title: Third party registration in sip protocol
body: <p>I am new to the sip protocol.I Understand the sip normal registration process where from and to header fields are same.however i didn't understand the third party registration where  from and to header fields are different.My questions are </p>
  
  <p>1) what is the third party registration. </p>
  
  <p>2) when this third party registrations are used.</p>
  
  <p>Any help would be great.</p>
  
  <p>Thank you</p>