITE method is sent ...

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