Abstract:
Communication switching apparatus for providing communication between a multiplicity of digital information processors, the apparatus including a plurality of ports each communicating with at least one of the multiplicity of digital information processors, and a port interconnector operative to provide communication between more than one pair of ports from among the plurality of ports, characterized in that, when an overflow of information is caused at the port interconnector or at one of the plurality of ports, an overflow indication is provided to the digital information processors which communicate with the port interconnector or with the overflowed one of the plurality of ports.

Description:
This is a continuation of application Ser. No. 08/217,328 filed on Mar. 24, 1994, abandoned. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to switching systems. 
     BACKGROUND OF THE INVENTION 
     State of the art switching systems are described in the following publications: 
     &#34;An In-Depth Look at Three Switching Hubs&#34;, (Translated reprint of) Telecoms &amp; Reseaux, No. 69, September, 1993, IDG Communications, France; 
     &#34;The Switching Advantage&#34;, Kalpana EtherSwitch Publication, Fall, 1991; 
     Axner, David H., &#34;Evaluating Switching Hub Architectures&#34;, Business Communications Review, July 1993, pp. 35-39; and 
     &#34;Novell Application Performance Testing&#34;, Synernetics Performance Networking, Aug. 25, 1993. 
     SUMMARY OF THE INVENTION 
     The present invention seeks to provide an improved switching system and methods for using the same. 
     There is thus provided in accordance with a preferred embodiment of the present invention communication switching apparatus for providing communication between a multiplicity of digital information processors, the apparatus including a plurality of ports each communicating with at least one of the multiplicity of digital information processors, and a port interconnector operative to provide communication between more than one pair of ports from among the plurality of ports, characterized in that, when an overflow of information is caused at the port interconnector or at one of the plurality of ports, an overflow indication is provided to the digital information processors which communicate with the port interconnector or with the overflowed one of the plurality of ports. 
     Further in accordance with a preferred embodiment of the present invention each individual port includes an information overflow sensor and indicator operative to sense an overflow arriving from an individual digital information processor communicating therewith and to provide an overflow indication to the digital information processors communicating with the individual port. 
     Still further in accordance with a preferred embodiment of the present invention the port interconnector includes an information overflow sensor and indicator operative to sense an overflow arriving from an individual digital information processor and to provide an overflow indication to the digital information processors associated with the port interconnector. 
     Additionally in accordance with a preferred embodiment of the present invention each digital information processor is operative to refrain from transmitting information when it encounters a traffic congestion symptom and wherein the overflow indication includes an artificially generated occurrence of the traffic congestion symptom. 
     Also in accordance with a preferred embodiment of the present invention the communication provided includes LAN communication. 
     Further in accordance with a preferred embodiment of the present invention the multiplicity of processors includes at least one printer. 
     Still further in accordance with a preferred embodiment of the present invention the multiplicity of processors includes at least one workstation. 
     Additionally in accordance with a preferred embodiment of the present invention the multiplicity of processors includes at least one computer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be understood and appreciated from the following detailed description, taken in conjunction with the drawings in which: 
     FIG. 1 is a simplified functional block diagram of a plurality of interconnected communication switching systems 10 which are each constructed and operative in accordance with a preferred embodiment of the present invention; 
     FIG. 2 is a simplified block diagram of an individual one of ports 60; and 
     FIG. 3 is a simplified flowchart of a preferred method for selective activation of congestion symptom simulation. 
     FIG. 4 is a simplified flowchart illustration of a preferred method by which a back-pressurizing port of FIG. 1 generates back-pressure by simulating traffic on a line connecting elements 30 and 60 or 50 and 60; 
     FIG. 5 is a simplified flowchart illustration of a preferred method by which the RX buffer full flag of FIG. 4 is updated as a result of a port sending packets to the switching fabric; and 
     FIG. 6 is a simplified flowchart illustration of a preferred method by which the RX buffer full flag of FIG. 4 is updated as a result of a port receiving packets from digital information processors. 
    
    
     Attached herewith are the following appendices which are useful in generating a communication switching module which is constructed and operative in accordance with a preferred embodiment of the invention shown and described herein: 
     Appendices 1-5 are program listings which relate to a first LSI Logic ASIC (application specific integrated circuit) chip netlist which is useful in constructing communication switching apparatus constructed and operative in accordance with a preferred embodiment of the present invention. Specifically, Appendix 1 includes computerized starting information useful for setting up a working environment of LSI Logic tools; 
     Appendix 2 is the netlist itself according to which the chip layout may be generated; 
     Appendix 3 is RAM generating information; 
     Appendix 4 is a listing of test vectors useful in verifying the operation of the chip; and 
     Appendix 5 is layout information indicating a preliminary placing of the elements of the ASIC chip. 
     Appendices 6-9 are program listings which relate to a second LSI Logic ASIC chip netlist which is useful in constructing communication switching apparatus constructed and operative in accordance with a preferred embodiment of the present invention. Specifically, Appendix 6 includes computerized starting information useful for setting up a working environment of LSI Logic tools; 
     Appendix 7 is the netlist itself according to which the chip layout may be generated; 
     Appendix 8 is a listing of test vectors useful in verifying the operation of the chip; and 
     Appendix 9 is layout information indicating a preliminary placing of the elements of the ASIC chip. 
     Appendices 10-13 are program listings which relate to a third LSI Logic ASIC (application specific integrated circuit) chip netlist which is useful in constructing communication switching apparatus constructed and operative in accordance with a preferred embodiment of the present invention. Specifically, Appendix 10 includes computerized starting information useful for setting up a working environment of LSI Logic tools; 
     Appendix 11 is the netlist itself according to which the chip layout may be generated; 
     Appendix 12 is a listing of test vectors useful in verifying the operation of the chip; and 
     Appendix 13 is layout information indicating a preliminary placing of the elements of the ASIC chip. 
     Appendix 14 is a program listing for a Motorola 68HC11K1 microcontroller useful in the module. 
     Appendices 15-32 are listings of computerized manufacturing instructions for various layers and other portions of a printed circuit board; and 
     Appendices 33-42 are JEDEC files for programming GALs. 
     As a matter of practicality, these appendices will not appear as part of the printed patent, but remain as part of the application file. 
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Reference is now made to FIG. 1 which is a simplified functional block diagram of a plurality of interconnected communication switching systems 10 which are each constructed and operative in accordance with a preferred embodiment of the present invention. Each system 10 typically interfaces with and provides communication between a multiplicity of digital information processors 20 such as but not limited to PC&#39;s 30, printers 40 and workstations 50. Alternatively or in addition, each system 10 may interface with one or more similar systems 10 as shown. 
     Each switching system 10 typically includes a plurality of ports 60, each of which is connected to one or more of the digital information processors 20. The plurality of ports 60 are interconnected through a switching fabric 70, also termed herein a &#34;port interconnector&#34;. 
     It is a particular feature of the present invention that, when an overflow of information arrives from one or more digital information processors 20 which flow toward a common element such as an individual port 60 or the switching fabric 70, an overflow indication is provided to the digital information processor/s which flow toward the common element. 
     According to one preferred embodiment of the present invention, the ports 60 each comprise back pressurizing ports which implement the above overflow indication providing feature. Alternatively, the switching fabric 70 may comprise a back pressurizing switching fabric which implements the above overflow indication providing feature. 
     It is appreciated that, commonly, conventional digital information processors are operative to refrain from transmitting information when they encounter a traffic congestion symptom. Accordingly, the back pressurizing port or back pressurizing switching fabric of the present invention is preferably operative to artificially generate an occurrence of the traffic congestion symptom. 
     For example, in Ethernet and in the IEEE 802.3 protocol, the associated digital information processor only transmits information over the communication link (e.g. the communication link to a corresponding port, in FIG. 1) if it does not sense a carrier signal. If a carrier signal is sensed, no information is transmitted. Accordingly, the back pressurizing port or back pressurizing switching fabric of the present invention is preferably operative to transmit an artificial &#34;carrier signal&#34; to the offending digital information processor. 
     In the present specification, the term &#34;carrier signal&#34; is intended to include any type of signal which indicates to a digital information processor receiving the carrier signal that there is traffic and that, therefore, no information should be transmitted at the present time. 
     Reference is now made to FIG. 2 which is a simplified block diagram of an individual one of ports 60. 
     The port 60 preferably includes a line interface 100 which receives and transmits information from and to the digital information processors. The line interface 100 preferably carries out all information processor-switching system interface operations such as regulating use of the transmission line between the system and the information processor, interpretation of data and extracting clocks from data, all during reception, as well as converse operations during transmission to the information processors. 
     A received information buffer 110 stores information received from the digital information processors via the line interface 100 until it can be dealt with by controller 120. According to a first preferred embodiment of the present invention, an entire unit of data, such as an entire packet or an entire cell, is received from the digital information processors and stored in RX buffer 110 before the unit of data is forwarded by controller 120 to a switching fabric interface 130. Alternatively, data is transferred to the switching fabric interface 130 as it is received in which case the RX buffer 110 is only employed to stored data which cannot be transferred due, typically, to congestion at the switching fabric interface. 
     The switching fabric interface 130 performs all necessary interface operations in order to transmit and receive data from the back-pressurizing port 60 to the switching fabric 70 and vice versa. 
     A TX buffer 140 is provided which stores information being transferred from the switching fabric interface 130 to the digital information processors via line interface 100. Typically, information is transferred as soon as it is received unless there is congestion at the line interface 100. Alternatively, however, an entire data unit, such as a packet or cell, is accumulated in the TX buffer before being transferred to the line interface 100. 
     A congestion symptom simulator 150 is operative to simulate a symptom of congestion which is transferred to the digital information processors via the line interface 100, thereby to prevent the processors from transmitting any more information until the congestion situation is alleviated. For example: 
     a. In Ethernet or IEEE 802.3 applications, a carrier is transmitted to the digital information processors. The carrier may, for example, comprise a square wave of frequency 5 MHz transmitted for 1.8 msec, followed by a 5.6 microsec pause, and then followed by the square wave again, and so on. 
     If a digital information processor initiates transmission during one of the pauses, this occurrence is dealt with the same as an occurrence of collision, which eventuality is dealt with in the IEEE 802.3 protocol. 
     Preferably, the carrier is discontinued if information arrives from the switching fabric interface which is intended for the digital information processors whose transmission it is desired to block. In this case, the information is allowed to reach the digital information processor, via TX buffer 140 and the line interface since transmission of genuine information to the digital information processor is effective in blocking transmission from the processor. Once all the information has reached the processor, and if the port 60 is still congested, transmission of the carrier signal is renewed. 
     b. In Token Ring applications (IEEE 802.5), the processors and the port to which they are linked belong to a Ring which shares a single token. Each processor only transmits when it is in possession of the token. In this case, the congestion symptom simulator 150 prevents the processors from ever obtaining a token while congestion of the port exists. This is typically done by utilizing the priority system. The processors only obtain a token when their own priority is greater than or equal to the token&#39;s priority. Therefore, the processors&#39; ability to gain the token can be eliminated by giving the token a priority level, such as priority level 7, which exceeds the priority level of all of the processors. 
     The operation of all units of the port 60 are controlled by a controller 120. The controller is responsible for: 
     a. Monitoring transfer of information from the line interface 100 into the RX buffer, from the RX buffer onto the switching fabric interface 130, from the switching fabric interface 130 onto the TX buffer and from the TX buffer onto the line interface; and 
     b. Selectively activating congestion symptom simulation by the simulator 150. A preferred method for selective activation of congestion symptom simulation is now described with reference to FIG. 3. 
     FIG. 3 is a simplified flowchart of a preferred method for selective activation of congestion symptom simulation. The method of FIG. 3 preferably includes the following steps: 
     STEP 200: Initially, the back pressurizing function is not activated. In the illustrated embodiment, this is implemented by deactivation of the congestion symptom simulator 150. 
     STEP 210: A congestion criterion is inspected. For example, the criterion may be whether or not there is a predetermined amount of space left in the RX buffer 110. If the congestion criterion is not satisfied, return to step 200. If the congestion criterion is satisfied (STEP 220), operate the back pressurizing function, or, in other words, activate congestion symptom simulator 150. 
     STEP 230: A congestion criterion is inspected. For example, the criterion may be whether or not there is a predetermined amount of space left in the RX buffer 110. If the congestion criterion is satisfied, return to step 220. If the congestion criterion is not satisfied, return to step 200. 
     A very detailed description of a preferred method for constructing a communication switching module constructed and operative in accordance with one preferred embodiment of the present invention is as follows: 
     a. Elements U70-U73 of the module each comprise a first ASIC chip, also termed herein &#34;MTR&#34;, which is generated as follows: 
     i. Generate digital UNIX files whose contents is the contents of the listings of Appendices 1 to 5, except that the first line of each page should be ignored. One file should be generated for Appendix 3. One file should be generated for each of the three pages of Appendix 1. A plurality of files should be generated for Appendices 2 and 4 as indicated by the pagination thereof. Two files, named &#34;15a4170s.bdcmd&#34; and &#34;15a4170s.cfun&#34; should be generated for Appendix 5 as indicated by the pagination of Appendix 5. Editing software suitable for the Sun workstation may be employed to generate these digital files. 
     ii. Set up a LSI Logic working environment on a Sun workstation. 
     iii. Initialize the working environment using the three files generated using Appendix 1, which may be named &#34;setuproj.dat&#34;, &#34;LCB007.CELLIBS&#34; and &#34;M --  T --  R.OPTSPEC&#34;. 
     iv. Install the LSI memory library specified by the RAM information of Appendix 3. 
     v. Purchase from LSI Logic a Cellbase 1 micron ASIC using a LCB7050P die in a 160PQFP package designed in accordance with Appendices 1-3 and 5. Use the test vectors of Appendix 4 for verification. 
     b. Element U14 of the module comprises a second ASIC chip, also termed herein &#34;MBLI&#34;, which is generated as follows: 
     i. Generate digital UNIX files whose contents is the contents of the listings of Appendices 6 to 9, except that the first line of each page should be ignored. One file should be generated for Appendix 7. One file should be generated for each of the two pages of Appendix 6. A plurality of files should be generated for Appendix 8, as indicated by the pagination thereof. Two files, named &#34;MBLI --  IO --  PINS.BDCMD&#34; and &#34;MBLI --  IO --  PINS.BLOCKS&#34; should be generated for Appendix 9 as indicated by the pagination of Appendix 9. Editing software suitable for the Sun workstation may be employed to generate these digital files. 
     ii. Set up a LSI Logic working environment on a Sun workstation. 
     iii. Initialize the working environment using the two files generated using Appendix 6, which may be named &#34;setuproj.dat&#34;, and &#34;MBLI --  IO --  PINS.OPTSPEC&#34;. 
     iv. Purchase from LSI Logic a Cellbase GATE ARRAY ASIC using a L100073P die in a 208PQFP package designed in accordance with Appendices 6, 7 and 9. Use the test vectors of Appendix 8 for verification. 
     c. Elements U41 and U39 of the module each comprise a third ASIC chip, also termed herein &#34;MPR&#34;, which is generated as follows: 
     i. Generate digital UNIX files whose contents is the contents of the listings of Appendices 10 to 13, except that the first line of each page should be ignored. One file should be generated for Appendix 11. One file should be generated for each of the two pages of Appendix 10. A plurality of files should be generated for Appendix 12 as indicated by the pagination thereof. Two files, named &#34;L5A4124.bdcmd&#34; and &#34;mpr.cfun&#34; should be generated for Appendix 13 as indicated by the pagination of Appendix 13. Editing software suitable for the Sun workstation may be employed to generate these digital files. 
     ii. Set up a LSI Logic working environment on a Sun workstation. 
     iii. Initialize the working environment using the two files generated using Appendix 10, which may be named &#34;setuproj.dat&#34; and &#34;L5A4124.OPTSPEC&#34;. 
     iv. Purchase from LSI Logic a GATE ARRAY ASIC using a L100066P die in a 144PQFP package designed in accordance with Appendices 10, 11 and 13. Use the test vectors of Appendix 12 for verification. 
     c. Generate 18 DOS files from the listings of Appendices 15-32 respectively. The file names should be as follows: 
     Appendix 15--424L10G.LGR 
     Appendix 16--424L1G.LGR 
     Appendix 17--424L2G.LGR 
     Appendix 18--424L3G.LGR 
     Appendix 19--424L4G.LGR 
     Appendix 20--424L5G.LGR 
     Appendix 21--424L6G.LGR 
     Appendix 22--424LGG.LGR 
     Appendix 23--424L7G.LGR 
     Appendix 24--424L8G.LGR 
     Appendix 25--424L9G.LGR 
     Appendix 26--424DG.LGR 
     Appendix 27--424EG.LGR 
     Appendix 28--424FG.LGR 
     Appendix 29--UN424A.APR 
     Appendix 30--UN424A.DRL 
     Appendix 31--UN424A.MFG 
     Appendix 32--424LHG.LGR 
     d. Purchase a printed circuit manufactured in accordance with the 18 DOS files generated in step c, from a printed circuit manufacturer such as Diceon Electronics Inc., 18522 Von Karman, Irvine, Calif. 92714, U.S.A. 
     e. Generate a DOS file from the listing of Appendix 14 and program a 32K×8, 120 nanosec EPROM (code 27C256-120), using a suitable programming device such as a Data I/O Model 2900, commercially available from Data I/O Corporation, POB 97046, Redmond, Wash., 98072-9746, U.S.A. 
     f. Generate JEDEC files in accordance with the listings of Appendices 33-42. Use these 10 files to program 10 respective GALs of the following types: 
     Appendices 33--40:GAL 22V10B-10 
     Appendix 41: GAL 16V8-15 
     Appendix 42: GAL 6001. 
     g. Purchase the off-the-shelf elements listed in the following partlist: 
     
         __________________________________________________________________________Description     Reference     Manufacturer                                 Manufacturer Item__________________________________________________________________________CER 1 nF 50V 10% X7R           C264,265,268                  C274,279,283                         AUCERA  12062R102K500BLSMD 1206        C287,290,294                  C299,302,306                         AVX     12065C102KAT00J                         KEMET   C1206C102K5RAC                         SIEMENS B37872-K5102-K62                         VITRAMON                                 VJ1206Y102KXATCER 10 nF 50V 10% X7R           C263,266,269                  C275,278,282                         AUCERA  12062R103K500BLSMD 1206        C286,291,295                  C298,303,307                         AVX     12065C103KAT00J                         KEMET   C1206C103K5RAC                         SIEMENS B37872-K5103-K62                         VITRAMON                                 VJ1206Y103KXATCER 100 nF 50V 10% X7R           C29,30        AVX     SR205C104KAATRRADIAL 2.5 mm                 KEMET   C320C104K5R5CA                         VITRAMON                                 VP32BY104KATCER 100 nF 50V 10% X7R           C105-107,112                  C120-155,161                         AUCERA  12062R104K500BLSMD 1206        C158,159,404                  C162-166,101                         AVX     12065C104KAT00J           C2-8,81,82                  C267,270,276                         KEMET   C1206C104K5RAC           C277,281,285                  C292,296,297                         SIEMENS B37872-K5104-K62           C304,308,50                  C32,33,35,1                         VITRAMON                                 VJ1206Y104KXAT           C36-40,44-48                  C402,43,550           C405   C41,42,11-28           C411-417,400                  C51,52,54,55           C55l-561,721                  C60,64-66,77           C700-703,119                  C706-710,157           C722,110,262                  C78-79,68,69           C87,116,109                  C91-93,104,           C95,96,170CER 150 pF 50V 10% COG           C100   C56-59,70-73                         AUCERA  1206CG151K500BLSMD 1206        C83-86,97-99  AVX     12065A151KAT00J                         KEMET   C1206C151K5GAC                         SIEMENS B3787l-K5151-K62                         VITRAMON                                 VJ1206A151KXATCER 33 pF 50V 10% COG           C259-261,273                  C280,284                         AUCERA  1206CG330K500BLSMD 1206        C288,289,293                  C300,301,305                         AVX     12065A330KAT00J                         KEMET   C1206C330K5GAC                         SIEMENS B3787l-K5330-K62                         VITRAMON                                 VJ1206A330KXATCER 68 pF 50V 10% COG           R380-385,387                  R388-396,656                         AUCERA  1206CG680K500BLSMD 1206        R398-407,409                  R410-413,657                         AVX     12065A680KAT00J           R415-418,421                  R422-430,414                         KEMET   C1206C680K5GAC           R432-441,443                  R444-449,379                         SIEMENS B37871-K5680-K62           R664          VITRAMON                                 VJ1206A680KXATELEC 100 uF 16V RADIAL           C9,271,272    NIC COMP                                 NRSS101M16V5*112K Hrs 5.5*12.5 mm 2 mm       NICHICON                                 UVR1C101MDA-1TD                         NIPPON C                                 SMG16VB-100(M)CONN RJ-45 * 4 PORT 8/8           P1-8          STEWART SS-668804SANFR.H. PCB SHIELDEDCONN DIN 32PIN*3/96           J1,2          AMPHENOL                                 C133714A96PMALE R.A. PCB                 SIEMENS V42254B1300C960CONN 15PIN*4 FEAMLE           J3            LITTON  9151HS27500-246R.A. PCBCONN STRIP 2PIN*1 MALE           JMP1,7,10     KCC     1100S-2GSTRAIGHT PCB                  MOLEX   90120-0762COMM. 10BASE-T FILTER +           FL1,2         VALOR   FL1057-002CMC &amp; RES. 60PIN QUADTANTALUM 10 uF 16V           C10,31,49,53                  C63,67,76,80                         AVX     TAJC106K016R10% SMD SIZE C  C90,94,34     KEMET   T491C106K016AS                         SIEMENS B45196-B3106-K9TANTALUM 4.7 uF 16V           C111,113-115                  C117,118                         AVX     TAJB475K016R10% SMD SIZE B                KEMET   T491B475K016ASDIODE SWITCHING 4n 0.2A           D20-35,37     ITT     LL4151SMD CASE SOD-80 1N4151/M      PHILIPS PMLL4151DIODE SCHOTTKY 1.0A 40V           D18           PHILIPS BYV10-40T.H. CASE DO-41FILTER WOUND BEADS           CMC9          FAIR-RIT                                 2961666631EMI/RFIFUSE 12.0 A 32V F T.H.           RFUSE1        LITTELFU                                 251012. OR 255012.FUSE 4.0 A 125V F T.H.           RFUSE2        LITTELFU                                 251004. OR 255004.IC 26LS32B QUAD DIFFERE.           U55,51,47,43  AMD     AM26LS32BSCLINE RECEIVER SOIC 16PINIC 68HC11K4 uCONTROLLER           U26           MOTOROLA                                 XC68HC11K1CFN48bit PLCC 84PIN SMDIC LM35 TEMP. SENSOR           U32           N.S.C   LM35DZCASE to-92 3PINIC 88915T 100 MHz PLL           U20           MOTOROLA                                 MC88915TFN100PLCC 28PIN SMDIC VOLTAGE REF. 2.5V           U27           MOTOROLA                                 MC1403DSOIC 8PIN SMDIC 7705A SENSING UNDER           U25           T.I.    TL7705ACDVOLT 4.6V SOIC BPIN SMDINDUCTOR TOROID CHOKE           L1            R.A.M.  R1181150uHy 3ALOGIC 74AC00 SOIC 14PIN           U103,105      HARRIS  CD74AC00M 96150MILL SMD                   MOTOROLA                                 MC74AC00D R2                         N.S.C   74AC00SC X                         T.I.    SN74AC00D R                         TOSHIBA TC74AC00FN ELPLOGIC 74AC04 SOIC 14PIN           U23,108       HARRIS  CD74AC04M 96150MILL SMD                   MOTOROLA                                 MC74AC04D R2                         N.S.C   74AC04SC X                         T.I.    SN74AC04D R                         TOSHIBA TC74AC04FN ELPLOGIC 74AC05 SOIC 14PIN           U74,77        HARRIS  CD74AC05M 96150MILL SMD                   MOTOROLA                                 MC74AC05D R2                         TOSHIBA TC74AC05FN ELPLOGIC 74AC08 SOIC 14PIN           U79,87,109    HARRIS  CD74AC08M 96150MILL SMD                   MOTOROLA                                 MC74AC08D R2                         N.S.C   74AC08SC X                         T.I.    SN74AC08D R                         TOSHIBA TC74AC08FN ELPLOGIC 74AC157 SOIC 16PIN           U104          HARRIS  CD74AC157M 96150MILL SMD                   MOTOROLA                                 MC74AC157D R2                         N.S.C   74AC157SC X                         T.I.    SN74AC157D R                         TOSHIBA TC74AC157FN ELPLOGIC 74AC374 SOIC 20PIN           U59,58        MOTOROLA                                 MC74AC374DW R2300MILL SMD                   N.S.C   74AC374SC X                         T.I.    SN74AC374DW R                         TOSHIBA TC74AC374FW ELPLOGIC 74AC86 SOIC 14PIN           U49,48,45,44                  U57,56,53,52                         HARRIS  CD74AC86M 96150MILL SMD                   MOTOROLA                                 MC74AC86D R2                         N.S.C   74AC86SC X                         T.I.    SN74AC86D R                         TOSHIBA TC74AC86FN ELPLOGIC 74ACT04 SOIC           U2,1,33,18    HARRIS  CD74ACT04M 9614PIN 150MILL SMD             MOTOROLA                                 MC74ACT04D R2                         N.S.C   74ACT04SC X                         T.I.    SN74ACT04 DLOGIC 74ACT08 SOIC           U101   U19,24,100,                         HARRIS  CD74ACT08M 9614PIN 150MILL SMD             MOTOROLA                                 MC74ACT08D R2                         N.S.C   74ACT08SC X                         TOSHIBA TC74ACT08FN ELPLOGIC 74ACT32 SOIC           U102,40       HARRIS  CD74ACT32M 9614PIN 150MILL SMD             MOTOROLA                                 MC74ACT32D R2                         N.S.C   74ACT32SC X                         T.I.    SN74ACT32 D                         TOSHIBA TC74ACT32 FNLOGIC 74ACT74 SOIC           U15           HARRIS  CD74ACT74M 9614PIN 150MILL SMD             MOTOROLA                                 MC74ACT74D R2                         N.S.C   74ACT74SC X                         TOSHIBA TC74ACT74 FNLOGIC 74F125 SOIC 14PIN           U10,11,9,111  MOTOROLA                                 MC74F125D R2150MILL SMD                   N.S.C   74F125SC X                         PHILIPS N74F125D                         T.I.    SN74F125D XLOGIC 74HC04 SOIC 14PIN           U88           GOLDSTAR                                 GD74HC04D150MILL SMD                   HARRIS  CD74HC04M 96                         MOTOROLA                                 MC74HC04AD R2                         N.S.C   MM74HC04M X                         PHILIPS PC74HC04T                         SGS-THOM                                 M74HC04M1                         T.I.    SN74HC04D RLOGIC 74HC157 SOIC 16PIN           U64,65        HARRIS  CD74HC157M 96150MILL SMD                   N.S.C   MM74HC157M X                         PHILIPS PC74HC157T                         T.I.    SN74HC157D RLOGIC 74HC174 SOIC 16PIN           U22           HARRIS  CD74HC174M 96150MILL SMD                   MOTOROLA                                 MC74HC174AD R2                         N.S.C   MM74HC174M X                         PHILIPS PC74HC174T                         T.I.    SN74HC174D RLOGIC 74HC259 SOIC 16PIN           U69,68,60     HARRIS  CD74HC259M 96150MILL SMD                   MOTOROLA                                 MC74HC259D R2                         N.S.C   MM74HC259M X                         PHILIPS PC74HC259T                         T.I.    SN74HC259D R                         TOSHIBA TC74HC259AFN ELPLOGIC 74HC74 SOIC 14PIN           U54,50,46,42  HARRIS  CD74HC74M 96150MILL SMD                   MOTOROLA                                 MC74HC74AD R2                         N.S.C   MM74HC74AM X                         PHILIPS PC74HC74T                         T.I.    SN74HC74D R                         TOSHIBA TC74HC74AFN ELPLOGIC 74HC85 SOIC 16PIN           U34           HARRIS  CD74HC85M 96150MILL SMD                   MOTOROLA                                 MC74HC85D R2                         N.S.C   MM74HC85WM X                         PHILIPS PC74HC85T                         T.I.    SN74HC85D RLOGIC 74HCT4040 SOIC           U106          HARRIS  CD74HCT4040M 9616PIN 150MILL SMD             PHILIPS PC74HCT4040TLOGIC 74HCT74 SOIC           U83           HARRIS  CD74HCT74M 9614PIN 150MILL SMD             MOTOROLA                                 MC74HCT74AD R2                         N.S.C   MM74HCT74M X                         PHILIPS PC74HCT74TLOGIC 74ACT16245 SOIC           U28,31,82,81  N.S.C   74ACTQ16245 QC48PIN 300MILL SMD             T.I.    74ACT16245 DLLOGIC 74HC123 SOIC 16PIN           U66,63,62     HARRIS  CD74HC123M 96SMD DONT USE TOSHIBA !        N.S.C   MM74HC123AM X                         PHILIPS PC74HC123T                         T.I.    SN74HC123DLOGIC 74FCT16646AT SSOP           U6,8,7,8,4,3  IDT     IDT74FCT16646ATPV56PIN 300MILL SMDMEMORY SRAM 8K*8 100n           U29           EPSON   SRM2264LM10SOP 28PIN SMD                 HITACHI HM6264ALFP-10JUMPER 2.54 mm GOLD           JMP5,6        PRECI-DI                                 999-11-210-10INSULATED BLACKJUMPER SHUNT 1POSITION        PRECI-DI                                 999-19-210-00BLACKJUMPER 7.62 mm GOLD           PRECI-DI                                 999-11-230-10INSULATED BLACKFOR CMC1-CMC8LED HOLDER GREEN T-1           D9            IDEA    G61B/GLED HOLDER 2xGREEN T-1           D1-8,10-17    IDEA    G78B/2GASIC MPR        U41,39        LSI     L5A4124ASIC MBLI       U14    LSI    L5A4169ASIC MTR        U70-73 LSI    L5A4170NUT HEX M2.5 SST              PALBOREG                                 NA4402500FOR J1-2OSCILATOR TTL 16.0 MHz           X1            MODERN E                                 HXO-51B-16M50PPM 40/60 10n H.SIZE        RALTRON CO13-50-16M-N                         SHOWA   MC08050B-16MOSCILATOR TTL 80.0 MHz           X2            DALE    XO-52A-59-80MHz50PPM 40/60 6n H.SIZE         MODERN E                                 HXO-52B-80M                         RALTRON CO13-50-80M-N                         SHOWA   MCO8050B-80MNET BUSSED 10 KOHM*19           RN4,2,8,9     BOURNS  4820P-002-1030.08W SOIC 220 20PINNET BUSSED 1 KOHM*19           RN5           BOURNS  4820P-002-1020.08W SOIC 220 20PINNET BUSSED 1 KOHM*15           RN6           BECKMAN 628B-102-G-TR40.08W SOIC 220 16PIN          BOURNS  4816P-002-102                         DALE    SOMC16-01-102-GNET BUSSED 10 KOHM*15           RN1,3,7       BECKMAN 628B-103-G-TR40.08W SOIC 220 16PIN          BOURNS  4816P-002-103                         DALE    SOMC16-01-103-GRESISTOR 0 OHM 1/8W           R192,193,223                  R224,229,230                         BOURNS  CR1206-J-W-000-E5% SMD 1206     R261,262,730                  R267,268,732                         DRALORIC                                 CR1206-L-000-J-G4           R299,300,83                  R305,306,309                         KOA     RK73-K2B-TD-000-J           R310,314,312                  R318-320,323                         ROHM    MCR18-EZHU-J-W-000           R324,327-329                  R332,474-494                         SAMSUNG RC3216J-000-CS           R340,335-337                  R343-345                         TY-OHM  RMC-0 OHM           R736,182,183                  R737,78-80RESISTOR 10 OHM 1/8W           R550          BOURNS  CR1206-J-W-100-E5% SMD 1206                   DRALORIC                                 CR1206-L-100-J-G4                         KOA     RK73-K-2B-TD-10-J                         ROHM    MCR18-EZHU-J-W-100                         SAMSUNG RC3216J-100-CS                         TY-OHM  RMC-10 OHMRESISTOR 10K 1/8W           R100-116,130                  R127-129,99                         BOURNS  CR1206-J-W-103-E5% SMD 1206     R131-133,139                  R137,138,4,5                         DRALORIC                                 CR1206-L-103-J-G4           R140-141,136                  R145-147,126                         KOA     RK73-K2B-TD-10K-J           R150-155,450                  R175,164,213                         ROHM    MCR18-EZHU-J-W-103           R202,251,240                  R28,689-691                         SAMSUNG RC3216J-103-CS           R289,278,144                  R29-33,564                         TY-OHM  RMC-10 KOHM           R359,360,679                  R36,66,67,70           R451-455,88                  R495,34,76           R685,40,35                  R71,41,682           R738,739,747                  R8,9,11-26           R89-93,686RESISTOR 150K 1/8W           R348-353      BOURNS  CR1206-JW-154-E5% SMD 1206                   DRALORIC                                 CR1206-L-154-J-G4                         KOA     RK73-K-2BTD-150K-J                         ROHM    MCR18-EZHU-J-W-154                         SAMSUNG RC3216J-154-CS                         TY-OHM  RMC-150 KOHMRESISTOR 18K 1/8W           R161,162,166                  R173,199,200                         BOURNS  CR1206-JW-183-E5% SMD 1206     R204,211,237                  R238,242,249                         DRALORIC                                 CR1206-L-183-J-G4           R275,276,280                  R287   KOA     RK73-K-2B-TD-18K-J                         ROHM    MCR18-EZHU-JW-183E                         SAMSUNG RC3216J-183-CS                         TY-OHM  RMC-18 KOHMRESISTOR 1K 1/8W           R117-124                  R158,159,170                         BOURNS  CR1206-JW-102-E5% SMD 1206     R171,196,197                  R208,209,234                         DRALORIC                                 CR1206-L-102-J-G4           R235,246,247                  R272,273,284                         KOA     RK73-K-2B-TD-1K-J           R285,148,149  ROHM    MCR18-EZHU-J-W-102                         SAMSUNG RC3216J-102-CS                         TY-OHM  RMC-1 KOHMRESISTOR 1M 1/8W           R94           BOURNS  CR1206-JW-105-E5% SMD 1206                   DRALORIC                                 CR1206-L-105-J-G4                         KOA     RK73-K-2B-TD-1M-J                         ROHM    MCR18-EZHU-J-W-105                         SAMSUNG RC3216J-105-CS                         TY-OHM  RMC-1 MOHMRESISTOR 270 OHM 1/8W           R156,157,168                  R169,194,195                         BOURNS  CR1206-JW-271-E5% SMD 1206     R206,207,232                  R233,244,245                         DRALORIC                                 CR1206-L-27l-J-G4           R270,271,282                  R283   KOA     RK73-K-2B-TD-270-J                         ROHM    MCR18-EZHU-J-W-271                         SAMSUNG RC3216J-271-CS                         TY-OHM  RMC-270 OHMRESISTOR 2K 1/8W           R160,163,167                  R172,198,201                         BOURNS  CR1206-JW-202-E5% SMD 1206     R205,210,236                  R239,243,248                         DRALORIC                                 CR1206-L-202-J-G4           R274,277,281                  R286   KOA     RK73-K-2B-TD-2K-J                         ROHM    MCR18-EZHU-J-W-202                         SAMSUNG RC3216J-202-CS                         TY-OHM  RMC-2 KOHMRESISTOR 33 OHM 1/8W           R56-61,74,75  BOURNS  CR1206-JW-330-E5% SMD 1206                   DRALORIC                                 CR1206-L-330-J-G4                         KOA     RK73-K-2B-TD-33-J                         ROHM    MCR18-EZHU-J-W-330                         SAMSUNG RC3216J-330-CS                         TY-OHM  RMC-33 OHMRESISTOR 330 OHM 1/8W           R63           BOURNS  CR1206-JW-331-E5% SMD 1206                   DRALORIC                                 CR1206-L-331-J-G4                         KOA     RK73-K-2B-TD-330-J                         ROHM    MCR18-EZHU-J-W-331                         SAMSUNG RC3216J-331-CS                         TY-OHM  RMC-330 OHMRESISTOR 4.7K 1/8W           R458   R688,687,457                         BOURNS  CR1206-JW-472-E5% SMD 1206     R735   R95-98,125                         DRALORIC                                 CR1206-L-472-J-G4                         KOA     RK73-K-2BTD-4.7K-J                         ROHM    MCR18-EZHU-J-W-472                         SAMSUNG RC3216J-472-CS                         TY-OHM  RMC-4.7 KOHMRESISTOR 47 OHM 1/8W           R72,73        BOURNS  CR1206-JW-470-E5% SMD 1206                   DRALORIC                                 CR1206-L-470-J-G4                         KOA     RK73-K-2B-TD-47-J                         ROHM    MCR18-EZHU-J-W-470                         SAMSUNG RC3216J-470-CS                         TY-OHM  RMC-47 OHMRESISTOR 470K 1/8W           R62           BOURNS  CR1206-JW-474-E5% SMD 1206                   DRALORIC                                 CR1206-L-474-J-G4                         KOA     RK73-K-2BTD-470K-J                         ROHM    MCR18-EZHU-J-W-474                         SAMSUNG RC3216J-474-CS                         TY-OHM  RMC-470 KOHMRESISTOR 510 OHM 1/8W           R165,174,176                  R177,203,212                         BOURNS  CR1206-JW-511-E5% SMD 1206     R214,215,241                  R250,252,253                         DRALORIC                                 CR1206-L-511-J-G4           R279,288,290                  R291,37                         KOA     RK73-K-2B-TD-511-J                         ROHM    MCR18-EZHU-J-W-511                         SAMSUNG RC3216J-511-CS                         TY-OHM  RMC-510 OHMRESISTOR 820 OHM 1/8W           R178-181,216                  R187,188                         BOURNS  CR1206-JW-821-E5% SMD 1206     R217-219,254                  R222,228,260                         DRALORIC                                 CR1206-L-821-J-G4           R255-257,292                  R266,298,304                         KOA     RK73-K-2B-TD-820-J           R293-295      ROHM    MCR18-EZHU-J-W-821                         SAMSUNG RC3216J-821-CS                         TY-OHM  RMC-820 OHMRESISTOR 5.1 OHM 1/4W           R184,186,190                  R191   BOURNS  CR1206-J-W-5R1-E5% SMD 1206     R220,225,226                  R231,258,263                         DRALORIC                                 CR1206-L-5R1-J-G4           R264,269,296                  R301,302,307                         ROHM    MCR18-EZHU-J-W-5R1                         SAMSUNG RC3216J-5R1-CS                         TY-OHM  RMCQ-5.1 OHMSCREW PHILL M2.5*10 P/H       PALBOREG                                 DF1402510SSTFOR J1-2SOCKET DIP 28PIN PCB           U30           DSM     630-28-CC-D-14.50 mm 600mill               NEXTRON 100-286-10-1003                         PRECI-DI                                 110-91-628-41-001                         SOCKET E                                 SEO6-28-2TGSOCKET PLCC 20PIN SMD         AMP     822014-34.70 mm                       PRECI-DI                                 540-99-020-07-400FOR U12SOCKET PLCC 28PIN SMD           U107   U16,17,84,85                         AMP     822039-34.70 mm                       PRECI-DI                                 540-99-028-07-400FOR U35-38SWITCH ACCESSORY              ELMA    210-8301KNOB GREYFOR SW2SWITCH ACCESSORY              ELMA    300-8011CAP GREYFOR SW2SWITCH DIP SPST 6#           SW1           GRAYHILL                                 78B06STRAIGHT PCMSWITCH CODED BCD 2#           SW2           ELMA    BV17114R.A. PCMWIRE HOOK-UP PVC 30AWG        BELDEN  9930-10300V 80C BLACKFOR U27End of Report__________________________________________________________________________ 
    
     h. Assemble the parts listed in the above partlist onto the printed circuit board of step d, by matching the printed labels on the printed circuit board to the reference column of the partlist. The following instructions should preferably be followed: 
     1. Use jumpers to short legs 1-8, 2-7, 3-6, 4-5, of CMC1-CMC8. 
     2. Make the following patches, using wire-wrap black wire, 30 AWG, on the print side between: 
     U27(8)-U27(1) 
     U27(7)-U27(2) 
     U27(6)-U27(6) 
     U74(10)-U109(1) 
     U106(1)-U74(11) 
     J1B(10)pad-U74(10) 
     3. Connect the resistor RS-85-4.7K between resistor&#39;s R11 pad and J1B(10). 
     4. Disconnect the following legs: U74(11), U109(1). 
     5. Disconnect the wire which routed to U107(17) prior to socket insertion. 
     Notes: 
     The resistor should not stand out from the print side. 
     The resistor leg which is connected to the pad should have Teflon isolation. 
     The following parts should remain unassembled: Component side: 
     1. U78,75,200,90,91,110,21,61 
     2. C600,500,466 
     3. R500,501,681,683,677,678,743,744,666,134,135,189,185,227 
      R221,265,259,303,297,731,745,733 
     4. D19,36 
     5. L2 
     6. TP1-9, 11-13 
     7. JMP8,9 
     8. CON1,2,4-6 
     Print side: 
     1. C160,169,168 
     2. R634,635,470-473,466-469,50,51,665,668,321,700-703 
      R354-357,313,308,311,315,318,316,317,322,330,331,326,325, 
      R333,334,338,339,346,347,342,341,48,49,46,47,675,42,43,54, 
      R55,81,82,600,601,44,45,65,69,64,68,635,634,671,672,673,669 
      R748,742,741,674,496,10 
     3. D50 
     The EPROM of step e should be inserted into the U26 socket. 
     The 10 GALs programmed in accordance with Appendices 33-42 should be inserted into the following sockets, respectively: 
     Appendix 33: U85 
     Appendix 34: U36 
     Appendix 35: U38 
     Appendix 36: U35 
     Appendix 37: U37 
     Appendix 38: U84 
     Appendix 39: U17 
     Appendix 40: U16 
     Appendix 41: U12 
     Appendix 42: U107. 
     The assembled board is preferably used with LET 36/20 HUBS, commercially available from Lannet Data Communications Ltd., Tel Aviv, Israel. 
     FIG. 4 is a simplified flowchart illustration of a preferred method by which a back-pressurizing port of FIG. 1 generates back-pressure by simulating traffic on a line connecting elements 30 and 60 or 50 and 60; 
     FIG. 5 is a simplified flowchart illustration of a preferred method by which the RX buffer full flag of FIG. 4 is updated as a result of a port sending packets to the switching fabric; and 
     FIG. 6 is a simplified flowchart illustration of a preferred method by which the RX buffer full flag of FIG. 4 is updated as a result of a port receiving packets from digital information processors. 
     All of the steps in the flowchart illustrations of FIGS. 4-6 are fully disclosed in the description of a preferred implementation of the present invention which appears on page 12, third complete paragraph on to the paragraph bridging pages 33 and 34 and which makes reference to Appendices 1-42 described in the Brief Description section of this specification. The components which chiefly implement each of the steps of FIGS. 4-6 are as follows: 
     Steps 320, 380, 430, 440, 450, 460, 560, 570 and 580 of the flowcharts of FIGS. 4-6 are implemented chiefly in the component described in paragraph a on page 12. 
     Steps 300, 340, 360, 540 and 550 of the flowcharts of FIGS. 4 and 6 are implemented chiefly in the components described in paragraph a on page 12, paragraph b on page 13 and paragraph c on page 14. All three of these components are initialized by a microprocessor termed U26 on the partlist on page 19 (second part from the bottom of page 19). The code for the U26 microprocessors is provided in the listing of Appendix 14 as described in paragraph e on page 15. 
     Steps 400, 410, 420 and 470 of the flowchart of FIG. 5 are implemented chiefly in the components described in paragraph a on page 12 and paragraph b on page 13. 
     Steps 330, 350 and 370 of the flowchart of FIG. 4 are implemented chiefly in the components described in paragraph b on page 13 and paragraph c on page 14. 
     Step 310 of the flowchart of FIG. 4 is implemented chiefly in the component described in paragraph b on page 13. 
     All of the above components are mounted on a printed circuit board described on page 15 in paragraphs c and d. 
     It is appreciated that the chips described above with reference to the Appendices are intended only to provide an extremely detailed disclosure of a sample embodiment of the present invention and is not intended to be limiting. 
     It is appreciated that various features of the invention which are, for clarity, described in the contexts of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment may also be provided separately or in any suitable subcombination. 
     It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention is defined only by the claims that follow: