Commands of SIP

• INVITE :Invites a user to a call
  
  
• ACK : Acknowledgement is used to facilitate reliable message exchange for INVITEs.
  
  
• BYE :Terminates a connection between users
  
  
• CANCEL :Terminates a request, or search, for a user. It is used if a client sends an INVITE and then changes its decision to call the recipient.
  
  
• OPTIONS :Solicits information about a server's capabilities.
  
  
• REGISTER :Registers a user's current location
  
  
• INFO :Used for mid-session signaling
  
  

If you don't realise how the commands exactly work, don't worry. We will discuss the format of some of the above SIP commands in more detail shortly.
It's time to go through a typical SIP session so that you can appreciate what we have learnt so far and what follows in our journey through SIP.

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