Patent ID: 7639716

Claim:
A method operable in a local device for determining clock skew in a packet-based session between said local device and a remote device with a non-deterministic packet delay, said method comprising the steps of: receiving a sequence of control packets from the remote device transmitting media packets in a session, each control packet including a remote real time-stamp comprising a system clock time of the remote device and a separate remote media card clock time-stamp comprising a media card clock time of the remote device corresponding to the remote real time-stamp; comparing a first real-time stamp and a first remote media card clock time-stamp from a first received control packet with a second real-time stamp and a second remote media card clock time-stamp from a second received control packet, respectively, to determine from said two received control packets, a first relative rate of a remote media card clock to the remote real time system clock; transmitting a sequence of control packets from said local device transmitting media packets in said session, each control packet including a local real time-stamp comprising a system clock time of the local device and a separate local media card clock time-stamp comprising a media card clock time of the local device corresponding to the local real time-stamp; and comparing a third real-time stamp and a first local media card clock time-stamp from a first transmitted control packet with a fourth real-time stamp and a second local media card clock time-stamp from a second transmitted control packet, respectively, to determine from said two transmitted control packets, a second relative rate of a local media card clock to the local real-time system clock.