Low-latency buffering for packet telephony

• US 6,301,258 B1
• Filed: 12/04/1997
• Issued: 10/09/2001
• Est. Priority Date: 12/04/1997
• Status: Expired due to Term

• Current Assignee: AT&T Corporation (AT&T, Inc.)
• Original Assignee: AT&T Corporation (AT&T, Inc.)
• Inventors: Robinson, Bethany Scott, Katseff, Howard Paul, Lyons, Robert Patrick
• Primary Examiner(s): Vu, Huy D.
• Assistant Examiner(s): NGUYEN, TOAN D
• Application Number:
  US08/985,229
• Time in Patent Office: 1,405 Days
• Field of Search: 370/465, 370/468, 370/477, 370/508, 370/516-517, 370/519, 375/371-372
• 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 67/04 specially adapted for terminals or networks with limited capabilities; specially adapted for terminal portability
• CPC Class Codes: H04L 67/303 Terminal profiles
• CPC Class Codes: H04L 67/306 User profiles
• CPC Class Codes: H04L 69/329 in the application layer [OSI layer 7]
• CPC Class Codes: H04M 7/006 Networks other than PSTN/ISDN providing telephone service, e.g. Voice over Internet Protocol (VoIP) , including next generation networks with a packet-switched transport layer H04L65/00 takes precedence; aspects not specific to the type of network H04M3/00; special services in those networks H04M3/42

Abstract

In a method for reducing latency in packet telephony caused by anti-jitter buffering, audio data elements are received and placed in a telephony input buffer used for anti-jitter buffering. Rather than wait until the buffer is full, the audio data elements are clocked, or played, out of the buffer at a rate slower than the normal play rate. In this way, latency due to the initial buffer fill period is reduced or eliminated. Audio data elements continue to be played out at a slower than normal rate until the buffer fill level reaches a threshold. At that time, the play rate for sending data elements out of the telephony input buffer is adjusted to the normal play rate. In an alternative embodiment of the present invention, the fill level of the telephony input buffer is controlled within a desired range by speeding up or slowing down the rate at which audio data elements are played out of the telephony input buffer. In yet another alternative embodiment, the amount of latency jitter in the packet network is measured and the size of the telephony input buffer is adjusted based upon the relative amount of jitter, such that the relative size of the buffer is reduced when the packet network is quiet, and the size of the buffer is increased when the network is relatively jittery.

Claims

1. For use in a packet telephony communication system wherein data elements are received over a packet network into a buffer used for handling input data elements, a method for reducing latency after said buffer is empty, comprising the steps of:

a. determining a measure of the number of data elements contained in the buffer;

b. comparing the measure of the number of data elements contained in the buffer with a threshold value;

c. if the determined measure of the number of data elements is less than the threshold value, setting the rate at which data elements are played out of the buffer to a rate slower than a normal rate for playing data elements out of the buffer;

d. if the determined measure of the number of data elements is not less than the threshold value, setting the rate at which data elements are played out of the buffer to a rate equal to the normal rate; and

e. playing at least one data element out of the buffer at the set rate, after the buffer has filled with data elements to a predetermined level, the predetermined level being less than the threshold value.

2. The method according to claim 1, wherein the measure of the number of data elements contained in the buffer comprises a percentage corresponding to the ratio of the actual number of data elements in the buffer to the buffer'"'"'s full capacity.

3. The method according to claim 2, wherein the threshold value is approximately 50 percent.

4. The method according to claim 1, wherein the rate slower than the normal rate is approximately 90 percent of the normal rate.

5. The method according to claim 1, wherein the predetermined level is no more than two data elements.

6. A method for reducing latency in a packet telephony communication system, wherein data elements are received over a packet network into a buffer used for handling input data elements and then played out of the buffer, comprising the steps of:

a. determining a measure of the number of data elements contained in the buffer;

b. comparing the measure of the number of data elements contained in the buffer with a first threshold value;

c. if the determined measure of the number of data elements is less than the first threshold value, setting the rate at which data elements are played out of the buffer to a first rate; and

d. if the determined measure of the number of data elements is not less than the first threshold value;

i. comparing the measure of the number of data elements contained in the buffer with a second threshold value;

ii. if the determined measure of the number of data elements is greater than the second threshold value, setting the rate at which data elements are played out of the buffer to a second rate; and

iii. if the determined measure of the number of data elements is not greater than the second threshold value, setting the rate at which data elements are played out of the buffer to a third rate.

7. The method according to claim 6, wherein:

a. the first threshold is less than the second threshold value;

b. the first rate is a rate slower than a normal rate for playing data elements out of the buffer;

c. the second rate is a rate faster than the normal rate for playing data elements out of the buffer; and

d. the third rate is a rate equal to the normal rate for playing data elements out of the buffer.

8. The method according to claim 7, wherein:

a. the measure of the number of data elements contained in the buffer comprises a percentage corresponding to the ratio of the actual number of data elements in the buffer to the buffer'"'"'s full capacity;

b. the first threshold value is approximately 25 percent; and

c. the second threshold value is approximately 75 percent.

9. The method according to claim 8, wherein the rate slower than the normal rate is approximately 90 percent of the normal rate.

10. The method according to claim 7, wherein:

a. the first threshold value is equal to the second threshold value;

b. the first rate is a rate slower than a normal rate for playing data elements out of the buffer; and

c. each of the second rate and the third rate is a rate faster than the normal rate for playing data elements out of the buffer.

11. The method according to claim 10, wherein the measure of the number of data elements contained in the buffer comprises a percentage corresponding to the ratio of the actual number of data elements in the buffer to the buffer'"'"'s full capacity.

12. The method according to claim 11, wherein the threshold value is approximately 50 percent.

13. The method according to claim 11, wherein the rate slower than the normal rate is approximately 90 percent of the normal rate.

14. The method according to claim 7, wherein:

a. the first threshold value is equal to the second threshold value;

b. the first rate is a rate slower than a normal rate for playing data elements out of the buffer;

c. the second rate is a rate faster than the normal rate for playing data elements out of the buffer; and

d. the third rate is a rate equal to normal rate for playing data elements out of the buffer.

15. The method according to claim 14, wherein the measure of the number of data elements contained in the buffer comprises a percentage corresponding to the ratio of the actual number of data elements in the buffer to the buffer'"'"'s full capacity.

16. The method according to claim 15, wherein the threshold value is approximately 50 percent.

17. The method according to claim 15, wherein the rate slower than the normal rate is approximately 90 percent of the normal rate.

18. A method for reducing latency in a packet telephony communication system, wherein data elements are received over a packet network into a buffer used for handling input data elements and then played out of the buffer, comprising the steps of:

a. storing a measure of the number of data elements contained in the buffer over time;

b. determining a measure of the relative stability in time intervals between the receipt of data elements over the packet network;

c. comparing the determined measure of the relative stability in time intervals with a threshold value;

d. if the determined measure of the relative stability in time intervals is greater than the threshold value, reducing the size of the buffer; and

e. if the determined measure of the relative stability in time intervals is not greater than the first threshold value, increasing the size of the buffer.

19. The method according to claim 18, wherein the threshold value is obtained by determining the difference between the time at which the most recent measure of the number of data elements contained in the buffer was stored and a constant, and wherein the step of determining a measure of the relative stability in time intervals between the receipt of data elements over the packet network comprises determining a plurality of time values at which the measure of the number of data elements contained in the buffer was stored, said plurality of time values excluding the time at which the most recent measure of the number of data elements contained in the buffer was stored.

20. The method according to claim 19, wherein said plurality of time values further exclude those time values corresponding to a measure of the number of data elements within a predetermined number of the most recent measure of the number of data elements.

21. The method according to claim 19, further comprising the steps of:

f. determining a measure of the number of data elements contained in the buffer;

g. comparing the measure of the number of data elements contained in the buffer with a threshold value;

h. if the determined measure of the number of data elements is less than the threshold value, setting the rate at which data elements are played out of the buffer to a rate slower than a normal rate for playing data elements out of the buffer;

i. if the determined measure of the number of data elements is not less than the threshold value, setting the rate at which data elements are played out of the buffer to a rate equal to the normal rate; and

j. playing at least one data element out of the buffer at the set rate without waiting for the buffer to fill with data elements to a predetermined level.

22. A method for reducing latency in a packet telephony communication system, wherein data elements are received over a packet network into a buffer used for handling input data elements and then played out of the buffer, comprising the steps of:

a. storing a measure of the number of data elements contained in the buffer over time;

b. determining a measure of the relative stability in time intervals between the receipt of data elements over the packet network;

c. comparing the determined measure of the relative stability in time intervals with a first threshold value;

d. if the determined measure of the relative stability in time intervals is greater than the first threshold value, reducing the size of the buffer; and

e. if the determined measure of the relative stability in time intervals is not greater than the first threshold value;

i. comparing the determined measure of the relative stability in time intervals with a second threshold value;

ii. if the determined measure of the relative stability in time intervals is less than the second threshold value, increasing the size of the buffer; and

f. if the determined measure of the relative stability in time intervals is not less than the second threshold value, maintaining the current size of the buffer.

23. The method according to claim 22, wherein the first threshold value is obtained by determining the difference between the time at which the most recent measure of the number of data elements contained in the buffer was stored and a first constant, wherein the second threshold value is obtained by determining the difference between the time at which the most recent measure of the number of data elements contained in the buffer was stored and a second constant, and wherein the step of determining a measure of the relative stability in time intervals between the receipt of data elements over the packet network comprises determining a plurality of time values at which the measure of the number of data elements contained in the buffer was stored, said plurality of time values excluding the time at which the most recent measure of the number of data elements contained in the buffer was stored.

24. The method according to claim 23, wherein said plurality of time values further exclude those time values corresponding to a measure of the number of data elements within a predetermined number of the most recent measure of the number of data elements.

25. The method according to claim 23, further comprising the steps of:

g. determining a measure of the number of data elements contained in the buffer;

h. comparing the measure of the number of data elements contained in the buffer with a threshold value;

i. if the determined measure of the number of data elements is less than the threshold value, setting the rate at which data elements are played out of the buffer to a rate slower than a normal rate for playing data elements out of the buffer;

j. if the determined measure of the number of data elements is not less than the threshold value, setting the rate at which data elements are played out of the buffer to a rate equal to the normal rate; and

k. playing at least one data element out of the buffer at the set rate without waiting for the buffer to fill with data elements to a predetermined level.

26. An article of manufacture comprising a computer-readable medium having stored thereon instructions for use in conjunction with a computer-based packet telephony communication system wherein data elements are received over a packet network into a buffer used for handling input data elements, said instructions which, when executed, define a series of steps causing the packet telephony communication system to reduce latency after said buffer is empty, said steps comprising:

a. determining a measure of the number of data elements contained in the buffer;

b. comparing the measure of the number of data elements contained in the buffer with a threshold value;

c. if the determined measure of the number of data elements is less than the threshold value, setting the rate at which data elements are played out of the buffer to a rate slower than a normal rate for playing data elements out of the buffer;

d. if the determined measure of the number of data elements is not less than the threshold value, setting the rate at which data elements are played out of the buffer to a rate equal to the normal rate; and

e. playing at least one data element out of the buffer at the set rate, after the buffer has filled with data elements to a predetermined level, the predetermined level being less than the threshold value.

27. The article of manufacture according to claim 26, wherein the measure of the number of data elements contained in the buffer comprises a percentage corresponding to the ratio of the actual number of data elements in the buffer to the buffer'"'"'s full capacity.

28. The article of manufacture according to claim 27, wherein the threshold value is approximately 50 percent.

29. The article of manufacture according to claim 27, wherein the rate slower than the normal rate is approximately 90 percent of the normal rate.

30. The article of manufacture according to claim 26, wherein the predetermined level is no more than two data elements.

31. An article of manufacture comprising a computer-readable medium having stored thereon instructions for use in conjunction with a computer-based packet telephony communication system wherein data elements are received over a packet network into a buffer used for handling input data elements and then played out of the buffer, said instructions which, when executed, define a series of steps causing the packet telephony communication system to reduce latency, said steps comprising:

a. determining a measure of the number of data elements contained in the buffer;

b. comparing the measure of the number of data elements contained in the buffer with a first threshold value;

c. if the determined measure of the number of data elements is less than the first threshold value, setting the rate at which data elements are played out of the buffer to a first rate; and

d. if the determined measure of the number of data elements is not less than the first threshold value;

i. comparing the measure of the number of data elements contained in the buffer with a second threshold value;

ii. if the determined measure of the number of data elements is greater than the second threshold value, setting the rate at which data elements are played out of the buffer to a second rate; and

iii. if the determined measure of the number of data elements is not greater than the second threshold value, setting the rate at which data elements are played out of the buffer to a third rate.

32. The article of manufacture according to claim 31, wherein:

a. the first threshold is less than the second threshold value;

b. the first rate is a rate slower than a normal rate for playing data elements out of the buffer;

c. the second rate is a rate faster than the normal rate for playing data elements out of the buffer; and

d. the third rate is a rate equal to the normal rate for playing data elements out of the buffer.

33. The article of manufacture according to claim 32, wherein:

a. the measure of the number of data elements contained in the buffer comprises a percentage corresponding to the ratio of the actual number of data elements in the buffer to the buffer'"'"'s full capacity;

b. the first threshold value is approximately 25 percent; and

c. the second threshold value is approximately 75 percent.

34. The article of manufacture according to claim 32, wherein the rate slower than the normal rate is approximately 90 percent of the normal rate.

35. The article of manufacture according to claim 33, wherein:

a. the first threshold value is equal to the second threshold value;

b. the first rate is a rate slower than a normal rate for playing data elements out of the buffer; and

c. each of the second rate and the third rate is a rate faster than the normal rate for playing data elements out of the buffer.

36. The article of manufacture according to claim 35, wherein the measure of the number of data elements contained in the buffer comprises a percentage corresponding to the ratio of the actual number of data elements in the buffer to the buffer'"'"'s full capacity.

37. The article of manufacture according to claim 36, wherein the threshold value is approximately 50 percent.

38. The article of manufacture according to claim 37, wherein the rate slower than the normal rate is approximately 90 percent of the normal rate.

39. The article of manufacture according to claim 33, wherein:

a. the first threshold value is equal to the second threshold value;

b. the first rate is a rate slower than a normal rate for playing data elements out of the buffer;

c. the second rate is a rate faster than the normal rate for playing data elements out of the buffer; and

d. the third rate is a rate equal to normal rate for playing data elements out of the buffer.

40. The article of manufacture according to claim 39, wherein the measure of the number of data elements contained in the buffer comprises a percentage corresponding to the ratio of the actual number of data elements in the buffer to the buffer'"'"'s full capacity.

41. The article of manufacture according to claim 40, wherein the threshold value is approximately 50 percent.

42. The article of manufacture according to claim 41, wherein the rate slower than the normal rate is approximately 90 percent of the normal rate.

43. An article of manufacture comprising a computer-readable medium having stored thereon instructions for use in conjunction with a computer-based packet telephony communication system wherein data elements are received over a packet network into a buffer used for handling input data elements and then played out of the buffer, said instructions which, when executed, define a series of steps causing the packet telephony communication system to reduce latency, said steps comprising:

a. storing a measure of the number of data elements contained in the buffer over time;

b. determining a measure of the relative stability in time intervals between the receipt of data elements over the packet network;

c. comparing the determined measure of the relative stability in time intervals with a threshold value;

d. if the determined measure of the relative stability in time intervals is greater than the threshold value, reducing the size of the buffer; and

e. if the determined measure of the relative stability in time intervals is not greater than the first threshold value, increasing the size of the buffer.

44. The article of manufacture according to claim 43, wherein the threshold value is obtained by determining the difference between the time at which the most recent measure of the number of data elements contained in the buffer was stored and a constant, and wherein the step of determining a measure of the relative stability in time intervals between the receipt of data elements over the packet network comprises determining a plurality of time values at which the measure of the number of data elements contained in the buffer was stored, said plurality of time values excluding the time at which the most recent measure of the number of data elements contained in the buffer was stored.

45. The article of manufacture according to claim 44, wherein said plurality of time values further exclude those time values corresponding to a measure of the number of data elements within a predetermined number of the most recent measure of the number of data elements.

46. The article of manufacture according to claim 45, further comprising the steps of:

f. determining a measure of the number of data elements contained in the buffer;

g. comparing the measure of the number of data elements contained in the buffer with a threshold value;

h. if the determined measure of the number of data elements is less than the threshold value, setting the rate at which data elements are played out of the buffer to a rate slower than a normal rate for playing data elements out of the buffer;

i. if the determined measure of the number of data elements is not less than the threshold value, setting the rate at which data elements are played out of the buffer to a rate equal to the normal rate; and

j. playing at least one data element out of the buffer at the set rate without waiting for the buffer to fill with data elements to a predetermined level.

47. An article of manufacture comprising a computer-readable medium having stored thereon instructions for use in conjunction with a computer-based packet telephony communication system wherein data elements are received over a packet network into a buffer used for handling input data elements and then played out of the buffer, said instructions which, when executed, define a series of steps causing the packet telephony communication system to reduce latency, said steps comprising:

a. storing a measure of the number of data elements contained in the buffer over time;

b. determining a measure of the relative stability in time intervals between the receipt of data elements over the packet network;

c. comparing the determined measure of the relative stability in time intervals with a first threshold value;

d. if the determined measure of the relative stability in time intervals is greater than the first threshold value, reducing the size of the buffer; and

e. if the determined measure of the relative stability in time intervals is not greater than the first threshold value;

i. comparing the determined measure of the relative stability in time intervals with a second threshold value;

ii. if the determined measure of the relative stability in time intervals is less than the second threshold value, increasing the size of the buffer; and

f. if the determined measure of the relative stability in time intervals is not less than the second threshold value, maintaining the current size of the buffer.

48. The article of manufacture according to claim 47, wherein the first threshold value is obtained by determining the difference between the time at which the most recent measure of the number of data elements contained in the buffer was stored and a first constant, wherein the second threshold value is obtained by determining the difference between the time at which the most recent measure of the number of data elements contained in the buffer was stored and a second constant, and wherein the step of determining a measure of the relative stability in time intervals between the receipt of data elements over the packet network comprises determining a plurality of time values at which the measure of the number of data elements contained in the buffer was stored, said plurality of time values excluding the time at which the most recent measure of the number of data elements contained in the buffer was stored.

49. The article of manufacture according to claim 48, wherein said plurality of time values further exclude those time values corresponding to a measure of the number of data elements within a predetermined number of the most recent measure of the number of data elements.

50. The article of manufacture according to claim 49, further comprising the steps of:

g. determining a measure of the number of data elements contained in the buffer;

h. comparing the measure of the number of data elements contained in the buffer with a threshold value;

i. if the determined measure of the number of data elements is less than the threshold value, setting the rate at which data elements are played out of the buffer to a rate slower than a normal rate for playing data elements out of the buffer;

j. if the determined measure of the number of data elements is not less than the threshold value, setting the rate at which data elements are played out of the buffer to a rate equal to the normal rate; and

k. playing at least one data element out of the buffer at the set rate without waiting for the buffer to fill with data elements to a predetermined level.