## 3 Related Work  
The authors of [29] present a Variable CCH Interval (VCI) scheme for the US WAVE system of MCO. If there is no heavy traffic, the default timeout of 50 ms is too excessive and consumes unnecessary time from SCH intervals. The VCI protocol, therefore, divides the CCH interval into two parts, the safety interval and the WSA interval. VCI packages are broadcasted by Road Site Units (RSUs). The RSU calculates the optimal CCH interval according to the surrounding traffic in the area by using a Markov chain model to analyze the behavior of single nodes. ITS-S systems can then set the ratio of CCH and WSA time slots to achieve maximum utilization before each CCH interval since the safety window remains constant at all times. The authors of [30] present the DCI-MAC protocol for the US MCO architecture. The DCI_MAC protocol considers nearby vehicles, the size of the messages, the number of packets in the queue, and the priority of the packets. If all the vehicles start broadcasting BSM at the beginning of the CCH interval, the total number of BSMs is equal to the number of vehicles in the given time interval. Based on this, a function was created to determine the size of the safety time interval, which depends on the number of local vehicles, the size of the packets, and the available data rate. After the safety time interval, the WSA time slot will be calculated. Here, the number of packets in the queue and their sizes are taken into account. After that, the CCH interval was constructed. By default, the SCH interval can be obtained by subtracting, but in this strategy, a separate time interval is calculated for SCH based on the local traffic. This can be efficient; since the SCH-calculated interval is short, the remaining time can be assigned to the CCH. The DCI-MAC protocol was evaluated in the NS3.26 discrete event network simulator. For mobility generation, SUMO (Simulation of Urban Mobility) was used. In the simulation, the PDR (Packet Delivery Ratio) and throughput of both the BSM and event-driven safety messages were measured. In [31], the authors introduce two multi-channel models in the European architecture of MCO. The NS3 simulation environment was chosen to build the VANET under evaluation. The simulation model uses the NS3 UDP module to transmit the periodic CAM messages every 100 ms. They proposed two CBR-based channel assignment strategies, a local and a global one. As a local, every vehicle in the simulation calculates the channel load of the local vehicle; therefore, each vehicle may have a different value. The global CBR represents the max channel load within a 2-hop area. The length of the monitoring interval is 200 ms with the Global CBR (GCBR) strategy and 10 ms with the Local CBR (LCBR) strategy. The algorithm of the two models is the same, and it only differs in the measured CBR. As a result, for example, in the LCBR strategy, a short monitoring interval tends to utilize the CCH much more than the other service channels. In contrast, a longer monitoring interval tends to have an equal load for all channels. Besides that, the paper also presents SMR, Fairness, and MD parameters. In [32], a service-actuated channel-switching scheme called SAMCO is proposed, considering user preferences, SAMs, and the estimated channel load. They use the service provider (SP) and service user (SU) concept. The service provider generates advertisement data, while the service user consumes this information. The channel load estimation is SAM-based since SAMs can contain information on channel load, message sizes, and message frequencies. SPs always measure their SCH channels with SAMs to find the right one to provide their services. In addition, SUs can also estimate the SAM-based channel load. The simulation was performed with a purpose-built proprietary simulator that can simulate the channel load, SP, and SU models. The chosen use case is a highway scenario. The length is 10 km, and 500-2000 vehicles are simulated, with some of them in platoons.