KVM switch ( abbr. English: k eyboard, v ideo, m ouse “ keyboard , video , mouse ”) - a device designed to switch one set of input-output devices between several computers .
Initially, KVM switches, in accordance with their name, provided switching of the signal of the monitor , keyboard and mouse, but later KVM switches with support for switching sound and USB appeared .
In addition to directly switching the signal, the KVM switch should also emulate the presence of devices on disconnected ports so that there are no errors associated with polling them in disconnected machines. This was made possible due to the presence of generally accepted standards for communication protocols on D-sub , PS / 2 and USB buses.
Content
Video Features
KVM switches can have different video bandwidth, the level of which affects the cost of equipment. A standard mid-level KVM switch provides 200 MHz bandwidth allocated between available ports. Professional switches provide twice the bandwidth and cost twice as much. One of the important requirements is also support for various screen refresh rate modes. Inexpensive models usually support a refresh rate of 60 Hz, which is insufficient in some professional systems.
With the increase in the number of available monitors and various resolutions, support for EDID and DDC has become an important factor, which directly affects image quality and available video resolutions on the working console.
Video DynaSync ™. The function of reading the parameters of the connected monitor (EDID) by a switch, storing them and automatically transmitting information about the monitor to all connected servers for their automatic adjustment.
KVM Switch Evolution
The first models of KVM-switches were mechanical, they were a packet switch in the housing with standard connectors pulled out. Their main advantage was simplicity of design and reliability. The main disadvantages are the lack of keyboard emulation on “inactive” ports, direct galvanic contact of connected devices, inconvenience of control (a packet switch had to switch more than 20 contacts at the same time), and the inability to scale.
The following models used electronic switching, allowing you to control the switching process from the keyboard (usually, double-clicking Scroll Lock was used to activate the KVM control mode). The first models of electronic switches required external power, the subsequent ones use the power bus from the PS / 2 (or USB) port.
In the future, KVM switches appeared with the ability to transmit a signal over long distances due to the applied video signal correction.
The latest generation of KVM switches can transmit video and mouse / keyboard input over the network using the IP protocol (known as IP-KVM). To work with IP-KVM on a workstation, you may need a Java virtual machine or a special windows program with which the video signal will be transmitted to the user's monitor. IP-KVM manufacturers, as a rule, provide both software options: java client for Linux / MacOS / * BSD systems and Windows client for workstations running Microsoft Windows operating system.
Modern models of KVM switches are complemented by the ability to switch an audio signal, additional USB devices, digital video signals (such as DVI, Display Port). Now the actual problem when using KVM switches is switching various and non-standard USB devices - for example, a wireless mouse, scanner, graphic tablet , since most manufacturers use the "numbering" method or simple emulation when switching, then when switching such a device from one computer to another, it is not determined. This problem is solved using True USB emulation technology [1] [2]
KVM and Remote Access
Compared to remote access services ( SSH , Remote Desktop ), KVM with signal transmission via IP, being an independent device from the operating system, provides the ability to remotely perform operations that are not available for remote access (for example, configuring the BIOS ).
At the same time, the KVM switch is not subject to operating system policies (for example, blocking an account in Active Directory or / etc / passwd does not disable the user password in KVM).
It is worth noting the use of technology such as Virtual Media in KVM IP solutions - which allows the KVM device to transmit data over IP and thereby allows you to remotely install programs or the operating system.
KVM-equipment allows realizing remote access, by means of which video and audio signals can be extended to a distance of 40 km, providing a maximum resolution of 1920x1200. KVM-equipment in the work of various Control Centers allows you to transmit various types of signals, control the transmitted content and control over incoming and outgoing data.
Notes
- ↑ True USB Emulation article on the developer's site Archived on August 9, 2009.
- ↑ Translation of an article on True USB Emulation on kvminfo.ru unopened (inaccessible link) . Date of treatment August 30, 2010. Archived June 9, 2010.