A comparison of hard-state and soft-state signaling protocols

  • Authors:

  • Ping Ji;Zihui Ge;Jim Kurose;Don Towsley

  • Affiliations:

  • John Jay College of Criminal Justice, City University of New York, New York, NY;AT&T Labs Research, Florham Park, NJ;University of Massachusetts, Amherst, MA;University of Massachusetts, Amherst, MA

  • Venue:
  • IEEE/ACM Transactions on Networking (TON)
  • Year:
  • 2007

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Abstract

One of the key infrastructure components in all telecommunication networks, ranging from the telephone network to VC-oriented data networks to the Internet, is its signaling system. Two broad approaches towards signaling can be identified: so-called hard-state and soft-state approaches. Despite the fundamental importance of signaling, our understanding of these approaches--their pros and cons and the circumstances in which they might best be employed--is mostly anecdotal (and, occasionally, religious). In this paper, we compare and contrast a variety of signaling approaches ranging from "pure" soft state to soft-state approaches augmented with explicit state removal and/or reliable signaling, to a "pure" hard state approach. We develop an analytic model that allows us to quantify state inconsistency in single- and multiple-hop signaling scenarios, and the "cost" (both in terms of signaling overhead and application-specific costs resulting from state inconsistency) associated with a given signaling approach and its parameters (e.g., state refresh and removal timers). Among the class of soft-state approaches, we find that a soft-state approach coupled with explicit removal substantially improves the degree of state consistency while introducing little additional signaling message overhead. The addition of reliable explicit setup/update/removal allows the soft-state approach to achieve comparable (and sometimes better) consistency than that of the hard-state approach.