The rapid convergence of automotive electronics, connected mobility, and Internet of Things (IoT) diagnostics has precipitated an unprecedented demand for in-vehicle networks that are simultaneously deterministic, highbandwidth, low-latency, secure, and resilient. This article synthesizes recent developments across Automotive Ethernet, Time-Sensitive Networking (TSN), wireless TSN variants, Controller Area Network (CAN) transport adaptations, and IoT-enabled vehicle health monitoring to propose a unified conceptual framework for future invehicle communication architectures. Drawing directly from empirical studies, standards documents, and contemporary experimental analyses, the work articulates the fundamental trade-offs among latency, reliability, electromagnetic compatibility, and resource constraints; presents a methodological approach for evaluating protocol enhancements in heterogeneous vehicle contexts; and offers prescriptive, research-backed solutions to persistent challenges such as time determinism over shared media, wireless coexistence within the vehicle cabin, and secure health data transport for remote diagnostics. The article advances a taxonomy of communication patterns found in modern vehicles, maps those patterns to protocol primitives derived from IEEE TSN and automotive-centric transports, and explicates how scheduling, shaping, and prioritization mechanisms can be composed to meet end-to-end system requirements. Limitations and open research directions are discussed, including systematic validation methodologies and the need for toolchains integrating EMI/EMC simulation with protocol-level scheduling analysis. This comprehensive exposition aims to guide researchers and practitioners developing robust, standards-aligned in-vehicle networking solutions capable of supporting advanced driver assistance systems (ADAS), high-definition sensing, and continuous IoT health telemetry.