GB2169476A - Telephone system traffic analysis apparatus - Google Patents

Abstract

Apparatus for qualitative and quantitative analysis of traffic in a telephone system, comprises ATT modules for preparing line signals; FFT modules for converting such line signals to digital form and for their further processing in order to determine their instantaneous frequency spectrum; UEC (RFP) modules for real time analysis of spectra as processed by the FFT modules; UEC (CNP) modules for general control and exchange of data from and towards the outside world; and a PNS module for displaying analysis results. <IMAGE>

Description

SPECIFICATION Telephone system traffic analysis apparatus This invention relates to telephone system traffic analysis apparatus.

More particularly this invention relates to such apparatus which when inserted in a suitable data processing system, acts as the "front end" of the system, by directly deriving from the telephone subscriber lines all information necessary for qualita tive and quantitative traffic analysis.

Known telephone traffic analysis apparatus com mercially available, and particularly that manufac- tured byTEKNO INDUSTRIES INC. USA, by NORTH ERNTELECOM INC. USA, byCLEMESSYD.A.I. FRA., and by ELMI, Denmark, has a number of disadvantages.

1. In particularTEKNO INDUSTRIES INC., USA, manufactures the following apparatus for analysis of telephone traffic: PSO-HOOAPortable Service Observatorfortele phone traffic; CDR-HOOACall Disposition Recorder for PSO-HOOA.

MPS-HOOA Micro-processing System for CDR HOOA.

The first apparatus selects automatically or manual ly one out of 30 circuits under analysis, by showing "on-line" the number of the selected circuit, the subscriber number being called as well as the duration ofthecall.

The second apparatus is the true call analyzer (as selected by PSO), which performs the classification of the latter according to eleven categories (e.g. attempted call, completed call, busy, no answer, etc.). It can print locally ortransmitto MPS data of the various calls (subscriber called, time and duration of call) our a summary report concerning the number of analyzed calls, belonging to the specified categories.

The third apparatus is a message concentrator which serves upto five CDRs, and which records received data on cassettes orfloppydiscs.

Such apparatus has the disadvantage that it operates on only one line at a time, since the selection of one line for analysis excludes consideration ofthe other ones. Further, the apparatus provides insuffi- cient data for a real determination of the quality of the service. Finally, the apparatus is rather complex which limits to 150 the number of lines which can be controlled.

2. UTB-1 90A Universal Traffic Bufferfor Digital Switches.

The apparatus is used for electronic exchanges and records data coming from parallel gates provided in this type of system.

This apparatus depends totally upon the type of exchange to which it is connected, as it does not analyze the "live" traffic but it simply records the traffic reports generated by the exchange itself.

Information obtained is strongly dependent upon the state of "load" of the exchange, and therefore the apparatus is least usa ble at times when such information is most important.

NORTHERN TELECOM INC., USA supplies two types of analyzing apparatus namely: 1) MODEL 2776 Tru nk Access Unit 2) MODEL 2760 Universal Signalling Analyzer.

The first apparatus is an automatic selector of one out of 30 input lines.

The second apparatus is a monochannel, analog type, call analyzer, with the possibility of visualising the call parameters. In the whole, the performance of the Northern apparatus does not vary substantially from that of the TEKNO apparatus previously described, and therefore they suffer from the same disadvantages. Additionally, the Northern apparatus apparently cannot be connected to a processor, and thus cannot supply any statistical information.

CLEMESSY D.A.I. - FRANCE also manufacture two telephone traffic analyzers.

1) ATRAF64 This apparatus is an instrument of the "erlangmeter" class, and is used only to measurethe traffic intensity on trunk groups.

The measurement is of analog type, and involves measuring the resistance of as many resistive terminations as there are busy lines in the trunk group.

The apparatus can operate on 62 trunk groups each including no more than 100 lines, giving total of 6,200 measurement points, with resolution equal to 0.1 Erlang.The apparatus also providesforthe printing of traffic intensity reports for the various groups, at predetermined times.

ATFRAF apparatus therefore does not supply any information for a given line, but only for a whole group.

2) MOT32-32 This is a traffic analyzerwhich cannot operate on more than 32 subscriber lines, to be associated with 32 groups; it can be connected to a printer. The apparatus supplies for each group detailed service information derived from the state of two d.c. signals which some types of telephone exchange supplyforthe same purpose. Such apparatusgivesthereforeincomplete data, and requires the presence ofsignals available only in sometypes of exchange.

Finally, the known apparatus includes the ZTXK80101 TRAFFIC RECORDER, manufactured by ELMI (DENMARK).

This apparatus is a portable instrument of"erlang- meter" type, suitable for monitoring up to 60 inputs with the possibility of "single input" entry, whenever the exchange does not internally provide the termination resistances. The apparatus has, with reference to the problem under consideration, the same limitations as the apparatus produced by CLEMESSY, in particularthe MOT32-32 model.

According to this invention there is provided telephone systems traffic analysis apparatus, comprising modules (ATT) serving for the preparation of line signals; modules (FFT) forthe conversion of line signals into digital form and fortheir further processing in orderto determinetheirinstantaneousfre- quency spectrum; a module (UEC/RFP) for real time analysis of spectra processed by said FFT modules; a module (UECICNT) for general control and for data exchange to and from the outside world; and a module (PNS) for displaying a measured channel's condition.

This invention provides telephone system traffic analysis apparatus,forqualitative and quantitative analysis of traffic in a telephone system, hereafter identified by the acronym TETA (Telephone Traffic Analyzer), which is capable of supplying a quantity and quality of information which allows the implementation of systems having different levels of complexity.

In particularthefollowing can be carried out: a) Measurement of service qualityforthe intercontinental telephone system.

Such parameterwhich synthetically supplies an indication ofthe measure in which a subscriber obtains from the telephone system the performances forwhich the system has been conceived, may be evaluated according to standardized procedures (e.g.

CCITT, Recommendation E 420 and foll) with quite different methodologies.

As previously stressed, in the past thins measurement has been donethrough "manual" methods, exploiting data obtained from notes taken by operators, and by systematic traffic surveys performed by exchange technicians. Such systems have proved to be insufficient and unreliable. The recourse to automatic "ad hoc" instrumentation which measures the response oftelephone systems to artificially gener atedtestcalls has shown the undesirability of affectingthe phenomenon being tested, particularly during the busyhours,whenactuallythemeasure- ment is more interesting.

There is a need therefore for apparatus which allows the measurements to be performed on live traffic, without any alteration.

b) Check related to efficiency and utilization of each line, giving information useful for both operation and maintenance.

c) Quantitative and qualitative measurements of transit traffic for each traffic location.

d) Check ofsubscriber's behaviour.

Survey of tone waiting time, answertime, speech duration, as well as whole call's duration; control of dialling information transferto a display; control of redundancy or incompleteness of dialling.

This invention will now be described by way of example with reference to the drawings, in which: Figure lisa block diagram of a telephone system including apparatus according tothis invention; Figure 2 is a black diagram of apparatus according to this invention; Figure 3 is a block diagram of an ATT card module forming partofthe apparatus of Figure 2, such modules serving for incoming line signal preparation; Figure 4 is a block diagram of a FFT card module forming part of the apparatus of Figure 2, such modules serving forthe conversion of incoming line signals into digital form, as weli astheirfurther processing (Fast FourierTransformation), in order to determine their instantaneous frequency spectrum;; and Figure Sis a block diagram of an UEC card module; one such UEC card module carries out real time analysis offrequencyspectra processed by FFT modules, while another one serves the functions of general control and exchange of information with rh e outside world (CNT).

With reference to Figure 1, level 1 ofthesystem, therein shown as STEP 1, comprises a scanning unit (RSU)which, through an optionalswitching unit (RXU) is connected to the telephone lines, and which is able to supply data to a printer (TTY).

The number of lines which can be controlled at this level is 16 in the absence ofthe RXU, or 16 x 8 = 128 in the presence ofthe RXU. In any case the number of lines which can be contemporaneously checked is 16, since the selection of lines implemented by RXU is a semistatic operation which must be set up by an operator.

Level 2 (STEP 2) provides forthe connection to a processor (SPU, in Figure 1) of no morethan 16 RSU RXU groups, which brings the number of controlled lines upto 256 out of 2048.

The processorservesfor processing on a given data base in which the information obtained from the lines through the RSUs is stored, and also serves for implementing, upon an operator's request, a large variety of statistical surveys out of the stored data.

For instance the processor SPU may implement: - synthesis by company center and traffictype - synthesis by node and traffic type - synthesis by direction; type of traffic: route including all traffic distributions as functions of classifying codes; of destination irregularities, with computation of call and conversation times for normal classifications - synthesis by circuit,type oftraffic and direction, including the distribution of traffic by circuit and irregularity - analysis by company center, type oftraffic, route and destination - analysis by node, type of traffic, route and destination - analysis by direction, type oftraffic, route and destination, including distribution by DCC/DPC, as well as the classifying codes, with computation of call and conversion times for normal classifications - analysis by destination,type of traffic and route, including all traffic distributions by classifying codes, by origin, with computation of call and conversation times - standard CCITTtabulates (mod. E422/rand/or E423/r).

Level 3 (STEP 3) informed by connecting uptofour level 2 systems to a central processor(CPS in Figure 1), which has access to the stores ofthe peripheral systems, and which can implement the same processing as SPUs, but on a much more extended data base. Itis consequently possible to concentrate the control and supervision of 1024 (256 x 4) subscribers' circuits out of a total number of 8192 circuits which can be checked.

The analysis apparatus shown in Figure 2, includes the following modules: - two ATT modules serving forthe preparation of line signals; - four FFT modules, serving forthe conversion of line signals into digital form, and fortheirfurther processing (Fast FourierTransformation) in order to determine their instantaneous frequency spectrum; - two UEC modules, one of them (RFP in the drawing) for the real time analysis of spectra processed by FFTs, the other one (CNT) serving for general control and for data exchange from and to the outside world; - PNS module for displaying a measured channel's condition.

The functional nucleus of the apparatus comprises the FFT modules; their structure and the way in which they are connectedto line signals, arethe keystone of the whole apparatus. The modules, even if they have identical circuits, are functionally specialized, through suitable interconnections and control, to implement different functions, namely exploration (EXPL) and conversion (CONV).

Both FFT modules specialized as explorers (EXPL 1 and 2 in Fig. 2) are connected to 8 out ofthe 16 input lines, and they perform a circuiarscanning within the same, in orderto detectthe engaged condition. The time for a scanning of 8 lines is shorter than the minimum duration of the condition whereby it is assured that the condition is always detected.

The other two Fit card modules, specialized as converters (CONV 1 and 2 in Fig.2), are connected to all the input lines; upon the detection of an engaged condition by an explorer on a given line, the firstfree converter is assigned to that line forfurtherfrequency analysis ofthe call's phases, up to answering bythe called subscriber. There is therefore the possiblitythat when more than two calls take place in a time interval shorterthan that need forthe selection, the calls, being temporally the last ones, may not be analyzed as all converters are engaged.

In view of this, in orderto assure that the output information from the apparatus is sufficient, calls are split into two basic classes: "attended to" calls which have undergone a complete analysis in all their phases, and "unattended to" calls for which no converter has taken action.

This event, which underthe conditons of regular traffic takes place in only a limited percentage of cases, limits only slightly the information related to "unattended to" calls, as can be deduced from both of the following lists which show the contents ofthe information forwarded from the apparatus to the central processor forthe two types of call.

ATTENDEDTO UNATTENDEDTO Line number * * Hour, Minutes * * Engagement number Numberattendedto calls * * Route * * Called number * Classification code Preselection time + time Waiting time * * Conversation duration Call duration * * //Called hangups * * fiOperator's intervention * * Irregularities * * - Line number. Conventional line number withinthetrunkgroupconnected to the unit.

- Hour, minutes. To be set by the operator or by higher level processors and automatically brought upto date by the apparatus.

- Engagement number. Progressive number, within he current hour, ofthe engagement concerning each call.

- Number of unattended to calls. Progressive number, within the hour, of unattended to calls.

- Route. Incoming/outgoing.

- Called number. Number called subscriber.

- Classification code: Answer Free Busy Busy Busyflash Busy flash Deadline - Anticipated clearing PTS (Proceed to Send) absence No answer conversation - Test - Unclassified - Preselection time. Time elapsing between line engagement and the start of the dialling phase - Waiting time. Time elapsing betweenthe end of the dialling phase and the free/busytone - Duration of conversation - Durationofcall - Numberofhangups by called subscriber.

- Numberofoperator's interventions.

- Irregularities: Some 39 types of irregular situations are listed, all related to line criteria and to register signalling, caused by out of limits frequencies and levels.

The individual modules ofthe apparatus will now be described with reference to Figures 3 to 5 of the drawings.

1) ATTmodule (Figure 3) The signals incoming from subscriber lines are sent, after d.c. uncoupling, obtained through a series capacitance, to an inputtransformerwith 1:1 coil ratio, which galvanically separates the line from the system.

The signal outgoing from the transformer's secondary, being unbalanced, is subjected to amplitude limitation, in orderto avoid any damage ofthe downstream elements, in case of transient phenomena on outgoing lines.

The limited signal is sent to one out of two inputs of an analog multiplexer, driven-through an optically uncoupled signal - by the control microprocessor (CNT). The other input of the multiplexer is a test signal which can, on its turn, be selected by CNT between an external signal and another one internally generated by a quartz oscillator and supplied via a frequency divider (upto 2100 Hz) and an active low pass filter.

The circuit above described is repeated 1 6times within the module, with the exception ofthetest signal generating part, which is provided only once.

2) FFTmodule (Figure 4) This is the module in which there are embodied in a greater measurethose combinations of innovative elements which permit the implementation offrequencies' as well as of line signalling levels' measurement, using a technique which, when compared to the conventional ones, offers a series of decisive advantages from the point of view of functional performances, running stability, compactness and economy.

Such advantages are obtained by making recourse to a totally digital processing of line signals, in the following way: - the required functions (filtering, individuation offrequencies, and measurements ofsignal amplitude) are performed with non-analog circuitry and therefore unaffected from deviations as well as from inevitabie periodicsettings,with a consequentstability of running and economy of operation; - the processing resources, designed in orderto obtain a very high operational speed, are shared by all lines using a time division technique, instead of by using a plurality of individual circuits as is unavoidablewheneverconventional analog systems are used.

This provides a physical compactness and a consequent reduction of production costs, which otherwise are difficultto obtain; - the exchange of data obtained through the analysis ofthe line signals bythe upper level processors is enormously simplified, inasmuch asthe latter ones already exist within the apparatus in the most convenient form fortheir outside transmission; - thetotaltechnological uniformityinherentto theapparatus so designed, requirestheuseofonly three differenttypes of card module, so obtaining a strong advantage asfar as simplicity and maintenance economy, and logistic support in general, are concerned.

With reference to Figure 4, input signals, coming from ATTmodules described above, are selected, one at a time, by two analog multiplexers, and then sent through a low pass filter having an "anti-aliasing" function. The phenomenon of"aliasing", or of spectrum multiplication, takes place when as in the case oftheapparatus underconsideration-one might need to derive the spectral characteristics of a signal through its sampling at an "fc" frequency since the contributions offrequencies higherthan fc/2, possibly included inthesignal, are erroneously interpreted as belonging to frequencies lowerthan the latterone.

Such a case of possible error is eliminated by strongly attenuating all the frequencies higherthan halfthatof the sampling frequency.

Thefilteredsignal isthensampledatafixed frequency (6.402 KHz).Through an analog circuitfor sampling and holding a signal, "sample and hold",the analog value ofthe signal at the instant ofsampling is kept constantfor all the time required to convertsuch a value into diqital form. Such conversion is effected by an A-D converter, whose 12 bit binary output represents a number proportional to the value of the signal at the moment ofsampling.

Values which have been progressively converted, are held in a FIFO (First-ln-First-Out) buffer device, before being sent to the input bus ofthe microprocessor (16 bit CPU matrix in Fig. 4). Such expedient eliminates the risk of data loss in the case in which L,le processing cycle, which does not have a constant duration, might accidentally exceed the time lapsing between the conversion of one signal value and the following one.

The computing structure ofthe module is made up, beyond the already described 16 bit- CPU matrix, by the following elements, the functions of which are briefly listed hereafter MICROPROGRAM MEMORY This informed by 5 1 Kx8 PROM memories, which contain the microprogram's instructions.

They are capable of implementing atwin selectionable matrix (through a bit test), each one having dimensions equal to 32 lines x 16 columns, giving 512 elements (i.e.: 512 possible microprogram's instructions).

Each microinstruction provides the following fields: a) JUMP FIELD (7 bit) b) FUNCTION FIELD + CONDITIONAL CLOCK (7 + 1 bit) c) FLAG-CONTROL FIELD (4 bit) d) DEVICE SELECT FIELD (4 bit) e) MASKFIELD(K-BUS) (16 bit) It should be noted that a)-d) fields are of a fixed length forthe structure using MCU & CPE modules, while the last one depends upon the HW configuration in which the bit slice is to operate.

MICROPROGRAM CONTROL UNIT The microprogram control unit (MCU), implements two basic control functions: - Sequencerforfetching operations of microprogram's instructions from the corresponding memory.

Forthis purpose MCU includes internally a register and associated logicfor processing and selection of further microprogram's instructions for the memory.

- Control, both input and output, offlip-flops related to carry and zero flags, through which it can: a) interact with the row of CPE, in arithmetical computations (carry's propogation).

b) perform prepared hopswhilethemicropro- gram is run.

PIPE-LINE REGISTER The "Pipe-line bitslice" structure has been implemented by using a series of D type (edge triggered) registers, placed between the microprogram memory and the devices controlled bythe latter.

Through this expedient one can delay by one microinstruction the hop prepared forthe execution of an arithmetical instruction inasmuch astheoperation- al phase ofthe current instruction is superimposed to the "fetching" phase of the following instruction. This is essentially done in orderto get stabilized delays of carry propogation in operations of a mathematical type. Such delays are as big as deep the row of CPEs (number of "slices").

Forthis purpose the "carry" output of a CPE is connected to the carry input ofthefollowing CPE.

1 Kx 16 RAM (random access memory) provides recording of data relevant to processings performed by the microprocessor.

1 Kx8 ROM (random access memory) stores per manently the instructions related to the processing program.

PULSE GENERATOR Generates the clock pulses which generates the temporal evolution of processing operations.

Further,the Input-Output section of the module is made up ofthefollowing elements: SYSTEM GATE The system gate allows two way exchange of Information,through multibus, between RFPand FFT modules.

Through such gate the RFP module sends to the FFT modules various commands such as: start analysis, stop analysis, alternate exploration, fixed exploration, etc.

Also through the system gate, FFT modules send the "hand-shake" answers to received commands, so indicating acceptance of the RFP module.

1 28Wx 16 bit FIFO (First-ln-First-Out) This is the data gateforthe FFT module.

This data gate is directly connected to the mulibus, and is a one way gate which divides the information stream from the FFT module to the RFP module.

It isto be noted that the content which, as it is being filled by the FFT module or is unloaded from the RFP module, concerns the analysis results, in a time equal toabout20msec (time-slotinterval).

ADDRESS SELECTOR The address selector serves to associate both the System Gate and the Data Gate with suitable 1/0 addresses on the multibus, whereby it is possible to identify with an address mark, each ofthe FFT modules included in the structure.

Thetype of processing which is performed by the complex of elements described is known as Fast FourierTransformation (FFT), which is hereafter described.

It is well known that an x(t) signal can be represented undertheform:

where S(f) is the function which, for each "f" frequency, shows the contribution of such frequency within the signal's spectral composition.

S(f) "spectrum" of x(t) signal is given by:

which is known as the mathematical expression of "FourierTransformation" for x(t) signal.

In case of signals sampled within time x(Kt), (1) becomes:

or, in a matrical form, letW = exp (-j2rr/N) [S(n)] = [WnK] [x(t)] (3) which are known as the "discreet FourierTransformations" for signal x(t).

The computation of (3) for N points, which gives N values of S(n) spectrum, requires the execution of N2 complex multiplications as well as of N2 complex additions (W is a complex number).

Iffor N one selects a value equal to a powerof 2 (N = =2h), it is possible to prove, by exploiting the relationship: WnK = WnK modN that one can factorize the [WnK] matrix into the product of "h" matrixes, such that for each of them one should perform only N/2 complex multiplications and N complex additions. This algorithm, due to J.W. Cooley and J.W. Tuckey, allows therefore for the reduction of the number of elementary operations' from N2 to (N/2) log2 N.

Finally, by taking into consideration some operations which are redundant, it is possible to develop an algorithm which further reduces such number to N/4 log2 (N/2).

UECmodule (Figure 5) This module's structure, which includes a complete processing unit based on a Z-8002 microprocessor, is of a conventional type and it is made up by: 32 Kbyte (RAM) volatile memory 16 Kbyte (ROM) read only memory 38 bit two way parallel Input/Output gates 2 RS-232 type serial Input/Output gates Interface towards standard, LINTEL MULTIBUS type, communication bus, for exchange with other units (even ofthe same type) of 16 bit data, addresses up to 16 bit and u p to 8 prog ram interruption lines.

The difference between the modules which is Figure 2 are shown as RFP and CNT, lies in the program that they perform. This is shown hereafter, through the functions implemented by both modules.

FUNCTIONS OFRFP MODULE The RFP module, from the point of view of its multibus structure, is the master module, and it is therefore shaped in order to implement such function.

It guarantees the processing of data coming from declaration, acquisition and preprocessing modules (for instance: ATT & FFT), by suitably packeting them, and offering the results of such processing and analysis to CNT module.

The program of the RFP module operates: a) data stream from FFT module (INPUT stream), on which it performs: 1) Recognition of present frequencies (RFP), among a set of processablefrequencies, and to be associated to line and/or register criteria.

2) Processing ofoffsetlevelforthefrequencies under review.

3) Recognition of pertaining line and side offlowing information.

b) stream of information packets towards the CNT module (output stream), which receives a suitable format according to procedure as per par. c), and it is latersent asynchronously to CNTmodule.

c) Decoding ofcommands coming from CNT module, which can be: 1) request for configuration 2) command to modules (converter/explorer) 3) testofinternal orexternaltype 4) system reset d) Implementation and forwarding of commands to FFT modules, with processing of the obtained results and forward them to the CNT module. The answers which RFP program will abletoforward, in a suitable format, are as follows: 1) configuration 2) test data 3) spectral data (see par. a) and b)) 4) anomalies It is to be noted that HW modes, bywhich the operation is implemented, are essentially based upon an "INTERRUPT" logicto and from FFT and CNT modules.

FUNCTIONS OF CNTMODULE The CNT module from the HW point of view appears to be a "slave" device for the multibus structure, even if actually-from a logical point ofview-this same is the control module ofthe scanner (CNT acronym means, as a matter of fact, "Control").

The program operates: a) Stream of "input data", coming from RFP module.

Based on such data, the program sends some specific decision routines (logic routines) which operate the data processing to be associated to each operation phase within a telephone call (engagement, dialling phase, answer, etc.).

b) Forwarding ofcommandsto RFP module.

c) Man to Machinetalk,through the serial gate towardsTTY, by which theoperatorcan, locally: 1) Changethe distinctive parameters within the analysis of a call, 2) Run diagnostic routines.

3) Changethedistinctive parameters on the out- put stream towards TTY.

d) Operation of output stream towards TTY, both for "attended to" calls (analysis by explorer and converter) and for "unattended to" calls (analysis by explorer only), diagnostic results.

e) Operation of 1/0 stream towards statistical processing units (SPU),through which the functions underb) and c) are duplicated; howeverthe latter keep the central processorastheirinterface.

f) Selection of 1 out of 8 possible trunk groups each having 16telephonelines.

Claims (10)

1. Telephone system traffic analysis apparatus, comprising modules (ATT) serving forthe preparation of linesignals; modules (FFT) forthe conversion of line signals into digital form and fortheirfurther processing in orderto determine their instantaneous frequency spectrum; a module (UEC/RFP) for real time analysis of spectra processed by said FF1 modules; a module (UEC/CNT) for general control and for data exchange to and from the outside world; and a module (PNS) for displaying analysis results.

2. Apparatus as claimed in Claim 1, in which there are two ATT modules, four FFT modules, one UEC (RFP) module, one UEC (CNT) module, and one PNS module.

3. Apparatus as claimed in Claim 2, in which two FFT modules are each connected to eight out of sixteen input lines and serve to provide circular scanning thereof in ordertoascertain engagement, while the othertwo FFT modules are connected to all of the input lines.

4. Apparatus as claimed in any one of Claims 1 to 3, in which each ATT module comprises a plurality of circuits each including an inputtransformerto which the signals from subscriber lines are supplied and which serves to galvanically separate the line from the apparatus; an amplitude limiterfor avoiding any damage to downstream elements; an analog multiplexer controlled by a microprocessor (CNT), and to a second input of which there is supplied a test signal selected by the control microprocessor(CNT) between an external signal and an internally generated signal.

5. Apparatus as claimed in any one of Claims 1 to 4, in which each FFT module comprises two analog muitiplexers; a filter having an "anti-aliasing" function; an analog circuitforsampling and holding the signal; an A-D converter serving to keep the signal at a constant level during the time required for its conversion into digital form; a FIFO (First-ln-First-Out) buffer holding device; and a microprocessor.

6. Apparatus as claimed in Claim 5, in which said microprocessor comprises 5 1 Kx8 PROM memories containing the instructions of the microprogram; a microprogram control unit; a pipe-line registerfor one microinstruction's delay; a 1 Kx16 random access memory; 1 Kx8 read only memory; and a clock generatorwhich determines the temporal evolution of processing operations.

7. Apparatus as claimed in Claim 5 or Claim 6,in which each FFT module includes an input-output section comprising a system fortwo way exchange of informationthrough a multibus, between the UEC (RFP) module and the FFT module; a Data-Gate directly connected to the multibus and serving as a unidirectional gate, in which the information stream is directed from the FFT moduleto the UEC (RFP) module; and an Address Selector which allocates to the System Gate andthe Data Gate l/Oaddressesfor use on the multibus, in orderto identify with an address marking each FFT module in the apparatus.

8. Apparatus as claimed in any one of Claims 1 to 7, in which the UEC (RFP) and UEC (CNT) modules are each constituted buy a complete processing unit, including a volatile RAM (32 Kbyte) memory; a ROM (16 Kbyte) memory; three 8 bit two way, parallel, input/output gates, and two serial input/output (RS232) gates, with an interface to a communication bus forthe exchange with other elements of 16 bit data, addresses upto 16 bits and upto eight lines of program interruption.

9. Apparatus as claimed in any preceding claim, in which each module is a card module.

10. Telephone system traffic analysis apparatus, substantially as hereinbefore described with referenceto Figure 2, or Figures 2,3,4 and 5 ofthe drawings.