|The Tempest framework allows the dynamic introduction and modi cation of network services at two levels of granularity. First, the switchlet and associated virtual network concepts enable the safe introduction of alternative control architectures into an operational network. The timescales over which such new control architectures can be introduced might vary from, for example, a video conferencing speci c control architecture, which is active only for the duration of the conference, to a new version of a general purpose control architecture, which might be active for several months or longer. Second, the Tempest framework allows re nement of services at a ner level of granularity by means of the connection closure concept. In this case modi cation of services can be performed at an application speci c level. These attributes of the Tempest framework allows service providers to e ectively become network operators for some well de ned partition of the physical network. This enables them to take advantage of the knowledge they possess about how the network resources are to be used, by programming their own specially tailored control architecture. This, as our work with the Tempest shows, is a spur to creativity allowing many of the constraints imposed on operators and end-users to be rethought and for new techniques to be quickly and safely introduced into working networks.

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Most research in network programmability has stressed the exibility engendered by increasing the ability of users to con gure network elements for their own purposes, without addressing the larger issues of how such advanced control systems can coexist both with each other and with more conventional ones. The Tempest framework presented here extends beyond the provision of simple network programmability to address these larger issues. In particular we show how network programmability can be achieved without jeopardizing the integrity of the network as a whole, how network programmability ts in with existing networks and how programmability can be o ered at di erent levels of granularity. Our approach is based on the Tempest's ability to dynamically create Virtual Private Networks (VPNs) over a switched transport architecture, e.g. an ATM network. Each VPN is assigned a set of network resources which can be controlled using either a well known control system or a control system tailored to the speci c needs of a distributed application. The rst level of programmability in the Tempest is fairly course grained: an entire virtual network can be programmed by a third party. At a ner level of granularity the Tempest allows user supplied code to be injected into parts of an operational virtual network, thus allowing application speci c customisation of network control. The paper shows how the Tempest framework allows these new approaches to coexist with more conventional solutions.

Various species of cervid deer are the preferred hosts for adult, black-legged ticks (Ixodes scapularis and Ixodes pacificus) in the United States. Although frequently exposed to the agent of Lyme disease (Borrelia burgdorferi), these animals, for the most part, are incompetent as transmission reservoirs. We examined the borreliacidal activity of normal and B. burgdorferi-immune sera from sika deer (Cervus nippon) maintained in a laboratory setting and compared it to that of similar sera from reservoir-competent mice and rabbits. All normal deer sera (NDS) tested killed > 90% of B. burgdorferi cells. In contrast, normal mouse and rabbit sera killed < or = 22% of the Borrelia. Anti-B. burgdorferi antibodies could not be detected in any normal sera by indirect fluorescent antibody assay (IFA). Sera collected from deer 6 wk after exposure to B. burgdorferi by tick feeding exhibited IFA titers of 1:256, whereas sera from mice and rabbits similarly exposed had titers of > 1:1,024. Heat treatment (56 C, 30 min) of NDS reduced borreliacidal activity, with < 20% of the B. burgdorferi cells killed, suggesting complement-mediated killing. The chelators EGTA and EDTA were used to block the classical or both the classical and alternative complement pathways, respectively. Addition of 10 mM EGTA to NDS had a negligible effect on borreliacidal activity, with > 90% of the cells killed. Addition of 10 mM EDTA reduced the killing to approximately 30%, whereas the addition of Mg2+ (10 mM) restored borreliacidal activity to NDS. The addition of zymosan A, an activator of the alternative pathway, increased the survival of B. burgdorferi cells to approximately 80% in NDS. These data suggest that the alternative complement activation pathway plays a major role in the borreliacidal activity of NDS. Additionally, 10 mM EGTA had almost no effect on the killing activity of B. burgdorferi-exposed deer sera, suggesting that the classical pathway is not involved in Borrelia killing, even in sera from B. burgdorferi-exposed deer.

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