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Background Toxoplasma gondii is an obligate parasite of all warm-blooded animals around the globe. Once infecting a cell, it manipulates the host’s DNA damage response that is yet to be elucidated. The objectives of the present study were three-fold: (i) to assess DNA damages in T. gondii-infected cells in vitro; (ii) to ascertain causes of DNA damage in T. gondii-infected cells; and (iii) to investigate activation of DNA damage responses during T. gondii infection. Methods HeLa, Vero and HEK293 cells were infected with T. gondii at a multiplicity of infection (MOI) of 10:1. Infected cells were analyzed for a biomarker of DNA double-strand breaks (DSBs) γH2AX at 10 h, 20 h or 30 h post-infection using both western blot and immunofluorescence assay. Reactive oxygen species (ROS) levels were measured using 2′,7′-dichlorodihydrofluorescein diacetate (H2DCFDA), and ROS-induced DNA damage was inhibited by a ROS inhibitor N-acetylcysteine (NAC). Lastly, DNA damage responses were evaluated by detecting the active form of ataxia telangiectasia mutated/checkpoint kinase 2 (ATM/CHK2) by western blot. Results γH2AX levels in the infected HeLa cells were significantly increased over time during T. gondii infection compared to uninfected cells. NAC treatment greatly reduced ROS and concomitantly diminished γH2AX in host cells. The phosphorylated ATM/CHK2 were elevated in T. gondii-infected cells. Conclusions Toxoplasma gondii infection triggered DNA DSBs with ROS as a major player in host cells in vitro. It also activated DNA damage response pathway ATM/CHK2. Toxoplasma gondii manages to keep a balance between survival and apoptosis of its host cells for the benefit of its own survival.

Diverse delay-sensitive realtime applications, e.g., Voice over IP, are emerging in the Internet and bringing a rigorous requirement on the transmission delay. Therefore, several IP Fast Reroute (IPFRR) schemes have been proposed. However, these schemes are all either too computationally expensive or unsatisfactory in protection coverage. In this paper, we propose Minimum Protection Cost Tree (MPCT), a tunnel-based IP Fast Reroute Scheme. First, MPCT provides 100% single-node protection coverage with direct forwarding (DF). Second, the computational complexity of MPCT is less than one full shortest path first (SPF) calculation. Third, by simulation with the data from China Education and Research Network (CERNET), Rocketfuel and BRITE, we show that even without DF, MPCT can provide more than 99% protection coverage. Besides, the protection path stretch ratios in real topologies are between 10% and 20%, which is acceptable compared with the corresponding achievement of reducing the algorithm complexity. We believe that our scheme MPCT moves a big step towards practical deployment.

Network failures occur frequently, and self-healing ability of existing routing protocols cannot guarantee fast route convergence under these failures without impacting packet forwarding. During routing convergence, network routes may be incorrect and even routing black holes and loops occur, which will result in extensive packet loss and thus influence network performance. To solve this problem, several improved routing solutions have been proposed. In this paper, we propose the concept and model of self-healing routing and analyze the key problems in current intra-domain and inter-domain self-healing routing protocols after briefly reviewing the characteristics of network failures. We classify the different self-healing solutions into two categories based on their design principles: routing restoration and routing protection, and systematically analyze these different typical solutions. Finally, we discuss several key issues in self-healing routing and propose a hybrid protection and restoration based routing scheme.

Fast convergence in IGP is very important for widespread deployment of real time applications. Many efforts, such as fast hello and fast flooding, have been proposed to reduce the convergence time in IGP. However, these solutions need to consume a large amount of CPU and memory resources in routers. Furthermore, they require collaboration of two neighbor routers. In this paper, we analyze the limitations in traditional Open Shortest Path First (OSPF), which causes slow (or not so fast) convergence based on failure data collected in real ISP networks. To address these issues, we propose a distributed OSPF (DOSPF) scheme to schedule routing computation through self-adaptively adjusting SPT waiting time. We analyze the convergence performance with DOSPF with Petri net. We then build a simulation tool to with routing trace in China Education and Research NETwork 2(CERNET2) to evaluate our DOSPF scheme. Our simulations show that DOSPF can effectively improve the IGP convergence performance.

Recent routing failure accidents show that routing systems are not so stable as we estimated because most of accidents caused packet delivery failure in Internet. In order to resolve this problem, many fast reroute solutions are proposed to guarantee reroute path provision after network failures without high packet loss. However, most of these solutions are not deployed in practice, and some key issues still need further consideration, such as the route loop issue and the deployment cost issue. In this paper, we present state machine models to analyze how path protection works in self-healing routing solutions and identify the drawbacks in traditional path protection approaches. We identify several requirements of path protection approaches, and present principles of our path protection approach to protect Internet routing based on our analysis result. Furthermore, we conduct a detailed study to measure our proposed path protection approach in production networks and the study shows that availability and stability of routing systems is improved in real production networks.

The exponential growth of Internet traffic requires that routers should be scalable. Cluster is an easy and flexible scalable way to improve the performance of the router. A critical issue in the design of cluster router is to provide a global and consistent routing table in such distributed architectures. In order to shorten the time of OSPF routing table computation, accelerate the network convergence, improve the reliability of the router and avoid the overload of the single control element CPU, distributed homogeneous OSPF is proposed in this paper. Each routing node of cluster router runs the OSPF protocol process on its own control element respectively, and keeps up the identical link-state database (LSDB). The shortest expected delay (SED) task scheduling algorithm is designed for the cluster router to compute the routing table on demanding. Compared with some improved OSPF schemes, our distributed homogenous OSPF can calculate routing table in real time and speed up LSAs processing in parallel. It decreases the internal communication overhead and provides a redundant backup scheme among these routing nodes to improve the reliability of cluster routers.