This article is part of a three part series that examines networking structures in the automobile. Part 1 discusses how consumer technologies, such as USB and Ethernet, are integrated into the vehicle and connected with the vehicle backbone, using a technology called Media Oriented Systems Transport (MOST®). Part 2 describes why a network is needed for the vehicle backbone, why MOST was developed, and what its advantages are over other networking choices. This series conclusion offers a detailed explanation of MOST and examines the new Intelligent Network Interface Controller (INIC) architecture that simplifies how MOST systems are integrated.
The Media Oriented Systems Transport (MOST) architecture provides the physical interconnection and the software layers to ensure that automotive electronics devices interoperate. The International Standards Organization (ISO) has developed a model called the Open Systems Interconnect (OSI) Reference Model for creating the MOST architecture. The model defines seven layers of interoperability where each layer in one device communicates with the corresponding layer in another device. The figure below shows the various layers and the corresponding MOST concepts.
In MOST, NetServices is the software component that implements the Application Programming Interfaces (APIs) needed to establish communication between devices. In the first MOST implementations, NetServices was managed by an External Host Controller (EHC). The EHC had to ensure that all real-time requirements of the communication link were met. It typically ran whatever application was implemented on a device (e.g. user interface, amplifier, AM/FM tuner, CD changer, etc.) along with the network management tasks. The EHC was connected to a Network Interface Controller (NIC) that then connected to the physical link, which was typically Plastic Optical Fiber (POF).
The new INIC (Intelligent NIC) generation of MOST not only reduces software overhead, but it allows the use of Unshielded Twisted Pair (UTP) wiring. UTP copper wiring is an attractive solution to some carmakers because they want to continue using their existing manufacturing processes for wire harnesses and don't want to introduce new technologies like optical fiber.
There are now tens of millions of devices on the road using the NIC architecture. When implementing it, the network is dependent on each EHC controller to properly implement network management functions. Thus each EHC has to respond within the very specific timeframes to ensure proper network operations, which makes the real-time nature of these low level functions taxing on the EHC.
With the new INIC architecture, some of the burden is taken off the EHC by bringing the real-time functions needed for the MOST network into the INIC IC. The figure below shows the migration from the NIC to the INIC architecture.
This new INIC architecture results in the network becoming its own entity even though it is distributed among various devices connected to it. The individual INIC chips connect with each other and start the network without any intervention from an EHC. The network then exists as a standalone unit and does not rely on functions running on the various devices connected to it.
As each EHC finishes its boot-up process and becomes ready, it registers the particular functions with its individual INIC. The functions then become visible to the rest of the network. Each INIC monitors its EHC through a watchdog timer. If the EHC ever stops responding, the watchdog timer triggers the INIC into a protected mode that keeps the network alive even if the EHC no longer functions properly.
The INIC architecture is backward-compatible with the original NIC architecture. Both can co-exist in a single MOST system. The actual commands that travel over the physical conductor are the same whether they are going to a NIC or an INIC. The INIC architecture makes the network more robust and the software design easier.