[Partysip-dev] sfp plugin or imp plugin?

[Roland Zheng]

Hi,
  Here is my case. please help me to figure out.
  I need an plugin which will track a call and change something in requests whithin the call.
  I need first determine if a request is associated with an existing call,
  then change the request according to the first INVITE for the call.
  So I have to mantain all the information about the call until it released.
  My question is what kind of plugin I should build , imp or sfp?
  if it's sfp, there is no sample, can you give me any ideas?
  Can you give me any advice how to handle this case?

Thanks,

Roland