A Comparison of Hard-State and Soft-State Signaling Protocols

• Published in: IEEE/ACM transactions on networking Vol. 15; no. 2; pp. 281 - 294
• Main Authors: Ping Ji, Zihui Ge, Kurose, J., Towsley, D.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.04.2007; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Communication system signaling; Computer crashes; Consistency; Cost analysis; Costs; hard-state; Internet; Internet telephony; IP networks; Mathematical analysis; Messages; Networks; performance evaluation; Protocols; Signal analysis; Signal processing; Signal restoration; soft-state; Studies; Telecommunication network reliability; Telecommunications; Timing devices
• ISSN: 1063-6692; 1558-2566
• DOI: 10.1109/TNET.2007.892849

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 singleand 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