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Method and apparatus for detecting impending overflow and/or underrun of elasticity buffer

  • US 4,945,548 A
  • Filed: 10/14/1988
  • Issued: 07/31/1990
  • Est. Priority Date: 04/28/1988
  • Status: Expired due to Term
First Claim
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1. A parallel asynchronous elasticity buffer in a repeater node for transferring data in a data communication system, the data communication system including a plurality of nodes coupled in a network for transferring frames of data from a source node to a destination node through the repeater node, wherein the repeater node receives a plurality of bits of data in a frame from an upstream node and transmits the plurality of bits of data in the frame to a downstream node, and wherein each node in the network transmits data in synchronism with an independent clock, the elasticity buffer comprising:

  • receiving means for providing in parallel format, in response to a transmit multibit clock signal that is in synchronism with an independent clock of the upstream node, a multibit data unit received from the upstream node;

    storage means including a fixed number of multibit storage elements, coupled to the receiving means, for storing the multibit data unit in parallel format in one of the storage elements, wherein each storage element has a unique address;

    transmitting means, coupled to the storage means, for outputting in parallel format, in response to a local multibit clock signal that is in synchronism with the independent clock of the repeater node, one of the multibit data units stored in the storage means;

    write pointer means, coupled to the storage means, for selecting as a write address the address of a storage element to store the next multibit data unit provided by the receiving means;

    read pointer means, coupled to the storage means, for selecting as a read address the address of a storage element to provide the next multibit data unit output by the transmitting means, wherein each multibit data unit is output in first-in, first-out order;

    initialization means for initializing the elasticity buffer to prevent simultaneous selection of the same address as a read address and a write address, wherein in response to initialization, a write address is selected as a read address after a predetermined delay; and

    detection means for detecting whether an error condition corresponding to a write overflow or read underrun of a storage element is impending by determining whether the same address is selected as the write address and as the read address during an overlap time period having a duration equal to a threshold time period.

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