## 5 Conclusions  
The results presented in the previous sections demonstrate that the real-time data transmission protocol described in this paper effectively establishes communication between the vehicle's ECU and a destination server via voice phone calls, transmitting DTC codes at a rate of approximately 4 bits/s. A key advantage of this protocol is its reliance on the existing cellular infrastructure for voice channels, ensuring extensive coverage across Mexican territory. This infrastructure guarantees communication in regions where data channel coverage remains inconsistent or unavailable, making this approach highly practical for real-world V2X applications in Mexico.  
The developed protocol leverages V2X communication via voice channels, offering a cost-effective solution to real-time data transmission. Future work aims to enhance this protocol by integrating compatibility between voice and data channels, which would combine the extensive coverage of voice channels with the higher data transmission speeds of data channels. This hybrid approach could further optimize V2X communication by taking full advantage of the current infrastructure.  
This study provides a foundation for further research, particularly in improving V2X communication systems using low-cost, real-time data transmission protocols. The implementation of Dual Tone Multi-Frequency (DTMF) in this context opens new possibilities for V2X system applications and offers a novel approach that could inspire advancements in vehicle-to-everything communication, particularly in regions with limited data channel availability. The proposed system is not compatible with the OBDII interface for now, in future work a system that is compatible could be implemented. It is proposed that this protocol be adapted to different vehicle models, considering that with more vehicles it can be expanded to more complex data transmission, mainly real-time sensor data, it would be very important to know the type of sensor that is failing, as well as the location of the vehicle in case of mechanical failure.  
The prototype developed in this work has a Technology Readiness Level (TRL) maturity level on a scale of 5, which corresponds to the validation of components and/or their disposition in a relevant environment. However, future work will include the suggestions made in the experimentation to continue developing technology at higher TRL levels. Therefore, it is considered to continue working on the accuracy of the data, improving the communication protocol, carrying out tests in more territories to achieve increased accuracy, as well as, in a mathematical model that allows considering the messages sent, repetitions, number of times sent, time interval, type of technology, existence of infrastructure, type of area or territory, among others.  
**Author Contributions:** Contributing activities related to this paper were distributed as follows. General conceptualization, Data acquisition and writing--original draft preparation, J.P.Z.D.P; methodology, software and writing--original draft preparation, C.I.; validation and formal analysis, C.F.R.-G.; investigation, resources and data curation, E.K.A.; writing--review, editing and visualization, J.A.R.S; supervision, project administration and funding acquisition, P.R.I.T. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research received no external funding.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.  
**Acknowledgments:** The authors are eternally grateful for the scholarships provided by the SNII program from SECIHT-Mexico.  
**Conflicts of Interest:** The authors declare no conflict of interest.