Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
ZO~)43~5
- 1 - P. JOOS-W. VERBIEST 2-4
STATISTICAL M~ASUREMENT 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 p~tent application No 08701481
(W. VERBIEST 3) and the international patent application
No PCT~EP88~00594 (P. JOOS 1). It forms part of a
telecommunication switching system operatiny according to
the Asynchronous Transfer Mode (ATM), i.e. wherein data are
transmitted under the form of cells or packets of bits and
with a variable celI rate. 'An individual cell stream is
'allowed to be multiplexed on a same telecommunication link
( 15 together with a PluralitY of other individual cell streams
already multiplexed thereon~ if an allocation formula is
satisfied. This formula is based on the exPected values of
the mean and variance of the probability distribution
function of the cell rate of the individual cell stream, on
?O the expected values of the mean and variance of the
probability distribution function of the cell rate of each
of the above mentioned other individual cell streams
already multiplexed on the link, as well as on the maximum
allowable bandwidth on ~his link. This allocation formula
-25 is based on the assumption that a multiplex of a relatively
high number-of uncorrelated probability distribution
functions leads to the normal probability distribution
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- 2 - P. JOOS-W. VERBIEST 2-4
function, as follows from the Central Limit Theorem.
However, because the mean and variance do not sufficiently
define 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 link.
- As also desribed 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 values
thereof. 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.
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 particularly, it has been
found that errors are especially due to the ~act that the
tail of the probability distribution function of the cell
rate is not sufficiently defined by these two parameters.
An object of the present invention is to provide a
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- 3 - P. JOOS-W. VERBIEST 2-4
statistical measurement equipment of the above type, but
which allows the probability distribution function of the
variable to be defined in a more accurate way than by the
above known mean and variance parameters.
According to the invention this object is achieved
due tn 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
10 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
deviation, 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 tD 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 measurement equipment is that it further
includes means associated to said counter and able to
detect when said counter reaches a position indicative of a
maximum allowable deviation and means coupled to said
35 detecting means and able to reduce said deviation and -
.
2004375
- 4 - P. JOOS-W. VERBIEST 2-4
therefore said Probabilities by changing the value of said
variable when said detecting means have detected said
maximum allowable deviation.
In this way the equipment limits a number of
probabilities to exceed a corresponding number of
predetermined values of the variable and thus suitably
monitorS ~ 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 includes a plurality uf 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.
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
variable.
The Present invention also relates to a
telecommunication switching system with a plurality of user
stations coupled to a switching network through a
statistical measurement equipment of the tYpe described
abDve, the variable being the cell rate of a cell stream
generated by at least one of said user stations.
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- 5 - P. JOOS-W. VERBIEST 2-4
The above mentioned and other obiects 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
conjunction with the accompanying drawings wherein :
Fig. 1 is a schematic diagram of a statistical
measurement equipment SME and of part of a
telecommunication switching system in which it is included,
both according to the invention;
Figs. 2 and 3 together represent in detail a
( statistical measurement circuit SMC forming part of the
statistical measurement equipment SME of Fig. l;
- Fig. 4 represents a comlementary cumulative Gaussian
- probability distribution function of the variable cell rate
and othèr parameters used to illustrate the operation o~
the equipment of Fig. l;
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.
Referrin~ to Fig. 1 the ATM (Asynchronous Transfer
Mode) data packet or data cell telecommunication system
( shown therein incIudes a digital switching network DSN
which is for instance of the type disclosed in the Belgian
patent No 905 982 ~De Pryc~er et al 2-2). This digital
switching network DSN has a plurality of inputs I1 to IN
and outputs 01 to ON which are coupled to user stations
(nst shown) via input and output multiplex links and
statistical measurement equipments . For instance, a user
station is connected to the input Il of DSN via an inPut
multiplex link ML and a statistical measurement equipment
SME having an input I and an output 11.
The statistical measurement equipment SME comprises
a receive port RX and a transmit port TX which are
': . . . . .
,
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- 6 - P. JOOS-W VERBIEST 2-4
connected in cascade between the input I and the output Il.
The receive port RX includes a receive buffer RBUF, a
processor PR, a memorY MEM, a statistical measurement
circuit SMC and a clock extraction circuit CEC, whilst the
transmit port TX includes a transmit buffer TBUF. The
receive and transmit buffers RBUF and TBUF are connected in
cascade between the input I and output Il. The processor
PR 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
extractinn 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 detai~ 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 nf each of the individual cell
streams of the multiplex, a measurement interval counter
MIC, a cell rate interval counter CRI, a measurement
interval selection register MIS, decoder circuits DECl and
DECZ, registers REGO/5, credit counters CR0~3, increment
registers IRO~14, intermediate storage circuits ISO~4,
adder circuits AD0~3, comparator circuits CD0~5, 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 extractîon circuit CEC are connected to
the control circuit CC having outputs Tl to Tll which
control various circuits of the equipment, as indicated in
a schematic way. This control will become clear from the
operation of the equipment. The cell clock output CL is
also connected to the input of the cell counter CR through
the divider circuit DIY which is able to divide by 10Z4.
The cell cGunter CR comprises 12 stages S0~11 whose outputs
~: "' - - ' .
'. ' .
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- 7 - P. JOOS-W. VERBIEST 2-4
sOfll are subdivided in four groups sO~Z, s3~5, s6~8 and
s9~11, the three outPuts of each group being connected to
respective data inputs of the.multiplexers MUX 1~3. Each
of these multiplexers MUXl~3 has two selection inputs sa
and sb provided by the measurement interval selection
register MIS. The outPuts of the multiplexers MUXl~3 are
connected to first inputs of the comparator C04 whose
second inputs are connected to the output 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 MIC, to the reset input R of
the cell rate interval counter CRI, to the set inputs of
the cell eounter CCR, and to inputs of the gates GO to G3.
The outputs of the cell rate interval counter CRI are
connect~ed to the decoder circuits DECl and DEC2 as well as
to the gating circuit GC15.
The decoder circuit DECl is able to translate the
4-bit cell rate interval code CRI provided at the output of
CRI into a 4-out-of-15 increment code IO/14 according to
the following table wherein CRI is rePresented in decimal
form.
.( .
: 35
2:00~75
- 8 - P. JOOS-W. VERBIEST 2-4
_able 1
¦ I~CRI ¦ O ¦ 1 ¦ 2 ¦ 3 ¦ 4 ¦ 5 ¦ 6 ¦ 7 ¦ 8 ¦ 9 ¦ 10
. I I I I I 1 1, 1 1 1 1 1
O 1 1'1 0 I O I O I O I O I O I O I O I O I O I O I
1 o 1 1 1 o I o I O 1 I I I I I I I
2 1 0 1 o 1 1-1 I I I I I 1 I O I U
1 3 1 0 1 0 1 0 1 1 1 0 1 O I O I O I O l o I O I O
lO I 4 1 O I O 1 0 1 0 1 1 1 O I I I 1 I I
1 5 1 0 1 O I O I O I O I 1 1 1 1 -1 1 1 1 1 1 1 1 1 1 (
1' 'I
6 1 1 1 1 ~ 1 1 0 1 0 1 O I O I O I O I O
1 7 1 O I O I O I O I O 1 1 1 O I O I O I O I O I O
1 8 1 O l I ~ I I O I O 1 1 ! 1 1 1 1 1 1 1 ~ 1
I I I I I I I I I I I I I
9 1 1 1 1 1 1 7 1 1 1 1 1 1 1 1 o I o I o I o I o I
¦ 10 ¦ O ¦ O ¦ O ¦ D ¦ O ¦ O ¦ O ¦ 1 ¦ O ¦ O ¦ O ¦ O
'' ' I 11 I O I O j' O I O I O I O I O I O I 1 1 1 1 1 1 1 I
20 1 1 1 ~ I I 1 1 1 1 1 1.
12 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 O I O I O
13 1 I ! I I I I I I I 1 1 O I O
I 1~ I O I O I O I O I O I O I O I O I O I O I 1 I 1 I
The bits IOil4 of the increment code thus provided
by the decoder DECl control the respective gating circuits
6C0~14 (Fig.3) interconnecting the increment registers
IRO/14, storing the respective increment values INO~14. to
a first input the adder circuits ADO~3. More particularlY
IRO~5. IR6~8, IR9~11 and IR12~14 are connected to the first
inputs of the adder circuits ADO, ADl, AD2 and AD3 via the
gating circuits GC0~5, ~C6~8, GC9~11 and 6C12~14 and the
intermediate storage circuits ISCO~3 respectively. These
adder circuits ADO/3 further have an enable input
controlled by the outputs of the gates 60~3 respectively.
.
', ' -'~ ,
,: ,
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- 9 - P. JOOS-W. VERBIEST 2-4
The second inputs of these adder circuits ADO/3 are
connected to the outputs of resPective credit counters
CRO~3 having an 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
- COO/3 whose second inputs are connected to the outputs of
the registers REG0~3 respectively. Each of these registers
stores all l's.
The comparators C00~3 have outputs ALO/3 which are
( connected J together with other input signals which are
continuously on O and 1 respectively, to the data inputs of
the multiPlexer MUX4 whose selection inputs are connect~d
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 ~f said inPUts 0, AL0~3 and 1 according
to the following table, wherein CRI is represented in
decimal form :
. Table 2
: 1. 1 1 1 1 1 1 1 I I I I I I .
¦SC/CRI ¦ O ¦-1 ¦ 2 ¦ 3 ¦ 4 ¦ 5 ¦ 6 ¦ 7 ¦ 8 ¦ 9 ¦ 10
1 0 ~ I I I o l I I I I I
¦ AL-O ¦ û ¦ O ¦ O ~ O ¦ O ¦ O ¦ O ¦ O ¦ O ¦ O ¦
~: ¦ ALl ¦ O ¦ O ¦ O ¦ O ¦ O ¦ 1 ¦ 1 ¦ O ¦ O ¦ O ¦ O ¦ O ¦
¦ AL2 ¦ O ¦ O I o ¦ O ¦ O ¦ ~ ¦ O ¦ 1 ¦ 1 ¦ O ¦ O ¦ O ¦
¦ AL3 ¦ ¦ O ¦ O ¦ O ¦ O ¦ O ¦ O ¦ O ¦ O ¦ 1 ¦ 1 ¦ O ¦
1 1 1 I I I I ~ I I I I I I O l 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 Tl.
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- 10 - P. JOOS-W. VERBIEST 2-4
The multiplexer MUX4 also has an outPut ALB providing an
output signal which is the comPlement of that ~enerated on
AL and which controls the gate G5 connecting 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 STB
which is connected to the increment input of the cell
counter CCR through the gate 66.
' 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
C05 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 from
Fig. 3 and from'Table 1 that : .
- CRO is able to be increment'ed by one of six
increment/decrement values INO/5 under the control of
I0~5. INO, INl, IN2, IN3, IN4 and IN5 are used for the
cell rate intervals 0, 1, 2, 3, 4 and 5 to 11
respectively;
- CRl is able to be incremented by one of the increment
values IN6/8 under the control of I6/7. IN5, IN7 and
IN8 are used for the cell rate intervals 0/4, 5 and
6/11 respecti'velY;
- CR2 is able to be incremented by one of three increment
value IN9/11 under the control of I9/11. IN9, IN10 and
INll are used for the cell rate intervals 0/6, 7 and
8/11 respectively;
- CR3 is able to be incremented by one of three increment
values IN12/14 under the control of I12/14. IN12, IN13
and IN14 are used for the cell rate intervals 0/8, 9
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- 11 - P._JOOS-W VERBIEST 2-4
and 10~11 respectivelY.
Before describing the operation of the equipment the
choice of the counters CRO~3, the cell rate intervals
CRIO~ll and the steps or increment values INO~14 will be
explained by making reference to Fig 4.
This figure represents on the abscis the cell rate
CR and on the ordinate ~on a logarithmic scale) the
Gaussian probability to exceed this cell rate. This
function is therefore called the complementary ~with
respect to 1) cumulative Gaussian probability distribution
( function of the cell rate. It is derived from a Gaussian
probability distribution function with mean m=M~A and
standard destination s=S/A, wherein M, S and A are integer
values obtained ih a way which will be explained later.
Fig. 4 also a represents a staircase function
comprising the points AO to A-ll and approximating the curve
CCP versus CR. For these points the cell rates are equal
to O, (M-S)~A, (M-S~2)~A, ..., (M+4S)~A resPectively,
whilst the corresponding complementary cumulative
2n probabilities are PAD=l, PA1, PA2, ..., PA10, PA11=0
respectively. Also shown in Fig. 4 are the cell rate
- - intervals CRIO, CRIl, ... , CRI11 delimited by the last
mentioned cell rates. The probabilities of the cell rates
to be in these intervals CRIn to CRI11 are PO to Pll,
defined 3S follows :
PO = P (O =< CR =~ (M - S?~A) (13
Pl = P l(M - S)~A < CR =< (M - S~23~Al (2)
.
P10 = P [(M + 7S~2)~A < CR =~ (M + 4S)~A] (3)
Pll = P l(CR ~ (M + 4S)~A] = 0 (4)
The above complementary cumulative probabilitY
values PA0 to PAll may therefore be written :
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- 12 - P. JOOS-W. VERBIEST 2-4
PA0 = 1 (5)
PAl = Pl+P2+P3~P4+P5~P6lP7+P8~P9+P10 (6)
PA2 =P2~P3~P4~P5+P6~P7~P8+P9~P10 (7~
PA3 =P3~P~+P5+P6+P7+P8+P9+P10 ~8)`
PA5 =P5+P6+P7+P8+P9+P10 (9)
'.
10 PA7 =P7+P8~P9+P10 (10)
PA9 =P9+P10 ~li)
PA10=P10 ~iZ)
15 PAll- 0 (13)
The above described equipment is able to monitor the
above staircase approximation AO to A11 of the
complementary cumulative probability distributinn curve CCP
versus CR, shown in Fig. 4, by using the four counters
CRO~3. These counters are more partifularly used to
monitor the probabilities in the points Al, A2, A3, A4; A5,
A6; A7, A8i and A9, A10 respectively and this is possible
due to a suitable choice of the corresponding increment
values IND/5, IN6~8, IN9/11 and IN12/14 respectively, as
explained hereafter.
The three increment values IN6/8, IN9/11 and IN12~14
for the counters CRl, CR2 and CR3 are determined in a like
way and therefore only the choice of IN12/14 for CR3 is
described in detail.
Upon the receipt of each cell of an individual cell
stream the cell rate interval CRI0/11 to which it belnngs
is measured and for each cell received at the end of a
measurement time interval the credit counter CR3 is
decremented by IN12 when the measured cell rate then
belongs to one of the intervals CRI0/8 and is incremented
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- 13 - P. JOOS-W. VE~BIEST 2-4
by IN13 or IN14 when the cell rate measured then belongs to
the interval CRI9 or CRI10 respectively. It is clear that
after a sufficiently large number of measurements the
number of time the counter CR3 is incremented or
decremented by IN12, IN13 and IN14 is proportional to the
probability PO+Pl~ .... ~P8 that the cell rate is smaller
than (M+3S)/A, to the probability P9 that this cell rate is
comprised between (M+3S)/A and (M+7S/2~A. and to the
probability P10 that the cell rate is comprised between
(M+7S~2)~A and (M+~S)~A respectivelY.
.( The increment~decrement values IN12~14 are now so
chosen that after such a large number of measurements, and
supposing that the counter CR3 was started from its zero
position, it is then again in this zero position. This
happens ~when :
(PO+Pl~ ... + P8).(-IN12~+P9.IN13+PlO.IN14 = O (14)
or because PO+Pl+ .... P10 = 1 (15)
when ll-(P9+P10)].(-IN12)+P9.IN13+P10.IN14 = O (16)
or when
Sl-PA9).(-IN12)+P9.IN13+PlO.IN14 = O (17~
The increment values IN13 and IN14 are for instance
so chosen that :
. P9.IN13 = PlO.IN14 (18)
thus giving a greater weight to the interval CRI10.
The relation ~17) may then be written :
-lN12+PA9.IN12+2PlO,IN14 = O - (19)
and may be satisfied by a suita~ble choice of the ratio
IN12/IN14.
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 A9 and A10 from their expected values. More
particularly, the counter is negative or zero when these
expected probabilities are not exceeded whereas it becomes
positive when at least one of these probabilities exceeds
~'004375
- 14 - P. JOOS-W. VERBIEST 2-4
its expected value PA9 or PA10. Far this reason the
counter CR3 may be used to monitor the probabilities in the
points A9 and A10.
As will be described later this is done by limiting
the cell rate and therefore the probabilities to exceed the
.expected values when the counter CR3 contents exceed a
predetermined credit value.
For the ~ounter CRO the increment~decrement values
INO~5 are determined in such a way that the following
relation is satisfied :
PO.(-INO)+Pl.(-INl~+P2.(-IN2)+P3.IN3+P4.IN4 +
(P5+P6~ ... + PlO).IN5 = O (20~
Because of the symmetry around the cell rate M~A of
. the Gaussian probability distribution function from which
the function CCP~CR was derived one has :
PO = P5 + P6 + .... ~ P10 (21)
Pl = P4 (22)
P2 = P3 (23)
so that the relation (20) is satisfied for
INO = IN5 (24)
INl = IN4 (25)
IN2 = IN3 t26)
The increment values INO~2 are now for instance so
chosen that : : (
PO.INO = Pl.INl = P2.IN2 (27)
and for these values and those of (25) and (26) the
relation (20) may be written :
-3PO.INO+P3.IN2+P4.INl+(P5+P6+... +PlO).INO=0 (28)
Because
30 - P2 > Pl ~ PO (29~
one has INO > INl > IN2 . (30)
so that one may write
INO = IN2 + IN'O . t31)
IN1 = IN2 ~ IN'l C32)
wherein IN'O and IN'1 are positive values.
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- 15 - P. JOOS-W._VERBIEST 2-4
By taking the relations (31) and (32) into account
the relation (28) becomes :
-3PO.INO+PA3.IN2+P4.IN'l+(F5~ PlO).IN'0=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 AO/ll and because
PA3=1-PO-Pl-P2, also in the points Al, A2 and A3 thereof.
In connection with the staircase of Fig.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 :
m'= l/A[(M-S).PO+(M-S/2).Pl~... +(M+4S).P10] (34)
or m'= 1/AIM+0.3S] = M'/A (35)
In a similar way one may calculate that
s'=s-O.lS/A = S'~A (36)
Reference is now made to Figs. 1, 2, 3, 5 and 6 for
- the description of the operation of the equipment.
The user station (not shown) connected to the input --
multiplexer 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. Fach 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 dïgital
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 Iabel, e.g. Llr
and the values of various other parameters defining the
data cell stream to be subsequently transmitted on the path
to be established and if the path setup operation is
successful.
For instance, when the user station wants to
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- 16 - P. JOOS-W. VERBIEST 2-4
transmit a cell stream having the arbitrary probability
distribution function shown in Fig. 5, first the
corresponding complementary cumulative probabilitY
distribution function of the cell rate is determined and
afterwards a complementary cumulative Gaussian probability
distribution function enveloping this corresponding
function is determined. The mean and standard deviation of
this Gaussian curve are transmitted with the path setup
cell.
lQTo approximate this complementary cumulative
Gaussian probability distribution function by a staircase,
in the same way as described above with resPeCt to Fig. 4i
- use is made of the counters CRO~3 with the same increments.
~owever 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'O, P'1, ...... shown
in Fig. 5 are all not larger than the corresponding
20 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
3û the memory MEM shown in Fig. 6 to the communication with
label Ll and determines from the expected values of the
traffic ParameterS m and s the following other parameters :
MIS (measurement interval select) o a 2-bit interval
selection parameter to select one of 4 measurement time
intervals having a duration of A = 1024 x Z exP 3a
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- 17 - P. JOOS-W. VERBIEST 2-4
cells with a = O, 1, 2, 3;
M : an 8-bit number of cells with label Ll such that the
expected value of the mean m is equal to M~A;
S : an 8-bit number of cells with label Ll 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 Fig.
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
Bel~ian patent No 08701481 (W. Verbiest 3~ in each stage of
this nètwork 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. However, 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 Ll 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
Ll in the buffer circuit RBUF of the receive port RX, the
- 35 processor PR detects the presence of this data cell it
200~75
- 18 - P. JOOS-W. VER8IEST 2-4
transmits to the memory MEM a partial memory address PA
which is function of the label Ll contained in the data
cell. It also stores the following parameters which are
updated upon 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 L1 was received;
CCR : the contents of the cell counter CCR;
CRO~3 : the contents of the credit counters CRO'~;
CRI : a 4-bit cell rate interval indicating one of 12
cell rate intervals CRIO to ~RIll (Figs 5~ 6).
The clock extraction circuit CEC extracts a blt
clock BCL and a cell rlock CL from the incoming data cell
stream and applies both BCL and ~L to the control circuit
CC which in response thereat provides at its outputs Tl to
Tll a set of 11 successive non-overlapping timing pulses Tl
to Tll (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 realis~s a division by 1024
the resulting clock signal CL increments the cell counter
CR by l each time 1024 cells have been counted.
With a bitrate of the incoming cell stream 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 Megac-ells~sec. In this case each cell has a
duration of 4S6.67 nanoseconds and Tl to Tll each have a
duration of l~llth of this value. The control of SMC by
the timing pulses Tl to Tll is now considered :
Timina 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
2004375
- 19 - P. JOOS-W. VERBIEST 2-4
outputs sa and sb of the measurement interval selection
register MIS controlling the multiplexers MUXl/3 are on O
and 1 respectively, so that only the outputs s3, s4 and s5
of the stages S3, S4 and S5 of the counter CR are connected
to the associated comparator C04~ This means that the cell
counter CR and the multiplexers MUXl/3 are used to provide
the successive identities of measurement intervals having
each a duration of 1024 x 8 data cells~ The 3-bit value
MIC identifying the last measurement time interval during
which a data cell with label L1 was received is applied to
( the comparator C04. Finally, the cell counter value CCR is
applied to the comparator C05.
By the timing pulse Tl also the D-flipflop DFF is
reset. Thus the status output -signal ST of this flipflop
is brought in the condition O indicating that the cell with
label L1 is in Principle allowed to be transmitted further.
Timina Pulse T2
The processor PR loads the cell rate interval value
CRI and the credit value 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 Ll was received is comPared with the
- value stored in the stages S3, S4 and S5 of the counter CR
and constituting the identity of the measurement time
interval during which the data cell which is being
processed is received. If both the compared identities are
equal the output signal MTI of 004 is on O and in this case
MIC is the identitY o~ the present measurement interval.
On the contrary, when both the comp~red identities are
different the output MTI is on 1 indicating that the
measurement interval has elapsed and that the value MIC has
to be updated.
Timin~ Pulse T3
The processor PR lsads the values M-S and S~2 from
20~375
- 20 - P. JOOS W. VERBIEST 2-4
the memory MEM into the respective registers REG4 and REG5
and enables the operation of the decodeP circuits DECl and
DEC2. As a consequence the latter decodes the cell rate
interval CRI into the 15-bit increment code IO~14 according
to the Table 1. Thus one gating circuit is enabled for
operation in each of the groups GCO~5, GC6~B. GC9~11 and
GC12~14 (Fig. 3)
Timina Pulse T4
The processor PR enables the gating circuit GC15 so
that it is checked if the cell rate interval CRI is O or
not. In the former case the output ID of GC15 is on 0.
whereas in the latter case it is on i. As a result either
the gating circuit GC16 or GC17 is enabled, so that either
the value M-S or S~2 stored in REG4 or REG5 is ~tored in
the int~ermediate storage circuit ISC4 associated to the
comparator C05.
The processor PR also loads the credit value CR3
from the me~ory MEM into the like named credit coun~er 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 brought in the
position 1. Thus the receipt of the first cell during
the new measurement interval is registered;
- final}y, via the same gate G7 alsp the cell rate
interval counter CRI i5 reset due to its reset input R
being activated. Thus the counter CRI indicates the
identity 0000 of the first cell rate interval.
Timina Pulse T5
The processor PR loads the credit value CR2 from the
.
'
~01)4375
- 21 - P. JOOS-W. VERBIEST 2-4
memory MEM into the like named credit counter CR2 and
enables the intermediate storage circuit ISC3 associated to
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.
Timinq pulse T6
The processor PR loads the credit value CRl from the
memory MEM into the like named credit counter CRl 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 l's.
Finally, during the time interval T6 the comparator
( C03 compares the contents of CR3 and REG3 which stores all
1's and produces an outPut signal AL3 which is on 1 when an
equality is detected and on O in the other case. This
means that AL3 is on 1 when the adder circuit AD3 has
detected an overflow.
Timinq 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 ISCl and ISCO associated to
the adder circuits AD1 and ADO respectively. Thus one of
the increment values IN6/8 stored in the increment
registers IR6/8 and one of the increment values INO/5
Z00(~375
- 22 - P. JOOS-W. VERBIEST 2-4
stored in the increment registers IRO~5 are transferred via
GC6~8 and GCO/5 into the intermediate storage circuits ISCl
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
A02 is operated. This operation as well as that of C02,
REG2 is similar to that of AD3, C03, REG3 considered above.
This means that the output AL2 is on 1 when AD2 has
detected an overflow.
Timina 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 Gl are activated and if the measurement
interval has elapsed, the output MTI of C04 being then on
1, the~adder circuits ADO and ADl are operated. This
operation as well as that of COO. REGO and COl, REGl 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.
Timina Pulse T9
The processor PR loads the credit value CRl stored
in CRl 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 O of this multiplexer is connected to the output
AL if the cell rate interval CRl is 0,-1 or Z;
- ALO is connected to AL if CRI is 3 or 4 ;
- ALl is connected to AL if CRI is 5 or 6 ;
- ALZ is connected to AL if CRI is 7 or 8 ;
- AL3 is connected to AL if CRI is 9 or 10 ;
- 1 is connected to AL if CRI is 11 ;
Also the comparator C~5 is enabled so that it
compares the cell counter value stored in CCR with either
the value M-S or S~2 dePending Gn the cell rate interval
stored in CRI being the interval O or one of the intervals
2004375
- 23 - P. JOOS-W. VERBIEST 2-4
1-10 respectively. If the values compared are equal this
is indicative of the fact that the cell interval has
elapsed. In this case and when the output AL is on 0, or
ALB on 1, then the cell rate interval counter CRI is
incremented by 1 via the gate G~. Also the cell counter
CCR is reset via the same gate G5 in order that a new cell
count should be started.
iminq Pulse T10
The processor PR loads the credit value CRO stored
in CRO back into the memory MEM. In a first portion of T10
( and via the gate G4 it brings the D-flipflop in the
1-condition if the output AL is on 1. As a consequence the
status output 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 remalns in the
O-condition, or STB in the l-condition, then the processor
PR during a second Portion of T10 increments the cell
counter CCR by 1 via the gate G~
Timin~ Pulse Tll
The processor PR 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 Ll 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 on 1 or O respectively;
- by DECl the increment values IOfl4 for the previous cell
rate interval CRI stored in CR~ are determined for each
of the counters CR0~3 and by DEC2 one of the inputs 0,
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 O
and the new cell is counted by CCR. On the contrarY if
21~0~3'7S ''
- 24 - P. JOOS-W. VERBIEST 2-4
the measurement interval is the same as the previous one
MIC, CRI and CCR are not changed. Moreover, in both
cases it is checked by ~C15 if CRI is on O 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 mDre of these counters
reach a predetermined Positive credit value in which
case the corresponding output AL0~3 is activated;
- depending on the cell rate interval CRI previouslY
selected by DEC2 the multiplexer MUX~ connects one of
the inputs 0, ALO/3 and 1 to its output AL. More
particularly 0, ALO, ALl, AL2, AL3 and 1 are connected
to AL if the cell rate interval is 0, 1 or 2; 3 or 4; 5
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+S)/A, (M~2S)/A and ~M~3S)/A
respectivel~. 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=l) and when a number of cells equal to M-S or S/2
has been counted indicating the end of the cell rate
Z5 interval, the cell rate counter CRI is incremented by 1
so as to indicatesa 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 ~STB=l)
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 and 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
;2C)(:)~375
- 25 - P. JOOS-W. VERBIEST 2-4
predetermined credit value and when simultaneously the cell
rate is higher than a predetermined one the cell is
dropped.
While the principles of the invention have been
described above in connection with specific apparatus, it
is to be clearly understood that this description is made
only by way of example and not as a limitation on the scope
of the invention.
