# Investigation of Data Quality Assurance across IoT Protocol Stack for V2I Interactions
## 6 Findings and Discussion
### Discussion  
CoAP and MQTT protocols notably distinguish themselves within this multifaceted landscape, largely owing to their broad research base and wide deployments. From our in-depth analysis, both protocols satisfactorily address five of our specified ten dimensions, including Availability, Completeness, Consistency, Data Integrity, and Reliability. The successful adherence to these critical DQ dimensions has effectively positioned CoAP and MQTT as the predominant protocols in the application layer for V2I communication scenarios. However, their prevalence is not a testament that they are the ultimate solution. Rather, it indicates the efficacy of these protocols at their domiciled layer. They possess a unique characteristic that is beneficial to V2I systems. Nonetheless, acknowledging that they can fulfil only five of the ten dimensions effectively either due to their design, leveraging the capabilities of their associated transport protocol, or other mechanisms infer the importance of employing a variety of other methodologies, e.g., cross-layer approach [108, 109] to compensate for other dimensions. For example, the reliability of data is one of the most coveted dimensions in IoT communications and is predominantly supported by layers underneath the application layer, the path layers (network and transport layer), and the link layers (data link and physical layer) [110]. Protocols such as MQTT and CoAP effectively support reliability due to mechanisms present in the protocols [111]. This is a testament to the heterogeneous and complex nature of V2I communication, which necessitates a versatile mix of protocols for optimal performance. \begin{table}
\begin{tabular}{l c c c c c c c c c c c c c c c} \hline \hline  & & & & & & & & & & & & & & & \\ \hline \multicolumn{1}{c}{**Application Layer**} & \multicolumn{1}{c}{**Transport Layer**} & \multicolumn{1}{c}{**Internet Layer**} \\ \hline
**DQ Dimensions** & **AMQP** & **CoAP** & **DDS** & **MQTT** & **XMPP** & **HTTP REST** & **WebSocket** & **TCP** & **UDP** & **QUICK** & **DCCP** & **SCTP** & **Ipv6** & **RTL** & **6 LoWPAN** \\ \hline Availability & \(\surd\) & \(\surd\) & \(\surd\) & & & \(\surd\) & & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) \\ \hline Data Accuracy & & & & & & \(\surd\) & & \(\surd\) & \(\surd\) & \(\surd\) & & & & \\ \hline Completeness & \(\surd\) & \(\surd\) & \(\surd\) & & \(\surd\) & & \(\surd\) & & & & & \\ \hline Confidentiality & & & & & & & & & \(\surd\) & & \(\surd\) & \(\surd\) \\ \hline Consistency & & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & & & & \(\surd\) & \\ \hline Data Integrity & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & & \(\surd\) & & \(\surd\) & & \(\surd\) & \(\surd\) & \\ \hline Reliability & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) \\ \hline Timeliness & & \(\surd\) & & \(\surd\) & & & & \(\surd\) & \(\surd\) & \(\surd\) & \(\surd\) & & \\ \hline Traceability & & & & & & & & \(\surd\) & \(\surd\) & \(\surd\) & & & \\ \hline Validity & & & & & & & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3. Dimensions of DQ against IoT protocols. In the transport layer, TCP has always been a dominant force. The inherent characteristics of reliability, guaranteed packet delivery, and error-checking ensure relevance, which has earned the trust of numerous developers. UDP, on the other hand, offers an effortless 'fire and forget' transmission model which excels in availability due to its connectionless nature and timeliness, making it a suitable choice for use cases like Emergency Vehicle Pre-emption [85] where low overhead and latency are prioritised. In addition, DCCP mirrors UDP's connectionless architecture but further augments it with a built-in congestion control mechanism, making it a promising candidate for streaming media feeds.