Single-Bit Messages Are Insufficient in the Presence of Duplication

  • Kai Engelhardt
  • Yoram Moses
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 3741)


Ideal communication channels in asynchronous systems are reliable, deliver messages in FIFO order, and do not deliver spurious or duplicate messages. A message vocabulary of size two (i.e., single-bit messages) suffices to encode and transmit messages of arbitrary finite length over such channels. This note proves that single-bit messages are insufficient once channels potentially deliver duplicate messages. In particular, it is shown that no protocol allows the sender to notify the receiver which of three values it holds, over a bidirectional, reliable, FIFO channel that may duplicate messages. This implies that messages must encode some additional control information, e.g., in the form of headers or tags.


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Copyright information

© Springer-Verlag Berlin Heidelberg 2005

Authors and Affiliations

  • Kai Engelhardt
    • 1
  • Yoram Moses
    • 2
  1. 1.School of Computer Science and EngineeringThe University of New South Wales, and NICTASydneyAustralia
  2. 2.Department of Electrical EngineeringTechnionHaifaIsrael

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