# An Optimization Framework for Data Collection in Software Defined Vehicular Networks
## 4 Results
### Configuration of the Simulation Environment
#### 4.2.5 Data and Metadata Packets  
We collect the status data (\(L_{st}\)), namely the node Identifier (ID), timestamp, three-dimensional position, velocity, and acceleration of nodes in the vehicular network. These status data are collected by the control plane to make network decisions. We create a packet tag to embed the status data into a User Datagram Protocol (UDP) packet. Due to the use of real traffic data for vehicular nodes using a TCL file in Network Simulator 2 (NS2) mobility model, vehicular acceleration cannot be directly obtained from the mobility model. However, the position and velocity of vehicular nodes at a given instant of time can be obtained directly from the mobility model. Using the velocities and elapsed time between two positions (100 ms unless otherwise specified), we manually calculate the acceleration of a given node at runtime. **Data packet**: For the hybrid architecture, we embed the set of one-hop neighbors (\(\mathcal{S}_{i}\)) in the broadcasting data packet to reduce the transmission overhead. Thus, we consider the total broadcasting payload size in distributed and centralized architectures containing status information as 84 bytes and the broadcasting payload size of the hybrid architecture as \(84+4\mathcal{N}_{i}\). Thus, the total broadcasting encapsulated data packet size is 204 bytes for the DSRC communication channel (status data broadcasting takes place only in the DSRC channel) for centralized and distributed architectures. The total broadcasting encapsulated packet size of the hybrid architecture is \(204+4\mathcal{N}_{i}\) in the DSRC communication channel. Note that the payload sizes of the packets unicast to the control server by the agents differ based on the number of neighbors broadcasting to the agent/node in the hybrid and centralized architectures. In a hybrid architecture, a set of \(\mathcal{S}_{i}\) of the neighbors is also transmitted  
Figure 6: The placement and the connections of the RSUs in a given map. in addition to the status data payload. Therefore, the unicasting payload size of an agent in a hybrid architecture is at most \(4\sum_{m\in\mathcal{S}_{i}}(N_{m}Z_{m}+1)+84(\mathcal{N}_{i}+1)\). In hybrid architecture, we use an adaptive approach where \(\mathcal{S}_{m}\) of broadcasting nodes will be sent by an agent only if it changes compared to the previous data-gathering cycle. The unicasting payload size of a node in centralized architecture is \(84(\mathcal{N}_{i}+1)\). Thus, the total unicasting data payload size of an agent in a hybrid architecture is at most \(92+4\sum_{m\in\mathcal{S}_{i}}(\mathcal{N}_{m}Z_{m}+1)+84(\mathcal{N}_{i}+1)\) and \(110+4\sum_{m\in\mathcal{S}_{i}}(\mathcal{N}_{m}Z_{m}+1)+84(\mathcal{N}_{i}+1)\) for Ethernet and LTE communication channels, respectively. Furthermore, the total unicasting data payload size of a node in the centralized architecture is \(92+84(\mathcal{N}_{i}+1)\) and \(110+84(\mathcal{N}_{i}+1)\) for Ethernet and LTE communication channels, respectively. **Metadata packet:** In order to solve the data collection problem for optimization, metadata should be collected by the controller. As specified in the methodology section, there is a broadcasting metadata packet and a unicasting metadata packet. In the first data-gathering cycle, all nodes broadcast the metadata, and in subsequent data-gathering cycles, only the agent nodes broadcast metadata in the hybrid architecture. The broadcasting metadata packet consists of the node ID and timestamp information only, thus its payload size is limited to 12 bytes. However, the total size of a broadcasting metadata packet for DSRC is 132 bytes and 104 bytes for Ethernet. The broadcasting frequency is equal to the data collection frequency (\(f\)), which we vary to evaluate the performance of the solution. When broadcasting metadata is received at a given node, if the sender node already exists in the neighbor list, its timestamp will be updated. Otherwise, if the node does not exist in the neighbor list, it will be added as a new node with a new timestamp value.