Space-Terrestrial Integrated Networks (STINs) serve as the crucial infrastructure for future 6G Networks, while network failures in STINs pose serious threats to the services provided by such networks. This paper focuses on the service request recovery in STINs against a satellite failure. For the uplink requests, downlink requests, and relay requests disrupted by a satellite failure, we explore both independent recovery and joint recovery. In independent recovery where each type of requests is recovered independently and sequentially, an Integer Linear Programming (ILP) model and related heuristic are proposed to identify the optimal recovery solution for each type of requests. We further explore the joint recovery where all requests are recovered jointly and simultaneously to achieve a high recovery efficiency. The ILP formulation and time-efficient heuristic are developed as well for the joint recovery. Finally, extensive numerical results are provided to demonstrate the effectiveness of the joint recovery and proposed heuristics in service recovery under a satellite failure.

By exploiting the high directivity of directional antennas and severe propagation loss, covert Terahertz (THz) communication can better suppress detection by wardens while achieving high-performance legitimate transmission. This emerging technology can achieve a higher level of covertness and can be applied in Internet of Things networks, such as smart senior care. In this work, we explore a one-hop system of covert THz communication, comprising a transmitter-receiver pair and multiple randomly distributed wardens. Utilizing the high directivity of antennas and the molecular absorption effect of THz signals, we can achieve transmissions with high covertness over THz bands. We divide the propagation area around Alice into several regions and propose a covert THz communication protocol in the considered scenario. Specifically, a circular area around Alice is divided into three regions based on a transmission model of directional antennas and the distance to Alice, and Alice decides to conduct transmissions if no warden exists in the insecure region (IR). Meanwhile, the theoretical expression of detection error probability (DEP) at a warden is derived and given. Numerical results demonstrate that our proposed protocol can increase the overall DEP of multiple wardens in both noncolluding and colluding modes compared to the case where no protocol is used.

As important network infrastructures to support data storage and service delivery for worldwide users, cloud data centers are facing great threaten by frequent disasters around the world and thus the survivability of cloud data centers becomes a critical issue. Since both data and service evacuations are desired at the same time under a real disaster scenario, this paper studies a joint design of them to fight against disasters. We consider a disaster that can present an early warning time before it really affects cloud data centers, and by exploiting the intrinsic interplay between data and service evacuations and efficiently utilizing the early warning time we propose a joint data and service evacuation scheme for emergency protection. We first formulate the joint design as two optimal Integer Linear Program (ILP) models. Notice that the protection process is highly time-sensitive due to the early warning time constraint, two time-efficient heuristics are then designed by carefully selecting evacuated services and candidate evacuation nodes to achieve a better sharing of network resources between data backup and service migration. Extensive numerical results demonstrate the efficiency of the proposed scheme on improving survivability of data and services in cloud data centers. With a set of given resource and early warning time constraints, this work can guide data center operators to achieve a tradeoff between data backup and service migration.

Highly fault-tolerant optical switch is becoming a critical network element for large wavelength division multiplexing mesh networks. Optical nodes built on replicated banyan network (RBN) structures are attractive for serving as optical switching systems due to the nice properties of banyan network structures. Furthermore it is expected that an optical RBN structure also has a good fault-tolerant capability because it consists of multiple identical banyan networks. Previous analytical models have been developed to understand the blocking behaviors of optical RBN networks without taking into account the link failure in optical RBN networks. In this paper, we conduct the link failure-tolerant analysis of optical RBN networks and present an analytical model for the blocking probability of optical RBN networks when link failures are taken into account. The model is significant because it provides network developers a quantitative guidance to determine the effects of network failure on the overall blocking behaviors of optical RBN networks and enables a desirable tradeoff to be made between blocking probability and hardware cost in a faulty optical RBN network.

Banyan networks serve as a class of important switching network architecture, whose multicast capability is critical for future high-performance switches to support multicast-intensive applications. The available literature indicates that, in order to construct optical multicast banyan networks based on the directional coupler (DC) technology, a high-hardware cost is usually involved to ensure the nonblocking property. In this paper, we conduct blocking probability analysis for such networks to explore the inherent tradeoff between blocking probability and hardware cost. In particular, we focus on a class of DC-based optical networks built on the replicated banyan network (RBN) architecture, and develop a theoretical upper bound on blocking probability for such networks under the general f-cast traffic, which covers the unicast and multicast as special cases. This bound captures the overall blocking behavior of f-cast optical RBN networks and agrees with the conditions of strictly nonblocking f-cast optical RBN networks. The proposed bound is significant because it provides a fundamental guideline to achieve the desirable tradeoff between blocking probability and hardware cost. This paper shows that the hardware cost of an f-cast optical RBN network can be dramatically reduced if a small blocking probability is allowed.

Data backup in data center networks (DCNs) is critical to minimize the data loss under disaster. This paper considers the cost-efficient data backup for DCNs against a disaster with ε early warning time. Given geo-distributed DCNs and such a ε-time early warning disaster, we investigate the issue of how to back up the data in DCN nodes under risk to other safe DCN nodes within the ε early warning time constraint, which is significant because it is an emergency scheme for data protection against a predictable disaster and also help DCN operators to build a complete backup scheme, i.e., regular backup and emergency backup. Specifically, an Integer Linear Program (ILP)-based theoretical framework is proposed to identify the optimal selections of backup DCN nodes and data transmission paths, such that the overall data backup cost is minimized. Extensive numerical results are also provided to illustrate the proposed framework for DCN data backup.

Data center network (DCN) placement with the consideration of potential large-scale region failures is critical to ensure its functionality under such catastrophic scenarios. This paper considers the optimal DCN placement for DCN failure risk minimization against such region failures. We first apply a general probabilistic region failure model to determine the failure probability of a node/link, and then propose a general grid partition-based scheme to flexibly define the global distribution of a region failure in terms of its occurring probability and intensity. Such grid partition scheme also helps us to evaluate the vulnerability under a region failure. With the help of the vulnerability information, we further propose an Integer Linear Program-based theoretical framework to identify the optimal DCN placement to lead to the minimum DCN failure risk under a region failure. An example and extensive numerical results are also provided to illustrate the proposed framework for DCN placement.

Vertical stacking of banyan networks has been an attractive architecture to construct optical switching networks due to its small depth, absolute signal loss uniformity and good fault tolerance property. Recently, F.K. Hwang extended the study of banyan-based networks to the general f-cast case, which covers the unicast (f = 1) and multicast (f = N) as special cases. In this paper, we study the blocking probability of f-cast optical banyan networks under crosstalk-free constraint. It is expected that the proposed probability model can be used to dimension such an f-cast network and achieve a graceful tradeoff between hardware cost and blocking probability.