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Ethernet over USB is the use of a USB link as a part of an Ethernet network, resulting in an Ethernet connection over USB (instead of e.g. PCI or PCIe).
USB over Ethernet (also called USB over Network or USB over IP) is a system to share USB-based devices over Ethernet, Wi-Fi, or the Internet, allowing access to devices over a network. It can be done across multiple network devices by using USB over Ethernet Hubs.
There are numerous protocols for Ethernet-style networking over USB. The use of these protocols is to allow application-independent exchange of data with USB devices, instead of specialized protocols such as video or MTP (Media Transfer Protocol). Even though the USB is not a physical Ethernet, the networking stacks of all major operating systems are set up to transport IEEE 802.3 frames, without needing a particular underlying transport.
The main industry protocols are Remote NDIS (RNDIS, a Microsoft vendor protocol), Ethernet Control Model (ECM), Ethernet Emulation Model (EEM), and Network Control Model (NCM). The latter three are part of the larger Communications Device Class (CDC) group of protocols of the USB Implementers Forum (USB-IF). They are available for download from the USB-IF (see below). The RNDIS specification is available from Microsoft's website. Regarding de facto standards, some standards, such as ECM, specify the use of USB resources that early systems did not have. However, minor modifications of the standard subsets make practical implementations possible on such platforms. Remarkably, even some of the most modern platforms need minor accommodations and therefore support for these subsets is still needed.
Of these protocols, ECM could be classified as the simplest—frames are simply sent and received without modification one at a time. This was a satisfactory strategy for USB 1.1 systems (current when the protocol was issued) with 64-byte packets but not for USB 2.0 systems which use 512-byte packets.
One significant problem is the Ethernet frames are about 1500 bytes in size—about 3 USB 2.0 packets, and 23 USB 1.1 packets. The USB system works by each packet being sent as a transfer, a series of maximum-length packets terminated by a short packet or a special ZLP (zero-length packet). After this, there is bus latency, where nothing is sent until another transfer can be initiated. Such reduces bus occupancy, meaning that nothing is sent for considerable fractions of bus time. A gap every 23 frames is not noticeable, but a gap every three frames can be viewed as very costly to throughput.
As USB has become faster, devices utilize more data and hence there is now demand for sending large amounts of data—either to be stored on the device or be relayed over wireless links (see 3GPP Long Term Evolution).
These new devices are still much lower in power than desktop PCs, thus the issue of careful data handling arises, to maximize use of DMA resources on the device and minimize (or eliminate) copying of data (zero-copy). The NCM protocol has elaborate provisions for this. See the link below for protocol comparisons.
The USB-eth module in Linux makes the computer running it a variation of an Ethernet device that uses USB as the physical medium. It creates a Linux network interface, which can be assigned an IP address and otherwise treated the same as a true Ethernet interface. Any applications that work over real Ethernet interfaces will work over a USB-Ethernet interface without modification, as there is no distinction between utilizing proper or improper Ethernet hardware. [1] [2]
On Linux hosts, the corresponding Ethernet-over-USB kernel module is called usbnet. The Bahia Network Driver [3] is a usbnet-style driver available for Win32 hosts.
The approach allows devices with very limited communications hardware to operate over IP networks. The Linux kernel for the iPAQ uses this communications strategy exclusively since the iPAQ hardware has neither an accessible legacy (RS-232/RS-422) serial port nor a dedicated network interface.
AppleTalk is a discontinued proprietary suite of networking protocols developed by Apple Computer for their Macintosh computers. AppleTalk includes a number of features that allow local area networks to be connected with no prior setup or the need for a centralized router or server of any sort. Connected AppleTalk-equipped systems automatically assign addresses, update the distributed namespace, and configure any required inter-networking routing.
In computer networking, the maximum transmission unit (MTU) is the size of the largest protocol data unit (PDU) that can be communicated in a single network layer transaction. The MTU relates to, but is not identical to the maximum frame size that can be transported on the data link layer, e.g., Ethernet frame.
Wake-on-LAN is an Ethernet or Token Ring computer networking standard that allows a computer to be turned on or awakened from sleep mode by a network message. It is based upon AMD's Magic Packet Technology, which was co-developed by AMD and Hewlett-Packard, following its proposal as a standard in 1995. The standard saw quick adoption thereafter through IBM, Intel and others.
The data link layer, or layer 2, is the second layer of the seven-layer OSI model of computer networking. This layer is the protocol layer that transfers data between nodes on a network segment across the physical layer. The data link layer provides the functional and procedural means to transfer data between network entities and may also provide the means to detect and possibly correct errors that can occur in the physical layer.
In IEEE 802 LAN/MAN standards, the medium access control (MAC), also called media access control, is the layer that controls the hardware responsible for interaction with the wired or wireless transmission medium. The MAC sublayer and the logical link control (LLC) sublayer together make up the data link layer. The LLC provides flow control and multiplexing for the logical link, while the MAC provides flow control and multiplexing for the transmission medium.
A network interface controller is a computer hardware component that connects a computer to a computer network.
The Point-to-Point Protocol over Ethernet (PPPoE) is a network protocol for encapsulating Point-to-Point Protocol (PPP) frames inside Ethernet frames. It appeared in 1999, in the context of the boom of DSL as the solution for tunneling packets over the DSL connection to the ISP's IP network, and from there to the rest of the Internet. A 2005 networking book noted that "Most DSL providers use PPPoE, which provides authentication, encryption, and compression." Typical use of PPPoE involves leveraging the PPP facilities for authenticating the user with a username and password, via the PAP protocol or via CHAP. PAP was dominant in 2007 but service providers have been transitioning to the more secure CHAP, because PAP is a plain-text protocol. Around 2000, PPPoE was also starting to become a replacement method for talking to a modem connected to a computer or router over an Ethernet LAN displacing the older method, which had been USB. This use-case, connecting routers to modems over Ethernet is still extremely common today.
AX.25 is a data link layer protocol originally derived from layer 2 of the X.25 protocol suite and designed for use by amateur radio operators. It is used extensively on amateur packet radio networks.
The Parallel Line Internet Protocol (PLIP) is a computer networking protocol for direct computer-to-computer communications using the parallel port, normally used for connections to a printer.
TCP offload engine (TOE) is a technology used in some network interface cards (NIC) to offload processing of the entire TCP/IP stack to the network controller. It is primarily used with high-speed network interfaces, such as gigabit Ethernet and 10 Gigabit Ethernet, where processing overhead of the network stack becomes significant. TOEs are often used as a way to reduce the overhead associated with Internet Protocol (IP) storage protocols such as iSCSI and Network File System (NFS).
ifconfig is a system administration utility in Unix-like operating systems for network interface configuration.
In computer networking, jumbo frames are Ethernet frames with more than 1500 bytes of payload, the limit set by the IEEE 802.3 standard. The payload limit for jumbo frames is variable: while 9000 bytes is the most commonly used limit, smaller and larger limits exist. Many Gigabit Ethernet switches and Gigabit Ethernet network interface controllers and some Fast Ethernet switches and Fast Ethernet network interface cards can support jumbo frames.
EtherCAT is an Ethernet-based fieldbus system developed by Beckhoff Automation. The protocol is standardized in IEC 61158 and is suitable for both hard and soft real-time computing requirements in automation technology.
On Linux, network block device (NBD) is a network protocol that can be used to forward a block device from one machine to a second machine. As an example, a local machine can access a hard disk drive that is attached to another computer.
The Remote Network Driver Interface Specification (RNDIS) is a Microsoft proprietary protocol used mostly on top of USB. It provides a virtual Ethernet link to most versions of the Windows, Linux, and FreeBSD operating systems. Multiple revisions of a partial RNDIS specification are available from Microsoft, but Windows implementations have been observed to issue requests not included in that specification, and to have undocumented constraints.
IEEE 1394 is an interface standard for a serial bus for high-speed communications and isochronous real-time data transfer. It was developed in the late 1980s and early 1990s by Apple in cooperation with a number of companies, primarily Sony and Panasonic. It is most commonly known by the name FireWire (Apple), though other brand names exist such as i.LINK (Sony), and Lynx.
Generic Stream Encapsulation, or GSE for short, is a Data link layer protocol defined by DVB. GSE provides means to carry packet oriented protocols such as IP on top of uni-directional physical layers such as DVB-S2, DVB-T2 and DVB-C2.
The Linux-IOTarget (LIO) is an open-source Small Computer System Interface (SCSI) target implementation included with the Linux kernel.
RTP-MIDI is a protocol to transport MIDI messages within Real-time Transport Protocol (RTP) packets over Ethernet and WiFi networks. It is completely open and free, and is compatible both with LAN and WAN application fields. Compared to MIDI 1.0, RTP-MIDI includes new features like session management, device synchronization and detection of lost packets, with automatic regeneration of lost data. RTP-MIDI is compatible with real-time applications, and supports sample-accurate synchronization for each MIDI message.
Distributed Overlay Virtual Ethernet (DOVE) is a tunneling and virtualization technology for computer networks, created and backed by IBM. DOVE allows creation of network virtualization layers for deploying, controlling, and managing multiple independent and isolated network applications over a shared physical network infrastructure.