USB and K-V-M switches - The Implementation can Make the Difference 2007 ATEN
Historical Overview The offi cial standard symbol for a USB connection The past 12 years have seen the Universal Serial Bus (USB) grow from pipe dream into the de facto standard to power devices such as peripherals, portable memory devices, video game consoles, PDAs and portable media players. USB was originally designed to bring all serial and parallel ports on PCs to obsolescence since these were not standardized and required multiple device drivers to be continually developed and updated. The original implementation of the Universal Serial Bus (USB) was driven by three things: 1. A desire for a more universal means to connect PCs to the telephone, 2. Greater ease of use and flexibility in connecting computers to peripheral hardware 3. The need for inexpensive, user-friendly port expansion for bi-directional devices In its early years, the market was unsure of the direction to take with this emerging technology. USB was officially introduced by a consortium of seven computer and telecommunications industry leaders in 1995 and today is a truly universal technology playing a major role in the convergence of consumer and business products. Today, the 1000-member USB Implementers Forum, Inc. (USB-IF) is steered by many USB promoters that are optimizing the technology. Originally, the USB 1 standard specified 1.5 megabits/second (Mb/s) and 12 Mb/s data rates. USB truly went mainstream with the introduction of USB 2.0 which increased the bus speed from 12 Mbps to 480 Mbps, a forty time increase. The original USB specification called for 12 Mbps for full-speed and 1.5 Mbps for low-speed (for human interface devices such as mouse device). Unfortunately, these speeds were not enough for simultaneous applications such as video, audio, and printing -- bandwidth limitation was an issue. Hi-Speed USB 2.0 solves this problem reducing the time for downloading information and images in seconds versus minutes. 2007 ATEN Technology, Inc. -P01-
USB 2.0 also needed to maintain compatibility with the lower rate USB 1.1 devices. Devices of both types may be connected to the same hub or computer. For optimal data transfer rate, it is recommended that users segregate USB 1.1 and 2.0 devices. While USB has definitely made inroads within the home and SOHO environments, what are the implications on an enterprise level within the server room or data center? For many years, PCs have been manufactured with both PS/2 and USB ports which may be used for connection of the keyboard and mouse; the USB ports, of course, may also be used for connection of a wider variety of peripherals such as printers, scanners, network adaptors, cable/dsl modems, external storage media and so forth. Sun and Macintosh computers have, for the last several years, been sold with only USB ports for keyboard and mouse connection -- no more ADB (Apple Desktop Bus) or Mini DIN-8 connectors are built into these computers. Today, virtually all computers sold have USB ports, and the once ubiquitous PS/2 port is beginning to fade into the distance. KVM (keyboard/video/mouse) switch manufacturers have not fully embraced the USB paradigm but are starting to understand its value within the data center as complementary peripherals start to play an expanded role. The key lies in the implementation and optimization of USB. This document will explain the nature of USB connectivity and its role within KVM. One Size Does Not Fit all USB Ports Differ Physically and Logically USB connectors are keyed to ensure proper connectivity. According to the official USB specification, an A type connector serves as the primary connection to USB devices directly to a host or a downstream port of a hub. A B type connector is used on an external device if the manufacturer designs that device with a detachable USB cable. a) Series A plugs are always oriented upstream towards the Host System b) Series B plugs are always oriented downstream towards the USB Device Figure 1. Primary USB keyed connectors 2007 ATEN Technology, Inc. -P02-
Most keyboards and mice predominantly offer USB Series A connector cables. When plugged into an A type receptacle on a hub or computer or KVM switch, these keyboards will not be damaged or harm that device. However, on occasion the computer may not correctly recognize the keyboard if it s booted with the keyboard connected to the hub rather than directly. It should, but sometimes the O/S won t load the correct driver for the keyboards. In other words, plug and play is usually but not always the case. The Series A and Series B connectors (Fig. 1) are identical for USB 1.1 and USB 2.0; the connector does not visibly discern the speed of the USB hub or device. USB Hosts and Hubs USB systems generally have a single host or computer to which various devices connect, either directly, or via one or more USB hubs. The host has a host controller function that may be implemented in software, firmware or hardware (so, for example, the Operating System could provide the USB host functionality, or the motherboard, or a plug-in card with firmware on it). These hubs extend USB functionality to more than one device. Such hubs may be physically implemented as stand-alone devices, or they may be built into certain peripherals. Typically, the host computer includes a so-called root hub the built in device that allows it to have more than one USB port. If a computer has 2 or more USB ports (not counting add-in circuit boards), these are supported by the internal root hub of the PC. In USB architecture, the host computer is considered to be Tier 1. An external device (performing a function ) can be plugged into the host computer s USB port, or in an external hub (which isn t considered a function in this context). Whatever devices or hubs you plug directly into the host computer are considered to be in Tier 2, as shown in Figure 2. The USB specification allows for up to 7 such tiers of physical connectivity. External hubs may be cascaded from the root hub and from one another. However, there cannot be more than 5 external hubs in the path between the computer and the target external device. 2007 ATEN Technology, Inc. -P03-
Figure 2. USB bus topology model (derived from the offi cial USB 2.0 specifi cation) The U in USB is not Always Universal In theory, the U in USB infers that any USB device should be supported by any USB port in reality that is not usually the case. USB hosts must be able to correctly recognize and communicate with connected devices. This assumes that the host has in its memory suitable firmware or software (typically accomplished by loading a driver). Most modern operating systems have built-in support for basic USB functionality, such as support of basic 101- or 104-key keyboards and 2 or 3 button mice. However keyboards with special function keys, mice with various tilt/scroll wheels and programmable buttons, printers, scanners and so forth all require customized USB drivers if they are to be correctly recognized and handled by the host. Categories of USB devices For the context of this document, it is helpful to divide USB devices into two categories: HID and Everything Else. 2007 ATEN Technology, Inc. -P04-
HID is an acronym for Human Interface Device, and that basically suggests keyboard or mouse. HIDs could also be a graphic tablet, joystick, gaming control, and so forth. HIDs almost always use conventional USB series A connectors (see Fig. 1) to plug into the host computer. Everything Else (our terminology, not a standard) includes such devices as printers, scanners, hard disk drives, thumb drives (the tiny USB-connected solid state memory devices that act like hard drives), digital cameras, and so forth. Often, everything else devices have USB series B receptacles with detachable cords; these cords have a USB series B plug on one end and a USB series A plug on the other end. In terms of the Everything Else USB category, ATEN Technology was an early pioneer in the development of USB technology. ATEN s innovation led to the industry s first USB 2.0 Certified Host Controller Card. In 2000, ATEN worked with Intel to develop a USB controller card based on the 2.0 standard. Without this vital technology, the surge in digital cameras, Flash drives and SD cards would not have been possible. The company s USB vision has led to the creation of a line of products built on a standard of excellence that has now evolved into USB 2.0 hubs, peripherals and storage devices and even KVM switches offering USB functionality. KVM Switches and USB When USB was first integrated into PCs, KVM manufacturers offered adaptors that converted the PS/2 keyboard and mouse cable ends to a single USB Series A cable connection. The console side of such switches would still connect to standard PS/2 peripherals at that point USB keyboard and mouse could not be used with the KVM. A few manufacturers offered small (2 to 4 port) USB KVM switches that supported USB console peripherals and USB computers, but these were handled with crude pass through wiring. One of the challenges of USB arises when a user moves a USB device from one computer (host) to another. Since KVM switches essentially move the console s keyboard and mouse from one connected computer to another, the potential exists for USB driver loading failure, driver incompatibility and other connectivity problems. The first attempts by manufacturers were KVM switches that electronically supported USB from within the switch chassis yet relied on legacy keyboards and mice. If a PC had a USB keyboard or mouse with special functions, the ability to use other HIDs with the KVM switch was not possible. However, ATEN introduced the one exception to this legacy peripheral situation. ATEN s approach was (and remains) unique because the company s USB KVM switches provide full keyboard/mouse emulation at each computer port so that attached computers see they are connected to USB peripherals and load the correct drivers upon bootup. ATEN s USB switches take the technology to new levels by allowing the connection of a USB keyboard and mouse. The port emulation works for a standard 104-key PC or Macintosh or Sun keyboard and 2 or 3-button mouse, even supporting Sun computer hotkey command key sequences. Other manufacturers now sell switches that support USB keyboard/mouse connectivity on the console side, but none with the same range of functionality provided by ATEN. 2007 ATEN Technology, Inc. -P05-
USB KVMs with Added USB Peripherals Several manufacturers now offer KVM switches that support both USB keyboard/mouse ports as well as the switching of USB peripherals that can be accessed from multiple PCs. For example, the same KVM that handles the keyboard and mouse signal is enhanced to reroute a USB-connected printer. Many manufacturers, outside of ATEN, offer this capability by moving the printer or other peripherals when a user switches the keyboard and mouse from computer to computer such functionality may not be acceptable. If an IT administrator is helping a colleague spool a large printing job and decides to work on different project midstream on another PC, the printer should not follow when switching since that would abort the print job. ATEN s KVMP (KVM with Peripheral ) switches offer a patented method for USB (and audio) peripherals to be assigned independently of the keyboard/mouse so the printer does not abort but remains connected while controlling a monitor, keyboard and mouse on a different computer. USB ports specifi cally for peripherals that can be switched independently of the K-V-M ports Console port for Keyboard Console port for Mouse Figure 4. KVMP Switch handles USB Keyboard and Mouse as well as USB Peripherals. However, specifi c USB connectors must be used for Keyboard and Mouse in order to assure correct emulation and pass-through of special keystroke sequences from keyboard to attached computers. The ports on KVM switches that support a USB keyboard and USB mouse on the console side should be used solely for that purpose. Unlike USB ports on a host device (a computer), these ports are device specific since the KVM switch must provide the correct drivers for the keyboard and mouse. A KVMP offers additional USB ports, as shown in Fig. 4, and gives the option of using these ports for other peripherals. These KVMP switches have much potential within the data center, especially within large enterprise organizations. Recent offerings include a KVMP switch specifically targeted to data center administrators such as a 16-port rackmount LCD model that features an extra local console port, USB peripheral sharing technology, and an external mouse port. 2007 ATEN Technology, Inc. -P06-
Power via USB USB ports are able to provide power to attached devices, including hubs, HIDs and other peripherals. However, the amount of power that can be delivered by a given computer s USB port is limited (some computers, particularly notebook/laptop class computers, have very limited USB power available). KVM switches that provide USB console connections will supply the modest amount of power needed for a standard keyboard and mouse, and no boost is needed. When using a KVMP, it is recommended to use the available external power supply for that switch so that the USB peripherals receive adequate power. Wireless HIDs vs. Wireless USB Today, many users enjoy the freedom from cables afforded by wireless keyboard and mouse systems. Many manufacturers offer such systems that typically interface to the computer with a USB dongle and provide an RF link (typically 900 MHz or 2.4 GHz radio frequency). These low-data-speed, devicespecific USB interfaces may require special drivers for the particular keyboard or mouse to be recognized. For example ATEN USB KVM switches, work seamlessly with major manufacturers wireless keyboards and mice in terms of basic functionality some KVM switches may not work with any wireless HIDs. There are two categories of wireless when it comes to USB. The category above is the most common but a new standard for wireless high-speed USB connectivity is emerging to support shared wireless USB hard drives, video/audio links, and more. Certified Wireless USB (WUSB) has become the logical extension of USB to make it easier to connect peripherals and other devices. Wireless USB is based on the ultrawideband (UWB) technology which supports the same 480 Mbps data rate over a distance of two meters (about 6.6 feet). Although these devices will work at transfer rates up to 480 MHz, such ultra wideband USB is not necessary for basic KVM control functions. However, future KVMPs will support the high-speed wireless USB standard. Summary The overall outlook for the USB KVM is very promising. With more than a billion USB PCs in the market and many times more in USB devices, the potential is limitless as there will continue to be many opportunities for both new designs and add-on products. USB provides a common connection standard for all peripherals. Its topology design hardware via USB hubs and its ability to carry power and data over a single cable have inspired numerous innovations from USB flash drives to USB KVM switches. A well designed USB KVM switch will correctly emulate the constant presence of a keyboard and mouse to each connected computer, will allow the use of actual USB keyboards and mice for control, and will offer much flexibility in the data center of tomorrow. 2007 ATEN Technology, Inc. -P07-
ATEN Technology, Inc. 23 Hubble, Irvine CA 92618, U.S.A 1-888-999-ATEN (2836) ATEN New Jersey 155 Pierce St. Somerset, NJ 08873 732-356-1703