Communications network

• US 6,330,313 B1
• Filed: 03/05/1998
• Issued: 12/11/2001
• Est. Priority Date: 01/22/1997
• Status: Expired due to Term

• Current Assignee: British Telecommunications PLC (BT Group PLC)
• Original Assignee: British Telecommunications PLC (BT Group PLC)
• Inventors: Hunt, Rowland Geoffrey
• Primary Examiner(s): Kuntz, Curtis
• Assistant Examiner(s): BARNIE, REXFORD N
• Application Number:
  US09/029,546
• Time in Patent Office: 1,377 Days
• Field of Search: 379/112, 379/113, 379/133, 379/134, 379/136, 379/137, 379/220, 379/221, 379/229, 379/230, 379/34
• US Class Current: 379/133
• CPC Class Codes: H04M 2201/18 Comparators
• CPC Class Codes: H04M 3/38 Graded-service arrangements, i.e. some subscribers prevented from establishing certain connections queuing arrangements H04Q3/64
• CPC Class Codes: H04M 3/5158 in combination with automated outdialling systems devices for signalling identity of wanted subscriber H04M1/26
• CPC Class Codes: H04Q 2213/13036 Serial/parallel conversion, parallel bit transmission
• CPC Class Codes: H04Q 2213/13166 Fault prevention
• CPC Class Codes: H04Q 2213/13173 Busy signals
• CPC Class Codes: H04Q 2213/13213 Counting, timing circuits
• CPC Class Codes: H04Q 2213/13274 Call rejection, call barring
• CPC Class Codes: H04Q 2213/13352 Self-routing networks, real-time routing
• CPC Class Codes: H04Q 2213/13387 Call gapping
• CPC Class Codes: H04Q 2213/13388 Saturation signaling systems
• CPC Class Codes: H04Q 3/0016 Arrangements providing connection between exchanges
• CPC Class Codes: H04Q 3/0091 Congestion or overload control

Abstract

In a communications network, a count is maintained of the number of calls made to a selected number. The number may be that of an answering center or of any other destination which has the capacity to handle a multiplicity of calls simultaneously. The count is automatically updated when calls are admitted to the number and when they are terminated. If a new call would take the number of calls in progress above a stored value for the maximum capacity of the number, then the call is rejected. In one implementation, resources are allocated dynamically on an Overload Control Server to a particular destination number only when congestion occurs. The stored value for the capacity may be amended automatically depending on the response of the network to admitted calls. The value for the capacity may initially be estimated as a function of the holding times for calls to the destination number.

Claims

1. A method of operating a communications network including steps of:

a) maintaining, for a selected destination number which has the capacity to receive a multiplicity of calls, a count of the number of calls currently in progress;

b) automatically updating the said count when calls are admitted to the selected destination number and when calls are terminated;

c) storing a value for the maximum capacity of the selected destination number;

d) when a new call is made to the selected destination number, comparing the count of the number of calls in progress and the said value for the maximum capacity and rejecting the new call when admitting the call would cause the maximum capacity to be exceeded;

e) subsequently amending, in dependence upon the response of the network to an admitted call, the value for the maximum capacity which was stored in step (c);

wherein the step of estimating the capacity includes;

for a period of time monitoring the number of calls N_C to the destination number which are completed, and recording the time T_C taken to compensate each of the calls; and

calculating an estimate for the capacity from the mean holding time for calls to the number which are completed, and recording the time T_C taken to complete each of the calls; and

calculating an estimate for the capacity from the mean holding time for calls to the number where the mean holding time is derived from the values of N_C and T_C which are recorded during the same period of time; and

wherein the holding times of calls to the destination number have a negative exponential distribution and in step (c) the estimate of the capacity of the destination is derived from the relationship;

${\hat{T}}_H=\frac{\underset{N_C}{\sum <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>T_C+\underset{N_I}{\sum <br><br>}<br><br>T_I}{N_C}$

 

where {circumflex over (T)}_H is the mean holding time, T_C is the time taken to finish a monitored call which has ended, N_C is the number of such calls, T_I is the time taken so far by a monitored call which has yet to end, and N_I is the number of such calls.

2. A method according to claim 1, in which steps (a) to (d) are initiated only when congestion is detected at the destination number.

3. A method according to claim 2, in which steps (a) to (d) are carried out at a single server which serves a plurality of the said selected destination numbers, and in which resources for carrying out steps (a) to (d) are allocated on the server to a respective destination number when congestion is detected at the said destination number.

4. A method according to claim 2, in which steps (a) to (d) are carried out only when the rate of calls to the destination number is above a first, lower threshold level and is below a second, upper threshold level.

5. A method according to claim 1, in which step (c) includes:

estimating the maximum capacity of the destination number and storing the estimated value.

6. A method according to claim 5, in which the step of estimating the capacity includes:

for a period of time, monitoring the number of calls N_C to the destination number which are completed, and recording the time T_C taken to complete each of the calls; and

calculating an estimate for the capacity from the mean holding time for calls to the number, where the mean holding time is derived from the values of N_C and T_C which are recorded during the said period of time.

7. A method of operating a communications network including steps of:

a) maintaining, for a selected destination number which has the capacity to receive a multiplicity of calls, a count of the number of calls currently in progress;

b) automatically updating the said count when calls are admitted to the selected destination number and when calls are terminated;

c) storing a value for the maximum capacity of the selected destination number;

d) when a new call is made to the selected destination number, comparing the count of the number of calls in progress and the said value for the maximum capacity and rejecting the new call when admitting the call would cause the maximum capacity to be exceeded;

e) subsequently amending, in dependence upon the response of the network to an admitted call, the value for the maximum capacity which was stored in step (c);

wherein step (c) includes estimating the maximum capacity of the destination number and storing the estimated value;

wherein the step of estimating the capacity includes;

for a period of time, monitoring the number of calls N_C to the destination number which are completed, and recording the time T_C taken to complete each of the calls; and

calculating an estimate for the capacity from the mean holding time for calls to the number, where the mean holding time is derived from the values of N_C and T_C which are recorded during the said period of time; and

wherein the holding times of calls to the destination number have a negative exponential distribution and in step (c) the estimate of the capacity of the destination is derived from the relationship;

${\hat{T}}_H=\frac{\underset{N_C}{\sum <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>T_C+\underset{N_I}{\sum <br><br>}<br><br>T_I}{N_C}$

 

where {circumflex over (T)}_H is the mean holding time, T_C is the time taken to finish a monitored call which has ended, N_C is the number of such calls, T_I is the time taken so far by a monitored call which has yet to end, and N_I is the number of such calls.

8. A method of operating a communications network including steps of:

a) maintaining, for a selected destination number which has the capacity to receive a multiplicity of calls, a count of the number of calls currently in progress;

b) automatically updating the said count when calls are admitted to the selected destination number and when calls are terminated;

c) storing a value for the maximum capacity of the selected destination number;

d) when a new call is made to the selected destination number, comparing the count of the number of calls in progress and the said value for the maximum capacity and rejecting the new call when admitting the call would cause the maximum capacity to be exceeded;

e) subsequently amending, in dependence upon the response of the network to an admitted call, the value for the maximum capacity which was stored in step (c);

wherein step (c) includes estimating the maximum capacity of the destination number and storing the estimated value;

wherein the step of estimating the capacity includes;

for a period of time, monitoring the number of calls N_C to the destination number which are completed, and recording the time T_C taken to complete each of the calls; and

calculating an estimate for the capacity from the mean holding time for calls to the number, where the mean holding time is derived from the values of N_C and T_C which are recorded during the said period of time; and

wherein the holding times of calls to the destination number are generally constant and in step (c) the estimate of the capacity of the destination is derived from the relationship;

${\hat{T}}_H=\frac{\underset{N_C}{\sum <br><br>}<br><br>T_C}{N_C}.$

9. A call control server suitable for use in a communications network which comprises a plurality of interconnected nodes arranged to provide connections between terminal resources, the call control server comprising:

a) a call counter which is assignable to a selected destination number and which is arranged to maintain a count of the total number of calls in progress to the destination number;

b) a network signalling interface arranged to receive network signals which are generated when calls to the selected destination number are completed

c) a counter controller which is connected to the network signalling interface and to the call counter and which is arranged, in response to the said signals received at the network signalling interface, to update automatically the count which is maintained by the call counter;

d) a store which is programmed with a value for the capacity of the selected destination number; and

e) a call controller which is connected to the call counter and to the store and which includes

a comparator for comparing the value of the call counter and the value programmed in the said store; and

a control signal generator, arranged, when completion of a new call would cause the capacity of the destination number to be exceeded, to generate a control signal to cause the new call to be rejected without the new call being routed to the destination; and

wherein the call controller includes a capacity tracker which is arranged automatically to write an amended value for the capacity in the store (d) in dependence upon the response of the network to an admitted call; and

wherein the capacity tracker is arranged, when the number of calls in progress is equal to the stored value for the maximum capacity, to increment the stored value for the maximum capacity, to monitor the response of the network to a further admitted call, if a BUSY signal is returned then decrements the stored value for the maximum capacity, and otherwise maintains the stored value for the maximum capacity at the incremented level.

10. A communications network comprising:

a) a plurality of interconnected nodes arranged to provide connections between terminal resources; and

b) a call control server according to claim 9.

11. A call control server according to claim 9, further comprising a congestion detector which is arranged to initialise the call counter, the counter controller and the call controller in response to a signal from the network which indicates congestion at the destination number.

12. A call control server according to claim 11, further comprising a resource allocator which is connected to the congestion detector, and which in response to the detection of congestion at a destination number allocates server resource to the respective number.

13. A method of operating a communications network including steps of:

a) maintaining, for a selected destination number which has the capacity to receive a multiplicity of calls, a count of the number of calls currently in progress;

b) automatically updating the said count when calls are admitted to the selected destination number and when calls are terminated;

c) storing a value for the maximum capacity of the selected destination number;

d) when a new call is made to the selected destination number, comparing the count of the number of calls in progress and the said value for the maximum capacity and rejecting the new call when admitting the call would cause the maximum capacity to be exceeded; and

e) subsequently amending, in dependence upon the response of the network to an admitted call, the value for the maximum capacity which was stored in step (c);

f) incrementing the stored value for the maximum capacity;

g) admitting a further call; and

h) if a BUSY signal is returned than decrementing the stored value for the maximum capacity, otherwise maintaining the stored value for the maximum capacity at the incremented level.

14. A method of operating a communications network including steps of:

a) maintaining, for a selected destination number which has the capacity to receive a multiplicity of calls, count of the number of calls currently in progress;

b) automatically updating the said count when calls are admitted to the selected destination number and when calls are terminated;

c) storing a value for the maximum capacity of the selected destination number;

d) when a new call is made to the selected destination number, comparing the count of the number of calls in progress and the sid value for the maximum capacity and rejecting the new call when admitting the call would cause the maximum capacity to be exceeded;

(e) incrementing the stored value for the maximum capacity;

(f) admitting a further call; and

(g) if a BUSY signal is returned then decrementing the stored value for the maximum capacity, otherwise maintaining the stored value for the maximum capacity at the incremented level.

15. A method of operating a communications network including steps of:

a) maintaining, for a selected destination number which has the capacity to receive a multiplicity of calls, a count of the number of calls currently in progress;

b) automatically updating the said count when calls are admitted to the selected destination number and when calls are terminated;

c) storing a value for the maximum capacity of the selected destination number;

d) when a new call is made to the selected destination number, comparing the count of the number of calls in progress and the said value for the maximum capacity and rejecting the new call when admitting the call would cause the maximum capacity to be exceeded; and

decreasing the stored value for the maximum capacity if at any time a busy signal is received in response to a calf admitted when the call counter has a value less than the stored value of the maximum capacity.

16. A call control server suitable for use in a communications network which comprises a plurality of interconnected nodes arranged to provide connections between terminal resources, the call control server comprising:

a) a call counter which is assignable to a selected destination number and which is arranged to maintain a count of the total number of calls in progress to the destination number;

b) a network signalling interface arranged to receive network signals which are generated when calls to the selected destination number are completed

c) a counter controller which is connected to the network signalling interface and to the call counter and which is arranged, in response to the said signals received at the network signalling interface, to update automatically the count which is maintained by the call counter;

d) a store which is programmed with a value for the capacity of the selected destination number; and

e) a call controller which is connected to the call counter and to the store and which includes

a comparator for comparing the value of the call counter and the value programmed in the said store; and

a control signal generator, arranged, when completion of a new call would cause the capacity of the destination number to be exceeded, to generate a control signal to cause the new call to be rejected without the new call being routed to the destination; and

wherein the call controller includes a capacity tracker which is arranged automatically to write an amended value for the capacity in the store (d) in dependence upon the response of the network to an admitted call; and

wherein the capacity tracker is arranged to decrease the stored value for the maximum capacity if at any time a busy signal is received in response to a call admitted when the call counter has a value less than the stored value of the maximum capacity.

17. A method of operating a communications network including steps of:

a) maintaining, for a selected destination number which has the capacity to receive a multiplicity of calls, a count of the number of calls currently in progress;

b) automatically updating the same count when calls are admitted to the selected destination number and when calls are terminated;

c) storing a value for the maximum capacity of the selected destination number;

d) when a new call is made to the selected destination number, comparing the count of the number of calls in progress and the said value for the maximum capacity and rejecting the new call when admitting the call would cause the maximum capacity to be exceeded; and

e) subsequently amending, in dependence upon the response of the network to an admitted call, the value for the maximum capacity which was stored in step (c);

f) incrementing the stored value for the maximum capacity;

g) admitting a further call; and

h) if a BUSY signal is returned them decrementing the stored value for the maximum capacity, otherwise maintaining the stored value for the maximum capacity at the incremented level.

18. A method of operating a communications network including steps of:

a) maintaining, for a selected destination number which has the capacity to receive a multiplicity of calls, a count of the number of calls currently in progress;

b) automatically updating the same count when calls are admitted to the selected destination number and when calls are terminated;

c) storing a value for the maximum capacity of the selected destination number;

d) when a new call is made to the selected destination number, comparing the count of the number of calls in progress and the said value for the maximum capacity and rejecting the new call when admitting the call would cause the maximum capacity to be exceeded; and

e) subsequently amending, in dependence upon the response of the network to an admitted call, the value for the maximum capacity which was stored in step (c); and

f) decreasing the stored value for the maximum capacity if at any time a BUSY signal is received in response to a call admitted when the call counter has a value less than the stored value of the maximum capacity.