AU622424B2 - Statistical measurement equipment and telecommunication system using same - Google Patents

Description

?a OPI DATE 28/05/90 APPLN- ID 26223 88 AOJP T 5 79 PCT NUMBER iCT/EP88/01037

PCT

INTERNATIONAL APPLICATI N D USt D UkD HE TENT COOPERATION TREATY (PCT) (51) International Patent Classification 4 (il) International Publication Number: WO 90/05416 H04J 3/16, H04L 11/20 Al (43) International Publication Date: 17 May 1990 (17.05.90) (21) International Application Number: PCT/EP88/01037 (81) Designated States: AT (European patent), AU, BB, BE (European patent), BG, BJ (OAPI patent), BR, CF (OA- (22) International Filing Date: 10 November 1988 (10.11.88) PI patent), CG (OAPI patent), CH (European patent), CM (OAPI patent), DE (European patent), DK, FI, FR (European patent), GA (OAPI patent), GB (European (71) Applicant (for BE only): BELL TELEPHONE MANUFAC- patent), HU, IT (European patent), JP, KP, KR, LK, LU TURING COMPANY, NAAMLCZE VENNOOTS- (European patent), MC, MG, ML (OAPI patent), MR CHAP [BE/BE]; Francis Wellesplein 1, B-2018 Antwerp (OAPI patent), MW, NL (European patent), NO, RO, SD, SE (European patent), SN (OAPI patent), SU, TD (OAPI patent), TG (OAPI patent), US.

(71) Applicant (for all designated Slates except BE US): ALCAT- EL N.V. [NL/NL]; Strawinskylaan 341, NL-1077 XX Amsterdam Published With international search report.

(72) Inventors; and Inventors/Applicants (for US only) JOOS, Peter, Frans, Adelaide [BE/BE]; Tulpenlaan 30, B-2550 Kontich (BE).

VERBIEST, Willem, Jules, Antoine [BE/BE]; Smisstraat 27, B-2730 Zwijndrecht (BE).

(74)Agents: VERMEERSCH, Robert et al.; Patent Department, Bell Telephone Manufacturing Company, N.V., Francis Wellesplein I, B-2018 Antwerp (BE).

(54) Title: STATISTICAL MEASUREMENT EQUIPMENT AND TELECOMMUNICATION SYSTEM USING SAME d, i 'i

B

i; i

B

IFI~

(57) Abstract The measurement equipment (SMC) is used in a telecommunication switching system to check if the cell rate of each of a plurality of individual cell streams multiplexed in a same link remains within the limits on the basis of which its multiplexing was allowed. To this end the equipment checks at the end of each measurement interval (MTI) and for a plurality of cell rates if the expected probabilities to exceed these cell rates are exceeded or not. In the positive the cell rate is limited by dropping cells. Thus an expected complementary (with respect to 1) cumulative probability distribution function of the cell rate is approximated by a staircase-shaped function.

hi r I l '1i i; WO 90/05416 PCT/EP88/01037' S 14 cournter CR3 niay be used to imonitor the probsbilities in the S' WO 90/05416 pCT/EP88/01037 1 STATISTICAL MEASUREMENT EQUIPMENT AND TELECOMMUNICATION SYSTEM USING SAME The present invention relates to a statistical measurement equipment to determine the value of a statistical parameter of a variable.

Such a statistical measurement equipment is already known from the Belgian patent application No 08701481 and the international patent application No PCT/EP88/00594. It forms part of a telecommunication switching system operating according to the Asynchronous Transfer Mode (ATM), i.e. wherein data are transmitted under the form of cells or packets of its and with a variable cell rate. An individual cell stream is allowed to be multiplexed on a same telecommunication link together with a plurality of other individual cell streams already multiplexed thereon, if an allocation formula is satisfied. This formula is i based or the expected values of the mean and variance of the probability distribution function of the cell rate of the individual cell streami on the expected values of the mean ard variance of the probability distribution function of the cell rate of each of the above mentioned other individual cell streams already multiplexed on the linky as well as on the maximum allowable bandwidth on this link.

This allocation formula is based on the assumption that a miultiplex of a relatively high number of uncorrelated probability distribution functions leads to the normal probability distribution function, as follows from the Central Limit Theorem. However, because the mean and i WO 90/05416 PCT/EP8Q/01037variance do not sufficiently defin e an arbitrary probability distribution function of the cell rate of a cell stream and if the number of cell streams of a multiplex is relatively low, e.g. 10, the resultant probability distribution function may be far from a normal one. As a consequence the use of the above allocation formula may give rise to an overload of the communication linsk.

As also described in the above literature the known statistical measurement equipment is able to measure the values of the mean and variance of the cell rate of each individual cell stream of a multiplex. The purpose of this measurement is to check if the source of this individual cell stream operates within the limits on the basis of which its multiplexing on the link was allowed. To this end the measurement equipment more particularly determines the value of the mean and variance of the cell rate of each individual cell stream at the receipt of each cell of this individual cell stream and compares the thus measured values with the above mentioned respective expected valuesthereof. Depending on the result of this comparison the received cell is then either allowed for further processing or discarded, But because the probability distribution function of the cell rate of the multiplex is not a normal one it may happen that the equipment erroneously allows a cell to be processed further.

i From the above it follows that errors may occur because the probability distribution function of the cell rate of each cell stream is not always sufficiently defined by its mean and variance. More particularlvy it has been found that errors are especially due to the fact that the tail of the probability distribution function of the cell rate is not sufficiently defined by these two parameters.

Ari object of the present invention is to provide a statistical measurement equipment of the above type, but l Si__ 'WO 90/05416 PCT/EP88/01037 3 which allows the probability distribution f.unction of the variable to be defined in a more accurate way than by the above known mean and variance parameters.

According to th invention this object is achieved due to the fact that the present statistical measurement equipment includes means for measuring the value of said variable at least at the end of each measurement interval and means for then stepping at least one counter by a step which is function of the value thus measured, the steps being so determined that after a plurality of time intervals said counter is in a position indicative of the deviations from one or more expected values, of the probabilities to exceed corresponding predetermined values of said variable.

Another characteristic feature of the present statistical measurement equipment is that said predetermined values of said variable separate intervals to which distinct ones of said counter steps are assigned, that said measurement means measure said variable by determining the interval to which it belongs and that said counter position is indicative of the deviation, from expected values, of the probabilities to exceed said predetermined values of said variable.

Still another characteristic feature of the present statistical measurement equipment is that said counter is stepped in the one or other direction depending on the measured value of said variable belonging to an interval at the one or other side of a selected one of said predetermined values, of said variable, Yet another characteristic feature of the present statistical measu.rement equipment is that it further includes means associated to said counter and able to detect when said cou..inter reaches a position indicative of a maximnm allowable deviation and means coupled to said detecting means and able to reduce said deviation and

I

i WO 90/05416 PCT/EP88/01037 therefore said probabilities by chan:in the value of said variable when said detecting: nearis have detected said max imum allow able deviation.

In this way the equipment limits a number of probabilitis to exceed a correspondini, number of predetermined values of the variable and thus suitably monitoring this variable.

Another characteristic feature of the present statistical measurement equipment is that it includes a plurality of said counters able to perform distinct sets of steps assigned to distinct sets of intervals, and that the intervals of all said sets are separated by successive predetermined values of said variable.

Yet another characteristic feature of the present equipment is that it ir..ludes a plurality of detecting means each associated to a respective one of said counters for detecting when this counter reaches a position indicative of a maximum allowable deviation and means coupled to said detecting means for reducing said deviation by changing said variable when at least one of said detecting means has detected a maximum allowable deviation and when the variable then has a value exceeding the selected predetermined value.

i: In this way the equipment limits the probabilities not to exceed predetermined values of the variable according to a staircase-shaped function and thus realises an approximation of an expected complementary (with respect to 1) cumulative probability distribution function of the v variable i.

The present invention also relates to a telecommunication switchinr system with a pluralitv of user stations coupled to a switching network through a statistical measurement equipment of the type described above, the variable being the cell rate of a cell stream generated by at least one of said user stations, k 4%

I;

P

SWO 90/05416 PCT/EP88/01037 The above mentioned and other objects and features of the invention will become more apparent and the invention itself will be best understood by referring to the following description of an embodiment taken in conjjunction with the accompanying drawings wherein Fig. 1 is a schematic diagram of a statistical measurement e.qu.ipment SME and of part of a telecommunication switching system in which it is included, both according to the inventiont Figs. 2 and 3 together represent in detail a statistical measurement circuit SMC forming part of the statistical measurement equipment SME of Fig, 1; Fig. 4 represents a comlementarv cumulative Gaussian probability distribution function of the variable cell rate and other parameters used to illustrate the operation of the equipment of Fig. 1; Figs. 5 shows a probability distribution function of the variable cell rate also used to illustrate this operation? Fig. 6 shows part of the memory MEM of Fig. 1 in more detail.

Referring to Fig. 1 the ATM (Asynchronous Transfer Mode) date packet or data cell telecommunication system shown therein includes a digital switching network DSN which is for instance of the type disclosed in the Belgian patent No 905 982. This digital switching network DSN has a plurality of inputs II to IN and outputs 01 to ON which are coupled to user stations (not shown) via input and output multiplex links and statistical measurement 0S equipments For instancer a user station is connected to the input Il of DSN via an input multiplex; link ML arid a statistical measurement equipment SME having an input I and an output 11i The statistical measurement equipment SME comprises a receive port RX and a transmit port TX which are WO 90/05416 PCT/EP88/01037' 6 connected in cascade between the input I and the output I1.

The receive port RX includes a receive buffer RBUF, a processor F'R a memory MEM, a statistical measurement circuit SMC and a clock extraction circuit CEC, whilst the transmit port TX includes a transmit buffer TE:UF. The receive ard transmit buffers RBUF and TBUF are connected in cascade between the input I and output 11, The processor FR has access to these buffers as well as to the statistical measurement circuit SMC and the memory MEM via connections which although represented by a single wire are in fact constituted by a plurality of these. The clock extraction circuit CEC is connected to the input I and has a bit clock, output BCL and a cell clock, output CL which are both connected to the measurement circuit SMC.

This circuit SMC which is shown in detail in Figs. 2 and 3, includes a control circuit CC, a cell counter CR to count all the cells on the above link ML, a cell counter CCR to count the cells of each of the individual cell streams of the multiplex, a measurement interval counter MIC, a cell rate interval counter CRIr a measurement interval selection register MISr decoder circuits DEC1 and DEC2, registers REGO/5, credit counters CRO/3, increment registers IRO/14, intermediate storage circuits ISO/4, adder circuits ADO/3, comparator circuits C00/5, a D-flipflop DFF a divider circuit DIV, gating circuits GCO/17, AND-gates GO/7.

The cell clock output CL and the bit clock output BCL of the clock extraction circuit CEC are connected to the control circuit CC having outputs T1 to Til which control various circuits of the equipment, as indicated in a schematic way. This control will become clear from the operation of the eLquipment. The cell clock output CL is also connected to the input of the cell counter CR through the divider circuit DIV which is able to divide by 1024.

The cell counter CR comprises 12 stages SO/11 whose outputs ,i NVO090/05416 PCI'/EP88/01037 sO/li are subdivided in four ,qroups sOl/2, s3/5y s6/8 arid ~9/i1 the three outputs of each group bein-:i connected to respective data inputs of' the 17UltLiplP>,erS MUX 1/3. Each of these multi.plexers MUX1/3 has two selection inputs sa and sb provided by the measuremrent interval selection register MIS. The outputs of the multiplexers MUXI/3 are connected to first inputs of' the comparator COA whose second inputs are connected to the outpu~t of the measurement interval counter MIC. The output MTI of' this comparator C04 is connected via the gate G7 to the increment input of the counter MICY to the reset input R of' the cell rate interval courter CRI, to the set inputs of the cell courter CCR, and to inputs of the gates GO to G3.

The outputs of the cell rate interval counter CR1 are corrected to the decoder circuits DEC1 arid DEC2 as well as to the gatirng circuit GCiS.

The decoder circuit DECI is able to translate the q-bit cell rate interval code CR1 provided at the output of CR1 into a 4-out-of-15 increment code I1/1A according to the followirg table wherein CR1 is represented in decimal f or m.

PCT/EP88/01037 WO 90/05416 a Table 1 I/ICRI 0 1 2 3 4 5 6 17 8 9 10 11 0 1 0 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 2 0 0 1 0 0 0 0 0 0 0 0 0 3 0 0 0 1 0 0 0 0 0 0 0 0 4 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 6 1 1 1 1 1 0 0 0 0 0 0 0 7 0 0 0 0 0 1 0 0 0 0 0 0 8 0 0 0 0 0 0 1 1 1 1 1 1 1 9 1 1 1 1 1 1 1 0O 0OO 0 0 0 0 0 0 0 0 0 1 0 0 0 0 11 0 0 0 0 0 0 0 0 1 1 1 1 12 1 1 1 1 1 1 1 1 1 0 0 0 13 0 0 0 0 0 0 0 0 0 1 0 0 01 0 0 0 0 0 10 10 10 1 1 The bits IO/IA of the inicremnrt code thus provided by the decoder DECI control the respective gating~ circuiits GCC/14 (Ficg.3) in~terconnrecting the inicremneit reg~isters IR0/149 storing'~ the respective inicremnet values IINO/14Y to a -first input the adder circuits AD0/3. More pzarticularly IR6/8P IR9/11 arid IPR12/14. are cortnectad to the first inputs of the adder circuits AD0, ADI, (AD2 arid AD3 via. the gatiri circuits GCO/5Y GC6/8, GC9/11 arid uC12/14 arid the initermiediate storag.e circuits ISCO/3 respectively. These adder circuits AD0/3 further have art enable input controlled by the outputs of the gates G0/3 respectively.

The second inputs of these adder circuits AD0/3 are WO 90/05416 PCT/EP88/01037 connected to the outputs of respective credit counters CRO/3 having ar input connected to an output of the associated adder circuit ADO/3. Each of the credit counters CRO/3 has a further output which is connected to the first input of a respective one of the comparators C00/3 whose second inputs are connected to the outputs of the registers REGO/3 respectively. Each of these registers stores all 1's.

The comparators COO/3 have outputs ALO/3 which are connected, together with other input signals which are continuously on 0 and 1 respectively, to the data inputs of the multiplexer MUX4 whose selection inputs are connected to the outputs of the decoder circuit DEC2. The latter is able to translate the 4-bit cell rate interval code CRI provided at the output of CRI into a 6-bit selection code which selects one of said inputs 0, ALO/3 and-1 according to the following table, wherein CRI is represented in decimal form Table 2 SC/CRI 0 1 2 3 4 5 6 7 8 9 10 11 0 1 1 1 0 0 0 0 0 0 0 0 0 ALO 0 0 0 1 1 0 0 0 0 0 0 0 AL1 0 0 0 0 0 1 1 0 0 0 0 0 AL2 0 0 0 0 0 0 0 1 1 0 0 0 AL3 0 0 0 0 0 0 0 0 0 1 1 0 S 0 0 0 0 0 0 0 0 0 0 0 1 The multiplexer MUX4 has an output AL which is connected through gate G4 to the clock input CL of the D-flipflop DFF whose data input D is contineously on 1 and whose reset input R is controlled by the timing pulse TI, The multiplexer MUX4 also has an output ALE providing an

L,

W90/05416 CT/EP88/0103 7 WO 90/05416 output signal which is the complement of that generated on AL rnd which controls the gate G5 connectin, the output of the comparator C05 to the increment input of CRI as well as to the reset input of CCR. The flipflop DFF has a status output ST as well as a complementary status output STE which is connected to the increment input of the cell counter CCR through the gate G6.

The above mentioned gating circuit GC15 is able to detect the presence of the code 0000 at the output of CRI and has an output ID which controls both the gating circuits GC16 and GC17 interconnecting the respective registers REG4 and REG5 to a first input of the comparator via the intermediate storage circuit ISC4. The second input of this comparator C05 is connected to the output of the cell counter CCR.

Because the above mentioned increment' registers IRO/14 store the increment values INO/14 it follows friom Fig. 3 and from Table 1 that CRO is able to be incremented by one of six increment/decrement values INO/5 under the control of 10/5. INO, INIr IN2, IN3, IN4 and IN5 are used for the cell rate intervals 0 1i, 2, 3, 4 and 5 to 11 respectively; CR1 is able to be incremented by one of the increment values IN6/8 under the control of 16/7. IN6, IN7 and IN8 are used for the cell rate intervals 0/4, 5 and 6/11 respectively; CR2 is able to be incremented by one of three increment value IN9/11 under the control of 19/11. IN9Y IN10 and INI1 are used for the cell rate intervals 0/6, 7 and 8/11 respectively; SCR3 is able to be incremented by one of three increment values IN12/14 runder the control of 112/14. IN12, IN13 and IN14 are used for the cell rate intervals 0/8, 9 and 10/11 respectively.

'WO90/05416 PCT/EP88/01 037 Bef'ore descr ibiriP the operation of the equlipm~enit the, choice of the counters CR0/3 p the cell rate intervals CRI0/11 arid the steps or increment values 1140/14 will be explained by making reference to Fig q1.

This f'igure represents on the absci~s the cell rate CR arid on the ordinate (on a lo!?arithmic scale) the Gaussiani probability to ex,.ceed this cell rate. This fu nc t ion is therefore called the comiplemenitary (with resectto 1) cumulative Gaussian probability distribution f unction of the cell rate. It is derived from, a Gaussian standard destination s=S/Ap wherein My S arid A are initeger values obtained ir a way which will be explained later, 4 Fig. 4 also a represents a staircase function comlprising. the points AO to All arid approximating the curve CCF versus CR. For these points the cell rates are eq~ual to OP (M-S)/Ar (M-S/2)/Ay #y (M+4S)/A respectivelyp whilst the corresponiding complementary cumuIlative probabilities are PA01,Y PAlY PA27 PAlO, FA11=0 respectively. Also shown in Fig. 4 are the cell rate intervals CR10, CR11,P CR111 delimited by the last mentioned cell rates. The probabilities or the cell rates to be in these intervals CR10 to CR111 are PO to Fury defined as follows PO P 0 C R MI S)/A)1 P F'P E(M 3)/A CR (M (2) P1 0 P 4. 76/2)/A CR (3) P11I P [(CR M 43)/A] 0() The above complementary cumulative probabil1itv values PAO to Prill may therefore be written FAG0 1 WO 90/05416 PCf/EP88/01 0 3 7 PA P P2 +FP3 PF4 P5+P6 P7+F8 4 9 +P 106 I A2 P'2+P3 P4 P5 +P6 +FP7 PO 4- 9 Pl0 (7) PA ~3 P3 '+FPI+FP5 +P6 P7 +FP8 P9 +P10 (8) PA 5 =F5 +P6 +FP7 +F'8 +P9 +FPI (9) PA 7 =F7 P8+FP9 PI0 P9= P9 P 0 1 PA~ 10 =P10 (12) P A11 0 (13) The above described eq~uipmnt is able to monitor the above staircase approximation AO to All1 of the com~plemnertary cumulative probability distribution curve CCF versus CRY shown in Fig. 4I, by u!sing, the four courters CRO/3 These counters are more particularly used to monitor the probabilities irn the points Alp AZY A3Y A4; IA6- A7Y AB; arid A10 respectively arid this is possible d ue to a suitable choice of the corresponding incremfenit valu~es IN0/5, IN6/GY 1N9/11 arid IN12/1q respectivelvy as explained hereafter, The three increment values IN6/8Y IN9/11 arid IN12/14 for the courters CR1y CR2 arid CR3 are determined irn a li[ke way arid therefore only the choice of IN12/'14 for CR3 is described in detail.

Lporn the receipt of each cell of an individual cell strTe am the cell rate interval CRI0/li to which it belonis ics measured arid for each cell received at the end of a mteasurenient time irterval the credit counter CR3 is decremferted by IN12 wher the measured cell rate then belongs to one of the intervals CRI0/B ari is irncremented by IN13 Or IN14 when the cell rate measured then belongs to WO090/051416 PCU/EP88/01037 th2 iterval CR19 or CRI10 respectively. It is clear that after a sufficiently larcie number of mieasuremnirts the rnum~ber of time the couriter CR3 is incremented or decremerited IN12 7 y IN13 arnd INlI is proportional to the probability PO+P1+ +P8 that the cell rate is smaller than (M+3S)/Ay to the probability P9 thcit -this 'ell rate is comprised between (M+3S)/A and (M+7S/2)/Ay and to the probability P10 that the cell rate iS compr'ised between (M+7S/Z)/A and (M+4S)/A respectively.

The increment/decrement values IN12/,'1 are now so choseni that after such a large number of measuremfents, arid supposii' that the counter CR3 was started f'rom its zero position? it is then aqaiin in this zero position. This happens when: (F0+F'1+ F'B)4(-IN12)+F,9.IN13+F'10.IN1q 0 (14) or because F0O+F'1+ .,P10 =1 when E1-(FP9+F10)3 .(-N12)+F,91N13+Fl,0IN14 0 (16) or when (1 -A9 (-IN12)+P9.IN13+P10,IN14 0 (17) The increment values IN13 ari IN14 are for instance sCo chosen that P9.T.N13 FP10.IN14 (18) thus :ilvi-q a greater weiqht to the interval CRI110 The relation (17) may then be written -IN12+PA9.IN12+2F'10.IN14 0 (19) arid mjay be satisfied by a suitable choice of the ratio From the relation (19) it follows that at the end of a measurement interval the contents of the counter CR3 are indicative of the deviation of the real probabilities in the points Ai9 arid A10 from their expected values. More particular lvy the couniter is rie*ative or zero when, these expected probabilities are riot exceeded whereas it beL,mes positive when at least one of these probabilities exceeds its ex,.pectedj value F'g9 or PA10. For this reason the WO090/05416 PC1/EP88/01037 J.4 counter CR3 mlay be used to mioitor the probabilities in the p~oinits 69? arir ,6 will be described later this is done by limiting the cell rate and therefore the probabilities to exceed the expected values when counter CR3 contents exceed a predetermined credit value.

For the counter CR0 the i ncremtent/ decr ement values INO 1 are determiined in such a way that the f'ollowing3 relation is satisfied F0,.(-INO)+F'1*(-INI)+FP2,(-IN2)+F3, )IN3+F'qINq (P5+F'6+ F10).IN5 =0 B~ecause of the symmnetry around the cell rate M/A of the Gaussian probability distribution function from, which the function CCP/CR was der ived one has P0 P5 P6 P1 0 (21) P1 P4 (22) P2 P3 (23) s~o that the relation (20) is satisfied for INO IN5 (24) INi IN4 IN2 N3 (26) The incremient values INC,'2 are now for instacice so chosen that 4PO.INO P1.INi F2.INZ (27) arid for these values and those of' (25) arid (26) the relation (20) miay be written -3FP0.INO+P,3.IN2+P,4.IN1+(P5+FP6+...+FP10).INC=C (28) E: ecau se P 2 P I Po (29) one has INC0 Ni I1 so that one miay write INO IN2 IWO0 (31) IN1 IN2 IN' (32) wherein IWO( arid IN' 1 are positive values.

B v ta kin_9 the relations 31) ard 32) into accourt the relation (28) becomies PCT/EP88/01037 WO 90/05416 P/EP88/01037 -3POF INO+PA3.INI2+P'.IN' ,+P10).IN'O=0 (33) From the relation (33) it again follows that the counter CRO may be used to monitor the probabilities in the points A3 and A4 of the staircase A0/11 and because PA3=1-PO-FI-P2, also in the points Al, A2 and A3 thereof.

In connection with the staircase of Fi3.5 it should further be noted that it has a mean m' and a standard deviation s' which are different from the mean m=M/A and the standard deviation s=S/A of the Gaussian probability distribution function which it envelopes. Indeed, the value m' is given by the relation I./AE(M-S)F'PO+(M-S/2) F. 103 (34) or 1/ACM+0.3S] M'/A In a similar way one may calculate that s'=s-0.1S/A S'/A (36) Reference is now made to Figs. 1i 2, 3, 5 and 6 for the description of the operation of the equipment.

The user station (not shown) connected to the input multiplex;er link ML is able to multiplex thereon a plurality of streams of data cells or packets of bits. The cells of a same data stream belong to a same communication and are identified by a same label. Each time this user station wants to transmit such a data stream towards a destination user station via the input link ML, the statistical measurement equipment SME and the digital switching network DSN in cascade, it starts a virtual path setup operation by transmitting towards the DSN a path setup control cell containing a distinct label, e.g. Li, and the values of various other parameters defining the data cell stream to be sui.bsequently transmitted on the path to be established and if the path setup operation is successful.

For instance, when the user station wants to transmit a cell stream having the arbitrary probability distribution function shown in Fig. 5, first the

I

"i4 WO90/05416 PCT/EP88/010 3 7 WO 90/05416 16 corresponding complementary cumulative probability distribution function of the cell rate is determined and afterwards a complementary cumulative Gaussian probability distribi-ition function enveloping this corresponding function is determined. The mean and standard deviation of this Gaussian curve are transmitted with the path setup cell.

To approximate this complementary cumulative Gaussian probability distribution function by a staircase, in the same way as described above with respect to Fig. 4, use is made of the counters CRO/3 with the same increments.

However these counters are not able to count negatively.

These are shown in Fig. 5 together with the cell rate intervals determined by the mean and the standard deviation.

Because the probability values P'0, P'1, shown in Fig. 5 are all not larger than the corresponding probability values PO, Pl, of Fig. 4 it is clear that after a measurement interval each of the counters CRO/3 will normally be in a negative position, but will reach a positive position when at least one of the monitored probabilities is exceeded, as described above.

When the above mentioned such a path setup control cell is received in the measurement equipment SME it is stored in the receive buffer RBUF thereof and processed by the processor PR. When the latter finds out that a path setup control cell is concerned it allocates a portion of the memory MEM shown in Fig. 6 to the communication with label L1 and determines from the expected values of the traffic parameters m and s the following other parameters MIS (measurement interval select) a 2-bit interval selection parameter to select one of 4 measurement time intervals having a d.uration of A 1024 x 2 exp 3a cells with a O, 1, 2, 3 M an 8-bit number of cells with label L1 such that the i SWO 90/05416 PCT/EP88/01037 17 expected value of the mean mn is equal to M/A; S an 8-bit number of cells with label LI such that the expected value of the standard deviation s is equal to

M/A

The processor PR stores the values M-S and S/2 in the above mentioned portion of the memory MEM shown in Fiq.

6 and subsequent to this storage operation it controls the transmission of the path setup control cell to the transmit buffer TBUF of the transmit port TX which afterwards transfers the control cell to the digital switching network DSN. In a manner similar to the one described in the Belgian patent No 08701481 in each stage of this network an output link is selected and an allocation formula is calculated to check if the control cell and the data cells of the same communication following it may be multiplexed on this output link. Howeverr because the user station wants the curve of Fig. 4 to be approximated by the staircase shown therein in the allocation formula use is made of the above given values m' and s' instead of m and s. Assuming that following the calculation a virtual path may thus be set up to the destination user station, the latter transmits a confirmation cell to the originating user station which may then start the transmission of the corresponding individual data cell stream with label L1 on the multiplex- link ML on which other individual data cell streams are possibly already multiplexed. For this data stream the statistical measurement equipment SME checks if it operates within the traffic limits defined by the parameters which were stored in the memory MEM in the way described above.

When following the receipt of a data cell with label L1 in the buffer circuit REUF of the receive port RX, the processor PR detects the presence of this data cell it Stransmits to the memory MEM a partial memory address PFA which is function of the label LI contained in the data 1 WO 90/05416 PCT/EP88/01037 1 cell. It also stores the following parameters which are updated ipon the receipt of the data cells, as will become clear later: MIC a 3-bit counter value indicating the measurement interval during which the last data cell having label LI was received; CCR the contents of the cell counter CCR; CRO/3 the contents of the credit counters CRO/3; CRI a 4-bit cell rate interval indicating one of 12 cell rate intervals CRIO to CRI11 (Figs 5, 6).

The clock extraction circuit CEC extracts a bit clock BCL and a cell clock. CL from the incoming data cell stream and applies both BCL and CL to the control circuit CC which in response thereat provides at its outputs Tl to T11 a set of 11 successive non-overlapping timing pulses Ti to Til (not shown) which cover a period equal to the duration of the received data cell and which are used to control various circuits of the SMC, as already mentioned.

Because the cell clock signal CL is also applied to the divider circuit DIV which realises a division by 1024 the resulting clock signal CL increments the cell counter CR by 1 each time 1024 cells have been counted.

With a bitrate of the incoming cell straam equal to 600 Megabits/sec and with cells having a length of 280 bits, BCL and CL are respectively equal to 600 Megabits/sec and 2.14 Megacells/sec. In this case each cell has a duration of 466.67 nanoseconds and T1 to T11 each have a duration of 1/lith of this value. The control of SMC by S*the .timing pulses Ti to Tl1 is: now considered Timing pulse T1 The processor PR loads the parameters MIC, MIS and CCR from the memory MEM into the like named circuits of SMC. Assuming that MIS is equal to 01 the selection outputs sa and sb of the measuremert interval selection register MIS controlling the multiplexers MUX1/3 are on 0 l WO 90/05416 PCT/EP88/01037 19 and 1 respectively, so that only the outpus s3, s4 and of the stages S3, 94 and S5 of the counter CR are connected to the associated comparator C04. This means; that the cell counter CR and the multiplexers MLUX1/3 are used to provide the successive identities of measurement intervals having3 each a duration of 1024 x 8 data cells. The 3-bit value MIC identifyi ng the last measurement time interval during which a data cell with label LI was received is applied to the comparator C04. Finally, the cell counter value CCR is applied to the comparator By the timing pulse Ti also the D-flipflop DFF is reset. Thus the status output signal ST of th .s flipflop is brou3ght in the condition 0 indicating thdt the cell with label L1 is in principle allowed to be transmitted further.

Timing pi.lse T2 The orocessor PR load the cell rate interval value CRI and the credit vali', CRO from the memory MEM into the like named circuits CRI and CRO of SMC. Also the comparator C04 is enabled so that the 3-bit value MIC identifying the last measurement interval during which a data cell with label L1 was received is compared with the value stored in the stages S3, S4 and 35 of the counter CR and constituting. the identity of the measurement time interval d..uring which the data cell which is being processed is received. If both the compared identities are equal the output signal MTI of C04 is on 0 and in this case MIC is the identity of th.e present measurement interval.

Si On the contrary, when both the compared identities are different the output MTI is on 1 ir'dicating that the measurement interval has elapsed and that the value MIC has to be updated.

Timing pulse T3 The processor FR loads the values M-S and S/2 from the memory MEM into the respective registers REG4 and and enables the operation of the decoder circuits DEC1 and WO 90/05416 PCT/EP88/01037 DEC2. As a consequence the latter decodes the cell rate interval CRI into the 15-bit increment code 10/14 accordin, to the Table 1. Thus one gatiring circuit is enabled for operation in each of the groups GCO/5, GC6/8. GC9/11 and GC12/14 (Fig 3) Timing pulse T4 The processor PR enables the gating circuit GC15 so that it is checked if the cell rate interval CRI is 0 or not. In the former case the output ID of GC15 is or 0, whereas in the latter case it is on 1. As a result either the gating circu..it GC16 or GC17 is enabled, so that either the value M-S or S/2 stored in REG4 or REG5 is stored in the intermediate storage circuit ISC4 associated to the comparator The processor PR also loads the credit value CR3 from the memory MEM into the like named credit counter CR3.

It moreover performs the following functions if the output MTI of the comparator C04 is on 1, indicating that the measurement time interval has elapsed via the gate G7 the identity of the measurement interval stored in the counter MIC is incremented by 1 so that this counter then stores the identity of the new interval; via the same gate G7 the set input S of the cell counter CCR is activated so that it is broug-ht in the position 1. Th.us the receipt of the first cell during the new measurement interval is registered; finally, via the same gate G7 also the cell rate interval coiunter CRI is reset due to its reset input R being activated. Thus the counter CRI indicates the identity 0000 of the first cell rate interval.

Timing pulse The processor PR loads the credit value CR2 from the memory MEM into the like named credit counter CR2 and enables the intermediate storage circuit ISC3 associated to 1 WO 90/05416 PCT/EP88/01037 the adder circuit AD3. Thus one of the increment values IN12/14 stored in the increment registers IR12/14 is transferred via GC12/14 into this intermediate storage circuit ISC3, Timing pulse T6 The processor PR loads the credit value CR1 from the memory MEM into the like named credit counter CR1 and enables the intermediate storage circuit ISC2 associated to the adder cicuit AD2. Thus one of the increment values IN9/11 stored in the increment registers IR9/11 is transferred via GC9/11 into this intermediate storage circuit ISC2, Also an input T6 of the gate G3 is activated so that if the measurement interval has elapsed MTI being then on 1, the adder circuit AD3 is operated. As a consequence it adds the increment values stored in ISC3 to the credit value stored in ISC3, the result of this operation being stored in CR3. However, in case this adding operation exceeds a predetermined positive credit value, i.e. when AD3 overflows, it changes the contents of CR3 to all 1's.

Finally, during the time interval T6 the comparator C03 compares the contents of CR3 and REG3 which stores all 1's and produces arn output signal AL3 which is on 1 when an equality is detected and on 0 in the other case. This means that AL3 is or 1 when the adder circuit AD3 has detected an over flow.

Timing pulse T7 The processor PR loads the credit value CR3 stored in CR3 back into the memory MEM. It further enables the intermediate storage circuits Ibt. arnd ISCO associated to the adder circuits AD1 and ADO respectively. Thus one of the increment values IN6/B stored in the increment registers IR6/8 and one of the irncrement values stored in the increment registers IRO/5 are transferred via GC6/8 and GCO/5 into the intermediate storage circuits ISCI ii r -I WO 90/05416 PCT/EP88/01037 22 -i and ISCO respectively. Also the input T7 of the gate G2 is activated so that if the measurement interval has elapsed, the output MTI of C04 being then on 1, the adder circuit AD2 is operated. This operation as well as that of C02, REG2 is similar to that of AD3, C03, REG3 considered above4 This means that the output AL2 is on 1 when AD2 has detected an overflow.

Timing pulse T8 The processor PR loads the credit value CR2 stored in CR2 back into the memory MEM. Because the inputs T8 of the gates GO and G1 are activated and if the measurement interval has elapsed? the output MTI of C04 being then on 1? the adder circuits ADO and ADi are operated. This operation as well as that of COO. REGO and C01, REG1 is similar to that of AD3, C03, REG3 considered above. Hence, the output AL2 or AL3 on 1 when ADO or AD1 has detected an overflow respectively, Timing pulse T9 The processor PR loads the credit value CR1 stored in CR1 back. into the memory MEM and enables the operation of the multiplexer MUX4. As a consequence and as follows from the above Table 2 input 0 of this multiplexer is connected to the output AL if the cell rate interval CR1 is O 1 or 2; ALO is connected to AL if CRI is 3 or 4 AL1 is connected to AL if CRI is 5 or 6 AL2 is connected to AL if CRI is 7 or 8 AL3 is connected to AL if CRI is 9 or 1 is connected to AL if CRI is 11 Also the comparator C05 is enabled so that it compares the cell counter value stored in CCR with either the vale M-S or S/2 depending on the cell rate interval stored in CRI being the interval 0 or one of the intervals 1-10 respectively. If the values compared are equal this is. indicative of the fact that the cell interval has ii i S WO 90/05416 PCT/EP88/01037 23 elapsed. In this case and when the output AL is on 0, or ALE: on 1, then the cell rate interval counter CRI is irncremented by 1 via the gate G5. Also the cell counter CCR is reset via the same gate G5 in order that a new cell count should be started.

Timing pulse The processor FR loads the credit value CRO stored in CRO back into the memory MEM. In a first portion of and via the gate G4 it brings the D-flipflop in the 1-condition if the output AL is on 1. As a con sequence the status outp..ut ST is then on 1 indicating to the processor PR that the cell received should be dropped. On the contrary, if the status output ST remains in the 0-condition, or STEB in the 1-condition, then the processor PR durirng a second portion of T10 increments the cell counter CCR by 1 via the gate G6 Timing pulse Ti1 The processor FR stores the values of the parameters MIC, MIS and CCR back into the memory MEM.

From the above it follows that after the receipt of each cell with label L1 the following operations are performed by the measurement circuit SMC -by MUX1/3, C04, MIC it is checked if the present measurement interval provided by the cell counter CR is a new one or not. This is indicated by the latched output MTI of C04 being zr 1 or 0 respectively; by DEC1 the increment values 10/14 for the previous cell rate interval CRI stored in CRI are determined for each of the counters CRO/3 and by DEC2 one of the inputs O0 ALO/3, 1 of MUX4 is selected; -if the measurement interval is a new one it is counted by MIC, the cell rate interval CRI is made equal to 0 and the new cell is counted by CCR. On the contrary if the measurement interval is the same as the previous one MIC, CRI rand CCR are not changed; Moreovery in both i WO 90/05416 PCT/EP88/01037 24 cases it is checked by GC15 if CRI is on 0 or not and accordingly M-S or S/2 is registered in ISC4; in case the measurement interval is a new one the above mentioned increment values for the counters CRO/3 are added to the credit values already stored therein by the respective adders ADO/3. By the circuits COO/3, REGO/3 it is then checked if one or more of these counters reach a predetermined positive credit value in which case the corresponding output ALO/3 is activated? depending on the cell rate interval CRI previously selected by DEC2 the multiplexer MUX4 connects one of the inputs Or ALO/3 arnd 1 to its output AL. More particularly 0, ALO, ALl, AL2, AL3 and 1 are connected to AL if the cell rate interval is O, 1 or 2; 3 or 4; or 6; 7 or 8; 9 or 10, 11. In this way cells will only be dropped when CRO/3 overflows and the cell rate is higher than M/A, (M+2S)/A and (M+3S)/A respectively. If AL is activated the status bit ST is changed to 1 indicating that the received cell has to be dropped. On the contrary, when AL is deactivated (or ALB=1) and when a number of cells equal to M-S or S/2 has been counted indicating the end of the cell rate interval, the cell rate counter CRI is incremented by 1 so as to indicate a new cell rate interval and the cell counter CCR is reset so that a new count can start; when the status bit ST is not activated (STE=1) indicating that no cells have to be dropped the counter CCR is incremented.

It is clear from the above that for each received cell of an individual cell stream the cell rate interval is determined arid in function of this measurement the credit counters CRO/3 are incremented or decremented at the end of each measuring interval., When such a counter exceeds a predetermined credit value and when simuiltaneously the cell rate is higher than a predetermined one the cell is WO090/05416 PCT/EP88/01037 dropped, While the prrinciples of the inventior have been, described above in conrnectior with specific apparatus, it is to be Clearly understood that this description is made by way of examiple, and rnot as a limitation or the scope of the inventijon.

Claims (10)

1. Statistical measurement equipment to determine the value of' a statistical parameter of a variable (CR), character'ized ir that ilt includes means (REGq/5, GC~I6/17y ISCL1, C05, CCR) for masuring the value (CRI0/li) of' said varijable (CR) at least at the end of each measurement interval (MTI) and means (IR12/Iq, CC12/14? ISC3, AD3) for .1 then stepping at least one counter (CR3) by a step (1N12/14) which is function of' the value (CR10/By 9Y then meas.redy the steps being so determined that af ter a V plurality of' time intervals said counter (CR3) is in a V position indicative of' the deviation, from one or more ex.,pected values (FA9Y PAlO)y of' the probabilities to exceed ti corresponding predetermined values E(M+3S)/A, (M+7S/2)/Al of' said variable (CR'.

2. Statistical measurement equipment according to claim I1Y characterized in that sai2 predetermined values E(M4+3S)/A, (M+7S/2)AI of' said variable separate intervals (CRI0/8, 9 10 to wh -ch distinct ones of' said courter steps (IN12/13/14) are assigned, that said measuremfent mears mieasu-re said variable by determining the interval to which it belongs, and t at said counter position is in-icative of' the deviationy fr'om expected values-. of' the probabilities to exceed said predetermined values (M+7S./2)AJ of' ,aid variable (CR).

3. Statistical measurement equipment according to claim 2Y characterized ir that said counter (CR3) is stepped in the ore or other direction dependingi on the 27 measured value of said variable belonging to an interval at the one (CRIO/8) or other (CRI9/10) side of a selected one [(M+-t3S)/AI of said predetermined values 3S)/A, (M 7S/2)/A1 of said variable (CR).

4. Statistical measurement equipment according to claim 3, characterized in that said steps are positive for values of said variable (CR) larger than said selected value 3S)/A] of said variable (CR) and increase with increasing values of said variable (CR). Statistical measurement equipment according to claim I, characterized in that it further includes means (REG3, C03) associated to said counter (CR3) and able to detect when said counter reaches a position indicative of a maximum allowable devi- ation, and means (MUX4, DFF, PR) coupled to said detecting means (REG3, C03) able to reduce said deviation and therefore said probabilities by changing the value of said variable when said detecting means (REG3, C03) have detected said maxi- mum allowable deviation. 15 6. Statistical measurement equipment according to claim 2, characterized in that it includes a plurality of said counters (CR0/3) able to perform distinct sets of steps (IN0/5, IN6/8, IN9/11, IN12/14) assigned to distinct sets of intervals (CRI),1,2,3,4,5/10; 0/4,5,6/10; 0/6,7,8/10; 0/8,9,10), and that the intervals of all said sets are separated by successive predetermined values I of 20 said vaiable (CR).

7. Statistical measurement equipment according to claims 3 and 6, characterized in that it includes a plurality of detecting means (REGO, COO to REG3, C03) each as- sociated to a respective one of said counters (CRO/3) for detecting when this counter reaches a position indicative of a maximum allowable deviation, and means (MUX4, DFF) coupled to said detecting means for reducing said deviation by changing said variable when at least one of said i I 28 detecting means has detected a maximum allowable deviation and when the variable then has a value exceeding the selectccl prcdctcrmined value lM/S, (M S)/A, M 2S)/A, (M 3S)/Al.

8. Statistical measurement equipment according to clainm I, characterized in that said expected probabilities are those of a complcmcntary (with respect to cumula- tive Gaussian probability (listribution function of said variable.

9. Statistical masurement cquipmcnt to dctermine the value of a statistical pa- rameter of the probability distribution function of a variable and to substantially limit the thus measured value to an expected value thereof, characterized in that it is able to determine for at least one predc(.termined value of the variable the probability to exceed this predctermined value an1d tC lim it the thus measured probability to an expected value thereof. Telecommunication switching va luie thereof, plurality of user stations coupled to a switching network through a statitistical measurement cquipment, characterized in that said equipment is as per any of the claims 1 to 9, the variable being the cell rate of a cell stream generated by at Icast one of said user stations. I1. Telecommunication switching system according to claim 10, characterized in that a user station in order to be able to transmit a cell stream whose cell rate has an S" arbitrary probability distribution fu nct ion coni mu n ica tes to said switching network 20 the mean and standard devia (ion values of a complementary (with respect to I) cumulative Gaussian orobability d istri io funion tio of the cell rate, enveloping 1. the comi plementary cumulative probabi Ii ty distribution function of the cell rate de- rived from said arbitrary probability distrib Ition fu nction.

12. Telecom mu n ica tion switching system according to claim 11, characterized in that said switching network upon the receipt of said ncan and standard deviation values from W,4 U L 29 said user station- calculates thecfroni thc mecan (mn) and standard deviation val- Lics of a staircase probability dlistribution function or the cell rate approxirnaied by said statistical. mecasurement equipmcnt and uscs thicsc valucs in a link allocation formula oni the basis of -which said cell stream is allowed to bc multiplexed on an output link of said network.

13. Telecommu nication switching elcmen t according to claim 10, characterized in that said statistical rncasurcement cquipm11cntL is uIsed in multilcx for' a plurality of ccli streamns and that this equipment ineCLudcs a memiory (MEN/) to temporarily store values to be used in mu1Ltillcxcr control circuitry (MIS, N/IIC, CR1, CCR, CR0/3) of said equipment. 4* 4 4.

55.5 SO -a a 4*t&@S 5.5.55 C