Digital data communication system

Abstract

A digital data transmission system comprising a plurality of interconnected switching units, each such unit having connected thereto at least one transmission loop, and each such loop having at least one digital device attached thereto. The system provides controllable buffering of digital data thereby allowing digital devices having different data transfer speeds and storage capabilities to communicate asynchronously. The system allocates communication resources upon request but only creates actual communication paths when the requesting device is transmitting data. Thus system resources need not remain committed between bursts of data.

What is claimed is: 
     
       1. A data transmission system for .Iadd.supporting data cells among .Iaddend.a plurality of digital devices, .Iadd.a data call being comprised of randomly occurring bursts of data with intervening pauses, .Iaddend.comprising means for virtually allocating transmission paths upon request .Iadd.preparatory to establishing data calls .Iaddend.from any of said digital devices to any other of said digital .[.device.]. .Iadd.devices by assigning to each call a description of transmission resources to convey the data .Iaddend.and means for activating said virtually allocated transmission for .[.paths.]. .Iadd.path in accordance with the assigned description .Iaddend.only .[.when.]. .Iadd.upon determination that a .Iaddend.data .Iadd.burst of the call .Iaddend.is actually transmitted. 
     
     
       2. A digital data transmission system .Iadd.for supporting data calls among a plurality of digital devices, a data call being comprised of randomly occurring bursts of data with intervening pauses .Iaddend.including a plurality of transmission loops, each including at least one digital device, comprising: means for virtually allocating a transmission path from a digital device in one loop to a digital device in another loop comprising a plurality of asynchronous links .Iadd.by assigning to each call a description of the links in the path, .Iaddend.and means for activating particular ones of said links .Iadd.in accordance with the path description .Iaddend.only when .Iadd.a .Iaddend.data .Iadd.burst of the call .Iaddend.is actually available at said particular ones for transmission.   
     
     
       3. A data transmission system comprising: means for receiving requests to virtually allocate communication paths;   means for storing descriptions of requested communication paths; and   means for using the stored descriptions to create the requested communication paths only when data is actually available for transmission.   
     
     
       4. A data transmission system comprising: means for receiving requests to establish communication paths;   means for storing descriptions of requested communication paths comprising a plurality of asynchronous links; and   means for activating particular ones of the plurality of links only when data is actually available at the particular ones for transmission.   
     
     
       5. A system for providing data communication between a plurality of digital devices comprising: means for receiving requests for the use of communication paths from each one of said plurality of digital devices;   means for virtually allocating communication paths in response to said requests and prior to actual use of said paths; and   means for actually connecting said virtually allocated communication paths at the time data is actually transmitted.   
     
     
       6. A digital data transmission system comprising: a first switching unit;   a first digital device attached to said first switching unit;   a second switching unit connected to said first switching unit;   a second digital device attached to said second switching unit;   means for virtually allocating a first transmission path between said first digital device and said first switching unit;   means for virtually allocating a second transmission path between said first switching unit and said second switching unit;   means for virtually allocating a third transmission path between said second switching unit and said second digital device; and   means for selectively activating each of said first, second, and third virtually allocated transmission paths.   
     
     
       7. The digital data transmission system of claim 6 wherein each of the three means for virtually allocating a transmission path further comprises: means for storing parameters characterizing the data which is to be transmitted; and   means for initiating the virtual allocation of the next succeeding transmission path.   
     
     
       8. The digital data transmission system of claim 6 wherein said means for selectively activating each of said first, second, and third virtually allocated transmission paths further comprises: means for activating said first virtually allocated transmission path only when said first digital device is actually transmitting data;   means for activating said second virtually allocated transmission path only when said first switching unit is actually retransmitting data received from said first digital device;   means for activating said third virtually allocated transmission path only when said second switching unit is actually retransmitting that data received from said retransmission by said first switching unit.   
     
     
       9. The digital data transmission system of claim 8 wherein each of the three means for activating a transmission path further comprises: means for receiving incoming data which is to be retransmitted on said transmission path;   means for storing said incoming data; and   means for retransmitting said data on said transmission path.   
     
     
       10. The digital data transmission system of claim 9 wherein said means for storing said incoming data further comprises: means for selectively limiting the total amount of incoming data which is stored at any time.   
     
     
       11. The digital data transmission system of claim 10 wherein said selectively limiting means further comprises: means for causing the device that is transmitting said incoming data to cease transmission when the amount of said incoming data that has not been retransmitted on said transmission path reaches a prespecified value.   
     
     
       12. A system for transmitting data between digital devices comprising: a plurality of interconnected program-controlled switching units;   at least one program-controlled terminal interface unit attached to each one of said plurality of interconnected program-controlled switching units for communication therewith by a digital device.   
     
     
       13. The system of claim 12 further comprising: means for selectively limiting the amount of buffering that said system provides in each switching unit for each digital device that is attached thereto.   
     
     
       14. The system of claim 13 further comprising: means for selectively limiting the minimum amount of data that said system permits each digital device attached thereto to transmit in a single burst of transmission.   
     
     
       15. The system of claim 14 further comprising: means for selectively limiting the minimum amount of data that said system transmits to each digital device attached thereto in a single burst of transmission.   
     
     
       16. The system of claim 14 further comprising: means for selectively limiting the rate at which said system permits each digital device attached thereto to transmit data.   
     
     
       17. The system of claim 15 further comprising: means for selectively limiting the rate at which said system transmits data to each digital device attached thereto.   
     
     
       18. The method of transmitting data comprising the steps of: receiving requests for the use of transmission resources from transmitting devices;   storing descriptions of the transmission resources necessary to honor the received requests;   committing transmission resources to particular transmitting devices in accordance with the stored descriptions only at the time data is actually transmitted. .Iadd. 19. The method of transmitting data in data calls comprised of randomly occurring bursts of data with intervening pauses, comprising the steps of:   receiving requests for the use of transmission resources from transmitting devices;   storing a description of the transmission resources necessary to honor each received request; and   committing transmission resources to particular transmitting devices in accordance with the stored descriptions only at a time when it is determined that a data burst is actually transmitted. .Iaddend.