Patent ID: 6600759
Filing Date: 2003-07-29
Classification: H04L

Abstract:
Apparatus for estimating interarrival jitter J(i) between a current voice packet and a previous voice packet both transmitted over an IP network by a transmitter and received at a receiver, according to a formulaJ(i)=J(iâˆ’1)+|D(i)|âˆ’((J(iâˆ’1)+8)>>4), where J(iâˆ’1) represents the interarrival jitter between said previous voice packet and a packet previous to said previous voice packet, and D(i) represents a difference in packet spacing between said current voice packet and said previous voice packet according to a further formula D(i)=(RTS(i)âˆ’TTS(i))âˆ’(RTS(iâˆ’1)âˆ’TTS(iâˆ’1)), where RTS(i) represents a time stamp value at said receiver for said current voice packet, TTS(i) represents a time stamp value at said transmitter for said current voice packet, RTS(iâˆ’1) represents a time stamp value at said receiver for said previous voice packet and TTS(iâˆ’1) represents a time stamp value at said transmitter for said previous packet, comprising:a plurality of memory elements for storing RTS(i), TTS(i), RTS(iâˆ’1)âˆ’TTS(iâˆ’1) and J(iâˆ’1); first, second and third subtractors; an adder; a 2's complement circuit; a combined adder and shift register; and a state machine for i) causing said first subtractor to subtract TTS(I) from RTS(i) thereby yielding RTS(i)âˆ’TTS(i); ii) causing said second subtractor to subtract RTS(iâˆ’1)âˆ’TTS(iâˆ’1) from RTS(i)âˆ’TTS(i) thereby yielding |D(i)|; iii) causing said 2's complement circuit to set a 2's complement value of D(i) in the event of underflow resulting from said second subtractor subtracting RTS(iâˆ’1)âˆ’TTS(iâˆ’1) from RTS(i)âˆ’TTS(i) thereby yielding |D(i)|; iv) causing said combined adder and shift register to add 8 to J(iâˆ’1) thereby yielding J(iâˆ’1)+8 and to shift J(iâˆ’1)+8 four bits rightward thereby yielding (J(iâˆ’1)+8) >>4 ; v) causing said third subtractor to subtract (J(iâˆ’1)+8) >>4 from D(i) thereby yielding |D(i)|âˆ’((J(iâˆ’1)+8) >>4); and vi) causing said adder to add J(iâˆ’1) to |D(i)|âˆ’((J(iâˆ’1)+8) >>4) thereby yielding J(i).