This encoding works very well if only a small portion of the screen changes from one frame to the next (as when a mouse pointer moves across a desktop, or when text is 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).
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The simplest encoding, supported by all clients and servers, is raw encoding, which sends pixel data in left-to-right scanline order, and after the original full screen has been transmitted, transfers only rectangles that change. The VNC protocol allows the client and server to negotiate which encoding they will use. For example, there are various encodings (methods to determine the most efficient way to transfer these rectangles). In its simplest form, the VNC protocol can use a lot of bandwidth, so various methods have been devised to reduce the communication overhead. The server sends small rectangles of the framebuffer to the client. One advantage of listening mode is that the server site does not have to configure its firewall to allow access on port 5900 (or 5800) the duty is on the viewer, which is useful if the server site has no computer expertise and the viewer user is more knowledgeable. And a server can connect to a viewer in "listening mode" on port 5500. Alternatively (depending on the implementation) a browser can connect to the server (default port: 5800). In the normal method of operation a viewer connects to a port on the server (default port: 5900). The VNC protocol ( RFB protocol) is very simple, based on transmitting one graphic primitive from server to client ("Put a rectangle of pixel data at the specified X,Y position") and event messages from client to server.The VNC client (or viewer) is the program that represents the screen data originating from the server, receives updates from it, and presumably controls it by informing the server of collected local input.The VNC server is the program on the machine that shares some screen (and may not be related to a physical display – the server can be "headless"), and allows the client to share control of it.At the time, network computer was commonly used as a synonym for a thin client VNC is essentially a software-only (i.e. The Videotile had an LCD display with pen input and a fast ATM connection to the network. The name Virtual Network Computer/Computing (VNC) originated with ORL's work on a thin client called the Videotile, which also used the RFB protocol. VNC clients and servers negotiate their capabilities with handshaking in order to use the most appropriate options supported at both ends.Īs of 2013, RealVNC Ltd claims the term "VNC" as a registered trademark in the United States and in other countries. Such forking has not led to compatibility problems because the RFB protocol is designed to be extensible.
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The original GPLed source code has fed into several other versions of VNC.
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In 1999, AT&T acquired the lab, and in 2002 closed down the lab's research efforts.ĭevelopers who worked on VNC while still at the AT&T Research Lab include: įollowing the closure of ORL in 2002, several members of the development team (including Richardson, Harter, Weatherall and Hopper) formed RealVNC in order to continue working on open-source and commercial VNC software under that name.
The Olivetti & Oracle Research Lab (ORL) at Cambridge in the UK developed VNC at a time when Olivetti and Oracle Corporation owned the lab.
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