Increasing use of the Internet for critical services makes flooding distributed denial-of-service (DDoS) a top security threat. A distributed nature of DDoS suggests that a distributed mechanism is necessary for a successful defense. Three main DDoS defense functionalities -attack detection, rate limiting and traffic differentiation -are most effective when performed at the victim-end, core and sourceend respectively. Many existing systems are successful in one aspect of defense, but none offers a comprehensive solution and none has seen a wide deployment. We propose to harvest the strengths of existing defenses by organizing them into a collaborative overlay, called DefCOM, and augmenting them with communication and collaboration functionalities. Nodes collaborate during the attack to spread alerts and protect legitimate traffic, while rate limiting the attack. DefCOM can accommodate existing defenses, provide synergistic response to attacks and naturally lead to an Internet-wide response to DDoS threat.

By streaming potential measurements, the zero point of charge (zpc) of or-AlzO~ having a fully hydroxylated surface was found to occur at pH 9.2 f 0.2. By calcining the alumina at temperatures above 1000°C, the zpc was lowered to about pH 6.7. By aging the calcined material in water at room temperature for a period of weeks, the surface was rehydroxylated and the zpc increased. The zpc of MgO occurred at pH 12.5 f 0.5. Because of its high solubility, the zpc of MgO was not affected by heat treatment.affect the usefulness of the suspension in fabrication processes such as slip casting. Furthermore, the presence or absence of and the relative sign and magnitude of the surface charge

Polycrystalline A1,OJ was chemically vapor-deposited onto sintered AL03 substrates by reaction of AlCl, with (1) HzO, (2) C02:Hz, and (3) 0, at 1000" and 1500°C and 0.5 and 5.0 torr. Although the thermodynamics of all these reactions predict the formation of solid A1,0, the deposition rate of the first reaction was considerably greater than that of the second. The third reaction was so slow that no measurable deposit was formed in 6 h at 1500°C. Formation of dense deposits of 0r-A1,0~ was favored by increasing temperature and decreasing pressure. Microstructural examination of the dense deposits showed long columnar grains, the largest of which extended through the deposit from the substrate to the surface.

Currently, there is no effective defense against large-scale distributed denial-of-service (DDoS) attacks. While numerous DDoS defense systems exist that offer excellent protection from specific attack types and scenarios, they can frequently be defeated by an attacker aware of their weaknesses. A necessary requirement for successful DDoS defense is wide deployment, but none of these systems can guarantee wide deployment simply because deployment depends more on market and social aspects than on the technical performance of the system.To successfully handle the DDoS threat we must abandon the current paradigm--the design of defense systems that operate in isolation--and shift toward a new paradigm, a distributed framework of heterogeneous systems that coopcrate to achieve an effective defense. Heterogeneity is dictated by two major factors. First, the necessary requirements for a successful defense are detection, response and traffic differentiation. These requirements must be met at disjoint points in the Internet and require a disjoint set of functionalities from the defense systems. Second, heterogeneity is dictated by the current state of the DDoS defense field in which numerous systems exist that can offer similar performance and compete for market share. In this paper we show how the paradigm shift can be accomplished quickly and painlessly through the design of DefCOM, a distributed framework that enables the exchange of information and services between existing defense nodes.

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