Towards asymptotic optimality in probabilistic packet marking

  • Authors:
  • Micah Adler;Jeff Edmonds;Jivri Matousek

  • Affiliations:
  • University of Massachusetts, Amherst, MA;York University, Toronto, ON, Canada;Charles University, Czech Republic

  • Venue:
  • Proceedings of the thirty-seventh annual ACM symposium on Theory of computing
  • Year:
  • 2005

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Abstract

There has been considerable recent interest in probabilistic packet marking schemes for sending information from nodes (routers) along one or more paths traveled by a stream of packets to the end-host receiving that stream. A central consideration for such schemes is the tradeoff between the number B of possible states of the marking bits in a packet, the number of bits n of information being sent by the nodes, and the expected number of packets T required to reconstruct this information. For the case where the packets all travel along the same path, we prove a lower bound of T ≥ Ω(B22n/(B-1)), roughly the square of an earlier lower bound of Adler.For an upper bound, we consider a model where each of m nodes along a single path must send one of s possible messages (thus n = m log2 s total bits are sent). We prove that T ≤ O(m • 22m(log2 s)/(B-1)) suffices (the implicit constant depends on B and s); this almost matches the lower bound, and is roughly the square root of an earlier upper bound of Adler. The new bound holds for all B and s in two slightly relaxed models, while under the strictest requirements we prove it only for some special values of B and s. This is related to a challenging geometric problem: the existence of an s-reptile (B-1)-dimensional simplex, i.e. a simplex S that can be tiled by s congruent simplices similar to S.We also consider the case where the packets travel along multiple paths to the same destination. In this case, we present a new protocol and analysis technique that together allow us to significantly generalize over previous work the scenarios where the protocol is effective.