In SIP Basics we discussed about components of SIP. It's time to understand a sample call flow. Before we start I would like to discuss few components of call flow:
Request: When a UAC (User Agent Client) wants to initiate a call it sends an Invite to the UAS (User Agent Server). In this case Invite is a request .
Response: A reply to UAC's request is called a response. In this case it would be 100 Trying, which we will discuss in a moment.