Real-Time VoIP Transmission Quality Predictor and Quality-Driven De-Jitter Buffer

• US 20120300769A1
• Filed: 12/14/2010
• Published: 11/29/2012
• Est. Priority Date: 12/14/2009
• Status: Active Grant

• Current Assignee: Dublin Institute of Technology
• Original Assignee: Dublin Institute of Technology
• Inventors: Narbutt, Miroslaw Andrzej
• Granted Patent: US 9,380,100 B2
• Time in Patent Office: Days
• US Class Current: 370/352
• CPC Class Codes: H04L 65/65 Network streaming protocols, e.g. real-time transport protocol [RTP] or real-time control protocol [RTCP]
• CPC Class Codes: H04L 65/80 Responding to QoS

Abstract

Voice over Internet Protocol (VoIP) transmission quality predictor working in real-time provides feedback information regarding transmission impairments, transmission quality and end-user satisfaction to quality enhancement mechanisms along the transmission path. Quality enhancement mechanisms use this feedback information in the process of tuning their control parameters. The transmission quality predictor calculates the transmission rating factor R at each of the outputs based on the information regarding voice codec, packet loss, and mouth-to-ear delay. Information regarding voice codec and packet loss is determined from VoIP packet headers. Information regarding mouth-to-ear delay is determined from an additional time stamp that is inserted into each RTP packet header by the VoIP sender. Finally, the play-out delay of received VoIP packets for the actual time window is set equal to the play-out buffer output in the prior time window which gave the highest R-factor value.

Claims

1. A method of operating a VoIP device having a de-jitter buffer, the method comprising the steps of

a) determining the end to end delays of received VOIP packets at the VOIP device from a transmitter across a network, the VOIP packets containing an audio payload, by extracting an absolute timestamp contained after the SSRC identifier within the VOIP packet, and comparing the value of the absolute timestamp with a local clock synchronized to a universal clock to determine an absolute time delay for each VOIP packet, and

b) determining an optimal operating point for the de-jitter buffer using the determined absolute delays.

2. A method according to claim 1, wherein the optimal operating point of the buffer is determined from predetermined quality curves in which regions of different user satisfaction are identified and the method seeks to maintain the operating point in the region of maximum possible user satisfaction for current conditions.

3. A method according to claim 1, wherein the absolute timestamp is selectively extracted from a group comprising:

a) at least one CSRC field of the header of the received VoIP packets, and

b) a field following the CSRC list.

4. A method according to claim 1, wherein the absolute timestamp is extracted from two CSRC fields of the received packet.

5. A method according to claim 1, wherein the absolute timestamp is in NTP format.

6. A method of transmitting a VOIP packet containing an audio payload, the method comprising the step of embedding an absolute timestamp into the VOIP packet after the SSRC identifier in the header of the VoIP packet, wherein the absolute time stamp is obtained from a local clock which has been synchronized to a universal clock.

7. A method according to claim 6, wherein the absolute timestamp is selectively embedded within:

a) at least one CSRC field of the header of the received VoIP packets, and, alternatively

b) a field following the CSRC list.

8. A method according to claim 6, wherein the absolute timestamp is extracted from two CSRC fields of the received packet.

9. A method according to claim 6, wherein the absolute timestamp is in NTP format.

10. A method according to claim 6, further comprising the step of synchronizing the local clock to a universal clock.

11. A method according to claim 10, wherein the step of synchronizing comprises the use of a GPS receiver.

12. A VoIP device for receiving VoIP packet data and providing an audio signal to a user from said received VoIP data, the VoIP device comprising a de-jitter buffer having a variable buffering delay, and a local clock, wherein the device is configured to determine an absolute end to end delay of each packet received by extracting an absolute timestamp contained after the SSRC identifier of the VOIP packet headers of the received VoIP packets and comparing the value of the absolute timestamp with the local clock and wherein the VOIP device is further configured to determine an optimal operating point for the de-jitter buffer using the determined absolute delays.

13. A VoIP device according to claim 12, wherein the device is adapted to determine the optimal buffering delay from predetermined quality curves in which regions of different user satisfaction are identified by seeking to maintain the operating point in the region of maximum possible user satisfaction.

14. A VoIP device according to claim 12, wherein the absolute timestamp is selectively extracted from:

a) at least one CSRC fields field of the header of the received VoIP packets, and, alternatively

b) a field following the CSRC list.

15. A VOIP device according to claim 12, wherein the absolute timestamp is extracted from two CSRC fields of the received packet.

16. A VoIP device according to claim 12, further comprising means for synchronizing to a universal clock, suitably a GPS receiver.

17. A VoIP device according to claim 12 wherein the timestamp is in NTP format.

18. A VoIP device for transmitting a VoIP packet containing an audio payload across a network, the device comprising:

a local clock,

means for synchronizing the local clock to a universal clock, and

means for embedding an absolute timestamp within a VOIP packet for transmission wherein the absolute time stamp is obtained from the local clock and where the absolute time stamp is embedded after the SSRC identifier in the header of the VoIP packet.

19. A VoIP device according to claim 18, wherein the absolute timestamp is selectively embedded within:

a) at least one CSRC field of the header of the received VoIP packets, and, alternatively

b) a field following the CSRC list.

20. A VOIP device according to claim 18, wherein the absolute timestamp is embedded within two CSRC fields of the received packet.

21. A VOIP device according to claim 18, wherein the absolute timestamp is in NTP format.

22. A VOIP device according to claim 18, wherein the means for synchronizing comprises a GPS receiver.