Supported Physical Layer Technologies
The Bristlemouth PHY and MAC layers, while initially designed around 10BASE-T1L single pair ethernet, are designed to be agnostic to both PHY technologies and MAC layer protocols.
10BASE-T1L supports 10Mbps full-duplex communication, over transmission lengths up to 1000m. It is expected that its characteristics will sufficiently cover the bandwidth, latency, distance, and power requirements of many subsea applications. That said, there are also many applications that will have requirements that it cannot meet, which might include:
- High-bitrate optical and acoustic data streams
- Applications with very specific power requirements that available SPE PHY/MACPHY components may not be able to support
- Applications that wish to bridge Bristlemouth-based systems over wireless links
- Applications that desire a scalable number of devices over a single physical connection point (in the vein of CANbus, multi-drop serial, ethernet buses, etc.)
By creating the proper abstractions in the PHY and MAC layers of the Bristlemouth networking stack, the goal to support seamless extension of a Bristlemouth network to application-specific technologies can be supported. The following sections will describe how this can be achieved.
Network Interfaces
We will start by establishing some terminology around the physical and logical components that comprise the Bristlemouth L2 network stack, and how it can support different types of PHY technologies and technology-specific MAC protocols.
- Port: A physical connection interface, associated with one-and-only-one PHY, through which data is ultimately sent and received. A port is associated with a specific network technology (such as single pair ethernet).
- Network Device Instance: A logical interface which consists of one or more ports. Like ports, a Network Device Instance is specific to a PHY technology, and may have specific MAC protocol or wire-level encoding requirements (such as manchester coding).
- Network Interface: A logical interface which consists of one or more Network Device Instances, each potentially using different underlying technologies. A Bristlemouth network interface serves as the principle gateway for all L2 layer communication and has a single MAC address which is used for all communication, regardless of which Device Instance or port that data is ultimately sent through or received from. The Bristlemouth Network Interface normalizes incoming data to both a standardized 802.3 Ethernet Frame format (excluding the pre-amble and trailing FCS) and IPv6 Header format. Given any particular IP stack or library (such as LwIP, FreeRTOS+TCP, etc), the network interface implements the IP stack's lowest level input/output interface.
Below is a simple diagram that illustrates the layered components at a high level:
An implementation of this stack for a Bristlemouth processor that has a total of four ports, exposed via ADIN2111 two-port 10BASE-T1L MACPHY chips might look like:
A mixed-technology network deployment might look like:
