# Software-Defined Small Cell-Linked Vehicular Networks: Architecture and Evaluation
## 2 Related Works
### Small Cells-Linked RSU Paradigm for V2X Services
#### 2.1.2 Difficult Route forwarding for Small Cell Linked RSU in Vehicular Network  
The routing and forwarding of traditional VNs depend on the vehicular node's address. The software-defined vehicular network (SDVN) packet forwarding is based on node address in the shape of flow table [17]. However, in a small cell-linked RSUs network, there may be such a situation when other small cell-linked RSU nodes in the same site density may have the most recent road traffic data of the small cell-linked RSU area, and the ROs consumers can disregard information from the nodes themselves. Thus, the small cell-linked RSU node aggregates the safety traffic data. In this scenario, the data name can be used to request the data, regardless of which small cell-linked RSU node fulfills the data request. The requesting small cell-linked RSU node sends a message containing the requested content name to request data or content. When any small cell-linked RSU node with the required data receives the message of interest, it only sends the required data message. Recently, the research community proposed the vehicular named data network (VNDN) architecture [22] for this use case, but these architectures are only intended for content-based routing and are incapable of supporting other routing schemes such as geographic-location-based routing [23]. To meet the requirements of distributed small cell-linked RSU methods, a small cell-linked RSU framework supporting multiple 5G V2X communication modes is needed. With the development of V2X applications, 5G-SCN requires the scalability and capabilities of heterogeneous wireless communications which are challenging to manage. The current 5G-V2X systems are normally vehicular network communication-oriented [24] and the system design for one V2X network communication cannot be used to other V2X network communications. With the development of 5G-V2X applications, traditional V2X onboard (communication equipped with the vehicle) network communication-oriented unit architecture has struggled to meet the increasing complexity of V2X service requirements. The existing onboard vehicle network unit cannot meet the requirements of all communication traffic in a unified way. With the assistance of the same network architecture, multiple V2X communication configurations interrupt each other, and cannot offer personalized network forwarding for each V2X network communication. This affects the normal V2X routing of the entire 5G V2X architecture communication. Therefore, we propose an onboard V2X unit framework that can enable multiple V2X network communications to use simultaneously on the same onboard vehicle network unit equipped with a 5G V2X system without interrupting each other. 1.3 Vehicular Network Management for Distributed Small Cell-Linked RSU for 5G V2X Services Requirements  
The current 5G V2X system based on small cell-linked RSUs are V2X network communication oriented. Even the emerging 5G V2X architecture only allocates the V2X network resources to the vehicle's onboard unit, and cannot realize customized vehicular network traffic routing based on the requirements of small cell-linked RSU. Because of the multi-mode V2X network and small-cell network characteristics, the traditional VN communication resource (routing and forwarding) allocation model cannot fully exploit the benefits of a multi-mode 5G V2X network, but also cannot meet the customized requirements of 5G V2X network communication resources (routing). Therefore, it is necessary to develop a distributed software-defined small cell vehicular network architecture that can adapt to multiple modes and diversified V2X networks and provide differentiated V2X network resource services. System Architecture of Distributed Software Defined Small Cell Linked-Up Road Side Unit Vehicular Network  
Next-generation vehicular networks must support heterogeneous radio access technology while also implementing a dependable data dissemination routing protocol.