System and method for learning transmission band of multiplex packet

A multiplex-packet band learning system and method wherein management of the transmission band of a trunk suitable for an actual packet communication amount can be established to contribute to efficient multiplex packet communication. The number of communication packets per unit time for each medium pattern corresponding one of combinations of call terminal attributes is measured for the trunk interface of each exchange, a normal distribution of the numbers of communication packets in actual communication is estimated on the basis of the measured number of communication packets per unit time for each medium pattern, and its estimated value is updatingly held as index data of permission or prohibition of a new call registration. The number of communication packets in the actual communication is measured at a terminal interface so that a terminal band table for the terminal interface has packet rates at which the terminal has been so far communicated, mean and variance values of the past packet rates are calculated on the basis of the actually measured number of communication packets, a normal distribution is estimated at packet rate estimation circuits PPLs of a controller with use of its measured statistical data, and it is judged whether the packet communication of a call requiring the registration to the corresponding trunk line is permitted or prohibited.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a system and method for learning the 
transmission band of a multiplex packet transmitted through a trunk of a 
packet exchange or an asynchronous transmission mode exchange. 
2. Description of the Related Art 
Referring to FIG. 1, there is shown a functional block diagram of a general 
packet exchange system, in which a terminal 110 belongs to a packet 
exchange 100 with which a packet exchange 100' is connected through a 
trunk 109, and a terminal 111 belongs to the packet exchange 100'. 
Assume now that the terminal 110 generates a communication request directed 
to the terminal 111. In this case, prior to its communication, the 
terminal 110 informs a controller 101 provided in the exchange 100 of a 
call message via a call signal line 105. The controller 101, in response 
to the call message, secures the necessary communication route, 
communication channel, etc. between the terminals 110 and Ill and informs 
the adjacent exchange 100' of the call message through a call signal line 
107 of the trunk 109 according to preset route information on different 
destinations, while performing various sorts of controls to be described 
later. 
On the side of the adjacent exchange 100', a controller 101' in the 
exchange 100', when receiving the aforementioned call message, secures the 
necessary communication route and channel up to the destination terminal 
111 and informs the terminal Ill of the call message through a call signal 
line 105'. 
Thereafter, when it is desired to perform a packet communication between 
the terminals 110 and 111, the packet communication is carried out in 
accordance with the communication route set by the exchange 100 based on 
the call message received from the terminal 110. 
More specifically, when the terminal 110 is sending a packet through a data 
line 106 to a trunk interface 103 for example, the exchange 100 functions 
to further transmit the packet from the trunk interface 103 through a 
trunk interface 103' of the opposing exchange 100' to the terminal 111. In 
this connection, if another packet is already being transmitted through 
the corresponding trunk, then the packet to be next transmitted is once 
stored in a memory 102-for later transmission after the trunk becomes not 
in use. 
Shown in FIG. 2 is an exemplary format of the call message used in this 
sort of packet transmission control, and FIG. 3 shows the structure of a 
packet actually transmitted in the control. 
In FIG. 2, the illustrated call message comprises a call number for 
identification in a call exchange; a message code indicative of the sort 
of the message such as, e.g., `01` (call setting), `02` (call acceptance) 
or `03` (call release)(in the case of the call acceptance and release, 
constituent data which will be explained become unnecessary); destination 
number data indicative of a destination exchange number and a destination 
terminal number; a seized-channel number seized as the corresponding 
terminal line or trunk according to the route data with respect to the 
destination number of the packet receiver; a medium code indicative of the 
medium type of the communication terminal as the call-message issuer such 
as, e.g., `01` (voice), `02` (data) or `03` (television conference 
terminal); a request packet rate (for example, 125 packets/sec.) required 
by the call message; and additional data such as other terminal 
communication attributes. 
FIG. 4 shows a functional structure of the controller 101 of the prior art 
exchange for processing such a call message as containing these data 
elements. In operation of the controller 101, when a `call setting` 
message is supplied to a call message buffer 201 of the controller 101 in 
the exchange through the call signal line 105, this causes the buffer 201 
to send a request packet rate to a subtracter 210 through a signal line 
209. At the same time, the subtracter 210 also receives an output of a 
residual-trunk- capacity register 204 through a signal line 208. The 
output of the residual-trunk-capacity register 204 indicates the current 
residual trunk capacity value which is set as its initial value at a 
maximum packet rate value of associated one of trunks predetermined for 
each trunk and which is sequentially modified through such control as to 
be described later. The subtracter 210 performs a subtraction of the 
residual trunk capacity value minus the request packet rate value and 
applies its subtraction result to a comparator 203. The comparator 203 
compares the received subtraction result with zero. 
When the subtraction result is equal to or larger than zero, the comparator 
203 applies the subtraction result through a signal line 207 to the 
residual-trunk- capacity register 204 to modify the residual trunk 
capacity value. The comparator 203 also informs the trunk interface 103 
and the terminal interface 104 of a `call acceptance` message via a signal 
line 205, the call message buffer 201 and the other of the call signal 
line 105 for call registration. 
On the other hand, when the aforementioned subtraction result value is 
smaller than zero, the comparator 203 cancels the subtraction result value 
and informs the terminal interface 104 of a `call release` message via a 
signal line 206, the call message buffer 201 and the call signal line 105 
for call release. In this case, the residual trunk capacity value is kept 
at the previous value. Thereafter, if the call is accepted, then a packet 
communication is carried out between the terminals 110 and 111. 
As has been already explained above, the exemplary format of the 
communication packet is expressed, as shown in FIG. 3, in terms of the 
channel number seized at the time of the call setting and communication 
data. 
Using communication packets having such a format as mentioned above, packet 
communication is carried out between the terminal 110 and the exchange 100 
and between the exchanges 100 and 1001. At this time, when the exchange 
100 temporarily receives many packets from its terminals, the exchange 100 
might not be able to immediately send them to the trunk 109. For the 
purpose of avoiding such a situation, such packets are temporarily stored 
in the memory 102 (refer to FIG. 1) of the exchange 100 so that as the 
trunk 109 becomes empty, the packets stored in the memory 102 are sent 
onto the trunk 109. 
Shown in FIG. 5 is a transmission characteristic showing how to transmit 
each call generated based on such conventional control operation. 
It will be clear from FIG. 5 that, in the prior art, the request packet 
rate at the stage of the call setting is set usually at the maximum 
transmission packet rate (in other words, transmission bearer rate), which 
results in that the request packet rate becomes extremely large when 
compared with the packet rate (measured packet rate) at which 
communication is actually effected. In other words, the transmission 
characteristic of the trunk through which such requested calls are 
multiplexed has such an idle band as shown in FIG. 5. 
Such transmission characteristic adversely affects greatly a communication 
efficiency. For this reason, it has been impossible to realize such effect 
unique to the packet multiplex communication as obtained, e.g., when a 
call communication packet becomes temporarily idle, by transmitting 
another communication packet during the temporary idle period. 
In this way, the prior art system of managing the transmission band of 
multiplex packets is arranged so that when a terminal issues a 
communication request, its residual trunk capacity is found usually on the 
basis of the request packet rate given as the maximum packet rate of the 
associated terminal so that a call is accepted during zero or more of the 
residual trunk capacity. As a result, the prior art system has had such a 
problem that not only the request trunk capacity per call becomes much 
larger than the actual packet communication amount (traffic) of the trunk 
per call in the actual communication but also the packet multiplex effect 
of the trunk cannot be obtained, thus making it impossible to manage and 
operate the trunk transmission band efficiently. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a system and 
method of learning the transmission band of a multiplex packet, which can 
establish management of the transmission band of a trunk suitable for the 
actual packet communication amount (traffic), thus contributing to 
efficient multiplex packet communication. 
The multiplex-packet band learning system and method in accordance with the 
present invention are featured in that the number of communication packets 
per unit time for each medium pattern corresponding one of combinations of 
call terminal attributes is measured for the trunk interface of each 
exchange, a normal distribution of the numbers of communication packets in 
actual communication is estimated on the basis of the measured number of 
communication packets per unit time for each medium pattern, and its 
estimated value is updatingly held as index data of permission or 
prohibition of a new call registration. 
To this end, the present invention is arranged as follows. 
First, a counter for measuring the number of packets per unit time is 
provided in the trunk interface of each packet exchange. A controller in 
each packet exchange is provided therein with a medium pattern register, a 
medium pattern control table, a normal estimation circuit and a 
medium/reference packet rate table to allow learning of the transmission 
band of a multiplex packet on the trunk. The medium pattern register is 
used to store therein traffic patterns (such, for example, as telephone 
terminal traffic patterns and television terminal traffic patterns, which 
will be referred to as the medium patterns, hereinafter) for different 
medium codes of the current call. 
The medium pattern control table previously stores therein as limit medium 
patterns the maximum number of combinations from the maximum number of the 
communication packets per unit time previously registered for each medium 
as the initial values of the maximum medium patterns registerable for the 
trunk. When the medium traffic reaches the limit medium pattern during 
exchanging operation, a predetermined upper limit of significance level 
(risk rate) based on normal distribution estimation of past packet number 
samples measured per unit times at the trunk interface is given as a 
residual trunk capacity band, additions of combination patterns@of the 
maximum medium traffics addible for the residual trunk capacity band to 
the limit medium patterns are all combined to be replaced by limit medium 
patterns as new limit medium patterns, whereby the contents of the table 
are sequentially learned as the limit medium patterns. 
The normal estimation circuit is provided to estimate the residual trunk 
capacity band on the basis of the number of packet samples per unit time 
measured at the trunk interface for each medium pattern. 
The normal estimation circuit, in particular, when finding the combination 
medium pattern of the maximum terminal traffic addible for the residual 
traffic capacity band in the above estimation, has such a control 
parameter that allows a combination medium pattern to be regarded as the 
combination medium pattern of the maximum medium traffic if the residual 
trunk capacity band is between the normal distribution estimate value of 
samples of that combination medium pattern and a region slightly smaller 
than the estimate value. 
In order to avoid abnormal estimation with use of a very small number of 
samples, the normal estimation circuit has also an estimation .phi. value 
register which instructs to set the number of samples at a value that is 
equal to or larger than a preset value. 
The medium/reference packet rate table is used to register therein 
reference packet numbers per unit time for respective media to determine 
the combination pattern of the maximum medium traffic addible for the 
residual trunk capacity. 
In the present invention, when the maximum traffic pattern (medium pattern) 
of the medium code registerable for the trunk is used as a limit medium 
pattern, the maximum combination medium patterns registerable for the 
trunk determined by the maximum numbers of communication packets per unit 
time for different media are previously stored as their initial values so 
that, when the medium traffic reaches the limit medium pattern during 
exchanging operation, a predetermined upper limit of significance level is 
provided as the residual trunk capacity band through the normal 
distribution estimation based on the past packet number samples measured 
per unit time at the trunk interface, additions of the maximum medium 
traffic combination patterns addible to the residual trunk capacity band 
to the corresponding limit medium pattern are all combined, the 
corresponding limit medium pattern is additively replaced by a new limit 
medium pattern, whereby the contents are sequentially learned as the limit 
medium pattern. 
Through this learning operation, the actually measured values of the 
communication packet number of the medium pattern actually occurred in the 
past are used in the judgment of the new call registration so that the 
registered traffic is set to be suitable for the actual communication 
packet amount, thereby realizing the efficient use of the trunk 
transmission band. 
In the case where it is desired to find the maximum terminal traffic 
combination pattern addible for the residual trunk capacity band, the 
learning divergence, which might occur through the statistical processing 
of the measured samples, can be prevented and stable convergence can be 
realized, because the control parameter is provided which, when the 
residual trunk capacity band is between the normal distribution estimate 
value of samples for each medium pattern and a very small region smaller 
therethan, regards it as the maximum medium traffic combination pattern. 
Further, since there is provided an estimate .phi. value register which 
sets the number of samples at a value that is equal to or larger than a 
preset value to avoid the learning operation with use of improper estimate 
values, abnormal estimation based on a very small number of samples can be 
inhibited from being performed. 
The multiplex-packet band learning system and method are featured in that 
the number of communication packets per unit time on the corresponding 
terminal line is measured for each exchange terminal interface, a normal 
distribution of the communication packet numbers in actual communication 
is estimated with use of mean and variance values of the measured 
communication packets, and its estimated value is updatingly held as index 
data of new-call registration permission/prohibition. 
To carry out the above learning system, in accordance with the present 
invention, the terminal interface comprises a counter for measuring the 
number of communication packets; a timer for timing the unit time of 
count-value collection of the counter; a terminal band table for holding 
therein mean and variance values of the packet number values calculated 
based on the collected packet number values per unit time (packet rate), 
an initial packet rate value obtained from bit clocks applied to the 
terminal, and statistical- processing start threshold values for 
determining whether the initial packet rate value is used as a band value 
or a statistical value of the collected packet rates is used therefor, 
etc.; a microprocessor and its program for generating the terminal band 
table or substituting the mean and variance values in the table for the 
request packet rate value in the calling message for transmission to the 
controller. 
The controller comprises a packet rate estimation circuit (PPL) for 
estimating the multiplex packet rate of the trunk line on the basis of the 
packet rates of respective terminals for the call as circuit for judging 
whether the call received from the terminal is to be accepted for the 
trunk line corresponding to the destination of the call, and an estimation 
correction circuit for performing such correction as to return the packet 
rate of the registered terminal to its initial packet rate when remarkable 
packet discard takes place in the communication of the call registered 
through the estimation. 
The memory comprises a counter for counting the number of discard packets 
occurred when the number of packets transmitted exceeds the memory 
capacity allocated to each trunk, a microprocessor and its program for 
carrying out estimation correction when the count value of the counter 
exceeds a preset threshold value. 
In the present invention, the number of communication packets in the actual 
communication is measured at a terminal interface so that a terminal band 
table for the terminal interface has mean and variance values of packet 
rates at which the terminal has been so far communicated, the mean and 
variance values of the past packet rates are calculated on the basis of 
the measured samples of the communication packets, a normal distribution 
is estimated at PPLs of a controller with use of its measured statistical 
data, and it is judged whether the packet communication of a call 
requiring the registration to the corresponding trunk line is permitted or 
prohibited. 
That is, in accordance with the present invention, the transmission band 
required by a terminal is considered not to be specified in the calling 
massage from the terminal but to be estimated on the basis of measured 
samples on the past communication. As a result, a more practical data can 
be obtained as index data of new-call registration permission or 
inhibition so that the transmission band of the trunk line of the call 
suitable for the actual communication packet amount can be selected, 
whereby the trunk line transmission band can be highly efficiently used. 
Since there is provided a detection means in the memory for detecting such 
a situation that the number of discard packets per trunk line is 
remarkably large, when such situation is detected, the request packet rate 
of the terminal corresponding to the registered call is returned to its 
initial packet rate, whereby communication of a less number of discard 
packets can be ensured.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiments of the present invention will be described in detail with 
reference to the accompanying drawings. Even in the explanation of the 
embodiments of the present invention, the basic arrangement of the packet 
exchanges of FIG. 1, the call message of FIG. 2 and the format of the 
communication packet of FIG. 3 are used as they are. 
A first embodiment of the present invention is featured in that a trunk 
interface learns a new medium pattern registerable for a trunk line from 
the number of communication packets per unit time measured for each medium 
pattern corresponding to a media combination to use the learned data in 
judging permission or non-permission of registration of a new call. 
The first embodiment of the present invention having such a feature will be 
explained by referring to FIGS. 6 to 17. Referring first to FIG. 6, there 
is shown a functional arrangement of the controller 101 of a packet 
exchange in the present embodiment, which corresponds to the controller 
101 in the system of FIG. 1. 
In FIG. 6, when a `call setting` message is applied from a terminal through 
a terminal interface associated with the terminal to the controller 101, 
the `call setting` message is sent to a medium pattern register (MPR) 303 
through the call signal line 105, a signal line 105a and a call message 
buffer 302. 
The medium pattern register 303 is used to store therein the numbers of 
calls in different media currently being registered as shown in FIG. 7. 
The respective initial values of the respective media stored in the medium 
pattern register 303 are all zero and each time a call corresponding to 
each medium is registered, the associated initial value is added by 1. 
It is now assumed that a call is not input until registration judgment for 
a series of calls is completed. The values stored in the medium pattern 
register 303 are sent to a comparator 304 to be compared with an output of 
a medium pattern control table (MPCT) 305 storing therein a limit medium 
pattern obtained through a learning system (which will be explained later) 
for call registration judgment based on its comparison results. 
When the call registration judgment is made that the respective medium 
traffics stored in the medium pattern register 303 are smaller than the 
medium traffics of the limit media pattern stored in the medium pattern 
control table 305 (MPR&lt;MPCT), the comparator 304 informs the trunk and 
terminal interfaces of a `call acceptance` message via a signal line 312, 
the call message buffer 302, a signal line 105c and the call signal line 
105 to accept the registration of a new call. 
When the call registration judgment is made that the respective medium 
traffics stored in the medium pattern register 303 are larger than the 
medium traffics of all the limit media patterns stored in the medium 
pattern control table 305 (MPR&gt;MPCT), the comparator 304 informs the 
terminal interface of a `call release` message via a signal line 310, the 
call message buffer 302, a signal line 105b and the call signal line 105 
and at the same time, subtracts 1 from ones of the traffics of the 
respective media stored in the medium pattern register 303 and 
corresponding to the released call to reject the call. 
If the traffics of the respective media stored in the medium pattern 
register 303 coincide with the traffics of the respective media of the 
limit medium pattern stored in the medium pattern control table 305 
(MPR=MPCT), then the comparator 304 informs the trunk and terminal 
interfaces of a `call acceptance` message via a signal line 311, the call 
message buffer 302, a signal line 105c and the call signal line 105 and 
also informs the trunk interface of a measurement command via a signal 
line 112a and an internal control bus 112 to accept a new call and start 
measuring the number of packets per unit time. 
In the case where the traffics of the respective media stored in the medium 
pattern register 303 coincide with the traffics of the respective media of 
the limit medium pattern stored in the medium pattern control table 305, 
the call message buffer 302, when receiving a `call release` message, 
informs the trunk interface of a measurement end command via a signal line 
112b and the internal control bus 112. 
FIG. 8 shows an arrangement of the trunk interface in the present 
embodiment. More precisely, FIG. 8 shows only the packet counting function 
among the functions of the trunk interface. 
The trunk interface 103, during a period from the reception of the 
measurement command through the call signal line 105 from the controller 
101 to the reception of the measurement end command, monitors 
communication packets on the internal data line 106 of the packet exchange 
applied to a trunk driver 403 and the packer counter 402 incrementally 
counts the number of such communication packets. 
The count value of the packet counter 402 is sent, as a unit time measured 
value 404, to and collected at a controller 401 of the trunk interface at 
intervals of a unit time. The controller 401, when informed of the 
measurement end command from the controller 101, informs a normal 
estimation control circuit (NCL) 306 provided in the controller 101 of 
measurement data corresponding to the structure elements of the medium 
pattern control table 305 (which will be detailed later), that is, of a 
measurement unit time number (occurrence frequency), a sum of unit time 
packet numbers (packet rate sum) and a sum of squared unit time packet 
numbers (squared packet rate sum), via the internal control bus 112 and a 
signal line 112c. 
FIG. 9 is a flowchart for explaining the internal control operation of the 
normal estimation control circuit 306. More specifically, measurement data 
measured at the trunk interface 103 during existing period of one medium 
pattern is applied to the normal estimation control circuit 306 which in 
turn executes its necessary control operation on the basis of the applied 
measurement data. For this control operation, the normal estimation 
control circuit 306 is required to receive a normal estimation parameter 
314 from the medium pattern control table 305. 
The structure of the medium pattern control table 305 will be explained by 
referring first to FIG. 10. In the drawing, the medium pattern control 
table 305 comprises a limit flag (FLG) indicative of a limit medium 
pattern obtained as a result of learning a medium pattern (which will be 
explained later), medium patterns (medium 1 traffic (ME1), medium 2 
traffic (ME2), medium 3 traffic (ME3), . . . ) obtained through the 
learning operation of the initial registration medium patterns to be 
described later, a total pattern occurrence frequency (N) for estimating 
measured packet numbers per unit time for each medium pattern based on 
normal distribution, a total packet rate sum (.SIGMA.) corresponding to a 
sum of accumulated measured packet numbers per unit time, and a total 
packet rate squared-sum (.SIGMA..sup.2) corresponding to a sum of squared 
measured packet numbers per unit time. Stored in the table 305 are all the 
limit medium patterns when the maximum packet rates are assumed as their 
initial values for the respective media. 
Turning back to FIG. 9, explanation will be made as to the internal control 
operation of the normal estimation control circuit 306. 
When a modification circuit 501 of the normal estimation control circuit 
306 receives measured data values (1) (occurrence frequency=n, packet rate 
sum=s, packet rate squared-sum=s.sup.2) from the trunk interface and also 
received limit medium pattern parameters (2) (FLG=1, ME1, ME2, ME3, . . . 
, N, .SIGMA., .SIGMA..sup.2) from the medium pattern control table 305, 
the modification circuit 501 executes the following calculations to find 
measured data for each total medium pattern and sends the measured data to 
the medium pattern control table 305 as a pattern addition/modification 
313 to modify the limit medium pattern parameters so far stored in the 
medium pattern control table 305 to new parameters (3)(FLG=0, ME1 ,ME2, 
ME3, . . . , new N value, new .SIGMA. value, new .rho..sup.2 value). 
EQU N.rarw.N+n 
EQU .SIGMA..rarw..SIGMA.+s 
EQU .SIGMA..sup.2 .rarw..SIGMA..sup.2 +s.sup.2 
And when a comparator 503 compares the new N value with a preset value 
previously set in an estimate .phi. register 502 and determines that the 
new N value is equal to or larger than the estimate .phi., the comparator 
issues an operation request to an estimation circuit 504 to start 
estimating operation therein. 
The estimation of normal distribution is carried out by performing the 
following calculations with use of a sample average (ave) and an unbiased 
variance (var). 
EQU Xave=.SIGMA./N 
##EQU1## 
EQU .mu..rarw.ave+t(N-1,.alpha..sub.1)(var/N).sup.1/2 
EQU .sigma..sup.2 .rarw.1/(.chi..sup.2 (N-1,1-.alpha..sub.2 
/2)).times.(N-1).times.var 
EQU A.rarw..mu.+N(.alpha..sub.3).times..sigma. 
EQU R.rarw.(trunk packet rate)-A 
In the above calculations, a table 505a for storing therein the value 
t(N-1, .alpha.1) corresponding to the sample number N, a table 505b for 
storing therein the value .chi..sup.2 (N-1), 1-.alpha.2/2), and a table 
505c for storing therein the value N(.alpha.3) are used as estimation 
coefficients for estimation of the value A. 
Examples of data to be stored in these tables 505a, 505b and 505c are shown 
in FIGS. 11 to 13 respectively. In estimation of the value A, preset 
significance levels .alpha.1, .alpha.2 and .alpha.3, the values t(N-1, 
.alpha.1), .chi..sup.2 (N-1, 1-.alpha.2/2) and N(.alpha.3) corresponding 
to the sample number N are sent from the tables 505a, 505b and 505c 
respectively to the estimation circuit 504. 
The estimation circuit 504, when estimating the value A, further calculates 
a residual trunk capacity (R) with use of the estimated value A to cause 
respectively independent pattern addition circuits 506 and 507 to start 
their operation according to the positive or negative of the calculated 
residual trunk capacity value R. 
More specifically, if R.gtoreq.0 then the pattern addition circuit 506 is 
operated to add or insert all medium patterns which do not allow further 
additional media insertion any longer in the residual trunk capacity R (in 
other words, close to the trunk rate) into the medium pattern control 
table 305 as new limit medium patterns in the form of an INSERT signal (5) 
(FLG=1, ME1+i, ME2+j, ME3+k, . . . , nop, nop, nop, where `nop` represents 
the same value as that stored in the medium pattern control table 305). 
Although i, j, k, . . . are retrieved from 0 to 00 to find all the medium 
patterns in FIG. 9, in practical cases, a suitable value is allocated 
.infin.. In this case, for judgment of permission or non-permission of 
addition to the residual trunk capacity R, reference packet rate values 
for the respective media are previously registered in a 
media/reference-packet-rates table (MUT) 307 shown in FIG. 6. That is, 
reference packet rate values v1, v2, v3, . . . are applied to the pattern 
addition circuit 506. An example of contents of the 
media/reference-packet-rates table (MUT) 307 is shown in FIG. 14. 
If R&lt;0 then the pattern addition circuit 507 is operated. In this case, 
since the packet rates of the previous limit medium patterns have been too 
large, negative feedback operation is applied as illustrated so that all 
medium patterns close to their trunk rates are added to the medium pattern 
control table 305 as an INSERT signal (5') (FLG=1, ME1-i, ME2-j, ME3-k, . 
. . , nop, nop nop, where `nop` represents the same value as that stored 
in the medium pattern control table 305). 
The additional operation to the medium pattern control table 305 is 
realized, in the case of a new combination of medium patterns, by adding 
the data of the INSERT signal into the medium pattern control table 305 
and when the medium patterns already exist in the medium pattern control 
table 305, by rewriting the FLG in the corresponding medium patterns to 
"1". 
The value close to the trunk rate, i.e., the `esp` in the drawing is 
previously set in an `esp`-value register 508. 
Shown in FIG. 15 is part of an example of limit medium pattern learning 
actually carried out based on this transmission band learning system. In 
the drawing, symbol ME1 corresponds to a telephone terminal medium 
(maximum packet rate =125 packets/sec.), ME2 corresponds to a data 
terminal medium (maximum packet rate=125 packets/sec.), and ME3 
corresponds to a television conference terminal medium (maximum packet 
rate=750 packets/sec.). Further, the trunk packet rate is 3000 
packets/sec. The initial values of the medium pattern control table 305 
are given as mentioned above in forms of all the limit medium patterns 
based on the maximum packet rates of the respective media, and in the 
illustrated example, the table 305 comprises 65 of the limit medium 
patterns one of which has an ME1 of 10, an ME2 of 8 and ME3 of 1 (refer to 
FIG. 15(a)). 
Thereafter, when the system is operated and a specific limit medium pattern 
occurs 10 or more times (estimate .phi. value=10), estimation is carried 
out under the condition that esp=250, .alpha.1=.alpha.2=.alpha.3=0.01 by 
the timing of FIG. 15(b), whereby such limit medium pattern learning as 
shown in FIG. 15(c) is realized. 
FIG. 16 shows a convergence in one learning process with respect to the 
learning frequency (estimation frequency) carried out in the same example 
as in FIG. 15. It will be seen from FIG. 16 that the effective trunk use 
system can be realized by means of the learned limit medium pattern and at 
the same time the stable convergence can be obtained. In the present 
embodiment, there is a possibility that the packet rate of the learned 
limit medium pattern exceeds the trunk packet rate, but the discard of the 
exceeded packets in this case can be prevented by storing the exceeded 
packets in a memory (for example, memory 102 in the system of FIG. 1) 
provided in the packet exchange. 
The present embodiment utilizes the fact that the packet rate distribution 
based on infinite sampling operations for each medium pattern becomes 
substantially a normal distribution as shown in FIG. 17. The control 
explained in connection with the present embodiment may be similarly 
realized not only by means of the controller mounted in the packet 
exchange but also by means of an external control computer externally 
connected to the packet exchange. 
As has been described in the foregoing, in accordance with the present 
embodiment, the management of the trunk transmission band is sequentially 
learned by means of the limit medium pattern so that the actually measured 
value of the communication packet number of the medium pattern actually 
occurred in the past is used in the registration judgment of a new call, 
whereby the request packet rate can correspond to the actual packet 
communication amount and thus the efficient use of the trunk transmission 
band can be realized. 
In the present embodiment, further, in finding a combination medium pattern 
of the maximum terminal traffic addible to the residual trunk capacity 
band, if the combination pattern, as the residual trunk capacity band, is 
between the normal distribution estimate value of samples for each medium 
pattern and a region slightly smaller than the estimate value, then the 
combination medium pattern is regarded as a limit medium pattern. As a 
result, the learning divergence caused by statistical processing of 
measured samples can be prevented and therefore stable convergence can be 
realized. Further, according to the present embodiment, since the sample 
number larger than the specified value is assigned, stable estimation can 
be realized. By virtue of the synergistic action of the aforementioned 
effects, the present embodiment can be highly effectively applied to such 
a packet exchange that requires various sorts of media to be efficiently 
connected thereto. 
Explanation will next be made as to a second embodiment of the present 
invention. Even in the explanation of the second embodiment, the basic 
arrangement of the packet exchanges of FIG. 1, the call message of FIG. 2 
and the format of the communication packet of FIG. 3 are employed without 
any modifications as they are. The second embodiment is featured in that 
the multiplex packet rate of a trunk line multiplexed for every call is 
estimated on the basis of samples of the packet rates measured at the 
terminal interface and the estimated value is used for judgment of 
permission or nonpermission of registration of a new call. 
The second embodiment having such a feature will be explained by referring 
to FIGS. 18 to 32. 
FIGS. 18 to 21 are for explaining the terminal interface used in the 
present embodiment. More specifically, FIG. 18 shows a functional block 
diagram of the terminal interface 104. The terminal interface 104 
comprises a circuit for measuring packet rate samples for each terminal 
and calculating its mean value and variance value and a circuit for adding 
these calculated values to the call message and informing the controller 
of the added call message. In FIG. 18, when a terminal receives a call and 
is in communication with the party, the number of packets transferred 
through the data line 106 therebetween is measured by a packet counter 
605. 
Shown in FIG. 19 is a procedure according to which a mean value and a 
variance value for the packet number are prepared on the basis of the 
count value of the packet counter 605.., In more detail, in this 
procedure, a microprocessor 601 of the terminal interface 104 prepares a 
terminal band table (TBT) 603 while executing a program 602. An example of 
contents of the terminal band table 603 prepared according to this 
procedure is shown in FIG. 21. 
Turning back to FIG. 19, explanation will be made as to the preparation 
procedure of the terminal band table 603. In carrying out this procedure, 
an initial packet rate (Bi) value indicative of the transmission band of a 
call generated from the associated terminal when the measuring frequency 
of the packet rate is less as well as a statistical-processing start 
threshold (.DELTA.i) for judgment of whether or not the statistical 
processing is possible due to the less measuring frequency are previously 
set, as initial data, in the terminal band table 603 by means of manual 
setting operation or the like (step 611). 
And when a call is set in communication between terminals and packet 
communication is actually started, the microprocessor 601 reads the count 
value of the packet counter 605 at intervals of a constant time set by a 
timer 604 and holds therein the read count value as one packet rate sample 
(step 612). The microprocessor 601 further performs calculations in 
accordance with illustrated computation equations as the number of samples 
increases and rewrites the data contents of the terminal band table 603 to 
the corresponding calculated values (step 613). 
As a result of the measurement of the packet rate based on the calculation 
processing, a mean value and a variance value (in the illustrated example, 
arithmetic average value and an unbiased variance) of the terminal band 
packet rates are set in the terminal band tables 603 of the respective 
terminals. 
Thereafter, when the terminal interface 104 receives a call message from a 
terminal, it carries out such calling procedure as shown in FIG. 20. 
In more detail, when the terminal interface 104 receives the aforementioned 
call message (step 621), the microprocessor 601 judges whether or not the 
measuring frequency (ni) of the terminal band table 603 is equal to or 
larger than the statistical-processing threshold value (.DELTA.i) (step 
622). When the measuring frequency (ni) is equal to or larger than the 
statistical-processing threshold value (.DELTA.i), that is, when the 
microprocessor 601 judges that the statistical values (mean and variance 
values) obtained through the measurement are sufficiently reliable with 
respect to the population of the communication packet rate distribution of 
the terminal, the microprocessor 601 substitutes the mean value (Ei) and 
the variance value (Vi) for the request packet rate values of the call 
message and sends the call to the controller 101 through a call signal 
line 606 (step 623). 
When the measuring frequency (ni) is smaller than the 
statistical-processing threshold value (.DELTA.i), on the other hand, the 
microprocessor 601 substitutes the initial packet rate value (Bi) for the 
maximum packet rate value Ei of the associated terminal and also zero for 
the variance value Vi to apply the call to the controller 101 via the call 
signal line 606 (step 624). 
FIGS. 22 to 30 are reference diagrams for explaining the functional 
operation of the controller 101 when receiving the call through the 
aforementioned processing. Of these drawings, FIG. 22 shows a functional 
arrangement of the controller 101. 
In FIG. 22, the controller 101, when receiving the call via the call signal 
line 105 from the terminal interface 104 (refer to FIG. 18)(in case of a 
relay office, from the trunk line), selects one of outgoing trunk lines 
from a routing circuit 702 through an input-call message register 704 and 
sends the number value (=j) of the selected trunk line to a trunk-j 
registration call table (TRT(j)) 703. Previously registered in the trunk-j 
registration call table 703 are, as shown in FIG. 23, the mean value Ei 
and variance value Vi of the packet rates informed from the caller 
terminals already registered for the trunk line. And when the controller 
101 receives the aforementioned new call, a packet estimation circuit 
(PPL) 701 receives all call statistical values (Ei, Vi) of the 
corresponding trunk line from the trunk-j registration call table 703 and 
also statistical values (Ei', Vi') of the new call from the routing 
circuit 702. The functional arrangement of the packet estimation circuit 
701 for judging permission or non-permission of registration of the new 
call with respect to the trunk line based on these input statistical 
values is shown in FIG. 24. 
In the packet estimation circuit 701 of FIG. 24, circuits (PPL1 to PPL5) 
801 to 805 have respectively a microprocessor and a memory in which a 
program is stored. The processing of these circuits based on the program 
are shown by flowcharts in FIGS. 25 to 29 respectively. 
First, the mean/variance estimation circuit (PPL1) 801 in FIG. 24, when 
receiving all the call statistical values (Ei, Vi) already registered for 
the corresponding trunk line as well as the statistical values (Ei', Vi') 
of the received new call, starts such processing procedure as shown in 
FIG. 25. In this procedure, the mean/variance estimation circuit (PPL1) 
801 calculates a mean value (E), a variance value (V) and a maximum 
variance value max(Vi, Vi') with respect to the multiplex packet rate of 
the corresponding trunk line (step 811) and sends its calculated results 
to the estimation-logic judgment circuit (PPL2) 802 (step 812). The 
estimation-logic judgment circuit (PPL2) 802 in FIG. 24, when receiving 
the above results from the mean/variance estimation circuit (PPL1) 801, 
starts such processing procedure as shown in FIG. 26. 
In this procedure, the estimation-logic judgment circuit (PPL2) 802 
compares a V/max(Vi, Vi') calculated from the output of the mean/variance 
estimation circuit (PPL1) 801 with a previously-registered estimation 
threshold value 802a to judge whether or not the multiplexing number input 
to the trunk line can be processed as normal distribution (step 813). When 
determining that the V/max(Vi, Vi') is equal to or larger than the 
estimation threshold value 802a (that is, the number of terminals 
belonging to the corresponding trunk line is sufficiently large when 
compared with a reference number of terminals having the maximum variance 
values to thereby allow approximation to normal distribution), the 
estimation-logic judgment circuit 802 sends the multiplex mean value (E) 
and multiplex variance value (V) to the normal-distribution estimation 
circuit (PPL3) 803 (step 814); whereas, when determining that the 
V/max(Vi, Vi') is smaller than the estimation threshold value 802a, the 
estimation-logic judgment circuit 802 sends the values (E) and (V) to the 
Chebyshef estimation circuit (PPL4) 804 (step 815). 
When receiving an input from the estimation-logic judgment circuit (PPL2) 
802, the normal-distribution estimation circuit (PPL3) 803 in FIG. 24 
starts such a processing procedure as shown in FIG. 27. In this procedure, 
for performing the normal distribution estimation, the normal-distribution 
estimation circuit (PPL3) 803 previously registers therein a significance 
level (.alpha.) as a value 803a of the significance level. The 
normal-distribution estimation circuit (PPL3) 803 first finds a reference 
normal-distribution value (N 0.1) through the retrieval of a value of a 
reference normal-distribution table (N 0.1 table 803b) of FIG. 30 
corresponding to the significance level .alpha. value 803a. 
In the retrieval example of FIG. 30, when .alpha. is set at 0.01, the 
.alpha. approximation is carried out with 0.01 to 1.00-0.4949.times.2.0 in 
the N 0.1 table to thereby find N 0.1=2.57. 
Thereafter, the normal-distribution estimation circuit (PPL3) 803 
calculates an estimate (A) of the multiplex packet rate based on the 
normal distribution in accordance with the following equation with use of 
the found N 0.1 value as well as the multiplex mean value (E) and 
multiplex variance value (V) received from the estimation-logic judgment 
circuit (PPL2) 802 (step 816) and sends the calculated result to the 
input-call acceptance judgment circuit (PPL5) 805 (step 817). 
EQU A=E+N 0.1.times.sqrt (V) 
On the other hand, when the Chebyshef estimation circuit (PPL4) 804 in FIG. 
24 receives an input from the estimation-logic judgment circuit (PPL2) 
802, the circuit 804 starts such a processing procedure as shown in FIG. 
28. In this procedure, for performing estimating operation without being 
affected by the distribution of Chebyshef inequality, the Chebyshef 
estimation circuit (PPL4) 804 previously registers therein a significance 
level (.beta.) as a value 804a of the significance level (.beta.). The 
Chebyshef estimation circuit (PPL4) 804 calculates an estimate (A) of the 
multiplex packet rate in accordance with the following equation with use 
of the value 804a of the significance level (.beta.) (step 818) and sends 
its calculated result to the input-call acceptance judgment circuit (PPL5) 
805 (step 819). 
EQU A=E+[V/(1-.beta.)].sup.1/2. 
Further, when receiving an input from the normal-distribution estimation 
circuit (PPL3) 803 or the Chebyshef estimation circuit (PPL4) 804, the 
input-call acceptance judgment circuit (PPL5) 805 starts such a processing 
procedure as shown in FIG. 29. In this procedure, the input-call 
acceptance judgment circuit (PPL5) 805 compares the maximum packet rate 
value of the corresponding trunk previously registered in a trunk-j 
maximum packet rate value 805a with the estimate A received from the 
normal-distribution estimation circuit (PPL3) 803 or from the Chebyshef 
estimation circuit (PPL4) 804 (step 820). When the comparison result 
satisfies a condition A.ltoreq.(trunk-j maximum packet rate value), the 
input-call acceptance judgment circuit (PPL5) 805 outputs such an 
acceptance signal as shown in FIG. 22 to the trunk-j registration call 
table 703 (step 821) to register the new input call in the table 703 and 
to output the calling message to the next-stage relay exchange or the 
call-destination exchange. When the comparison result in the step 820 does 
not satisfy the condition A.ltoreq.(trunk-j maximum packet rate value), on 
the other hand, the input-call acceptance judgment circuit (PPL5) 805 
outputs such an acceptance reject signal as shown in FIG. 22 (step 822) 
and returns a `REL` message to the caller terminal of the new input call 
to cancel the call. 
Explanation will next be made as to another feature of the present 
embodiment, that is, the correction system when an error resulting from 
the above estimation exceeds an expected value, by referring to FIGS. 18, 
21, 22, 31 and 32. The packet exchange in the present embodiment is 
arranged so that packets transmitted on every trunk line basis are once 
accumulated in the memory of the exchange, which function may be carried 
out by the trunk interface 103 having such an arrangement as shown in FIG. 
31. 
In FIG. 31, more specifically, packets input to the trunk interface 103 via 
the data line 108 are once stored in that part of a memory 906 
corresponding to the corresponding trunk and when the corresponding trunk 
line becomes idle, the packets are output onto the corresponding trunk 
line. 
Such a type of packet exchange is arranged so that, when the exchange 
receives packets exceeding the capacity of the memory 906, the exceeded 
packets are discarded. 
To avoid this, in accordance with the present embodiment, a microprocessor 
901 is activated under control of a program 902 according to the number of 
such discarded packets counted by a discarded packet counter 905 in the 
trunk interface 103 (refer to FIG. 31), an estimation correction circuit 
706 (comprising a microprocessor and a program) in the controller 101 is 
activated under control of its program (refer to FIG. 22), the 
microprocessor 601 in the terminal interface 104 is activated under 
control of the program 602 (refer to FIG. 18), whereby the correcting 
operation is carried out following such a flowchart as shown in FIG. 32. 
In the correcting operation, the microprocessor 901 reads the number of 
discarded packets occurred per unit time from the discard packet counter 
905 at intervals of a constant time set by a timer provided in the memory 
906 (the old count value of the counter 905 is cleared at the time of 
reading the new discard packet number) (step 911). Then the microprocessor 
901 compares the read discarded-packet number per unit time with a preset 
error threshold value 904 (step 912). 
When the discarded-packet number per unit time is equal to or larger than 
the error threshold value 904 (or when the accumulated number of discarded 
packets accumulated during a continuous unit time is equal to or larger 
than the error threshold value 904), the microprocessor 901 issues a 
command to the estimation correction circuit 706 of the controller 101 in 
such a manner that the estimation correction circuit 706 reads 
communication terminals now registered for the corresponding trunk line j 
from the trunk-j registration call table 703 and sets the statistical- 
processing start threshold value of the terminal band table TBTI at the 
time of registering the trunk j at .DELTA.i.rarw..DELTA.i+ni with respect 
to all the read terminals and the contents of the TBTI table with respect 
to all the call terminals registered in the trunk-j registration call 
table TRT (j) are changed with .DELTA.i.rarw..DELTA.i+ni (steps 913 and 
914). 
The transfer of such signal is realized by sequentially transmitting the 
request signal to the associated packet exchange via the internal control 
bus 112 when the caller terminal belongs to the packet exchange having the 
operated estimation correction circuit 706 or via the control signal line 
of the data line bus 106 when the caller terminal belongs to another 
packet exchange and then via the internal control bus 112. 
The terminal, when receiving the request, updates the values of the 
terminal band table 603 in such a manner as to increase the 
statistical-processing start threshold values further by .DELTA.i (which 
may be another preset value) from the current packet rate sample number 
(ni) to demand the communication band at the maximum packet rate (step 
915). 
In this way, through the estimation correcting operation taking the 
discarded-packet number into consideration, the present embodiment can 
further improve its estimation reliability. 
As has been disclosed in the foregoing, in accordance with the present 
embodiment, the communication packet rate between terminals is measured, 
the measured sample is statistically processed to obtain mean and variance 
values, normal distribution is estimated from the obtained mean and 
variance values, and permission or non-permission of registration of the 
call for the specified trunk line is judged on the basis of the estimated 
value. As a result, the efficient use of the trunk transmission band 
suitable for the actual packet communication amount can be realized. 
Further, the statistical processing is started when the number of packet 
rate samples measured at a terminal becomes sufficiently large, prior to 
which the maximum packet rate is used as its communication band value. As 
a result, abnormal estimation resulting from a sufficient number of 
samples can be avoided. 
Furthermore, methods for estimating the multiplex packet rate of the trunk 
line for a terminal are selected in such a manner that when approximation 
is realized as the normal distribution, the approximate value based on the 
normal distribution can be used, while otherwise the calculated band value 
based on the generally-established Chebyshef inequality can be used. As a 
result, suitable estimation can be realized flexibly according to the size 
of the number of terminals registered for the trunk line. 
In addition, when an abnormal estimation is detected, the correcting 
operation of the estimate value is provided for setting the communication 
band value of the corresponding terminal at the maximum packet rate, thus 
contributing to additional improvement of the estimation reliability.