Telephonic communications – With usage measurement – Call traffic recording or monitoring
Reexamination Certificate
2001-01-09
2004-01-06
Kuntz, Curtis (Department: 2643)
Telephonic communications
With usage measurement
Call traffic recording or monitoring
C379S133000, C379S139000
Reexamination Certificate
active
06674847
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for performing a traffic measurement in a telecommunication network, like a public switched telephone network (PSTN) or a public land mobile network (PLMN).
BACKGROUND OF THE INVENTION
An understanding of the nature of the telephone traffic and its distribution with respect to time and destination is essential in determining the amount of telephone facilities required to serve the subscribers' needs.
The telephone traffic is defined as the aggregate of telephone calls over a group of circuits or trunks with regard to their durations of the calls as well as there numbers. Traffic flow through a switch or trunk group is defined as the product of the number of calls during a period of time and their average holding times. In traffic theory, the unit of time is one hour. Let C be the number of calls originated in one hour, and T be the average holding time, then the traffic flow intensity A is calculated on the basis of the following equation:
A=C×T
For example, if there are 200 calls of average length of 3 minutes between Atlanta and Los Angeles in one hour, then the traffic intensity is:
A=
200×3=600 minute−calls
Expressed in hours, A=600/60=10. This value is dimensionless but a name was given to it. The international unit of telephone traffic is called “erlang”, named after the Danish mathematician A. K. Erlang, founder of the theory of telephone traffic.
From the example above, A=10 erlangs. This number represents:
1. The average number of calls in progress simultaneously during the period of one hour, or
2. The average number of calls originated during a period of time equal to the average call holding time, or
3. The total time, expressed in hours, to carry all calls.
In the US, the term Unit Call (UC) or its synonym “Centium Call-Second”, abbreviated CCS is generally used.
To estimate traffic intensity, mechanical devices were invented to sample or observe the number of busy circuits. These devices can sample each trunk group once every 100 seconds (or 36 times per hour). If the measuring device found that in one hour, all 36 samples show that a particular trunk is being used, it is concluded that the trunk is being used the whole hour, thus by definition this trunk carries 1 erlang or 36 CCS (i.e. 1 erlang=36 CCS).
In the above example, if the average holding time is 5 minutes instead of 3 minutes, then the traffic intensity is:
A=
(200×5)/60=16.67 erlangs
According to the above first definition, the average number of busy trunks between Atlanta and Los Angeles has just increased to 16.67 from 10, because the average subscriber holds a conversation 2 minutes longer
In a known traffic measurement performed for example in a fixed exchange switch of a PLMN, a sampling method is used. According to this method, traffic samples are taken continuously. The traffic intensity corresponds to the average value of these samples.
FIG. 2
shows a time diagram used for explaining the known traffic measurement.
It is assumed that the measurement starts at 12:15:00, wherein a result accumulation period is 15 minutes. The samples are shown and numbered in FIG.
2
. In this connection, it is to be noted that sampling is running although measurement has not yet started.
The measurement is performed on the basis of counters for counting predetermined parameters used for calculating the resultant traffic. In the present case, counters are used for a current sample amount sa, an previous sample amount sap, an instantaneous load ld, a cumulative load lc and a previous cumulative load lcp.
At 12:15:00, the measurement starts and the counters are initialized. As call
1
is running, the instantaneous load amounts to ld=1. Since, according to
FIG. 2
, the measurement starts after 29 samples, the counters are initialized to a previous sample amount sap=29, a sample amount sa=29, a cumulative load lc=0 and a previous cumulative load lcp=0.
After the sample number
30
, the counter are updated to ld=1, sap=29, and sa=30. The cumulative load lc is calculated on the basis of the equation lc=lc+ld=0+1=1.
At sample number
31
, ld=1, sap=29, sa=31, lc=lc+ld=1+1=2.
Since call
2
starts at the time 12:18:00, the instantaneous load ld is increased to 2. Accordingly, at the sample number
32
, ld=2, sap=29, sa=32, lc=lc+ld=2+2=4.
At sample number
33
, ld=2, sap=29, sa=33, lc=lc+ld=4+2=6.
Since call
3
starts at the time 12:22:00, the instantaneous load ld is increased to ld=3.
Accordingly, at the sample
34
, ld=3, sap=29, sa=34, lc=lc+ld=6+3=9.
At the sample number
35
, ld=3, sap=29, sa=35, lc=lc+ld=9+3=12.
Since the call
3
is released at the time 12:27:00, the instantaneous load ld is decreased to ld=2.
Accordingly, at the sample number
36
, ld=2, sap=29, sa=36, lc=lc+ld=12+2=14.
At the sample number
37
, ld=2, sap=29, sa=37, lc=lc+ld=14+2=16.
At the time 12:30:00, 15 minutes after the start of the measurement, the first reporting is performed and the traffic intensity is calculated according to the following equation:
tr
=(
lc−lcp
)/(
sa−sap
)=(16−0)/(37−29)=16/8=2
wherein tr denotes the calculated traffic in erlang.
After the above calculation, the previous sample amount is set to sap=37 and the previous cumulative load to lcp=16. In this respect, it is to be noted that the correct traffic value is 2.133 erlang. Thus, the calculation error is −6.7%.
Until the second reporting at 12:45:00, the updating of the above counters is performed in the same manner as described above.
After the sample number
45
, the following values are obtained: lc=30, lcp=16, sa=45 and sap=37.
Thus, the traffic intensity value amounts to tr=(30−16)/(45−37)=14/8=1.75 erlang. In the present case, the correct value is 1.667 erlang, such that the error amounts to +4.9%.
Thereafter, the previous sample amount is set to sap=45 and the previous cumulative load to lcp=30.
When the third report is issued at 13:00:00, the following values are obtained from the counters: lc=35, lcp=30, sa=50 and sap=45.
Thus, the traffic intensity value amounts to tr=(35−30)/(50−45)=5/5=1 erlang. In this case, the correct value of the traffic intensity is 1 erlang, such that the error is 0%.
Thereafter, the previous sample amount is set to sap=50 and the previous cumulative load to lco=35.
When the fourth report is issued at 13:15:00, the following counter values are obtained: lc=40, lcp=35, sa=57 and sap=50.
Accordingly, the traffic intensity value amounts to tr=(40−35)/(57−50)=5/7=0.714 erlang. In this case, the correct traffic value is 0.667 erlang, such that the error is −7.0%.
Thereafter, the previous sample amount is set to sap=57 and the previous cumulative load to lcp=40.
Accordingly, with this method of performing traffic measurement, the accuracy of the measurement as well as the load of a CPU performing the traffic calculation is obviously dependent on the sampling period. If the sampling period is short, accuracy and CPU load are both increased. However, if the sampling period is long, the accuracy will decrease so that short calls between samples will not be registered at all. In practice, a default sampling period is set to 36 seconds.
Another known method of performing traffic measurement is a time-based me
Kuntz Curtis
Nokia Corporation
Squire Sanders & Dempsey L.L.P.
Taylor Barry W
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