USB (short for Universal Serial Bus ), is an industry standard developed to define cables, connectors and protocols for connections, communications, and power supplies between personal computers and peripheral devices.
There are three generations of USB specs:
- USB 1. x
- USB 2.0, with some updates and additions
- USB 3. x
Released in 1996, the USB standard is currently managed by the USB Implementers Forum (USB IF).
Video USB
Ikhtisar
USB is designed to standardize peripheral connections (including keyboards, pointing devices, digital cameras, printers, portable media players, disk drives and network adapters) to personal computers, both to communicate and to supply electrical power. It has replaced interfaces such as serial port and parallel port, and has become commonplace in various devices. The USB connector has replaced another type for a portable device battery charger.
Identify sockets
This section is intended to enable quick identification of USB containers (sockets) on the equipment. More diagrams and discussions about plugs and containers can be found on USB (Physical) Ã,§ Liaison.
Destination
Universal Serial Bus was developed to simplify and improve the interface between personal computers and peripheral devices, when compared to the standard or ad-hoc interfaces previously owned.
From a computer user's perspective, the USB interface improves ease of use in several ways. The USB interface is self-configuring, so users do not need to adjust the settings on the device and interface for speed or data format, or configure interruptions, input/output addresses, or direct memory access channels. The USB connectors are standardized on the host, so each device can use the available containers. USBs take full advantage of the additional processing power that can be economically incorporated into peripheral devices so they can manage themselves; USB devices often do not have user-customizable interface settings. The USB interface is "hot pluggable", which means the device can be exchanged without rebooting the host computer. Small devices can be switched directly from the USB interface, replacing the extra power supply cables. Because the use of the USB logo is only permitted after compliance testing, users can be assured that USB devices will function as expected without extensive interaction with settings and configurations; The USB interface defines protocols for recovery from common errors, increasing reliability over previous interfaces. Installation of devices that rely on USB standards requires minimal operator action. When the device is plugged into a port on a running personal computer system, it is fully automated configured using an existing device driver, or the system prompts the user to locate the drivers that are then installed and configured automatically.
For hardware manufacturers and software developers, the USB standard eliminates the requirement to develop proprietary interfaces to new peripherals. Various transfer rates are available from the appropriate USB interface from the keyboard and mouse to the video streaming interface. The USB interface can be designed to provide the best latency available for a time-critical function, or it can be set to perform mass data background transfers with minimal impact on system resources. USB interface is generalized without a dedicated signal line for only one function of a single device.
Limitations
USB cable is limited in length, because the standard is intended to connect to peripherals on the same table, not between rooms or between buildings. However, the USB port can be connected to a gateway that accesses the remote device. USB has strict "tree" and "master-slave" protocols to handle peripheral devices; peripheral devices can not interact with each other except through a host, and two hosts can not communicate via their USB port directly. Some extensions to this restriction are made possible via USB On-The-Go. Hosts can not "broadcast" signals to all peripherals at once, each of which must be handled individually. Some very high speed peripheral devices require sustained speeds that are not available in the USB standard. While the converter exists between certain "legacy" and USB interfaces, they may not provide full implementation of legacy hardware; for example, a USB to parallel port converter works well with the printer, but not with a scanner that requires two-way use of data pins.
For product developers, USB usage requires the implementation of complex protocols and implies "smart" controllers on peripheral devices. Developers of USB devices intended for public sale generally need to get a USB ID that requires fees paid to the Forum Implementer. Developers of products using the USB specifications must sign an agreement with the Forum Implementer. The use of the USB logo on the product requires an annual fee and membership in the organization.
Maps USB
History
A group of seven companies started USB development in 1994: Compaq, DEC, IBM, Intel, Microsoft, NEC, and Nortel. The goal is to make it easier to connect external devices to the PC by replacing multiple connectors on the back of the PC, overcoming the usability issues of the existing interface, and simplifying the software configuration of all devices connected to USB, and enabling greater data rates for the device external. A team including Ajay Bhatt worked on standards at Intel; the first integrated USB-supported circuit was manufactured by Intel in 1995.
The original USB 1.0 specification, introduced in January 1996, specifies a data transfer rate of 1.5 Mbit/s Low Speed ​​ and 12 Mbit/s Full Speed ​​. Microsoft Windows 95, OSR 2.1 provides OEM support for devices. The first USB version used was 1.1, released in September 1998. The data rate of 12 Mbit/d is intended for higher-speed devices such as disk drives, and lower 1.5 Mbit/s rate for low data rate devices. like a joystick. Apple Inc. iMac is the first mainstream product with USB and iMac's success popularized the USB itself. Following Apple's design decisions to remove all the old ports of the iMac, many PC manufacturers are starting to build legacy-free PCs, leading to a wider PC market using USB as a standard.
The USB 2.0 specification was released in April 2000 and ratified by the USB Implementers Forum (USB-IF) in late 2001. Hewlett-Packard, Intel, Lucent Technologies (now Nokia), NEC, and Philips jointly led the initiative to develop transfer speeds higher data, with the resulting specification reaching 480 Mbit/s, 40 times faster than the original USB 1.1 specification.
The USB 3.0 specification was published on November 12, 2008. The main purpose is to increase data transfer rate (up to 5 Gbit/s), reduce power consumption, increase power output, and be compatible with USB 2.0. USB 3.0 includes a new high speed bus called SuperSpeed ​​â € <â € As of 2008, about 6 billion USB ports and interfaces are in the global market, and about 2 billion are sold annually. The USB 3.1 specification is presented in July 2013. In December 2014, USB-IF sends USB 3.0 specifications, USB Power Delivery 2.0 and USB Type-C to IEC (TC 100-Audio, video and multimedia systems and equipment) for inclusion in international standards IEC 62680 Universal Serial Bus Interface for data and power , which is currently based on USB 2.0. The USB-3.2 specification was published in September 2017. USB 1.x
Released in January 1996, USBÃ, 1.0 specifies a data rate of 1.5 Mbit/s (Low Bandwidth or Low Speed) and 12 Mbit/s (Full Speed) . It does not allow for extension cords or pass-through monitors, due to time and power constraints. Some USB devices made it into the market until USB 1.1 was released in August 1998. USB 1.1 was the earliest widely adopted revision and led to what Microsoft called the "Legacy Free PC".
Both USB 1.0 and 1.1 do not specify designs for connectors that are smaller than standard A or type B. Although many designs for miniature Type B connectors appear in many peripherals, conformance to USB 1.x standards is hampered by treating peripherals that have miniature connectors as if as they have a tethered connection (ie: no plug or container at the peripheral end). No miniature connectors of type A to USB 2.0 (revision 1.01) are introduced.
USB 2.0
USB 2.0 was released in April 2000, adding a maximum signaling rate higher than 480 Mbit/s (High Speed ​​ or High Bandwidth) , in addition to USB 1.x Full Speed ​​ signaling rate 12 Mbit/s. Due to bus access constraints, the effective throughput of the High Speed ​​ signal rate is limited to 280 Mbit/s or 35 MB/s.
Modifications to the USB specification have been made through Change Notification Technique (ECN). The most important of these ECNs are included in the USB 2.0 specification packages available from USB.org:
- Mini-A and Mini-B Connectors;
- USB-Micro Cable and Specification Connector 1.01;
- Ease of Additional USB;
- Additional On-The-Go 1.3 The USB On-The-Go allows two USB devices to communicate with each other without requiring separate USB hosts;
- Battery Charging Specification 1.1 Additional support for specific chargers, host charger behavior for devices with dead battery;
- Battery Charging Specification 1.2 : with a 1.5 A current rise on the charging port for an unconfigured device, enabling High Speed ​​communication while having current up to 1.5 A and allowing a maximum current of 5 A ;
- ECN Power Management Addendo that adds power status sleep .
USB 3.x
The USB 3.0 specification was released on November 12, 2008, with its management transferring from the USB 3.0 Promoter Group to the USB Implementers Forum (USB-IF), and announced on November 17, 2008 at the SuperSpeed ​​Developer Conference â € <â € USB.
USB 3.0 adds the transfer mode of SuperSpeed ​​â € <â € <, by plugging into plugs, receptacles, and backward compatible cables. SuperSpeed ​​plugs â € <â € The SuperSpeed ​​bus provides transfer mode at a nominal rate of 5.0 Gbit/s, in addition to the three existing transfer modes. Its efficiency depends on a number of factors including the encoding of the physical symbol and the level of the link above it. In a 5 Gbit/s (625 Mbyte/s) signal with 8b/10b encoding, the raw throughput is 500 Mbyte/s. When flow control, framing packets and protocol overhead are considered, it is realistic for 400 Mbyte/s (3.2 Gbit/s) or more to be sent to the application. Communication is full duplex in SuperSpeed ​​transfer mode; previous mode half duplex, advocated by the host. Low-power and high-power devices continue to operate with this standard, but devices using SuperSpeed ​​â € <â € USB 3.1, released in July 2013, maintains the SuperSpeed ​​transfer rates under the new label USB 3.1 Gen 1 , and introduces the transfer of SuperSpeed â € <â € < new mode, USB 3.1 Gen 2 with maximum data signal level up to 10 Gbit/s (1250 MB/s, twice the rate of USB 3.0), which reduces the above line encoding becomes only 3% by changing the encoding scheme to 128b/132b USB 3.2, released in September 2017, retains existing USB 3.1 SuperSpeed ​​and SuperSpeed ​​data modes but introduces two new "SuperSpeed" transfer mode via USB-C connector with data rates of 10 and 20 Gbit/s (1250 and 2500 MB/sec). Increased bandwidth is the result of a multi-path operation over existing cables intended for the flip-flop capability of the Type-C connector. The USB system consists of hosts with one or more downstream ports, and many peripherals, forming a star-stelled topology. Additional USB Hubs may be included, allowing up to five levels. USB hosts may have multiple controllers, each with one or more ports. Up to 127 devices can be connected to a single host controller. The USB device is connected in series via the hub. Hubs built into a host controller are called root hubs. USB devices may consist of several logical sub-devices referred to as device functions . The composite device can provide multiple functions, for example, a web camera (video device functionality) with an internal microphone (audio device function). The alternative to this is the aggregated tool, where the host assigns each logical device a different address and all logical devices connected to a built-in hub that is connected to a physical USB cable. The communication of USB devices is based on pipes (logical channels). A pipe is a connection from the host controller to the logical entity, found on the device, and is named end point . Since the pipes correspond to the end point, the term is sometimes used interchangeably. USB devices can have up to 32 endpoints (16 IN, 16 OUT), although it is very rare to have so many. The end point is defined and numbered by the device during initialization (period after physical connection is called "enumeration") and so is relatively permanent, while the pipe can be opened and closed. There are two types of pipes: flow and message. The message pipeline is bidirectional and is used for transfer of controls . The pipeline is typically used for short, simple commands for devices, and status response, used, for example, by the bus control pipeline number 0. A flow pipe is a uni-directional pipe connected to a uni-directional endpoint that transfers data using isochronous , interrupt , or bulk transfers: Version history < span id = "0.99">
Release version
System design
- Interrupt transfers
- Devices that need guaranteed quick responses (limited latency) such as pointing device, mouse, and keyboard
- Mass transfers
- Sporadic transfers use all remaining bandwidth, but without warranty on bandwidth or latency (e.g., file transfer)
When a host initiates a data transfer, it sends a TOKEN packet containing a specified endpoint with a tuple (device_address, endpoint_number) . If transfer from host to endpoint, the host sends the OUT packet (TOKEN packet specialization) with the desired device address and endpoint number. If the data transfer from the device to the host, the host sends the IN packet instead. If the destination endpoint is a uni-directional endpoint that the manufacturer's designated direction does not match the TOKEN packet (eg the factory's designated direction is IN while the TOKEN packet is the OUT package), the TOKEN packet is ignored. Otherwise, it is accepted and transaction data can be initiated. The two-way endpoint, on the other hand, receives packets IN and OUT.
Endpoints are grouped into the interface and each interface is associated with a single device function. An exception to this is the zero endpoint, which is used for device configuration and is not associated with any interface. A device function consisting of an independently controlled interface is called a composite device . The merge device has only one device address because the host simply assigns the device address to a function.
When a USB device is first connected to a USB host, the USB device enumeration process begins. The enumeration begins by sending a reset signal to the USB device. The speed of USB device data is determined during re-signaling. Once reset, the USB device information is read by the host and the device is assigned a unique 7-bit address. If the device is supported by the host, the device driver required to communicate with the device is loaded and the device is set to a configured state. If the USB host is restarted, the enumeration process will be repeated for all connected devices.
The host controller directs the flow of traffic to the device, so no USB devices can transfer any data on the bus without explicit request from the host controller. In USB 2.0, the host controller polls the bus for traffic, usually in round-robin mode. The throughput of each USB port is determined by the slower speed of the USB port or USB device connected to the port.
The high-speed USB 2.0 hub contains a device called transaction translator that converts between high speed USB 2.0 buses and full and low speed buses. There may be one translator per hub or per port.
Since there are two separate controllers on each host of USB 3.0, USB 3.0 devices will transmit and receive at USB 3.0 data rates regardless of USB 2.0 or previous devices connected to the host. The operating data speed for the previous device is set by legacy.
Device class
The functionality of a USB device is determined by the class code sent to the USB host. This allows the host to load software modules for the device and to support new devices from different manufacturers.
The device classes include:
USB mass storage/USB drive
The class of USB mass storage devices (MSC or UMS) standardizes the connection to storage devices. Originally intended for magnetic and optical drives, it has been extended to support flash drives. It has also been expanded to support a variety of new devices as many systems can be controlled by the metaphor of manipulation of known files in the directory. The process of creating a new device looks like a known device known as an extension. The ability to boot a write-up SD card with a USB adapter is very beneficial for maintaining integrity and non-corruption, the original state of the boot medium.
Although most personal computers since mid-2004 can boot from USB mass storage devices, USB is not intended as a primary bus for internal storage of computers. However, USB has the advantage of allowing hot-swapping, making it useful for mobile peripherals, including drives of various types.
First conceived and still used today for optical storage devices (CD-RW drives, DVD drives, etc.), Some manufacturers offer an external USB portable hard disk drive, or an empty case for disk drives. The performance of this offer is proportional to the internal drive, limited by the number and type of USB devices currently installed, and by the upper limit of the USB interface. Other competing standards for external drive connectivity include eSATA, ExpressCard, FireWire (IEEE 1394), and lastly Thunderbolt.
Another use for USB mass storage devices is the portable execution of software applications (such as web browsers and VoIP clients) without the need to install them on the host computer.
Media Transfer Protocol
The Media Transfer Protocol (MTP) is designed by Microsoft to provide higher access to the device file system than USB mass storage, at the file level rather than disk blocks. It also has an optional DRM feature. MTP is designed for use with portable media players, but has since been adopted as the main storage access protocol of the Android operating system of version 4.1 Jelly Bean and Windows Phone 8 (Windows Phone 7 devices have used the Zune-evolution MTP protocol). The main reason for this is that MTP does not require exclusive access to storage devices as UMS does, reducing potential problems if an Android program requests storage when it is attached to a computer. The main drawback is that MTP is not well supported outside the Windows operating system.
Human interface device
Joysticks, keypads, tablets, and other human interface devices (HIDs) are also increasingly migrating from MIDI, and PC gaming port connectors to USB.
USB and keyboard mice can usually be used with older computers that have PS/2 connectors with the help of a small USB-to-PS/2 adapter. For mice and keyboards with dual-protocol support, adapters that do not contain logic circuits can be used: hardware on a USB keyboard or mouse is designed to detect whether it is connected to a USB or PS/2 port, and communicate using the appropriate protocol. Converters also exist that connect the PS/2 keyboard and mouse (usually one from each) to the USB port. This device presents two HID end points to the system and uses a microcontroller to perform two-way data translation between two standards.
Device Firmware Upgrade
Device Firmware Upgrade (DFU) is an independent vendor and device mechanism for upgrading USB device firmware with an improved version provided by their manufacturer, offering (for example) ways to apply firmware bug fixes. During firmware upgrade operations, USB devices change their mode of operation effectively into PROM programmers. Each class of USB devices can apply this capability by following the official DFU specification.
In addition to the intended legitimate purpose, DFU can also be exploited by uploading a maliciously created firmware that causes USB devices to spoof different types of other devices; one such utilization approach is known as BadUSB.
Streaming audio
The USB Device Working Group has exposed the specifications for streaming audio, and specific standards have been developed and implemented for the use of audio classes, such as microphones, speakers, headsets, telephones, musical instruments, etc. DWG has published three specific audio device versions: AudioÃ, 1.0, 2.0, and 3.0, referred to as "UAC" or "ADC".
UAC 2.0 introduces support for High Speed ​​USB (in addition to Full Speed), allowing greater bandwidth for multi-channel interfaces, higher sample rates, inherent lower latency, and 8-time resolution improvements in sync and adaptive modes. UAC2 also introduces the concept of clock domain, which provides information to hosts about which input and output terminals are getting their watch from the same source, as well as enhanced support for audio encodings such as DSD, audio effects, channel grouping, user controls, and device descriptions.
UAC 3.0 primarily introduces enhancements to portable devices, such as reduced power usage by blowing up data and staying in the low-power mode more often, and the power domains for various components of the device, allowing it to be turned off when not in use.
UAC 1.0 devices are still common, due to cross platform compatibility compatibility, and Microsoft's failure to implement UAC 2.0 for more than a decade after publication. Android also only implements a subset of UAC 1.0. UAC 2.0 is supported by MacOS, iOS, and Linux.
USB provides three types of isokron synchronization (fixed bandwidth), all of which are used by audio devices:
- Asynchronous - ADC or DAC is not synced to the host computer's clock at all, operating from a free-running local clock to the device.
- Sync - The device clock is synchronized to a start-of-frame (SOF) USB signal or Interval Bus. For example, it can synchronize 11.2896 MHz clock to 1 kHz SOF signal, large frequency multiplication.
- Adaptive - The device clock is synchronized with the amount of data sent per frame by the host
While the USB specification initially describes the asynchronous mode used in "low-cost speakers" and adaptive modes in "high-end digital speakers," the opposite perception is in the hi-fi world, where asynchronous mode is advertised as a feature, and adaptive./sync mode has a bad reputation. In fact, all types can be of high quality or low quality, depending on the quality of their techniques and applications. Asynchronous has an unbound benefit of computer clock, but disadvantages require sample level conversion when combining multiple sources.
Connector
Connectors defined by the USB committee support a number of basic USB destinations, and reflect on the learning of the many connectors used by the computer industry. The female connector mounted on the host or device is called receptacle , and the male connector connected to the cable is called plug . The official USB specification document also periodically defines the terms male to represent the plug, and female to represent the container.
By design, it is difficult to insert the USB plug into its outlet incorrectly. The USB specification requires that the cable plug and power outlet be marked so that the user can recognize the correct orientation. The C-type plug is reversible. The USB cable and the small USB device are held by the gripping power of the outlet, without screws, clips, or thumbs like the other connectors use.
Different A and B plugs prevent accidentally connecting two resources. However, some of these directed topologies are lost with the emergence of multi-purpose USB connections (such as USB On-The-Go in smartphones, and USB-powered Wi-Fi routers), which require A-to-A, B- to-B, and sometimes Y/splitter cable.
The type of USB connector is multiplied by the specification developed. The original USB specifications are A-standard detailed and standard-B plugs and containers. The connectors are different so the user can not connect one computer container to another. The data pin in the standard plug is hidden compared to the power pin, so the device can turn on before making a data connection. Some devices operate in different modes depending on whether the data connection is made. Charging docks supply power and do not include host devices or data pins, enabling USB devices capable to charge or operate from a standard USB cable. The charging cable provides a power connection, but not the data. In a charge-only cable, the data cable is shortened at the end of the device, otherwise the device may refuse the charger as inappropriate.
Cable
Standard USBÃ, 1.1 specifies that a standard cable can have a maximum length of 5 meters (16Ã, ft 5Ã, in) with devices operating at full speed (12 Mbit/s), and a maximum length of 3 meters (9Ã, ft 10Ã, in) with the device operates at low speed (1.5 Mbit/s).
USB 2.0 provides for a maximum cable length of 5 meters (16 ft 5 inches) for devices running at high speed (480 Mbit/s).
The USB 3.0 standard does not directly determine the maximum cable length, requiring only that all cables meet the electrical specifications: for copper wires with AWG 26 the maximum practical length cable is 3 meters (9 ft 10 inches).
Power
USB supplies 5 V Â ± 5% power to deliver USB downstream device power.
Low-power and high-power devices
Low-power devices (such as a regular USB keyboard) can pull at most 1 unit of load (1 unit load is 100mA for USB devices up to USB 2.0, while USB 3.0 defines the unit load as 150mA), and all devices must act as low-power devices when starting as not configured.
High-power devices (such as typical 2.5-inch USB hard disks) attract at least 1 load unit and at most 5 load units (500 mA) for devices up to USB 2.0 or 6 load units (900 mA) for SuperSpeed ​​devices.
To recognize Battery Charging, the special charging port puts a resistance not exceeding 200? across D and D- terminals.
For USB Power, see USB Power.
Signaling
Electrical specifications
The USB signal is transmitted using differential signals on twisted-pair data cable with 90? Ã, Â ± 15% characteristic impedance.
- Low speed mode (LS) and Full speed (FS) uses a single data pair, labeled D and D-, in half-duplex. The transmitted signal level is 0,0-0,3 V for low logic, and 2,8-3,6 V for logical high level. The signal line is not stopped.
- High speed mode (HS) uses the same wire pair, but with different electrical conventions. Signal voltage lower than -10 to 10 mV for low and 360 to 440 mV for logical high levels, and termination 45Ã? to the ground or 90 Â °? differential to match the impedance of the data cable.
- SuperSpeed ​​â € <â € <(SS) adds two additional pairs of shielded twisted wire (and most new connectors are compatible). It is dedicated to SuperSpeed ​​operations â € <â €
- SuperSpeed ​​â € <(SS) uses an increase in data rate (2x1 Gen mode) and/or additional paths in the Type-C connectors (Gen 1x2 and 2x2 Genes mode).
The USB connection is always between the host or hub on the end of the A connector, and the "upstream" port of the device or the hub at the other end.
Protocol layer
During USB communication, data is sent as a packet. Initially, all packets are sent from the host through the root hub, and possibly more hubs, to the device. Some of the packages direct the device to send some packets in return.
Transactions
The basic USB transactions are:
- Outgoing transactions
- IN transactions
- SETUP transactions
- Transfer transfer control
Related standards
The USB Implementers Forum works on wireless networking standards based on the USB protocol. Wireless USB is a cable replacement technology, and uses ultra-wideband wireless technology for data rates up to 480 Mbit/s.
InterChip USB is a chip-to-chip variant that eliminates conventional transceivers found in normal USB. The physical layer of HSIC uses about 50% less power and 75% less area board compared to USB 2.0.
Comparison with other connection methods
FireWire
Initially, USB was regarded as a complement to the IEEE 1394 (FireWire) technology, designed as a high-bandwidth serial bus that efficiently interconnects peripherals such as disk drives, audio interfaces, and video equipment. In the initial design, USB operates at a much lower data rate and uses less sophisticated hardware. It is suitable for small peripherals such as keyboards and pointing devices.
The most significant technical differences between FireWire and USB include:
- The USB network uses multilevel topology, while the IEEE 1394 network uses tree topology.
- USBÃ, 1.0, 1.1, and 2.0 use the "talk-when-talking-to" protocol, which means that each device communicates with the host when the host specifically requests it to communicate. USB 3.0 allows communication initiated by the device to the host. FireWire devices can communicate with other nodes at any time, according to network conditions.
- The USB network depends on a single host at the top of the tree to control the network. All communications are between host and one device. In FireWire network, each node is capable of controlling the network.
- USB runs with 5 V power lines, while FireWire in the current implementation supplies 12 V and can theoretically supply up to 30 V.
- A standard USB hub port can provide from 500 mA/2.5 W current, only 100 mA from non-hub ports. USB 3.0 and On-The-Go USB 1.8 A/9.0 W (for special battery charging, 1.5 AA/7.5 W bandwidth) or 900 mA/4.5 W high bandwidth), while FireWire can supply theories up to 60 watts, although 10 to 20 watts is more common.
These and other differences reflect different design goals of both buses: USB is designed for simplicity and low cost, while FireWire is designed for high performance, especially in time-sensitive applications such as audio and video. Although similar in theoretical maximum transfer rate, FireWire 400 is faster than high bandwidth USB 2.0 in real usage, especially in high bandwidth usage such as external hard drives. The newer FireWire 800 standard is twice as fast as FireWire 400 and faster than the high bandwidth USB 2.0 both theoretically and practically. However, the advantages of FireWire speed depend on low-level techniques such as direct memory access (DMA), which in turn has created opportunities for security exploits such as DMA attacks.
Chipsets and drivers used to implement USB and FireWire have an important impact on how much bandwidth is determined by the specifications achieved in the real world, along with compatibility with peripherals.
Ethernet
IEEE 802.3af Standards Power over Ethernet (PoE) sets up a more complicated power negotiation scheme than USB supported. It operates on 48Ã, VÃ, DC and can provide more power (up to 12.95 W, 25.5 W PoE) above cables up to 100 meters compared to USB 2.0, which provides 2.5Ã,W with maximum cable length 5 meters. This has made PoE popular for VoIP phones, security cameras, wireless access points, and other network devices in the building. However, USB is cheaper than PoE as long as the distance is short and power demand is low.
Ethernet standards require electrical isolation between network devices (computers, phones, etc.) and network cables up to 1500Ã, VÃ, AC or 2250Ã, DC for 60Ã ¢, sec. USB does not have such requirements because it is designed for peripherals that are closely related to the host computer, and in fact it connects the peripheral and host places. This gives Ethernet significant security advantages over USB with peripherals such as cable and DSL modem connected to external cables that can assume dangerous voltage under certain fault conditions.
MIDI
The Classroom Definition of USB Devices for MIDI Devices allows music data of the Digital Interface Music Instrument (MIDI) to be sent via USB. The MIDI capability is extended to allow up to sixteen simultaneous virtual MIDI cables, each of which can carry sixteen regular MIDI channels and clocks.
USB is highly competitive for low-cost and physically adjacent devices. However, Power over Ethernet and MIDI plug standards have advantages in high-end devices that may have long cables. USB can cause ground loop problems between equipment, as it links ground references on both transceivers. By contrast, standard MIDI and Ethernet plugs have built-in isolation to 500 V or more.
eSATA/eSATAp
The eSATA connector is a stronger SATA connector, intended for connection to an external hard drive and SSD. The transfer speed of eSATA (up to 6 Gbit/s) is similar to USB 3.0 (up to 5 Gbit/s on current device; 10 Gbit/s speed via USB 3.1, announced on 31 July 2013). ESATA-connected devices appear as ordinary SATA devices, providing full performance and full compatibility associated with internal drives.
eSATA does not supply power to external devices. This is an increasing loss compared to USB. Although USB 3.0's 4.5W is sometimes not enough to power an external hard drive, advanced technology and external drives gradually require less power, reducing eSATA gain. eSATAp (power over eSATA; aka ESATA/USB) is a connector introduced in 2009 that supplies power to the attached device using a new backward compatible connector. In eSATAp notebooks usually only provide 5 V to turn on 2.5-inch HDD/SSD; on desktop workstations it can also provide 12 V for larger device power including 3.5 inch HDD/SSD and 5.25 inch optical drive.
The eSATAp support can be added to the desktop machine in the form of a bracket that connects the SATA motherboard, power, and USB resources.
eSATA, such as USB, supports hot plugging, although this may be limited by the OS driver and device firmware.
Thunderbolt
Thunderbolt combines PCI Express and Mini DisplayPort to a new serial data interface. The original Thunderbolt implementation has two channels, each with a transfer rate of 10 Gbit/s, resulting in a 20 Gbit/s aggregate directional bandwidth.
Thunderbolt 2 uses link aggregation to combine two 10 Gbit/s channels into one bi-directional channel of 20 Gbit/s.
Thunderbolt 3 uses a Type-C USB connector. ThunderboltÃ, 3 has one channel 40Ã, Gbit/s.
Interoperability
Source of the article : Wikipedia
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