How Internet Latency Could Be Erased From Remote Car Computer Testing

Every modern car is, in essence, a rolling network of small computers. Electronic control units, or ECUs, govern everything from engine performance and transmission behavior to safety systems and the central door locking function. Because automakers rely on a global web of specialized suppliers to build and optimize these devices, the physical hardware must traditionally travel to a central testing facility before vehicles can be validated. A new conceptual framework published in Frontiers in the Internet of Things argues that this costly logistics chain could be loosened: by treating ECUs as Internet of Things components, geographically dispersed control units could be integration-tested over the Internet, with the disruptive effects of network latency mathematically corrected after the fact.

The research, conducted by Stefanos Tziampazis and Pascal Hirmer of Mercedes-Benz AG and the University of Stuttgart, together with Michael Weyrich of the University of Stuttgart’s Institute of Industrial Automation and Software Engineering, addresses a problem that has long limited remote testing in the automotive sector. Integration testing, in which multiple ECUs are evaluated for their interdependent operation, has historically required all external suppliers to ship their devices to the automaker’s premises. With suppliers scattered across the globe, this co-location requirement creates time pressure, accumulates costs, and complicates efforts to meet vehicle release schedules. The authors’ earlier theoretical work had outlined how distributed integration over the Internet could enhance agility in outsourced development; the new paper builds on that foundation by confronting the practical obstacle of long-distance latency.

Latency is not a minor nuisance in this context. When test cases involve dynamic scenarios with temporal constraints, such as verifying that a response signal arrives within a defined window, even modest network delays can cause tests to fail for reasons that have nothing to do with the hardware under examination. The framework’s answer is a hybrid synchronous methodology that deliberately combines two modes of operation. Test management is asynchronous, meaning events are processed independently by the testing authority after they occur, while time referencing relies on synchronous timestamping techniques. Latency introduced across the distributed links is calculated and corrected after each event through the exchange of timestamps between nodes, allowing the execution time of a test case to be adjusted as if the components had been sitting side by side on a local bench.

To make this compensation possible, the framework leans on established time synchronization protocols, and the paper provides a technical tour of three of them. The Network Time Protocol, one of the oldest synchronization mechanisms, operates through a hierarchical, stratum-based structure and a bidirectional handshake between master and slave nodes, achieving precision on the millisecond scale, though its assumption of symmetrical network links is often invalid in real-world conditions. The Precision Time Protocol, introduced in 2002 under the IEEE 1588 standard, offers a significant leap in accuracy, guaranteeing at least one microsecond of precision across up to seven hops. Its latest revision, the generalized Precision Time Protocol known as gPTP, forms part of the Time-Sensitive Networking framework and introduces peer delay mechanisms, boundary clocks, and transparent clocks that adjust time packets as they traverse the network, a feature the authors note is particularly useful in automotive gateways.

The third protocol is the Controller Area Network, or CAN, the communication backbone that still underpins numerous critical vehicle functions. Time synchronization over CAN is described by the AUTOSAR standard and differs from NTP and PTP in a key respect: the handshake is unidirectional rather than bidirectional. A time reference, typically consisting of 48 bits for seconds and 32 bits for nanoseconds, is transmitted across two CAN frames, with the SYNC frame carrying the seconds portion and the FUP frame carrying the nanoseconds portion. Master and slave nodes each record timestamps at the start and end of the exchange, and the slave adjusts its internal clock based on the calculated propagation delay. The authors chose PTP for the higher levels of their architecture partly because it does not depend on external references such as GPS, which are often inaccessible in closed laboratory setups.

The framework itself is organized into three hierarchical levels. At level 1, physical ECUs remain housed locally by suppliers in their own geographical locations, with the study focusing on ECUs operating over CAN. Level 2 consists of external gateways placed close to each ECU, one provided to each supplier. These gateways bridge the low-level CAN bus and the Internet, encapsulating CAN frames into higher-layer packets and vice versa, much like the transparent clocks used in Time-Sensitive Networking. Crucially, the gateways also operate as independent CAN nodes that interact with their adjacent ECUs over a dedicated local channel, enabling specific events to be reproduced without coordinating all three levels simultaneously. Level 3 is the automotive OEM’s central node, which manages test coordination and result evaluation, with communication secured through VPN traffic channels to address data security and intellectual property concerns.

To demonstrate the approach, the authors modeled a remote test of the central door locking function, involving a body control module and two door ECUs supplied by different companies at separate locations. The scenario unfolds in eight steps: synchronization across all three levels, a locking request timestamped and forwarded to the body control module, the module’s response captured and returned with timestamps, the door ECUs triggered with that response, their replies collected, a second trigger sent back to the body control module, its final response recorded, and finally a latency correction and verification step. The test succeeds only if the final response matches the CAN frame indicating all doors are locked and the corrected execution time, calculated by subtracting the total latency introduced by the Internet links, falls within the predefined limit.

The elegance of the method lies in how it decouples testing time from global time. In a conventional local setup, where all devices are co-located, a sequence of messages arrives within its specified interval and the test passes. In a naive global setup without compensation, latency pushes the final message past the deadline, producing a failure that reflects the network rather than the hardware. With the hybrid approach, every message is timestamped, allowing post hoc reconciliation of the discrepancies. The deadline on the testing timeline is effectively shifted forward, and success is evaluated against this decoupled axis, bringing the global setup into closer alignment with local conditions. This expands the spectrum of remotely testable cases beyond purely functional attributes, such as whether a signal occurs, to temporal characteristics like signal response times.

The authors are candid about the challenges that remain. Replicating the locally broadcast behavior of CAN over the Internet raises questions of atomic commitment, the principle that all nodes in a group must engage in message exchanges within non-overlapping epochs. Their answer draws on checkpointing and message logging, techniques from fault-tolerant distributed computing, in which the OEM acts as a leader node that gathers checkpoints, reassembles the events of a test case, and compensates for latency through timestamp recording. Synchronization accuracy is another concern: PTP handshakes largely assume symmetrical links and locally proximate nodes, conditions that are difficult to meet across long distances, and imprecision at the top of the hierarchy propagates downward to the gateway-to-ECU level. Performance requirements add further strain, since nanosecond-precision timestamping demands specialized hardware that cost-sensitive automotive gateways often lack, though emerging platforms such as advanced field programmable gate arrays may close that gap.

The broader significance of the work extends beyond the automotive industry. By framing ECUs as geographically dispersed IoT components and remote testing as a distributed IoT process, the authors position latency, timeliness, and synchronization as shared challenges across both domains, suggesting the hybrid approach could benefit distributed IoT testing processes that are not bound by strict real-time requirements. Future research, the team notes, will aim to formalize the equivalence between local and global testing environments through communication calculus and to validate the framework empirically through an end-to-end latency analysis. If those efforts succeed, the days of crating control units and flying them across continents for integration testing may finally be numbered, replaced by a world where a supplier’s hardware in one country can be exercised, timed, and verified from an automaker’s laboratory thousands of kilometers away, with the Internet’s delays accounted for to the nanosecond.

Subject of Research: A hybrid latency-compensation framework for remote Internet-based integration testing of automotive electronic control units

Article Title: A hybrid framework for latency compensation in remote testing of automotive electronic control units

Article References: Tziampazis, S., Hirmer, P., & Weyrich, M. (2024). A hybrid framework for latency compensation in remote testing of automotive electronic control units. Frontiers in the Internet of Things, 3, Article 1433903. https://doi.org/10.3389/friot.2024.1433903

Image Credits: AI Generated

DOI: 10.3389/friot.2024.1433903

Keywords: automotive, electronic control units, remote testing, latency compensation, time synchronization, Internet of Things, Precision Time Protocol, Controller Area Network, distributed systems, integration testing, automotive suppliers, Time-Sensitive Networking