- Virtual Network Computing
In computing, Virtual Network Computing (VNC) is a graphical
desktop sharingsystem which uses the RFB protocolto remotely control another computer. It transmits the keyboard and mouse events from one computer to another, relaying the graphical screen updates back in the other direction, over a network.
VNC is platform-independent — a VNC viewer on any
operating systemusually connects to a VNC server on any other operating system. There are clients and servers for almost all GUI operating systems and for Java. Multiple clients may connect to a VNC server at the same time. Popular uses for this technology include remote technical support and accessing files on one's work computer from one's home computer, or vice versa.
VNC was originally developed at the
Olivetti Research Laboratoryin Cambridge, United Kingdom. The original VNC source codeand many modern derivatives are open sourceunder the GNU General Public License.
VNC was created at the
Olivetti & Oracle Research Lab(ORL), which was then owned by Olivettiand Oracle Corporation. In 1999AT&T acquired the lab, and in 2002 closed down the lab's research efforts.
Developers who worked on VNC while still at the AT&T Research Lab are:
Andy Harter(project leader)
* James Weatherall
* Ken Wood
* Paul Webster
Hendrik Ekkelenkamp, Ekkelenkamp IT, advisor
Following the closure of ORL in 2002, several members of the development team (including Richardson, Harter, Weatherall and Hopper) formed
RealVNCin order to continue working on open sourceand commercial VNC software under that name.
Several other versions of VNC have been developed from the original GPLed source code. Such forking has not led to compatibility problems because the RFB protocol is designed to be extensible. VNC clients and servers negotiate their capabilities when
handshakingin order to use the most appropriate options supported at both ends.
The name 'Virtual Network Computer/Computing' originates from ORL's work on a
thin clientcalled the Videotile which also used the RFBprotocol. This was essentially an LCD with a pen input and a fast ATM connection to the network. At the time, network computerwas commonly used as a synonym for 'thin client'. VNC is essentially a software-only (i.e virtual) version of this network computer.
A VNC system consists of a client, a server, and a communication protocol.
* The VNC server is the program on the machine that shares its screen.
* The VNC client (or viewer) is the program that watches and interacts with the server.
* The VNC protocol (RFB) is very simple, based on one graphic primitive from server to client ("Put a rectangle of
pixeldata at the specified X,Y position") and event messages from client to server.
The server sends small rectangles of the
framebufferto the client. In its simplest form, the VNC protocol can use a lot of bandwidth, so various methods have been devised to reduce the communication overhead. For example, there are various "encodings" (methods to determine the most efficient way to transfer these rectangles). The VNC protocol allows the client and server to negotiate which encoding will be used. The simplest encoding, which is supported by all clients and servers, is the "raw encoding" where pixel data is sent in left-to-right scanlineorder, and after the original full screen has been transmitted, only transfers rectangles that change. This encoding works very well if only a small portion of the screen changes from one frame to the next (like a mouse pointer moving across a desktop, or text being written at the cursor), but bandwidth demands get very high if a lot of pixels change at the same time, such as when scrolling a window or viewing full-screen video.
VNC by default uses TCP ports 5900 through 5906, each port corresponding to a separate screen (:0 to :6). A Java viewer is available in many implementations such as
RealVNCon ports 5800 through 5806, allowing clients to interact through, among other things, a Java-enabled web browser. Other ports can be used as long as both client and server are configured accordingly.
Using VNC over the Internet works well if the user has a
broadbandconnection at both ends. However, it may require advanced NAT, firewalland routerconfiguration such as port forwarding in order for the connection to go through. Some users may choose to use instant private networking applications such as Remoboor VPNapplications such as Hamachito make usage over the Internet much easier.
Note that on some machines, the server does not necessarily have to have a physical display. "Xvnc" is the Unix VNC server, which is based on a standard X server. Xvnc can be considered to be two servers in one; to applications it is an X server, and to remote VNC users it is a VNC server. Applications can display themselves on Xvnc as if it were a normal X display, but they will appear on any connected VNC viewers rather than on a physical screen. [cite web | url=http://www.cl.cam.ac.uk/research/dtg/attarchive/vnc/xvnc.html | title=X-based VNC server | author=AT&T Laboratories Cambridge | date=1999 | work=Virtual Network Computing | accessdate=2007-03-24]
In addition, the display that is served by VNC is not necessarily the same display seen by a user on the server. On Unix/Linux computers that support multiple simultaneous X11 sessions, VNC may be set to serve a particular existing X11 session, or to start one of its own. It is also possible to run multiple VNC sessions from the same computer. On
Microsoft Windowsthe VNC session served is always the current user session.
VNC is commonly used as a cross-platform remote desktop system. For example,
Apple Remote Desktopfor Mac OS X(and more recently, " Back to My Mac" in 'Leopard' - Mac OS X 10.5) interoperates with VNC and will connect to a Linux user's current desktop if it is served with x11vnc, or to a separate X11 session if one is served with TightVNC. From Linux, TightVNC will connect to an OS X session served by Apple Remote Desktop if the VNC option is enabled, or to a VNC server running on Microsoft Windows.
By default, VNC is not a secure protocol. While
passwords are not sent in plain-text (as in telnet), brute-force cracking could prove successful if both the encryptionkey and encoded password are sniffed from a network. For this reason it is recommended that a password of at least 8 characters be used. On the other hand, there is also an 8-character limit on some versions of VNC; if a password is sent exceeding 8 characters, the excess characters are removed and the truncated string is compared to the password.
However, VNC may be tunnelled over an SSH or VPN connection which would add an extra security layer with stronger encryption. SSH clients are available for all major platforms (and many smaller platforms as well); SSH tunnels can be created from
UNIXclients, Microsoft Windowsclients, Macintoshclients (including Mac OS Xand System 7and up) — and many others. There are freewareapplications that create instant VPN tunnels between computers such as Remobo. Hamachihas been purchased by LogMeInand is no longer freeware. UltraVNCsupports the use of an open-source encryption plugin which encrypts the entire VNC session including password authentication and data transfer. It also allows authentication to be performed based on NTLMand Active Directoryuser accounts. RealVNCoffers high-strength encryption as part of its commercial package. Workspotreleased AES encryption patches for VNC.
Remote Desktop Protocol
Virtual private network
Comparison of remote desktop software
X Window System
* [http://www.hep.phy.cam.ac.uk/vnc_docs/index.html AT&T VNC] - Original AT&T-Cambridge VNC website
* [http://gentoo-wiki.com/VNC Gentoo-wiki/VNC] - An overview and a set of guides to the various flavours of VNC
* [http://www.realvnc.com/products/beta/ce VNC Enterprise Edition (beta) Viewer for PocketPC] - RealVNC beta viewer for PocketPC (ARM)
* [http://ple-q.com/2008/01/03/membuat-vnc-server-di-ubuntu/ Setup VNC Server on Ubuntu (Indonesian Version)]
* [http://www.karlrunge.com/x11vnc/ x11vnc: a VNC server for real X displays] (with acceleration)
* [http://variableghz.com/2008/09/getting-serious-about-vnc/ a how-to prevent dynamic IP issues with VNC and routers]
* lists available VNC viewers and servers.
* [http://www.sinfocol.org/herramientas/vncauth.php VNC Hash] VNC Hash, is an online tool that allow to cipher and decipher VNC Hash
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