Delay variation buffer control technique
A delay variation buffer controller allowing proper cell delay variation control reflecting an actual network operation status is disclosed. A detector detects an empty status of the data buffer when data is read out from the data buffer at intervals of a controllable time period. A counter counts the number of contiguous times the empty status was detected. A proper time period is calculated depending on a value of the counter at a time when the empty status is not detected and the value of the counter is not zero. A timing corrector corrects the controllable time period to match the proper time delay and setting the controllable time delay to a predetermined value when the empty status is not detected and the value of the counter is zero.
1. A controller for controlling a data buffer, comprising
a detector for detecting an empty status of the data buffer when data is read out from the data buffer at intervals of a controllable time period;
a counter for counting number of contiguous times the empty status was detected;
a calculator for calculating a proper time period depending on a value of the counter at a time when the empty status is not detected and the value of the counter is not zero; and
a timing corrector for correcting the controllable time period to match the proper time period and setting the controllable time period to a predetermined value when the empty status is not detected and the value of the counter is zero.
2. The controller according to claim 1 , wherein the calculator calculates the proper timing period such that the proper time period increases linearly with an increase of the value of the counter.
3. The controller according to claim 2 , wherein the calculator calculates the proper time period X by an expression as follows:
X=Y×Z+B,
where Y is a value of the counter, Z is a current controllable time period, and B is a minimum value of controllable time period.
4. The controller according to claim 1 , wherein the timing corrector sets the controllable time period to the predetermined value when the empty status is not detected and the value of the counter is zero, wherein the predetermined value is an initial value which is a minimum value of the controllable time period.
5. The controller according to claim 1 , further comprising:
a determiner for determining whether a value of the counter exceeds a predetermined threshold; and
a message creator for creating a message when the value of the counter exceeds the predetermined threshold, the message indicating that the number of contiguous times the empty status was detected exceeds the predetermined threshold.
6. The controller according to claim 5 , wherein the counter is reset after correcting the controllable time period to match the proper time period or creating the message.
7. A control method for controlling a data buffer, comprising:
a) detecting an empty status of the data buffer when data is read out from the data buffer at intervals of a controllable time period;
b) counting number of contiguous times the empty status was detected to produce a count value;
c) calculating a proper time period depending on a count value at a time when the empty status is not detected and the count value is not zero;
d) correcting the controllable time period to match the proper time period; and
e) setting the controllable time period to a predetermined value when the empty status is not detected and the count value is zero.
8. The method according to claim 7 , wherein in the step (c), the proper time period is calculated such that the proper timing period increases linearly with an increase of the count value.
9. The method according to claim 8 , wherein the proper timing period X is calculated by an expression as follows:
X=Y×Z+B,
where Y is a count value, Z is a current controllable time period, and B is a minimum value of controllable time period.
10. The method according to claim 7 , further comprising:
f) when the empty status is not detected and the count value is zero, setting the controllable time period to the predetermined value, which is an initial value that is a minimum value of the controllable time period.
11. The method according to claim 7 , further comprising:
f) determining whether a count value exceeds a predetermined threshold; and
g) creating a message when the count value exceeds the predetermined threshold, the message indicating that the number of contiguous times the empty status was detected exceeds the predetermined threshold.
12. The method according to claim 11 wherein the count value is reset after one of the step (d) of correcting the controllable time period to match the proper time period or the step (g) of creating the message.
13. A device for use in a node connecting a first network and a second network, comprising;
a cell disassembler for converting a sequence of cells into a sequence of frames;
a buffer for storing a cell received from the first network and sending it to the cell disassembler with a controllable time delay to absorb cell delay variation;
a detector for detecting an empty status of the buffer when a cell is read out from the buffer at intervals of the controllable time delay;
a counter for counting a number of contiguous times the empty status was detected; and
a buffer controller for changing the controllable time delay depending on a value of the counter at a time when the empty status is not detected, the buffer controller comprising:
a calculator for calculating a proper time delay depending on a value of the counter at a time when the empty status is not detected and the value of the counter is not zero, and
a timing corrector for correcting the controllable time period to match the proper time delay and setting the controllable time delay to a predetermined value when the empty status is not detected and the value of the counter is zero.
14. The device according to claim 13 , wherein the calculator calculates the proper time delay such that the proper time delay increases linearly with an increase of the value of the counter.
15. The device according to claim 14 , wherein the calculator calculates the proper time delay X by an expression as follows:
X=Y×Z+B,
where Y is a value of the counter, Z is a current controllable time delay, and B is a minimum value of controllable time delay.
16. The device according to claim 13 , wherein the timing corrector sets the controllable time delay to the predetermined value when the empty status is not detected and the value of the counter is zero, wherein the predetermined value is an initial value which is a minimum value of the controllable time delay.
17. The device according to claim 13 , further comprising:
a determiner for determining whether a value of the counter exceeds a predetermined threshold; and
a message creator for creating a message to be sent to a network management section of the first network when the value of the counter exceeds the predetermined threshold, the message indicating that the number of contiguous times the empty status was detected exceeds the predetermined threshold.
18. The device according to claim 17 , wherein the counter is reset after correcting the controllable time delay to match the proper time delay or creating the message.