Method of conducting a communications session using incorrect timestamps
A wireless LAN can be used to support audio communication sessions between wireless communication devices and wired communication devices both configured to operate according to the Internet Protocol. Both the wired and wireless communication devices generate and transmit frames of voice information over the LAN to each other and in the process of generating these frames they place a timestamp in each frame that is used by a receiving communications device to determine when the frame should be played in relationship to all of the other frames of voice information it receives. At times these communication devices can place incorrect timestamp values in the frames of audio information which can affect the quality of the communication experience for a user. I propose to correct any incorrect timestamp values by first recognizing that a timestamp value is incorrect and then rounding the value to the nearest frame boundary.
1. In a local area network including a plurality of wireless communication devices and a plurality of intermediate communication devices, a method to conduct a communication session using incorrectly time stamped packets of audio information comprising the steps of:
detecting and storing a timestamp value associated with a current received packet of audio information by at least one of the plurality of the wireless communications devices;
determining that the stored timestamp value is not valid by calculating the difference between a synchronization point value and the stored timestamp value and dividing the difference by the number of audio samples in a frame resulting in an uneven timestamp error factor value;
determining the nearest frame boundary value to the invalid timestamp value;
modifying the stored timestamp value associated with the current packet of audio information to be a timestamp value associated with a nearest frame boundary; and
processing the current received packet of audio information.
2. In a local area network including a plurality of wireless communication devices and a plurality of intermediate communication devices, a method to conduct a communication session using incorrectly time stamped packets of audio information comprising the steps of:
detecting and storing a timestamp value associated with a current received packet of audio information by at least one of the plurality of the wireless communication devices;
determining that the stored timestamp value is not valid;
determining the nearest frame boundary value to the invalid timestamp value by rounding the timestamp error factor value to a nearest even integer, multiplying the rounded value by the number of audio samples in a frame which results in a timestamp correction value and adding the timestamp correction value to the synchronization point value to determine the nearest frame boundary timestamp value;
modifying the stored timestamp value associated with the current packet of audio information to be a timestamp value associated with a nearest frame boundary; and
processing the current received packet of audio information.
3. In a local area network including a plurality of wireless communications devices and a plurality of intermediate communication devices, a method to conduct a communication session using incorrectly time stamped packets of audio information comprising the steps of:
detecting and storing a timestamp value associated with a current received packet of audio information by at least one of the plurality of the wireless communication devices;
utilizing a synchronization point value, the stored timestamp value and the number of audio samples in a frame to determine that the stored timestamp value is not valid;
utilizing a rounded timestamp error factor value, the number of audio samples in a frame and the synchronization point value to determine the nearest frame boundary value;
modifying the stored timestamp value associated with the current packet of audio information to be a timestamp value associated with a nearest frame boundary; and
processing the current received packet of audio information.
4. The method of claim 3 wherein at least one of the plurality of the wireless communication devices is an IP capable mobile phone.
5. The method of claim 3 wherein the intermediate communication devices are one or more of a public branch exchange, a router, a switch and an access point.
6. The method of claim 3 wherein the step of determining the invalidity of the stored timestamp value is comprised of:
calculating the difference between a synchronization point value and the stored timestamp value; and
dividing the difference by a frame length resulting in an uneven timestamp error factor value.
7. The method of claim 3 wherein the step of determining the nearest frame boundary timestamp value is comprised of:
rounding the timestamp error factor value to a nearest even integer;
multiplying the rounded value by the number of samples in a frame which results in a timestamp correction value; and
adding the timestamp correction value to the synchronization point value to determine the nearest frame boundary timestamp value.
8. In a local area network including a plurality of wireless communication devices and a plurality of intermediate communication devices, a method to conduct a communication session using incorrectly time stamped packets of audio information comprising the steps of:
detecting and storing a timestamp value associated with a current received packet of audio information by at least one of the plurality of the wireless communication devices;
determining that the stored timestamp value is not valid by calculating the difference between a synchronization point value and the stored timestamp value and dividing the difference by a frame length resulting in an uneven timestamp error factor value;
rounding the timestamp error factor value to a nearest even integer, multiplying the rounded value by the number of samples in a frame which results in a timestamp correction value which is added to the synchronization point value to determine the nearest frame boundary value
determining that the difference between the stored timestamp value and the nearest frame boundary value is not greater than a specified tolerance;
modifying the stored timestamp value associated with the current packet of audio information to be a timestamp value associated with a nearest frame boundary; and
processing the current received packet of audio information.
9. The method of claim 8 wherein at least one of the plurality of the wireless communication devices is an IP capable mobile phone.
10. The method of claim 8 wherein the intermediate communication devices are one or more of a public branch exchange, a router, a switch and an access point.