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RFC 64 - Getting Rid of Marking

  • Status: Unknown
  • Published: July 1970
  • Stream: Legacy
  • Errata: No Errata

Document Information​

  • RFC Number: 64
  • Title: Getting Rid of Marking
  • Authors: M. Elie (UCLA)
  • Date: July 1970
  • Category: Unknown

Abstract​

RFC 64 argues that the marking convention of the IMP-HOST interface, introduced so that the sending Host could start the text of a message on a word boundary, does not suit a receiving Host with a different word length and needlessly adds bits to every message. Taking the authors' Sigma 7, a 32-bit machine, as the example, the note first quantifies the inefficiency in computation: the whole message must be shifted, at a cost of approximately 12 microseconds per double word, or 1.5 ms for a full regular message. It then quantifies the inefficiency in transmission, showing that a one-character text sent by the Sigma 7 requires 112 bits to carry 8 bits of information, an efficiency factor of 0.07. The remedy proposed is a simple modification of the Host-IMP interface sketched from diagrams of the BBN 1822 report: add a counter to 32, enabled at the beginning of a message and incremented for each bit passed to the IMP, which on reaching 32 forces a "word complete" signal asking for a new word in the shift register and resetting the word length counter. The unused bits in the last word of the leader are then not transmitted, in both the Host-to-IMP and the IMP-to-Host directions.

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