The aim of this paper was to study issues of network connectivity in vehicular ad hoc networks (VANETs) to avoid traffic congestion at a toll plaza. An analytical model was developed for highway scenarios where the traffic congestion could have the vehicles reduce their speed instead of blocking the flow of traffic. In this model, nearby vehicles must be informed when traffic congestion occurs before reaching the toll plaza so they can reduce their speed in order to avoid traffic congestion. Once they have crossed the toll plaza they can travel on at their normal speed. The road was divided into two or three sub-segments to help analyze the performance of connectivity. The proposed analytical model considered various parameters that might disturb the connectivity probability, including traveling speed, communication range of vehicles, vehicle arrival rate, and road length. The simulation results matched those of the analytical model, which showed the analytical model developed in this paper is effective.

Vehicular ad-hoc network (VANET) uses 'mobile internet' to facilitate the communication between vehicles and with the goal to ensure road safety and achieve secure communication. Thus the reliability of this type of networks is of paramount significance. The safety-related messages are disseminated in VANETs, on the wireless medium through vehicle to vehicle (V2V) and Vehicle to roadside (V2R) communications. Hence, the Reliability of network is an essential requirement. This paper considers the effect of vehicle transmission range and vehicle density on the connectivity probability. In addition, a reliability model which takes into account minimal safe headwayamong nearby vehicles at highway tunnel is specified. The reason is that under the tunnel Global Positioning System (GPS), a component of onboard unit (OBU) needs a rich line of sight for perfect services, because due to signal interference, the GPS does not work properly. Though, in the case of a fully connected network, there are chances of danger between vehicles which are close to each other. Therefore, the network is not safe, as accidents and collision can happen at any time. Hence, maintaining the minimal safe headway distance under the tunnel is interesting and useful for VANET. The obtained results show that the little difference of the minimal safe headway under the tunnel can cause a serious change in the entire network reliability. Suggesting that while designing the network reliability models the safe headway cannot be ignored.

Vehicular ad hoc networks (VANETs) provide alternative technology solutions to various transportation problems, and they provide a communication solution in intelligent transportation systems. However, the reliability and connectivity of VANET networks are subjects of concern. In building any routing protocol, a minimum level of network reliability must be ensured, which requires conducting a reliability analysis in order to investigate the different factors that affect reliability. Conducting a real-world reliability analysis is very expensive, and it requires significant preparation. Simulations are computationally costly due to the high number of available paths between the source node and the destination. In this article, a simplified approach is conducted that is mainly based on a simulation model of a road-type environment for a VANET network. A heuristic approach is developed for calculating the reliability based on the highest probability paths using the Dijkstra algorithm and the inclusion-exclusion approach for calculating the reliability of a given path. For vehicle-to-vehicle (V2V) communication, short-range protocols were considered-ZigBee (802.15.4), WiFi (IEEE 802.11), and Bluetooth (802.15.1)-as well as their standards for data rates, association time, and transmission range. On the other hand, the IEEE 802.11b was used for vehicle-toroadside (V2R) communications. Another parameter that was considered was the speed limit of the road environment, and three types of road environments were evaluated: highway, urban, and mixed. Other factors that were considered were the number of vehicles, the number of roadside units, and the type of message that was transmitted. The effects of all of these elements on the connectivity of the network were studied.

Modern data center networks typically adopt symmetric topologies, such as leaf-spine and fat-tree. When a large number of transmission control protocol (TCP) flows in data center networks send data to the same receiver, the congestion collapse, called TCP Incast, frequently happens because of the huge packet losses and Time-Out. To address the TCP Incast issue, we firstly demonstrate that adjusting the increasing speed of the congestion window during the slow start phase is crucially important. Then we propose the Gentle Slow Start (GSS) algorithm, which adjusts the congestion window according to real-time congestion state in a gentle manner and smoothly switches from slow start to congestion avoidance phase. Furthermore, we present the implementation and design of Gentle Slow Start and also integrate it into the state-of-the-art data center transport protocols. The test results show that GSS effectively decreases the Incast probability and increases the network goodput by average 8x.

Typically, the production data centers function with various risk factors, such as for instance the network dynamicity, topological asymmetry, and switch failures. Hence, the load-balancing schemes should consider the sensing accurate path circumstances as well as the reduction of failures. However, under dynamic traffic, current load-balancing schemes use the fixed parameter setting, resulting in suboptimal performances. Therefore, we propose a multi-level dynamic traffic load-balancing (MDTLB) protocol, which uses an adaptive approach of parameter setting. The simulation results show that the MDTLB outperforms the state-of-the-art schemes in terms of both the flow completion time and throughput in typical data center applications.