Method and system to compensate for the effects of packet delays on speech quality in a Voice-over IP system

• US 20030152093A1
• Filed: 02/08/2002
• Published: 08/14/2003
• Est. Priority Date: 02/08/2002
• Status: Active Grant

• Current Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Gupta, Sunil K., Vinchhi, Chetan
• Granted Patent: US 7,266,127 B2
• Time in Patent Office: Days
• US Class Current: 370/412
• CPC Class Codes: H04J 3/0632 Synchronisation of packets and cells, e.g. transmission of voice via a packet network, circuit emulation service [CES] queuing arrangements in packet switching elements H04L49/90; synchronising systems for the synchronous transmission of a pulse code modulated video signal with one or more other pulse code modulated signals H04N7/56
• CPC Class Codes: H04L 47/10 Flow control; Congestion control
• CPC Class Codes: H04L 47/2416 Real-time traffic
• CPC Class Codes: H04L 47/283 in response to processing delays, e.g. caused by jitter or round trip time [RTT]
• CPC Class Codes: H04L 47/30 in combination with information about buffer occupancy at either end or at transit nodes
• CPC Class Codes: H04L 47/34 ensuring sequence integrity, e.g. using sequence numbers
• CPC Class Codes: H04L 65/1101 Session protocols
• CPC Class Codes: H04L 65/764 at the destination reformatting of additional data in video clients H04N21/4355
• CPC Class Codes: H04L 65/80 Responding to QoS
• CPC Class Codes: H04L 9/40 Network security protocols
• CPC Class Codes: H04M 1/2535 adapted for voice communication over an Internet Protocol [IP] network Voice over Internet Protocol (VoIP) network equipment and services H04M7/006; implementation or adaptation of Internet protocol [IP], of transmission control protocol [TCP] or of user datagram protocol [UDP] H04L69/16

Abstract

The system includes a jitter buffer for receiving speech packets in a Voice over Internet Protocol (VoIP) system, a playback device for adjusting the playback speed of the received speed packets, and a jitter buffer manager for detecting out of sequence packets in the jitter buffer and for sending commands to the playback device to adjust playback speed based on the detection. The speech signal is played back at the nominal speed when there are no out of sequence packets. The playback speed is decreased when an out of sequence packet is detected, thereby tending to increase the jitter buffer length. When an out of sequence packet arrives, the playback speed is increased in order to restore jitter buffer length to its nominal length.

Claims

1. A system to compensate for the effects of packet delay on a voice over internet protocol (VoIP) system, comprising:

a buffer for receiving speech packets in the VoIP system;

a playback device for adjusting the playback speed of the received speech packets; and

a buffer manager for detecting packet jitter in the buffer and for sending commands to the playback device to adjust playback speed based on the detection.

2. The system of claim 1, wherein the buffer is a queue for handling incoming speech packets, the buffer performing jitter buffering and packet sequencing on the received speech packets.

3. The system of claim 1, wherein the buffer manager controls the playback device to decrease the playback speed when the buffer manager detects packet jitter that delays arrival of a speech packet.

4. The system of claim 3, wherein the buffer manager controls the playback device to increase the playback speed when the delayed packet arrives at the buffer.

5. The system of claim 3, wherein packet jitter is a variation in packet delay that causes packets to arrive out of sequence at an end-point in the system.

6. The system of claim 5, wherein an end-point is a client in the system.

7. The system of claim 1, wherein the buffer manager checks length of the buffer and instructs the playback device to increase playback speed until the length of the buffer returns to a nominal length, when the buffer manager determines that length of the buffer exceeds a specified length.

8. The system of claim 5, wherein the buffer manager detects packet jitter, the buffer manager measures a distance between an earliest detected out of sequence packet and a beginning of the buffer, and the buffer manager controls the playback device to decrease the playback speed when the distance is less than a predetermined distance.

9. The system of claim 1, wherein the buffer manager detects packet jitter, the buffer manager measures a distance between an earliest point of detected packet jitter in the buffer and a reference point in the buffer, and the buffer manager controls the playback device to decrease the playback speed when the distance is less than a predetermined distance.

10. The system of claim 1, wherein the buffer manager includes silence compression means that uses silence periods that are received between speech packets in the buffer to restore the length of the buffer to a nominal length.

11. The system of claim 10, wherein the buffer manager compresses the silence periods to return playback speed to a nominal speed.

12. The system of claim 1, wherein the buffer manager controls the playback device to adjust speed by an amount that is dependent on an expected or observed packet jitter.

13. The system of claim 12, wherein packet jitter is a variation in packet delay that causes packets to arrive out of sequence at an end-point in the system.

14. The system of claim 13, wherein an end-point is a client in the system.

15. A method of compensating for the effects of packet delay on a voice over internet protocol (VoIP) system, comprising the steps of:

detecting an amount of jitter in the arrival of speech packets; and

adjusting a playback speed for the speech packets based on the detection.

16. The method of claim 15, further comprising performing jitter buffering and packet sequencing on the speech packets prior to performing the detecting step.

17. The method of claim 15, wherein jitter is represented by an out of sequence packet, and wherein playback speed is decreased upon detection of an out of sequence packet, and increased upon arrival of the out of sequence packet.

18. The method of claim 17, wherein a length of a buffer storing the speech packets is checked against a specified length, and playback speed is increased until the length of the buffer returns to a nominal length, if the checked buffer length is less than the specified length.

19. The method of claim 17, wherein out of sequence packets are detected, a distance between an earliest detected out of sequence packet and a beginning of the buffer is measured, and playback speed is decreased when the measured distance is less than a predetermined distance.

20. The method of claim 15, wherein packet jitter is detected, a distance between an earliest point where packet is detected and a reference point is measured, and playback speed is decreased when the measured distance is less than a predetermined distance.

21. The method of claim 15, further comprising the step of restoring the length of a buffer storing the incoming speech packets to a nominal length, at a nominal playback speed, instead of at a higher playback speed, thereby compressing any silence intervals.

22. The method of claim 21, wherein the compressing step is performed when silence suppression is enabled in the VoIP system.