title: VOIP how to calculate RTP packages delay
body: <p>I am making a VOIP application for mobile platform. My question is what algorithms should be used to calculate whether the RTP package is "expired".
  I transfer PCMU encoded audio wrapped into RTP packages via UDP.
  As you know some of the datagrams are not delivered while others are delivered late and its pointless to play the audio in those packages.
  Using the sequence number in the RTP header you can calculate the lost packages, but I want to know how to calculate when a packet is late.
  I saw that there is something called jitter which basically measures the difference between the times for sending two consecutive packages and receiving them.
  Can I use that? Or something else?</p>