Consistent language for system bus, update modem definition

Virtual network interfaces are products with digital elements that directly or indirectly connect a device to a network via an API that emulates that of device drivers of physical network interfaces, typically operating at the data link layer.

This category includes but is not limited to wired and wireless network interface cards, controllers and adapters, such as for Wi-Fi, Ethernet, IrDA, USB, Bluetooth, NearLink, Zigbee, Fieldbus, or Infiniband. It also includes modems that are designed to connect directly to a system bus on the host and provide connection from the host to analog transmission media, as for example Power Line Communication devices.

Physical network interfaces are connected to a host system by a communications bus, such as PCIe or USB. Virtual network interfaces are software running on the host system, and communicate via the device driver interface.

FIXME: choose something consistent for:

 * system bus

 * communication bus

 * host bus

 * examples USB and PCI E

This category includes but is not limited to wired and wireless network interface cards, controllers and adapters, such as for Wi-Fi, Ethernet, IrDA, USB, Bluetooth, NearLink, Zigbee, Fieldbus, or Infiniband.

The term "modem" is used for two different kinds of products: a device with two or more network interfaces that routes network data between two different networks, such as a cable modem, and a single network interface that connects a physical adapter to a system bus, as for example a 5G modem interface or Power Line Communication devices. Modems of the second type are included in this standard.

This category includes purely virtual standalone products, such as virtual network interface cards, container network interfaces, VPN interfaces, and loopback interfaces.

This category includes products whose core function is a network interface and provides the feature of remote management interface for the network interface or the host system.

This category includes products whose core function is a network interface and provides the feature of remote management interface for the network interface or the host system. FIXME do we have time to do this?

FIXME what to do about network interfaces with multiple adapters that have a non-default switch mode?

### 4.3.2 Types of network interface

A physical network interface connects via the local communications bus to the host. The host transmits and receives data to the network by means of the local bus interface provided by the network interface. A physical network interface can typically directly read and write the host memory and raise interrupts. It sometimes has more advanced features that allow it to power cycle the entire system, download files using simple protocols, and act as a simple boot loader.

A physical network interface connects via a communications bus to the host. The host transmits to and receives data from the network by means of a device driver interface provided by the device driver for the network interface. A physical network interface might read and write the host memory directly and raise interrupts. It sometimes has more advanced features that allow it to power cycle the entire system, download files using simple protocols, and act as a simple boot loader.

![~~Physical network device architecture~~](media/physical_network_interface.drawio.png)

The device driver communicates with the host software or firmware by means of a network device driver API. This API abstracts the implementation details of the underlying network interface. Such network device driver API is typically defined by the host operating system or other software and is used by the host network stack to send or receive data through the network interface.

Physical interfaces require device drivers to make use of the physical hardware through the local communication bus. Virtual interfaces are effectively device drivers only, since they are made of software only without underlying hardware.

Physical interfaces require device drivers to make use of the physical hardware through a device driver interface. Virtual interfaces are effectively device drivers only, since they are made of software only without underlying hardware.

The device driver often needs elevated privileges to read and write memory. Device drivers for physical network interfaces often must have access also to the network interface control registers, directly or via host memory address space mapped to them; sometimes device drivers must as well enable or disable interrupts or other host hardware functions. This usually requires that the device driver has a high level of privilege on the host system.