AU623402B2 - Communication switching system - Google Patents

Description

OPI DATE 09/10/90 PCT. AOJP DATE 15/11/90 APPLN. I D 341379 89 PCT NUMBER PCT/EP89/00281 INTERNATIONAL APPLICATION PUBLISHED UNDER TII PATENT COOPERATION TREATY (PCT) (51) International Patent classification nt ntlii~pt~kii~tu WO 90/10984 "'Oor 15 43) International -Pulijjcgon Date; '-20 Se-r-mbcr 0990 (20,09.90) (21) International Application Nnmber: PCT/EP89/00281 (81) Designated States-, AT (European patent), AU, 1BE (European patent), Cl- (European patent), DE (European pa, (22) International Filing Date,, 14 March 1989 (14.03.89) tent), FR (European patent), GO (f uropoan patent), IT (European patent), JP, KR, LU (European patent), NL.

(7l)ppl~ant/brf~anykEELTEEPI-ONEMANUAC. (Etuopean pptent), S. (European patent),,US.

TUIRING COMPANY, NAAMLOZE VENNOOTS- CHAP LflE! lEJ; Francis Wellesplelii 1, 13-2018 Antwerp Published (B Wih jiltrntionial sgtirrch report.

(71) Applicant C/br all dcs~gnatee States escept BE6 US): ALCAT- El, N.V. ILINLI;, Strawlnskylaan 341, NI.-1077 XX Amsterdam (N4) (72) Invenfort and Inyentor/Applicant (for U$ onjlvy) BAR 1, Peter, Irma, Ali.

gust~~~ ll,/EI Jag edsra 12820 Bonheident (13 P,) (74) Age ntst VERMEERSCI-, Robert Qt al., Patent Depart.

ment- Bell Teephonec Manufacturing Company, Naan'loze Vennootschap, Francis Wellesplein l, 11.2018 Antwerpen (54) itk; CQMMW -iJN TIQN SWITFCH NQ SY$STEM RX4 (57) AbstractI Communication switching system wherin for eahp eelsra~to be transmitted through a switching element a 94UF virtual path is established fronm an input link to an output link of this element on the basis of the Individual bandwidth used by this cell stream and of the thent calculated total I C, -TMX4 P bandwidth used on this output link, For each cell stream, a

APU

Maintenance cell containlno the individual cell stream band- P~ width is transmitted on the correspondintg virtual path ari by mneans of these maintenance cells the total banowidth lr used on each output link Is revcalculatcd and it ii chcked If It Is equal to thie aboavc-metioncd calculated total band. f width, The latte is adjusted if a difference Is detected, LRT 2, A X- A SB MEMI 13 T I

T~T.

Sect 13 WC;90/10984 PCT/EP89/00281 COMMUNICATION SWITCHING SYSTEM The present invention relates to a communication switching system includinig a switching network with at least one switching element having a plurality of input links and at least one output link# and proqessing means for calculating the total bandwidth used by Virtual paths on said Output link from, individual bandwidth values contained In path setup Cells used for setting Up said virtual paths, 1 OsucSh a communication switchina system if, already described in the PCT application No PCT/ P88/0O40?, In this known switchino system the total bandwidith used by the virtual paths o:n anl Output link Is obtaine4 by calQulqtlng the sum of the Individual. bandwid~th values contained in the 1S path setup cells for these paths. A new virtual path As allowed tQ be multiplexed on the output link only when the thus calculated tot4l. bandwidth is omaller than- the maximu allowable bandwidth.

The t huA calculated tcal bandwlidth may be erroneous ZO due to a faulit for instanc e because an individual bandwidth value 1,s errQneous# or due to a calculation error# etc, Such o fault may viVo rise to a traf fic overload on the Output link or to an undue restriction of the traffic load on this li1nk sine the decision to allow or inhibit the Multiple~nX n Of a neW Virtual path on an output link is based oon thoe thus calculated total bandwidth, I I I -~rcap r~ WO 90/10984 PCT/EP89/00281' 2- An object of the present invention is to provide a communication switching system of the above type, but wherein the effect of previous, especially temporary errors, on the calculated total bandwidth is reduced.

According to the invention this object is achieved due to the fact that said processing means re-calculate said total bandwidth at least from said individual bandwidth values contained in maintenance cells transmitted on said virtual paths and adjust said calculated total bandwidth in function of said re-calculated total bandwidth, By thus recalculating the total bandwidth the effect of temporary errors which possibly occurred during a previous calculation is reduced if not eliminated, Another characteristic feature of the present communication switching system is that the transmission of said maintenance cells is interleaved with that of said path setup cells and that said processing means store said calculated total bandwidth in a first memory and at the start of a recalculation operation copy said calculated total bandwidth from said first memory into a second memory and reset the contents of a third memory, the total bandwidth stored in said second memory and said individual bandwidth values being then used to re-calculate said total bandwidth in a cumulative way and the successive partial results thus obtained being stored in said third memory.

Still another characteristic feature of the present communication swjthing system is that the transmission of said maintenance cells is also interleaved with the transmission of path release cells containing an individual bandwidth value relating to the virtual path to be released and that said processing means in addition to performing a path release operation process each of said path releaso cells in the same way as each of said maintenance cells.

Hence, although the normal operation of the system 1

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WO 90/10984 PCT/EP89/00281 3is continued, i.e. although virtual paths may be built up or released and thus give rise to a change of the contents of the first memory, such a change has no effect on the re-calculation operation since the latter makes use of the contents of the second and third memories only, In other words the bandwidth re-calculation is isolated from the normal bandwidth calculation.

The above mentioned and other objects and features of the invention will become more apparent and the invention itself will bebest understood by referring to the following description of an embodiment taken in conjunction with the accompanying drawings wherein Fig. 1 represents a communication switching system according to the invention and details of a switching element BSE used in a switching network BSN of this systen; Fig. 2 shows an example of this switching network BSN i Fig 3 represents the rents e eceive port RX4 and the control circuit SEC113 of a switching element E113 of Fig.

0O 2 in more detail; Pigs. 4 and 5 show the structure of a path setup control cell and of a maintenance cell respectively used in the system of Fig, 1.

The communication switching system shown in Fig# 1 is of the type described in the PCT application No PCT/EP88/00482 and includes a multi-stage broadband packet or eell switching network BSN having a plurality of input terminals II/N and a plurality of output terminals 01/N, as well as a plurality of user stations US1/N or outside nodes each comprising a sender equipment SEI/N and a receiver equipment RE1/N. The sender equipments SEI/N are coupled to the input terminals Il/N of BSN via respective asynchronous time division (ATO) or asynchronous* transfer node (ATM) input transmission links ILl/N and respective Anput interface circuits 111/N. The output terminals 01/N WO 90/10984 PCr/EP89/00281 of BSN are coupled to the receiver equipments REl/N througoi respective output interface circuits 01/N and respective ATO or ATM output transmission links OLI/N, Each of the user stations includes a traffic measurement equipment of the type described in the PCT application No FP88/01037.

In the cell switching network BSN the N input terminals II/N are coupled to the N output terminals 01/1N via a number of cascaded stages of switching elements or inside nodes of which only one, BSE Is shown in relative detail, This switching element has f$ Input terminals R1/8 connected to respective output terminals of a preceding stage via multiplex Input links (riot shown) and Es output terminals Ti/8l connected through multiplex output links.

(not shown) to respective input terminals of a following stage (not showi), This means that the switching element BSE may be considered as having 8 bidirectional terminals Ri/Ti to R8T8 oach connected to a bidirectional multiplex link on which a pluralityi of commtunication paths may be Inieteswitching lmn S!teip~ o multiplexed,. inid then 0Ete n~ terminals R1/8l areo connected to respective Input or, rereive ports RXI/6 which have a cell Output P and an address output A and which are further connected khrough ain Interconnection bus SB to a 4witdhino element common control tiroult $CC. The cell, outputs P Are0 Connected t-o inputs 1/8 of a Time Division Mujltiplex~ (TOM) intorconnection bus TB which is 0ontrolled by a control unit TM: to which the address outputs4 A of the receive ports RXi/fl oar connected, Eight ootPuts 1/8 of the bua TO are connected through rOespeCtive Output or transmit ports TX(1/4 to respective output termoinals TI/S and a ninth output 9 is connected to the control cirouit SeC via A transmit port TX9 havino terminal T?.

An example of th~e switchino network ASN Is roproented in rig 2 and% is also of the, typo disclosed in WO90/10984 PCT/EP89/00281 the first above mentioned PCT application. It is a folded one, with both the input and output terminals on one (left) side and a mirror plane at the other (right) side. Between a terminal used as input and the mirror plane, BSN is a distribution network where the path selection may be performed freely, whereas between the mirror plane and a terminal used as output it is a routing network wherein the path is predefined. A path selected in the distribution network may be extended in the routing network to any of the outputs, The switching network BSN includes three stages of switching elements whose terminals 1/8 each represent both a receive terminal Rl/8 and a transmit terminal Ti/8, These three stages of switching elements can be used to interconnect a terminal used as input with a 1$ terminal used as output through as many as five stages, While the third stage on the mirror side comprises four groups G31 to 634 each With four elements E311/314 to E341/344, the first and second stages each include eight groups each also with four elements Merely to illustrate a possible connection through five stages, the groupsi of the first stage have been labelled G11 to G14 and G51 to G54 and likewise for G21 to G24 and G41 to G44 constituting the second stage. Thus, with only groups Gil, G21, G31, G34, G44 and G54 shown on FPg, li a possible connection involving links L2~ LS3, L4 and L5 passes through QI and G54 both of the first switching stage but 011 being used as the first stage of this particular connection and G54 as the fifth, Likewise for G21 and G44 both of the second switching stage but With G21 as the second stage of this particular connexion and G44 as the fourth, But such connections in a folded network may also involve only 0G1 to G14 or only G51 to GS4 in the first stage and likewise for G21 to G24 or G41 to G44 in the second. The interconnection between the groups and the elements is such that the first group of the first stage can only access the WO 90/10984 WO 9010984PCT/EP89/0028 I 6 first groups of the second stage and likewise for the remaining 7 groups in these two stages. For each such Pair of groups, each of its 4 elements has access to the 4 elements of the paired group. Since there are only 4 groups in the stage, the 8 terminals of each of its 4 x 4f switching elements can be associated with 4 terminals of each of the 8 groups of 4 switching elements of the second stage also on a one to one basis, each element of the second stage having access to all groups of the third stage and vice-versa.

Fig. 3 shows for such a switching element as E113 i~n Fig, 2P the essential Parts of its receive port RXq and of its control circ-uit $EQ1l3.

Theq receive Port R)(4 includes a receive buffer RBUF4t a processor RPR4, a routing table RT4, an interface circuit 104, a Packet multiplexer PMUX4, an address multiplexer AMUX4 and a ca1culat$on circuit CC. The above mentioned bus SB is connected to the ititerface circuit 104 which has access to the processor RPR4 and to rooting table ZO RT4 arid the latter table is coupled to the Processor RPR4 which has access to the buffer RBUF4 and to the calculation circuit CC. The buffer RBUF4 has a cell input F94 and a cell) output P Which is connected to an Input of the cell multiplexer VMUX4 whose output is connected to the 28 calculation circuit C' A, cel~l output P of the interface circuit 104 is connected to another input of PHM4 The processor, RPR4 and the interface 104 further have outputs A which are, canneuted to r'espoctiLVe Inputs of tijo address rnUltiplexer AMIUX4 The multiplexers PtIUX4 and AMUX are controlled by the Interface circuit tC4, The outputs P of the calculation cir"cuit CC and A of the multiplexor AMUX4 constitute the outputs of the receivo port RX4.

'The switch element control Circuit SEC113 includes a 3$ processor PRilS% and an associated memory MEK113 which WO 90/10984 PCTIEP89/0028 I -7includes, amongst others, tables TI to T5.- The contents of Ti to T5 and of the above routing tabl~e RT4 will be described later.

In the present, system cell streams are transmitted comprising data cellsp control cells, e-g. of the type described in the first above mentioned PCT application and maintenance cells. In the following only the function of a path setup control cell, a path release control cell and a maintenance cell is Considered in detail,.

The structure of a path setup control cell is schematically represented in Fig, q. It Includes A header H and an information field IF. The header H. identifies the cell and includes a header error checking code, In the information field IF T ;is the type of cell, e.9, a Point-to-point Path set up control Packet; RT is a, routing tag containino for Instance five sets of 4 bits,, Each sot defines a respective one of the 16 terminals or links5 of a swtthing~ element and the zo sets- are assoCiated to respective switching elements of the five stoges via which a c0nnection may be sO is a selection code Indicating for each of the termitnals1 of RT if the selection thereof hai; to he, performed freely (FS or Is fixod (IF); LL are lAbqls AdentifYino the communication Paths or! the links of a connection; RP tIs the identify of a reO-urn Path In. th~o network;

LP

1 t are troffic load parame~ters cahoactorizIno the Indlividjual bandidth Used by A cojiX Stroam, Otii the, Average and Variancep as describad- In, tlO CUroan patont APP1104t$Qn 88202852.5; CRCt iIs A chock code whi~ch IA function of the contents of the Informaetion; field IF and used to chock tho la t t 0r PCr/EP89/00281 WO 90/10984PC/P902I The structure of a path release control cell is not given in detail but may be found in the second above mentioned PCT application.

A data cell includes a header constituted by a label identifying the virtual communication Path used on the link on which the cell is transmitted and an information field which comprises data.

The structure of a maintenance cell associated to a virtual path or cell stream defined by its traffic parameters is schematically represented in Fig, 5, It includes a header H and an information field IF, The header H is of the same type as of a data cell but includes a single last bit indicating that a maintenance cell is concerned, In the information field IF T is the type of maintenance cell;' F is a field to be modified in the switching element wherein the Pell Is procesed; X iIs A field containinq, amanst others, the Identity of the squrce of the cell stream and the abovye mentioned 2, 0 traffic load, parameters LP.

CRC: is1 a check code which is function of the contents of the information field IF and Used to check the 1at t e.r II, Roferonao~ 15 now made to Flost 2 to S for the 2S description of the establishment of a virtual communication path between An origin~ating user statIon UI$14 and a dostinition usor station, US823, To establish sUch a path thet User station US1:3( la'.nchos s path setup: control cell (Figi 4) which, 4mongst 3o others which are not considered here, contain:; the following fieoldst f, RT Ll X# FtX X API X* 0 X# X

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-ca W0O90/10984 PCT/EP89/00281 9 with X undetermined; FS free selection; F fixed selection.

This means that for the path to be established the selection of the output link to be used is free in the first and second stages of the network, that the output links 8, 2 and 3 whose identities are stored in the cell have to be used in the following three stages of this connection, and that the label LI is to be used for the virtual communication path on the link interconnecting US134 and the first stage of the network, When this cell is received on the input terminal R4 or input link 4 (Fig, 2) of the receive port RX4 of the switching element 1El3 (Fig, it is entered in the receive buffer RBUF4 thereof under the control of the processor RPRQ. This Processor reads the header H of the packet and a checking circuit (not shown) forming part of the buffer RBUF calculates the check code for the information, field IF and verifies if it is equal to the check code CRC of the cell or not# The result of this check is communicated to the processor RPR4 and when the latter detects that the header is a data cell this result is ignored since it then has no meaningq whereas otherwise it is used to continue or stop the processing of the cell, To be noted that if the cell were a malntenance cell the processor RPR4 would enable the operation of the calculation circui CC, However, because the cell is a control cell and sUpposing that the code check is successful the Processor RPR4 does not enable the operation of the calculation circuit CC, Instead it performs the following operations: it writes the address 4 of the input terminal or input link 4 (or R4) on Which the cell is received and of which the corresponding output link has to be used by a returtn or backWard cellb in the first position of the WO 90/10984 PC/P89/0028I return Path field RP of the cell, so that this field becomes; RP 4, X X, X, X and then supplies this cell from RBUF4 to the cell multiplexer PMUX4;1 via its address output A it applies, the address 9 of the ii output terminal or output link T9 of the transmit Port TX9 to the address multiplexor AMUX4; The processor RPR4 then controls the interface circu it lc4 In such a way that the latter operates the multiplexers PMUXe# and AMHX4, As a czonoeqence, from those multiplexers the Path setupp cell is supplied via the otut P o the :.*nput 4 (not shown) of the bus TO and the address is communicoteJ via the output A to the control unit TM of IS this bus TOAs a result the control unit TM connects the Anput 4 of U8 to the transmit Port TX9 and tran-smits the ce14 thereto, The latter port then routes the nel tS the skitcktng element control circuit vSC1 its outPut t Upon. the receipt of the path setup control qeli in ZO the C0rntroI Circuit 8'Ml the processor P~RI13 thereof performs the functions described hereinafter,, This processor PRI13 selects an utPuMt terminal or OUtput link of the switching elemient E114* eu, T8 or &o on i ths ~an~taiP th oetup cell, and late~~slar ata ifa:~-f which the Pit eu e~ n ~o the d.t cells ot the ~ecl stream tfoluwinq it) have to be transmitted to the secorni stage or jnod of the switching network 1 In the W ay described In the ibove European pRnt 4 ;application tho Processor PRI13 calculates the new bandwIth; on this link bYi means of the Previously calcu4tlCtef $Q bandwidh value or load coUrter value storeo in tad4s TI of the MEM113 and the traffic load Paraimete-rs Lf contained In. the cell, It then checks if the newly calcusXate( b~ndwidth or now ioad countpr value i s maler or lrger th:n the maximum alelOWabe bandwith B(O) Also 3 S %ctred in taibe T1 of the MEM113And Amcorcaingy i:iow3 the WO 90/10984 PCr/EP89/0028 I control cell to be multiplexed on the selected output link 8 or refuses to do so, in the latter case the processor sepects another output link and Performs similar calculations, etc. in this waY either a suitable ouItput 6 links ieP suitable virtoal qommunriaton, Path thereon, is found or not and in the latter gase the swithlnoj element ell is considered to constitute a blocked end for the qommwnlcatiton under 4onsiderotion, In the folawin oIt is supposed that F1Z is not i4 blocked end and that otp)ut link 4 may be used..

Under this assumption the Processor PRI11 selects- in MH113, a new lab01 L2 to indicate the selected virtual communication Path on this output link 8, The prcessor PRI13 also writes in the routing table RT4 of the receivo polrt RXet the routing information or relationship W Ot El linkingl the input communication path with label 41 on nput link I with the output communication, Path with lAbelI eZ on Output link 4 and with a busy/idle bit Ll oft I indOicaing that the virtual path is busyi (otherwitq this -Q bit is on This happOIs via the bus Bfl and the interface circuit I<C4 of this Port, The proeCssor FIRIft also ritprf H-i bit Ul in the table T2 of its memiqry t1EM113 t a havin the cooriates R4, L., Fnally# the Procssor P~RI13 also modifies the contents of the Path setup cell by Wr iting B nd L2 in the first pitins of the fields RP and I reOtivelV by changin g FS in the first position~ of SC by F Anid y then Sub4,cting RTf and SCto a circular shift in IntA-clckwiael direction. Thus the fields of thet celi become j, gQ iT tk P~ r; LL LZ* W#X Xi Xt Xt X The thu3 modified cell ind the addresN 8 are then transmAtted via the bS to one of the redeive Ports

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Vi WO 90/10984 PcEP89/0281 12 RXI/8 e.9, to RiX4 and more particularly to the interface circuit IC' which supplies the cell to the cell misltipiexer PMUX4 and applies the addre-ss 8 to the address mul :~.~xer AMUX4 via its outputs P and A respectively, Under the control. ol the cell is then transmitted from these multipleers and via the bUs TB to the transmit port TX$.

13Y this transmit pairt TX8 it is a4fterwards transmitted on the output link 8 of Eli$, to the input terminal 3 of the switching element 21 where operationsi similar to those V 10 described above are qxqcukted, etq, Thereby' the field. RT# V SC, LL and RP of the cell Ore modified as follows in the switching elements or inside nqdes B14, E14# 5t44 and F$4Z If these noes are not found to be dead ends and before being transmitted therefrom to a following node I RT 82 65; 2858; 38S82; 85823 SC FFFFF FFFFBF FFFFF; PFFF LL L3L2LXXX*, .4IL3 2LIXX; L5L6L3L2LL1X L5L41L32LI RP 3(sXXX, 134XX; S14X; 85134 in this wa-v the point-to-point virtual Path shown in o Figp. hs been established. TO bnodh this connection is similar to ehat derios(bed in the first abovo mentioned PCT applictin.e This, connbection- is as folilwst user station U$S14, link i1i34 en which tho COmMUniCAtion.

label Li is used, 1i134, R4 and T81 of Ell$# output link 0.

2 an which the label L? AS Used# R2 4n4 T5 of E24 output link 5 an which label L3 is used, RI and r8 of E314, otput link 8 on whichi label L4 is used, R5 andi T2 of E44* o# utPt link o an which laiel L5 usedi R8 and T3 of E562p 01823 .and Output link OL823 on wich label I. Is used., F I rom the above it follows that subsqqoont tO tho Successful tansidissin of a virtual path setup qontrol cell usiri% the iiput liR R4t and the output ltiRk 4 qlemqnt L13the tables RT4# TI, And T2 store the followino informastion rola1tino t.0 t5d virtual iath t RT4 stores LIP L, i &c El with$ EI 1; WO 90/10984 PCT/EP89/0028I 13 TI stores -the newly calculated bandwidth or load counter value B1(8)for output link 8; T2 stores the bsy/idle path bit E1 1 in a location determined by the coordinates R4 and i, S In a similar way as dcribed above other virtual paths are built up through, the switching network) as a conseuence of which the routing tables of the receive ports as well as the[ tables TI and T2 in the memory circPits of the qommon control circuits of the switching elomeoits are updated, As an example, the routing table RT4 and' the tables T1 and1 T2 Qf the meror MEMll of the SKll1 for instance stcre the following Information i RT4 i LW# 4Zt at 1 with: El 1 L~7 L8 Z with E2 1 for virtual paths using the output link a of E1$; L L1Q, 4,i w;t 1 f o r a virtual path using the ourtput link i of a toFe-,Other with 811,) t the allowable r2 l 1, E 1 1 in the locations having coordinates t4# Llt4 R4, L7 andt R4) LO ard E 0 in the other locations, A4tOr the establishmet of the above virtual 'pathst ,2 5data cell 51trams are transmitted thereon by, the u,-er stations, in Oach of these stations the traffiC Mea~uroont equipment Included therein checks for each cell stream if the corrosponcing traf f ic load paraieters on the basis of which the mpltiptleing of this call streanm oni on 0 output link w&as allowed are respected. This traffic msUremeint equipment als o dacapts the cell streams if recquire, e.j by dbciroppi ngcls. BY Proceedinu in thi4 waY it 1$ ensured that the traffic: lo0id pgrameOars reflect the exact traffic load and vice versa.

With the purpose of checking tho corractnoss of- the I ;I WO 90/10984 PCT/EP89/00281 14 various load counters stored in the tables Ti of the memories ofi the various control circuits each of the user stations from Which virtua- paths have been established transmits on each of these paths a series of maintenance cells at a predetermined frequency, These maintenance cells are interleaved with the path setup cells. The frequency and the length of a measurement time interval are so chosen that in each control circuit associated to a switching element and with a very high probability, i.e.

with a negligible loss, at least one maintenance cell is received on each of the virtual paths using this switching Alement.

As an example, when the maximum rate of the maintenance cells Is for instance equal to 100 Per link and 1$ per second and when the number of Virtual paths per link is equal to 8000, then the time to transmit one maintenance cell on each of these paths is equal to T80 secondso One may then calculate that for Anstance for a switching element having 16 input/o-utput links the measurement interval should be taken equal to 4T in order that the probability of loss of a maintenance cell in these links during this interval should be negligible, To be noted that the measurement intervals follow one another in a continuous way and are each initiated by the processor 2S PRI13.

Each such maintenance cell transmitted on a virtual Path contains the traffic load parameters LP definino the individual bandwidth of the cell streams oh this path, 0ocause these parameters are monitored by the traffic 0 measurement equipment they are indicative of the real bandwidth used on this Path. Por InStane, the user station US134 (FiS Z) enerates a series of maintenance cells for each of v the Virtual paths on the input link R4 of the receive por RX4 of the switching element E113# these virtual paths being defined in the routing table R4- I WO'90/10984 PC1/EP89/0028 1 At the start of each measurement interval the processor PR113 forming Part of E113 copies the load counters B1(1) to BlC8) of the switch element E113 and the E-bits of all the virtual paths on the input links of this element from the tables TI and T2 into the tables T3 and T4 respectively, It also resets all the so called auxiljary or shadow load counters SB() to SB1() stored in a table These measures are taken in order that the bandwidth re-calcuJation operation should be independent from chan-ges of the virtua. paths and therefore also of the bandwidth used on the links, in connecton wih the above it should Also he noted that as lonq it is storied In the routing tablde RT4 or T.It A I path bit E Indicate$ thjat the corrspondng virtaI path is 1$ busy or idle whoeea when i stored in the table T4 it indcipates that a maintenanco cell recsedO on the Corresponding Virtu.a j. pth has to be procesd or not by the processor As an oXampJle, the functlQn of the first of A Seraos Za of maintenane Cells reolatjnV to the virtual path L1lf Ot 0 defined In the rvootlno table RT4 and taeQlved during a measuremlent interval 1,s considere4d What! this first mointananca cq el is received in theq receive buffer RBUF'i Its- Check code C'RC is verified in the $same way as described above for, a Path setup control cell, Hwever, if this check is OCos!;fi4 the procesor RPRe# upon cJotectinu from the last bit of the header of this cell that a maintenance call2 i~ Comerned cisn uqt the routing tableRTf4 by means of tho 14bol, L contained i the heade~r Ono use4 this Infrr, Uatn As f&lows; f it $ubstlttutes L2 for U In. the cell hacdor; It Inserts the 1derttV R4s Of the input link, In this Information sAnd w~r9i te tho folawinfg da1t I r rW WO 90/10)984 PCI/EP89/00281 16 Ll, R4, 8, El in the field F of the celli Li, R4 and L2, 8 define the virtual paths on the input and output links respectively it then applies the thus obtained cell to the input P of the cell multiplexer PMUX4; it oper~ates the calculating circuit Cc in order that it should calculate a new check code for the information flkqld IF and sUbstitotes this conde for the old one.

ic Such a calculation is required because the F-field of the coll has been changed; It applies the addresses of the output links 8 and of the transmit ports TX8 and T to the input A of the address multiplexer AMUX4.

is The procsse4.r RPR4 then, controls the interface circu~it TC4 in such a Way that the latter operatqs the multiplexors PMUX4 0d4 AMOX4 As a 06nseqlUncq the min~teanoe coil is supplied via the output P to the input e of the bus TO and the aIddressos 8 and 9 are cmnionmimc4tod 2 0 via the output A to the. control unit TM of this buo As a resul the control Unrit TM connects the input 4 of TB to the transmit PortO TXO and TX9. The transmit pert TX8 then transmiit the cell to the follown0 sWItchjitnj Plemant E214t vI@ its ULItPLlt T8, whilst the transmit port TX9 sulies hth z4el to the switoehino element control crircUIt $rC113 VIA Its outpurt T9.

In the swithihn elment E216 the itAintennnQ cell Is proCqgS$d in a, slmilor Way as in the owoItchino oomsant t113 Ond t4s procOS.41Si Will therefore not be doscri-od $0 furhort 0ut It is clor that byi Procodina in this way the mointnaonoe cell w 'll, finally' be transmitted to tho destintio station if the path is not Interrupted, In other' words the mainteance cell Maoi be used for An ond-to-ohd VerifiCation of the path continuity, 3$ The maintonance coil supplied to SrC114 Is store d In W6 90/10984 PCT/EP89/0028 1 17 1.the memory MEM113 thereof and is then locally Processed by the processor PR113. More particularly, the latter uses the information R4, Li stored in the F~field of the cell to address the table T4 and to find therein the corresponding E-bit, i.e. E!l 1, Because this bit is on 1, as the maintenance cell is supposed, to be the first maintenance cell transmitted on the virtual Path L, LZ using the links UR4 and the processor PR11l3 Processes this Pell,, More particularly, it re-caloulates the total bandwidth used on the output link 8 fro.m the individual bandwidth defined by the traffic paaeters LP contained inthe X-field of the P ell and f rom the Previously Galculrtod bandwidth stored in I' the auxiliary load counter S81(a) Associated to this output link, 8, and found in the table TS by means of the Identity 8 of the output lJink, stored in the F- field of the cell.

PRII stotres the cumlative sum Obtained in this Auxiliary load counter SB1(8) associated to the output linkt Afterwards the processor PR113 re~ets the bit 01 to Of thus indicating that on- the virtual path Llo R4, 8' a first ZQ maintenance qell has4 been received arnd Processed and thot fur1ther maintenance cells on this path are not to boe In a similor way the load counter 941(o$) is again updated upon receipt, during the measuremenit Interval of the first maintenance cell on the virtual path OfL7 O 8# E? Including the output link 8, and the load counter S~t(4) is Uwidatqd upon receipt, durinoj this, Intervals of the first malntononco cell on the Virtual Path L~s LXOP 4t E3 Including the output link Ct Also the bits and E3 Are than resot in the table T4 thus indichting that a first maintenance cell, has boan reeived on these virtual Paths And that further mAintenance Cells received on these Paths shotfld not be procesed.

In the COUrSO Of A meaSUremeni. Interval it may 3$ haopn that a Virtoal path Is addod or released And in both WO 90/10984 PCr/EP89100281 cases the contents of the. tables TI and T2 are updated. in the first case no updating ol the tables T3/6/5 is required since the updating will take Place during a following measurement interval. On the cpntrary, in the second case precautions have to be taken beqawse the individual bandwidth of the released path on the one hand is already included in the total bandwidth information stored in the third table T3 and on the other hand It has not yet been taken into account for updating the corresponding auxiliary' 410 load counter when: the corresponding E-Ibit is still on 1, Also because of the path release no maintenance cells will it be received, For this reason the path release cell in addition to its path releasing Ifunction performs the same function as a 415 maintenance cell, in the tables T3/V/5, This is describedf Such a Path release cqlj Is generated in the manner described in the first above mentionopd PCI application when a dead$ endt of a virtual path Is detected In a node and is Zu Interleaved with the maintenance and Path setup cells, The Path release cell contains the Individual bandwidth information defined b-Y the traffic parameters L~P, Upon. Its receipt an Q,9. the above receive part RXA the processor RPRO thereof Inserts the identity R4 of the input link in the cell and routes it to the control circuit SEC0113 in a1 way tsimilar to that described AboVe for a maintenanrze ooll.

if the corresponding e-bit is In the set condition the processor PRI13 then increasos the contents of the, auxiliary load counter $91(8) In table T$ by the Individual bandwidth of the cell and resets the corresponding n-bit in table T4* In the usua~l wayt It also clear$ the connection by updatingj the tables Tl TZ and RT4.

As montioned above the measurement in-tarvol Is so chosen that, during this interval and with a Very high Probability -at, last one mointenance cell Is roceived for W0'90/10984 PCT/EP89/0028 I -19 I each of the virtual paths on all the input links of E113.

As a consequence at the end of the measurement interval all the E-bits of this table should normally be on 0 and the auxiliary load counters in the table TS should all be in a position equal to that of the real load counters B1(1) to B1(8) stored in the table T3 Differences only occur in case of error, e-g, when the values Bl~i) to Bl(8) are not correct and/or when the calculation has f ail1ed.

IAt the end of a measurement time interval the processor PR113 therefore compares each auxiliary load counter value stored In table T3 with the copy of the corresponding load. counter value stored in table TS and in case these values are different it algebraically acdds this 4 difference to the respective real load counter Value stored in table Ti! Thus this real load counter value is I adjusted.

In case at the end of a measuirement time interval one or more a-bits of table T4 are still on 1 thi's means ii that no maintenance cells have been received for theo corresponding virtual paths These Paths are ponsidered to Ibe I.4olateO ones and for this reason the Processor PRI1 Iresets these e-4its to z4ero in both tablles RT4 and TZ When all the -bjts of table T4 Are on 0 before the Vend of a measurement Inteotval the proqcessor PRI14 may either already start the Pd,~ustrnent Poration or Perform other fonctions, iiit should be noted' that instead of being trans!mitted'C by the usear statlorns the various cells could also be gienerated in other terminal circuits suh ais the interface O circul'ts While t'ho principles of the invention hove beon describod aboVe In connoctionv with specific apparatus# It is to be cloarlp understood tha*t this cOscriptiah Is made only by way of eXAmple and not As a limitation on the stoPa of the invention,

Claims (2)

1. 9. 9~ 9** 9. i 9. 9 04 9 4 Thc claims defining tho invcntion arc as follows: ,A conmmilcation switching system including a switching nietwork with at least one switching elcnint, having at plurality or inpuit links and at least. one outpot link, and processing means f~r caIlulating the total bandwidth, Used by Virtual Paths Onl Salid outpult link from Individual bandwidth valucos contained in path sotuip cells used for Setting uip 'sid Virtual paths, wherein thc said proccssing mcains recalculate said total bandwidth at Icast from said individual bandwidth vaIles contained, in mainte- nance cells transmitted on said Virtual Paths and adjust Said Calculated total band- width In function Of Said r-alulacd toal adil 2. A com n icatLion switching system, according to lm, 1, wherein the trans- mission ofsidd maintenaince MIlS Is in'terleavedl with that of said Path setup cells and1( that Said processing means store said calculated. totalf bandwidth, in a first memory and at the start of a ro-caloulationl opet'atlon copy Said calculated IotalI ban1dwidth from said first memory into at Seconld memtory and re0set, the con tts or' a third SMemory, the total blandwidth 'Stored[ Inl said second memriory anld said individutal, bandwidth. values Contained Inl sai aitnac cells being then used, to ro Oalotflate said total, biadwidth andt( the sulccessive partial resuilts thS obained, buing stred, In said third memnoty, 3. A (otfinieatiofl wxitching systemn accordling to claiml 2, whlerein Said ma1"in- 20 tenanc ell areS tramite on said virtual paths aIt at frequency "'uch thilt with, a predetermined probabilit'y and rl each of said virtual, paths oil said output link atf least one mla interanc lcel IO S rCeiVed by said pro-0cessinlg meWaS(11 durng at measuremlent, tinwe interval, &onch m in tiltnIce coil, Containilng Said individual hn itwidth valueo for thc path0 onl which it. is tralsiitied, and thatI said processing meaC.ns Co~eftlculatc Said Z$ total, banidwidth onl said output link dttrlnF said 1'masureent interval. 4, A% commnunication swltchlng. system according to claimn 3, wherein in that said moStitementL intervals follow one another In a continuouts wray, S. A. coninunicatlouN itching tyetem according to cli 3, Wherein is inclded, a fourth memory storing for each of said vitual path) R path hit Whose SeIt/t is indicative of, the busy/idle coniditioni of this path and that said processing ileens at the sLtr or said nwisurcnmnt interval copy thea pa'th bit'. of said fourth mormory into at fift memory, the vdtrest condition or each or the c lqtq then IUnii. cating that a intenance cAl rvecived ont the corresponding path is allowedI to/preventedl froml heing processed by vtid process ing means aind tie hit hcirtg reset Safter, suelh processing,. woo 44 4 9 .4 .9 .9 9 4.4 49 44 9 9 4 9 9949 44 44 4 9 9 9* 4 9. 9 9 4 .9 eq .9 99 9 4 .449 9 4 4 4 .94. '9 .4 4 494 94 4 q. 4 94 4 9 6, A commuinication. switching systcem according to claim 2, wherein the trans- mission of said maintenance cells is also interleaved with the transmission orf path release cells containing an individual bandwidth va1lue relating to the Virtual pIah to bc released and that said processing means in addit ion to perfornming a path the rc- lease operation process each of said path rclcase cells in the same way as each of said maintenance cells, 7. A commu nicatLion swvitching system, according to claim whereCin Said proc- cssing 1mans perform, Said adjustment at the end of said mea0"surceent interval, K A communication switching systemn according to claim 5, wherein said proc- essing menas perform said adjustmnta aftor all the path. bits of said fifth memory have been rest. 9, A conimunicationt switching systomn according to claimn 2, wherein said proc- essing meants after havinig rc-calcu fated said total bandwidth, and having Mtore it in said third memory calculate the difference of said re-ealculated bandwidth and the 1$ corresponding calculated total banidwidth stored, In- said second momory and algc- braically add thi difference to the corresponding total bandwidth stored in said first memory, this bandwidth being thus aIdjusted. 10,~ A communication switchinag system accordling to claimn wherein said Switefh- lag element each of smid input links is coupled to a receive portL inludtingl second. 20 pro'noslng means and a sIxtii memiory aind having access via switching meians to any or a plurwly of output link as wel as to a preyletcrmined output link which is corte tinuously connected to at control circuit icludig said first mentioned processing means and said first, second, third, fotii'th1 and, firth memorics,
2. 11. A communication switching syStem' 1QC01r(lhng tO claim' 10, wVheretn SUblsequent zs to the rocefit of a said path. setup Cell on an input link of Said rceive Port lit is transmlttel to said ontrol Circuit whereCin sail pr[ocessing means select a Virtual path using said input link and one of sad output links, calculnte~ sai total bandwidth to be used on said selected output link 1'rom ,,aid individuald balndwidth vajle contained in sai pat setup cell and rroni a provlottsly calculated total bandwidth already used so onl vald otpultt link 1 allowiiihib the uso of said selected virtual path fot, the trans- mnission of a subsequent colt stream dependling mn the reult or this calculatloth and store in coration witi saki second processing means virtual p~ath Information In said sixth memory, sai path information containing said path, bit. It, A communication switching systern according to claim It, in that subsequent to tho receipt of a sai maintenance cell on an input link of said recive port, sai /ttV second processing means use thc path~l Information stored in said sixth memory to form other path information, insert it into said mainitcniinc ccll and then transmit this cell to said control circuit wherein said processing means then use said other path information to find the corresponding calculatcd total bandwidth aind the corre- sponcling path bit in, said secondl and[ fifth memt-ories, rcspctivcly and perform said recalculation when said pahbit is in the set condition indicating that the mainte, nancc, cell is thc Or one received on said path dluring sai(I nueasurocnint interval, 1 3, A communication swithing system according to claim I I, wherein is included meanls to ver iIf a Cell stream transmiitted on a said virtual path stibseqoent to the transmission of a path setup cell therein, does not execel said ifldivIdual. bandwidthi on the basis of which. slid virtual' path Was allowed: to be used, said verifying means being able to. adapt the bandwidth of said cell steam If reqtilred arci the thus verified individual bandwidlth valoe; being Mrisorted in said maintenac Qcll transmitted on said virtual path, A commUn~cation switching system according to claimn 2, whereiai ite nanlce coll having said other informinaion inlser-ted there-inl Is also tranmiltted oil all :output or Soi kl- Pluality or~ outputf Inks Of Said switchling Oelmen t Via a ca Iculatio0n, circuit which caluolates. a protction Code for. iat least part or the dIaa stored. inl said maintenance col,~ A commniclationi switchinglj sys tem according to claim 11, whereill 'said, proccss( 1118 me101n1 at the0 end of sa id measuLlrceen illterval reCset all sald Path bits inl said4 *9 9 outli and Sixul 9